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POST Report March 2013 Stem Cell Research
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Contents
1 1.1 1.2 1.3 Introduction 1.4 1.5 1.6 2 2.1 2.2 2.3 2.4 2.5 2.6 3 Scientific background Regulatory and ethical framework 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Background Scientific background ‐ Chapter 2 Regulatory and ethical framework ‐ Chapter 3 Scientific advances ‐ Chapter 4 Clinical developments ‐ Chapter 5 General remarks ‐ Chapter 6 Cells and stem cells Sources of stem cells Human embryonic stem cells Adult stem cells Reprogrammed cells Other sources of stem cells 5 5 5 5 Different types of cells Components of cells Stem cells Differentiation and cell fate Early development of the embryo Deriving hES cell lines Testing for pluripotency Different types of adult stem cells Stem cell niches Cell nuclear transfer Interspecies cell nuclear transfer Induced pluripotent stem cells Directly switching cells of one type to another Human embryonic germ cells Parthenogenetic stem cells 5 6 6 7 7 7 7 7 8 8 8 8 8 10 10 10 10 10 10 11 12 12 13 13 13 15 Possible uses of stem cells Regulatory bodies and pathway Ethical review of research Research on human tissue Research involving human embryos Other research regulation Stem cells and clinical trials The Stem Cell Toolkit NHS requirements for REC review Legal requirements for REC review Other requirements for REC review The National Research Ethics Service NHS RECs and clinical trials The Integrated Research Application System (IRAS) UK human tissue legislation The Human Tissue Authority Licensing and inspection Approving donations Embryo research legislation The HFEA and embryo research Care Quality Commission (CQC) NHS research permissions Animal research Genetic modification Stem cells and medicinal products Different types of ATMP ATMPs in clinical trials The centralised procedure 15 15 17 17 17 18 18 19 19 19 19 20 20 21 21 21 22 24 24 24 24 25 25 25 26 26 27 28 POST Report March 2013 Stem Cell Research
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4 4.1 4.2 4.3 4.4 5 5.1 5.2 5.3 6 6.1 6.2 Scientific advances Clinical developments General remarks What makes stem cells different? Factors that control differentiation Directing cell fate in cell culture Reversing differentiation: iPS cells Stem cell therapies Autologous cell therapy trials Allogeneic cell therapy trials Background Regulatory issues Preventing differentiation Emergence of the trophectoderm Differentiation of the inner cell mass Adult stem (AS) cells Cell culture Deriving ES cell lines Culture conditions Reliably maintaining hES cell lines Clinical grade cell lines Stem cell banking Deriving different lineages from stem cells Endoderm Liver cells Beta cells Lung cells Mesoderm Mesenchymal stem (MS) cells Sources of cardiomyocytes Haematopoeitic stem (HS) cells Ectoderm Non‐neural ectoderm Neural crest stem (NCS) cells Directing hES cells to neural lineages The reprogramming process Comparing iPS and ES cells iPS cells in disease modelling Autologous and allogeneic approaches Types of cells used Cell therapy and blood cancers Cell therapy and cardiac function Cell therapy and stroke Cell therapy and immune disorders Other autologous cell therapy approaches Types of cells used Fetal neural stem cells Disorders of the Central Nervous System Stroke hES‐derived cell therapies Spinal cord injury Diseases of the eye Neurodegenerative disease Background DH review of arms length bodies Proposals for a health research agency Establishment of HRA The future of HFEA and HTA Consultation responses Government response Future regulation of stem cell research Review of the Clinical Trials Directive 29 29 29 30 31 31 32 32 32 32 34 34 34 35 36 36 36 36 37 37 37 38 39 40 41 42 42 44 45 46 48 51 51 51 52 52 53 53 54 54 54 55 55 56 56 56 56 56 57 58 59 59 60 60 60 60 60 61 61 63 64 64 POST Report March 2013 Stem Cell Research
6.3 6.4 6.5 A1 A2 Acronyms Glossary Commercialisation Potential benefits and risks of cell therapy Where next? Page 3
Conducting clinical trials in the NHS Patentability of hES cells The European patent system hES cells and the morality provisions Greenpeace versus Bustle The CJEU ruling Implications for patentability Non‐destructive methods Wider implications Current state of UK stem cell research Businesses and business models Businesses Business models Barriers to commercialisation UK life sciences strategy Research, clusters and collaborations Investment and incentives Streamlining regulation People Infrastructure 65 65 65 66 66 66 67 67 67 68 68 68 68 ff 70 70 70 71 72 72 72 73 Acellular products Endogenous repair Cells for screening and testing Cell therapy Autologous cell therapy Allogeneic cell therapy Cell therapy and clinical trials 73 74 74 74 75 76 76 77 78 79 Acknowledgements
POST would like to thank all contributors and reviewers, Dr Mara Almeida for her role in researching and writing this report
and the Fundação para a Ciência e a Tecnologia (FCT) which funded her fellowship.
POST Report March 2013 Stem Cell Research
Page 4
Boxes
Box 2.1 Box 2.2 Box 3.1 Box 3.2 Box 3.3 Box 3.4 Box 3.5 Box 3.6 Box 3.7 Box 3.8 Box 3.9 Box 3.10 Box 4.1 Box 4.2 Box 4.3 Box 4.4 Box 4.5 Box 4.6 Box 4.7 Box 4.8 Box 5.1 Box 5.2 Box 5.3 Box 5.4 Box 5.5 Box 5.6 Box 5.7 Box 6.1 Box 6.2 Box 6.3 Box 6.4 Differentiation in the early embryo DNA transfer and mitochondrial disease NHS requirements for REC review Composition and operation of RECs The different phases of clinical trials The Human Tissue Act 2004 The Human Tissue (Quality and Safety for Human Application ) Regulations 2007 Principle purposes for embryo research The Animals (Scientific Procedures) Act 1986 The EU Clinical Trials Directive Regulation of medical devices Exemptions to ATMP marketing authorisations Gene expression and epigenetics Transcription factors Directing cell fate Cell culture Autologous and allogeneic therapy Graft versus Host Disease (GVHD) and Graft versus Tumour (GVT) responses Stem cell models for motor neurone disease Reprogramming using small molecules Tissue engineered windpipe Gene therapy for X‐linked SCID Immune rejection Immune privilege Allogeneic cell therapy for venous leg ulcers The London Project to Cure Blindness The NeuroStemcell programme Capacity of CQC to take on new functions Efficiency savings already made by HFEA and HTA Non‐destructive derivation of hES cell lines Tumour stem cell 9 11 17 18 18 20 21 22 25 26 26 27 29 30 30 33 34 35 44 47 51 52 52 55 55 57 58 63 63 67 68 Figures
Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 3.1 Figure 4.1 Figure 4.2 Figure 4.3 Figure 4.4 Figure 4.5 Figure 4.6 Figure 6.1 Fertilisation Early stages in the development of the human embryo Deriving NTS cells Deriving PS cells UK regulatory pathway for health research Cell culture Deriving cardiomyocytes The hierarchy of intermediate cell types in blood formation Neural tube formation Steps in reprogramming iPS cells as disease models UK medical biotech pipeline 7 9 11 13 16 33 38 41 40 45 48 70 Tables
Table 3.1 Table 3.2 Table 3.3 Table 4.1 Table 4.2 Table 5.1 Table 5.2 Table 6.1 Table 6.2 Human tissue legislation in Scotland and the rest of the UK Activities and organisations licensed by the HTA Research projects licensed by the HFEA between April 2010 and March 2011 Comparison of iPS and ES cells iPS cell disease models Trials of fetal stem cells Trials of hES‐derived cells Summary of proposals to transfer HFEA and HTA functions Companies by location 19 20 23 46 49 56 56 62 69 POST Report March 2013 Stem Cell Research
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1 1 Introduction
Introduction
1.1 1.1
Background
Background
In 2001,
In 2001,
the the
UK UK
Parliament
Parliament
voted
voted
to permit
to permit
research
research
on embryos
on embryos
for afor
number
a number
of specified
of specified
therapeutic
therapeutic
purposes.
purposes.
In the
In the
wake
wake
of this
of this
debate,
debate,
the the
House
House
of of
Lords
Lords
established
established
an ad
anhoc
ad hoc
Select
Select
Committee
Committee
to to
explore
explore
the the
wider
wider
issues
issues
raised
raised
by stem
by stem
cell cell
research.
research.
ThisThis
Stem
Stem
CellCell
Research
Research
Committee
Committee
reported
reported
in February
in February
2002,
2002,
making
making
27 27
recommendations
recommendations
to Government.
to Government.
TheThe
necessity
necessity
of research
of research
on embryonic
on embryonic
stem
stem
(ES)(ES)
cellscells
waswas
a key
a key
strand
strand
of the
of the
Committee’s
Committee’s
enquiry.
enquiry.
On the
On the
oneone
hand
hand
it received
it received
submissions
submissions
about
about
the the
scientific
scientific
andand
medical
medical
benefits
benefits
thatthat
suchsuch
research
research
might
might
bring.
bring.
On the
On the
other,
other,
it heard
it heard
evidence
evidence
suggesting
suggesting
thatthat
research
research
on ES
on cells
ES cells
waswas
bothboth
unethical
unethical
andand
unnecessary:
unnecessary:
unethical
unethical
because
because
the the
act of
actderiving
of deriving
ES cell
ES cell
lineslines
involves
involves
the the
destruction
destruction
of embryos;
of embryos;
andand
unnecessary
unnecessary
because
because
of advances
of advances
in research
in research
using
using
adult
adult
stem
stem
(AS)(AS)
cellscells
andand
the the
development
development
of stem
of stem
cell cell
banks.
banks.
Overall,
Overall,
the the
Committee
Committee
considered
considered
thatthat
there
there
waswas
a a
strong
strong
scientific
scientific
andand
medical
medical
casecase
for continued
for continued
research
research
on ES
on cells.
ES cells.
It suggested
It suggested
thatthat
keeping
keeping
bothboth
avenues
avenues
of research
of research
(on (on
ES and
ES and
AS cells)
AS cells)
open
open
would
would
maximise
maximise
the the
medical
medical
benefits.
benefits.
However,
However,
it recommended
it recommended
thatthat
there
there
should
should
be abe a
review
review
“towards
“towards
the the
endend
of the
of the
decade”
decade”
to evaluate
to evaluate
whether
whether
research
research
on cells
on cells
derived
derived
fromfrom
embryos
embryos
1
1
waswas
still still
necessary.
necessary.
Much
Much
has has
changed
changed
since
since
the the
Stem
Stem
CellCell
Research
Research
Committee
Committee
published
published
its report.
its report.
For For
instance,
instance,
a a
whole
whole
newnew
fieldfield
of regenerative
of regenerative
medicine
medicine
has has
emerged.
emerged.
It aims
It aims
to use
to use
stem
stem
cellscells
and/or
and/or
other
other
approaches
approaches
to regenerate
to regenerate
diseased
diseased
or damaged
or damaged
tissue
tissue
to restore
to restore
normal
normal
function
function
andand
is currently
is currently
the the
subject
subject
of an
ofinquiry
an inquiry
by the
by the
House
House
of Lords
of Lords
Science
Science
andand
Technology
Technology
Committee.
Committee.
ThisThis
Report
Report
presents
presents
a a
summary
summary
of progress
of progress
in the
in the
underlying
underlying
science
science
of of
stem
stem
cell cell
research
research
overover
the the
last last
decade.
decade.
1
1
Report
Report
from from
the Select
the Select
Committee
Committee
on Stem
on Stem
cell Research,
cell Research,
House
House
of of
Lords,Lords,
HL 83(i),
HL 83(i),
February
February
2002 2002
1.2 1.2
Scientific
Scientific
Background
Background
– Chapter
– Chapter
2 2
Chapter
Chapter
2 provides
2 provides
the the
science
science
background
background
for the
for the
report.
report.
It describes
It describes
whatwhat
stem
stem
cellscells
are,are,
where
where
theythey
come
come
fromfrom
andand
howhow
theythey
maymay
be isolated.
be isolated.
It It
introduces
introduces
the the
processes
processes
of differentiation
of differentiation
andand
cell cell
proliferation
proliferation
by which
by which
stem
stem
cellscells
can can
multiply
multiply
andand
givegive
rise rise
to more
to more
specialised
specialised
cell cell
types.
types.
It also
It also
looks
looks
at the
at the
various
various
different
different
possible
possible
sources
sources
of stem
of stem
cellscells
including
including
human
human
embryos,
embryos,
fetalfetal
tissue,
tissue,
adult
adult
stem
stem
cellscells
andand
the the
relatively
relatively
newnew
process
process
by which
by which
somatic
somatic
(adult)
(adult)
cellscells
can can
be re-programmed
be re-programmed
to form
to form
induced
induced
pluripotent
pluripotent
stem
stem
(iPS)
(iPS)
cells.
cells.
It describes
It describes
the the
properties
properties
of cells
of cells
fromfrom
these
these
sources,
sources,
focusing
focusing
in in
particular
particular
on their
on their
potential
potential
to give
to give
rise rise
to more
to more
specialised
specialised
cell cell
types.
types.
1.3 1.3
Regulatory
Regulatory
andand
Ethical
Ethical
Framework
Framework
– –
Chapter
Chapter
3 3
Chapter
Chapter
3 sets
3 sets
out out
the the
current
current
regulatory
regulatory
framework
framework
for research
for research
on stem
on stem
cells.
cells.
It describes
It describes
the the
regulations
regulations
under
under
the the
Human
Human
Fertilisation
Fertilisation
andand
Embryology
Embryology
Act Act
thatthat
cover
cover
research
research
on embryos
on embryos
andand
those
those
under
under
the the
Human
Human
Tissues
Tissues
Act Act
concerning
concerning
the the
derivation,
derivation,
storage
storage
andand
use use
of human
of human
tissue.
tissue.
It It
looks
looks
at UK
at UK
arrangements
arrangements
for the
for the
central
central
banking
banking
of of
cell cell
lineslines
andand
outlines
outlines
regulations
regulations
covering
covering
the the
use use
of cells
of cells
in clinical
in clinical
trials.
trials.
Chapter
Chapter
3 also
3 also
looks
looks
at at
various
various
recent
recent
proposals
proposals
for reforming
for reforming
the the
regulation
regulation
of biomedical
of biomedical
research.
research.
1.4 1.4
Scientific
Scientific
Advances
Advances
– Chapter
– Chapter
4 4
Chapter
Chapter
4 examines
4 examines
the the
main
main
scientific
scientific
advances
advances
in in
basic
basic
stem
stem
cell cell
research
research
in recent
in recent
years.
years.
It looks
It looks
at at
the the
rapidly
rapidly
moving
moving
fieldfield
of epigenetics:
of epigenetics:
howhow
factors
factors
in the
in the
cell cell
interact
interact
withwith
DNADNA
to control
to control
which
which
genes
genes
are are
turned
turned
on and
on and
which
which
are are
blocked.
blocked.
It describes
It describes
howhow
variations
variations
in these
in these
signalling
signalling
pathways
pathways
determine
determine
the the
fatefate
of aof
stem
a stem
cell cell
in a in
living
a living
organism;
organism;
whether
whether
it turns
it turns
into into
(say)
(say)
a nerve
a nerve
cell cell
or or
a blood
a blood
cell.cell.
AndAnd
it examines
it examines
howhow
knowledge
knowledge
of of
suchsuch
factors
factors
can can
be used
be used
to direct
to direct
the the
fatefate
of cells
of cells
in in
the the
laboratory.
laboratory.
For For
instance,
instance,
howhow
stem
stem
cellscells
can can
be be
made
made
to differentiate
to differentiate
into into
specific
specific
types
types
of cells,
of cells,
or or
howhow
the the
process
process
can can
be run
be run
in reverse
in reverse
to reprogram
to reprogram
specialised
specialised
cellscells
into into
iPS iPS
cells.
cells.
It describes
It describes
recent
recent
evidence
evidence
on the
on the
extent
extent
to which
to which
iPS iPS
cellscells
resemble
resemble
andand
behave
behave
like like
ES cells.
ES cells.
Finally,
Finally,
it looks
it looks
at other
at other
potential
potential
usesuses
of stem
of stem
cells.
cells.
These
These
include
include
using
using
stem
stem
cellscells
to model
to model
andand
improve
improve
understanding
understanding
of of
the the
mechanisms
mechanisms
of diseases,
of diseases,
andand
to aid
to in
aidthe
in the
development
development
andand
screening
screening
of new
of new
drugs.
drugs.
Page 6
1.5 Clinical Developments – Chapter 5
Chapter 5 looks at the potential clinical uses for
stem cells. It presents details of clinical trials of cellbased therapy that have been conducted since the
Stem Cell Research Committee reported. Two main
types of clinical approaches are discussed in this
Section. The first is use of the patient’s own cells for
therapeutic purposes (autologous therapy). The
Report gives examples of some of the many, often
small scale, trials that have investigated such an
approach for treating a range of conditions from
heart attacks to stroke. The second is the
therapeutic use of cells from another person
(allogeneic therapy). Here the Report gives details
of the first few clinical trials involving cells derived
from hES cells as well as trials using fetal tissuederived cells.
POST Report March 2013 Stem Cell Research
1.6 General Remarks – Chapter 6
Chapter 6 wraps up the report, by offering some
general remarks about the potential of stem cell
research and cell-based therapies. It examines
some of the challenges that research in this area
may pose for regulators, policy makers and
parliamentarians. This includes proposed changes
to the regulation of research on human tissue and
embryos, the patentability of inventions involving
human embryonic stem (hES) cells and reform of
the EU legislation regulating clinical research. It
also looks at the commercial opportunities
presented by stem cell research and at the
challenges involved in translating world class
science in the laboratory into safe and effective
treatments in the clinic. Finally it examines the
potential risks and benefits of cell therapy
approaches and looks at where the science may be
heading in the next ten years or so.
POST Report March 2013 Stem Cell Research
Page 7
2 2 Scientific
Scientific
Background
Background
Overview
Overview
„ Cells
„ Cells
of the
ofearly
the early
embryo
embryo
(embryonic
(embryonic
stemstem
cells)cells)
havehave
the potential
the potential
to give
to give
rise to
rise
alltoofall of
the different
of found
cell found
the body
are pluripotent).
the different
typestypes
of cell
in theinbody
(they(they
are pluripotent).
„ The
process
by which
thesethese
embryonic
stemstem
cellscells
give give
rise to
more
specialised
cell types
„ The
process
by which
embryonic
rise
to more
specialised
cell types
is known
as differentiation.
is known
as differentiation.
„ While
ofcells
the cells
the adult
human
are highly
specialised,
„ While
mostmost
of the
in theinadult
human
bodybody
are highly
specialised,
somesome
adultadult
stemstem
retain
a more
limited
capacity
to give
rise
to multiple
cell types.
cellscells
retain
a more
limited
capacity
to give
rise to
multiple
cell types.
„ Differentiation
a one-way
process;
researchers
devised
„ Differentiation
is notisanot
one-way
process;
researchers
havehave
devised
waysways
of of
reprogramming
specialised
into pluripotent
reprogramming
specialised
adultadult
cellscells
backback
into pluripotent
cells.cells.
2.1 Cells
2.1 Cells
and stem
and stem
cellscells
Different
Different
typestypes
of cells
of cells
FIGURE
FIGURE
2.1 FERTILISATION
2.1 FERTILISATION
More More
complex
complex
organisms
organisms
such as
such
humans
as humans
are made
are made
up up
of many
of many
cells grouped
cells grouped
together
together
in different
in different
organs
organs
and and
tissues.
tissues.
Estimates
Estimates
of theoftotal
the number
total number
of cells
of in
cells
thein the
2
2
human
human
body body
vary from
vary around
from around
10 trillion
10 trillion
to 50 to
trillion
50 trillion
,
,
comprising
comprising
of more
of more
than 200
thandifferent
200 different
typestypes
(blood(blood
cells, cells,
skin cells,
skin cells,
nervenerve
cells, cells,
etc.). etc.).
StemStem
cellscells
Figure 2.1 Fertilisation
All living
All living
thingsthings
are made
are made
of oneoforone
more
or more
cells. cells.
The The
simplest
simplest
living living
organisms
organisms
are bacteria,
are bacteria,
whichwhich
consist
consist
of
of
singlesingle
cells. cells.
WhenWhen
such such
organisms
organisms
encounter
encounter
favourable
favourable
conditions
conditions
− for instance
− for instance
free availability
free availability
of water,
of water,
oxygen
oxygen
and nutrients
and nutrients
and an
and
appropriate
an appropriate
temperature
temperature
− they− are
they are
able to
able
grow
to grow
and reproduce
and reproduce
themselves
themselves
by a process
by a process
calledcalled
cell division.
cell division.
All of All
theofcells
the that
cellsmake
that make
up theuphuman
the human
body body
are are
specialised
specialised
to a greater
to a greater
or lesser
or lesser
extent.
extent.
For instance,
For instance,
mature
mature
red blood
red blood
cells are
cellstiny,
aredisk-shaped
tiny, disk-shaped
cells that
cellscan
that can
squeeze
squeeze
through
through
the narrowest
the narrowest
of capillaries
of capillaries
and and
transport
transport
oxygen
oxygen
around
around
the body.
the body.
In contrast,
In contrast,
human
human
nervenerve
cells (neurons)
cells (neurons)
can have
can have
branches
branches
(axons)
(axons)
that are
that are
more more
than athan
metre
a metre
long, long,
and specialise
and specialise
in transmitting
in transmitting
nervenerve
impulses
impulses
around
around
the body.
the body.
Yet both
Yet types
both types
of cells
of −cells −
alongalong
with all
with
theallother
the other
cell types
cell types
in theinbody
the body
− arose
− arose
from from
just ajust
single
a single
cell: the
cell:fertilised
the fertilised
egg. egg.
Components
Components
of cells
of cells
Virtually
Virtually
all of the
all ofcells
the of
cells
theofhuman
the human
body body
contain
contain
a
a
nucleus.
nucleus.
The nucleus
The nucleus
houses
houses
the cell’s
the cell’s
genetic
genetic
information
information
(DNA)(DNA)
in structures
in structures
knownknown
as chromosomes.
as chromosomes.
The human
The human
genome
genome
is splitisacross
split across
23 chromosomes.
23 chromosomes.
Most Most
human
human
cells carry
cells carry
two copies
two copies
(46) of(46)
theof the
chromosomes.
chromosomes.
One of
One
these
of these
can be
can
traced
be traced
back to
back
theto the
mother,
mother,
one toone
thetofather.
the father.
GermGerm
cells, cells,
the sperm
the sperm
and the
and the
eggs,eggs,
carry carry
only aonly
single
a single
set (23)
setof(23)
chromosomes.
of chromosomes.
WhenWhen
a sperm
a sperm
fertilises
fertilises
an egg,
an the
egg,nucleus
the nucleus
of theoffertilised
the fertilised
egg egg
contains
contains
the full
the
46full
chromosomes;
46 chromosomes;
23 from
23 the
frommother
the mother
(egg) (egg)
and 23
and
from
23 the
fromfather
the father
(sperm);
(sperm);
see Figure
see Figure
1.1. 1.1.
2
2
A trillion
Aistrillion
a million
is a million
million or
million
1012 or 1012
Any cell
Anythat
cellhas
thatthe
haspotential
the potential
to give
torise
givetorise
other
to other
typestypes
of cellofiscell
called
is called
a stem
a stem
cell. Stem
cell. Stem
cells have
cells have
two defining
two defining
features:
features:
„ continual
„ continual
self renewal
self renewal
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„ Fig 2.4 Deriving PS cells
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Figure 3.1 UK regulatory pathway for health research
up theupplacenta,
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„ Pluripotent
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Figure 2.3 D
POST Report March 2013 Stem Cell Research
Page 8
„
Unipotent stem cells are those that have
differentiated to the extent that they give rise to a
single type of cell.
Differentiation and cell fate
So what is the difference between a totipotent cell in the
very early embryo and a pluripotent cell found in the
same embryo one week later? Or between a pluripotent
embryonic cell and a multipotent stem cell found in the
developing foetus or taken from an adult? And what is the
process by which these cells develop from the early
embryonic stem cells? The answer to these questions lies
in gene expression.
All of the cells in the early embryo carry a complete set of
human genes. But not all of the genes are equally active
in all tissues at all times. Cells contain mechanisms for
turning genes on (expressing them) and off (repressing
them) and for modulating the extent of their activity. This
means that different genes will be active to different
extents in one cell type compared with another.
It is the processes that control which genes are promoted
and repressed that determine the eventual developmental
fate of a stem cell. In recent years, researchers have
made great progress in understanding some of these
processes (see Chapter 4). This allows cells to be
directed down different development pathways (lineages)
in the laboratory. For instance:
„ directing differentiation within a particular lineage (for
instance using regulatory factors to direct blood stem
cells to differentiate into specialised blood cells such
as lymphocytes)
„ converting cells of one lineage (e.g. skin stem cells)
into cells of another lineage (e.g. neurons)
„ reversing the differentiation process by transforming
partially differentiated multipotent cells back into cells
that act in a similar manner to pluripotent stem cells.
2.2 Sources of stem cells
Human stem cells can be derived in several different
ways. They can be:
„ Isolated from the early stages of the human embryo.
Such cells are called human embryonic stem (hES)
cells.
„ Isolated from various tissues and organs of the
human body. These cells are called human adult
stem (hAS) cells.
„ Derived by reprogramming other cells. One example
is reprogramming the DNA in an adult cell nucleus by
transferring it into an egg cell. Another is the
reprogramming of somatic3 cells to create induced
pluripotent stem (iPS) cells.
„ Other possible approaches involve deriving cells
from fetal tissue or using techniques such as
parthenogenesis that stimulate eggs to mimic the
fertilisation process.
2.3 Human embryonic stem cells
Early development of the embryo
All of the (human)4 cells found in an adult originate from a
single cell: the fertilised egg. Key stages in the
development of a human embryo are outlined in Box 2.1.
Within a week of fertilisation, multiple cell divisions have
resulted in a structure referred to as a blastocyst (see
Figure 2.2). It consists of around 200 cells, organised into
an inner layer called the inner cell mass and an outer
layer called the trophoblast. Cells from the trophoblast will
go on to form the placenta and umbilical cord. Those
found in the inner cell mass are called human embryonic
stem (hES) cells.
Within two weeks or so of fertilisation, hES cells in the
developing embryo have given rise to three distinct layers
of tissue. Each layer contains cells that have taken a
committed step down a different differentiation pathway,
or lineage. The three lineages (see Box 2.1) are the:
„ endoderm, that will give rise to the specialised cells
that line the tissue such as the lungs, alimentary
canal and airways (trachea)
„ mesoderm, which will go on to develop into tissues
such as bone, cartilage and muscle
„ ectoderm, that will give rise to the nervous system,
the sensory organs and structural features such as
skin, hair and nails.
Deriving hES cell lines
The hES cells found in the blastocyst (Box 2.1) are of
particular interest because they are a) pluripotent and b)
self-replicating. The ability to self-replicate effectively
means that the hES cells are immortal; they can be
harvested5 and cultured in the laboratory indefinitely as
stable hES cell lines under the correct conditions.6 Cell
culture is discussed in more detail in Chapter 4.
These two properties of hES cells arise because they
have the capacity to divide both symmetrically and
asymmetrically. Symmetric cell division produces two
identical daughter cells with similar properties to the
original hES cell. Asymmetric cell division produces two
daughter cells, only one of which is similar to the original
cell. The other daughter cell is a progenitor cell which will
go on to divide and differentiate into a more specialised
cell type. Complex signalling pathways control which of
these two routes − symmetric or asymmetric cell division
− the hES cells take in the developing embryo.
4
5
3
A somatic cell is an adult cell that is not a germ (egg or sperm) cell.
6
The human body contains an estimated ten times as many bacterial cells as
human cells. This is possible because bacterial cells are very much smaller
than human cells.
However this raises ethical issues as it entails destroying the blastocyst.
Thomson J et al, Science, 282, 1145–1147, 1998
POST Report March 2013 Stem Cell Research
Page 9
Box 2.1. Differentiation in the early embryo
Each of the 200 plus specialised cell types in an adult human develop from the early embryonic stem cells by a process known as differentiation,
the early stages of which are depicted in Figure 2.2 (below). In the first few days the fertilised egg undergoes a series of cell divisions to form a
solid block of cells known as the morula. At this stage no differentiation has occurred; all of the cells are the same and are totipotent because they
retain the ability to give rise to all embryonic and extra-embryonic tissues (placenta, chorion and the umbilical cord). By around day 5-7, the first
differentiation has occurred, resulting in a structure called the blastocyst (Figure 2.2). It contains two distinct cell types:
„ Cells that initially form an outer layer (the trophoblast) and eventually contribute to the placenta and other extra-embryonic tissue.
„ Cells in the inner cell mass that eventually go on to become the different specialised cell types found in human tissues and organs. It is these
cells that can be collected and cultured to form human embryonic stem cell lines.
By around day 16, cells from the inner cell mass have undergone further differentiation (see Figure 2.2) and have organised themselves into three
distinct layers:
„ An inner layer, the endoderm. These cells differentiate into the cells that line the inner layer of many of the structures in the adult human
including the alimentary canal, the lungs, trachea and larynx.
„ A middle layer, the mesoderm. These cells develop into tissues such as bone, cartilage and muscle, as well as providing the lining for blood
vessels and urinary tracts.
„ An outer layer, the ectoderm. Cells from this layer differentiate into the outer layer of skin, hair, nails, the tissues of the central nervous system
and the sensory organs.
FIGURE 2.2 EARLY STAGES IN THE DEVELOPMENT OF THE HUMAN EMBRYO
POST Report March 2013 Stem Cell Research
Page 10
Testing for pluripotency
There are tests that researchers can use to assess
whether a given cell line is pluripotent. Pluripotent hES
cells have been derived that pass each of the following
tests:
„ Injecting the cells into the skin or testes or under the
kidney capsule of immune deficient mice. If the mice
develop characteristic growths (teratomas)
containing differentiating cells from each of the three
main lineages − endoderm, mesoderm and ectoderm
− then this is taken as indicative that the cell line is
pluripotent.
„ Changing the culture conditions to allow the cells to
differentiate. If the cells differentiate spontaneously
into many cell types derived from all three main
lineages, then the cells are likely to be pluripotent.
„ Examining the pattern of genes being expressed in
the cells to see if they match those expected from
pluripotent cells. The most recent tests check
thousands of gene activities against a database of
genes known to be active in pluripotent cells.7
Another test for pluripotency that is used in animal
studies, but not in humans, is to inject ES cells that have
been labelled in some way into a blastocyst of the same
species. The ES cell line is pluripotent if it contributes to
all tissues in the developing (or adult) recipient.
2.4 Adult stem cells
Different types of adult stem cells
Many organs in the adult body contain a population of
stem cells that serve as sources of cell replacement
throughout life. These adult stem (AS) cells are partially
differentiated; they have already embarked down a
developmental lineage. Under normal circumstances,
they only give rise to cell types within their particular
lineage. They may be capable of generating several
different cell types or just one type of cell. For example:
„ Hematopoietic stem cells can give rise to all the
different types of blood cells including red blood
cells, B and T lymphocytes, natural killer cells,
neutrophils, basophils, eosinophils, monocytes, and
macrophages.
„ Epithelial stem cells have been identified in the lining
of the digestive tract. They can give rise to the
several cell types found in the tract including
absorptive cells, goblet cells and enteroendocrine
cells.
„ Mesenchymal stem cells can give rise to a variety of
cell types including bone, cartilage, fat and
connective tissue cells.
„ Neural stem cells in the brain can go on to form each
of the three main types of cell found in brain tissue.
„ Skin stem cells have been found in the bottom layer
of the epidermis and can give rise to the cells that
form the protective skin surface (keratinocytes). Skin
stem cells are also found in the base of hair follicles,
and can give rise to both the hair follicle and to the
epidermis.
Stem cell niches
The sites in the body where AS cells are located are
referred to as stem cell niches. However, a stem cell
niche is not just a physical location where stem cells are
found; it provides a complete micro-environment for
maintaining stem cells in the desired state. This may
mean providing an environment where the cells remain in
a non-dividing (quiescent) state. But the niche must also
respond to signals generated by external events such as
natural cell death or tissue injury, to allow the stem cells
to regenerate damaged or ageing tissue. The stem cell
niche must maintain this delicate balance between
inactivity, stem cell renewal and proliferation/
differentiation throughout an organism’s life.
Understanding the mechanisms that control this balance
is a key focus of research. It may prove to be vital in
understanding processes such as cancer/tumour
formation and how to use cell therapies to combat human
disease. Recent research in this area is summarised in
Chapter 4.
2.5 Reprogrammed cells
Cell nuclear transfer
In 1997, researchers at the Roslin Institute published a
paper detailing the reproductive cloning of a sheep using
an adult cell.8 The method they used was called somatic
cell nuclear transfer and the work followed on from Nobel
prize winning research by the British scientist Sir John
Gurdon in the late 1950s, who used a similar method to
clone frogs.9 It involves removing the nucleus from an
egg, and replacing it with a nucleus taken from an adult
cell. Factors present in the cytoplasm of the egg
reprogram the transferred nucleus and make it behave as
if it were part of a newly fertilised egg (see Figure 2.3).
In this case, the researchers implanted the resulting
‘embryo’ into the womb of another sheep to produce
Dolly. But in principle, the same sort of nuclear transfer
can be used to make ‘embryos’ from which ES cell lines
can be established. Cells derived in this way are called
nuclear transfer stem (NTS) cells.
8
9
7
Müller F et al, Nature Methods, 8, 315–317, 2011
Wilmut I et al, Cloning and Stem Cells, 9(1): 3-7, 2007
Sir John Gurdon and Shinya Yamanaka were jointly awarded the Nobel
Prize for their work on reprogramming mature cells into pluripotent cells in
2012
POST Report March 2013 Stem Cell Research
FIGURE 2.3 DERIVING NTS CELLS
Figure 2.3 Deriving NTS cells
Figure 4.1 Cell Culture
To date, NTS cells have been derived from a number of
animals including mice10, rhesus macaques11 and
humans.12 ,13 One factor limiting research in this area is
the inefficiency of the reprogramming process. For
instance, more than 300 rhesus macaque eggs were
used to produce just two NTS cell lines.
Cell nuclear transfer also raises ethical considerations.
While most of the DNA present in a cell is found in the
nucleus, the cytoplasm that surrounds the nucleus also
contains small amounts of mitochondrial DNA (mtDNA,
UK Medical biotech pipeline
see Box 2.2). Figure
This6.1means
that NTS cells derived from a
donated human egg cell would potentially contain DNA
from two people:
„ mtDNA from the egg donor
„ nuclear DNA (plus any mtDNA transferred along with
the nucleus) from the nucleus donor.
Donated human eggs have been used to reprogram adult
human fibroblasts to form viable blastocysts (see Box
2.1).14 Furthermore, scientists at Newcastle University
have investigated the potential of related transfer
techniques to allow women with rare metabolic disorders
caused by mutations in their mtDNA to have children
unaffected by the disease. This research is outlined in
Box 2.2.
