Download Stem Cell Research and Potential Medical Interventions

Stem Cell Research and Potential Medical Interventions
By
Rohit Pawar
28th May 2015
Grade awarded: Pass
RESEARCH PAPER
BASED ON
PATHOLOGY LECTURES
AT MEDLINK and VET-MEDLINK 2014
Abstract:
Stem cells – a remarkable and revolutionary discovery, the research on which is on-going, exciting and
worldwide; this is the future of medical research. Stem cells are extraordinary because of their ability to
differentiate, change into any type of cell of the body. The potential here is huge and will likely lead to
many treatments for the worst of the diseases. This paper introduces the basics of stem cell science, gives
information on current stage of research and outlines how current research can be used for medical
treatments for diseases such as cancer and auto-immune diseases. The central idea here is to use ‘offshoot’
research findings to devise treatments. The paper also studies the role of genetic switches and how they
can be incorporated into the research. The paper finally discusses important ethical and moral issues
surrounding the research.
Introduction:
Movies, science fiction and fantasy books often involve immortality which sounds quite farfetched to a
scientific mind but it is interesting to note that immortality does exist if one is simply talking about
individual body organs. It’s a well-known fact that several species of animals can regrow their body
parts. The phenomenon is called Autotomy (1). On a smaller scale, in humans, body parts do heal
themselves but unfortunately the humans cannot regrow body parts.
This ability to heal self or the ability of an embryo to grow into a human or animal is attributed to stem
cells. The Cambridge dictionary defines stem as - central part of something from which
other parts can develop or grow. Embryonic stem cells will divide, multiply and specialise to give rise to
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an animal. In a living animal, organ specific stem cells will replenish cells lost to injury and normal wear
or tear. Thus we have embryonic stem cells and non-embryonic (adult) or somatic stem cells.
Each organ in our body performs a specific function. The cells in our organs are specially made to
perform that function. Stem cells do not perform any particular body function but just like a log of
wood which can be made in to different furniture items, they can be divided and shaped and made in to
specialised cells which then perform the necessary function (Figure 1). Stem cells can multiply in to
more stem cells as well. Genes are responsible for turning on or off the process of specialisation.
Things can go wrong during this process. For example uncontrolled multiplication causes cancer and
abnormal differentiation causes birth defects.
Figure 1
We can think about the ways in which a human body can die. We usually die because one or more of
our specialised organs die. Heart attack causes death of cardiac muscle cells. Diabetes is due to
pancreatic failure. Obesity and alcoholism leads to death of liver cells and dementia or paralysis is
caused by death of brain cells. It is possible to say that these diseases could be cured or reversed if stem
cells are used to regenerate the necessary specialised cells.
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In order to produce specialised cells, it is first necessary to grow embryonic stem cells in laboratory.
Such cells can be derived from embryos from eggs that have been fertilized ‘in vitro’ or outside the
human body. Growing such cell cultures has been found to be a very difficult process and even when
successful, it still needs to be confirmed that the cells have the fundamental properties that characterises
them as stem cells (in other words, establishing pluripotency or the ability to differentiate into many
types of specialised cells) (2). There are many challenges (3) in characterisation but the idea is to show
that the cells are healthy, capable of self-renewal, capable of staying in an undifferentiated mode but
having the ability to differentiate into specialised cells.
It is known that clumped embryonic cells can spontaneously differentiate into different specialised cells.
Scientists are now working on directed differentiation or inducing stem cells to differentiate in to a
specific cell type. William L A and colleagues (2012) have produced an excellent poster (4) giving some
solutions in directing such differentiation. Another way of growing specialised cells is by using adult
stem cells. The technique has been used in treating diseases for many years now e.g. use of
hematopoietic and mesenchymal stem cells. The question is whether the somatic stem cells from one
organ can be induced to grow specialised cells of another type, a phenomenon called as transdifferentiation (5). Adult or somatic stem cells are found in many organs including brain and heart.
