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Human Gene Therapy : A Brief Overview of the …

JAPI february 2013 VOL. 61 41. Review Article Human gene Therapy : A Brief Overview of the Genetic Revolution Sanjukta Misra*. Abstract Advances in biotechnology have brought gene Therapy to the forefront of medical research. The prelude to successful gene Therapy the efficient transfer and expression of a variety of Human gene into target cells has already been accomplished in several systems. Safe methods have been devised to do this, using several viral and no-viral vectors. Two main approaches emerged: in vivo modification and ex vivo modification. Retrovirus, adenovirus, adeno-associated virus are suitable for gene therapeutic approaches which are based on permanent expression of the therapeutic gene .

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1 JAPI february 2013 VOL. 61 41. Review Article Human gene Therapy : A Brief Overview of the Genetic Revolution Sanjukta Misra*. Abstract Advances in biotechnology have brought gene Therapy to the forefront of medical research. The prelude to successful gene Therapy the efficient transfer and expression of a variety of Human gene into target cells has already been accomplished in several systems. Safe methods have been devised to do this, using several viral and no-viral vectors. Two main approaches emerged: in vivo modification and ex vivo modification. Retrovirus, adenovirus, adeno-associated virus are suitable for gene therapeutic approaches which are based on permanent expression of the therapeutic gene .

2 Non-viral vectors are far less efficient than viral vectors, but they have advantages due to their low immunogenicity and their large capacity for therapeutic DNA. To improve the function of non-viral vectors, the addition of viral functions such as receptor mediated uptake and nuclear translocation of DNA may finally lead to the development of an artificial virus. gene transfer protocols have been approved for Human use in inherited diseases, cancers and acquired disorders. In 1990, the first successful clinical trial of gene Therapy was initiated for adenosine deaminase deficiency. Since then, the number of clinical protocols initiated worldwide has increased exponentially.

3 Although preliminary results of these trials are somewhat disappointing, but Human gene Therapy dreams of treating diseases by replacing or supplementing the product of defective or introducing novel therapeutic genes. So definitely Human gene Therapy is an effective addition to the arsenal of approaches to many Human therapies in the 21 st century. Introduction An abnormal gene could be swapped for a normal gene homologous recombination J ames Watson was quoted as saying we used to think that our fate was in our stars, but now we know, in large measures, our fate is in our genes . Genes, the functional unit of heredity, An abnormal gene could be repaired through selective reverse mutation are specific sequences bases that encode instructions to make Regulation (degree to which a gene is turned on or off) of proteins.

4 Although genes get a lot of attentions, it is the proteins a particular gene could be altered that perform most life functions. When genes are altered, gene Therapy states and remains an experimental discipline encoded proteins are unable to carry out their normal functions, and many researches remain to be performed before the resulting in genetic disorders. gene Therapy (use of genes as treatment will realize its potential. Majority of the gene Therapy medicines) is basically to correct defective genes responsible for trials are being conducted in United States and Europe, with genetic disorder by one of the following approaches-1,2 only a modest number in other countries including Australia.

5 A normal gene could be inserted into a nonspecific location Scope of this approach is broad with potential in treatment of within the genome to replace the Nonfunctional gene (most diseases caused by single gene recessive disorders (like cystic common) fibrosis, hemophilia, muscular dystrophy, sickle cell anemia Infectious etc), acquired genetic diseases such as cancer and certain viral diseases infections like AIDS,3,4 as shown in Figure 1. Monogenic Other gene Therapy projects are targeted at conditions such 10% diseases as heart disease, diabetes mellitus, arthritis and Alzheimer's disease, all of which involve genetic susceptibility to 14%.

6 Table 1 shows a summary of approved current clinical gene Therapy protocols 6%. Other Historical Perspectives 70%. diseases Since the earliest days of plant and animal domestication, about 10,000 years ago, humans have understood that Cancer characteristics traits of parents could be transmitted to their offspring. The first to speculate about how this process worked were ancient Greek scholars, and some of their theories remained Fig. 1 : Proportion of protocol for Human gene Therapy trials relating in favor for several centuries. The scientific study of genetics to various types of diseases52. began in 1850s, when Austrian monk Gregor Mendel, in a *.

7 Asst. Professor, Dept. of Biochemistry, Institute of Medical Sciences series of experiments with green peas, described the pattern and SUM Hospital, Bhubaneswar 751 003, Orissa of inheritance, observing that traits were inherited as separate Received: ; Revised: ; Accepted: units we know as genes. Mendel's work formed the foundation JAPI february 2013 VOL. 61 127. 42 JAPI february 2013 VOL. 61. Table 1 : Summary of approved and published current clinical gene Therapy protocols50. Disorder Objective Target cells Mode of delivery Countries with protocols ADA deficiency ADA replacement Blood Retrovirus Italy, the Netherlands, United States Alpha-1-antitrypsin Alpha-1-antitrypsin Respiratory epithelium Liposome United States deficiency replacement AIDS Antigen presentation HIV Blood, marrow Blood, Retrovirus United States inactivation marrow Cancer Immune function Blood, marrow, tumour Retrovirus, liposome, Austria, China, France, enhancement electroporation, cell- Germany, Italy, the mediated transfer Nethelands, United States Tumour ablation Tumour Retrovirus.

8 Non-complexed United States DNA, cell-mediated transfer Chemoprotection Blood, marrow Retrovirus United States Stem-cell marking Blood, marrow, tumour Retrovirus Canada, France, Sweden, United States Cystic fibrosis Cystic fibrosis Respiratory epithelium Adenovirus, liposome United Kingdom, United transmembrane regulatory States enzyme replacement Familial Replacement of low-density- Liver Retrovirus United States hypercholesterolemia lipoprotein receptors Fanconi's anemia Complement group C gene Blood, marrow Retrovirus United States delivery Gaucher's disease Glucocerebrosidase Blood, marrow Retrovirus United States replacement Hemophilia B Factor IX replacement Skin fibroblasts Retrovirus China Rheumatoid arthritis Cytokine delivery Synovium Retrovirus United States for later scientific achievements that heralded the era of modern technical difficulties and ethical reasons make it unlikely genetics.

9 But little was known about the physical nature of genes that germ line Therapy would be tried in Human beings in until 1950s, when American biochemist James Watson and British near future. biophysicist Francis Crick developed their revolutionary model 2. Somatic gene Therapy :8 where therapeutic genes are transferred of double stranded DNA helix. Another key breakthrough into the somatic cells of a patient. Any modifications and came in the early 1970s, when researchers discovered a effects will be restricted to the individual patient only and series of enzymes that made it possible to snip apart genes at will not be inherited by the patients offspring or any later predetermined site along a molecule of DNA and glue them back generation.

10 Together in a reproducible manner. Those genetic advances set gene delivery the stage for the emergence of genetic engineering, which has produced new drugs and antibodies and enabled scientists to In most gene Therapy studies, a normal gene is inserted into contemplate gene Therapy . A few years after the isolation of genes the genome to replace an abnormal, disease causing gene . Of from DNA, gene Therapy was discovered in all challenges, the one that is most difficult is the problem of gene delivery how to get the new or replacement gene into Process of gene Therapy the patient's target cells. So a carrier molecule called vector must be used for the above The ideal gene delivery Approach vector should be very specific, capable of efficiently delivering The process of gene Therapy remains complex and many one or more genes of the size needed for clinical application, techniques need further developments.


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