Question

Which of the following methods is not used for treating SCID?

• A. Bone marrow transplantation
• B. Enzyme replacement therapy
• C. Gene therapy
• D. Antibody therapy

Answer 1

The correct option is D Antibody therapy

SCID (Severe Combined Immunodeficiency) is caused by a mutation of the gene encoding the enzyme adenosine deaminase (ADA). These patients have non-functional lymphocytes and so they cannot mount immune responses against invading pathogens.

ADA is involved in purine metabolism. When DNA is broken down, it generates a molecule known as deoxyadenosine which is toxic to lymphocytes. The enzyme ADA is crucial for the immune system to function as it is involved in the conversion of this toxic molecule, deoxyadenosine to a non-toxic molecule called deoxyinosine.

The ideal approach for SCID treatment would be to give patients a functional ADA that breaks down toxic biological products. Methods used to treat SCID includes the following:-

• Bone marrow transplantation if we receive a matching bone marrow.
• By enzyme replacement therapy, in which functional ADA is given to the patient by injection.
• Lymphocytes from the blood of the patient are grown in a culture outside the body. A good copy of human gene encoding a functional ADA cDNA is introduced into the lymphocytes (collected from patients) by using retroviral vectors, which are subsequently returned to the patient.
• Gene producing ADA is isolated from donor's bone marrow cells and introduced into patient's cells at early embryonic stage.