Gene therapy is a technique for replacing a faulty gene with a normal one in individuals with fatal or extremely debilitating genetic diseases. The inherent benefit of this therapy is to permanently cure the physiological dysfunction by repairing the genetic defect.
There are two strategies for this therapy: the ex vivo therapy and the in vivo therapy. In ex vivo therapy, the normal gene is cloned in vectors, such as retroviruses (e.g., mouse leukemia virus) or adenoviruses that are infectious but relatively harm-less. Tissues removed from the patient are incubated with these genetically modified viruses to transfect them with the normal gene. The transfected cells are then reintroduced into patient’s body by transfusion. In contrast, the in vivo type of therapy does not have the intermediate step of incubating excised patient tis-sue. Instead, the naked DNA or a virus vector is directly intro-duced into the patient’s tissues.
The first gene therapy experiment in humans was started in 1990 by researchers at the National Institutes of Health, USA. The subject was a 4-year-old girl suffering from a severe immu-nodeficiency disease caused by the lack of enzyme adenosine deaminase (ADA). She was transfused with her own blood cells that had been engineered to contain a functional ADA gene. Later, other children were given the same type of therapy. So far, the children have shown remarkable improvement and continue to be healthy, but the treatment is not permanent and must be repeated. Proper scientific controlled trials are required before induction of it as a routine clinical practice.