em cells which can be used in the reconstitution of an infant with SCID is the cord blood of unrelated normal infants. In several research studies, it has been shown that saving cord blood samples from normal infants can provide additional resource; as for bone marrow or other stem cell transplants, one attempts to match the donated stem cells to the infant. Restoration of normal cellular immunity occurs three to six months following a successful transplantation, while normal antibody production may take one to three years. During this period, gammaglobulin therapy may be used to provide protection against recurrent pyogenic (pus producing) infections. When successful, this treatment corrects the patient's immune system defect. Recent success rates for this procedure approach 80% for tissue matched bone marrow or stem cell donors. Other approaches to overcoming the patient's immune defect have been reported, but with varying success. One method, for infants or children with adenosine deaminase (an enzyme abbrevated with ADA) deficiency has been to infuse normal red cells which are a source of this enzyme, or treat with a drug called PEG-ADA. Another way to treat SCID, is Gene Therapy. Gene Therapy is only an option when an ADA deficiency is the cause of SCID, (ADA deficiency causes 25% of all SCID cases). Requirements for gene therapy are as follows:•The gene must be identified and cloned• The cloned genes must be inserted in cells that can take up long term residence in the patient. This means removing the patient's own cells, treating them in tissue culture, and then returning them to the patient. •The cloned genes must be inserted in the DNA so that it will be transcribed (DNA -* RNA) and translated (RNA -* Protein) so that useable quantities of the enzyme are produced.When all of these requirements are met, the patient is ready for gene therapy using a retrovirus (a virus whose genome is made up of RNA as o...
