How ADA deficiency is cured by gene therapy?

ADA deficiency is also called as Adenosine deaminase deficiency. It is an autosomal recessive disorder that causes the immunodeficiency. Treatment includes gene therapy. In this, lymphocytes from the blood of the patient are grown in a culture in vitro. A functional ADA cDNA is introduced into these lymphocytes using a retroviral vector. These lymphocytes are introduced back into the patient. Periodically, this process is repeated. If a functional ADA gene is isolated from bone marrow cells and is introduced at early embryonic stages, the deficiency could be a permanently cured.