Explain why ADA deficiency gene therapy often requires repeated treatment, while a bone marrow transplant can be a permanent cure.

• A. T lymphocytes have a limited life span; die off
• B. Bone marrow provides continual supply of T lymphocytes
• C. Gene therapy permanently cures ADA deficiency
• D. Repeated treatment is unnecessary

Answer: (B)

The durability of the immune correction depends on where the corrected cells come from and how long they persist. Gene therapy often fixes immune cells like mature T lymphocytes, which have a finite lifespan and die off after weeks to months. Once those corrected cells disappear, the immune system can revert toward the deficient state, so repeated rounds of therapy are needed to replenish them with newly corrected cells.

A bone marrow transplant, on the other hand, introduces donor hematopoietic stem cells that reside in the bone marrow and continually renew the immune system. After successful engraftment, these stem cells keep producing new T lymphocytes and other immune cells for the patient’s life, providing a long-lasting, often permanent cure—as long as engraftment is achieved and complications are managed.