Download Lec 19 Molecular Therapeutics

Lec 19
Molecular Therapeutics
Shah Rukh Abbas, PhD
I. Stem cells
• Unspecialised cells lacking any tissue-specific structure
• Can give rise to specialised cells through the process of
differentiation
• Stem cells are the raw material from which all of the
body’s mature, differentiated cells are made.
• A cell that has the ability to continuously divide and
differentiate (develop) into various other kind(s) of
cells/tissues
Kinds of Stem Cells
Cell type
Description
Totipotent
Each cell can develop into a
new individual
Pluripotent*
Cells can form any (over 200)
cell types
Multipotent*
Cells differentiated, but can
form a number of other
tissues
Examples
Cells from early (1-3
days) embryos
Some cells of
blastocyst (5 to 14
days)
Fetal tissue, cord
blood, and adult stem
cells
*The pluripotent stem cells are in fact derived from totipotent stem cells. The
pluripotent stem cells can develop into any cell type except for the extraembryonic tissue.
*Multipotent progenitor cells can give rise to many but limited types of cell.
For example, a hematopoietic cell can give rise to several types of blood cells
(i.e. red blood cells, white blood cells, platelets, etc.)
Totipotent Stem Cells
Day 2
2-cell embryo
Day 1
Fertilized egg
Day 11-14
Tissue Differentiation
Day 3-4
Multi-cell embryo
Day 5-6
Blastocyst
Multipotent Stem Cells
Stem Cell types: Origin
Stem Cells comprise the following Types
1. Embryonic Stem Cells
2. Fetal Stem Cells
3. Umbilical Stem Cells
4. Adult Stem Cell
A human embryo is considered fetus 8 weeks after the egg is fertilized
1- Embryonic Stem Cells
• Usually they are pluripotent cells
• Most valuable as it can become into any type
• 1998 first human embryonic cell was grown during in
vitro fertilization (IVF) where extra embryos that are not
implanted are frozen
Embryonic Stem Cells
Intra cytoplasmic sperm injection
2- Fetal Stem Cells
• These are also pluripotent
• Fetus brain tissue
• They are excellent source of cells for adults with Parkinson’s
disease
3- Umbilical Stem Cells
• The cells from cord blood are multipotent stem cell.
• They can naturally develop into blood cells and immune cells
• Cord blood cells are highly suitable because they have less
rejection.
• They also lack mature immune cells that can attack the
recipient body.
• Cord cells can be store and it can be denoted by woman after
giving birth.
• Cord blood bank
4- Adult Stem Cell
•
•
•
•
Numerous multipotent adult stem exist in body
Can develop into cells of specific types of the tissue
These are least plastic in term of differentiation
Much research is focused in this area
Application of Stem Cells
Induced pluripotent stem cells (iPS cells)
‘genetic reprogramming’
= add certain genes to the cell
adult cell
induced pluripotent stem (iPS) cells
behave like embryonic stem cells
differentiation
culture iPS cells
in the lab
all possible types of
specialized cells
Advantage: no need for embryos!
1 Remove skin cells
from patient.
2 Reprogram skin cells
so the cells become
induced pluripotent
stem (iPS) cells.
Patient with
damaged heart
tissue or other
disease
3 Treat iPS cells so
that they differentiate
into a specific
cell type.
4 Return cells to
patient, where
they can repair
damaged tissue.
2. Gene Therapy
Gene
•
Are carried on a chromosome
•
The basic unit of heredity
•
Encode how to make a protein
– DNARNA proteins
•
Proteins carry out most of life’s function.
•
When altered causes dysfunction of a protein
•
When there is a mutation in the gene, then it will change the codon, which
will change which amino acid is called for which will change the conformation
of the protein which will change the function of the protein. Genetic
disorders result from mutations in the genome.
Gene Therapy
• It is a technique for correcting defective
genes that are responsible for disease
development
• There are four approaches:
1. A normal gene inserted to compensate for a
nonfunctional gene.
2. An abnormal gene traded for a normal gene
3. An abnormal gene repaired through selective
reverse mutation
4. Change the regulation of gene pairs
• Gene therapy is the alteration of an afflicted
individual’s genes
• Gene therapy holds great potential for treating
disorders traceable to a single defective gene
• Vectors are used for delivery of genes into specific
types of cells, for example bone marrow
• Gene therapy provokes both technical and ethical
questions
The First Case
• The first gene therapy was performed on
September 14th, 1990
– Ashanti DeSilva was treated for SCID
• Sever combined immunodeficiency
– Doctors removed her white blood cells,
inserted the missing gene into the WBC, and
then put them back into her blood stream.
– This strengthened her immune system
– Only worked for a few months 
How It Works
• A vector delivers the therapeutic gene into
a patient’s target cell
• The target cells become infected with the
viral vector
• The vector’s genetic material is inserted
into the target cell
• Functional proteins are created from the
therapeutic gene causing the cell to return
to a normal state
Cloned gene
1 Insert RNA version of normal allele
into retrovirus.
Viral RNA
Retrovirus
capsid
2 Let retrovirus infect bone marrow cells
that have been removed from the
patient and cultured.
3 Viral DNA carrying the normal
allele inserts into chromosome.
Bone
marrow
cell from
patient
4 Inject engineered
cells into patient.
Bone
marrow
Problems with Gene Therapy
•
•
•
•
•
Short Lived
– Hard to rapidly integrate therapeutic DNA into genome and rapidly
dividing nature of cells prevent gene therapy from long time
– Would have to have multiple rounds of therapy
Immune Response
– new things introduced leads to immune response
– increased response when a repeat offender enters
Viral Vectors
– patient could have toxic, immune, inflammatory response
– also may cause disease once inside
Multigene Disorders
– Heart disease, high blood pressure, Alzheimer’s, arthritis and
diabetes are hard to treat because you need to introduce more than
one gene
May induce a tumor if integrated in a tumor suppressor gene because
insertional mutagenesis
Recent Developments
• Genes get into brain using liposomes coated in polymer
call polyethylene glycol
– potential for treating Parkinson’s disease
• RNA interference or gene silencing to treat Huntington’s
– siRNAs used to degrade RNA of particular sequence
– abnormal protein wont be produced
• Create tiny liposomes that can carry therapeutic DNA
through pores of nuclear membrane
• Sickle cell successfully treated in mice