Treatment of ADA- SCID is often considered the first success for gene therapy.Ashanti DeSilva is a young girl that suffered from an autosomal form of SCID and was treated using retroviral gene therapy.Explain why the treatment is not an undisputed success.

While Ashanti's immune system was bolstered by the gene therapy,she also received regular injections of adenosine deaminase enzyme.This made it unclear whether the adenosine deaminase found in her system was due to the active gene delivered by the gene therapy or the injections of purified adenosine deaminase.