Embryonic stem cells from mouse were derived in 1981(6) but it took another almost 20 years for
scientists to derive first human cells. Within 3 years first human embryos were cloned and in another 3
years first artificial liver cells were created. A few years ago, the BBC publicised (7) the work of John
Gurdon and Shinya Yamanaka who have managed to share a Nobel Prize. Gurdon’s work in 1962
showed that any cell in a frog had the genetic information and potential to create a whole new frog. He
experimented with this idea and placed the genetic information of one frog into another frog egg and a
normal tadpole grew out of it. This research created the foundations to the famous dolly the sheep who
was the first cloned mammal. This was a revolutionary result. Forty years later, Yamanaka decided that
he would “reset” a cell instead of transferring genetic information into an egg. He added 4 genes to skin
cells which converted them into stem cells which were undifferentiated and could become specialised.
For this discovery he was awarded a Nobel Prize. The discoveries of Gurdon and Yamanaka have
shown that specialized cells can turn back the developmental clock under certain circumstances.
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Jonathon Slacks (8) has also played an important role in the research. With his first degree in
biochemistry, he has been a scientist at the UK Imperial Cancer Research Fund and he studied how
chemical signals called inducing factors have been affecting early embryonic development. Using a frog
as a test organism, he was the first to discover an embryonic inducing factor and showed how inducing
factors played an important role in controlling the formation of the head-to-tail pattern on the embryo.
Recently, as the director of the stem cell institute at the University of Minnesota, he has focused his
work on regenerative tissue and trying to convert one type of tissue into another type. His main interest
is in attempting to reprogram some tissue types into pancreatic beta cells which could treat diabetes,
something that has been a growing issue for decades.
The current research is directed towards refining the method of growing cell culture, finding out the
different types of internal and external stimuli that induce specialisation of a particular type and learning
to direct differentiation. Not all the research so far has been only theoretical in its scope. Several
treatments based on stem cell research are currently in use. The most common treatments are based on
blood stem cell and skin stem cell transplants (9). The US national Marrow Donor Program (10) gives a
full list of diseases that can be treated with blood cell transplant. These mainly include several types of
blood cancer, bone marrow disease and auto-immune diseases. Skin grafts are mainly used in patients
with life threatening burns. Animal trials have been done for many more diseases such as spinal cord
injury, strokes, heart attacks and osteoarthritis amongst others (11). Stem cell research has also
benefitted medicine in an indirect way e.g. new drugs can be tested for toxicity on stem cells (12). Such
drug testing can save millions of dollars needed for animal testing but also ensure that drugs are safe for
human consumption. It’s not star trek science to suggest that there is a potential for any specialised
organ to be grown in vitro using adult stem cells and then transplanted back in to the donor. At the
moment it is done on a cellular level e.g. bone marrow cells. Current research is focused on repairing
tissue damage in injured organs. There are countless other research projects going on around the world.
The National Institute of Health (US) website (13) and Globalchange.com website (14) will provide the
reader with a full list of current projects around the world. However the challenges facing the scientist
are many.
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Discussion:
In my process of researching, I was overwhelmed by this extensive field of stem cell
research that is going on currently. A quick Google check shows that there are countless
links leading to a vast quantity of research papers and information sites and so I decided to
begin by summarising the challenges (15). As we know, stem cells are undifferentiated and
unspecialised cells that can become specialised. The main objective with stem cells is to be
able to introduce a stimulus to influence it to become into a specialised cell of our choice.
This however, has not been achieved as scientists are still trying to control the
differentiation of embryonic stem cells. There are other problems which include attempting
to identify stem cells from many different types of cells in a tissue (16). Even if the
objective of trying to specialise a stem cell is achieved, there are other problems e.g. other
body cells will recognize the differentiated stem cells as foreign cells and will attack them
and they may not work correctly among other similar cells (16). And, there are of course
legal, ethical and moral issues (17).
I therefore became more interested in looking at the challenges listed above and how scientists are
trying to find solutions. Such solutions have the potential to have a big impact in creating new
treatments. In the following paragraphs I now wish to summarise few ideas.
Cancer treatments:
Cancer is one of the biggest life threatening diseases in the world currently killing 150,000
people in the UK alone (18). Cancer is essentially a disease caused by an uncontrolled
division of abnormal cells in a part of the body resulting in a tumour. Cancer treatments aim
to limit cell growth or to kill cells themselves and while this is temporarily successful, the
cancer arises again at a later stage. It was thought that there are many different types of
cells in a tumour and that some survive the treatment and then reproduce but ever since the
discovery of stem cells, it is strongly thought that cancer cells originate from adult stem
cells that can self-renew and become resistant to the treatments and continue with tumour
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growth (18). In general, if treatments do not target the group of stem cells within the tumour
then the tumour will easily be able to grow back.
