why is the introduction of genetically enginered lymphocyte into an ada deficiency patient not apermanent cure ? suggest a possible permanent cure

The introduction of genetically engineered lymphocyte into an ADA (Adenosine Deaminase) deficiency patient is not a permanent cure as applying this technique for once is not sufficient. The deficiency needs several periodic infusions of such lymphocytes as these cells cannot survive long.

If the gene producing Adenosine Deaminase is isolated from bone marrow and is introduced into the cells of an organism in early embryonic cells, it can be a permanent cure of ADA deficiency.