Q.Assertion (A) : A patient of ADA deficiency undergoing treatment for gene therapy requires periodic infusion of genetically engineered lymphocytes. Reason (R) : Lymphocytes are immortal.

The Assertion is true. In the case of ADA deficiency, the first clinical gene therapy treatment involved removing lymphocytes from the patient, introducing a functional ADA gene into them using a retrovirus, and then infusing these genetically corrected lymphocytes back into the patient. Because these corrected cells are not permanent stem cells, they have a finite lifespan and the procedure must be repeated periodically. …

Let’s begin with the context. Severe Combined Immunodeficiency (SCID) caused by adenosine deaminase (ADA) deficiency was one of the earliest targets for gene therapy. The NCERT textbook describes the first successful clinical trial: lymphocytes were taken from the patient, the normal ADA gene was inserted into them using a retroviral vector, and these corrected cells were then infused back into the patient. This is the treatment the assertion refers to.

Now, why must these infusions be periodic? The reason lies in the nature of the cells used. Lymphocytes are a type of white blood cell, but they are not immortal. They have a finite lifespan — they divide, function for a while, and then die. Over time, the population of corrected lymphocytes declines, and the patient’s ADA levels drop again. So the treatment has to be repeated at intervals to maintain a sufficient number of functioning cells.

The reason given in the question — “Lymphocytes are immortal” — is simply incorrect. No normal human cell is immortal. Immortality in cells is a property of cancer cell lines (like HeLa cells) or certain stem cells under specific conditions, but not of ordinary lymphocytes. The NCERT does not state that lymphocytes are immortal; in fact, the need for repeated infusions implicitly confirms their limited lifespan. …