Interspecies cell nuclear transfer
One factor limiting the prospects for developing human
NTS cell is the scarcity of donated human eggs. This has
led researchers to investigate using eggs from other
species to reprogram human nuclei. However, this
approach is fraught with ethical difficulties as the resulting
cells contain a mixture of human DNA (nuclear DNA and
any mtDNA transferred along with the nucleus) and
animal DNA (mtDNA from the egg cytoplasm). 15
10
11
12
13
14
15
Munsie M et al, Current Biology 10(16), 989-992, 2000
Byrne J et al, Nature, 450, 497-502, 2007
A South Korean group reported the isolation of human NTS cells in 2004,
but the claim was subsequently found to be fraudulent. See Cho M et al,
Science, 311, 614-615, 2006
Paull D et al, Nature, published online 19 December 2012
French A et al, Stem Cells, 26 (2), 485-493, 2008
Skene L et al, Cell Stem Cell, 5 (1), 27-30, 2009
Page 11
Box 2.2. DNA transfer and mitochondrial disease
Mitochondria are organelles found in the cytoplasm of cells. They
perform a number of vital functions. For instance, they are involved in
cell signalling, control the cell cycle and differentiation and provide the
cell with energy. To perform such functions, mitochondria interact
closely with the genes contained in the cell nucleus. While the nucleus
contains the overwhelming majority of DNA in a cell (nuclear DNA),
the mitochondria also contain short stretches of mitochondrial DNA
(mtDNA). Mutations in this mtDNA can cause a range of different
mitochondrial disorders, including metabolic and neuromuscular
disorders.
Nuclear DNA and mtDNA are inherited in different ways. For nuclear
DNA, a child inherits two complete copies, one from each parent. For
most genetic disorders caused by mutations in nuclear DNA, a child
will inherit the disorder only if both parents have (or carry) it. In
contrast, mtDNA is inherited solely from the mother. This means that
any child born to a mother affected by a mitochondrial disorder will
inherit that disorder.
Researchers at the University of Newcastle have been investigating
DNA transfer methods as a possible way of preventing metabolic
diseases being inherited. They have looked at two similar transfer
techniques to that outlined in Figure 2.3:
„ Maternal spindle transfer (MST). The chromosomes and
associated structures from the mother’s egg are removed and
transferred to a (disease-free) donor egg from which the nucleus
has already been removed. The reconstituted donor egg is then
fertilised with the father’s sperm, and implanted in the mother’s
uterus.
„ Pronuclear transfer (PNT). The mother’s egg and a (diseasefree) donor egg are both fertilised with the father’s sperm. Each
cell contains two pronuclei, one containing the father’s DNA and
the mother’s or donor’s DNA). The pronuclei from the mother’s
egg are removed and transferred to the donor egg, from which
the pronuclei have already been removed. The resulting embryo
is then implanted in the mother’s uterus.
Although both techniques are similar to nuclear transfer (Figure 3),
they differ from it in one important respect; neither MST nor PNT
involve reprogramming of the nuclear DNA. In both cases, any
resulting embryo is the product of fertilisation, will be genetically
unique, and contain three people’s DNA:
„ the nuclear DNA of the mother
„ the nuclear DNA of the father
„ the mtDNA of the (disease-free) egg donor.
Studies in animal models and humans16 have shown that MST and
PNT can be used to produce viable blastocysts. One study in rhesus
macaques used MST to produce embryos that were implanted and
gave rise to the birth of four healthy offspring that were normal after
two years. The Human Fertilisation and Embryology Authority (HFEA)
convened an expert panel to review evidence on the safety and
effectiveness of such methods in February 2011. The panel reported
in April 2011 and March 2013 and made recommendations for further
research to be conducted before such methods could be considered
safe for clinical use.17 The Nuffield Council on Bioethics has
considered the ethical issues raised by MST and PNT. It concluded
that “provided that the techniques are proved to be safe and effective,
and an appropriate level of information and support is offered, it would
be ethical for families to use these techniques as treatment”.18 HFEA
conducted a public consultation on the use of such techniques in 2012
and reported the results in March 2013.19
16
17
18
19
Craven L et al, Nature, 465 (7294), 82-85, 2010
Scientific review of the safety and efficacy of methods to avoid
mitochondrial disease through assisted conception, HFEA 2011.Available at
www.hfea.gov.uk/docs/2011-04-18_Mitochondria_review__final_report.PDF
Novel techniques for the prevention of mitochondrial DNA disorders: an
ethical review, Nuffield Council on Bioethics, 2012
www.hfea.gov.uk/docs/March2013Authority-Paper-Mitochondria.pdf
POST Report March 2013 Stem Cell Research
Page 12
There is currently only one report of such an interspecies
approach being used to generate human stem cell lines.
Researchers in Shanghai used rabbit egg cells to
reprogram the nuclei of human somatic cells from four
donors of different ages (5, 42, 52 and 60 years).20 In
each case, the researchers were able to derive NTS cell
lines that appeared to be human and have similar
properties to hES cells. For instance, they were capable
of sustained growth in an undifferentiated state, but could
also be induced to give rise to cell types such as neuron
and muscle, as well as mixed cell populations from all of
the three main lineages.
Induced pluripotent stem cells
As outlined previously, it is different patterns of gene
expression that determine the developmental fate of a
cell. Patterns of gene expression are regulated by a
range of factors that can interact with DNA. Among the
most important of these are the transcription factors that
are encoded on the genes in the nucleus of a cell.
By comparing patterns of gene expression in
(undifferentiated) ES cells with those in differentiated
cells in mice, researchers were able to identify 24 genes
that were particularly active in the mouse ES cells. They
conducted experiments using viruses to transfer and
express different combinations of these genes into mouse
fibroblasts. They identified a cocktail of four genes that,
when transferred to fibroblasts, reverted the cells back
into undifferentiated, pluripotent, ES-like cells.21
Such cells are known as induced pluripotent stem (iPS)
cells. The four factors in question were all genes coding
for transcription factors. This cocktail of four
reprogramming factors has subsequently been shown to
produce iPS cells from a wide range of different types of
cells and from cells of different species, including
humans.22
More recent research suggests that at least two of the
factors can be left out or substituted by other transcription
factors or in some cases by small molecules. As
discussed in more detail in Chapter 4, research is
underway to examine the extent to which human iPS cells
behave like human ES cells and to find ways of deriving
iPS cells that do not involve gene transfer.
Directly switching cells of one type to another
Directly switching cells of one lineage to cells of another
lineage is called trans-differentiation. Each of the
reprogramming approaches described thus far aims to
produce fully pluripotent reprogrammed cells. In contrast,
trans-differentiation aims to convert differentiated cells of
one type into differentiated cells of another without going
through a pluripotent intermediate stage.
Trans-differentiation has long been known to occur
naturally in invertebrates. For instance, jellyfish striated
muscle can give rise to a wide range of (jellyfish) tissue
types in the laboratory, including functional organs such
as tentacles.23 Examples of trans-differentiation are also
known to occur in vertebrates, but are less common and
more restricted in their scope. For example, experiments
in animals have shown that pancreas cells can give rise
to liver cells and vice versa (the liver and pancreas both
arise from the same region of the endoderm). 24
More recently, a similar approach to that used to derive
iPS cells has been employed to convert mouse
fibroblasts directly into neurons (nerve cells).
Researchers identified a series of transcription factors
that are active in neurons. They found that transferring
the genes coding for three of these factors into fibroblasts
converted them into neurons.25 After a few days, the cells
began to behave like neurons, eventually producing
electrical signals and forming connections with each other
in culture. More recently, researchers have managed to
use similar methods to directly convert human donor
fibroblasts into neuron-like cells that produce the
neurotransmitter dopamine. 26
Two groups of researchers have recently shown that noncardiomyocyte mouse cells can be reprogrammed directly
into cardiomyocytes using transcription factors. One
group achieved this in the laboratory27, while the other did
so in the intact mouse in a clinically relevant model of
injury.28
23
24
25
20
21
22
Chen Y et al, Cell Research, 13: 251-263, 2003
Takahashi K and Yamanaka S, Cell 126 (4), 663–76, 2006
Takahashi K et al, Cell 131(5), 861-72, 2007
26
27
28
Shen C-N et al, Organogenesis, 1 (2), 36 – 44, 2004
Shen C-N et al, Mechanisms of Development, 120 (1),107-16, 2003
Vierbuchen T et al, Nature 463, 1035-1041, 2010
Liu X et al, Cell Res, 22 (2), 321–332, 2012
Song K et al, Nature, 485, 599–604, 2012
Qian L et al, Nature, 485 (7400), 593-8, 2012
POST Report March 2013 Stem Cell Research
2.6 Other sources of stem cells
Human embryonic germ cells
In 1998, the same year that the first hES cell lines were
reported, a group of researchers established human cell
lines derived from fetal tissue.29 They isolated primordial
germ cells − the cells that will form the eggs or sperm of
the adult − from 5-9 week old fetuses, and grew them in
cell culture with various growth/regulatory factors.
The researchers called the cell lines they had derived
human embryonic germ (hEG) cells. Whether or not
these hEG cells are pluripotent has been the subject of
some debate. On the one hand, after one to three weeks
in culture, some of the cells spontaneously formed
embryoid bodies in the cultured colonies. These are
disorganised clumps of cells that have started to
differentiate into various cell types. When the researchers
analysed the different cell types found in these bodies,
they discovered cells from each of the three main
lineages.
On the other hand, when the hEG cells were injected into
immune deficient mice, it was not possible to
demonstrate pluripotency by generating teratomas
containing differentiating cells from each of the three
main lineages. The pattern of gene expression found in
hEG cells is also different from that found in pluripotent
cells.30
Overall, the hEG cells ‘fail’ two of the three main tests for
pluripotency outlined previously. It appears that hEG cells
are capable of giving rise to multiple cell lineages, but are
unlikely to be truly pluripotent. The primordial germ cells
from which hEG cells are derived are specialised cells
that are destined to develop into sperm or egg cells. The
fact that they have become multipotent suggests that the
culture conditions may have triggered a reprogramming
process of some sort.
Parthenogenetic stem cells
Germ cells − eggs and sperm − each contain just a single
set of chromosomes. While this is true for sperm, it is not
strictly accurate for eggs. The nucleus of the egg contains
a single set of (23) chromosomes, but the egg cell also
harbours a second set of chromosomes in a residual
body called the polar body. This is a relic from the cell
division that led to the formation of the egg; it is usually
expelled from the egg when fertilisation occurs.
Page 13
FIGURE 2.4 DERIVING PS CELLS
Fig 2.4 Deriving PS cells
In parthenogenesis, mammalian eggs are stimulated to
mimic the fertilisation process. At the same time the egg
cell is treated with chemicals to prevent expulsion of the
polar body. If the polar body fuses with the egg nucleus,
the result is an egg cell with a single nucleus containing
two sets (46) of maternal chromosomes. Adjusting the
conditions to allow normal cell division can result in cells
called parthenogenetic stem (PS) cells. Figure 2.4 shows
how the process works.
Figure 3.1 UK regulatory pathway for health research
PS cells have been derived in a range of mammalian
species including mice, pigs, rabbits, primates31 and
humans.32 In none of the mammals studied so far have
the PS cells gone on to develop normally. In each case,
researchers have seen arrested development, usually
within two weeks.
This is thought to be due to the imprinting − patterns of
chemical modification − of the DNA and its associated
proteins. It is known that the imprinting patterns of the
paternal genome present in sperm and the maternal
genome in the egg are different. It appears that both
paternal and maternal imprints are required for normal
development.
Despite the fact that “embryos” produced by parthenogenesis do not develop normally, stem cell lines derived
from them resemble ES cell lines. For instance, in
monkeys, the extracted stem cells look and behave like
monkey ES cells, and express ES cell markers. They
have been cultured in the laboratory in an undifferentiated
state and differentiated into a range of different cell types.
31
Shamblott M et al, Proc Natl Acad Sci USA, A 95, 13726–13731, 1998
30 Shamblott M et al, Proc Natl Acad Sci USA, 98, 113–118, 2001
29
32
Hipp J and Atala A, Journal of Experimental & Clinical Assisted
Reproduction, 1, 3, 2004
Revazova E et al, Cloning and Stem Cells, 9 (3), 432–49, 2007
POST Report March 2013 Stem Cell Research
Page 14
Several different human PS cell lines have been reported.
They have been partially characterised, and share many
features in common with hES cell lines. For example they
express typical hES markers, and have the ability to form
teratomas containing various cell lines from each of the
three main lineages. However, because of their different
parentage − containing two copies of the maternally
imprinted genome − there are inevitable differences
between human PS and ES cells. For instance,
expression of paternally associated genes has been
shown to be absent while that of maternally associated
genes is doubled.33
33
Cheng L, Cell Research, 18, 215–217, 2008
A final property of human PS cells that may be of value is
their immunology. An individual’s immunological profile is
dictated by a complex set of proteins known as the
MHC34, encoded on chromosome 6 of the human
genome. In the course of normal fertilisation, the fertilised
egg receives two copies of the MHC: one from the mother
and one from the father. These recombine shortly after
fertilisation to give the resulting cells their own
immunological profile, which will be different from that of
either parent. In human PS cells, both copies of the MHC
come from the mother. Hence, the resulting PS cells will
have an immunological profile that is much more similar
to that of the mother. PS cells may thus represent a way
of generating cell lines with predictable immunological
properties for the purposes of stem cell banking and
tissue matching.
34
MHC stands for Major Histocompatibility Complex
POST Report March 2013 Stem Cell Research
Page 15
3 3 Regulatory
Regulatory
and
and
Ethical
Ethical
Framework
Framework
Overview
Overview
„ The
„ The
regulation
regulation
of stem
of stem
cell research
cell research
fromfrom
the laboratory
the laboratory
to the
to clinic
the clinic
is complex
is complex
and and
involves
researchers
dealing
many
different
agencies.
involves
researchers
dealing
withwith
many
different
agencies.
„ Recent
years
havehave
seenseen
some
moves
towards
streamlining
regulation
in this
areaarea
but but
„ Recent
years
some
moves
towards
streamlining
regulation
in this
is scope
for further
progress.
therethere
is scope
for further
progress.
„ The
Government
established
the Health
Research
Authority
(HRA)
to co-ordinate
„ The
Government
has has
established
the Health
Research
Authority
(HRA)
to co-ordinate
streamline
the regulation
of health
research.
and and
streamline
the regulation
of health
research.
„ HRA
taken
on responsibility
for National
the National
Research
Ethics
Service
„ HRA
has has
taken
on responsibility
for the
Research
Ethics
Service
and and
the the
Integrated
Research
Application
System.
Integrated
Research
Application
System.
3.1 Possible
usesuses
of stem
cellscells
3.1 Possible
of stem
StemStem
cell research
cell research
aims aims
to develop
to develop
betterbetter
treatments
treatments
for for
a range
a range
of diseases
of diseases
(see (see
Chapter
Chapter
5). This
5). may
This occur
may occur
in in
several
several
ways.ways.
For instance,
For instance,
new cell-based
new cell-based
therapies
therapies
are are
beingbeing
developed
developed
for treating
for treating
chronic
chronic
degenerative
degenerative
diseases
diseases
such such
as Alzheimer’s,
as Alzheimer’s,
diabetes
diabetes
and liver
and liver
cirrhosis.
cirrhosis.
OtherOther
typestypes
of stem
of stem
cells cells
− most
− most
notably
notably
mesenchymal
mesenchymal
stemstem
cells cells
− are−ofare
interest
of interest
because
because
of their
of their
suppressive
suppressive
effects
effects
on the
onimmune
the immune
system.
system.
TheyThey
are are
beingbeing
investigated
investigated
as the
asbasis
the basis
of therapies
of therapies
for for
minimising
minimising
the damage
the damage
caused
caused
by acute
by acute
events
events
such such
as as
heartheart
attacks
attacks
and stroke.
and stroke.
StemStem
cells cells
can also
can be
also
used
be used
as components
as components
in other
in other
constructs
constructs
to create
to create
devices
devices
or other
or other
functional
functional
or or
structural
structural
tissues.
tissues.
Examples
Examples
here here
mightmight
include
include
artificial
artificial
skin made
skin made
from from
fibroblasts
fibroblasts
in a supporting
in a supporting
matrix,
matrix,
the use
the use
of stems
of stems
cells cells
to reconstruct
to reconstruct
tissues
tissues
such such
as the
astrachea,
the trachea,
or theordevelopment
the development
of biomaterials
of biomaterials
containing
containing
growth
growth
factors
factors
to stimulate
to stimulate
bonebone
stemstem
cells cells
in theintreatment
the treatment
of of
fractures.
fractures.
In addition
In addition
to being
to being
usedused
directly
directly
in cell-based
in cell-based
therapies,
therapies,
stemstem
cells cells
can also
can deliver
also deliver
betterbetter
treatments
treatments
for disease
for disease
through
through
indirect
indirect
means
means
(see (see
Chapter
Chapter
4). For
4).instance,
For instance,
researchers
researchers
can now
can derive
now derive
iPS cell
iPSlines
cell lines
from from
individuals
individuals
suffering
suffering
from from
a specific
a specific
disease.
disease.
These
These
disease-specific
disease-specific
iPS cells
iPS cells
can be
can
used
be used
as models
as models
to study
to study
detailed
detailed
characteristics
characteristics
of diseases
of diseases
such such
as Duchenne
as Duchenne
Muscular
Muscular
35
35
Dystrophy.
Dystrophy.
They
They
can also
can be
also
used
be used
to screen
to screen
the the
effectiveness
effectiveness
and toxicity
and toxicity
of potential
of potential
new drugs.
new drugs.
hES hES
cells cells
are also
are useful
also useful
as disease
as disease
models
models
and are
andbeing
are being
usedused
to test
topotential
test potential
new drugs
new drugs
for toxic
for toxic
side effects
side effects
across
across
a wide
a wide
rangerange
of celloftypes.
cell types.
hES cells
hES cells
also offer
also offer
a
a
unique
unique
model
model
in which
in which
to study
to study
earlyearly
human
human
development
development
and stem
and stem
cell research
cell research
is delivering
is delivering
improved
improved
understanding
understanding
of basic
of basic
cell processes
cell processes
such such
as as
differentiation,
differentiation,
division,
division,
cell death,
cell death,
etc. This
etc. knowledge
This knowledge
couldcould
lead to
lead
new
to targets
new targets
for drug
for drug
design.
design.
35
Wu35SMWu
andSM
Hochedlinger
and Hochedlinger
K, Nature
K, Nature
Cell Biology,
Cell Biology,
13, 497–505,
13, 497–505,
2011 2011
3.2 3.2
Regulatory
Regulatory
bodies
bodies
and and
pathway
pathway
SuchSuch
activities
activities
cut across
cut across
a wide
a wide
rangerange
of regulatory
of regulatory
areas.
areas.
For instance,
For instance,
Figure
Figure
3.1 shows
3.1 shows
the main
the main
approvals
approvals
that may
that be
may
needed
be needed
to conduct
to conduct
clinical
clinical
trials trials
involving
involving
stemstem
cells cells
in theinUK.
theThey
UK. They
include
include
regulations
regulations
covering:
covering:
„ The
„ ethical
The ethical
review
review
of research
of research
involving
involving
human
human
subjects
subjects
through
through
the NHS
the NHS
National
National
Research
Research
Ethics
Ethics
Service
Service
(NRES).
(NRES).
NRES
NRES
is now
is part
now of
part
theofnew
the Health
new Health
Research
Research
Authority
Authority
(HRA).
(HRA).
„ Research
„ Research
on human
on human
tissuetissue
currently
currently
overseen
overseen
by the
by the
Human
Human
Tissue
Tissue
Authority
Authority
(HTA).
(HTA).
„ Research
„ Research
involving
involving
human
human
embryos,
embryos,
regulated
regulated
by by
the Human
the Human
Fertilisation
Fertilisation
and Embryology
and Embryology
Authority
Authority
(HFEA).
(HFEA).
„ Other
„ Other
research
research
areasareas
such such
as work
as work
involving
involving
genetic
genetic
modification
modification
(overseen
(overseen
by the
byHealth
the Health
and Safety
and Safety
Executive;
Executive;
HSE)HSE)
or animal
or animal
research
research
(Home
(Home
Office;
Office;
HO). HO).
„ The
„ marketing
The marketing
of new
of therapies
new therapies
and the
andconduct
the conduct
of of
clinical
clinical
trials trials
in humans
in humans
(regulated
(regulated
by the
byMHRA
the MHRA
and and
36
the EMA
the 36
EMA
depending
depending
on the
onnature
the nature
of theof the
therapeutic
therapeutic
product).
product).
This includes
This includes
the need
the need
to obtain
to obtain
research
research
permissions
permissions
from from
all of all
theofNHS
the NHS
truststrusts
involved
involved
in clinical
in clinical
trials.trials.
In December
In December
2011,2011,
the Government
the Government
established
established
the HRA
the HRA
as a Special
as a Special
Health
Health
Authority
Authority
(SHA).
(SHA).
Its purpose
Its purpose
is to is to
protect
protect
and promote
and promote
the interests
the interests
of patients
of patients
and the
and the
publicpublic
in health
in health
research.
research.
It willItalso
will work
also work
to combine
to combine
and and
streamline
streamline
the current
the current
approval
approval
system
system
and promote
and promote
a
a
consistent
consistent
and proportionate
and proportionate
approach
approach
to regulation.
to regulation.
An An
explicit
explicit
goal is
goal
to reduce
is to reduce
the regulatory
the regulatory
burden
burden
on on
37
37
businesses,
businesses,
universities
universities
and the
andNHS.
the NHS.
36
37
36 MHRA
MHRA
is the Medicines
is the Medicines
and Healthcare
and Healthcare
products
products
Regulatory
Regulatory
AgencyAgency
and and
EMA isEMA
the European
is the European
Medicines
Medicines
AgencyAgency
37 www.dh.gov.uk/health/2011/12/creation-hra/
www.dh.gov.uk/health/2011/12/creation-hra/
Page 16
POST Report March 2013 Stem Cell Research
FIGURE 3.1 UK REGULATORY PATHWAY OF CLINICAL TRIALS INVOLVING STEM CELLS
Figure 3.1 UK regulatory pathway for health research
Key
„ IRAS is the Integrated Research Application System
„ NRES is the NHS National Ethics Service
„ HFEA is the Human Fertilisation and Embryology Authority
„ HTA is the Human Tissue Authority
„ HO is the Home Office
„ HSE is the Health and Safety Executive
„ MHRA is the Medicines and Healthcare products Regulatory Agency
„ NIHR is the National Institute for Health Research
Figure
POST Report March 2013 Stem Cell Research
3.3 Ethical review of research
Research may involve an element of risk to those
participating in it. For instance, a new therapy may
have unforeseen side-effects that only become
apparent once it has been given to large number of
people. Research may also involve additional
burdens or intrusions such as the taking of blood
tests or other measurements or the collection of
detailed personal information.
The purpose of ethical review is to protect people
taking part in research. Before starting a proposed
research project, researchers must satisfy a
research ethics committee (REC) that their research
will be ethical and worthwhile. The committee will
weigh any expected benefits (to the participants or
more widely to society) against any anticipated risks
or intrusions. It will only approve the proposed
research if it is satisfied that the researchers have
minimised the risks and intrusions to participants
and that these are outweighed by the potential
benefits of the research.
There are a number of different requirements for
ethical review of research proposals. These include
governance of research in the NHS, legal
requirements and various other institutional or
funding requirements for REC review of research
proposals.
NHS requirements for REC review
Requirements for ethical review of research in the
NHS are laid down by the Department of Health
(DH). Details of these requirements are outlined in
Box 3.1. Broadly speaking, GAfREC requires REC
review of all research proposals involving:
„ NHS patients, facilities or staff (see Box 3.1)
„ tissue or information from NHS patients
„ xenotransplantation (putting into people living
cells, tissue or organs taken from an animal)
„ health-related research involving prisoners or
social care research funded by the DH.
Legal requirements for REC review
In addition to the requirements summarised in
GAfREC, there are other pieces of legislation that
may require research proposals to be reviewed by a
REC. There is a large amount of overlap between
many of the legal approvals required for stem cell
research and the research ethics review process.
Page 17
Box 3.1 NHS requirements for REC review
For research in the NHS, the Department of Health (DH) has
published a new (harmonised) edition of its governance
arrangements for research ethics committees (GAfREC)38 that
came into force in September 2011. The document covers the
following services provided by the four UK Health Departments:
„ NHS and adult social care provided by the DH in England
„ NHS and social care provided by the Department of
Health and Social Services in Wales
„ NHS care provided by the Scottish Government Health
Directorates in Scotland
„ Health and social care provided by the Department of
Health, Social Services and Public Safety in Northern
Ireland.
GAfREC requires all research proposals to be the subject of a
REC review if they involve:
„ participants who have been recruited because of their use
of any of the services outlined above; this includes all
NHS patients and also applies to the recruitment into
clinical trials of NHS patients as healthy (untreated)
controls
„ participants who have been recruited because they are
related to, or are a carer of, an existing or past user of
one of the services outlined above
„ the collection of tissue (any material consisting of or
including human cells) or information from users of these
services
„ use of previously collected tissue or information from
which individual past or present users of these services
could be identified.
„ xenotransplantation (putting into people living cells, tissue
or organs taken from an animal).
„ health-related research involving prisoners or social care
research funded by the DH.
Requirements potentially relevant to stem cell
research include research involving:
„ exposing people to ionising radiation
„ processing of confidential patient information
without consent where this would breach
confidentiality
„ material consisting of human cells taken from
the living or dead.
„ certain medical devices (those not conforming
to EU directives or devices that have been
modified)
„ potential new drugs (these are known as
investigational medicinal products)
„ people who lack (or lose) the capacity to
consent to taking part in research
„ protected information from the HFEA register.
38
www.dh.gov.uk/prod_consum_dh/groups/dh_digitalassets/
documents/digitalasset/dh_126614.pdf
Page 18
Other requirements for REC review
Outside of the NHS and legal requirements, there
may be other requirements for REC review of
research. For instance, clinical trials involving gene
therapy or stem cells used to require approval from
the Gene Therapy Advisory Committee (GTAC).
However, GTAC ceased to operate in November
2012 and its responsibilities have been subsumed
into the NRES system (see below). Guidance
published by research funders such as the Medical
Research Council (MRC)39 and the Wellcome
Trust40 may also require research proposals to
obtain a positive research ethics review as a
condition of funding. In addition, many research
institutions and universities have published
guidance on good research practice that requires
research proposals involving human subjects to be
reviewed by a REC. Many universities and other
research institutes also have institutional RECs that
consider research proposals for research involving
human subjects. The activities of and processes
used by such bodies are co-ordinated through the
Association of Research Ethics Committees.
The National Research Ethics Service
The National Research Ethics Service (NRES)
provides ethical guidance, training and
management support to NHS RECs, and runs a
quality assurance programme. Between April 2010
and March 2011 all UK committees considered
7,072 applications for ethical review of research
proposals. NRES was transferred to the newly
formed Health Research Authority in December
2011. The move paves the way to NRES
completing service improvements, such as UK-wide
electronic submission through the Integrated
Research Application System (see next page).
RECs must be independent and impartial, and
adopt standard operating procedures to ensure that
they operate in an efficient and timely manner.
GAfREC stipulates requirements for the
composition of NHS RECs and how they operate
(see Box 3.2).
39
40
www.mrc.ac.uk/Ourresearch/Ethicsresearchguidance/index.htm
www.wellcome.ac.uk/About-us/Policy/Policy-and-positionstatements/WTD002753.htm
POST Report March 2013 Stem Cell Research
Box 3.2 Composition and operation of RECs
GAfREC specifies that NHS RECs should have between 7 and
18 members. It notes that committees should contain a mix of
expert and lay members, with the lay members comprising at
least one third of the total membership. Expert members are
needed to ensure that the committee has the methodological
and ethical expertise needed to make decisions about research
proposals. Lay members are defined as people who are
independent of care services. At least half of the lay
membership must be people who have never been care
professionals or worked in care services.
All REC members are unpaid volunteers, although members
will usually receive expenses for attending meetings or
conducting other committee business. RECs do not charge
researchers for their services; the costs of ethical review are
met by the organisation that constituted the REC in question.
Costs for NHS RECs are met out of the NRES budget (£10.1
million in 2010).
Box 3.3 The different phases of clinical trials
New clinical interventions must be tested in clinical trials before
they can be marketed or introduced into practice. The phrase
clinical intervention covers a wide range of territory: drugs,
vaccines, cell therapies, medical devices, surgical procedures,
psychological therapies and diagnostic/screening procedures
are just some examples. Clinical trials are split into different
phases:
„ Phase I. The treatment is tried out in small numbers of
people. For drugs these are usually healthy volunteers.
The aim is to see how the body metabolises the drug and
how it tolerates different doses. For most types of cell
therapy and all gene therapy, the treatments are received
by small numbers of individuals affected by the disease in
question.
„ Phase II. The treatment is given to small numbers of
people who are affected by the disease in question. The
aim of this phase is to see whether the treatment is
effective and if so, what the optimal dose for treatment
might be.
„ Phase III. The treatment is given to large numbers of
patients with the condition in question, to determine
whether it is safe and effective. Because this may involve
recruiting thousands of patients suffering from a particular
condition, phase III trials are typically multi-centre, time
consuming and expensive to conduct.
Evidence from the different phases will be passed on to the
appropriate regulatory body which assesses safety, efficacy
and whether the treatment can be manufactured to appropriate
quality standards. If the regulatory body gives the go-ahead for
marketing a fourth phase follows:
„ Phase IV. Information is collected about the longer-term
risks and benefits of the treatment. This is necessary to
pick up rare adverse reactions or side effects, and to finetune guidance on which patients will benefit most.
POST Report March 2013 Stem Cell Research
NHS RECs and clinical trials
One of the functions of NHS RECs is to consider
applications for clinical research (see Box 3.3 for an
overview of the clinical trials process). Up to
November 2012, all applications involving gene or
cell therapy were considered by GTAC. From
December 2012, GTAC has been subsumed into
the NRES system. Its responsibilities have been
shared between three existing RECs in West
London, Oxford and York. The MHRA Clinical Trials
Advisory Group provides advice on first-time-in-man
studies and clinical trials involving other novel
approaches, including cell therapy. In practice,
applications to conduct clinical trials involving cell
therapy thus need to be submitted to one of the
GTAC RECs and to the MHRA Clinical Trials
Advisory Group.
Before the introduction of the Clinical Trials
Directive in UK law − as the Medicines for Human
Use (Clinical Trials) Regulations − in 2004, there
was no specified timeframe for completing an
ethical review. The clinical trials regulations
introduced a 60 day41 time limit for RECs to deliver
an opinion on proposed research and this has been
adopted as a permissible maximum by all the
different types of RECs.
Indeed, NRES guidance on standard operating
procedures for RECs states that the operational
target should be to deliver an opinion within 40 days
of a valid claim being received.42 Overall, the ethical
review process has been streamlined and speeded
up in recent years. The introduction of the
integrated research application system has also
made it easier for researchers to use. A review of
the regulation and governance of health research
highlighted the need for proportionate ethical review
and consistency of decision making between RECs
as being two key areas where there may still be
room for improvement.
The Integrated Research Application
System (IRAS)
IRAS is a web-based system that provides a single
point of entry for applying for the permissions and
approvals for health research in the UK. It allows
researchers to enter details of their project on a
single form, rather than duplicating the information
in separate application forms.
41
42
90 days for gene therapy, cell therapy or for trials involving
genetically modified organisms (180 days if a specialist body is
consulted). Also, for trials involving cell therapy using non-human
cells, there is no specified time limit.
www.nres.npsa.nhs.uk/news-andpublications/publications/standard-operating-procedures/
Page 19
IRAS was originally developed by NRES, the UK
Clinical Research Collaboration partners and the
UK Health Departments. Since its launch in January
2008, functions have been added to IRAS to
increase the number of regulatory bodies that the
system can interface with. By using filters, a single
set of information entered by a researcher can be
presented in multiple formats to be compatible with
the requirements of a wide range of assessments,
including:
„ NRES
„ Administration of Radioactive Substances
Advisory Committee
„ Ministry of Justice
„ MHRA
„ Ethics and Confidentiality Committee of the
National Information Governance Board
„ NHS R&D permissions.
3.4 Research on human tissue
UK human tissue legislation
Regulation of research involving human tissue
varies between Scotland and the rest of the UK.
There are two main laws: the Human Tissue
(Scotland) Act 2006 that applies in Scotland, and
the Human Tissue Act 2004 that applies in England,
Wales and Northern Ireland. Table 3.2 summarises
key features of each.
Perhaps the biggest difference between the two
laws is than in Scotland, the law seeks solely to
regulate the removal, storage and use of human
material from the deceased. It does not regulate the
use of human tissue from living donors for research
purposes (Table 3.1).
Table 3.1 Features of human tissue legislation in
Scotland (right) and the rest of the UK (left)
Human Tissue Act Human Tissue 2004 (Scotland) Act 2006 43
Applies in England, Wales & Scotland Underlying principle Legal framework covers 43
Northern Ireland Consent Removal, storage & use of human organs, tissue & cells from the dead Storage & use of human organs & tissue from the living HTA regulates the storage of tissue samples for research purposes Authorisation Removal, storage & use of human organs, tissue & cells from the dead Note that one part of the Human Tissue Act 2004, that relating to
non-consensual analysis of DNA (section 45 and schedule 4),
applies throughout the UK.
POST Report March 2013 Stem Cell Research
Page 20
Box 3.4 The Human Tissue Act 2004
Relevant material
The Act regulates retention and use of ‘relevant material’ and
defines it as material that has come from the human body and
that consists of, or may contain, human cells. Several human
tissues are specifically excluded from the Human Tissue Act.
These include gametes and embryos (which were already
regulated by the HFEA), cell lines which are regulated by the
Human Tissue (Quality and Safety for Human Application)
Regulations 2007 and hair and nails taken from living people.
Despite these exclusions, relevant material covers a very wide
range of human tissue.
Scheduled purposes
The Act lists ‘scheduled purposes’ for which consent is
required. From the point of view of stem cell research the most
relevant of these are research on human tissue and using
human tissue to treat patients. Other scheduled purposes listed
in the Act include teaching about or studying the human body,
carrying out post-mortem examinations and displaying human
bodies or tissue in public.
Appropriate consent
The Act identifies those people who can give appropriate
consent for the lawful retention or use of human tissue for
scheduled purposes. These include:
„ a living competent adult, or competent child for the
retention/use of their tissue
„ a person with parental responsibility for a child for the
use/retention of the child’s tissue
„ consent prior to death for the use/retention of tissue from
a dead adult, or failing that the consent of a nominated
representative or of a qualifying relative
„ consent procedures for those lacking the capacity to give
consent are covered by separate regulations.
Exceptions
The Act provides for a number of exceptions to the general rule
that consent is required. Broadly speaking these are:
„ the use of existing holdings (material already in storage
before the Act came into force)
„ surplus or residual tissue from diagnostic or surgical
procedures for clinical audit, education, performance
assessment, public health monitoring or quality assurance
purposes
„ residual tissue for research provided the research has
been approved by a REC.
