2. Introduction
• Gene therapy may be defined in broad general terms as introduction of a normal
functional gene into cells which contain the defective allele of concerned gene with
the objective of correcting a genetic disorder or an acquired disorder
• The meaning of gene therapy has now been made much broader to include
attempts to cure any disease by the introduction of cloned gene into the patient
• The first approved gene therapy experiment occurred on September 14,1990 in US
when ASHANTI DESILVA was treated for ADA-SCID
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4. Germ line gene therapy
• Therapeutic gene are transferred to the germ cells i.e. sperm and eggs
• Therefore the change due to this therapy would be heritable and would be
passed on to later generations
• For safety,ethical and technical reasons it is not being attempted at present
5. Somatic cell gene therapy
• Therapeutic genes are transferred into somatic cells i.e. bone marrow
cells,blood cells,skin cells etc
• It affects only the targeted cells in the patient and does not pass on to future
generations
• It is short lived because the cells of most tissues ultimately die and are
replaced by new cells
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8. In vivo gene therapy
• Direct delivery of therapeutic gene into the target cell into patient’s body.it is
carried out by viral and non viral vector systems
• It can be the only option in patients where individual cells can not be
cultured in vitro in sufficient numbers(e.g.-brain cells)
• In vivo gene transfer is necessary when cultured cells can not be re implanted
in patients effectively
9. Vectors in gene therapy
• To transfer a desired gene into a target cell a carrier is required ,such vehicles
of gene delivery is known as vectors
• There are two main classes of vectors
viral vectors
non viral vectors
10. Viral vectors
• Viruses have evolved a way of encapsulating and delivering their genes into
human cells in pathogenicmanner.scientists have tried to harness this ability
by manipulating the viral genome to remove disease causing genes and insert
therapeutic ones
11. i. Retrovirus vector system: the recombinant retrovirus have the ability to
integrate into the host genome in a stable fashion and can carry a DNA of
size less than 3.4 kb
ii. Adenovirus vector system : adenoviruses are large linear double stranded
DNA viruses that are commonly used for preparing gene transfer vectors
.these vectors are known to be the second most gene delivery vector for
gene therapy of various diseases llike cystic fibrosis and certain types of
cancer
iii. Herpex simplex vector system: viruses which have natural tendency to
infect a particular type of cell.they infect and persist in nervous cells
12. Non viral vectors
• Methods of non viral gene delivery have also been explored using
physical(carrier free gene delivery) and chemical approaches(synthetic vector
based gene delivery)
13. I. Pure DNA constrict: direct introduction of pure DNA construct into
target tissue ,efficiency of DNA uptake by cells and expression in rather
low and consequently large quantities of DNA have to be injected
periodically
II. DNA molecular conjugates: commonly used synthetic conjugate is poly-l-
lysine bound to specific target cell receptor ,therapeutic DNA is then made
to combine with the conjugate to form a complex .it avoids lysosomal
breakdown of DNA
III. Lipoplexes: these are lipid-DNA complexes ,DNA construct surrounded
by artificial lipid layer.most of it gets degraded by lysosomes
14. Human artificial chromosome: can carry a large DNA i.e. with one or more
therapeutic genes with regulatory elements
15. Methods of gene delivery
• Gene gun: employs a high-pressure delivery system to shoot tissue with gold
or tungsten particles that are coated with DNA
• Microinjection: process of using a glass micropipette to insert microscopic
substances into a single living cell.it is normally performed under a
specialized optical microscope setup called a micromanipulator
16. Chemical methods
• Using detergent mixtures: certain charged chemical compounds like calcium
phosphates are mixed with functional cDNA of desired function.the mixture
is introduced near the vicinity of recipient cells , the chemical disturbs the
cell membrane and widens the pore size ana allows cDNA to pass through
the cell
• Lipofection: it is a technique used to inject genetic materials into cell by
means of liposomes
17. Other types of gene therapy
• Gene augmentation therapy: most common gene therapy ,in this foreign
gene replaces missing or defective genes for e.g. replacement of defective
p53 gene by a normal one in liver cancer
• Gene inhibition therapy: done to block the overproduction of some proteins
18. Success cases of gene therapy
• Gene therapy cures blindness: cure blindness of inherited condition
• Leber’s congenital amaurosis-inherited disease caused by an abnormality in
gene called RPE65 ,the condition appears at birth or in the first few months
of life and causes progressive worse and loss of vision
• Gene therapy reduces Parkinson’s disease symptoms: it significantly improves
the weakness of the symptoms such as tremors,motor skill problems and
rigidity
• Done with local anesthesia,used a harmless inactive virus (AAV-2)
19. Advantages
• Gene therapy has the potential to eliminate and prevent hereditary diseases
such as cystic fibroses,ADA-SCID etc.
• It is a possible cure for heart disease,AIDS and cancer
• It gives someone born with a genetic disease a chance to life
• It can be used to eradicate diseases from future generations
20. Disadvantages
• Long lasting therapy is not achieved by gene therapy ,due to rapid dividing
cells benefits of gene therapy is short lived
• Immune response to transferred gene stimulates a potential risk to gene
therapy
• Disorders caused by multiple genes can not be treated effectively using gene
therapy
• The cost is very high and the patient might need an insurance to cover the
treatment
21. Recent developments
• In a new gene therapy method developed by university of florida in jan
2012,researchers found treatment for a common form of blindness (X-
linked retinitis pigmentosa ) that strikes both youngsters and adults
• A gene therapy called NLX-P-101 dramatically reduces movement
impairment in Parkinson’s patients,according to a result of a phase 2 study
published on march 2011 in the journl lancet neurology
