MP Board · Class 12 · Biology · Biotechnology and its ApplicationsWhat is gene therapy? Describe the first clinical gene therapy given in 1990 with steps and limitations.

Gene therapy is a collection of methods that allows correction or replacement of a defective gene that has been diagnosed in a child or embryo. Here, genes are inserted into a person's cells and tissues to treat a disease. Correction of a genetic defect involves delivering a normal gene into the individual or embryo to take over the function of and compensate for the non-functional gene. \nThe first clinical gene therapy was given in 1990 to a 4-year-old girl with Adenosine Deaminase (ADA) deficiency. ADA deficiency is caused due to the deletion of the gene for coding adenosine deaminase enzyme. This enzyme is crucial for the proper functioning of the immune system. \nSteps involved in the treatment:

1. In some children, ADA deficiency can be cured by bone marrow transplantation, while in others it can be treated by enzyme replacement therapy, but these are not completely curative.
2. In gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body.
3. A functional human ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes.
4. These genetically engineered lymphocytes are subsequently returned to the patient's body.
5. Since these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes. \nLimitations of this approach:
6. If the gene is isolated from bone marrow cells producing ADA can be introduced into cells at early embryonic stages, it could be a permanent cure.
7. The treatment is not completely permanent because lymphocytes have a limited lifespan, requiring repeated treatments.
8. Retroviral vectors used for gene transfer sometimes pose a risk of insertional mutagenesis or unintended activation of oncogenes.