5. What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.
Gene therapy refers to a collection of methods and technologies allowing correction or replacement of a defective or dysfunctional gene. While correcting, a normal gene is transferred into the individual's embryo to replace and perform the function of the original defective gene. One well-established example of gene therapy is ADA deficiency. This is caused by the deletion of a gene encoding for enzyme adenosine deaminase. The gene therapy for ADA deficiency was carried out in a 4-year-old patient by the following method:
1. The lymphocytes of a patient were grown in a culture in vitro.
2. A functional ADA cDNA was introduced in these lymphocytes using a retroviral vector.
3. The transformed lymphocytes were introduced back into the blood of the patient.
4. The patient is regularly infused with transformed lymphocytes
5. For a permanent cure of ADA deficiency, a gene isolated from bone marrow cell is introduced in the patient in the early stage.