GT supports ADA activity and lymphocyte function. All values shown are medians; black dotted lines represent minimum and maximum values. The number of patients contributing to each data point is indicated on the graph. (A) Lymphocyte ADA levels were measured in peripheral venous blood. ADA activity of ≥210 nmol/h per mg (blue line) represents 10% of normal and was considered as a threshold for adequate activity in subjects with ADA-SCID following treatment.²¹  (B) RBC dAXP levels were measured in peripheral venous blood. The blue line denotes dAXP levels found in successfully allogeneic transplanted patients (≤100 nmol/mL).^10,17  (C-D) Proliferative capacity was assessed following challenge with (C) anti-CD3 antibody and (D) phytohemagglutinin (PHA). Blue lines indicate normal response in healthy children.²⁸  (E) TREC abundance in whole blood was determined by qRT-PCR.