In order to develop a cancer treatment to fully cure cancer, scientists would need to target
the stem cells, specifically limit their growth. To do this, we can study factors that affect or
prevent stem cell growth like temperature, acidity or certain chemicals. While temperature
and acidity would be extremely effective at treating cancerous stem cells, they are factors
that affect the rest of the body, mostly enzymes, so therefore this is a difficult technique to
use. Dexter T M and his colleagues in his paper in 2005 (19) focused their work on
stimulating stem cell growth using a culture containing phagocytic mononuclear cells,
“epithelial” cells, and “giant fat” cells. They concluded that growing stem cells with this
culture at 33 degrees Celsius showed an increase in stem cell maintenance. They also tested
for colony stimulating activity (CSA) by adding exogenous CSA which cause a rapid
decline in stem cells. Perhaps a treatment can be designed from this where this is targeted at
the tumour stem cells so they are killed off so the tumour cannot grow back when standard
cancer treatments are used. Smith A G and his colleagues in 1988 (20) studied the
“inhibition of pluripotential embryonic stem cell differentiation by purified polypeptides.”
Here they show that a medium containing Buffalo rat liver cells which contains a
polypeptide factor which is an embryonic stem cell differentiation inhibitory activity (DIA)
that suppresses stem cell differentiation and hence prevents stem cell growth. Once again,
here is another possibility of a certain chemical that can be used to stop stem cell growth
and if applied to the stem cells in tumours, can possibly be used to treat cancer effectively.
Autoimmune Diseases:
Another dilemma that researchers face is that stem cells encounter immunological rejection.
This is when an immune response is developed against a transplanted stem cell as the body
recognizes it as foreign and therefore to be eradicated. If this problem is solved and stem
cells are not rejected then this research can be used to treat auto-immune disease which can
cause abnormally low activity or over activity of the immune system and hence attack and
destroy healthy cells. Auto-immune diseases include Addison’s disease, Celiac disease,
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Dermatomyositis, Graves’ disease, Hashimoto’s thyroiditis, multiple sclerosis, Myasthenia
gravis, Rheumatoid arthritis and Type 1 diabetes (21, 22). In general, the body produces
antibodies against self-cells which is extremely dangerous as it could result in damage to
body tissue, abnormal growth of an organ and changes in an organ function (21).
In order to be able to use stem cells for treatments, especially transplanted tissue, a solution needs to be
devised to stop immune responses against stem cells. There are many articles from various authors who
have done investigations to find ways to prevent stem cells from being rejected in the body. Bioscience
technology website (23) gives information on how immunosuppressant drugs have been used for short
term immune responses and how, if these drugs are used over a long period for stem cells, they can be
very harmful making you vulnerable to many other diseases. The article also describes an experiment
where a combination of the drug CTLA4-lg (used to treat rheumatoid arthritis by suppressing T cells)
and the protein PD-L1 (important for inducing immune tolerance in tumours) were introduced to
“humanized” mouse models which were mice that had a reconstructed human immune system. The
combination of these substances did not induce an immune rejection to foreign cells. Drukker M and
his colleagues (2005) inform us that it is T cells that cause rejection of stem cells (24). They also show
that mice that were conditioned to carry peripheral blood leukocytes from human origin were used to
test the human leukocyte alloresponse toward undifferentiated and differentiated human embryonic
stem cells and that there was a tiny immune response against the stem cells. Once again this can be
implemented in treatments for diseases with immunological rejection. Rutger-Jan Swijnenburg and
colleagues in 2010 (25) were able to produce a way to prevent rejection of stem cells by transducing
them with a double fusion reporter gene consisting of firefly luciferase (FLuc) and enhanced green
fluorescent protein (eGFP). They used bioluminescent imaging to track the stem cells and to see if they
were rejected which they weren’t. They also found results which showed that differentiated stem cells
suffered less rapid rejection. Xiangcan Zhan and colleagues in 2004 (26) describe the results when
specific growth factors stimulate the production and release of leucocytes expressing CD45which
eventually produced cells which functioned as antigen presenting cells that were capable of inhibiting
CD4 and CD8 T-cell responses in a culture. All the findings represent various ways in which the
immune system can be suppressed or make it accept the stem cells. Future developments should focus
on using these results to develop treatments for auto-immune diseases.
