Strategies of gene therapy

1. Strategies of gene therapy

2. INTRODUCTION
• Gene therapy is when DNA is introduced into a patient to treat a genetic
disease. The new DNA usually contains a functioning gene to correct the effects
of a disease-causing mutation.
• Gene therapy is a strategy used to treat disease by correcting defective genes or
modifying how genes they are expressed.
• Gene therapy will enable patients to be treated by inserting genes into their
cells rather than administering drugs or subjecting them to surgery.
• A gene that is inserted directly into a cell usually does not function. Instead, a
carrier called a vector is genetically engineered to deliver the gene.
• Gene therapy holds promise for treating a wide range of diseases, such as
cancer, cystic fibrosis, heart disease, diabetes, hemophilia and AIDS.

3. TYPES OF GENE THERAPY
• Somatic gene therapy: transfer of a section of DNA to any cell of the body that
doesn’t produce sperm or eggs. Effects of gene therapy will not be passed onto the
patient’s children. Somatic cells are nonreproductive, Often the effects of somatic
cell therapy are short-lived. Somatic gene therapy can be broadly split into two
categories:
• Ex vivo: where cells are modified outside the body and then transplanted back in
again. cells from the patient’s blood or bone marrow are removed and grown in the
laboratory.
• In vivo: where genes are changed in cells still in the body.

4. • Germline gene therapy: transfer of a section of DNA to cells that
produce eggs or sperm. Effects of gene therapy will be passed onto the
patient’s children and subsequent generations.
• The therapy alters the genome of future generations to come, the use of
germline therapy due to fears over unknown risks and long-term effects
in future generations is inhibited in various countries.
• In addition, the therapy is very costly.

5. Gene therapy using ADENOVIRUS VECTOR
• A gene that is inserted directly into a cell usually does not
function, instead a vector is used i.e. viruses such as
retroviruses, integrate their genetic material (including the new
gene) into a chromosome in the human cell.
• The vector can be injected or given intravenously (by IV)
directly into a specific tissue in the body, where it is taken up by
individual cells.
• If the treatment is successful, the new gene delivered by the
vector will make a functioning protein.

7. Strategies of gene therapy
• Gene augmentation therapy
• Targeted killing of specific cells
• Targeted mutation correction
• Targeted inhibition of gene expression

8. I. GENE AUGMENTATION THERAPY
• It is used to treat diseases caused by a mutation that stops a
gene from producing a functioning product, such as a protein.
• This therapy adds DNA containing a functional version of the
lost gene back into the cell.
• The new gene produces a functioning product at sufficient
levels to replace the protein that was originally missing.
• This is only successful if the effects of the disease are reversible
or have not resulted in lasting damage to the body.

9. • For example, this can be used to treat loss of function disorders such as
cystic fibrosis by introducing a functional copy of the gene to correct the
disease.

10. II.Targeted killing of specific cells
• Artificial cell killing and immune system assisted cell killing have been popular in the
treatment of cancers.
• The aim is to insert DNA into a diseased cell that causes that cell to die.
• Genes are directed to the target cells and then expressed so as to cause cell killing.
• It can be done by two ways:
1. Direct killing: the inserted DNA contains a “suicide” gene that produces a highly toxic
product which kills the diseased cell.
2. Indirect killing: uses immune-stimulatory genes to provoke or enhance an immune
response against the target cell. The inserted DNA causes expression of a protein that
marks the cells so that the diseased cells are attacked by the body’s natural immune
system.

11. • It is essential with this method that the inserted DNA is targeted
appropriately to avoid the death of cells that are functioning normally

12. III. Targeted mutation correction
• The repair of a genetic defect to restore a functional allele.
• Technical difficulties have meant that it is not sufficiently reliable
to warrant clinical trails.
• In principle, it can be done at different levels: at the gene level
or at the RNA transcript level.

13. IV. TARGETED INHIBITION OF GENE
EXPRESSION
• suitable for treating infectious diseases and some cancers.
• The basis of this therapy is to eliminate the activity of a gene
that encourages the growth of disease-related cells.
• If disease cells display an inappropriate expression of a gene
a variety of different systems can be used specifically to block
the expression of a single gene at the DNA, RNA or Protein
levels.

14. • For example, cancer is sometimes the result of the over-activation of an oncogene. So, by
eliminating the activity of that oncogene through gene inhibition therapy, it is possible to
prevent further cell growth and stop the cancer in its tracks.

15. SUCCESSES
• Successes represent a variety of approaches—different vectors, different target
cell populations, and both in vivo and ex vivo approaches for treating a variety
of disorders.
• Immune deficiencies
• Hereditary blindness
• Hemophilia
• Cancer
• Blood disease

16. Immune deficiencies
• Several inherited immune deficiencies have been treated
successfully with gene therapy.
• Most commonly, blood stem cells are removed from patients, and
retroviruses are used to deliver working copies of the defective
genes.
• Severe Combined Immune Deficiency (SCID) and Adenosine
deaminase (ADA) deficiency.

17. Hereditary blindness
• Gene therapies are being developed to treat several different
types of inherited blindness, especially degenerative forms,
where patients gradually lose the light-sensing cells in their
eyes.
• Most gene-therapy vectors used in the eye are based on AAV
(adeno-associated virus).
• In one small trial of patients with a form of degenerative
blindness called LCA (Leber congenital amaurosis), gene
therapy greatly improved vision for at least a few years.

18. Hemophilia and Cancer
• People with hemophilia are missing proteins that help their blood form
clots.
• In a small trial, researchers successfully used an adeno-associated viral
vector to deliver a gene for Factor IX, the missing clotting protein, to
liver cells. After treatment, most of the patients made at least some
Factor IX, and they had fewer bleeding incidents.
• CANCER: herpes simplex 1 virus was used (which normally causes cold
sores) has been shown to be effective against melanoma that has spread
throughout the body.

19. Blood disease
• Patients with beta-Thalassemia have a defect in the beta-globin gene, which
codes for an oxygen-carrying protein in red blood cells.
• In 2007, a patient received gene therapy for severe beta-Thalassemia. Blood
stem cells were taken from his bone marrow and treated with a retrovirus to
transfer a working copy of the beta-globin gene.
• The modified stem cells were returned to his body, where they gave rise to
healthy red blood cells.

20. Challenges of gene therapy
• Delivering the gene to the right place and switching it on.
• Avoiding the immune response.
• Making sure the new gene doesn’t disrupt the function of other genes.
• cost of gene therapy.