Inhibition of adenosine kinase prevents the accumulation of dATP in ADA-inhibited FTOC. FTOCs were performed with C57BL/6 thymuses at day 15 of gestation with media, 5 μM dCF, 1 μM 5′A5′dAdo, or 5 μM dCF plus 1 μM 5′A5′dAdo. After 2 days, the accumulation of dATP was measured by HPLC in extracts of thymocytes from 30–35 fetal thymic lobes. The dATP levels are expressed as a percentage (mean + SD) of those in the dCF-treated thymic lobes from four independent experiments.