Plots of dAXP percentage versus ANC. (A) Samples drawn during routine evaluation. P = .8369. (B) Samples drawn from patients who had had chemotherapy followed by gene therapy, starting from one month after gene therapy. P = .0015. Measurements were taken up to 4 years after gene therapy. (C) Samples drawn at diagnosis of ADA-SCID, before institution of PEG-ADA therapy. P = .1312.