Under the terms of the Human Tissue (Scotland)
Act 2006 authorisation for a hospital post-mortem
examination is required from an adult or mature
child prior to their death. Failing that, authorisation
should be obtained from a nominee of the dead
person, or their nearest relative. Tissue samples no
longer required for official purposes can be retained
and used without authorisation for diagnostic and
audit purposes. However, authorisation is required
for use of such tissue for education, training or
research.
In the rest of the UK, the Human Tissue Act 2004
requires consent for the lawful retention and use of
body parts from the living or the dead for scheduled
purposes (see Box 3.4). Consent is also required
for the removal of human material from the dead.44
The Act details what constitutes appropriate
consent and who can give it, and outlines certain
exceptions where the general requirement for
consent may be waived (see Box 3.4). Finally, the
Act contains a definition of ‘relevant material’ for
which consent is required.
The Human Tissue Authority
The HTA has two main areas of responsibility:
„ licensing and inspecting organisations that
store and use human tissue
„ approving donations of organs and bone
marrow from living people.
The Future of HTA was the subject of a DH
consultation between June and September 2012.
Two of the three proposals in the consultation
proposed to abolish HTA and transfer its functions
elsewhere. This is discussed in more detail in
chapter 6.
Licensing and inspection
As summarised in Table 3.2, the HTA licenses
organisations that store and use human tissue
under two main pieces of legislation:
„ The Human Tissue Act 2004 (Box 3.4).
„ The Human Tissue (Quality and Safety for
Human Application) Regulations 2007 (Box
3.5), referred to as the Q&S Regulations.
Table 3.2 Activities and organisations licensed
by the HTA
Activity Licensed under Organisations licensed45 Tissue & cells for patient treatment Post‐mortem examination Research Anatomy Public display 44
45
Quality & Safety Regulations 2007 (Box 5) Human Tissue Act 2004 Human Tissue Act 2004 Human Tissue Act 2004 Human Tissue Act 2004 181 205 136 35 13 Consent for removing human material from living donors is required
by common law.
As of 4th July 2011. Source www.hta.gov.uk/
licensingandinspections/licensedestablishments.cfm
POST Report March 2013 Stem Cell Research
The Human Tissue Act requires all organisations in
England, Wales and Northern Island that store and
use human tissue for scheduled purposes to be
licensed (see Box 3.4). This includes pathology
services, anatomy schools, establishments that
carry out anatomical examination and post-mortem
examination, research organisations and museums
that display human tissue.
The Q&S Regulations (Box 3.5) are designed to
ensure that human tissue used to treat patients is
safe and of high quality. It covers the procurement,
testing, processing, storage, distribution, import and
export of human tissues and/or cells intended for
human application. All organisations throughout the
UK (including Scotland) involved in such activities
must be licensed by HTA.
An organisation wishing to conduct one or more of
the activities outlined in Table 3.2 must apply to
HTA for a licence. It must provide information about
the intended activity and appoint a Designated
Individual who is responsible for ensuring that:
„ other people to whom the licence applies are
suitable to participate in the licensed activity
„ suitable practices are used in the course of
carrying out the activity and
„ users comply with the conditions of the licence.
Once HTA receives an application it will consider
the information provided. It may seek further
information from the applicant via email or phone.
HTA considers the information provided and may
decide to grant a licence, grant a licence with
additional conditions attached, or refuse the licence.
Over the course of a licence, HTA may seek further
information from the licence holder to check that the
licensing standards continue to be met. It also
conducts on-site inspections of those
establishments considered to be at highest risk of
not meeting the licensing requirements.
Approving donations
Under the terms of the Human Tissue Act 2004, the
HTA assesses all proposed transplants involving:
„ organs donated by living donors
„ bone marrow or peripheral blood stem cells
from adults who lack the capacity to consent or
children who lack the competence to consent.
Page 21
Box 3.5 The Human Tissue (Quality and Safety for Human
Application) Regulations 2007
The Quality and Safety (Q&S) Regulations implement the EU
Tissue and Cells Directive into UK law. The aim of the Directive
is to set a common standard across the EU for activities using
human tissues and cells to make sure that tissue is safe and of
high quality. It also allows tissue and cells to be traced from
donors to recipients and moved easily between European
countries. The Q&S Regulations implement the Directive
throughout the UK, including Scotland. Under the terms of the
Regulations the HTA is responsible for licensing organisations
that remove, store, test, process, use or distribute human
tissue or cells that will be used to treat patients. Examples
include:
„ collecting umbilical cord blood in maternity units
„ isolation and culture of human cell lines for therapeutic
purposes
„ storing corneas in eye banks
„ processing cartilage for repairing knee injuries.
Potential organ donors are interviewed by
independent assessors (IAs). IAs are accredited by
HTA and are usually based in hospital transplant
units. They act as a representative of the donor and
HTA in order to help the HTA ensure the
requirements of the Human Tissue Act 2004 have
been met. Following the interview, the IA submits a
report to HTA which then decides whether to
approve the proposed donation.
All potential donations of bone marrow or peripheral
blood stem cells from those unable to give consent
are assessed by accredited assessors (AAs). Once
the AA has assessed a potential donation, they
report to the HTA which decides whether to approve
it.
3.5 Research involving human embryos
Embryo research legislation
Research involving human embryos is regulated
under the Human Fertilisation and Embryology
(HFE) Act. The Act was passed in 1990 to regulate
all uses of human embryos outside of the body and
to provide the statutory basis for the Human
Fertilisation and Embryology Authority (HFEA). It
allows research on human embryos, but only under
licence, and only for certain purposes specified in
the Act. The Act prohibits the granting of a licence
that allows the keeping or use of an embryo for
more than 14 days.
POST Report March 2013 Stem Cell Research
Page 22
The purposes listed in the 1990 Act were mainly
concerned with licensing research on infertility,
miscarriage and contraception. The Act was
amended in 2001 to extend the allowable reasons
for embryo research to include therapeutic
purposes. In practice this allowed the HFEA to
licence research it deemed necessary or desirable
on ES cells and on techniques such as cell nuclear
replacement. The passing of the HFE Act 2008,
represented a major review of the legislation,
updating and amending the 1990 Act. This further
clarified the scope of legitimate embryo research
activities, including regulation of ‘human admixed
embryos’ (embryos combining both human and
animal material).
Box 3.6 outlines the principle purposes for which
the HFEA can licence research involving embryos.
Examples of recent research projects licensed by
the HFEA are shown in Table 3.3. It is important to
note that an HFEA licence is only required by
researchers whose research actually involves
human embryos. An HFEA licence is not required
to conduct research on existing human cell lines −
for instance from a stem cell bank − that were
originally derived from embryos.
In addition to the statutory controls in Box 3.6, the
use of stem cells in research is monitored by the UK
Stem Cell Bank Steering Committee. The
committee reviews all applications to deposit and
access hES cells and monitors the use of fetal and
adult stem cells. This review and monitoring
process is seen as an additional (non-statutory)
safeguard to prevent inappropriate use of stem cells
in research.
The Future of HFEA was the subject of a DH
consultation between June and September 2012.
Two of the three proposals in the consultation
proposed to abolish HFEA and transfer its functions
elsewhere. This is discussed in more detail in
chapter 6.
Box 3.6 Principle purposes for embryo research
The HFEA Licensing Committee can only licence embryo
research if it is satisfied that the use of embryos is necessary
and that the proposed research is necessary or desirable for
one of the following purposes:
„ increasing knowledge about serious disease or other
serious medical conditions
„ developing treatments for serious disease or other
serious medical conditions
„ increasing knowledge about the causes of any congenital
disease or congenital medical condition that does not fall
within the first bullet point
„ promoting advances in the treatment of infertility
„ increasing knowledge about the causes of miscarriage
„ developing more effective techniques of contraception
„ developing methods for detecting the presence of gene,
chromosome or mitochondrion abnormalities in embryos
before implantation
„ increasing knowledge about the development of embryos.
The HFEA and embryo research
Any researcher wishing to conduct research on
human embryos must first apply for approval from
an NHS REC. Once this has been received, HFEA
recommends researchers to contact the relevant
HFEA staff members to discuss the proposed
research prior to making a formal application. Once
HFEA has received a formal application along with
the appropriate administration fee46, it commissions
peer reviewers to assess the application and
arranges for an initial inspection of the research
establishment(s) in question.
The peer review process assesses whether the
application:
„ needs to use human embryos to fulfil its stated
objectives
„ needs to use the number and type of embryos
proposed
„ falls within the statutory requirements of the Act
„ meets the requirements of the HFEA’s Code of
Practice.
After an initial inspection of the research
establishment(s) making the application an
inspection report is prepared for the Research
Licensing Committee. The committee will consider
the inspection and peer reviewers’ opinions along
with any other relevant material. It can decide to:
„ grant a licence
„ grant a licence subject to certain conditions
„ refuse a licence.
46
Research licence fees reflect the complexity of the proposed
research. For small projects the charge is £500 whereas more
complex projects (such as the derivation of hES cells or cell nuclear
replacement) the fee is £750.
POST Report March 2013 Stem Cell Research
Page 23
Table 3.3 Research projects licensed by the HFEA between April 2010 and March 2011
Research group Assisted Conception Service, Glasgow Royal Infirmary Birmingham Women's Hospital/Institute of Biomedical Research Birmingham Women's Hospital Centre for Human Development, Stem Cells and Regeneration, University of Southampton Centre for Reproductive Medicine, Coventry Centre for Stem Cell Biology and Developmental Genetics, University of Newcastle Guy's Hospital, London Hull IVF Unit Human Genetics and Embryology Laboratories, University College, London Institute of Biomedical Research Institute of Reproductive and Developmental Biology, Imperial College, London IVF Hammersmith London Fertility Centre Manchester Fertility Services Ltd/St Mary's Hospital, Manchester/University of Manchester Newcastle Fertility Centre at Life Oxford Fertility Unit/University of Oxford, Dept of Obstetrics and Gynaecology Roslin Cells Limited Section of Reproductive and Developmental Medicine, University of Sheffield/Centre for Stem Cell Biology, Sheffield University of Cambridge Wales Heart Research Institute, Cardiff Welcome Trust Centre for Stem Cell Research, University College Cambridge 47
HFEA Annual Report 2010/11 (www.hfea.gov.uk/146.html)
47
Research area The effect of biomass reduction on embryo development after biopsy of either one or two blastomeres Human gamete interaction and signalling Genetic screening of the pre‐implantation embryo Environmental sensitivity of the human pre‐implantation embryo Indicators of oocyte and embryo development Derivation of ES cell lines from interspecies embryos produced by somatic cell nuclear transfer Improving methods for pre‐implantation genetic diagnosis (PGD) of inherited genetic disease and predicting embryo quality Developing criteria for estimating quality of stem cells derived from human embryos Biochemistry of early human embryos Genetic profiling for infertility and development of novel pre‐implantation diagnosis Derivation of GMP (Good Manufacturing Practice) hES cells Comparative studies on hES cells and stem cells derived from male germ cells The vitrification of blastocysts following biopsy at the early‐cleavage stage or blastocyst stage of embryo development Analysis of chromosomes in human preimplantation embryos using FISH and CGH In vitro development and implantation of normal human preimplantation embryos compared with uni‐ or poly‐ pronucleate pre‐embryos Derivation of hES cell lines from embryos created from clinically unused oocytes or abnormally fertilised embryos Pluripotency, reprogramming and mitochondrial biology during early human development Mitochondrial DNA Disorders: is there a way to prevent transmission? Development of a model to study implantation in the human To derive hES cells and trophoblast cell lines To develop PGD for mitochondrial DNA disease Platform technologies underpinning hES cell derivation Development of hES cell lines to GMP for treatment of degenerative diseases and conditions Derivation of hES cells from human surplus embryos: the development of hES cultures, characterisation of factors necessary for maintaining pluripotency and specific differentiation towards transplantable tissues Investigation into the role of sperm PLC zeta in human oocyte activation Derivation of pluripotent human embryo cell lines POST Report March 2013 Stem Cell Research
Page 24
Licences are granted for up to three years. It is a
condition of any licence of more than one year’s
duration that the licence holder submits an annual
progress report to HFEA and a condition of all
licences that an end of project report is submitted
once the licence has expired. If a licence is refused,
the applicants have 28 days in which to appeal
against the decision. HFEA aims to process 90% of
all research licence applications within three months
of receiving the formal application.
3.6 Other research regulation
Care Quality Commission (CQC)
CQC is the independent regulator of health and
social care services in England. Established in April
2009, CQC replaced three previous commissions:
the Healthcare Commission, the Commission for
Social Care Inspection and the Mental Health
Commission. One of CQC’s responsibilities is to
inspect facilities such as hospitals and clinics. This
means that there is some overlap between
inspections conducted by CQC and those carried
out by HFEA and HTA. For instance 40
establishments are subject to regulation/registration
by HFEA, HTA and CQC, 90 of the 100 or so HFEA
licensed centres are also regulated by CQC or are
located in premises that are CQC registered and
264 of the 440 HTA licensed establishments are
also regulated by CQC.48
Reducing this overlap is one of the factors that
prompted proposals to reform regulation in this
area. DH has consulted on proposals to abolish
HTA and HFEA and transfer their regulatory
functions to other regulators. Two of the three
proposals involved CQC taking on additional
responsibilities. As discussed in more detail in
Chapter 6 these options have now been rejected.
NHS research permissions
In addition to obtaining authorisation from the
MHRA for conducting clinical trials, research
permissions must be obtained from each of the
NHS trusts involved in a trial. Different bodies are
responsible for co-ordinating these R&D
permissions within the UK:
48
www.ialibrary.bis.gov.uk/uploaded/DH%206044%20%20Consultation%20IA-Transfer-Functions-from-the-HFEA-andHTA.pdf
„
„
„
„
The National Institute of Health Research
(NIHR) runs a co-ordinated system for gaining
NHS research permissions (CSP) in England.
In Scotland, NHS Research Scotland coordinates R&D permissions.
In Wales there is a Primary Care Co-ordinating
Office that handles R&D permissions for
research in primary care settings.
In other cases, research permissions are
handled by the relevant R&D Office of the NHS
organisation involved.
The Academy of Medical Sciences’ (AMS) review of
the governance of health research identified the
process of obtaining NHS R&D permissions as “the
most significant barrier to health research in the
UK”. 49 It suggested that changes were needed to
reduce bureaucracy and increase the speed of NHS
R&D permissions. The AMS recommended setting
up a new national body to oversee a streamlined,
common process for NHS R&D permission for all
single and multi-site studies in the NHS in England.
There is debate (discussed in Chapter 6) about
whether the new HRA should take responsibility for
research permissions.
Animal research
Stem cell researchers may also need to seek
regulatory approval from other authorities. For
instance, many recent advances in stem cell
research have first been achieved using animal
studies. Thus, ES cells and IPS cells were first
derived from studies in mice. Furthermore, animal
models are widely used to study human disease
and assess potential new therapies. All animal
research in the UK is regulated by the Home Office
under the Animals (Scientific Procedures) Act 1986.
As outlined in Box 3.7, all UK research involving
animals must:
„ take place in a designated research
establishment with appropriate facilities
„ be conducted by people who hold a personal
licence
„ be part of a programme of research that has
received a project licence.
49
A new pathway for the regulation and governance of health
research, AMS, January 2011
POST Report March 2013 Stem Cell Research
Box 3.7 The Animals (Scientific Procedures) Act 1986
The Animals (Scientific Procedures) Act 1986 was amended by
The Animals (Scientific Procedures) Act 1986 Amendment
Regulations 2012. It aims to safeguard animal welfare while
allowing scientific research involving animals. The Act requires
all proposed research involving animals to be assessed by
Home Office Inspectors who will weigh the potential benefits of
the research against the likely costs to animal welfare. An
Inspector will issue a project licence for the proposed studies
only if they are satisfied that:
„ the work can only be done by using animals
„ the potential benefits of the work justify the use of animals
„ the study has been designed to minimise a) the number
of animals used and b) the pain and suffering of those
animals through the use of anaesthetics and painkillers
„ the species chosen for the proposed work is appropriate
(use of higher order species such as primates is only
sanctioned where absolutely necessary).
In addition to project licences, the individual(s) conducting the
research and the premises where the research is to be
undertaken must also be licensed. Personal licences ensure
that people conducting research on animals have the
appropriate skills, experience and training. Designated
research establishments are inspected by Home Office
Inspectors to ensure that they have the appropriate facilities.
Finally, all designated establishments are required to have a
local ethical review process. This reviews the ethics of
proposed research and encourages the adoption of the 3 Rs
principles wherever appropriate: a reduction in the number of
animals used; replacement of animals wherever possible and;
refinement of procedures to minimise potential pain, suffering
or distress.
Genetic modification
Some areas of stem cell research involve the use of
viral vectors to transfer genes coding for
transcription factors or other regulatory proteins into
cells. For instance, genetic modification (GM) has
been used to derive IPS cells or to switch cells of
one lineage to those of another. Uses of such
techniques are regulated by the Genetically
Modified Organisms (Contained Use) Regulations
2000.50 These regulations classify GM activities
involving micro-organisms from Class 1 (no or
negligible risk) to Class 4 (high risk).51 They require
researchers to:
„ notify the Health and Safety Executive (HSE)
prior to a premises being used for GM activity
for the first time
„ conduct a risk assessment of activities
involving GM micro-organisms
„ notify the competent authority of all activities
involving Class 2 (low risk) to Class 4 (high
risk) microorganisms
„ await consent before proceeding with Class 3
(medium risk) and 4 activities.
50
51
As amended by Regulations in 2002, 2005 and 2010.
www.hse.gov.uk/pubns/misc208.pdf
Page 25
3.7 Stem cells and clinical trials
Stem cells and medicinal products
The regulations that apply to stem cell therapies
vary depending on whether or not the cells used are
classified as medicinal products. Blood stem cells
have been used in transplantation therapies since
the early 1980s. The cells used in such therapies
are not classified as medicinal products because:
„ they have undergone only very minimal
manipulation (such as basic purification and
preservation techniques);
„ they perform the same function in the recipient
as they did in the donor.
Because they are not classified as medicinal
products, the cells used in transplantation therapies
do not have to comply with ‘medicine’ regulations
(Box 3.8). Rather, minimally manipulated stem cells
used in transplantation therapies are regulated
under the EU Tissues and Cells Directive as
transposed into the UK Q&S Regulations (see Box
3.5). HTA is responsible for licensing organisations
involved in all stages of the preparation, distribution
and use of such cells in transplantation. Cells that
are classified as medicinal products include those
that:
„ have undergone more substantial manipulation
„ are not intended to perform the same function
in the recipient as they do in the donor.
Such products are known as Advanced Therapy
Medicinal Products (ATMPs). As outlined in the
following section, they are regulated by EU
directives and regulations that enshrine the same
principles as those in the existing legislation on
medicines (Box 3.8). These require medicines to be
made to very high (good manufacturing practice or
GMP) quality standards, and manufacturers to
submit data from clinical trials to show a medicine is
safe and effective before market authorisation can
be granted. There is also a requirement for postauthorisation vigilance to detect any adverse effects
once a medicine is in widespread use.
POST Report March 2013 Stem Cell Research
Page 26
Box3. 8 The EU Clinical Trials Directive
Potential new medicines are investigated in clinical trials, the
conduct of which is regulated by the Clinical Trials Directive
(2001/20/EU). This Directive was transposed into UK law as
the Medicines for Human Use (Clinical Trials) Regulations
2004. As well as regulating the conduct of clinical trials, these
regulations provide a legal basis for RECs, require phase I
trials (see Box 3.3) to be authorised by MHRA, require all
medicinal products used in trials to be made to Good
Manufacturing Practice (GMP) standards by a licensed
manufacturer and empower MHRA to perform statutory
inspections to maintain standards.
Different types of Advanced Therapy
Medicinal Products
ATMPs are defined by the 2001 EU Directive on
medicinal products for human use and by the 2007
Regulation on advanced therapy medicinal
products. Between them, these define three main
categories of ATMPs that may be used to treat,
diagnose or prevent disease in humans.
„ Somatic cell medicinal products use cells from
various sources. The cells used may come
from the patient receiving therapy, be donated
by another person or be of animal origin.
„ Gene therapy involves the transfer of a gene
into a patient in a way that ensures the gene
will be actively expressed in the human body. It
may be used to express a therapeutic protein in
the body, or to prevent one of the patient’s own
genes being expressed or for diagnostic
purposes. The gene to be transferred is often
tagged with other sequences to promote
expression and delivered using a vector which
is often viral in origin.
„ Tissue engineered products are defined as
those containing or consisting of engineered
cells or tissues that can be used to regenerate,
repair or replace human tissue. The cells or
tissue in a TEP may be of human or animal
origin (or both) and may be viable or nonviable. A TEP may also contain other
components such as cell products, biomolecules, biomaterials, chemical substances,
scaffolds or matrices.
Each of these three types of ATMP can be used in
conjunction with one or more medical devices to
give rise to fourth type of ATMP: a so-called
combined ATMP. The term medical device covers a
very diverse range of equipment that is regulated
under separate EU Directives (see Box 3.9).
Box 3.9 Regulation of medical devices
The term medical device covers a very wide array of medical
equipment, from stethoscopes to pacemakers. It is estimated
that there are around 200,000 different types of medical
devices on the market in the EU alone.52 Medical devices are
regulated under three Directives, 90/385/EEC relating to active
implantable medical devices, 93/42/EEC concerning medical
devices and 98/79/EC on in vitro diagnostic medical devices.
These Directives lay down essential requirements for medical
devices, set out conformity routes for manufacturers to follow
and require devices to be classified into one of four groups:
„ Class I for low-risk devices such as stethoscopes
„ Class IIa for low to medium risk devices such as
diagnostic equipment and blood pressure monitors
„ Class IIb for medium risk devices like X-ray machines
„ Class III for higher risk, implantable devices such as
coronary stents, prosthetic heart valves and defibrillators.
Manufacturers must undergo a conformity assessment process
and obtain approval from a Notified Body before marketing a
new device in classes IIa, IIb or III. For Class ll devices (a or b)
this involves the Notified Body reviewing a technical dossier
submitted by the manufacturer. For Class lll devices, the
manufacturer must conduct human clinical investigations, but
not necessarily randomised clinical trials. In September 2012
the European Commission published proposals for new
legislation on medical devices. An MHRA consultation on these
proposals closed in January 2013.
Provided the device is incorporated as an integral
part of the product, it will be classified as a
combined ATMP. In order to obtain a marketing
authorisation for a combined ATMP, the applicant
will have to show that the product satisfies the
medical devices requirements (Box 3.9) as well as
the ATMP regulations.
ATMPs in clinical trials
Cell therapies must be tested in clinical trials before
they can be widely used. The process was outlined
in Box 3.3. Researchers have to apply to the MHRA
for a manufacturer’s licence in order to make an
ATMP for use in clinical trials, to ensure that the
product conforms to the highest standards of GMP.
They also have to apply to the MHRA for
authorisation to conduct the clinical trial in
accordance with the EU Clinical Trials Directive
(Box 3.8).
Data from clinical trials are submitted to the
appropriate regulatory body (the European
Medicines Agency, see next section) which will then
decide whether to award marketing authorisation. In
making this decision, the EMA assesses the quality,
safety and efficacy of the ATMP in question.
52
www.europeanhospital.com/en/article/8649New_EU_medical_device_legislation.html
POST Report March 2013 Stem Cell Research
In practice, making such an assessment is more
difficult for a complex product such as an ATMP
than it is for a simple (small molecule) drug. For
instance, the applicant will have to show that the
therapy in question is a high quality, well defined
investigational product, such as a homogenous
population of viable cells. They will have to provide
details of the cell culture conditions, of the
composition of the culture medium, and show that
they can reliably and reproducibly manufacture a
pure, sterile, stable and well characterised product.
In addition to these quality considerations, the
clinical trial will also have to provide detailed
information about what happens to the ATMP once
it is administered. This will include proof of principle
− for example proof of regeneration from
appropriate animal models − that the approach
works, and details of the distribution, growth and
adherence of cells or tissue once given to patients.
Key safety concerns here include the potential for
cells to cause tumours and the likely immunological
reaction of the patient to cells, tissue or reagents.
Finally, applicants will have to provide information
on the potency of the ATMP − the relationship
between dose and clinical effect − so that efficacy
can be assessed and the optimum dose
determined.
The centralised procedure
All ATMPs must be assessed by the EMA through
its centralised procedure before they can be used
(marketed). A successful application through this
route leads to a single marketing authorisation that
is valid in all EU countries, as well as Iceland,
Liechtenstein and Norway. The centralised
procedure is compulsory for:
„ all ATMPs such as somatic cell therapy, gene
therapy, tissue engineered products and
combined ATMPs
„ other medicines derived from biotechnology
processes, such as genetic engineering
„ human medicines for the treatment of
HIV/AIDS, cancer, diabetes, neurodegenerative
diseases, auto-immune and other immune
dysfunctions, and viral diseases
„ veterinary medicines for use as growth or yield
enhancers
„ officially designated orphan medicines
(medicines used for rare human diseases).
Page 27
Box 3.10 Exemptions to ATMP marketing authorisation
Two exemptions allow the supply of unlicensed ATMPs within
the UK. Both focus on applying therapy to address specific
needs of individual patients rather than provision of a standard
therapy for multiple patients. They are:53
„ The hospital exemption. If an ATMP is prepared within the
UK on a non-routine basis for use in the UK only in a
hospital in accordance with a medical prescription for an
individual patient then marketing authorisation may not be
required.
„ The specials exemption. Marketing authorisation may
also not be required if an ATMP is supplied in response to
a bona fide unsolicited order, formulated in accordance
with the specification of a doctor, dentist or
supplementary prescriber and for use by his individual
patients on his direct responsibility in order to fulfil the
special needs of those patients.
Applications through the centralised procedure are
submitted directly to the EMA; evaluation by the
Agency's scientific committees takes up to 210
days. Applications involving cell therapy and other
types of ATMPs are considered by the EMA’s
Committee for Advanced Therapies (CAT). The
CAT considers the evidence submitted and makes
a recommendation to the EU Commission on
whether the product in question should receive a
marketing authorisation.
In practice, it can be difficult to determine whether
certain types of products should be classified as an
ATMP or (say) a medical device. Recognising this,
the CAT offers an optional procedure whereby
companies can apply to check the ATMP
classification of their product prior to submitting an
application for marketing authorisation through the
centralised procedure. The Committee will give its
opinion on whether the product in question satisfies
the criteria for being classified as an ATMP within
60 days.
As outlined in Box 3.10, there are two exemptions
to the centralised procedure outlined above. Both
allow the supply of unlicensed ATMPs − i.e. those
that have not received a marketing authorisation −
for use in the UK under certain, clearly defined,
circumstances.
53
www.mhra.gov.uk/Howweregulate/Advancedtherapymedicinal
products/FAQs/index.htm
Page 28
3.8 The Stem Cell Tool Kit
In order to help stem cell researchers navigate the
somewhat torturous regulatory pathway from
laboratory to clinic, the DH published the UK Stem
Cell Tool Kit in 2009. It is designed to be a
reference tool for those wishing to develop a
programme of human stem cell research and
manufacture, ultimately leading to clinical
application. It was a joint collaboration between
MRC, GTAC, DH and all of the regulatory bodies
involved in the pathway. The tool kit has been
updated on a regular basis to keep pace with
changes to the regulatory system. It is an iterative
tool which maps out a regulatory path for
researchers in response to their answers to a
succession of questions. The Tool Kit can be
accessed at www.sc-toolkit.ac.uk.
POST Report March 2013 Stem Cell Research
POST Report March 2013 Stem Cell Research
4
Page 29
Scientific advances
Overview
„ It is different patterns of gene expression that make one type of cell differ from another.
„ Recent years have seen great advances in understanding of the factors that control gene
expression.
„ This knowledge can be used to direct cells down specific differentiation pathways.
„ It can also be used to reprogram cells from a highly differentiated (adult) state to cells
that behave in a similar manner to embryonic cells.
„ Such approaches are delivering better disease models for research
4.1 What makes stem cells different?
Virtually all of the cells in the human body carry a
complete set of human genes. Cells contain
mechanisms for switching genes on and off and for
modulating their activity. Different subsets of genes
are expressed to different extents in different types
of cells. It is the mechanisms that control gene
expression that make a stem cell different from
other types of cell and that are responsible for its
pluripotency and ability for self-renewal. The same
mechanisms also direct the stem cell’s fate during
differentiation into more specialised cell types. This
chapter:
„ outlines some of the key factors that maintain
ES cells and direct their differentiation down
different cell lineages
„ describes how this knowledge can be used to
direct a cell’s fate in cell culture
„ looks at how such knowledge can be used to
reverse differentiation and produce iPS cells
from more specialised cell types
„ discusses the potential for using hES and iPS
cells in research
4.2 Factors that control differentiation
A cell’s fate is determined by the way its genome
interacts with its cellular and signalling
environments. Recent research has focused on
understanding the different processes that control
these interactions and ultimately regulate how a cell
behaves. Various mechanisms operate at different
levels and include:
„ epigenetic factors such as chemical
modification of the regulatory regions of the
genes, the proteins associated with gene
sequences or other factors that interfere with
the processes by which genes are copied and
translated into proteins (see Box 4.1)
„ proteins known as transcription factors that
bind to the regulatory regions of genes and
modulate their activity upwards or downwards
(see Box 4.2).
Box 4.1 Gene expression and epigenetics
Differentiation and gene expression
All of the cells in the early embryo carry a complete set of
human genes. But not all of the genes are equally active in all
of the tissues all of the time. Cells contain mechanisms for
turning genes on (expressing them) and off (repressing them)
and for modulating the extent of their activity. This means that
different genes will be active to different extents in one cell type
compared with another. It is the processes that control which
genes are promoted and repressed that determine the eventual
developmental fate of a stem cell.
Epigenetic factors involved in control of gene expression
Some of the epigenetic mechanisms that control gene
expression have been established for some time. They are
referred to as epigenetic mechanisms because they do not
involve changes to the sequence of the DNA, but do exert an
influence on gene expression and thus on protein synthesis
and the characteristics of the organism of which they are part.
For instance:
„ DNA methylation. Each gene has an associated
regulatory region. A range of different factors can bind to
the regulatory region of a gene and influence gene
expression. The extent to which the regulatory region is
available for binding and the type of factors that it can
bind to is affected by chemical modification (methylation)
of the DNA of the regulatory region.
„ Histone modification. The DNA sequences that make up
genes exist in the cell nucleus in close association with
proteins known as histones. Chemical modifications to
histone proteins – such as the addition or removal of
methyl, acetyl or phosphate groups – can affect the
strength of the interaction between histones and DNA.
This influences the extent to which a particular gene’s
regulatory region is available to interact with other factors.
The chemical modification patterns of histones and DNA
are known as imprinting.
„ RNA-mediated silencing. In order to generate a protein
from instructions encoded in the DNA of a gene, the gene
must first be copied (transcribed) into a (closely related)
RNA form. This is then transported from the nucleus to
the cytoplasm, where it forms the template for the
synthesis of a specific protein. It has been well
established that small strands of RNA can interfere with
the production of protein from RNA templates in the
cytoplasm. More recent research suggests that small
strands of RNA can also interfere with the regulatory
regions on the genes held in the nucleus, effectively
preventing the gene from being transcribed.54
54
Grimm D, Advanced Drug Delivery Reviews, 61, 672–703, 2009
POST Report March 2013 Stem Cell Research
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Box 4.2 Transcription factors
While the epigenetic mechanisms outlined in Box 4.1 are
important in controlling gene expression, research suggests
that there are other, overarching factors involved in directing
cell fate. Attention has focused on a group of proteins called
transcription factors. These factors exert their influence by
binding to regulatory regions and directing the modification of
histone proteins, thus controlling how accessible a gene is for
gene expression. There is evidence that it is these transcription
factors that are involved in directing stem cells down particular
differentiation pathways (lineages). For instance, the
transcription factor Runx1 is the major regulatory factor that
directs a stem cell down the haematopoietic (blood stem cell)
pathway. Another, related, transcription factor Runx2 guides
stem cells down the osteogenesis (bone stem cell) pathway.
Moreover, the continued presence of such transcription factors
is needed in order to maintain tissue specificity during cell
division.55 In other words, it is transcription factors that
effectively constitute a cell’s ‘memory’ of the differentiation
pathway it has taken. Further differentiation into more
specialised cell types occurs through the action of regulatory
factors that bind to restriction factors and modulate their action.
The mechanisms outlined in Boxes 4.1 and 4.2 act
together to orchestrate different patterns of gene
expression and direct cell fate down different
developmental pathways (lineages). Improved
understanding of such factors is allowing
researchers to control the direction of cell fate in a
range of ways (Box 4.3).
The binding of transcription factors to regulatory
regions of genes exerts the most profound influence
on what genes are expressed within a cell. A
defining feature of transcription factors is that they
are proteins − and hence are themselves coded for
by genes − that can bind to DNA. Analyses of the
human genome have identified around 2,600 genes
that code for proteins with DNA binding sites. Many
of these are thought to be transcription factors. This
section looks at recent research on the factors that
control the following processes:
„ preventing differentiation for example in
totipotent, pluripotent and germ line cells
„ the emergence of the trophectoderm
„ the emergence of each of the three main types
of cell (ectoderm, endoderm and mesoderm)
„ replenishing cells in adults from stores of Adult
Stem (AS) cells.
Box 4.3 Directing cell fate
Improved understanding of the mechanisms involved in
differentiation raises the possibility of being able to direct cell
fate, by reprogramming cells of one type into cells of another.
There are three main possibilities:
„ Directing differentiation within a particular lineage. For
instance, taking haematopoietic (blood) stem (HS) cells
and adding transcription and/or growth factors to
encourage differentiation into more specialised types of
blood cell.
„ Reversing differentiation to produce less specialised cells.
It is well established that factors in the cytoplasm of egg
cells (oocytes) can reprogram adult DNA. For instance,
the researchers who created Dolly the sheep did so by
removing the nucleus from a sheep’s egg and replacing it
with the nucleus of an adult (sheep) cell taken from the
udder. Factors in the egg’s cytoplasm effectively turned
back the clock on the nuclear DNA, making it ‘forget’ that
it had once been part of a highly specialised adult cell. In
its new environment, the nucleus behaved as if it were
part of a (totipotent) newly fertilised egg. Research has
now identified several key transcription factors involved in
pluripotent cells. It has been shown that transferring the
genes coding for these factors into adult skin cells
(fibroblasts) can induced pluripotency in those cells, both
in mice56,57 and in humans.58,59 As discussed in this
chapter, the resulting induced pluripotent stem (iPS) cells
are similar to embryonic stem cell lines.
„ Directly switching cells of one lineage to cells of another
lineage. A similar approach to that used to derive iPS
cells has been employed to convert mouse fibroblasts
directly into neurons (nerve cells). Researchers identified
a series of transcription factors that are active in neurons,
and found that transferring the genes coding for three of
these factors into fibroblasts converted them into
neurons.60 After a few days, the cells began to behave
like neurons, eventually producing electrical signals and
forming connections with each other in culture.
