Write short note on Gene therapy.

Explanation

It is technique of genetic engineering to replace a faculty gene by a normal healthy gene in humans. SCID or severe combined immunodeficiency is a hereditary defect in which infants antibody formation due to impairment of components of immune system (T-lymphocytes and Blymphocytes as well in many cases). Children suffering from SCID can die of even ordinary diseases, vaccination and blood transfusion. In 25% of SCID cases, patients have a defective autosomal gene for synthesis of enzyme adenosine deaminase or ADA. In the absence of enzyme, purine metabolism is disturbed and T-lymphocytes fail to function. ADA gene is taken out from leucocytes of a healthy person, amplified and inserted in a retrovirus from where viral genes have been taken out. A helper retrovirus devoid of packing sequence is also prepared . Lymphocyt stem cells from bonemarrow af patient are taken out and injection with the two types of retroviruse , one carrying ADA gene and the other as helper one . The gene begins to express in the stem cells. The cells also possess faulty gene but its effect is now suppresed. The transformed cell which are now healthy stem cells having functional ADA gene are introduced into bone marrow of the pateint . The immune system becomes functional .