Types of gene therapy

All the gene therapy are done on human and can be done in human and classified into following four types.

(1)Somatic gene therapy:­- The genetic defects are corrected in somatic cells of the body. It was initially formulated for the treatment of monogenetic defects, but now holds promises for a wide range of disorders such as cancer, neurological disorders, heart diseases and infectious diseases(Table 1).sufficient expertise in performing successful gene transfer in somatic cells is required before carrying out gene manipulation in human.

Fig:- DNA 

Table 1.Genetic disorder and acquired diseases amenable to gene therapy.

 

Diseases		Therapeutic  agent	Strategy	Vector	Target cell/tissue
Genetic disorder
Cystic fibrosis		CFTR	In vivo	Adenovirus	Nasal epithelium
Familial hypercholesterolaemia		LDL	In vivo	Cationic lipids	Nasal epithelium
SCID		ADA	Ex vivo	Retrovirus	T cell
Heamophilia		Factor 8/9	In vivo	Retrovirus	Hepatocytes,skin,muscles
DMD		Dysterophine	In vivo	Retrovirus	Skeletal muscles
Acquired disorder
Alzheimer’s disease		NGF	Ex vivo	Retrovirus	Tumour cells
AIDS		HIV agent	Ex vivo	Retrovirus	T cells
		RevM10	Ex vivo	Retrovirus	Hepatocyte
Cancer		Cytokine	Ex vivo	Retrovirus	Hepatopoitic stem cells
		Interleukins,	Ex vivo	Retrovirus	Tumour cells
		HSV-TK	Ex vivo	Retrovirus	Tumour cells
		HLA	In vivo	Cationic lipid	‘’
		Tumour suppressor gene	In vivo	Cationic lipid	‘’
Cardiovascular disease	tPA		In vivo	Adenovirus	Tumour cells
Parkinson’s disease	TH		Ex vivo	Retrovirus	Fibroblast

 CFTR, cystic fibrosis transmembrane regulator, SCID, sever combined immunodeficiency syndrome ,DMD , duchennne muscular systrophy, ADA, adenosine deaminase; HSV-TK, herpes simplex virus thymidine virus, NGF, nerve growth factor TH, tyrosine hydroxylase, tPA, tissue plasmogen activator.

(2) Germ line gene therapy. The functional gene are introduce into the germ cell for correction of genetic defects in the offspring. This therapy is being carried out in laboratory and farm animals. However,  it has not been attempted in humans due to technical and ethical problems. One of this type is embryo therapy where embryos are diagnosed for genetic defects. If any such disease is present the patient are adevised for embryo therapy or abortion. In young embryo a functional gene is transferred through microinjection technique.

(3)  enhancement genetic engineering. This type of gene transfer is done for the improvement of a specific trait in animals; for example introduction of growth hormone gene in to increase height. It is being carried out in laboratory and farm animals.

(4) Eugenic genetic engineering. Novel gene can be introduced in humans to alter or improve complex trait such as intelligence and personality. This type of therapy is not being attempted in humans because it is far away from technical capabilities, and ethical problems.

In 1990, for the first time , Michal Blease and w.french Andresco of national institute of health,Bethesda , U.S.A attempted gene therapy on a human patient. A four year old girl was suffering from ‘severe combined immunodeficiency’(SCID). This disease is caused by a faulty gene which express the enzymes adenosine deaminase (ADA). Deficiency of ADA result in the production of chemical which selectively distroyes the T- and B-cells of immune system. Finally, the patient die. The scientist finally introduce a healthy ADA gene in the body of girl who protect her immune system from damage. This successful trail has given the signal for the draw of new era in the field of medical science.

 

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