Preventing differentiation
While most of the cells found in a human embryo
will eventually differentiate into more specialised
cell types, some retain their undifferentiated
character. Examples include the totipotent cells
found in early embryos up until three days after
fertilisation, the pluripotent hES cells that make up
the inner cell mass of a blastocyst (see Chapter 2)
and the cells that are destined to become germ-line
cells (eggs or sperm) in adults.
56
57
58
55
Stein G et al, Advances in Enzyme Regulation, 50 (1), 160-167,
2010
59
60
Takahashi K and Yamanaka S, Cell, 126 (4), 663–76, 2006
Okita K et al, Nature 448 (7151), 313–17, 2007
Yu J et al, Science, 318 (5858), 1917–20, 2007
Takahashi K et al, Cell, 131 (5), 861–872, 2007
Vierbuchen T et al, Nature, 463, 1035-1041, 2010
POST Report March 2013 Stem Cell Research
Studies in mice, and more recently humans, have
implicated the transcription factor Oct 4 as playing a
key role in preventing differentiation in these cells.61
For instance, research has shown that Oct 4 is
expressed in all of the cells of the early embryo, and
in the hES cells of the inner cell mass. In contrast,
Oct 4 expression in adults is confined to the
developing germ cells. Experiments in mice show
that selectively disrupting the gene that codes for
Oct 4 produces embryos devoid of a pluripotent
inner cell mass.62 However, more recent research
suggests that Oct 4 is not the only factor involved.
Comparing patterns of gene expression in
(undifferentiated) ES cells with those in
differentiated cells allow researchers to identify
genes that are highly active in ES cells. Many of the
genes identified in this way code for transcription
factors. Researchers can investigate the function of
these factors in various ways. For instance, they
can ‘silence’ a gene by using RNA sequences and
see what effect this has on the cells being studied.
Or they can use viruses to transfer and express
different combinations of the genes into various
types of cells.
Such approaches have identified genes coding for
another two transcription factors that are highly
expressed in ES cells. In addition to Oct 4, the
others are:
„ Nanog (derived from 'Tir nan Og' the
mythologic Celtic land of the ever young)63,64
„ Sox 2 (sex determining region Y, Box 2).65
These three factors are implicated in supporting
self-renewal and maintaining pluripotency in ES
cells. They co-occupy binding sites on hundreds of
different genes in ES cells66 and also interact
directly with proteins; a recent study identified
nearly 100 proteins that interact with Oct 4.67
Furthermore, each may play a role in regulating the
other two. For example, the gene that codes for
Nanog contains binding sites for Oct 4 and Sox 2.68
Such arrangements provide a precise mechanism
for regulating the levels of these factors within ES
cells. This is important since research has shown
that ES cells will start to differentiate if Oct 4 levels
get too low or too high.69
61
62
63
64
65
66
67
68
69
Oct 4 is octamer-binding transcription factor. It is also sometimes
referred to as Oct 3 or Oct 3/4.
Pan GJ et al, Cell Research 12, 321-329, 2002
Chambers I, et al Cell. 2003;113:643–655
Mitsui K, et al Cell. 2003;113:631–642.
Avilion AA, et al Genes Dev. 2003;17:126–140
Lo, Y-H, et al Nature Genetics 2006, 38 (4) 431-440
Pardo M, et al J Cell stem cell 2010, 6, 4, 382-95
Kuroda T, et al Mol. Cell. Biol. 2005 25 (6) 2475-2485
Niwa, H, et al Nature. Genetics. 2000 24, 372– 76).
Page 31
It is thought that these three factors are at the top of
the regulatory hierarchy. Their continued presence
is required to prevent differentiation by controlling
the genes that code for many of the other
transcription factors that are involved in the
process. In practice, this means that maintaining
pluripotent ES cells in cell culture is a very fine
balancing act that requires precise control of the
culture conditions.
Emergence of the trophectoderm
The earliest differentiation event in the development
of the human embryo is the emergence of the
trophectoderm. After about three days, the embryo
forms a solid mass of cells (the morula) which then
develops into a blastocyst. The blastocyst is
organised into an inner cell mass of hES cells and
an outer layer (trophectoderm).
Researchers have started to unravel the complex
series of events behind this differentiation step.70
They have implicated an enzyme called YAP-1 in
triggering the process. In cells near the centre of the
morula, the enzyme is essentially inactivated.
These cells remain pluripotent and give rise to the
hES cells in the inner cell mass. In cells near the
outer edge of the morula, YAP-1 remains active and
triggers a complex series of events that results in
the expression of the transcription factor Cdx-2.
This factor represses the expression of factors such
as Oct 4 and Nanog, and this in turn triggers a
cascade of other factors that allow the outer cells to
start to differentiate into the trophectoderm. The
trophectoderm eventually develops into the fetal
portion of the placenta.
Differentiation of the inner cell mass
The hES cells in the inner cell mass have the ability
to give rise to all cell types present in the embryo.
This make such cells a valuable tool for
understanding the complex mechanisms involved in
the development of specialized cells and the
establishment of organ structures. These cells give
rise to extra-embryonic tissue and three different
cell layers: ectoderm (cells on the outside),
endoderm (cells on the inside), and mesoderm
(cells present in the middle). The development of
the cell layers gives rise to the organs and tissues
of the organism:
„ endoderm develops into structures like the
stomach, liver, lungs, and intestines
„ mesoderm forms structures like the skeleton,
spleen, heart, and blood
„ ectoderm differentiates into the central nervous
system, lens of the eye, the epidermis, hair,
and mammary glands.
70
Kuckenberg P, et al Molecular Cell Biology 2010, (30), 13, 3310-20
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Researchers have identified specific genes coding
for different transcription factors that are involved in
directing ES cells down each of these tissue
lineages. However, all of the genes investigated to
date are under the control of the overarching factors
Oct 4, Nanog and Sox 2.
Adult Stem (AS) cells
Many organs in the adult body contain a population
of cells that serve as sources of cell replacement
throughout life. Some of these are progenitor cells,
that have a limited capacity for self-renewal and
give rise to a very limited (usually just one) range of
cells. Others are adult stem (AS) cells that have
unlimited capacity for self-renewal and can give rise
to a wider range of cell types such as:
„ the hematopoietic stem cells present in adult
bone marrow that constantly produce red blood
cells and a wide range of other blood cells
„ stem cells present in the skin and gut which
also routinely renew depleted cells.
Smaller numbers of AS cells are also found in other
parts of the body. For instance, the adult brain
contains small numbers of stem cells in restricted
areas. However, these do not appear to routinely
contribute significantly to the replacement of
depleted cells. Nor do they appear to be capable of
aiding functional recovery in the event of tissue
damage.
AS cells in the human body are found in so-called
stem cell niches (see Section 2.4). These are
microenvironments that provide the necessary
physical and chemical factors that allow the AS
cells to tick over while maintaining their
multipotency. The AS cells interact with the stem
cell niche and respond to signals indicating, for
example, cell depletion or tissue damage. The
complex nature of the stem cell niche makes it
difficult to recreate in the laboratory when
attempting to grow AS cells in cell culture (see next
section).
4.3 Directing cell fate in cell culture
The advances outlined in the previous section has
allowed researchers to direct cells down different
development pathways in the laboratory. For
instance:
„ directing differentiation within a particular
lineage (for instance using regulatory factors to
direct blood stem cells to differentiate into
specialised blood cells such as lymphocytes)
„ converting cells of one lineage (skin stem cells)
into cells of another lineage (neurons)
„
reversing the differentiation process by
transforming partially differentiated multipotent
cells back into cells that act in similar manner
to pluripotent stem cells (see next section).
Cell culture
Cell culture refers to the practice of cultivating living
cells in the laboratory. Box 4.4 outlines the basic
principles involved. A wide range of chemical and
physical factors can determine the fate of
pluripotent or multipotent stem cells grown in
culture. Chemical factors include specialised growth
factors that promote self renewal, boost the
expression of certain genes needed to maintain
pluripotency and prevent cell death. Physical factors
include the surface or other support matrix the cells
grow on as well as factors such as the
concentration of salts and the availability of oxygen.
The aim is to produce culture conditions to
encourage self-renewal while preventing the cells
from differentiating.
Deriving ES cell lines
ES cells were first derived from cultured mouse
embryos in 1981 by two independent groups: a UK
team based in Cambridge and a US group at San
Francisco (which coined the term embryonic stem
cell). However it was not until the mid 1990s that
the first ES cell lines from mice were established.71
Advances in culture techniques led to the
establishment of human ES cell lines by the late
1990s.72 In 2003 the first hES cell lines were
derived in the UK. 73 Since then much research has
been done to establish standardised methods to
derive and maintain hES cells.
Human ES cell lines are derived from embryos
donated by patients attending in vitro fertilisation
(IVF) clinics who may consent to surplus embryos
being used for research. The embryos are usually
cultured to the blastocyst stage (day 6 of culture)
and then micromanipulated under the microscope to
remove the outer shell (the zona pellucida). The
whole embryo or just the inner cell mass is cultured
in inactivated mouse or human embryonic
fibroblasts and specialised culture medium
containing growth factors (see Box 4.2). Some of
the cells from the inner cell mass will proliferate and
remain pluripotent under the appropriated culture
conditions. The hES cells are maintained in culture
and their adaptation to the culture conditions
analysed to check that they show consistent
characteristics. At this stage the cells can be
considered to be an hES cell line.
71
72
73
Thomson et al., 1995; Thomson et al., 1996
Thompson and co-workers in 1998, Reubinoff et al., 2000
Pickering SJ et al., 2003; Stojkovic M et al., 2004
POST Report March 2013 Stem Cell Research
Page 33
Box 4.4 Cell culture
Cells growing as part of a living organism such as an animal are supplied with all the water, nutrients and oxygen they need via the blood
system, which also removes waste products such as metabolites and carbon dioxide. In order to grow cells in the laboratory, ways must
be found to supply all the necessary nutrients and remove the waste products. As outlined in Figure 4.1 below, this involves:
„ Using a growth medium containing water, sugars (for energy), vitamins, amino acids, lipids and inorganic salts.
Figure 2.3 Deriving NTS cells
„ Other factors to regulate cell growth and prevent differentiation. These may be provided by culturing stem cells with inactivated
feeder cells. The feeder cells are inactivated by irradiation or chemical treatment to prevent them from dividing and competing with
the cultured cells. An alternative is to use ‘conditioned’ media that contains secretions from feeder cells but not the cells themselves.
„ Providing a suitable surface for the cells to grow on. In their natural environment cells are used to being surrounded by other cells on
all sides. Feeder cells not only provide essential regulatory and growth factors, but also a physical substrate for the hES cells to grow
on. An alternative is to provide an extracellular matrix such as a gel.
„ Aseptic culture conditions to prevent (slow growing) stem cells being swamped by faster growing microbes such as bacteria or yeast.
„ Frequent sub-culture onto new growth media. This ensures that the cells get sufficient nutrients and prevents the build up of waste
products.
Traditionally, hES cells have been maintained in culture on layers of mouse embryonic fibroblasts. The culture media itself may contain
undefined components such as bovine fetal serum and other supplements. Recent years have seen a shift away from such culture
methods towards more carefully defined culture conditions. There are several factors driving this trend:
„ Cell-based therapies intended for clinical use will have to be derived and cultured without the use of animal feeder cells. This is
because of the possibility of the therapeutic cell lines being contaminated by harmful elements (viruses, antigens, etc.) potentially
associated with animal cells.
„ The need to reduce variability from batch to batch. Feeder cells can vary considerably from one strain of mice to another, and have
markedly different effects on the hES cells grown on them.
„ The need to reduce variability from one laboratory to another. Using fully defined culture conditions make it easier for one laboratory
to verify or reproduce research carried out in another.
There are two key challenges to achieving fully defined cell culture conditions:
„ Fully defining the chemical components of the culture medium. Considerable progress has been made on this front. For instance,
researchers at Yale University reported a fully defined medium for the cultivation of hES cells in 2006.74 It contained basic fibroblast
growth factor, Wnt3a (a protein involved in regulating cell fate), April (a proliferation-inducing cytokine), BAFF (B cell-activating
factor), albumin, cholesterol, insulin, and transferrin (an iron binding protein). Other chemically defined culture conditions have been
described75 and some chemically defined growth media are commercially available.
„ Defining the surface the cells grow on. Cells are very fussy about the surfaces they grow on, and surface can influence whether a
cell grows at all, whether it maintains pluripotency or starts to differentiate. Approaches here include the use of gels and plastics or
other polymers coated with proteins, peptides or other bio-molecules.76 Several of these surfaces are commercially available, and
have been used in conjunction with chemically defined media to maintain hES cells.
FIGURE 4.1 CELL CULTURE
Figure 4.1 Cell Culture
Figure 6.1 UK Medical biotech pipeline
74
75
76
Lu J et al, Proc. Natl. Acad. Sci. USA, 103(15), 5688-93, 2006
Rajala K et al, Stem Cell Studies; volume 1, e3, 2011
Baker M, Nature Methods, Volume 8, 293–297, 2011
POST Report March 2013 Stem Cell Research
Page 34
The state of the donor embryo and the culture
conditions affect the characteristics of the derived
cells. Only a minority of the embryos used
successfully generate hES cell lines, and not all of
these turn out to be stable in the longer term.
Despite technical improvements over the past
decade the success rate of the procedure is still
low, indicating the complexity of the processes
involved. Procedures to derive hES cell lines are
essentially similar from one UK stem cell centre to
another. Factors that improve the likelihood of
successfully deriving hES cell lines include using
earlier stage embryos, culturing them on defined
substrates rather than feeder cells, and culturing
them in lower oxygen levels (similar to those found
in the womb).
Culture conditions
The first culture conditions described for hES cells
used an array of animal components. For instance,
the main medium consisted of fetal bovine serum
and the cells were co-cultured with inactivated
mouse embryonic fibroblasts. These so-called
feeder cells not only provide the growth factors
needed to keep the hES cells in an undifferentiated
state, but also act as a support matrix for cell
growth. However, such components are poorly
defined and have the potential to vary from batch to
batch or from one laboratory to another. They also
raise concerns about possible contamination of cell
cultures with animal pathogens or components that
could cause an adverse immune response.
Because of these concerns, researchers are
moving towards more strictly defined culture
conditions. As outlined in Box 4.4 this involves
developing chemically defined growth medium and
defined structures for cell to grow on.
Reliably maintaining hES cell lines
While culture conditions have been refined in recent
years, the efficient and reliable long-term
maintenance of hES lines presents researchers with
a number of challenges. These include:
„ devising new methods to improve the efficiency
by which cell lines can be derived from
embryos, which may involve studies to
investigate what (if any) are the differences
between hES cells grown as cell lines and hES
cells in the inner cell mass of an embryo
„ defining growth conditions that allow robust
maintenance of ES cell lines for large scale
expansion
Box 4.5 Autologous and allogeneic therapy
There are two main ways that human cells can be used directly
for therapy.
„ Autologous therapy, where a patient’s own cells are
isolated, processed, possibly multiplied or manipulated in
some way(s), then used for therapeutic purposes at the
appropriate site in the body. Such an approach has the
advantage that the cells are unlikely to be
immunologically rejected by the patient.
„ Allogeneic therapy, where cells from one person are used
to treat another person. One advantage of this approach
is that of immediacy; cells can be banked ready for
immediate use, rather than having to be isolated and
multiplied up in number prior to use. However, a
disadvantage of allogeneic therapy is the possibility that
the patient will immunologically reject the therapeutic
cells. One potential way round this is to bank cells with
different tissue types, and to match the cells used for
therapy to the patient. Another is to limit allogeneic
therapy to those sites in the human body − such as parts
of the central nervous system − where immune reactions
may be less likely to occur. Such sites are referred to as
immune privileged sites and are described in more detail
in Chapter 5 (Box 5.4).
„
„
defining derivation and growth conditions that
allow for consistent batches of hES cells
the production of clinical grade cell lines for
clinical use.
Clinical grade cell lines
The first hES cell lines have proved to be useful
research tools and are designated as research
grade cell lines. Interest in using stem cells in
clinical applications has risen in recent years. As
outlined in Box 4.5, they may be used
therapeutically in two main ways. Autologous
therapy involves using the patient’s own cells for
therapy whereas allogeneic therapy involves using
cells taken from another person. A major potential
drawback with allogeneic therapy is graft versus
host disease (GVHD, see Box 4.6). This arises
when a certain type of T cells originating from the
donor recognise the host’s tissue as being foreign
and start to attack it. However, as outlined in Box
4.6, other types of donor T cells can exert beneficial
effects such as graft versus tumour (GVT)
responses.
Any cells used for clinical purposes must be
isolated, processed, stored and tested to current
appropriate quality standards. These standards are
laid down in the Quality and Safety Regulations
(Box 3.5) and are designed to ensure that the cell
lines are free from contamination, well
characterised, stable and predictable over time and
can be produced and maintained in a consistent
manner.
POST Report March 2013 Stem Cell Research
Box 4.6 Graft versus Host Disease (GVHD) and Graft
versus Tumour (GVT) responses
HS cell preparations (grafts) transplanted from a donor to
another individual will contain − or have the ability to develop
into − cells of the immune system called T cells. The job of
these cells is to identify proteins (antigens) on the surface of
cells and attack any that are foreign or abnormal. This can
have both harmful and beneficial results for patients.
„ The harmful results are called graft versus host disease
(GVHD) which results from the transplanted T cells
attacking host cells in tissue such as the gut, liver, skin,
and lungs. GVHD manifests itself in a variety of ways, but
can result in graft rejection and the death of the patient.
„ Beneficial results include attacking foreign cells such as
pathogenic viruses and bacteria thus conferring immunity
to some infectious diseases. Transplanted T cells can
also identify and attack abnormal cells such as tumour
cells, resulting in a beneficial graft versus tumour (GVT)
response.
These harmful and beneficial effects are caused by different
sub-populations of T cells. Broadly speaking, GVHD is caused
by so-called naive T cells (TN) that have yet to encounter a
specific antigen and thus attack any cells they recognise as
being foreign. The beneficial effects are largely caused by TM
cells that have already encountered an antigen and specialise
in attacking cells that carry it. A third group of T cells called
TREG cells can also exert beneficial effects by suppressing T
cell responses and thus aiding acceptance of the graft.
The current strategy for minimising GVHD is to use tissue
typing to ensure that antigens found on the host cells match
those found on the donor cells as closely as possible. However,
researchers are now trying to develop strategies to ‘tweak’ the
transplanted graft by removing the TN cells while retaining or
expanding the beneficial TM and TREG cells.
In practice, the standards for stem cells for clinical
use involve quality control measures to minimise
variability across all stages of manufacture
validated to demonstrate generation of a
reproducible product. These cover:
„ Avoidance of contamination. Standard methods
of sterilising the final product may not be
applicable for products such as stem cells, so
the emphasis is on aseptic processing
throughout the manufacturing process. In
practice this means using a specific clean
environment where all the equipment and
reagents are tested independently, the air
quality monitored, etc.
„ Robust manufacturing processes. This involves
making and testing appropriate master cell
banks of cells and developing in-line testing to
ensure that derived cell type meets the
required standards. Tese must be able to deal
with managing the risk of cells becoming
genetically (or epigenetically, see Box 4.2)
aberrant or changing in some other way that
increases the eventual risk to the patient.
Page 35
„
Traceability. It is important that all substances
that have come into contact with the cells or
tissue to be used in clinical applications can be
traced. In practice this means using carefully
defined culture media and monitoring of
process conditions.
Stem cell banking
It is a condition of an HFEA research licence that all
hES cell lines generated by UK researchers be
deposited in the UK Stem Cell Bank (UKSCB). In
the UK there are five centres for Stem Cell Biology
that have facilities that comply with clinical grade
cell line standards. In December 2011 the National
Clinical Stem Cell Forum published a statement
summarising the progress made in this area during
2011.77 It noted that:
„ Edinburgh (Roslin Cells) has derived ten new
hES cell lines under licence from the HFEA and
HTA to quality assured standards stipulated for
human clinical use. These have been isolated
free from animal-derived products (xenofree)
using human cell feeders and banked as
feeder-free cultures. Applications to deposit all
of these lines in the UKSCB were submitted in
2011.
„ Manchester has derived five lines on human
feeders under HTA licence in 2011, all of which
could be considered clinical grade. The most
recent of these is entirely xenofree. All of the
lines will also be submitted (to UKSCB) for
unrestricted access.
„ Kings College London has recently submitted
applications to UKSCB to deposit, for
unrestricted access, the first two clinical grade
hES cell lines derived in an HTA-licensed
facility at Guy’s Hospital. These two clinical
grade lines are xenofree.
„ Newcastle has derived an hES cell line which is
in compliance with GMP standards. Both the
clinical and research grade versions of this
(Ncl14) line have been banked with the NSCB
and are available to the scientific community
without restriction. The researchers have also
derived a human foreskin fibroblast line
(NclFed1A) in compliance with GMP standards
which they hope to bank with the UKSCB.
„ Sheffield has 8 newly derived hES cell lines to
clinical standards using human feeder cells.
Two research lines (Shef3 and Shef6) have
also been re-derived to meet clinical
requirements. All lines are deposited in the
UKSCB for unrestricted access.
77
www.clinicalstemcellforum.org.uk/NChESCF_
UpdateDec2011_V03.pdf
POST Report March 2013 Stem Cell Research
Page 36
In total, the UK Stem Cell Bank’s Steering
Committee has approved more than 100 cell lines
including 28 potential clinical grade lines. Currently
23 hES cell lines are available on application to the
Steering Committee. More are in the process of
being released as samples are submitted to the
UKSCB and banking and testing are completed.
„
„
Deriving different lineages from stem cells
Much recent research on stem cells has focused on
understanding the induction of hES and other stem
cells into specific lineages. Laboratories are
investigating the combination of factors and
conditions necessary to direct specific cell fate
decisions. As outlined previously, during normal
embryonic development the pluripotent hES cells
that make up the inner cell mass of the early
embryo give rise to three different cell layers:
endoderm, mesoderm and ectoderm.
These differentiation events can be re-created in
the laboratory. For instance, simply removing hES
cells from the support cells with which they are cocultured causes the hES cells to clump together into
embryoid bodies. These are aggregates of hES
cells that can be grown in suspension that have the
potential to differentiate into each of the three main
cell layers. More recently, monolayer systems have
been developed which allow researchers greater
control in directing the differentiation of cells under
defined culture conditions.78,79 The following
sections look at how such methods may be used to
direct differentiation of cell lineages in the
laboratory.
Endoderm
Liver cells
It is possible to induce differentiation of hES cells
into endoderm cells in the laboratory which can then
be differentiated into liver cells. Hepatocytes (liver
cells) are a particular focus of attention. One
interest here is that it may prove possible to
regenerate damaged liver tissue using hepatocytes
as a potential alternative to liver transplant. Another
is the use of hepatocytes for toxicity screening of
new drugs in clinical development. A method for
differentiating hES cells into hepatocytes through
the main developmental stages seen during normal
development was recently reported.80 The
researchers:
78
79
80
Metallo C et al, Methods Mol Biol, 585, 83, 2010
Niwa A et al, PLoS ONE 6(7), e22261, 2011
Touboul T et al, Hepatology, 51(5),1754-65, 2010
„
differentiated hES cells into a homogenous
population of endoderm cells using a defined
combination of factors (activin, fibroblast
growth factor 2 and bone morphogenetic
protein 4 together with phosphoinositide 3kinase inhibition)
induced further differentiation of the endoderm
cells into hepatic progenitors using another set
of defined factors (fibroblast growth factor 10,
retinoic acid, and an inhibitor of activin/nodal
receptor)
cultured the progenitors into mature
hepatocytes that expressed markers typical of
these types of cell and exhibited hepatic
functions such as glycogen storage, cytochrome activity, and low-density lipoprotein
uptake.
Beta cells
Another potential application for endoderm cells is
to use them to derive the glucose-stimulated insulinproducing beta cells found in the pancreas. Type 1
diabetes is caused by the immune system mistaking
beta cells as foreign invaders and attacking them. In
humans, researchers have succeeded in using hES
cells to derive endoderm cells and then
differentiating these into foregut and pancreatic
endoderm lineages, including immature pancreatic
endocrine cells.81 More recently, glucoseresponsive insulin-producing cells with the capacity
to correct induced hyperglycaemia have been
derived from endometrial stromal stem cells in
mice.82
The aim of research in this area is to find a reliable
source of human beta cells that can be transplanted
into type 1 diabetes patients. Strategies include
developing robust differentiation pathways to derive
mature beta cells from hES cells and from AS cells
such as those found in the endometrium.
Alternatively some research groups are looking at
ways of trying to stimulated insulin production from
the beta progenitor cells found in the pancreas.
81
82
Baetge EE, Diabetes Obes Metab. 2008 Nov;10 Suppl 4:186-94.
Santamaria X, et al Molecular Therapy 19, 2065-2071 (2011)
POST Report March 2013 Stem Cell Research
Lung cells
A final example of a potential application for
endoderm cells is in the treatment of lung injury.
The inner surface of the lung is lined with two types
of alveolar epithelial cells. Alveolar type 2 (AT2)
cells produce surfactants and also give rise to the
AT1 cells that are responsible for gas exchange in
the lung. Researchers have developed
differentiation pathways to derive AT2 cells from
hES cells. Furthermore, they have shown that the
AT2 cells can reduce inflammation and improve
survival when administered to mice with
experimentally induced lung injury.83 A current
research priority in this area is to develop a robust
differentiation pathway to derive AT1 cells from AT2
cells.
Mesoderm
The mesoderm layer is located between the
endoderm and ectoderm in the embryo. In the
normal course of embryonic development different
parts of the mesoderm give rise to different tissues
and organs. For instance, the paraxial mesoderm
goes on to form the kidney and body wall. The
mesoderm thus gives rise to a very wide range of
cell types. These include mesenchymal stem cells
that have the potential to differentiate into:
„ chondrocytes that make up cartilage
„ osteocytes responsible for bone formation;
myoblasts that give rise to muscle cells,
including the cardiomyocytes found in the heart
„ the cells that form and line the circulatory
system
„ heamoatopoietic stem (HS) cells found in bone
marrow which produces the various different
blood cells.
Mesenchymal stem (MS) cells
Human mesenchymal stem (hMS) cells have been
widely studied as possible therapeutic agents. The
diversity of sources and types of hMS cells means
that it is difficult to generalise their properties. Pretty
much all hMS cells are capable of differentiating
into cartilage, muscle and bone cells. It is thought
that some precursor cells found in the mesoderm
can give rise to an even wider range of cell types,
possessing haematopoietic (blood forming) and/or
angiogenic (blood vessel forming) potential. Indeed,
such precursor cells have been isolated from ES
cells grown in culture.84 These cell types could
potentially be used for blood transfusion and to
analyse hematopoietic and vascular defects.
Page 37
Interest in hMS cells for therapeutic purposes
initially centred on them being an ethically
acceptable and potentially safe85 source of cells for
regenerative therapy. However more recent
research has focused on their immunological
properties. It has been well documented that hMS
cells interact with local immune signals in the body
and exert wide-ranging, mainly suppressive, effects
on the immune system. They produce soluble
factors that result in increased local production of
anti-inflammatory factors such as cytokine
interleukin (IL)-10 and other factors that suppress
the proliferation of the cells of the immune system
that normally orchestrate the immune response to
foreign cells.86
hMS cells have several potential advantages for
therapeutic applications. First, they may prove
useful in treating immune disorders and in aiding
the repair of injured tissue more generally. For
instance, preclinical studies in animals have shown
promising results in using MS cells to treat immune
disorders such as systemic lupus erythematosus,
rheumatoid arthritis, autoimmune type 1 diabetes
and inflammatory bowel disease as well as in aiding
tissue repair − or limiting tissue damage − following
heart attack, in lung injury, bone fracture, skin
wounds and spinal cord injury.87 As discussed in the
next chapter some of these applications have been
the subject of clinical trials.
Second, MS cells appear to be able to avoid or
suppress many of the immune responses that
would normally attack and destroy foreign cells.
However, the exact extent of their immunity to the
immune system − known as immune privilege − is
the subject of academic debate (see Box 5.4 in the
next chapter). Nevertheless, if the immune privilege
status of hMS cells can be established, this raises
the possibility of being able to establish
(allogeneic)88 hMS cell lines for clinical applications.
85
86
87
83
84
Wang D, et al, Mol Ther 18: 625–634, 2010
Vodyanik MA et al, Cell Stem Cell, 7(6): 718–729, 2010
88
As outlined in Chapter 2, hES cells form non-cancerous tumours
called teratomas when injected into animals. hMS cells do not have
this property.
Griffin MD et al, Hum Gene Ther 21(12), 1641-55, 2010
Ren G et al, Stem Cells Translational Medicine, 1, 51–58,
December 2011
As outlined in Box 4.5 allogeneic simply refers to using cells taken
from one individual to treat another.
POST Report March 2013 Stem Cell Research
Page 38
A final property of MS cells that may prove
therapeutically useful is their role in tumours. MS
cells are known to be tumour-homing, preferentially
migrating to tumours from distant sites. Once there,
they have been implicated in a wide range of
tumour support activities. However, their tumourhoming capabilities mean that they could potentially
be used to deliver anti-cancer agents to the site of a
tumour. A number of studies have used genetically
modified MS cells to deliver anti-cancer agents to
experimentally induced tumours in animal models89.
To date such approaches have not been attempted
in humans.
FIGURE 4.2 DERIVING CARDIOMYOCYTES95
Sources of cardiomyocytes
Most of the cells in the human heart are fully
differentiated. The adult heart does contain a small
population of cardiac progenitor cells, but these are
insufficient to replace injured or dead cells following
injury such as a heart attack.90 Much research on
mesodermal cells has thus focused on the process
by which mesoderm differentiates into the
cardiomyocyte cells that comprise heart muscle.
The hope here is to try and derive pure cultures of
these cells to repair damaged tissue in the heart.
A wide range of human tissues has been proposed
as the source of stem cells to generate new
cardiomyocytes91. These include pluripotent hES
cells, fetal cardiomyocytes, umbilical cord-derived
stem cells and multipotent adult stem cells such as
cardiac progenitor cells, skeletal myoblasts, bone
marrow-derived stem cells and adipose-derived
stem cells. However, the differentiation potential of
the multipotent stem cells found in adult and fetal
tissue has proved to be controversial.92
To date, the only adult stem cells that have clearly
been shown to have the potential to produce
beating cardiomyocytes are cardiac progenitor
cells.93 However, access to human tissue is limited
and, as noted previously, the heart contains just a
small population of progenitor cells. Researchers
are currently trying to find ways of culturing cardiac
progenitor cells in the lab to increase their number
while retaining their multipotent state.94
89
90
91
92
93
94
MR Reagan and DL Kaplan, Stem Cells, 29, 920–927, 2011
Rajala K et al, Stem Cells International, 2011, 383709
Steinhauser ML and Lee RT, EMBO Mol Med 3, 701–712, 2011
Anversa P, et al Stem Cells. 25(3):589–601, 2007.
Blin G, et al Journal of Clinical Investigation,120(4),1125–39, 2010
Rajala K et al, Stem Cells International, 2011, 383709
Several research groups have also shown that
beating cardiomyocytes can be derived from
pluripotent cells. These include hES96 and hiPS
(discussed in a later section) cells. Three different
methods have been developed including
spontaneous differentiation from embryoid bodies
and co-culture of hES cells with mouse cells that
provide the various factors required. It is also
possible to direct the differentiation of hES cells into
cardiomyocytes through several stages using
defined transcription factors. These various different
stages mimic those observed in the normal
development of the heart. These are illustrated in
Figure 4.2, along with some of the factors thought to
be involved. While the first step (mesoderm
induction) is well documented, much less is known
about subsequent steps in the process.
95
96
Adapted from Rajala K, et al Stem Cells International, 2011, 383709
Kehat I, et al Journal of Clinical Investigation, 108(3),:407–14, 2001;
Xu C, et al Circulation Research, 91(6),501–08, 2002; He JQ, et al
Circulation Research, 93(1), 32–39, 2002;. Mummery C, et al
Circulation, 107(21), 2733–40, 2003.
POST Report March 2013 Stem Cell Research
One potential application for cardiomyocytes is to
use them for screening of toxicity and efficacy of
potential new drugs under clinical development.
Indeed GE Healthcare, in collaboration with Geron,
has developed a process for producing industrial
quantities of cardiomyocytes from hES cells for just
such purposes. But the main thrust of much
research in this area remains the derivation of
cardiomyocytes for repairing damaged tissue.
Work done in rats has shown that transplantation of
cardiomyocytes into damaged heart tissue in
combination with insulin-like growth factor 1 (IGF-1)
and a multi-component pro-survival cocktail results
in the improvement of heart function.97 While
several types of adult progenitor and stem cells
have been used for cardiac repair in clinical trials in
humans98 (see Chapter 5), no human trials have yet
been conducted on cardiomyocytes derived from
pluripotent stem cells.
There are several key challenges to be resolved
before clinical trials of cardiomyocytes derived from
pluripotent stem cells are likely to be approved.
First, researchers need to find a way of generating
highly purified cell preparations that contain only the
potentially therapeutic cardiomyocytes. A concern
here is to exclude any of the original pluripotent
stem cells from the preparation used for therapy, as
these have the potential to form teratomas.
Several strategies have been used to obtain
enriched cardiomyocyte populations.
„ Mechanical isolation of the cells by microdissection.
„ Use of fluorescent dye to stain mitochondria in
cell populations. Because cardiomyocyte cells
contain many more mitochondria than hES
cells, the extent of fluorescence can be used as
the basis for cell sorting.
„ Cell sorting based on the detection of cell
proteins that are expressed on the outer
surface of differentiated cardiomyocytes.
„ Use of genetic selection techniques. This
involves inserting a selection gene (such as an
antibiotic resistance gene) into one of the
regulatory sequences that is switched on when
an hES cell differentiates into a cardiomyocyte.
Subsequent exposure of the cells to the
antibiotic will kill all the cells except those
(cardiomyocytes) carrying the resistance gene.
The down side of this approach is that it carries
the usual risks associated with genetic
modification. The upside is that it yields very
pure cell populations.
97
98
Laflamme et al., 2007).
Wollert K and Drexler H, Nature Reviews Cardiology 7, 204-215,
2010l
Page 39
A second challenge is to gain a better
understanding of the maturation process. A
comparison of cardiomyocytes derived from
pluripotent stem cells with those found in adult heart
tissue shows that they share many of the same
characteristics. However, in terms of appearance
and functional capacity, the cells derived from
pluripotent stem cells more closely resemble
immature cardiomyocytes. Further research is thus
needed to understand how to obtain mature
pluripotent stem cell-derived cardiomyocytes in
culture.
Further challenges regarding the use of
cardiomyocytes from pluripotent stem cells in
clinical trials concern:
„ the method, site and timing of delivery of the
cells
„ the optimum dose of cells
„ the persistence and survival of the cells after
transplantation
„ integration of the cells into the patient’s heart
„ the avoidance of immune rejection.
