Download Gene therapy- Methods, Status and Limitations

Gene therapy- Methods, Status
and Limitations
Methods of gene delivery (therapeutic
constructs)
It Includes two methods:
•Nonviral gene-delivery systems
•Virus-Mediated gene-delivery
systems
Non viral gene-delivery
systems
• Naked DNA injection
• Gene gun
• Lipofection
Naked DNA gene therapy
•This is the simplest method i.e.
the direct introduction of
therapeutic DNA into target
cells.
•Very cheap.
Microprojectile gene transfer (gene guns)
therapy
Gene transfer through
Liposomes
•Positively charged lipid droplets can
interact with negatively charged DNA
to wrap it up and deliver to cells.
•Inside liposomes DNA is resistant to
degradation and is capable of passing
the DNA through the target cell's
membrane.
•Used in cystic fibrosis, cancer,
parkinson’s disease.
Therapeutic drugs
Non viral gene-delivery
systems
Advantages:
• DNA can be of any size
• Non-infectious and
• Can’t replicate; no inflammatory
response
Disadvantages:
• low efficiency
• non-specific
Virus-mediated gene-delivery systems
• Include Biological vehicles (vectors) such as viruses
and bacteria.
• Viruses are currently the most efficient means of
gene transfer.
• Viruses attack their hosts and introduce their genetic
material containing genetic material into the host cell
as part of their replication cycle.
Some viral vectors used in
gene therapy are:
•
Retroviruses
• Adenoviruses
• Adeno-associated viruses
• Herpes simplex virus
Single most optimal vector for all gene
therapies
• No optimal gene therapy vector.
• Different sites on the body requires
different vectors
different durations of treatment .
• For example
treatment of cancer requires short-term efficiency,
just enough to kill the cancer cells;
whereas,
treatment of Huntington's disease would likely
require life-long gene expression from a single
injection.
Genetic Defects that are Candidates
for Gene Therapy
Successful Gene Therapy for
Severe Combine Immunodeficiency
• SCID caused by a number of defects:
Example:
ADA (adenosine deaminase) gene defect.
X – linked SCID.
• Lack of functional lymphocytes.
• No T-cell dependent antibody response.
• Block the DNA Synthesis.
• No cell mediated immune response.
SCID: Ex vivo gene therapy
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 
Photo courtesy of Van de Silva
Gene Therapy Successes
Ashanti de Silva
successfully treated for
ADA deficiency - 1990
Ryes Evans successfully
treated for SCID - 2001
Current status in GT
• August 30,2006, Researchers at the National
Cancer Institute (NCI), part of the National
Institutes of Health, successfully reengineer
immune cells, called lymphocytes, to target and
attack cancer cells in patients with advanced
metastatic melanoma.
• May 1, 2007): A team of British doctors from
Moorfields Eye Hospital and University College in
London conduct first human gene therapy trials to
treat Leber's congenital amaurosis, a type of
inherited childhood blindness caused by a single
abnormal gene.
• 28 April 2008, UK researchers from the UCL
institute of Opthalmology and Moorfields Eye
Hospital NIHR Biomedical research centre have
announced results of World’s first gene therapy for
inherited bilndness .
Current status in GT in India
• Very little gene therapy work being done in India
• Metro heart Institute in Noida is used the GT in
production of vascular endothelial growth
protein.
• Indian dept. of Bio-tech. has been given the
permission to use the GT for treat renal cell
carcinoma, colon, breast, & lung cancer by
country’s regulators
Hurdles In Gene Therapy
• Short lived nature of gene therapy
• Immune response
• Problems with viral vectors
• Insertional mutagenesis.
Major Problems that Scientists Must
Overcome
• Identify more efficient ways to deliver the genes
to the patients’ genetic material
• Develop vectors that can specifically focus on the
targeted cells
• Ensure that vectors will successfully insert the
desired genes into each of these target cells
• Deliver genes to a precise location in the
patient’s DNA
• Ensure that transplanted genes are
precisely controlled by the body’s normal
physiologic signals