Dose- and time-dependent apoptosis induced in ADA-deficient T cells by ADA substrates. (A) Bulk T-cell lines were incubated with the indicated concentrations of purine metabolites and cultured for 15 hours (dAdo) or 6 hours (Ado). In time course experiments, T cells were incubated with dAdo (5 mM) or Ado (1 mM) for the indicated period. The percentages of early apoptotic cells (annexin V⁺/PI⁻) are shown for Pt3 (ADA^−/− and GT) and one ND as representative experiment. (B) Bulk T-cell lines from 5 patients (ADA^−/− and GT) and 6 NDs were cultured for 15 hours with dAdo (5 mM) or 6 hours with Ado (1 mM) in the absence or presence of the inhibitor of nucleoside transporter, dipyridamole (1 μM). The percentages of annexin V⁺/PI⁻ cells as mean plus or minus SD are shown. Data are representative of at least 5 independent experiments (**P < .01).