Gene switches:
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A genetic switch is a very recent and revolutionary idea. Every cell in the human body
contains many genes but only a small quantity of these genes is expressed to form the
characteristics of the cell. This means that each cell can carry out a different function
depending on the genes it is expressing. The other genes are suppressed and not expressed,
they are tuned off. The process of turning on and off is known as gene regulation (27). The
idea of gene regulation is being used in stem cells to enable them to differentiate. Sean
Bettam from the University of Toronto (28) describes discovery of a gene that effectively
regulates other genes that controls early development. The gene in particular called the
Sox2 gene and the investigators used mice to find the region of the genome that controlled
this gene.
This particular gene in stem cells enables the stem cells to maintain their ability to become
any type of cell. If this Sox2 genes is missing in the cells of an early embryo then the
embryo will die as the genes that need to be turned on or off will not do so. It is clear that
current research has been successful to discover how genes in stem cells are regulated and it
has been proven in mice and in vitro. The next step therefore is to attempt to use this
technique in vivo to control which cell type a stem cell will differentiate into. This
technique can be used for tissue regeneration as a group of stem cells can be controlled via
the controller gene to differentiate into e.g. liver cells and so liver tissue can be repaired.
Ethical/Moral issues:
I now wish to talk about the ethical and moral dilemma in this field. While this research is
new and exciting and is bringing in revolutionary techniques, there are many moral and
ethical issues associated with the use of stem cells for research. The largest and most
difficult issue here is whether the embryo, from which the stem cells are taken from, is
viewed as a human being, a person with full moral status. Many people believe that an
embryo is a potential person and therefore we are destroying a human life every time we
use embryonic stem cells for research while the benefits of this mean that research can
improve and maybe a treatment can be found that will significantly reduce human suffering.
This is extremely difficult to solve because there is a mixed opinion in the population, some
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who think that every embryo is a potential human life and the others who think that
embryos are not “people” who have psychological, emotional and physical properties and
do not have any interests to be protected (29). A government has to weigh the benefits and
disadvantages and the success of the research and decide whether it wants to allow stem
cell research to continue to bring extraordinary treatments.
Religion also has to be considered when studying the moral and ethical issues. Many
religions will view the research in different ways. For example, the Roman Catholic,
Orthodox and conservative Protestant Churches believe the embryo has the status of a
human from conception and no embryo research should be permitted. Other religions, like
Judaism believe that an embryo is not a human being until a certain stage in development
while there are some religions who believe that embryos have no human status until the
baby is born.
Therapeutic cloning is where stem cells are produced specifically for a medical treatment.
To achieve this, a technique called somatic cell nuclear transfer (SCNT) is used. Here an
embryo is made by removing the nucleus from an empty adult skin cell and inserting it into
an empty egg cell from which the previous nucleus has been removed from. The embryonic
cells can then reproduce. Once again this brings you to the first issue of embryos being a
potential human life but benefits from the treatment can outweigh this. This technique can
be used to create clones since it is a similar method to how Dolly the sheep was produced.
Cloning is however banned in many countries. If this is used excessively then potential
human life will just be a resource to scientists. The eggs used in this technique need to be
donated by women and there is a potential here for women to be exploited for eggs
especially in poorer, developing countries with less legal restrictions.
Even if there are alternate ways to achieve the same result, there will always be ethical
issues surrounding human embryonic stem cell research. Alternative is that stem cells can
be obtained from other sources like tissues and adult bone marrow. It can be argued that if
the same can be achieved via alternate means then why a potential human life should be
destroyed. Research should therefore be focused away from embryos and towards bone
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marrow even if it is more difficult (30). If embryonic stem cells are easier to work with then
new treatments can be discovered more quickly and people suffering currently can be
treated. Again the population faces a dilemma.
