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. |