Haematopoietic stem (HS) cells
Sources of HS cells include bone marrow,
peripheral (circulating) blood and umbilical cord
blood. Blood from such sources contains a mixture
of different types of cells including:
„ the full range of blood cell types
„ progenitor cells that can proliferate but can only
give rise to a limited subset of blood cell types
„ short-term progenitor cells that can give rise to
the full range of blood cell types but which
cannot themselves proliferate in the long-term
„ HS cells that can proliferate over the lifespan of
the organism in questions and give rise to the
full range of blood cell types.
HS cells could potentially have a wide range of
clinical applications. For instance they are used to
repopulate the bone marrow of leukaemia patients
following intensive chemotherapy and could be
used as alternative source of blood for transfusion.
However, researchers trying to isolate HS cells from
the above sources face three major problems:
„ HS cells are present only in very low numbers
„ it is very difficult to distinguish HS cells from
other blood and progenitor cells
„ it is very difficult to expand HS cell numbers
outside of the human body, a factor which
currently limits the therapeutic potential of such
cells beyond procedures such as direct bone
marrow transplantation.
Page 40
Recent years have seen some progress made
towards resolving some of these problems. One
way of distinguishing HS cells from other types of
blood cells is by the marker proteins found on the
outer surface of the cells. By making antibodies that
bind to specific marker proteins, researchers were
able to use cell sorting techniques to derive different
subsets of cells, each with a different pattern of
marker proteins. They were then able to grow the
cells in culture and look at the range of cells each
were able to differentiate into.
Using such techniques researchers have managed
to disentangle the hierarchy of cells involved in
blood formation (Figure 4.3, next page). At the top
of the hierarchy are very small numbers of HS cells,
which are capable of long-term self-renewal. In the
middle, are a series of multipotent and oligopotent
progenitors that can give rise to a variety of different
blood cells but which lack the capacity for long-term
self-renewal. At the bottom are the lineage
restricted progenitors that can each give rise to just
a single, specialised form of blood cells. Each of the
different types of cells shown in Figure 4.3 is
characterised by a specific pattern of surface
protein markers, although the details have been
omitted from the Figure for the sake of clarity.99
HS cells are already used in clinical applications
(see Chapter 5). The development of cell selection
and sorting techniques has the potential to
significantly enhance current approaches. For
instance cell selection and sorting methods may
give clinicians the tools needed to selectively
remove the T cells responsible for GVHD and
enhance those that cause beneficial effects such as
GVT (see Box 4.6).100
Ectoderm
At an early stage of embryonic development, the
ectoderm gives rise to three distinct regions (see
Figure 4.4, right).
„ Non-neural ectoderm (blue in Figure 4.4),
which gives rise to the epidermis.
„ Neuroectoderm (yellow) which forms the neural
plate that folds on itself and gives rise to the
neural tube that will eventually develop into the
structures of the central nervous system.
„ Border regions (green) between these two,
most of which will form the neural crest when
the neural tube is formed. Neural crest cells
detach themselves from the neural crest itself
and migrate throughout the developing embryo,
giving rise to a very wide range of different cell
types.
99
100
Weissman IL and Shizuru JA, Blood, 112(9): 3543–3553, 2008
Riddell SR and Appelbaum FR, PLoS Med 4(7), e198, 2007
POST Report March 2013 Stem Cell Research
FIGURE 4.4 NEURAL TUBE FORMATION
As illustrated in Figure 4.4, the process is
orchestrated by two main transcription factors: bone
morphogenic protein 4 (BMP) and sonic hedgehog
(SHH). BMP is secreted by the non-neural (blue)
ectoderm but its secretion is suppressed in a
medial/lateral (middle to left and right) axis. Low
levels of BMP in the middle of the ectoderm direct
its fate to a neural (yellow) lineage. Moderate levels
of BMP between the middle and sides direct the
ectoderm to become the border regions (green).
Sonic hedgehog is secreted by the notochord, a
structure that sits underneath the ectoderm. SHH
forms the dorsal/ventral (top to bottom) axis and
drives formation of the floor plate (red). As the
neural tube develops, the two (green) border
regions fuse to form the neural crest and close the
neural tube. At this point the medial/lateral BMP
axis has become a dorsal/ventral one. This results
in two opposing gradients along the length of the
neural tube: a high at the top, low at the bottom
BMP gradient (purple triangle in Figure 4.4); and, a
high at the bottom, low at the top SHH gradient (red
triangle). These two opposing gradients cause a
patterning of the neural tube into different domains
(represented by the coloured areas in Figure 4.4),
each of which will go on to give rise to different
components of the central nervous system.
POST Report March 2013 Stem Cell Research
Page 41
Figure 4.3 The hierarchy of intermediate cell types in blood formation
Source: Adapted from Weissman IL and Shizuru JA, Blood, 112(9): 3543–3553, 2008
Non-neural ectoderm
Non-neural ectoderm include keratinocytes, which
are major components of the skin, and the retinal
pigment epithelial cells which are important
components of the retina in the eye.
From a clinical point of view, keratinocytes are of
interest because of their potential applications in
wound healing. Research has shown that hES cells
can be directed down the ectoderm route by using
just two factors:
„ Retinoic acid, which is a derivative of vitamin A
that has been shown to be an important
determinant of ectodermal fate in simple model
organism such as the zebrafish.101
„ Bone morphogenic protein 4 (BMP) is a protein
found in humans that is part of a larger family
of growth and differentiation factors. Localised
suppression of the BMP signal is one of the
factors responsible for the emergence of the
neural plate and neural plate border regions.
A recent paper has reported a robust protocol using
these two factors to obtain relatively pure
keratinocyte progenitors from hES cells.102 The
researchers showed that the derived keratinocyte
progenitors:
„ retained the capacity to fully differentiate into
keratinocytes
„ expressed cell markers typical of keratinocytes
„ did not express cell markers typical of nonectodermal lineages
„ could be maintained in culture without any
deterioration in the appearance of the cells or
of their chromosomes (karotype).
In addition to potential therapeutic applications, the
derived keratinocyte progenitors can be used to
construct models of complex tissue such as skin.
For instance, researchers have used ectodermal
cells in conjunction with fibroblasts to produce skin
models to investigate how the different cells
communicate with, and support each other.103
102
101
Bakkers J et al, Dev Cell, 2, 617–27, 2002
103
Metallo CM et al, Methods Mol Biol, 585, 83, 2010
Hewitt KJ et al, Tissue Eng Part A, 15, 3417-26, 2009
POST Report March 2013 Stem Cell Research
Page 42
Loss and dysfunction of the retinal pigment
epithelium is of clinical interest because it can lead
to age-related macular degeneration (AMD). AMD is
one of the leading causes of human blindness and
there is considerable interest in using retinal
pigment epithelial cells derived from hES cells to
treat it (see Chapter 5).
Research has shown that the conversion process is
enhanced by co-culturing hES cells with human
retinal pigment epithelial cells or with other human
derived components.104 Animal studies have shown
that transplanted retinal epithelium can support
photoreceptor survival and restore visual function in
animals with degenerated retinal pigment
epithelium.105 As discussed in Chapter 5,
preparatory work has been conducted to clear the
way for clinical trials in humans.
Another possible application for hES cell-derived
retinal pigment epithelial cells is in patients suffering
from acute retinal tear. This condition results in the
loss of retinal pigment epithelial cells and can cause
complete loss of vision within the space of six
weeks.
Neural crest stem (NCS) cells
In the embryo, the neural crest is a source of
migratory cells that will eventually differentiate into a
diverse range of cell types including bones,
cartilage, neurons and their supporting glial cells,
endocrine cells, vascular smooth muscle cells and
the pigment-producing melanocytes. This diversity
has made NCS cells a potential target for
researchers looking for sources of multipotent cells
for research and potential clinical applications.
There are several potential sources of NCS cell
progenitors in the adult human body. For example,
these types of cells are found in hair follicles, in the
gastro intestinal tract as well as in various parts of
the central nervous system such as the sciatic
nerve and the spinal ganglia.
Of these, perhaps the best studied are the
epidermal NCS derived from the bulge of hair
follicles.106 Research has shown that such cells
have the potential to generate all of the major
neural crest derivatives, are capable of selfrenewal, and can be derived and cultured in a
robust and reproducible fashion in the laboratory.107
Moreover, epidermal NCS cells have other features
that make them promising candidates for possible
clinical use, particularly in autologous therapy (Box
4.3). For instance, they are readily accessible using
minimally invasive techniques and do not cause
teratomas when injected into mice.
One example of a possible clinical application for
NCS cells is neurosensory hearing loss, a common
condition that has major social and economic
impacts. It is caused by damage to the auditory hair
cells and their associated neurons. Several cell
types have been explored as being therapeutically
suitable for this condition, including NCS cells.108
NCS cells have also been investigated as possible
treatments for neurodegenerative conditions such
as Parkinson’s and Alzheimer´s disease.109
Directing hES cells to neural lineages
Another potential source of NCS cells is to obtain
them from hES cells via directed differentiation. For
example, recent research has shown that NCS cells
can be derived from hES cells using a combination
of growth factors in medium conditioned on stromal
cells.110 The resulting NCS cells were purified by
fluorescence-activated cell sorting, cultured and
shown to express cell markers characteristic of
NCS cells.
The researchers were able to further differentiate
the NCS cells into a variety of neurons and glial
cells of the peripheral nervous system, as well as
other cell types. Using a defined medium, they
generated a nearly pure population of glial cells.
These supporting cells were able to form a sheath
around the ganglia of rat neurons when the two cell
types were mixed in the laboratory. This finding
suggests that such cells may be used for tissue
engineering.
106
107
108
104
105
Gong J et al, Exp Eye Res. 2008 Jun;86(6):957-65
Coffey PJ et al, Nat Neurosci, 5, 53-56, 2002
109
110
Sieber-Blum M at al, Molecular And Cellular Neurosciences, 32, (12), 67-81, 2006
Clewes O et al, Stem Cell Reviews, 7 (4) 799-814, 2011
Huisman MA & Rivolta MN, Front Biosci, 1 (4), 121-32, 2012
Achilleos A & Trainor PA, Cell Research 22, 288-304, 2012
Liua Q et al, Stem Cells Trans Med, 2011-2042, April 2012
POST Report March 2013 Stem Cell Research
Other studies have focused on understanding the
many different kinds of neurons involved in the
complex interconnections of the human central
nervous system. hES cells have become a powerful
tool in the field of developmental neurobiology as
they provide researchers with experimental access
to the developing human nervous system.
The focus of much research in this area has been
on the generation of the neurons of the midbrain
subtype that are the main source of the signalling
molecule dopamine. It is the loss of these dopamine
producing neurons that is associated with one of the
most prominent human neurological disorders,
Parkinson’s disease. Ultimately, the goal of
research in this area is to develop an effective cell
therapy to replace the dopamine producing neurons
in patients with the disease.
Protocols for deriving dopamine producing neurons
from hES cells have been established. For instance,
researchers have shown that it is possible to derive
midbrain neural precursor cells from hES cells and
use these to obtain an enriched population of
dopamine producing neurons.111
However, a major drawback with these neural
precursor cells is that it is difficult to derive large
numbers of dopamine producing neurons from
them, and those neurons that are produced do not
survive very long when transplanted into animals.
Researchers have found that the cell survival
problems can be overcome by genetically modifying
the cells to overproduce levels of two transcription
factors.112 But the genetic modification of cells
raises additional risks that need to be considered
before using such cells in clinical trials in humans.
More recently, researchers have used small
molecules (see next section) to direct differentiation
of hES cells down a different pathway to derive
dopamine producing neurons.113 The process yields
larger numbers of neurons that can be maintained
in culture in the laboratory for several months.
Furthermore, the dopamine producing neurons
showed long-term survival when engrafted into
three different animal models of Parkinson’s
disease (mice, rats and monkeys). The cells also
showed functionality by improving performance in
two of the models (mice and rats).
111
112
113
Ko J-Y et al, Molecular Therapy 17 (10), 1761–70, 2009
The two transcription factors are sonic hedgehog and Bcl-XL, a
protein that has been implicated in the survival of cancer cells.
Kriks S et al, Nature, 480 (7378), 547-51, 2011
Page 43
Other key research targets involve deriving neural
progenitor cells for selective differentiation into
neurones that produce other important signalling
molecules in the brain such as serotonin,
acetylcholine and GABA (gamma aminobutyric
acid). Various studies have reported deriving neural
precursor cells capable of differentiating into
different neuronal subtypes using defined culture
conditions.114 More recently, researchers have
derived GABA producing spinal cord neurones from
hES cells exposed to retinoic acid and SHH. When
these cells were transplanted into a mice model of
Huntington’s disease, the cells survived
transplantation, reconnected circuitry in the inner
part of the forebrain (striatum) that is most affected
by the disease and improved the mice’s
performance in behavioural tests.115
In the last 10 years, hES cells have emerged as a
means of deriving better models of
neurodegenerative diseases. For example, recent
research outlined in Box 4.7 has paved the way
towards developing better models of the various
different forms of motor neurone disease.
hES cells have proved to be an invaluable resource
for furthering understanding of the development of
the central nervous system, and for developing
better models of the diseases that affect it.
However, a range of issues will need to be resolved
before cell-based therapies can be developed for
such diseases. These include:
„ The extent to which therapeutic cells actually
resemble the cells being regenerated. For
example, the dopamine producing neurons
derived from hES cells express some of the
key markers typical of midbrain neurons, but it
is not clear whether they produce all of them.116
„ How the cells behave after they have been
transplanted. Questions here include whether
the cells become integrated into local neural
networks or migrate to other locations.
„ The optimal source of cells and stage of
development for transplantation.
114
115
116
.
Erceg et al, PLoS ONE, 3(5), e2122, .2008
Ma L et al, Cell Stem Cell, 10 (4), 455-64, 2012
Zeng X et al, Stem Cells, 22(6), 925-40, 2004
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Page 44
Box 4.7 Stem cell models for motor neurone disease
Motor neurone disease (MND) is a generic term used to
describe several diseases caused by degeneration of the motor
neurones in the brain and spinal cord. It encompasses:
„ amyotrophic lateral sclerosis (ALS)
„ progressive muscular atrophy (PMA)
„ progressive bulbar palsy (PBP)
„ primary lateral sclerosis (PLS)
„ spinal muscular atrophy (SMA)
A key aim of research on these diseases has been to develop
accurate disease models. Two recent advances in stem cell
research have made important contributions towards this. In
the first, researchers have discovered a novel pathway to direct
neural precursor cells derived from hES cells towards a wide
variety of different sub-types of motor neurones.117 The ability
to manipulate motor neurone subtype could eventually lead to
more accurate, clinically relevant disease models. These can
be used to build up a better understanding of the underlying
mechanisms behind the various diseases, and as a means of
testing potential new drugs.
In the second, researchers have managed to derive a stem cell
line that carries one of the key mutations linked to ALS. Studies
of inherited ALS had implicated a mutation in the gene coding
for a protein called TDP-43. This protein is normally found in
the nucleus of motor neurone cells. In many ALS patients
however, a key feature of disease progression is a build-up of
an abnormal form of TDP-43 in the cytoplasm surrounding the
nucleus of the motor neurone cells. The researchers took skin
cells from a patient with an inherited form of ALS and used
them to derive iPS (induced pluripotent stem) cells that carried
the TDP-43 mutation.118 They used the iPS cells to derive
neurones and functional motor neurones and showed that the
cells accumulated the abnormal TDP-43 protein and had
decreased survival rates over time. Again it is hoped that these
cells will lead to better models for studying progression of the
disease and for screening potential drugs.
4.4 Reversing differentiation: iPS cells
The discovery of induced pluripotency is based on a
number of key advances:
„ the demonstration by somatic cell nuclear
transfer that differentiated cells retain the same
genetic information as early embryonic cells
(see Chapter 2)
„ the development of techniques that allowed
researchers to derive, culture, and study
pluripotent cell lines
„ the observation that transcription factors are
key determinants of cell fate whose enforced
expression can switch one cell type into
another.
117
118
Patani R et al, Nature Communications, 2, 214, 2011
Bilican B et al, 2012,
www.pnas.org/content/early/2012/03/20/1202922109.full.pdf+html
Induced pluripotent stem (iPS) cells were first
derived in 2006 (see Chapter 2). Researchers
identified a cocktail of four transcription factors that
could convert (fully differentiated) mouse fibroblast
cells back into a pluripotent state.119 The four
factors were:
„ Oct 4 and Sox 2, which were discussed earlier
in the context of maintaining pluripotency in ES
cells.
„ Klf4 (Krupple like factor 4) one of a series of
closely related proteins that are known to play
a role in cell proliferation, differentiation and
survival, especially in the context of cancer.
„ c-Myc, a gene coding for a transcription factor
that is known to regulate the activity of a wide
range of other genes and that has been
implicated in important cellular processes such
as cell proliferation and cell growth.
The researchers found that inserting a viral vector
containing the genes coding for these four
transcription factors into mouse fibroblast cells
could induce developmental reprogramming of
some of the cells into pluripotent stem cells. Only a
very small proportion of the cells treated in this way
were reprogrammed. By culturing these cells under
embryonic stem (ES) cell conditions the
researchers were able to derive iPS cells that
closely resembled hES cells. Within a year
researchers had shown that the same four factors
could be used to reprogram human120 fibroblasts
into iPS cells. Other research groups reproduced
the findings and devised reprogramming protocols
using different transcription factors. For instance,
one group used a combination of Oct 4, Sox 2,
Nanog (all key factors in maintaining pluripotency)
and Lin 28 (a marker of undiffentiated hES cells) to
derive iPS cells from human somatic cells.121
This research prompted a huge amount of interest.
It was not the first time that adult (differentiated)
cells had been reprogrammed; this had already
been achieved using cell nuclear transfer (Chapter
2). But it was the first time that reprogramming had
been achieved using defined factors. In theory at
least, human iPS cells offer a number of potential
advantages. They could be used:
„ to derive hES-like cells without requiring human
the use of embryos
„ to develop better models of disease for
research purposes (for instance the iPS cells
containing a mutation linked to one of the main
motor neurone diseases outlined in Box 4.7)
119
120
121
Takahashi K & Yamanaka S, Cell 126 (4): 663–76, 2006.
Takahashi K. et al, Cell, 131(5), 861-72, 2007
Yu J et al, Science, 318 (5858), 1917-20, 2007
POST Report March 2013 Stem Cell Research
„
„
to use the disease models to screen for
potential new drugs
for therapeutic purposes since deriving iPS
cells from a patient’s own cells should minimise
concerns about immune rejection.
Page 45
FIGURE 4.5 STEPS IN REPROGRAMMING124
However, a key question here is: how similar are
iPS cells to ES cells? This is important because
before they can be considered for use in clinical
trials in humans, researchers need to be confident
that iPS cells will behave in a stable and predictable
manner and will not revert back to their original
(differentiated) state. In order to answer this
question, researchers have been trying to get a
better understanding of the reprogramming process.
This is discussed in the following section.
The reprogramming process
One of the interesting features of the
reprogramming process is its inefficiency. Only a
small proportion of the cells expressing the cocktail
of transcription factors are converted into iPS cells.
Even where this does occur, the conversion is a
slow process taking one to two weeks.122
Various hypotheses have been advanced to
account for this inefficiency. One suggestion was
that not all of the treated cells expressed
appropriate levels of all of the reprogramming
factors. Another was that only a small subset of the
starting cell population − for example cells not yet
committed to a particular lineage or adult stem cells
− are able to undergo reprogramming. A third theory
was that reprogramming depended on whereabouts
in the cell genome the viral vector carrying the four
factors inserts itself.
Each of these theories has been investigated and
the available evidence does not support any of
them.123 Rather it is now thought that
reprogramming involves a series of steps, as shown
in Figure 4.5. While most of the starting cells may
begin the reprogramming process, only a small
proportion successfully complete all of the main
steps to become fully reprogrammed iPS cells. The
barriers to achieving successful completion of each
step are thought to be mainly epigenetic (see Box
4.1) in nature.
122
123
Hanna J et al, Nature, 462, 595–601, 2009
Plath K and Lowry WE, Nat Rev Genet, 12(4), 253–265, 2011
As outlined in Figure 4.5, successful reprogramming
requires the completion of at least three main steps.
Evidence for this comes from imaging studies that
can retrospectively piece together the path followed
by cells that successfully complete the
reprogramming process. In the early phase, the
starting cells (usually fibroblasts) start to proliferate
and change in appearance, becoming rounder.
Following the mid-phase clusters of round cells are
apparent and the cells have completed the
transition from one cell type (mesenchymal in the
case of fibroblasts) to another (epithelial cells).
Finally, after the late phase, distinct colonies of iPS
cells are apparent.
124
Adapted from Plath K and Lowry WE, Nat Rev Genet, 12(4), 253–
265, 2011
POST Report March 2013 Stem Cell Research
Page 46
Studies of cells that only make it part of the way
through this process have started to reveal what is
going on at a molecular level. The early phase is
characterised by the silencing (down regulation) of
fibroblast-specific genes and the reawakening (up
regulation) of genes for cell proliferation and DNA
replication. During the middle phase, epithelial
genes are up regulated as are some of the markers
that are specific for ES cells. The late stage
involves the activation of the remaining pluripotency
genes such as Nanog. These events are
orchestrated by the reprogramming factors through
their actions on an array of other transcription
factors and epigenetic mechanisms, such as
changes to the histone proteins that are associated
with DNA (see Box 4.1).
Also shown in Figure 4.5 are a population of cells
known as pre-IPS cells that are only partially
reprogrammed. These cells have silenced many of
the genes responsible for their previous
differentiated state and acquired many of the
properties of pluripotent ES cells. But they have
fallen at the final hurdle by failing to reawaken the
full network of pluripotency genes.
Pre-iPS cells can be isolated from a population of
treated cells, grown in culture and used to study the
late phase of the reprogramming process. For
instance, it has been observed that different types
of starter cell give rise to pre-IPS cells that have all
stalled at the same phase of the reprogramming
process.125 Research is currently underway to
identify the exact nature of this common stumbling
block. A number of research groups have reported
that treatment of pre-iPS cells with various small
molecules can cause them to give rise to fully
reprogrammed cells that express the full range of
pluripotency genes.
Comparing ES and iPS cells
Research on the reprogramming process has
informed the debate on how similar iPS cells are to
ES cells derived from embryos. On the face of it,
fully reprogrammed iPS cells appear very similar to
embryo-derived ES cells. However, researchers
have used a number of techniques to compare the
cells at the molecular level and these include
comparisons of:
„ Messenger RNA (mRNA) expression. This
assesses what genes are active and which
proteins are likely to be made.
„ Expression patterns of other RNA sequences
(miRNA and lincRNA) that do not code for
proteins but that play a role in gene regulation
and reprogramming.
125
Mikkelsen TS et al, Nature;454, 49–55, 2008
TABLE 4.1 COMPARISON OF IPS AND ES
CELLS126
Characteristic mRNA expression patterns miRNA expression patterns lincRNA expression patterns DNA methylation patterns Histone modification Metabolic profile „
„
iPS versus ES cells iPS cells have distinct patterns straight after reprogramming. Patterns are identical/near identical once iPS cells have been cultured for extended periods. Applies to mouse and human cells. Some miRNA not expressed in most mouse iPS cells. Differences described in human iPS cells but these are not consistent. Not studied in mice. Differences found in human iPS cells, some lincRNA known to play a role in reprogramming. Mouse iPS cells have distinct patters straight after reprogramming. Patterns are identical/near identical once iPS cells have been cultured. Human iPS cells are more variable in their methylation patterns than human 127
ES cells. The two modifications studied in mice were identical. In humans, three modifications were studied: two were identical, one was different. Not studied in mice. Identical/nearly identical in humans. Imprinting patterns of the DNA and its
associated proteins (histones). These are
important because DNA methylation and
histone modification are both mechanisms for
regulating gene expression (see Box 4.1).
Metabolic profile of the cells. This reveals what
chemical processes are active in the cells.
The results of such studies are summarised in
Table 4.1 for ES and iPS cells in both humans and
mice. They suggest that for both mice and human
cells, iPS cells retain an ‘epigenetic memory’ of their
starting cells when compared to embryo-derived ES
cells. For some characteristics this memory appears
to be transient. For instance in both humans and
mice, iPS cells show mRNA expression patterns
that share some characteristics of the starting cells
− and are distinct from the respective ES cells −
when studied immediately after the reprogramming
process has finished. However these distinct
patterns have faded after the iPS cells have been
cultured for some time.
126
127
Adapted from Plath K and Lowry WE, Nat Rev Genet, 12(4), 253–
265, 2011
Bock C et al, Cell, 144, 439–52, 2011
POST Report March 2013 Stem Cell Research
A similar phenomenon is seen in the DNA
methylation patterns of mice iPS cells. Immediately
after reprogramming the cells exhibit methylation
patterns that share some characteristics with the
starting cells. However after culturing, the iPS cells’
methylation patterns more closely resemble those
of mice ES cells.128 The DNA methylation patterns
in human ES and iPS cells are more variable. A
recent study looked at 20 different human ES cell
lines and 12 human iPS cell lines.129 It found
considerable variation in the methylation patterns
between different ES lines, between iPS lines and
between ES and iPS lines. The study concluded
that the human iPS cells showed more variation at
the molecular level than human ES cells.
Other differences between iPS cells and ES cells
have also been reported (see Table 4.1). These
include differences in miRNA in both human and
mice studies and differences in lincRNA and histone
modifications in human studies. There is also
evidence of functional differences between hiPS
cells and hES cells. For instance a recent study
showed that hiPS derived from insulin-producing
beta cells were more likely differentiate into insulinproducing cells when compared with hES cells.130
Overall, iPS cells look and behave in a very similar
fashion to embryo-derived ES cells. They are
capable of self-renewal, are pluripotent and have
similar patterns of gene expression. However, when
studied at the molecular level, there is evidence of
subtle differences between iPS and ES cells. In
particular, iPS cells appear to retain an epigenetic
memory of their former state. For some
characteristics there is some evidence that this may
be a temporary phenomenon that fades once the
cells have undergone several rounds of cell culture.
The significance of these small molecular
differences between iPS and ES cells is currently
the subject of much debate. On the one hand, the
differences are very small, and do not appear to
affect the overall appearance or behaviour of the
cells. On the other hand, very small molecular
changes are known to have a very big impact on
the developmental fate of cells. Further research on
the functional significance of the observed
differences between ES and iPS cells is thus
needed before iPS cells can be used for therapeutic
purposes. This is discussed in more detail in
Chapter 6.
Page 47
Box 4.8 Reprogramming using small molecules
To date, protocols for achieving cell reprogramming involve
inserting genes coding for the chosen reprogramming factors
into the starting cells. This is because the reprogramming
factors are large molecules (proteins) and the best way of
getting large molecules inside cells is to manufacture them in
situ using genes. However such an approach has several
disadvantages:
„ It involves genetic manipulation of the starting cells and
any modifications made will persist in the resulting iPS
cells. This raises additional regulatory concerns and may
limit the clinical usefulness of iPS cell lines.
„ Some of the protocols involve inserting gene sequences
into the DNA of the starter cell. Such methods raise
additional risks of introducing mutations into the starting
cells if the site of insertion is a functionally important DNA
sequence. Non-insertional protocols have been
developed, but are generally less efficient.
„ Some of the reprogramming genes have the potential to
cause cancer (they are so-called oncogenes) and are
thus not suitable for clinical applications.
One approach would be to replace the genes with purified
copies of the proteins they code for. Such a protocol has been
developed and used to successfully reprogram somatic cells
into iPS cells.131 However, the efficiency of this method is low.
Another approach is to replace each of the reprogramming
factors with small molecules. This would allow cell
reprogramming under chemically defined conditions and would
obviate the need for genetic modification. The principle of such
an approach has already been proven. For instance in 2009,
researchers showed that the gene for Sox 2 could be replaced
by a small molecule that inhibited one of the key signalling
pathways involved in the reprogramming process.132 More
recently, researchers have developed a protocol where three of
the four reprogramming factors have been replaced by small
molecules.133 The one remaining gene for which a small
molecule substitute has yet to be found is the Oct4 gene.
Research has already demonstrated that replacing or
augmenting some of the genes with small molecules can also
greatly increase the efficiency of the reprogramming process.
The Holy Grail for research in this area is to develop a protocol
that uses a defined cocktail of small molecules to achieve
reprogramming at much higher efficiency than is currently
possible.
Another main target for researchers is to refine the
reprogramming protocols. A key aim here is to
develop protocols that are more efficient than
current ones and that do not involve inserting genes
into the starter cells. Some recent developments
are outlined in Box 4.8. The disadvantages outlined
in Box 4.8 limit the clinical usefulness of current iPS
cell lines. However, they have the potential to be a
valuable research tool for the study of normal cell
development and for disease-modelling. This is
discussed in the next section.
131
128
129
130
Polo JM et al, Nature Biotechnology,28, 848–55, 2010
Bock C et al, Cell, 144, 439–52, 2011
Bar-Nur O et al, Cell Stem Cell 9, 17–23, 2011
132
133
Zhou H et al, Cell Stem Cell 4 (5): 381–84, 2009
Li W and Ding S, trends in Pharmacological Sciences, 31 (1), 3645, 2009
Zhu S et al, Cell Stem Cell, 7 (6), 651-55, 2010
POST Report March 2013 Stem Cell Research
Page 48
FIGURE 4.6 IPS CELLS AS DISEASE MODELS134
Oct 4, Sox 2, Klf 4, cMyc
Cells from patient
Reprogramming
Directed differentiation
Compound screening (chemicals, proteins, miRNA)
Disease models
Better understanding of disease mechanisms
iPS cells in disease-modelling
In addition to being an exciting research tool to
probe mammalian development and epigenetic
reprogramming, iPS cells have great potential as a
system to model human diseases. iPS cells can be
generated from skin biopsies or blood samples of
patients. They can then be differentiated in the
laboratory to give rise to cell types that are:
„ not easily accessible in patients, such as
neurons and cardiomyocytes, and/or
„ the cell types affected by the disease in
question.
The iPS cells and the differentiated cell types
derived from them should retain the genetic
information from the original patients, including any
genetic factors implicated in causing the disease in
the first place. By studying disease models derived
in this way, researchers can better understand the
underlying mechanisms behind the disease. This
may lead to the identification of possible new
therapeutic agents and these can be screened for
efficacy using the disease model. The process is
outlined in Figure 4.6.
134
Adapted from Unternaehrer JJ and Daley GQ, Phil Trans R Soc B,
366 (1575) 2274-85, 2011
iPS cells have now been derived as potential
models for a wide range of different diseases (see
Table 4.2). A key question in such models is
whether the iPS cells and the differentiated cells
derived from them recapitulate some of the diseasespecific characteristics. This has been
demonstrated for some, but not all, of the disease
models developed so far. For example, of the
disease models listed in Table 4.2, only 12 have
successfully shown that a disease characteristic is
present in the differentiated cells of interest. In
some cases this was because the researchers did
not investigate the characteristics of the derived
cells.
An example where disease characteristics have
been demonstrated in iPS cells and the
differentiated cells derived from them is
amyotrophic lateral sclerosis (see Box 4.7). Another
is iPS cells generated from patients with spinal
muscular atrophy, a disease caused by mutations in
the survival motor neuron 1 (SMN1) gene. When
the iPS cells are differentiated into motor neurons,
researchers have been able to demonstrate that the
motor neurons show deficits that reflect some of the
defects seen during the development of the
disease.135 Such disease models therefore have the
potential to be used to screen for possible new
therapeutic agents.
However, iPS cells are not always the best
available disease models. Two examples of
diseases where iPS cells may not yield appropriate
models are:
„ Fanconi anaemia, a genetic syndrome that
involves failure of the bone marrow
„ Fragile X syndrome, an inherited form of
mental retardation.
In the case of Fanconi anaemia, the nature of the
condition itself precludes cell reprogramming.
Attempts to reprogram fibroblasts or keratinocytes
from patients suffering from the condition have
proved unsuccessful. It appears that the pathway
affected by the disease is itself needed for the
reprogramming process.136 Researchers have thus
developed a disease model using hES cells which
have had the key genes that cause the disease
inactivated.
135
136
Ebert AD et al, Nature, 457, 277-80, 2009
Raya a et al, Nature 460, 53-59, 2009
POST Report March 2013 Stem Cell Research
TABLE 4.2 iPS CELL DISEASE MODELS137
Neurological diseases Amyotrophic lateral sclerosis Spinal muscular atrophy Parkinson disease Huntington disease Down’s syndrome Fragile X syndrome Familial dysautonomia Haematological diseases ADA‐SCID Fanconi anaemia Scwachman‐Bodian‐Diamond syndrome Sickle cell anaemia Beta thalassemia Polycythemia vera Primary myelofibrosis Metabolic diseases Lesch‐Nyhan syndrome Diabetes type 1 Gaucher disease type 3 Alpha 1‐antitrypsin deficiency Glycogen storage disease type 1a Familial hypercholesterolemia Crigler‐Najjar syndrome Hereditary tyrosinemia type 1 Progressive familial hereditary cholestasis Hurler syndrome Cardiovascular diseases LEOPARD syndrome Long QT syndrome Arrhythmogenic right ventricular cardiomyopathy Supravalvular aortic stenosis Dilated cardiomyopathy Other diseases Duchenne muscular dystrophy Becker muscular dystrophy Dyskeratosis congenital Cystic fibrosis Scleroderma Osteogenesis imperfect In the case of fragile X, it is possible to obtain iPS
cells from patients but the cells are not an adequate
model of the disease. Fragile X is caused by an
accumulation of short repeat gene sequences in the
promoter region of a specific gene on the X
chromosome. The gene is active early on in
development, but the build-up of repeat sequences
leads to it being inactivated. Researchers thus want
a model in which to study the accumulation and
inactivation processes. In iPS cells from patients
with fragile X, the gene of interest is already
inactivated. In other words, the reprogramming
process has failed to reactivate it.138 For this
disease, an hES cell line derived from an embryo
diagnosed with fragile X syndrome has proved to be
a better disease model.
137
138
Adapted from Unternaehrer JJ and Daley GQ, Phil Trans R Soc B,
366 (1575) 2274-85, 2011
Urbach A et al, Cell Stem Cell, 6, 407-11, 2010
Page 49
Other conditions that are challenging to model
include diseases of aging such as Parkinsons and
Huntingtons. This is because the differentiated cells
derived from iPS cells have a limited lifespan, which
makes it difficult to model the disease
characteristics over the required timeframe. Better
models for these conditions may depend on
developing ways of mimicking ageing of the cells.
In addition to ensuring that iPS cells reflect features
of the disease they are being used to model,
several other challenges regarding iPS cells as well
as hES cells need to be addressed. These include:
„ The lack of robust, lineage-specific,
differentiation protocols to generate the large
quantities of cells needed for screening.
Although significant advances have been made
to direct the differentiation of ES cells and iPS
cells into certain types of neurons,
cardiomyocytes, blood and pancreatic cells,
none of these protocols generate cell
populations of the required purity.
„ Current differentiation protocols tend to
produce immature cell populations rather than
fully mature adult cells.
„ Variation in the ability of different iPS cell lines
to differentiate into different cell types. This
might reflect variations in the starting cells or in
the reprogramming process.
