Figure 3.
ADA enzyme activity in PBMCs and dAXP in RBCs. (A-B) PBMCs isolated from peripheral blood samples by Ficoll-Hypaque separation were counted, frozen, and assayed for ADA enzyme activity using a radiochemical assay. (C-D) Deoxyadenosine nucleotides (dAXP = dAMP + dADP + dATP) were measured in RBCs, as described.20 The test results are displayed chronologically (A,C) or group by patient for samples 2 years or later after gene therapy (B,D). The horizontal dashed red line is the upper limit for normal control samples in the testing laboratories (<0.2%); the horizontal dashed blue line is the median value for %dAXP in 22 recipients of allogeneic HSCT for ADA SCID (median = 4.8%; mean = 7.0 ± 11.0% [standard deviation]; M.S.H., unpublished observation).