Q.A patient is suffering from ADA deficiency. Can he be cured? How?

Yes, a patient suffering from ADA deficiency can be cured, and the standard method is gene therapy.

ADA (adenosine deaminase) deficiency is a severe combined immunodeficiency caused by a defect in the gene that produces the ADA enzyme. Without this enzyme, toxic metabolites build up and destroy immune cells, leaving the patient vulnerable to infections.

The cure involves the following steps, as described in the NCERT textbook:

• First, lymphocytes (a type of white blood cell) are taken from the patient's blood and grown in culture outside the body.
• A functional ADA cDNA is introduced into these lymphocytes using a retroviral vector — a retrovirus that has been genetically engineered to carry a normal copy of the human ADA gene.
• The retrovirus inserts the normal ADA gene into the patient's own lymphocytes.
• These genetically corrected lymphocytes are then returned to the patient's body by infusion. …

ADA deficiency, or adenosine deaminase deficiency, is a severe genetic disorder that cripples the immune system. Children born with it lack a working ADA enzyme, leading to a buildup of toxic metabolites that destroy their lymphocytes — the very cells the immune system depends on. Without treatment, even a mild infection can be fatal. The question of whether such a patient can be cured is not just theoretical; it has been answered in practice, though with important caveats.

The NCERT textbook describes a pioneering approach to treating ADA deficiency using gene therapy. The core idea is elegant: instead of merely managing symptoms, you fix the root cause by giving the patient a working copy of the ADA gene. But how do you deliver that gene into the right cells, and make sure it stays active?

The first step is to isolate lymphocytes from the patient's blood and grow them in culture outside the body. Lymphocytes are the cells most affected by ADA deficiency, since the toxic build-up caused by the missing enzyme specifically cripples them.

Once the lymphocytes are in culture, they are infected with a specially engineered retrovirus. This virus has been modified to carry a normal, functional copy of the human ADA gene (as ADA cDNA). Retroviruses are particularly useful here because they have a natural ability to insert their genetic material into the host cell's DNA. So when the virus infects the lymphocytes, it delivers the ADA gene into them, and the cells are now genetically corrected — they can produce the missing enzyme.

These corrected lymphocytes are then infused back into the patient's bloodstream. Once inside the body, they function normally and produce ADA, gradually restoring immune function. …

Method — trace the same lymphocyte-correction pathway used for gene therapy generally, then answer "yes, with a caveat"

1. Isolate lymphocytes from the patient's blood.
2. Correct them outside the body with a retroviral vector carrying a functional ADA gene.
3. Re-infuse the corrected lymphocytes. …