Page 50
POST Report March 2013 Stem Cell Research
POST Report March 2013 Stem Cell Research
5
Page 51
Clinical Developments
Overview
„ Numerous clinical trials have investigated the therapeutic use of a patient’s own cells to
treat a range of different diseases (autologous therapy).
„ Some such trials have shown evidence of clinical benefit but there is a need for bigger
trials to optimise factors such as cell type and dose, timing and administration.
„ Trials using fetal stem cells or hES cells (allogeneic therapy) have recently started.
„ Concerns over immune rejection mean that allogeneic approaches are largely confined
to sites of the body where the immune system is largely suppressed.
5.1 Stem cell therapies
Ultimately the aim of stem cell research is to
develop better treatments for use in the clinic.
Various different approaches are possible:
„ Cell therapy, where cells of various types are
administered to the body. In some cases the
aim is that the cells regenerate a tissue that is
diseased or damaged. In other cases the aim
may be to limit tissue damage by ‘damping
down’ the body’s immune response to a
trauma.
„ Tissue engineering, where cells are used in
conjunction with a matrix or scaffold to
reconstruct damaged or diseased tissue.
Perhaps the best known example of this type of
therapy was the use of epithelial cells and
cartilage cells to tissue engineer a new section
of trachea for a patient in Barcelona whose
airways had been severely damaged by
tuberculosis (see Box 5.1).
„ Using stem cells as a vehicle for delivering
gene therapy. An example of this approach is
treatment of a particular form of severe
combined immune-deficiency (SCID) with stem
cells that have been genetically modified to
contain a good copy of the gene implicated in
this type of the disease (Box 5.2). The cells are
used to repopulate the patient’s bone marrow
and restore his or her immune response.
This Chapter will focus on the first of these various
different approaches, cell therapy. If new, cellbased therapies are going to make it into clinical
use, they must first be tested in clinical trials to
prove their safety and efficacy. Before giving
permission for an early stage clinical trial, regulators
need data from pre-clinical studies to show that the
treatment is safe and potentially effective. The four
basic phases of clinical trials were summarised in
Chapter 3 (see Box 3.2), with the early stages
(phase I) being largely concerned with
demonstrating safety and the later phases (III)
focusing more on establishing efficacy.
Box 5.1 Tissue engineered windpipe139
In March 2008, Claudia Castillio, a 30 year old Colombian
woman was admitted to hospital in Barcelona suffering from
collapsed airways following a severe case of tuberculosis.
Previous attempts to surgically replace large airways have
proved unsuccessful; the only conventional option for such
patients is to remove the affected lung and airway. However,
the doctors offered to try and tissue engineer a new section of
trachea. A scaffold was prepared by Italian scientists in Padua
who took a section of trachea from a donor and removed all of
the living cells by a process involving 25 washing cycles. Two
types of cell were used to line this scaffold to make it biocompatible with the patient:
„ epithelial cells taken from the patient’s trachea were used
to line the inner surface of the scaffold
„ chondrocytes (cartilage cells) derived from stem cells
from the patient’s bone marrow lined the outer surface.
The cells were cultured at the University of Bristol, and flown to
Barcelona where scientists reseeded the cells onto the
scaffold. Spanish doctors extracted the damaged section of
trachea from the patient and replaced it with the tissue
engineered section in June 2008. No immune-suppression was
required because the cells used to tissue engineer the scaffold
came from the patient herself. Within two months of the
operation the patient had a normal lung function and was able
to lead an independent life.
Autologous and allogeneic approaches
The Regenerative Medicine in Europe (REMEDiE)
project surveyed all European small and mediumsized enterprises (SMEs) developing cell-based
therapy in 2010.140 It identified 65 SMEs developing
cell therapy, of which the majority (50) were
pursuing approaches that used the patient’s own
cells (autologous therapy). The remaining 15 SMEs
were developing approaches where the cells used
for therapy originated from another person
(allogeneic therapy).
139
140
POSTnote 333, Regenerative Medicine, May 2009
Taking Stock of Regenerative Medicine, BIS/DH, 2011
POST Report March 2013 Stem Cell Research
Page 52
Box 5.2 Gene therapy for X-linked SCID
X-linked severe combined immune deficiency (X-linked SCID)
is a rare disease that affects less than 1 in 200,000 baby boys.
It is caused by a fault in the gene coding for the common
cytokine receptor γ-chain, and leaves the immune system
incapable of mounting an effective immune response to
common infections. Boys with X-linked SCID have a very poor
prognosis if the condition is untreated, usually dying from
infectious disease before they reach the age of one year. The
condition can be treated by bone marrow transplantation, but a
suitably matched donor (usually a close relative) is only
available in around one in three cases.
Box 5.3 Immune rejection
All of the cells in a human body display proteins (antigens) on
their outer surface. These antigens are coded for by a cluster of
genes found on chromosome 6 of the human genome and
collectively known as the major histocompatibilty complex
(MHC). The presence of these MHC antigens143 on the outer
surface of cells is the body’s way of marking cells as belonging
to ‘self’. Under normal circumstances, an immune system will
recognise its own particular pattern of MHC antigens and will
not attack cells displaying it. Cells from another (‘foreign’)
source will display a different pattern of MHC antigens, and will
be attacked by the immune system.
The first gene therapy trials for treating this disorder were
reported in 2000.141 The strategy involved using a viral vector
to insert a ‘good’ copy of the ‘faulty’ gene into HS cells taken
from the patient, and these cells were then used to repopulate
the patient’s bone marrow. The treatment restored normal
immune responses in both of the patients receiving it in the
initial trial. However, this approach received a major setback
when five out of 20 boys in subsequent trials in the UK and
France developed leukaemia. In these patients, the act of
inserting the gene into a chromosome in the HS cells had
inadvertently activated a proto oncogene (a gene that has the
potential to cause cancer) near the site of insertion (this is
known as insertional mutagenesis). One of the children died
from leukaemia; the others survived following chemotherapy
and were among the majority of children receiving the
treatment whose immune responses were restored. The
episode led to a suspension of some types of gene therapy
trial, and to the development of safer vector designs. The
advent of new vectors has led to the recruitment of patients into
a new trial split between hospitals in London, Paris, and the
USA.142
It is these immune responses to different patterns of MHC
antigens that cause the immunological rejection of cells, tissue
or organs that have been transplanted from one individual to
another. The chances of immune rejection can be minimised by
trying to match the tissue type of the donor to that of the host.
Donation between identical twins is the best way of ensuring
that immune rejection does not occur, but this is not possible in
most cases. Tissue typing between close family members is
another common strategy for reducing the risk of immune
rejection. A combination of tissue typing and the use of immune
suppressing drugs is usually needed for allogeneic cell therapy.
The main reason why autologous trials are further
advanced than allogeneic is that the approach
avoids most of the issues associated with immune
rejection (see Box 5.3). It is thus usually easier to
secure regulatory approval for an autologous trial
than it is to get approval for an allogeneic approach.
The following sections look at some of the cell
therapies currently under development in the UK
and elsewhere. Rather than attempt a
comprehensive list of all the trials of autologous
therapy being undertaken, Section 5.2 gives an
overview of the different types of trials to date.
Allogeneic therapies are covered in Section 5.3.
5.2 Autologous cell therapy trials
Types of cells used
Cells most commonly used in autologous therapy
fall into one of the following three categories.144
„ Mesenchymal stem (MS) cells. MS cells are of
interest for two main reasons. First they readily
differentiate into bone and cartilage lineages,
so their ability to repair such tissues is the
subject of a number of early stage clinical trials.
Second, MS cells also exhibit immune
suppressive effects and so there are trials
underway investigating whether such
properties can be used to treat heart disease,
immune rejection or autoimmune disorders
such as multiple sclerosis.
„ Haematopoietic stem (HS) cells. HS cells are
among the best characterised stem cells (see
Chapter 4) and researchers have considerable
experience in using such cells in the clinic and
in directing their differentiation down different
lineages in the laboratory.
„ Tissue-specific progenitor cells with a more
restricted differentiation capacity responsible
for normal tissue renewal and turnover, such as
neurons, intestine, skin, lung and muscle.
143
141
142
Cavazzana-Calvo M et al, Science, 288 (5466), 669-672, 2000
Herzog R, Molecular Therapy, 18(11): 1891, 2010
144
In humans, the antigens coded for by the genes in the MHC are
often referred to as human leukocyte antigen (HLA)
Reflection paper on stem cell-based medicinal products, EMA 2011
POST Report March 2013 Stem Cell Research
It has also been suggested that induced pluripotent
stem (iPS) cells could be used for autologous
therapy. Such an approach would combine the
advantage of autologous therapy (avoidance of
immune rejection) with that of allogeneic therapy
(the ability to create cells of any type). However, no
clinical trials of iPS cells have been undertaken to
date because of concerns over the potential safety
of such approaches. These include (see Section
4.4):
„ the subtle differences in gene expression and
regulation seen between hES and iPS cells
„ concerns that iPS cells may retain an
epigenetic memory of their previous state
„ concerns over the stability of iPS cells and their
potential to cause tumours.
Cell therapy and blood cancers
Among the most established autologous therapies
are the use of HS cells for the treatment of blood
cancers such as lymphoma and multiple myeloma.
Here the cell therapy is not being used to treat the
cancer directly; this is done using aggressive
chemotherapy to kill the cancerous cells and with
them, wipe out virtually all of the cells in the
patient’s bone marrow. The HS cells, which are
collected prior to chemotherapy and stored, are
then re-introduced into the patient, where they
repopulate the bone marrow and go on to produce
the full range of blood cells. This approach is the
treatment of choice in patients with Hodgkin or nonHodgkin lymphoma who have relapsed following
conventional treatment. It allows the use of much
higher doses of chemotherapy, increasing the
chances of curing the disease. Auotologous HS
therapy in conjunction with chemotherapy has also
been shown to increase the survival time of patients
with multiple myeloma.
Cell therapy and cardiac function
There have been numerous trials using HS cells or
mesenchymal stem (MS) cells in patients with
various forms of heart disease.145 The initial aim of
many such trials was to investigate whether such
cells could assist cardiac repair following a heart
attack. Such studies have shown little evidence of
physical regeneration of heart tissue. However,
there is evidence from some of the studies that
infusion of the heart with HS cells following a heart
attack may help to limit the extent of the damage
incurred and improve certain aspects of heart
function, at least in the short-term.
Page 53
It is now thought that these effects may be caused
by HS cells stimulating endogenous repair of heart
tissue rather than by direct repopulation and
regeneration of heart tissue.146 However, there is
considerable variation from one study to the next
about the extent of such effects suggesting that
there is a need to optimize treatment timing, cell
type and dose, and delivery methods.147
There have also been trials to investigate the
possible regenerative effects of cells derived (by
biopsy) from the heart itself following a heart
attack.148 In the so-called SCIPIO trial, cells cultured
from atrial tissue were injected back into the
patient’s heart. In a similar study (CADUCEUS)
cardiospheres − spherical structures of cardiac cells
− cultured from ventricular tissue were used. In both
studies the treatments were well tolerated and both
resulted in a reduction in the amount of scarred
tissue. One of the trials showed a modest
improvement in one measure of heart function.
However, both trials involved a small number of
treated patients (16 in SCIPIO and 17 in
CADUCEUS); larger trials would be needed to show
clear evidence of clinical benefit.
Several UK clinical trials are currently looking at cell
therapy and cardiac function. For instance, one trial
is investigating whether infusion of autologous bone
marrow derived progenitor cells to patients
undergoing treatment for heart attack will lead to an
improvement in cardiac function. Another trial is
investigating whether the same procedure is
effective in improving cardiac function in patients
suffering from chronic heart failure. And a third trial
is looking at the effects of Granulocyte-colony
stimulating factor (GCSF), which stimulates the
production of circulating blood progenitor cells. It
will compare GCSF given on its own with GCSF
given in conjunction with autologous bone marrow
derived stem cells administered in two different
ways.
146
147
145
Ptaszek LM et al, Lancet, 379, 933–42, 2012
148
Loffredo F et al, Cell Stem Cell 2011, 8(4), 389-398, 2011
Trounson A et al, BMC Medicine, 9:52, 2011
Ptaszek LM et al, Lancet, 379, 933–42, 2012
POST Report March 2013 Stem Cell Research
Page 54
Cell therapy and stroke
Cell therapy and immune disorders
There is a large body of evidence from pre-clinical
studies that stem cell therapy can improve
outcomes following ischaemic149 stroke in animal
models for this condition. Such studies have used
MS cells, HS cells or various other cell populations
isolated from bone marrow. A number of possible
mechanisms have been proposed for such effects
and these include:150
„ cell replacement, where the transplanted cells
migrate to the affected area of the brain and
differentiate into neural/glial cells
„ protective effects, where the transplanted cells
produce factors that support the survival of
existing neurones and/or support the
production of new neurons and connections
„ angiogenesis, where the transplanted cells
promote the formation of new blood vessels
„ protective effects where the transplanted cells
modulate immune responses and help to limit
the resulting damage.
Autoimmune disorders such as multiple sclerosis,
scleroderma and lupus are the result of immune (T)
cells attacking the body’s own tissue. Autologous
HS cells have been used in early stage clinical trials
for each of these diseases. The strategy is to use
aggressive immune suppression to deplete the
population of rogue T cells that are causing the
problem followed by transplantation of HS cells to
re-establish the patient’s immune system. The
results from early phase trials show evidence of
clinical benefit for each of these diseases. For
instance, in trials with patients with multiple
sclerosis, the therapy slowed progression of the
disease and reduced inflammation.152 Larger-scale
trials are needed to show whether such benefits
translate into longer-term clinical benefits or disease
remission. Such trials would also reveal whether the
benefits outweigh the risks inherent in therapies that
involve aggressive immune suppression.
A number of small scale clinical trials have taken
place using autologous MS or bone marrow cells
administered to stroke patients. While the
treatments were well tolerated in most cases, there
is little clear-cut evidence of clinical benefits from
the trials conducted to date.151 The studies varied in
the choice of cells used, in the route of
administration for cell transplantation and in the
timing of the cell transplantation. It is not clear what
the optimum approach is for any of these factors.
A wide range of other sources of autologous cells
have been used in small scale clinical trials to treat
various conditions. Examples include:
„ Adipose stem cells have been have been used
in trials to investigate soft tissue repair. They
can be used along with scaffolds for
procedures such as breast reconstruction, and
also form the basis of commercial treatments
for burns.
„ Endothelial cells are thought to stimulate
angiogenesis (the formation of new blood
vessels) and have been used in trials for
conditions such as stroke. Results are variable,
and the exact mode of action is uncertain.
„ Limbal stem cells found in the eye have been
shown to be a safe and effective way of
restoring vision due to loss or damage of
corneal epithelial cells.
149
150
151
Ischaemic refers to a condition caused by a decrease in the blood
supply to a tissue or organ, so an ischaemic stroke results in a
restriction of the blood supply to the brain
Sahota P and Savitz S, Neurotherapeutic, 8(3), 434–451, 2011
Sahota P and Savitz S, Neurotherapeutic, 8(3), 434–451, 2011
Other autologous cell therapy approaches
152
Capello E et al, Neurol Sci, 30(Suppl 2), S175-177, 2009
POST Report March 2013 Stem Cell Research
Box 5.4 Immune privilege
It has been known for many years that some tissues of the
body tolerate tissue grafts better than others. In particular, the
eye, brain, spinal column, pregnant uterus and testes are
known to tolerate tissue grafts that would normally be rejected
at other sites within the body.
It was widely assumed that this so-called immune privilege was
the result of the exclusion of immunologically active cells from
these tissues. For instance, it was thought that physical barriers
such as the blood-brain, blood-retina, blood-placenta and
blood-testis barriers prevented immune cells such as
leukocytes from entering immune privileged tissue.
However, more recent research suggests that immune privilege
is more likely to be the result of a number of highly active,
localised mechanisms that act to suppress normal immune
responses in such tissue.153 This has implications for the way in
which diseases that affect immune privileged tissues such as
the eye are treated. Better understanding of the mechanisms
by which immune privileged tissue is able to suppress normal
immune responses may help researchers develop allogeneic
therapies that are more widely applicable within the body.
5.3 Allogeneic cell therapy trials
Allogeneic therapy is less well advanced than
autologous therapy. This is mainly because of
concerns about immune rejection (see Box 5.3).
These concerns mean that many of the allogeneic
trials to date have targeting diseases of immune
privileged sites of the human body such as the eye,
brain and spinal column (see Box 5.4). Such
approaches may allow researchers to transplant
allogeneic cells without having to use aggressive
immune suppression strategies.
Types of cells used
Allogeneic approaches have included the use of
cells such as keratinocytes and fibroblasts derived
from new born babies. Such cells can be cultured in
the laboratory and frozen, then thawed and used
when needed in applications such as wound
healing. The use of cultured cells of this type
appears to avoid the extreme immune rejection
responses often seen with allogeneic therapy.154 An
example of their use is in the healing of venous leg
ulcers, where they have been shown to be safely
tolerated and clinically effective (see Box 5.5).
153
154
Benhar I et al, Front. Immun, 3, 296, 2012
www.frontiersin.org/Immunological_Tolerance/10.3389/fimmu.2012.
00296/full
Dominguez-Castillo R et al, Immunology, 125, 370–376, 2008
Page 55
Box 5.5 Allogeneic cell therapy for venous leg ulcers
Venous leg ulcers are persistent ulcers of the legs that are
caused by high blood pressure that damages small blood
vessels to the point where ulceration occurs. They affect
around 1 in 500 people in the UK, although this rate rises
sharply with age with an estimated 1 in 50 people over the age
of 80 developing them. People who are obese, unable to
exercise or who have varicose veins are also at higher risk of
developing venous leg ulcers. They can be treated by cleaning
and dressing the wound, and use of compression bandages to
restrict blood flow. However, they are slow to heal and prone to
infection by bacteria.
Various allogeneic cell therapy approaches have been
investigated as possible treatments for venous leg ulcers.
Some of these have involved use of cultured cells alone, and
others have used cells in combination with a matrix of some
description. In general, trials of these approaches have been
too small to demonstrate clinical effectiveness. However a
recent large, properly randomised, study looked at the use of
growth-arrested neonatal keratinocytes and fibroblasts in a
spray-applied matrix for treating venous leg ulcers. It provided
clear evidence of significantly greater reduction in wound area
associated with the cell-based treatment compared to the
control (placebo) treatment.155 It also provided evidence for
optimum dose and timing of dose.
There have also been a number of trials looking at
transplanted pancreatic beta cells for treatment of
diabetes. These have shown promise, with around
70% of patients becoming insulin independent.156
However, insulin independence is only maintained
for a relatively short time, with all of the treated
patients eventually reverting back to insulin
replacement therapy. Furthermore, the treatments
are limited by the availability of suitable donors
(each patient needs multiple donors) and it is
unclear whether the clinical benefits are outweighed
by the need for immune-suppression. Allogeneic
therapy using HS cells has also been used to treat
leukaemia (and acute myeloid leukaemia) using
tissue typing to match donors and hosts.
However, much of the recent interest in allogeneic
cell therapy has been in trials using two main types
of cells:
„ neural stem cells derived from fetal tissue
„ differentiated cells derived from hES cell lines.
155
156
Kirsner R et al, The Lancet, 2012 published online at
http://dx.doi.org/10.1016/S0140-6736(12)60644-8
Matsumoto S, J Diabetes, 2(1), 16-22, 2010
POST Report March 2013 Stem Cell Research
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Fetal neural stem cells
Disorders of the Central Nervous System
Current trials of fetal-derived stem cells are
summarised in Table 5.1. An American company,
Stem Cells Inc, is currently conducting trials of a
fetal-derived neural stem (NS) cell line in treatments
of three diseases:
„ Batten disease, a rare neurodegenerative
disorder affecting children
„ Pelizaeus–Merzbacher disease, a rare disorder
of the central nervous system affecting
coordination, motor abilities, and intellectual
function
„ chronic spinal cord injury.
Another American company, Neuralstem Inc is
testing fetal-derived spinal cord neural stem (NS)
cells in clinical trials for the treatment of
amyotrophic lateral sclerosis, a form of motor
neurone disease (see Box 4.5 in Chapter 4). All of
these trials are in early (phase I) stage, where the
object is primarily to establish that the procedures
are safe and well tolerated by the patients.
Stroke
A British company ReNeuron is conducting early
stage (phase I) clinical trials on fetal-derived NS
cells. These cells have been modified in the
laboratory to immortalise them. This means that
they are capable of propagating indefinitely, but this
is controlled by a promoter that can be switched on
and off for manufacturing purposes. The cells are
being implanted into the brains of disabled stroke
patients at three different doses to check that the
treatment is safe. Early results from the trial are
promising, with all five of the first patients treated
showing reductions in neurological impairment and
spasticity. The Company has submitted an
application to the UK regulatory authority to start a
multi-site Phase II clinical trial in mid 2013 to
examine the efficacy of the cells in treating disabled
stroke patients. The proposed study is expected to
take up to 18 months.
TABLE 5.1 TRIALS OF FETAL STEM CELLS157
Company Stem Cells Inc Neuralstem Inc ReNeuron Disease Batten disease Pelizaeus‐
Merzbacher Disease Chronic spinal cord injury Amyotrophic lateral sclerosis Stroke Cells Phase Fetal‐derived NS cells Fetal‐derived NS cells I I Fetal‐derived NS cells Fetal‐derived spinal cord NS cells Immortalised fetal‐derived NS cells I I I TABLE 5.2 TRIALS OF HES-DERIVED CELLS
Company Disease ACT Stargardts macular dystrophy Age related macular degeneration Spinal muscular atrophy Geron ACT CSC London project/ Pfizer Spinal cord injury Age related macular degeneration Cells Oligo‐
dendrocyte progenitor cells Retinal pigment epithelium Retinal pigment epithelium Motor neurone progenitor cells Retinal pigment epithelium 158
Phase I dis‐
continued I I I submitted I submitted hES-derived cell therapies
Spinal cord injury
A number of trials involving hES-derived cell lines
are underway or poised to start (see Table 5.2). The
first such trial was Geron’s trial of cells derived from
hES cells to treat patients with severe spinal cord
injury. This type of injury is caused by trauma to the
spinal cord and results in a complete loss of
sensory or motor function below the site of the
injury. The trial was open to patients who met
specific criteria, namely a traumatic spinal cord
injury to the middle (thoracic) region of the spine
between the third and eleventh vertebrae.
157
158
Adapted from Trounson A et al, BMC Medicine, 9:52, 2011
Adapted from Trounson A et al, BMC Medicine, 9:52, 2011
POST Report March 2013 Stem Cell Research
The trial recruited five such patients. Each received
a single injection of cells derived from hES cells into
the spinal cord at the site of injury one to two weeks
after the injury occurred. The cells used were
oligodendrocyte progenitor cells. These are
naturally occurring cells in the nervous system that
are known to be lost following traumatic spinal cord
injury. They produce the myelin sheath that protects
nerves in the spinal cord. They also produce protein
factors that are responsible for the growth and
survival of developing nerve cells and the
maintenance of mature nerve cells.
However, the trial was discontinued in November
2011. Geron announced that in view of the current
economic climate, it was going to focus on
experimental cancer therapies, which are further
along in development. The patients already
recruited and treated in the trial will continue to be
monitored in accordance with the clinical trial
protocol. But the trial itself is now closed and will not
be recruiting any more patients.
Diseases of the eye
The American company Advanced Cell Technology
(ACT) has derived retinal pigment epithelium from
hES cells and is undertaking phase I clinical trials to
assess its suitability for treatment of two diseases of
the eye:
„ Stargardts macular dystrophy (SMD), a genetic
eye disorder that causes progressive loss of
vision. It typically affects people in late
childhood and early adulthood.
„ Age-related macular degeneration (AMD, a
leading cause of vision loss in adults over 50,
see Box 5.6).
Each trial will recruit 12 patients who will receive the
retinal epithelial cells as a transplant under the
retina. The first three patients receive the lowest
dose, with the dosage increasing with each
subsequent cohort of three patients. Initial results of
the first two patients – one with AMD and one with
SMD – were published in February 2012.159
159
Schwatrz S et al, The Lancet, 379 (9817), 713-720, 2012
Page 57
Box 5.6 AMD and The London Project to Cure Blindness
The London Project to Cure Blindness is a on-going project led
by Professor Pete Coffey at the University College, London
(UCL) Institute of Ophthalmology to develop a stem cell-based
therapy for AMD. It aims to prevent blindness, restore sight and
improve the quality of life for people with AMD. It was set up in
2007 and was initially funded through philanthropic donations
and by the charitable sector, including the UK charity the
Macular Disease Society and the US-based Lincy Foundation.
In April 2009, UCL announced that the pharmaceutical
company Pfizer will provide funding to enable research into the
development of stem cell-based therapies for AMD as well as
other retinal diseases.
Proof-of-concept trials were conducted at Moorfields Eye
Hospital in 2007 and 2008 using retinal pigment epithelium
cells taken from non-diseased parts of the patient’s eye. Such
trials showed that transplanting ‘healthy’ cells under the
damaged area of the eye (the macular) can prevent blindness
and restore sight. However, the complexity of the surgery and
its associated complications mean that this is not a viable
method for treating the estimated 550,000 UK cases of AMD in
2012. This figure is projected to increase to 679,000 cases by
2020 as the proportion of older people in the UK population
increases.160
Having demonstrated that retinal pigment epithelium could
restore vision in patients suffering from AMD, the London
Project researchers started looking for alternative sources of
these cells. They found that they could derive healthy, fully
functional retinal pigment epithelial cells from hES cells.
Furthermore, they have developed methods for growing sheets
of these cells, and relatively simple surgical techniques for
transplanting them into the eye. This may make it possible to
conduct the required surgery in around an hour on a day-care
basis which would represent a much more practical approach
to treating the projected increase in cases of AMD in the UK.
The researchers have successfully demonstrated that the hESderived cells can restore visual function in an animal model of
AMD and are awaiting regulatory approval to start recruiting
patients in a phase I clinical trial.
Checks conducted four months after the treatments
showed that both patients tolerated the treatment
well. There was no evidence of runaway cell growth
or tumour formation (a particular concern with cells
derived from pluripotent ES cells). Nor were there
any signs of immune rejection or abnormal
signalling. There was clear evidence that the retinal
pigment epithelial had successfully been
transplanted in the patient with SMD and was
growing in a normal, controlled fashion. Evidence of
a successful transplant was not seen in the patient
with AMD. However, both patients showed some
signs of improved vision.
160
Owen C et al, Br J Ophthalmol, 96 (5), 752-756, 2012
Page 58
The Advanced Cell Technology trial has now
obtained clearance from the MHRA to begin treating
patients as part of a Phase I/II clinical trial for SMD
in the UK. Patient enrolment has begun and the first
patient was treated at Moorfields Eye Hospital in
London in January 2012.
The London Project to Cure Blindness (see Box
5.6), in conjunction with Pfizer has also derived
retinal pigment epithelium from hES cells. It has
conducted extensive pre-clinical studies and is
awaiting regulatory approval to start phase I clinical
trials to treat patients with AMD. If such approval is
forthcoming, the trial will also take place at
Moorfields Eye Hospital in London.
Neurodegenerative disease
There is also considerable interest in using cells
derived from hES cells for treating a range of
neurodegenerative diseases. To date no such
approaches have received regulatory approval for
clinical trials to start. An American company,
California Stem Cells (CSC, see Table 5.2) has
derived motor neurone progenitor cells from hES
cells and is awaiting regulatory approval for a trial to
treat spinal muscular atrophy (SMA). SMA is the
leading genetic cause of death in infants. It is a
disorder caused by a deficiency in a protein which is
essential to the proper functioning of the motor
neurons in the spinal cord. It causes deterioration of
the muscles that control walking, swallowing and
breathing. There are currently no treatments for the
disease.
Looking further ahead, the EU’s seventh
Framework Programme is funding the
NeuroStemcell programme to develop treatments
for Huntington’s disease and Parkinson’s disease
(see Box 5.7). Both of these diseases are caused
by degeneration of specific types of neurons. The
approach involves deriving safe, well-characterised
and pure populations of the specific neuronal types
and investigating their performance in animal
models of these diseases. Researchers from three
UK institutions are participating in the project (see
Box 5.7).
POST Report March 2013 Stem Cell Research
Box 5.7 The NeuroStemcell programme
The NeuroStemcell programme is an €11.9 million research
project funded for four years under the EU’s Seventh
Framework Programme. It consists of a consortium of 13
research institutions and three SMEs from six EU Member
States with one US collaborator. Its aim is to develop better
treatments for two diseases: Huntington’s disease (HD) and
Parkinson’s disease (PD). Both diseases are associated with
degeneration of specific types of neurons: striatal neurons in
HD and dopamine-producing neurons in PD. The project aims
to deliver safe and validated cells of these types that can be
used therapeutically (via transplantation into patients) and in
research for drug discovery purposes.
Three UK institutions are taking part in the consortium:
„ The University of Cardiff’s Brain Repair Group which has
an international reputation in assessing motor and
cognitive function associated with cell transplantation in
animal models of HD and PD. This group will provide
simple standardised tests of motor function for use by all
groups in the consortium for screening stem cell grafts. It
will also develop more sophisticated tests of motor and
cognitive function to assess the efficacy of promising
stem cell transplants in animal models of HD and PD.
„ The University of Cambridge, which will be involved in
producing the stem cells and in translational research
towards their use in clinical studies. A group at the
Wellcome Trust Centre for Stem Cell Research will focus
on the production and stable expansion of neural stem
cells from ES cells and fetal tissue sources. It will provide
the consortium with neural stem cells derived from
animals (rats) and humans. A second, clinical, group will
focus on the translation of stem cell therapies to patients
with PD. This will include defining subtypes of PD so that
novel therapies can be targeted to appropriate groups of
patients. It will also develop new markers of disease to
assess therapeutic effects of any stem cell therapies.
„ Imperial College, London’s Clinical Science Centre which
will develop defined population of specific types of
neurons and progenitor cells. This will involve directing
the differentiation of ES cells to produce defined neural
cell populations and studying their survival, differentiation
and integration following transplantation.
POST Report March 2013 Stem Cell Research
6
Page 59
General Remarks
Overview
„ Stem cell research is regulated by many different agencies, and there is some overlap
between them. Recent years have seen progress in reducing this overlap, but there is
scope for further streamlining of both regulation and legislation.
„ The UK is one of the world leaders in stem cell research, but the challenge is translating
this research from the lab into the clinic. The Government is supporting this translation
through initiatives such as the Cell Therapy Catapult and the Biomedical Catalyst Fund.
„ There are many potential benefits arising from stem cell research, including cell-based
therapy. The next few years should see firm evidence available from clinical trials to
better assess the potential of cell-based therapy.
6.1 Background
This section of the report looks at the issues raised
by the advances in stem cell research made over
the 10 years since the House of Lords Stem Cell
Research Committee published its report. In its
report, the committee grouped its conclusions and
recommendations under four main headings:
„ Stem cell research. This was primarily
concerned with the availability of alternatives to
hES cells, and the continued necessity for
research on hES cells.
„ Status of the early embryo. Among the issues
here were whether the potential benefits of hES
cell research outweigh the possible moral
objections, and whether embryos should be
created specifically for research purposes.
„ Cell nuclear replacement (CNR) and cloning. At
the time the committee reported, there was
debate over whether embryos created using
CNR should be regulated in the same way as
those created by fertilisation. And there was
concern that CNR might be used for human
cloning in countries that did not explicitly
prohibit it.161
„ Future legislation and regulation. Here the
committee focussed on mechanisms to review
progress in stem cell research, on the need to
ensure that the HFEA was adequately
resourced, on the creation and maintenance of
a stem cell bank and on the consents obtained
to those individuals donating embryos from
which cell lines are derived.
Many of the issues considered by the Committee
are still of interest today. For instance, debate about
the continued necessity for hES cell research and
alternatives sources of stem cells intensified
following the development of iPS cells.
Similarly, while the debate over the moral status of
the embryo has not moved on much since the
Committee’s report, discussion on the potential
risks and benefits of embryo research continues.
For some of the other issues considered by the
Committee, the debate has shifted its focus in the
last ten years. Nuclear transfer is one such
example. When the Committee published its report,
the main concern was the possible use of such
techniques for human cloning. Now, however, the
debate is largely about whether related techniques
are safe enough to be used in the clinic to prevent
mitochondrial disease (Box 2.2). A similar shift has
occurred on the issue of the regulation of health
research in general, and of embryo research in
particular. In 2002, the Committee was concerned
to ensure that the government keep HFEA’s funding
“under review and ensure that it is commensurate
with its increased responsibilities”.162 In June 2012
the Government consulted on proposals (since
dropped) to abolish HFEA163 and is now considering
options for merging it with HTA.164
This section of the report will look at these issues
under the following headings.
„ Regulatory issues such as the establishment of
the HRA, the future of the HTA and HFEA,
possible reform of the Human Tissue Act 2004,
NHS research permissions, reform of the
Clinical Trials Directive and intellectual property
issues.
„ Commercialisation of stem cell research.
„ Potential benefits and risks of cell therapy.
„ Where stem cell research might go in the next
few years.
162
163
161
Human cloning was prohibited in the UK by the Human
Reproductive Cloning Act 2001
164
Report from the Select Committee on Stem cell Research, House of
Lords, HL 83(i), February 2002
www.dh.gov.uk/health/files/2012/06/Consultation-on-proposals-totransfer-functions-from-the-Human-Fertilisation-and-EmbryologyAuthority-and-the-Human-Tissue-A.pdf
www.wp.dh.gov.uk/publications/files/2013/01/Terms-ofreference.pdf
POST Report March 2013 Stem Cell Research
Page 60
6.2 Regulatory Issues
Background
The current regulatory system for stem cell
research was described in chapter 3. From a stem
cell researcher’s point of view the current system is
complex, and involves dealing with multiple
agencies. For example, a researcher may need to
seek permissions from the following bodies:
„ HFEA (for research on human embryos)
„ HTA (for research on human tissue)
„ Home Office (for research on animals)
„ HSE (for research involving genetic
modification)
„ Research Ethics Committee (for research
involving human subjects)
„ Individual primary care trusts (until 1 April
2013, for NHS research permissions)
„ MHRA (for clinical trials)
„ EMA (for clinical trials involving stem cells,
tissue engineered products or other advanced
therapy medicinal products).
Recent years have seen several initiatives to
streamline the regulation of health research in
general. These include the DH review of armslength bodies, the Academy of Medical Sciences’
(AMS) review of the regulation and governance of
health research and the establishment of the Health
Research Authority as a single regulatory body for
health research. These are discussed in the
following sections.
DH Review of arms-length bodies
The DH’s review of arms-length bodies published in
July 2010, proposed setting up a single regulator for
health research.165 It saw such an approach as
having a number of advantages. For instance, it
would provide a single point of contact for
researchers, and have the potential to increase
efficiency, shorten the time taken to consider
applications and lead to a more proportionate
approach to regulation of research.
Among the arms-length bodies considered in the
DH review were two of the key organisations
involved in regulating stem cell research: HFEA and
HTA. The review proposed abolition of both HFEA
and HTA with their functions being split between the
new health research regulator and CQC.
