Biology · Ch 10 — Biotechnology and Its Applications
Gene Therapy
Gene Therapy
The Idea Behind Gene Therapy
If a person is born with a hereditary disease, can anything be done to correct it? Gene therapy is the attempt to do exactly that. It is a collection of methods that allow a gene defect — diagnosed in a child or even in an embryo — to be corrected. The core idea is to insert a normal, functional gene into the person’s cells and tissues so that it takes over the function of the defective gene and compensates for it.
The First Success: ADA Deficiency
The first clinical gene therapy was given in 1990 to a four-year-old girl suffering from adenosine deaminase (ADA) deficiency. ADA is an enzyme crucial for the proper functioning of the immune system. The disorder is caused by the deletion of the gene that codes for this enzyme.
Before gene therapy, two treatments existed for ADA deficiency, but neither was completely curative:
- Bone marrow transplantation — works for some children.
- Enzyme replacement therapy — functional ADA is injected into the patient.
Both approaches manage the disease but do not provide a permanent cure.
How the First Gene Therapy Was Done
The procedure used for the 1990 case was a landmark. Here is the step-by-step process:
- Lymphocytes (a type of white blood cell) were taken from the patient’s blood.
- These cells were grown in culture outside the body.
- A functional ADA cDNA was introduced into these lymphocytes using a retroviral vector (a disabled virus that carries the gene into the cell).
- The genetically engineered lymphocytes were then returned to the patient.
The lymphocytes used in this method are not immortal — they have a limited lifespan. Therefore, the patient requires periodic infusion of such genetically engineered lymphocytes to maintain the effect. This is not a one-time cure.