Question

Explain the steps in the gene therapy to treat SCID patient.

Answer 1

A form of severe combined immune deficiency (SCID) can result from deletion or defect of the gene for adenosine deaminase (ADA). Without functional ADA, development of T and B lymphocytes is impaired and the patient’s immune system is severely weakened.

Steps in ADA gene therapy:

1. Bone-marrow stem cells that produce lymphocytes are removed from the ADA-deficient patient.
2. A functional ADA gene is cloned using recombinant DNA technology and inserted into a harmless, engineered retroviral vector.
3. The patient’s stem cells are exposed to this retrovirus. The vector delivers the functional ADA gene into the stem-cell chromosomes.
4. The genetically corrected stem cells are returned to the patient’s bone marrow.
5. These cells multiply and produce ADA, helping restore immune function.

Introducing a functional ADA gene into bone-marrow stem cells can provide a lasting source of ADA-producing cells; gene introduction into lymphocytes alone would require periodic infusions.