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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).

(ii)
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.

 

Content

Cloned genes and production of chemicals

 

Human peptide hormone genes

 

 

Insulines

 

 

Somatotropin

 

 

Somatostatin

 

 

b-endorphin

 

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

 

 

Phenylketonuria

 

 

Urokinase

 

 

Thalassaemia

 

 

Hemophilia

 

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. 

Diseases                 

Therapeutic agent

Strategy

Vector

Target cell/tissue

Genetic Disorders

 

 

 

 

Cystic fibrosis

CFTR

In vivo

Adenovirus

Nasal epithelium

Familial hyper-

LDL

In vivo

Cationic lipid

Nasal epithelium

cholesterolaemia

 

 

 

 

SCID

ADS

Ex vivo

Retrovirus

T cells

Haemophilia

Factor VIII/IX

In vivo

Retro virus

Hepatocytes, skin, muscles

DMD

Dystrophin

In vivo

Retrovirus

Skeletal muscles

 

Ex vivo

Retrovirus

Myoblasts

Acquired Disorders

 

 

 

 

Alzheimer's disease

NGF

Ex vivo

Retrovirus

Tumour cells

AIDS

HIV antigen

Ex vivo

Retrovirus

T cells

RevMlO

Ex vivo

Retrovirus

Hepatocyte

Cytokine

Ex vivo

Retrovirus

Hematopoietic stem cells

Cancer

Interleukins,

Ex vivo

Retrovirus

Tumour cells

HSV-TK

Ex vivo

Retrovirus

Tumour cells

HLA-B4

In vivo

Catonic lipid

Tumour cells

Tumour suppressor

In vivo

Catonic lipid

Tumour cells

gene

 

 

 

Cardiovascular

disease

tPA

In vivo

Adenovirus

Tumour cells

Parkinson's

disease

TH

Ex vivo

Retrovirus

Fibroblast

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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