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  Section: General Biotechnology / Genes & Genetic Engineering
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Genetic Engineering for Human Welfare


Gene Therapy
There are many diseases which can be cured by using specific medicine synthesized biochemically. Now-a-days techniques have been developed to produce recombinant therapeutic biochemicals, for example, insulin, interferon, somatotropin, somatostatin, endorphin, human blood clotting factor VIII:C, immunogenic proteins, etc. Several companies viz., Eberstadt & Co. (New York), E. Lily (USA), National Pituitary Agency (USA), Kabi Vitrum AB (Sweden), Genetech Co (USA), Biogen (Switzerland), Hybritech (USA), Astra Research Center (India), etc. are producing or trying to produce on mass scale to make available at low cost.

However, after 1975, a remarkable advancement in recombinant DNA technology has occurred and accumulated such knowledge that has made possible to transfer genes for treatment of human diseases. Several protocols have been developed for the introduction and expression of genes in humans, but the clinical efficiency has to be demonstrated conclusively. Success of gene therapy depends on the development of better gene transfer vectors for sustained, long term expression of foreign gene as well as a better understanding of gene physiology of human diseases (Rangarajan and Padmanaban, 1996).

Genes are the ultimate molecular switches that control various cellular process. The abnormal gene expression can manifest in the form of specific genetic disorders. Until the last decade, delivering genes into humans to correct diseases has been accepted as scientifically viable and recognized as an independent discipline and christened 'gene therapy'.

The ultimate goal of gene therapy is the gene replacement therapy. Gene replacement therapy permits physiological regulation of the transgenes and elimination of the possibility of insertional activation of other cellular genes which occur at the time of random integration of the foreign gene. At present the current strategy for gene therapy largely centers around gene augmentation therapy, where the foreign gene replaces the detective or missing gene.

Overall, there are two gene transfer strategies: (i) the in vivo approach which involves introduction of genes directly into the target organs of an individual (it is done in patients therefore, also called patient therapy), (ii) ex vivo approach where cells are isolated for gene transfer in vitro followed by transplantation of genetically modified cells back into the patients (Verma. 1990).

Types of gene therapy
All the gene therapies that can be done in humans can be classified into the following four types :

(i) 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 5.2). Sufficient expertise in performing successful gene transfer in somatic cells is required before carrying out gene manipulation in humans (Anderson, 1992).

Germ-line gene therapy. The functional genes are introduced into the germ cells 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 its types is the embryo therapy where embryos are diagnosed for genetic defects. If any such disease is present the patients are advised for embryo therapy or abortion. In young embryo a functional gene is transferred through microinjection technique (Mandal, 1988).

(iii) 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 to increase height. It is being carried out in laboratory and farm animals.



Cloned genes and production of chemicals


Human peptide hormone genes














Human interferon genes


Genes for vaccines



Vaccine for hepatitis-B virus



Vaccines for Rabies virus



Vaccines for poliovirus



Vaccine for foot and mouth disease virus



Vaccines for small pox virus



Malaria vaccines



DNA vaccines


Genes associated with genetic diseases














Enzyme engineering


Commercial chemicals

Prevention, diagnosis and cure of diseases


Prevention of diseases


Diagnosis of diseases



Parasitic diseases



Monoclonal antibodies



Antenatal diagnosis


Gene therapy



Types of gene therapy



Methods of gene therapy



Success of gene therapy



Potential of gene delivering system



Future needs of gene therapy in India

DNA profiling (fingerprinting)


Methods of DNA profiling


Application of DNA profiling



Genetic databank



Reuniting the lost children



Solving disputed problems of parentage, identity of criminals, rapists, etc



Immigrant dispute


Hurdles of DNA profiling

Animal and plant improvement


Transgenic Farm Animals


Crop Improvements



Transgenic plants



Nif gene transfer



Phaseolin gene transfer



Conversion of C3 plants to C4 plants



Herbicide resistant plants



Insect pest resistant plants



Plant improvement through genetic transformation


Crop Protection



Use of antagonists



Use of insecticides

Abatement of pollution

Table 5.2. Genetic disorders and acquired diseases amenable to gene therapy. 


Therapeutic agent



Target cell/tissue

Genetic Disorders





Cystic fibrosis


In vivo


Nasal epithelium

Familial hyper-


In vivo

Cationic lipid

Nasal epithelium








Ex vivo


T cells


Factor VIII/IX

In vivo

Retro virus

Hepatocytes, skin, muscles



In vivo


Skeletal muscles


Ex vivo



Acquired Disorders





Alzheimer's disease


Ex vivo


Tumour cells


HIV antigen

Ex vivo


T cells


Ex vivo




Ex vivo


Hematopoietic stem cells



Ex vivo


Tumour cells


Ex vivo


Tumour cells


In vivo

Catonic lipid

Tumour cells

Tumour suppressor

In vivo

Catonic lipid

Tumour cells








In vivo


Tumour cells




Ex vivo



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

(iv) Eugenic genetic engineering. Novel genes can be introduced in humans to alter or improve complex traits such as intelligence and personality. This type of therapy is not being attempted in humans because it is far beyond our technical capabilities, and ethical problems.

In 1990, for the first time, Michaele Blease and W. French Andresco of National Institute of Health, Bethesda, U.S.A. attempted gene therapy on a human patients. A four year old girl was suffering from 'severe combined immunodeficiency' (SCID). This disease is caused by a faulty gene which expresses the enzymes adenosine deaminase (ADA). Deficiency of ADA results in the production of a chemical which selectively destroys the T- and (3-cells of the immune systems. Finally, the patients die. The scientists introduced a healthy ADA gene into the body of the girl who protected her immune system from damage. This successful trial has given the signal for the dawn of a new era in the field of medical sciences.


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