Which kind of therapy was given in 1990 to a four-year-old girl with adenosine deaminase (ADA) deficiency?

Gene therapy is the process of introduction of DNA into living human beings in order to treat disease. It is used to replace a missing gene product or to correct mutant alleles permanently. The ex vivo introduction of functional ADA gene in bone marrow cells of the patient, suffering from SCID, through an engineered retrovirus containing a functional ADA gene was followed by reintroduction of treated cells into the patient’s marrow treat the disease permanently.Therefore, the correct answer is option C.