165
‘Liberating the NHS: report of the arm’s-length bodies review, DH,
2010
Proposals for a health research agency
This approach was endorsed by the AMS review
which recommended setting up a health research
agency. The AMS review envisaged that such an
agency would work as a “one-stop shop” for the
regulation of health research and would have the
following core functions.
„ Be responsible for all aspects of the ethical
review of health research. AMS recommended
moving NRES into the new agency.
„ Be the appointing authority for phase I RECs
for clinical trials and advise on ethical issues
relating to the processing of health and social
care information.
„ Be responsible for some other research
regulation functions. AMS recommended that
the new agency would be responsible for
advising ministers on the administration of
radioactive medicinal products to patients.
„ Work closely with MHRA to streamline the
regulation of clinical trials by providing clear
guidance on the Clinical Trials Directive and
ensuring that good clinical practice inspections
are proportionate.
„ Be responsible for streamlining the process for
obtaining NHS R&D permissions and
establishing consistent practices and timelines.
AMS also recommended transferring the researchrelated regulatory functions of HTA to the new
agency. It noted the Government’s intention to
reform the HFEA by the end of the current
parliament. It recommended that, if this remained
the Government’s intention, the research-related
regulatory functions of HFEA should also be
transferred to the new agency.
Establishment of HRA
In December 2011, the Government established
HRA as a Special Health Authority (SHA). Its
purpose is to protect and promote the interests of
patients and the public in health research. However,
HRA will also work to combine and streamline the
current approval system and promote a consistent
and proportionate approach to regulation. An
explicit goal is to reduce the regulatory burden on
research-active businesses, universities and the
NHS.166
166
www.dh.gov.uk/health/2011/12/creation-hra/
POST Report March 2013 Stem Cell Research
The National Research Ethics Service has been
transferred to the HRA and the authority has also
taken on the functions of the National Patient Safety
Agency. HRA is providing the Integrated Research
Approval Service (IRAS) and working towards
establishing a unified approval process. The draft
Care and Support Bill will establish the HRA as a
statutory non-departmental public body. As
discussed in the next section it envisages that
further regulatory responsibilities will be transferred
to the HRA.
The future of HTA and HFEA
In June 2012, DH published a consultation on
options to transfer the research functions regulated
by HFEA and HTA to other bodies.167 It invited
opinions on three main options:
„ Option one (the Government’s preferred option)
− all HTA and HFEA regulatory functions to be
transferred to the Care and Quality
Commission (CQC) except those HFEA
functions relating to research which will be
transferred to HRA. HFEA and HTA will be
abolished.
„ Option two – all functions to be transferred to
CQC/HRA as above, with the exception of a
limited set of functions that will be transferred
to other organisations. HFEA and HTA will be
abolished.
„ Option three – HFEA and HTA will retain their
current functions but deliver further efficiency
savings.
Further details of the three options are summarised
in Table 6.1. The consultation closed at the end of
September 2012, and the Government published
the responses in January 2013.168 The impact
assessment that accompanied the consultation
identified a number of potential benefits and
risks.169 The main benefits were seen as:
„ reduced running costs estimated at £370,000380,000 a year arising from abolition of HFEA
and HTA
„ reduced administration costs, although these
were not quantified
„ savings arising from a reduction in regulatory
overlap and the reduced regulatory burden on
those regulated (again, not quantified).
167
168
169
http://data.parliament.uk/DepositedPapers/Files/DEP20121078/Consultation.pdf
www.wp.dh.gov.uk/publications/files/2013/01/Stakeholderresponses.pdf
www.ialibrary.bis.gov.uk/uploaded/DH%206044%20%20Consultation%20IA-Transfer-Functions-from-the-HFEA-andHTA.pdf
Page 61
As far as potential risks were concerned, the impact
assessment suggested that these were:
„ fragmentation and loss of expertise and
knowledge arising from dispersing the functions
of a single regulator between multiple
regulators
„ loss of cumulative expertise arising from
abolition of HFEA and HTA
„ the standard of regulation could be adversely
affected during the transition period
„ loss of reputation and confidence in the
regulatory system resulting from the abolition of
two tried and trusted regulators such as HFEA
and HTA.
Consultation responses
The Government received and published over one
hundred responses. Overall, 60% of respondents
agreed that HFEA and HTA should retain their
functions; 75% disagreed with the proposal to
transfer HFEA and HTA functions to CQC and HRA.
Key themes identified by the responses were:170
„ Around half of respondents favoured retention
of HFEA and HTA because of concerns over
whether CQC has the expertise or capacity to
take on regulation of these fields. Some
referred to reports by the National Audit Office
and the Public Accounts Committee (see Box
6.1) which concluded that extending CQC’s
remit might affect its capacity to deliver its core
functions.
„ Many respondents cited concerns over the
potential loss of expertise built up by HFEA and
HTA over the years as a reason for retaining
these bodies. Many also suggested that HFEA
and HTA were well known, respected and
trusted brand names.
„ Around half of respondents commented on the
impact assessment. Many of these felt that the
transition costs had been underestimated.
Overall, the message that emerged was that
the potential benefits of options one and two
were somewhat modest and outweighed by the
risks associated with the abolition of the two
regulators.
„ Many respondents supported further reduction
in regulatory overlap and more streamlining of
the regulatory landscape. Some referred to
recent cost efficiencies and closer working
practices made by HFEA and HTA (see Box
6.2) citing them as evidence that abolition was
unnecessary. Around a quarter of respondents
saw a need for a review of the way the bodies
undertake their functions.
170
www.dh.gov.uk/health/files/2013/01/Government-response-toconsultation1.pdf
POST Report March 2013 Stem Cell Research
Page 62
TABLE 6.1 SUMMARY OF PROPOSALS TO TRANSFER HFEA AND HTA FUNCTIONS
Agency HFEA HTA Function Licensing research involving human embryos/admixed embryos Inspection and regulation of licensed embryo research centres Issuing guidance on embryo research (e.g. on obtaining consent from people providing gametes or embryos for research) Functions relating to exemptions (which are specific to research projects) from the normal requirements Licensing treatment services Approving embryo tests (e.g. PGD) Procuring/distributing sperm Licensing the storage of human gametes, embryos/admixed embryos Powers of inspection Maintaining a register of information relating to treatments Authorising disclosure of information for medical/research purposes Provision of information to donors, donor conceived people and donor siblings Setting remuneration levels for gamete and embryo donors Licensing organisations that store/use human tissue for research Licensing anatomical and post‐mortem examinations Licensing the removal of tissue from a dead body for use for a scheduled purpose other than transplantation or research Licensing the storage of anatomical specimens Licensing the storage of a dead body for use for a scheduled purpose Licensing the public display of human bodies or tissue Assessing donations from living persons for transplantation Consent to DNA analysis of tissue from a living person for the benefit of another person Powers of inspection Licensing the storage/use of tissues and cells intended for human application Licensing activities in accordance with regulations relating to the procurement, testing, processing, distribution, import or export of tissues and cells intended for human application Authorisation of persons to distribute, import or export tissues or cells from where procurement takes place for immediate transplantation to humans Authority to disclose identifying information about a donor Option 1 Option 2 Option 3 HRA HRA HFEA CQC CQC CQC CQC CQC CQC CQC CQC HFEA HFEA HFEA HFEA CQC CQC CQC CQC HSCIC HSCIS HFEA HFEA HFEA CQC DH HFEA CQC CQC CQC CQC DH HRA CQC CQC HFEA HTA HTA HTA CQC CQC CQC CQC HTA HTA CQC CQC CQC ACE NHSBT CQC HTA HTA HTA CQC CQC CQC MHRA or CQC MHRA or CQC HTA HTA CQC CQC HTA CQC CQC HTA HRA HRA HRA CQC HRA HRA HRA HFEA HFEA HFEA HTA Key
„ HFEA Human Fertilisation and Embryology Authority
„ HTA Human Tissue Authority
„ HRA Health Research Authority
„ CQC Care and Quality Commission
„ HSCIC Health and Social Care Information Centre
„ DH Department of Health
„ MHRA Medicines and Healthcare products Regulatory Agency
„ ACE Arts Council England
„ NHSBT national Health Service Blood and Transplant
Source:
Compiled from www.dh.gov.uk/health/files/2012/06/Consultation-on-proposals-to-transfer-functions-from-the-HumanFertilisation-and-Embryology-Authority-and-the-Human-Tissue-A.pdf
POST Report March 2013 Stem Cell Research
Box 6.1 Capacity of CQC to take on new functions
A potential problem flagged up by the impact assessment for options
one and two was the risk that current HFEA/HTA functions would not
be delivered as effectively during the transition period as
organisations adapted to the changes. It also suggested that
increasing the regulatory functions of CQC might “overstretch” the
organisation, and adversely affect delivery of its current functions.171
This was identified as a risk both under options one and two, but was
greatest under option one because this option involved more
functions being transferred to CQC. Others also questioned whether
CQC has the capacity to take on new functions. For instance, a
National Audit Office report in 2011 noted that CQC would start
registering thousands of primacy care services in July 2012. It
concluded that further extending CQC’s role could “distract it from its
core work of regulating health and adult social care” .172 Moreover,
an inquiry into CQC by the Public Accounts Committee in 2012
concluded that CQC “should not take on the functions of” HFEA at
this time.173 It went on to say that CQC “does not have the capacity
to take on oversight of such a complex area, and the change would
undermine its ability to focus on the improvements it needs to make
in relation to its existing regulatory functions”.
Overall, the responses showed that there is widespread
support for HFEA and HTA throughout the research
sector, with the majority of respondents wishing to see
these bodies retained, albeit for a range of different
reasons. That said, many respondents expressed a wish
to see further streamlining of regulation in this area. For
instance, some respondents identified the full integration
of HFEA research approvals into the IRAS system as a
priority. Others called for a review of human tissue
legislation, for instance to make RECs responsible for
regulating the storage of tissue taken from the living for
research purposes rather than requiring an HTA licence.
There was also strong support among respondents for
the HRA, particularly with respect to it becoming the
single point of contact for all research permissions and
approvals. Finally, respondents also identified scope for
streamlining inspections. For instance AMS noted that
HTA and HFEA are working to move towards joint
inspections for research centres that are licensed by
both organisations because they use human embryos to
derive embryonic stem cells for therapeutic purposes.
171
172
173
www.ialibrary.bis.gov.uk/uploaded/DH%206044%20%20Consultation%20IA-Transfer-Functions-from-the-HFEA-and-HTA.pdf
The Care Quality Commission: Regulating the quality and safety of health
and adult social care, NAO, December 2011
www.publications.parliament.uk/pa/cm201012/cmselect/
cmpubacc/1779/177904.htm
Page 63
Box 6.2 Efficiency savings already made by HFEA and HTA
HFEA and HTA have both made cost efficiencies since the arms
length body review was announced in July 2010. For instance, HFEA
has reduced its total expenditure by 25% (from £8m to £6m), and the
total number of staff it employs (from 86 in 2010/11 to 70 staff now).
At the same time it has reduced the fees it charges for licensed
centres to provide treatment cycles and co-located with CQC
resulting in an annual saving of around £400,000 in office
accommodation costs. Over the same period, HTA has made 27%
savings and reduced its fees across sectors by an average of around
17%.
There is also scope for achieving efficiency savings in terms of
reduced regulatory overlap under the current system (option three)
and progress has been made towards this. For instance:
„ HFEA, HTA and CQC have convened a joint working group
with the aim of avoiding duplication and streamlining regulation.
The working group is developing a system whereby centres
licensed for particular activities by HFEA are exempt from
requiring a CQC licence.
„ CQC has agreed two joint working agreements (memoranda of
understanding), one with HFEA and one with HTA. Each
ensures that the regulators will share information about
services that fall under the remit of all three bodies, respect
each organisation’s independence, and continue to explore
ways to develop more effective and efficient ways to work
together to promote quality and safety.
„ HTA has undertaken joint inspection visits with MHRA on 12
establishments licensed by both for development of medicinal
products.
„ HFEA and HTA are planning to hold joint inspections of ten
research centres that do research on stem cells or that store
ovarian/testicular tissue.
Government response
The government Response stated that HFEA and HTA
will remain as separate statutory bodies, at least for the
time being.174 It intends to introduce further efficiencies
in the way in which HFEA and HTA undertake their
functions and operations and has announced a review to
inform this process. The review will report by April 2013
and is being conducted by the Chief Executive of the
Health Protection Agency. The terms of reference for the
review include examining the scope:175
„ to streamline the way in which the two bodies
undertake their regulatory and statutory functions,
including through joint working, sharing resources
and information and working more closely with other
health sector regulators
„ to reduce and rationalise the burden of inspection,
information collection and process of research
approvals that falls on the regulated sector, without
compromising the safeguards in the respective Acts
„ for shared Authority membership and leadership,
and of a merger of the two bodies functions and
operations.
174
175
www.dh.gov.uk/health/files/2013/01/Government-response-toconsultation1.pdf
https://www.wp.dh.gov.uk/publications/files/2013/01/Terms-ofreference.pdf
POST Report March 2013 Stem Cell Research
Page 64
The Government response addresses many of the
issues raised by respondents to the consultation.
However, it falls short of reviewing aspects of the
legislation itself. For instance a number of respondents
called for a review of various aspects of the Human
Tissue Act (2004) to further reduce the burden of
regulation.
The new review also reawakens the possibility of a
merger between HFEA and HTA. This was discussed in
some detail in 2007 during pre-legislative scrutiny of the
draft Human Tissue and Embryos Bill. The draft Bill
contained measures to set up a single competent
authority for tissue and embryos. This would have
involved replacing HFEA and HTA with a new single
body called the Regulatory Authority for Tissue and
Embryos (RATE).
The Joint Scrutiny Committee that conducted the prelegislative scrutiny in 2007 heard evidence on the
proposed risks and benefits of such a merger that was
strikingly similar to that submitted to the 2012
consultation. 176 In 2007, the main potential benefits of a
merger were avoidance of duplication, increased
efficiency, exploitation of synergies between HFEA and
HTA and cost savings (at that time estimated as
£700,000 a year). Potential risks were seen as the loss
of expertise, loss of trust in the system, loss of two
highly visible brands, concerns about whether the new
regulator would be able to handle its broader remit and
scepticism about whether the potential benefits would be
delivered in practice.
Having considered the evidence the Joint Scrutiny
Committee noted that it “found the evidence against
establishing RATE overwhelming” and recommended
the Government to abandon the proposed merger. The
Government decided to accept this recommendation
and the Bill was subsequently amended accordingly.177
Future regulation of stem cell research
In addition to the proposed changes to the regulation of
human tissue and embryos, recent years have also seen
regulatory developments in two other areas relevant to
stem cell researchers. These are:
„ a review of the Clinical Trials Directive
„ streamlining and co-ordination of the system for
obtaining the various permissions needed to
conduct clinical trials in the NHS.
Review of the Clinical Trials Directive
Clinical trials are regulated under the Clinical Trials
Directive, introduced in 2001. The Directive was
intended to protect patient safety, but it is widely
recognised that this has been achieved at the expense
of increasing the administrative burden and cost of
conducting clinical trials within the EU. The number of
applications to conduct trials in the EU fell by 25%
between 2007 and 2011 (from more than 5,000 to
3,800).178 Between 2000 and 2006, the UK’s share of
clinical trials fell from 6% to just over 2% globally.179
Among the main problems associated with the Directive
are:180
„ Inconsistent implementation across EU member
states. This increases the complexity of conducting
multinational trials, and thus also the cost and time
taken to gain approvals. It can also leads to a
divergence in the outcome of assessments between
member states.
„ The broad scope of the Directive. As implemented
in the UK, studies involving minor changes to
authorised clinical procedures are classified as
clinical trials. For instance, a study using a drug in
accordance with its marketing authorisation but with
the addition of an imaging step to investigate the
drug’s effect on a particular part of the body would
need full clinical trials approval.
„ A lack of proportionality in the requirements. For
instance a trial involving the first use of a product in
humans would be subject to the same requirements
as a potentially ‘lower risk’ one involving a new use
of a product that was widely available without
prescription.
„ Duplication in the requirements for safety reporting.
For instance adverse reactions must be reported to
the relevant ethics committees in all of the
participating member states.
178
176
177
Joint committee on the Human Tissue and Embryos (Draft) Bill - First
Report, July 2007
Government Response to the Report from the Joint Committee on the
Human Tissue and Embryos (Draft) Bill, Cm 7209, October 2007
179
180
http://ec.europa.eu/health/files/clinicaltrials/2012_07/
proposal/2012_07_proposal_en.pdf
Kinapse (2008). Commercial clinical research in the UK: report for the
Ministerial Industry Strategy Group Clinical Research Working Group.
A new pathway for the regulation and governance of health research,
AMS, 2011
POST Report March 2013 Stem Cell Research
In July 2012, the Commission adopted a proposal for a
clinical trials regulation181 to replace the current
Directive. The proposed regulation has yet to pass
through the European Parliament and Council, and is
not expected to be in place before 2016. Among its main
proposals are:
„ a streamlined authorisation procedure which will
allow for a rapid assessment by all Member States
and which will deliver a single outcome
„ simplified reporting procedures which will spare
researchers having to submit the same information
in different formats to multiple bodies in different
member states
„ more transparency on the progress of a trial and on
its results
„ the possibility for the Commission to make sure the
rules are being properly supervised and enforced in
different countries.
Conducting clinical trials in the NHS
Researchers wising to conduct clinical trials in the NHS
need to obtain a wide range of approvals from various
bodies before they can start recruiting patients. These
were outlined in Chapter 3 and include ethical approval,
approval(s) from MHRA and any other appropriate
regulator, as well as NHS R&D permissions from all of
the health trusts participating in the trial. They also need
to obtain funding for the trial, draw up contracts for
research and NHS staff, and report details of the
progress of the trial (including any adverse effects) to
the relevant authorities.
Recent years have seen a number of initiatives to
reduce the administrative burden of conducting clinical
research in the NHS. For instance
„ NRES, now established within HRA, provides a
single, UK-wide ethical opinion on proposed
research
„ IRAS provides an integrated approach to obtaining
regulatory, ethics and governance approvals
„ NIHR’s Co-ordinated Systems for gaining NHS
Permissions (CSP) reduces NHS R&D approval
times for studies run through the NHS Clinical
Research Network
„ model agreements, drawn up by the UK health
departments, NIHR, and industry speed up the
contracting process for clinical trials carried out in
the NHS.
181
2012/0192 (COD), Proposal for a Regulation of the European Parliament
and of the Council on clinical trials on medicinal products for human use,
and repealing Directive 2001/20/EC
Page 65
Of the various different requirements needed to conduct
clinical research, AMS highlighted the need to obtain
research permissions from every NHS trust participating
in a trial as the major bottleneck.182 It recommended
setting up a new national research governance service
within HRA to provide a single portal for rapidly
obtaining NHS R&D permissions.
However, the Plan for Growth in March 2011183 made it
clear that the Government sees NIHR’s CSP as the best
way of speeding up NHS R&D permissions. It contained
a requirement (from 2012) for NIHR to publish data
showing how long it takes between a provider receiving
a valid research protocol and recruiting the first patient
into a study. It set a 70 day benchmark for this and, from
2013, performance against this benchmark will affect
funding from NIHR.
While NIHR’s CSP may reduce NHS R&D approval
times, it is only open to research trials that are eligible
for support by the Clinical Research Network. All clinical
research trials that are fully funded by NIHR or some
other government body such as a research council or by
an NIHR non-commercial partner are automatically
eligible for such support. Commercially funded trials may
be eligible for such support and thus benefit from the
CSP process. But the funder will have to show that the
funding was open to all qualified researchers in England,
and that the research is of high quality, benefits the NHS
and takes account of the priorities, needs and realities of
the NHS.
Patentability of hES cells
The European patent system
The European Patent Convention (EPC) is a treaty
signed by 38 European countries including all EU
member states. It provides an autonomous legal system
for granting patents operated by the European Patent
Office (EPO). It enables a patent to be granted across
all EPO signatories circumventing the need to apply to
an individual national patent office such as the UK
Intellectual Property Office (UKIPO). National courts are
responsible for enforcing the patents; EU national courts
are subject to the Court of Justice of the European
Union (CJEU) which interprets and enforces approved
legislation drafted by the EU.
182
183
A new pathway for the regulation and governance of health research,
AMS, 2011
The plan for Growth, HM treasury and BIS, 2011
Page 66
Attempts to establish a single European patent system
have been underway for 50 years. Although EPO can
grant Europe-wide patents, post-grant patents are
subject to national legislation. The goal of the unitary
patent is to reduce the cost and time it takes to get a
patent in Europe by establishing a centralised court
system to deal with litigation of European patents. Under
the current system, EPO sits outside EU jurisdiction. For
instance, it is not bound by rulings of the CJEU, but
chooses to align itself with them, and with other EU
policy such as the so-called Biotech Directive.184
The Biotech Directive was adopted in 1998 to harmonise
patent law for biotechnological inventions across Europe
and encourage innovation within the field. It contains
morality provisions that (among other things) state that
uses of human embryos for industrial or commercial
purposes shall be considered unpatentable. The
provisions note that the commercial exploitation of such
inventions is contrary to ordre public or morality.
hES cells and the morality provisions
In 2008, the Enlarged Board of Appeal at the EPO heard
an appeal on a patent held by the Wisconsin Alumni
Research Foundation (the WARF case). At issue was
whether the EPC forbids the patenting of claims directed
to hES cells which, at the time of filing, could only have
been prepared by a method which necessarily involved
the destruction of human embryos. The appeal board
found that a product that necessarily involved the
destruction of a human embryo could not be patented
because this amounts to the use of an embryo for
commercial or industrial purposes.
Following the appeal board’s decision EPO adopted the
position of allowing claims directed to hES cells filed
after 9 May 2003. The significance of this date is that it
represents the first time that an hES cell line was
submitted to a stem cell bank. The logic of EPO’s
position was that from this time onward, claims involving
hES cells did not necessarily involve the (further)
destruction of a human embryo because the cells could
have been obtained from a stem cell bank. However, a
ruling by the CJEU in October 2011 raised further
doubts over the patentability of hES cell lines in Europe.
184
Directive on the legal protection of biotechnological inventions 98/44/EC
POST Report March 2013 Stem Cell Research
Greenpeace versus Bustle
An NGO (Greenpeace) challenged a patent held by a
German researcher (Professor Oliver Brustle) in
Germany’s Federal Court of Justice. The patent in
question concerned the use of neuronal precursor cells
derived from hES cells to treat diseases such as
Parkinson’s disease. At the heart of the Greenpeace
case was whether the patent contravened the morality
provisions of the Biotech Directive.
The German court referred the case to the CJEU
seeking advice on three questions.
„ What is meant by the term “human embryos”?
Specifically, is an hES cell isolated at the blastocyst
stage to be considered a human embryo?
„ What is meant by exclusion from patentability of
“human embryos for industrial or commercial
purposes”? Specifically, does this include use of
hES cells for the purpose of research?
„ If a patent does not explicitly mention using human
embryos to derive hES cells, but their use is
required, should the patent be granted? This
question arose because the Bustle patent made no
reference to how the hES cells were derived.
The CJEU ruling
On the first question, the CJEU took a wide view of the
term “human embryo”, essentially ruling that it included
all human (totipotent) cells that have the capacity to
develop into a human being. This includes embryos that
have been created by fertilisation as well as those
created using techniques such as parthenogenesis or
nuclear replacement (Chapter 2). However, the CJEU
declined to rule on the specific question of whether an
hES cell isolated at the blastocyst stage constituted a
human embryo, noting that this was for the referring
(German) court to decide.
On the second question, the CJEU ruled that the use of
embryos for scientific or medical research is not
patentable in itself unless it is associated with an
invention which can be useful to embryos. And on the
final question, the CJEU ruled that inventions which
require the prior destruction of human embryos, or their
use as base material, are not patentable even if the
patent does not refer to their use.
POST Report March 2013 Stem Cell Research
Implications for patentability
Taken together these rulings have significant
implications for the patentability of inventions involving
hES cells in Europe. In June 2012, the European Patent
Office (EPO) published new guidelines for patent
examiners to take account of the rulings.185 The
following month the UKIPO published new guidelines for
patent applications relating to biotechnological
products.186
Broadly speaking, under the new guidelines:
„ Inventions using hES cells, the derivation of which
has involved the destruction of a human embryo at
any point in the past, cannot be patented. This
includes all current hES cell lines plus any cell lines
derived by methods such as nuclear transfer or
parthenogenesis.
„ Inventions that use human embryos for industrial or
commercial purposes (including research) cannot
be patented. The sole exception is if they involve
therapeutic or diagnostic purposes which are
applied to the human embryo and are useful to it.
„ Inventions using human iPS cells can be patented
(because they have been derived by reprogramming adult cells rather than by destruction
of an ‘embryo’).
„ Inventions using stem cells derived from adults can
be patented (because this does not involve the use
or destruction of human embryos).
Non-destructive methods
One interesting test for the new guidelines is the
availability of methods for deriving hES cell lines from
human embryos (see Box 6.3) that do not involve
destruction of the embryo. The existence of such nondestructive methods raises the question of whether
claims directed at hES cells derived using such methods
are patentable in Europe.
185
186
http://documents.epo.org/projects/babylon/eponet.nsf/0/6c
9c0ec38c2d48dfc1257a21004930f4/$FILE/guidelines_for_examination_2
012_part_g_en.pdf
Examination Guidelines for Patent Applications relating to
Biotechnological Inventions in the Intellectual Property Office, UKIPO, July
2012
Page 67
Box 6.3 Non-destructive derivation of hES cell lines
In 2006, a paper was published detailing a method of deriving hES
cell lines from single cells taken from a human embryo.187 The
method used was very similar to that used for pre-implantation
genetic diagnosis (PGD). In this proof of principle study, single cells
removed from human embryos were cultured overnight and used to
derive two hES cell lines. Both cell lines proliferated in an
undifferentiated state for more than eight months and expressed
normal markers of pluripotency. The method has been patented and
commercialised by an American company, Advanced Cell
Technology. It is currently being considered by the National Institutes
of Health as an alternative source of pluripotent stem cell lines.
The embryos from which the single cells were taken were not
allowed to develop further in this study. However, the authors
suggest that the technique’s similarity to PGD means that the
embryos would be undamaged by the procedure and capable of
developing normally if implanted into a woman. PGD has been
widely used to select embryos for implantation that are free from
specific genetic disorders. It has been shown to be safe and effective
and to have no impact on the development potential of the embryo.
Prior to the publication of the new guidelines it was
widely thought that such claims might be patentable
because they did not result in the destruction of an
embryo. However, the new UKIPO guidelines make it
clear that they are not. It states that “claims to methods
and processes where stem cells are obtained from an
embryo yet the embryo remains intact are also excluded
as even though the embryos are not destroyed, it is still
considered to be used for an industrial or commercial
purpose”. The new guidelines have not been challenged
in a national court or in an EPO Board of Appeal.
Wider implications
In the immediate aftermath of the Bustle vs Greenpeace
case there was speculation that the inability to gain
intellectual property rights in Europe would drive stem
cell research abroad. However, this is not necessarily
the case. For instance, inventions arising from stem cell
research conducted in Europe can still be patented
elsewhere. Furthermore, stem cell researchers may be
still be able to gain intellectual property rights on their
inventions within Europe by seeking patents on
downstream processes instead of the cell lines.188 For
example, Europe’s first clinical trial using hES cells
(testing a UK-developed treatment for age related sight
loss) is not affected by the ruling as the researchers
patented the method of delivering the hES cells to the
back of the eye rather than the cells themselves. Finally,
it has also been suggested that making Europe a
“patent-free zone” for hES cells might stimulate rather
than stifle innovation and research.
187
188
Klimanskaya I et al, Nature, 444 (7118), 481-485, 2006
Nature 478, 441, 2011
POST Report March 2013 Stem Cell Research
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Box 6.4 Tumour stem cells
The idea that cancers could be caused and sustained by populations
of abnormal stem cells (tumour stem cells) first arose in the late
1990s. Experiments in mice with leukaemia showed that a subpopulation of leukemic cells were capable of initiating tumours when
injected into normal (but similar) mice. Since this time, evidence has
emerged that a range of solid tumours also contain sub-populations
of cells capable of initiating tumours when injected into healthy
animals.
Whether or not this constitutes proof of tumours being caused and
sustained by tumour stem cells has been hotly debated in recent
years. At the heart of the debate has been whether the act of
transplanting tumour cells from one animal to another changes the
behaviour of the cells. More recently, researchers have looked at
tumours of the skin,189 gut190 and brain191 in mice using labelling
techniques that allow the origin of cells to be traced back. In each
case, they found that large populations of tumour cells originated
from small subsets of cells that they hypothesised were tumour stem
cells. If this hypothesis turns out to be true, it would have major
implications for the way that tumours were treated. For example, it
would mean that a successful treatment would have to specifically
target the subset of tumour stem cells.
3.9 Commercialisation
Regenerative medicine is one of the areas identified as
a key UK growth opportunity for the 2020s by the
Government Office for Science Foresight programme.192
This section looks at the:
„ current state of UK stem cell research compared to
other countries
„ the number and type of companies developing cell
therapies
„ various different business models by which stem
cell research could be commercialised
„ some of the main challenges that need to be
overcome during the commercialisation process
„ the UK life sciences strategy.
Current state of UK stem cell research
One of the reasons why stem cell research is seen as a
future growth opportunity is the strength of the UK
research base in this area. Evidence for this comes from
an analysis of primary peer-reviewed papers on
regenerative medicine193 commissioned by BIS in 2011.
The study looked at papers on stem cells (including
tumour stem cells, see Box 6.4), stem cell
transplantation, tissue-engineering and regenerative
medicine. It found that the UK is producing world class
research which has a significant impact across the field.
189
190
191
192
193
Driessens G et al, Nature, 488, 527–530, 2012
Schepers A et al, Science, 337 ( 6095), 730-735, 2012
Chen J et al, Nature, 488, 522–526, 2012
www.bis.gov.uk/assets/foresight/docs/general-publications/10-1252technology-and-innovation-futures.pdf
A bibliometric analysis of regenerative medicine, Evidence, Thomas
Reuters (www.bis.gov.uk/assets/BISCore/innovation/docs/B/11-1059bibliometric-analysis-of-regenerative-medicine.pdf)
However, the field is getting increasingly competitive
with a rapid increase in the total volume of papers
published between 2005 and 2009. While this increase
in volume has been faster in Asia than in either North
America or Europe, the USA is still recognised as the
world leader. UK policy has been to support research
across the full field to maximise the likelihood of medical
advances being made.194 As discussed in more detail
later, the Government has committed to continue to
support this sector in the long-term.
Businesses and business models
Turning stem cell research into cell-based therapies will
require businesses to participate in translational
research and clinical trials. The Regenerative Medicine
in Europe (REMEDiE) project is an EU-funded
programme that has tracked developments in the stem
cell field. One of its strands has been to track the
number and type of businesses involved in the area and
to identify the different possible business models.
Businesses
Data from the REMEDiE project shows that the
regenerative medicine sector is dominated by
companies in three geographical locations: North
America, Europe and the Far East. In total, North
America has the most regenerative medicine companies
(183) followed by Europe (145) and the Far East (37). In
each case most of the companies are small or medium
enterprises (SMEs, see Table 6.2) with only a small
number of large pharmaceutical companies (‘big
pharma’) getting involved at this stage. Within Europe,
most of the companies (big or small) are located within
the UK, Germany or France.
Business models
The REMEDiE project also looked at the type of
products under development by SMEs and ‘big
pharma’.195 It identified three distinct cell therapy
business models:
„ service model, where a clinic treats a patient with
cells taken from the patient’s own body
„ product model, where stem cells are used to make
product that can treat many patients
„ tissue matching model where banked stem cells are
matched to the patient.
194
195
Taking Stock of Regenerative Medicine, BIS/DH, 2011
(www.bis.gov.uk/assets/BISCore/innovation/docs/T/11-1056-taking-stockof-regenerative-medicine.pdf)
www.york.ac.uk/media/satsu/res-remedie/remedie-policy-brief.pdf
POST Report March 2013 Stem Cell Research
TABLE 6.2 COMPANIES BY LOCATION196
North Europe Far East America Total companies 183 145 37 Of which SMEs 167 132 34 Of which ‘big 16 13 3 pharma’ Service model
Using the patient’s own cells for therapy is known as
autologous therapy. In the simplest form, this might
consist of harvesting a selected population of cells from
the patient (such as mesenchymal stem cells),
multiplying up the cell number, and then re-introducing
them to a diseased site in the patient’s body.
In more complex guises, such a therapy might include
one or more manipulation steps, whereby the harvested
cells are differentiated, engineered or manipulated in
some other way before re-introduction into the patient’s
body. Examples of this type of therapy were given in
Chapter 5 and include use of mesenchymal stem cells to
treat bone/cartilage disease, heart disease, diabetes or
neurodegenerative disorders.
Autologous therapies account for the vast majority of
approaches being developed by SMEs in Europe and
elsewhere. The approach has a number of advantages.
For instance, using the patient’s own cells sidesteps the
problem of immune rejection. Furthermore, such
approaches require lower levels of capital investment
than that needed for the development of new drugs.
Finally, trials of such approaches are usually fairly
straightforward from a regulatory perspective, although
this will vary depending on the extent of manipulation of
the cells. This means that it may be possible to move
promising research from the laboratory to the clinic
relatively rapidly.
A disadvantage of this approach is that there is less
scope for companies to protect their investment in
research by securing intellectual property rights for their
therapy. Rather than developing a single product that
can be used for many patients, companies are
developing a service that can be applied to individuals.
In this respect, the delivery of autologous therapy is
envisaged as being comparable to the way that IVF
clinics operate.
196
Taking Stock of Regenerative Medicine, BIS/DH, 2011
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Product model
Using stem cells to develop a single product that can be
used to treat many patients is known as allogenic
therapy. In many respects this is more like the standard
pharmaceutical model of product development and
delivery where companies seek intellectual property
rights to protect their research investment. It is these
types of products that the big pharma companies are
interested in developing. An example is the use of stem
cells to treat age-related macular degeneration (AMD),
an approach that is currently in clinical trials and was
outlined in Chapter 5.
The main disadvantage of this approach is the risk of
immune rejection, because the cells used for therapy
are not from the patient receiving the treatment. They
are thus likely to be recognised by the patient’s immune
as foreign and attacked. As noted in Chapter 5), this is
not a problem for (immunologically privileged) areas of
the body such as the central nervous system where the
immune system is effectively switched off. Other
disadvantages include the fact that capital investment
costs are high and product development times are long.
Patient matching
A third type of model identified by the REMEDiE project
was a model where stem cells are cryo-preserved and
banked. Patients needing cell therapy are tissue typed,
and cells that closely match their profile are used for
therapy. This kind of approach is similar to that used for
skin grafts such as Apligraf, a commercial product
derived from human cells that is used to treat venous
ulcers (see Box 5.5 in Chapter 5). Such approaches can
minimise (but not eliminate) problems with immune
rejection. However, they require significant investment to
set up and maintain the cell banking infrastructure.