Conclusions:
As seen above, stem cells have the potential to be the solution to some of the most harmful diseases on
the planet including cancer and auto-immune diseases. We can see how we can affect the environment
around stem cells to inhibit or stimulate growth; the inhibition can be used to treat cancer that is to
prevent the growth of tumours. Stem cells can be used in many treatments; however they suffer an
immune rejection. Possible solutions have been explored. We know that stem cells can be used to
correct birth defects by making them differentiate into the cells the organ requires and we can control
all these stem cells to become specialised by using genetic switches to make them differentiate into
specific types of cells.
While any of these solutions in the discussion may sound promising there are several issues present that
will have to be investigated. First of all, it is suggested that we use certain chemicals to limit the growth
of stem cells in tumours. These chemicals may also harm other cells in the body and tests will have to
be done to see the effects of these chemicals on all different types of body cells. The use of these
chemicals to inhibit stem cell growth should only be accepted if it is proven that the chemicals have no
harmful effect on any cell in the body since cancer tumours can occur almost anywhere. To prevent
immunological rejection of stem cells, the primary ideas consist of inhibiting the immune system which
would stop the T cells from attacking the stem cells. This weakened immunity may likely make the
individual susceptible to other diseases so this could be quite dangerous. If this is the case, then future
developments should focus on trying to only prevent immune responses against stem cells instead of
inhibiting the whole immune system. Maybe these stem cells should be genetically engineered so that
they display only one type of antigen; an antigen the body recognizes and therefore doesn’t produce an
immune response against. Finally, public support and wider discussion is necessary to explore the moral
and ethical objections to stem cell research.
References:
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1.
en.wikipedia.org/wiki/Autotomy
2.
stemcells.nih.gov/info/basics/pages/basics1.aspx
3.
the-scientist.com/?articles.view/articleNo/40981/title/Stem-Cell-Characterization-Challenges-and-Strategies/ Stem Cell Characterization: Challenges and Strategies
4.
stemcell.com/en/Technical-Resources/964c5/Snapshot-Directed-Differentiation-ofPluripotent-Stem-Cells.aspx
5.
Graf Thomas (Nov 2014), Cell replacement therapies: iPS technology or
transdifferentiation?, www.eurostemcell.org
6.
Martin GR, 1981, Isolation of a pluripotent cell line from early mouse embryos
cultured in medium conditioned by teratocarcinoma stem cells, Current Issue, vol.
78 no. 12
7.
bbc.co.uk/news/health-19869673
8.
thenode.biologists.com/author/jslack/
9.
eurostemcell.org/faq/what-diseases-and-conditions-can-be-treated-stem-cells
10.
bethematch.org/Transplant-Basics/How-transplants-work/Diseases-treatable-bytransplants/
11.
en.wikipedia.org/wiki/Stem_cell
12.
Cressey Daniel, Stem cells take root in drug development, Increasing use by
industry showcases stem cell technology as research tool, www.nature.com
13.
www.nih.gov
14.
globalchange.com/stemcells2.htm
15.
eurostemcell.org/faq/what-are-current-challenges-embryonic-stem-cell-research
16.
explorestemcells.co.uk/OverviewStemCellTherapy.html
17.
spinalcordinjuryzone.com/info/7356/obstacles-facing-stem-cell-research
18.
stemcells.ox.ac.uk/cancer-stem-cells
19.
onlinelibrary.wiley.com/doi/10.1002/jcp.1040910303/abstract;jsessionid=09774392
D20991D3F63AE06219EF88E3.f03t03
20.
nature.com/nature/journal/v336/n6200/abs/336688a0.html
21.
nlm.nih.gov/medlineplus/ency/article/000816.htm
22.
webmd.com/a-to-z-guides/autoimmune-diseases
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23.
biosciencetechnology.com/news/2014/01/overcoming-stem-cell-rejection-immunesystem
24.
onlinelibrary.wiley.com/doi/10.1634/stemcells.2005-0188/full
25.
online.liebertpub.com/doi/abs/10.1089/scd.2008.0091
26.
thelancet.com/journals/lancet/article/PIIS0140-6736(04)16629-4/abstract
27.
ghr.nlm.nih.gov/handbook/howgeneswork/geneonoff
28.
news.utoronto.ca/cell-biologists-discover-switch-key-stem-cell-gene
29.
stemcells.nih.gov/info/pages/ethics.aspx
30.
bbsrc.ac.uk/documents/1007-stem-cell-resourse-edition3-pdf/
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