In children with ADA deficiency, a functional gene is introduced into lymphocytes using a vector:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Retrovirus
ADA is adenosine deaminase, an enzyme that the immune system needs. A child who lacks it has a weak immune system. In gene therapy, lymphocytes are taken from the patient and grown outside the body. A functional ADA gene is put into them with a vector, and the cells are returned to the patient.
(1) Escherichia coli — Incorrect. This is a bacterium used as a host in cloning. It cannot carry a gene into human lymphocytes.
(2) Retrovirus — Correct. Retroviruses can enter animal cells and put their genes into them. A harmless retroviral vector therefore carries the ADA gene into the lymphocytes.
(3) Bacteriophage — Incorrect. A bacteriophage is a virus that infects bacteria, not human cells.
(4) Agrobacterium — Incorrect. It delivers its T-DNA into plant cells. It is used as a vector for plants.
NCERT Extract:
Gene Therapy – “… As a first step towards gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body. A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are subsequently returned to the patient.”