Indirect commercial applications
In addition to the three business models discussed
above, stem cells can be used for a variety of other
commercial applications. For instance, iPS cells have
been used to model a wide range of diseases (Chapter
4). Such models can be used to develop a better
understanding of the underlying causes of a disease as
well as to rapidly screen potential new treatments.
Stem cells can also be used to screen potential new
drugs for possible toxicity effects. Such an approach
may reduce the number of animals used in toxicity
testing and help to produce safer medicines. A
collaboration between government, academia and
industry − Stem Cells for Safer Medicines − was
launched in 2008 to explore the use of stem cells in
early drug discovery. Public sector funding is coordinated by the Technology Strategy Board (TSB) with
funding from MRC, BBSRC, ESRC and DH.
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197
FIGURE 6.1 UK MEDICAL BIOTECH PIPELINE
Figure 6.1 UK Medical biotech pipeline
„
„
„
„
Taken together, pharmaceutical companies hope that
the use of cell-based models for safety and efficacy will
save them time and money in the development process.
A particular aim is to reduce the number of drugs that
fail the most expensive (phase III) part of the clinical
trials process.
Barriers to commercialisation
The Government’s Strength and Opportunity 2011 report
highlighted a strong and resilient UK life sciences
sector.198 It identified a total of 841 new biomedical
products under development in the UK (Figure 6.1). Of
these around half (423) were biotech products
(antibodies, proteins, etc.) or advanced therapy products
(gene therapy, cell therapy). However, as shown in
Figure 6.1, most of these are in the discovery/preclinical
phase, with only a small proportion in the translational
research stage (phase I or II) and a tiny proportion being
in the later stages (phase III, regulatory filing) of
commercialisation.
Aside from the regulatory issues discussed previously,
the other main barrier to the commercialisation of cell
therapy in the UK is the lack of funding available to
move promising research from the lab, through clinical
trials, and into the NHS.199,200 For conventional drugs or
biotech treatments the source of such funding would
normally be pharma/biotech companies. However such
companies are being cautious. On the one hand, they
are looking to diversify into new areas with the decline of
the so-called blockbuster drugs that have generated
their funding for further R&D in the past. On the other
hand, a range of uncertainties mean that, for the time
being, many companies are playing a waiting game with
respect to cell therapy. These uncertainties include:
197
198
199
200
Strength and Opportunity 2011, BIS, 2011
Strength and Opportunity 2011, BIS, 2011
(www.bis.gov.uk/assets/biscore/innovation/docs/s/11-p90-strength-andopportunity-2011-medical-technology-sectors.pdf)
www.york.ac.uk/media/satsu/res-remedie/remedie-policy-brief.pdf
Taking Stock of Regenerative Medicine, BIS/DH, 2011
the limited evidence of efficacy currently available
from clinical trials of cell therapy
the fact that cells are more difficult to scale up and
manufacture to the required standards than small
molecule drugs or protein-based biotech treatments
continued uncertainty about the regulatory
requirements for cell based therapy
concerns about the patentability of hES cell-based
therapy in Europe.
These uncertainties mean that government support and
funding is needed to help drive the commercialisation of
cell-based therapy in the UK. In December 2011, BIS
launched its UK life sciences strategy.201 Its aim is to
develop the infrastructure to link UK academic
researchers with industry, investors, clinicians and the
NHS. The following sections look at progress in
implementing those parts of the strategy most relevant
to stem cell research and cell-based therapy.
UK life sciences strategy
Implementation of the UK life sciences strategy has
focused on 5 areas:
„ research, clusters and collaborations
„ investment and incentives
„ streamlining regulation
„ people
„ infrastructure.
Research, clusters and collaborations
Cell Therapy Catapult
A key component of the strategy is the establishment of
a Cell Therapy Catapult at St Guy’s and St Thomas’
Hospital in London. Core funding for the Catapult is from
the Technology Strategy Board (TSB) which is providing
£10 million per year over 5 years. Its aim is to identify
cell therapy research projects with high growth potential
and drive them through the translational research stage
so that they are ready for phase III clinical trials. It is
hoped that the demonstration of successful projects will
stimulate inward investment, and help to grow a UK cell
therapy industry.
201
Strategy for UL Life Sciences, BIS, 2011 (www.bis.gov.uk/assets/biscore/
innovation/docs/s/11-1429-strategy-for-uk-life-sciences.pdf)
POST Report March 2013 Stem Cell Research
UK Regenerative Medicine Platform
To assist the Catapult in identifying opportunities for
commercialisation, the Research Councils have
established a £25 million UK regenerative medicine
platform. The platform will fund interdisciplinary research
hubs such as the new NIHR biomedical research
centres and units. Once the Catapult has identified
promising research projects, it can ease the project
through the translational research stage. This will
involve identifying leading clinicians in the area, helping
the researchers through the regulatory requirements,
and giving assistance with manufacturing, supply and
scale-up. Finally, the Catapult can help with
commercialisation issue such as licensing, intellectual
property and identifying investment partners for phase III
clinical trials.
UK strategy for regenerative medicine
In parallel with the life sciences strategy the Research
Councils and TSB have collaborated to develop a
strategy for UK regenerative medicine.202 This includes
a joint MRC/TSB Biomedical Catalyst Fund to support
translational research by academics or SMEs
(discussed below). Another key part of the strategy is
the support of underpinning research through response
mode funding.
Among the areas identified for such funding are
improved understanding of:
„ cellular reprogramming
„ differentiation and ageing
„ disease and repair mechanisms
„ stem cell niches
„ the extracellular environment
„ genetic instability
„ harnessing immune responses
„ advanced bio-processing
„ development of predictive models for innovation
and value systems.
Clinical and research data
Another key strand of the UK life science strategy is
opening up clinical and research data. For example,
MHRA and NIHR have invested £60 million in a clinical
practice research data link. This gives biomedical
researchers access to anonymised patient data for
clinical trials or other studies. It is hoped that making
such data more accessible will strengthen the UK’s
position as a country for conducting biomedical
research.
Page 71
Patients can also benefit from the opening up of data.
For instance NIHR supports a clinical trials gateway
website that provides patients with easy to understand
information about clinical trials currently being
conducted in the UK.203 Patients and their doctors can
search the site to see whether there are any trials that
might be of benefit to them.
Investment and incentives
Biomedical Catalyst Fund
The availability of funding for translational research has
been a significant barrier to cell therapy. To address
this, the MRC/TSB Biomedical Catalyst Fund was
launched in April 2012. The fund is a £180 million
programme to support translational research from
concept to commercialisation. It is available to UK SMEs
and academics either individually or in collaboration. So
far funding of around £10 million has been awarded
through the program. MRC has awarded £7.41m of
funding to 14 UK universities for around 150 projects,
while TSB has awarded £2.45m to SME-led projects.
Applications are currently being accepted for a second
round of funding.
Promotion and inward investment
Global marketing of the UK as a place to conduct life
science research is seen as an important part of the life
sciences strategy. Activities here include the UK hosting
the 2012 Healthcare and Life Sciences Global Forum in
August. UK Trade and Investment is also:
„ developing a tool that can be used by the
government, companies and trade associations to
promote investment in UK life sciences
„ running targeted business development campaigns
to highlight recent advances in UK capabilities
„ creating a venture capital unit to encourage
investment into UK companies and funds.
Patent Box
Other incentives include the Patent Box announced in
the 2012 Budget.204 This will be phased in from 2013
and provides companies with a reduced rate (10%) of
corporation tax on profits from patents and certain other
types of intellectual property.
203
202
A UK Strategy for Regenerative Medicine, MRC, BBSRC, EPSRC, ESRC,
TSB, March 2012
204
www.ukctg.nihr.ac.uk/default.aspx
The Patent Box: Technical Note and Guide to the Finance Bill 2012
clauses, HM Revenue and Customs, November 2012
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Streamlining regulation
Proposals for streamlining of the regulation of health
research were discussed earlier. At the European level
this includes the revision of the Clinical Trials Directive.
At the UK level, key priorities are establishing HRA as a
non-departmental public body, simplifying the process
for obtaining NHS R&D permissions and making
decisions on the future regulation of embryo research
and of research that uses human tissue. In addition to
these, MHRA is looking at ways of reducing the burden
of regulation on researchers and SMEs. It has published
guidance on its website about schemes that that support
drug development, licensing and patient access to
innovative therapies.205 These include schemes that:
„ Allow an unlicensed medicine to be used for the
treatment of a single patient under certain
circumstances, such as if a suitable licensed
medicine is not available in the UK.
„ Result in fast tracked assessments for new
medicines. Companies may apply for fast tracking if
they can show that a medicine would provide a
major breakthrough in the treatment of patients for
certain conditions.
„ Allow patients earlier access to medicines. MHRA
recently consulted on a scheme that would allow
patients access to promising new (unlicensed)
medicines for treating life-threatening diseases. The
scheme is envisaged as applying to just one or two
medicines a year that have passed through phase
III clinical trials but are not yet licensed.
People
Another implementation strand in the life science
strategy is to ensure that the UK is able to develop,
recruit and reward the best talent in the life sciences
sector. To this end, NIHR has funded three rounds of
recruitment for its new research professorships. The
scheme is open to Higher Education Institutions in
partnership with NHS organisations based in England. It
is looking to recruit researchers who are at a relatively
early stage in their careers and have an outstanding
record of clinical and applied health research and its
effective translation for improved health. Successful
nominees receive a package to support a Professorship,
a Post-Doctoral appointment, research running costs, a
travel fund, access to the NIHR Leadership Programme
and the opportunity for a sabbatical, as well as basic
salary and indirect costs.
205
www.mhra.gov.uk/Howweregulate/Medicines/Licensingofmedicines/
Regulatory schemes that support drug development licensing and patient
access to innovative therapies/EUschemes/index.htm
The first two rounds are now complete. Eight new
professorships were awarded in the first round (2011)
and this included one award where the research
interests included cell therapy approaches. The second
round (2012) resulted in five further awards, with up to
this number being available in the final round (2013)
which closes in December 2012. The successful
applicants cover a very wide range of research interests.
In addition to developing clinicians and researchers,
trained support staff will be needed if cell-based therapy
is to become more widespread. These will need to
include engineers and production staff who are trained
in good manufacturing practice (GMP) for the production
of cell-based products. The BIS review of regenerative
medicine published in 2011 suggested that the number
of staff with the necessary core skills and knowledge to
deliver regenerative therapies was limited.206 A recent
initiative here is the Society of Biology’s degree
accreditation programme which aims to address
concerns about the quantity and quality of practical
training, numerical and analytical skills offered by
biological degrees. Another initiative accredited by the
University of Kent and run by the company Cogent is the
high level apprenticeship for professional technicians
launched in February 2012 that aims to provide an
alternative pathway to enter the life sciences industry at
the technician level.
Infrastructure
If cell-based therapy is to become more widely used,
then the UK will need to develop infrastructure to:
„ supply clinical grade cell lines
„ manufacture and process cells in accordance with
good manufacturing practice (GMP) for phase I
clinical trials and then scale up manufacture for later
phase clinical trials
„ store, distribute and deliver cells for use in cell
therapy facilities.
Cell supply
The UK Stem Cell Bank is currently focused on
generating clinical-grade hES cell lines to supply phase I
clinical studies. The MRC has invested £3 million in
three derivation centres with the aim of providing 25 hES
cell lines to the Bank. As noted in Chapter 4, the first
xenofree (grown without the use of animal cells or
products) hES cell lines have now been deposited. The
UK Stem Cell Bank is also leading an international
initiative to standardise global approaches to the
validation and distribution of clinical-grade hES cell
lines. Continued support for the UK Stem Cell Bank will
be necessary if the UK is to develop and grow a cell
therapy industry.
206
Taking Stock of Regenerative Medicine, BIS/DH, 2011
POST Report March 2013 Stem Cell Research
Cell manufacture
Cells are difficult to grow in a reproducible way. The
manner in which a cell is grown will affect its properties
as a therapeutic agent. This means that, for cell
therapies, manufacturing is a vital consideration from a
very early stage of the development process. The
manufacturing stage must be able to reliably and
reproducibly propagate, expand and differentiate cells to
produce a well characterised, pure and safe cell
population of known potency.207 In the first instance,
relatively small batches of cells will be needed for
research and phase I clinical trials. But as the
development process continues, manufacturing will
need to be scaled up to provide cells for later stage
(phase II and III) trials and ultimately for therapeutic
purposes.
Research into some of the problems posed by
reproducible cell manufacture has been supported by
the Biomedical Catalyst Fund and the British Standards
Institution recently published guidelines on the
characterisation of human cells for clinical use.208
Furthermore, the Cell Therapy Catapult is specifically
designed to drive promising cell therapy projects through
the manufacturing and scale-up stages while complying
with regulatory requirements.
However, if such initiatives do succeed in helping to
establish and grow a UK cell therapy industry then
further manufacturing infrastructure will be required. A
survey conducted by the ATMP Manufacturing
Community in 2011 found that the UK currently has 12
MHRA-licensed facilities for ATMP manufacture and that
a further eight are planned.209 It concluded that this
relatively wide distribution of small facilities matched the
current need to supply research projects and phase I
clinical trials. But it noted that more capacity is likely to
be needed in the future. This increased demand could
come from an increase in the use of autologous cells for
therapy. In this case, the demand would be for more,
smaller, facilities attached to NHS hospitals.
Alternatively (or additionally) there could be a demand
for larger, high throughput manufacturing facilities for the
production of allogenic cells. The development,
accreditation and standardisation of such large-scale
cell culture facilities is likely to present “significant
technical and regulatory challenges”.210
207
208
209
210
A UK Strategy for Regenerative Medicine, MRC, BBSRC, EPSRC, ESRC,
TSB, March 2012
BSI Characterization of human cells for clinical application PAS 15 93,
2011
Foley L et al, Regenerative Medicine, 7(3), 285–289, 2012
A UK Strategy for Regenerative Medicine, MRC, BBSRC, EPSRC, ESRC,
TSB, March 2012
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Cell storage and distribution
Looking further ahead, if cell therapy is to become an
established part of the NHS landscape, then further
infrastructure will be needed for cell storage, transport
and distribution to clinics. The experience and facilities
of the NHS Blood and Transplant Authority could form
the basis for such infrastructure. However, this will
require further research into areas such as storage
processes as cryopreservation and cell hibernation.
While, cryopreservation protocols have been developed
for a wide range of stem cells (including hES cells),
many involve the use animal products which render
them unsuitable for clinical use.
6.3 Potential benefits and risks of cell therapy
Potential applications of stem cell research have been
referred to throughout this report. To recap, these can
be grouped into the following categories:
„ acellular products
„ endogenous repair
„ use of cells for drug testing or as toxicity platforms
„ use of autologous or allogeneic cells for therapy.
The following sections look at some of the potential
benefits and risks of these approaches.
Acellular products
Acellular products are medical devices that are used to
provide a matrix which can regenerate damaged tissue
when naturally repopulated by human cells and blood
vessels. They include both natural and synthetic
products. Examples include:
„ AlloDerm Regenerative Tissue Matrix. This is a
commercially available product made from donated
human skin which has been aseptically processed
to remove the epidermis and any other cells that
may cause problems with immune rejection. The
resulting biological matrix can be used in
procedures such as hernia repair, abdominal wall
repair and breast replacement following
mastectomy.
„ Actifuse is another example of a commercially
available product that can be used to promote bone
repair. It is a synthetic silicate matrix that can be
used to fill gaps and voids in bone. In animal
studies, it has been shown to encourage the growth
of new bone and the development of capillary blood
vessels, while the matrix itself is slowly resorbed.
Evidence from the clinical use of such products
suggests that they are well tolerated and safe. The
absence of cells in the transplanted matrix means that
there is minimal risk of immunological problems such as
rejection. However, effectiveness can vary significantly
from one patient to another, with some showing
significant benefit and others exhibiting little or no
response.
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Endogenous repair
There is considerable interest in using small molecules,
proteins or other factors to stimulate the body’s own
(endogenous) repair mechanisms to regenerate tissue.
Examples already in widespread clinical use include:
„ Using granulocyte-colony stimulating factor to
mobilise blood (haematopoietic) stem cells after
chemotherapy. This rapidly increases the number of
white blood cells (neutrophils) and helps to protect
against bacterial infection.
„ Using erythropoietin to stimulate red blood cell
production in patients suffering from severe
anaemia. This includes cancer patients who receive
radiation or chemotherapy and those with chronic
kidney disease.
Numerous other factors to stimulate endogenous repair
are the subject of research. For example, studies have
looked at thymosine beta-4, a small protein (peptide)
that may be able to reactivate cardiac progenitor cells to
repair damaged heart tissue following a heart attack.211
There is also interest in the use of leukaemia inhibitory
factor to stimulate the self-renewal of neural stem cells
and the proliferation of various glial cells.212 The interest
here is that harnessing such cells to boost myelin
protein production may prove effective in treating
diseases such as multiple sclerosis.
The pharmaceutical sector is interested in such
approaches because they are a good match with its
expertise and its existing business model. In principle,
factors that stimulate endogenous repair pose no
greater risk than those raised by conventional small
molecule or current biotech treatments, and the current
regulatory system is well equipped to assess such risks.
Future success in this area will depend on continued
research to improve understanding of the signalling
pathways and factors that control endogenous repair
mechanisms.
Cells for screening and testing
Another use of stem cells is for testing the efficacy and
toxicity of potential new drugs. As discussed in Chapter
4, hiPS cells may prove to be particularly valuable for
the screening of efficacy because they can be used to
create models for a wide range of diseases (see Table
4.2 for examples). The iPS cells can be differentiated
into cells of the type predominantly affected by the
disease. Such models can lead to better understanding
of the underlying mechanisms behind a disease and
allow drug developers to develop potential new
treatments for it. These can be screened for efficacy
using the disease model. Promising new treatments can
also then be screened for toxicity against a range of cell
populations such as kidney cells, liver cells and heart
cells.
Such approaches have a number of advantages. They
can provide models of disease in tissue that otherwise
may be inaccessible for study (such as brain or heart
tissue). They provide a platform for the rapid screening
of large numbers of potential new drugs for efficacy and
safety. And they can identify potential toxicity problems
at an early stage of drug development before expensive
clinical trials have been started.
There are no additional risks as such associated with
using stem cells for safety and toxicity testing during
drug development. Pharmaceutical companies will still
have to do conventional toxicity testing and clinical trials
to show that a new drug is safe and effective. However,
there is some scope for improvement of existing disease
models. For example, some diseases are particularly
difficult to model using hiPS cells; Franconi anaemia and
Fragile X syndrome are two examples of such diseases
discussed in Chapter 4. And the cell populations
resulting from current differentiation and expansion
systems tend to be immature cells of varying purity.
Progress in addressing such issues would be widely
applicable across the whole field of cell therapy and
regenerative medicine.
Cell therapy
The benefits and risks of cell therapy depend on the
whether the therapy uses the patient’s own cells
(autologous therapy) or uses cells from another person
(allogeneic therapy). Within these categories the
benefits and risks may vary depending on how the cells
were derived and the extent to which they have been
manipulated before being used for treatment.
211
212
Crockford D et al, Ann N Y Acad Sci 1194, 179–89, 2010
Deverman B and Patterson P, The Journal of Neuroscience, 32(6), 21002109, 2012
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Autologous therapy
Simple autologous therapy
In its simplest form, autologous therapy involves taking
cells from a patient’s body, processing them and
reintroducing them into the patient. Examples of this
type of approach include using haematopoietic stem
(HS) cells following chemotherapy for treating lymphoma
or multiple myeloma, use of HS cells following acute
myocardial infarction (heart attack), use of keratinocytes
for treatment of burns and the use of chondrocytes and
mesenchymal stem cells for cartilage repair.
The main advantage of such approaches is that there is
little risk of immune rejection of the cells and, in the trials
reported to date, relatively low risk of other serious
adverse effects. However, such treatments tend to be
relatively expensive because they are tailored to
individual patients. Moreover, the approach is limited to
readily accessible cells such as mesenchymal stem
cells, HS cells and keratinocytes. There is on-going
debate about just how much of a limitation this is in
practice. As described in Chapter 4, a very wide range
of cell types can now be derived from stem cells that are
readily accessible in the human body.
Overall, the evidence from clinical trials on the benefits
of such treatments is variable. In some cases, such as
use of HS cells following chemotherapy for cancer
treatments, there is good evidence of clinical benefit and
the treatments are well established. In other cases, such
as the use of HS cells following heart attack, the
evidence of long-term clinical benefit is less clear cut.
There is evidence that the HS cell treatment improves
short-term measures (reducing tissue damage and
maintaining heart function). But small study sizes and
variations in patient selection, stem cell delivery (timing
and dose) and patient follow up mean that the evidence
for increased long-term survival is variable.213
Advanced autologous therapy
Looking further ahead, it is likely that more advanced
autologous therapies will be developed. Researchers
might develop treatments based on differentiated and
purified cell populations derived from autologous cells,
or even genetically modify autologous cells to improve
their efficacy.
213
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pone.0037373
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For instance, circulating angiogenic (CA) cells from
patients with coronary artery disease have limited
regenerative capacity. Researchers recently showed
that the regenerative capacity of these cells can be
restored by genetically modifying them to over-produce
a signalling factor (nitric oxide).214 This raises the
possibility of using genetically modified autologous CA
cells to treat patients with coronary artery disease.
However, the greater the extent of manipulation applied
to an autologous cell before it is re-introduced into the
body, the greater the potential risks associated with the
therapy are likely to be. This in turn means that it is likely
to be much more difficult to gain regulatory approval for
a clinical trial involving an advanced autologous therapy
than it is for a trial involving a more straightforward
therapy.
hiPS cells
In theory at least, hiPS cells could be used for
autologous therapy. Adult cells from the patient could be
reprogrammed into hiPS cells, and these could then be
used to derive a very wide range of cell types for use in
autologous therapy. On the face of it such an approach
would appear to offer the best of both worlds. It has the
advantage of lack of immune rejection associated with
autologous therapy. And it has the advantage of being
able to generate the widest possible range of cell types
usually associated with allogeneic hES therapy (see
next section).
However there are two main drawbacks that make it
highly unlikely that hiPS therapy will be used in the near
future. First, the derivation of hiPS cell lines from
individual patients is likely to be very expensive and time
consuming, which may limit their clinical utility. For
instance, techniques that take weeks to yield enough
cells for treatment are unlikely to be useful for treating
conditions such as heart attack or stroke.
Second is the continued uncertainty about the safety
and efficacy of cell populations derived from hiPS cell
lines. This was discussed in Chapter 4, where it was
noted that hiPS cell lines show very subtle differences in
their characteristics when compared with hES cell lines.
Researchers believe that hiPS cells retain an ‘epigenetic
memory’ of their former state. It is not clear what impact
these subtle differences would have on the safety or
efficacy of hiPS-derived cells. But their very existence
means that for the immediate future hiPS cells are best
considered as useful disease models rather than likely
candidates for cell therapy.
214
Ward M et al, Molecular Therapy, 19 (7), 1323–1330, 2011
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Allogeneic cell therapy
In some respects, allogeneic cell therapy is a well
established treatment. For instance donor HS cells have
been used for many years to treat patients suffering
from various forms of leukaemia. A combination of
tissue matching between the patient and donor (often a
close relative) and immune suppressing drugs are used
to minimise problems with immune rejection. However,
in other respects allogeneic cell therapy lags behind
autologous therapy. The big hope is that cell lines
derived from pluripotent hES cells will eventually lead to
better treatments for a wide range of diseases. In the
last couple of years, clinical trials of this new generation
of allogeneic cell therapy have started to gain regulatory
approval and recruit patients. Examples of such trials
were detailed in Chapter 5 and include:
„ Geron’s trial for treatment of spinal cord injuries
(now discontinued)
„ Applied Cell Technology’s trials using retinal
pigment epithelium derived from hES cells to treat
Stargardt’s Macular Dystrophyand age-related
macular degeneration (AMD)
„ The London Project for curing blindness backed by
Pfizer has applied to conduct a trial using hES
derived cells to treat AMD
„ California Stem Cell has applied for a licence to
conduct a clinical trial using hES derived cells to
treat type 1 spinal muscular atrophy.
Main advantages
Among the key advantages of these allogeneic cell
therapies is that researchers can use hES cells to derive
the full range of human cell types, so in principle at least
the treatments are applicable to a wide range of
diseases affecting different parts of the body. A further
advantage is that the approach fits neatly with the
current pharmaceutical business model; a company
investing in such research has a product that it can
potentially sell to recoup its investment.
Disadvantages
However, a major downside is how well such therapies
are tolerated by the patient’s immune system. This may
be less of an issue in parts of the body that are immune
privileged such as parts of the central nervous system.
This special status is thought to be a defence
mechanism to protect highly sensitive parts of the body
with a limited capacity for regeneration from the damage
that an immune response could cause. It is no
coincidence that all of the most advanced trials and
planned trials of allogeneic cell therapy target immune
privileged sites of the body, where the treatments are
expected to be well tolerated.
Tissue matching
So what are the prospects for allogeneic therapies that
target body systems that are not immune privileged?
The experience with using HS cells in combination with
tissue matching and immune suppression to treat
various forms of leukaemia suggests that the problems
of immune rejection are not insurmountable.
An individual’s immunological identity consists of two
main components: their blood type and their human
leukocyte antigen (HLA) profile. HLA’s are proteins
(antigens) found on the outer surface of cells and are
the main cause of immune rejection of organ
transplants. An approach where hES cells representing
all of the main blood groups and HLAs were derived and
banked would allow accurate tissue matching between
the cells used for therapy and the patient. Depending on
the exactness of the match required, it has been
estimated that a bank containing as few as 10 and no
more than 150 hES cell lines could provide adequate
coverage.215
Novel methods
Other strategies for minimising immune rejection of
allogeneic therapy have also been suggested. For
example, the California Institute for Regenerative
Medicine is funding a group of researchers trying to
develop a treatment for diabetes using beta cells derived
from hES cell lines.216 The group has reported
successful results from using novel encapsulation
methods to ‘hide’ the transplanted cells from the host’s
immune system. The encapsulation method is
permeable to small molecules such as signalling factors
and small peptides such insulin, does not itself elicit an
immune response and prevents the cells of the host’s
immune system accessing the transplanted beta cells
and recognising them as foreign.
Cell therapy and clinical trials
The coming years are likely to see an increase in the
number of cell therapies being investigated in clinical
trials. Irrespective of the approach used – autologous or
allogeneic – such therapies pose a number of
challenges for the clinical trial regulatory system.
Regulators want details of a drug’s potency, purity and
dose. Such concepts are difficult to translate into the
world of cell therapy. How does one measure the
potency of a complex, multi-functional structure like a
cell? How does one define dose for a product that is
capable of multiplying? Or define purity in a population
of cells that is capable of differentiation?
215
216
Taylor C et al, The Lancet, 366 (9502), 2019-2025, 2005
http://www.cirm.ca.gov/content/cell-therapy-diabetes
POST Report March 2013 Stem Cell Research
Such considerations mean that clinical trials may need
to adapt to the new challenges posed by cell therapy.
Researchers may need to develop better biomarkers to
track cells in the body and allow a more accurate
estimation of the extent of therapeutic effect. They need
better methods of cell sorting to achieve ‘pure’
populations of cells. But at the same time the regulatory
system may have to develop more flexibility about the
design of clinical trials to reflect the special challenges
posed by cells.
6.4 Where next?
Much has happened since the House of Lords Stem Cell
Research Committee published the report of its inquiry
in 2002. Researchers have made huge leaps in
understanding the factors that interact with DNA and its
surrounding protein to control fundamental cellular
processes such as the cell cycle, cell death, cell division
and differentiation. These leaps mean that they can
maintain embryonic stem cells in a pluripotent state or
direct their differentiation down a specific lineage almost
at will. They can reverse this process using a defined
cocktail of transcription factors to reprogram adult cells
back to pluripotent iPS cells. And, within limits, they can
trans-differentiate cells from one lineage to another
without going through a pluripotent stage.
The next decade will likely see more of the same sort of
advances in the laboratory. Researchers are rapidly
reaching a stage where they can master the direction of
cell fate in the laboratory. The efficiency with which iPS
cells can be produced is likely to improve, and scientists
are likely to learn more about the potential usefulness or
limitations of such cells for therapy. Similarly, the range
of cell lineages that can be produced by transdifferentiation is likely to increase. Such cells are a
potentially useful source of cells for therapy as deriving
them does not involve transition through a pluripotent
stage and this minimises concerns about their safety.
Researchers are also likely to pursue approaches where
cells are used as the vehicle to deliver gene therapy.
Few in the field doubt that these advances will lead to
significant clinical benefits to patients. What is in doubt
is how, when and where this will happen.
It is likely that better models of disease provided by
advances such as hiPS cells will suggest new targets for
the stimulation of endogenous repair by conventional
drugs or biotech products. The development of such
products may be aided by the use of stem cells for
safety and efficacy screening of potential new drugs.
While the UK is well poised to exploit any such
opportunities, such approaches are likely to take ten
years or more.
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To date much of the clinical trials activity in the area of
cell therapy has focused on autologous therapy. In
general, such trials have been small and the evidence of
clinical benefit they have yielded has been variable. The
next few years should see some of the more promising
approaches progressing to later stage trials, possibly
yielding more clear-cut evidence of clinical benefit.
However, there are still questions about how to
commercialise such approaches.
The big hope for the coming decade is allogeneic cell
therapy. Trials of such approaches have only recently
started. In the first instance, the trials are principally
designed to show how well tolerated the treatments are;
any evidence of clinical benefit would be regarded as an
added bonus. But a successful allogeneic trial could act
as the catalyst to kick start further investment in such
approaches. At present allogeneic cell therapy is
confined to certain parts of the body that are more or
less immune privileged. However, this could change if
ways could be found to make the treatments more
immunologically acceptable to the host. For the
foreseeable future it is likely that such approaches will
continue to depend on cells derived from hES cell lines.
The UK government is currently funding research across
the entire spectrum of these activities, investing in
infrastructure and supporting translational research in
activities such as manufacturing, scale up and bioprocessing. However, at some point in the coming
decade or so, choices will have to be made and funding
prioritised accordingly.
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A1
ACE
AMD
AMS
AS
ATMP
BIS
CJEU
CQC
CSP
Annex A1 Acronyms
Arts Council for England
Age-related macular degeneration
Academy of Medical Sciences
adult stem (cells)
Advanced therapy medicinal product
Department for Business Innovation and Skills
Court of Justice of the European Union
Care Quality Commission
Co-ordinated system for gaining NHS research
permissions
DH
Department of Health
EG
embryonic germ (cells)
EMA
European Medicines Agency
EPC
European Patent Convention
EPO
European Patent Office
ES
embryonic stem (cells)
EU
European Union
GAfREC Governance Arrangements for Research Ethics
Committees
GMP
good manufacturing practice
GTAC Gene Therapy Advisory Committee
GVHD graft versus host disease
GVT
graft versus tumour (response)
hAS
human adult stem (cells)
hEG
human embryonic germ (cells)
hES
human embryonic stem (cells)
HFE
HFEA
hiPS
hMS
HO
HRA
HS
HSE
HSCIC
HTA
iPS
IRAS
MHRA
Human Fertilisation and Embryology (Act)
Human Fertilisation and Embryology Authority
human induced pluripotent stem (cells)
human mesenchymal stem (cell)
Home Office
Health Research Authority
haematopoietic stem (cells)
Health and Safety Executive
Health and Social Care information Centre
Human Tissue Agency
induced pluripotent stem (cells)
Integrated Research Application System
Medicines and Healthcare products Regulatory
Agency
MRC
Medical Research Council
MS
mesenchymal stem (cell)
mtDNA mitochondrial DNA
NHSBT National Health Service Blood and Transplant
NIHR
National Institute for Health Research
NRES National Research Ethics Service
NTS
nuclear transfer stem (cells)
PS
parthenogenetic stem (cells)
REC
Research Ethics Committee
SHA
Special Health Authority
TEP
Tissue engineered product
TSB
Technology Strategy Board
UKSCB United Kingdom Stem Cell Bank
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A2
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Annex A2 Glossary
Blastocyst
Blastomere
BMP
Early stage (5-7 days) of developing embryo consisting of trophoblast and inner cell mass
One of the cells found in the inner cell mass of the blastocyst
Bone morphogenic protein 4, a protein that plays a critical role as a signal factor in
the early differentiation of the embryo
Chorion
One of the membranes that allows nutrients to pass from the mother to the developing embryo
c-Myc
A gene coding for a transcription factor that is one of the four factors used in reprogramming
adult cells into iPS cells
Ectoderm
One of three types of tissue found in the early embryo that gives rise to the outer layer of skin
and the central nervous system
Embryoid bodies Clusters of embryonic stem cells that arise during cell culture and from which embryonic stem
cell lines can be derived
Endoderm
One of three types of tissue found in the early embryo that gives rise to the lungs, liver,
pancreas and other internal organs
Epigenetic
Refers to various mechanisms whereby environmental factors in the cell modify patterns of
gene expression
Gametes
Sperm or eggs
Histones
Proteins found in close association with DNA in chromosomes; the histone-DNA association is
one of the (epigenetic) mechanisms for controlling patterns of gene expression
Inner cell mass The 200 or so pluripotent cells found inside the blastocyst from which embryonic stem cells can
be derived
Klf4
Krupple like factor 4, a transcription factor found in stem cells and one of the four factors used
in reprogramming adult cells into iPS cells
Mesoderm
One of three types of tissue found in the early embryo that gives rise to the heart, kidney, blood
system, bone and muscle
Morula
Early stage (3 days) of developing embryo containing totipotent stem cells
Multipotent
Stem cells that have the ability to give rise to some or all of the cell types found in the tissue
they are associated with
Nanog
A key transcription factor involved in maintaining pluripotency and supporting self-renewal
Oct 4
Octamer-binding transcription factor, a key factor in preventing differentiation and maintaining
pluripotency and one of the four factors used in reprogramming adult cells into iPS cells
Oligopotent
Stem cells that have the ability to give rise to just a few different cell types
Parthenogenesis A process that can stimulate an unfertilised egg into (temporarily) behaving as if it had been
fertilised and from which parthenogenetic stem cells can be derived
Pluripotent
Cells that have the ability to give rise to all of the cell types found in the adult human body
SHH
Sonic hedgehog, a protein that plays a key role in patterning of the neural tube in early
embryonic development
Somatic
Refers to a (differentiated) cell of adult origin
Sox 2
A key transcription factor involved in maintaining pluripotency and supporting self-renewal and
one of the four factors used in reprogramming adult cells into iPS cells
Teratomas
Tumour-like growths containing each of the main classes of differentiating cells that form when
pluripotent cells are injected into various sites in immune deficient mice
Totipotent
Cells that have the ability to develop into a complete organism
Transcription
A protein that binds to specific DNA sequences and thereby controls patterns of gene
factor
expression
Trophectoderm The name given to the trophoblast after around 12-15 days
Trophoblast
Outer layer of cells found in an early embryo that give rise to the placenta and other extraembryonic tissue
Unipotent
Cells that have the ability to give rise to a single cell type
Xeno-free
Refers to cell lines that have been isolated/grown without the use of animal-derived products
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