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.