Proliferation of activated T lymphocytes after exposure to cytarabine, ATRA and valproic acid alone or in combinations. PBMCs derived from healthy blood donors (n = 7) were stained with the cell proliferation dye CellTrace™ Violet and subsequently activated by in vitro culture in the presence of anti-CD3 and anti-CD28. Flow cytometric analysis of proliferation was done after 4 days of culture in medium without drugs (control) or in the presence of drugs/drug combinations. (A) The gating strategy to measure the proliferative response of CD5+ T lymphocytes is shown for three representative samples (two control samples –unstimulated and stimulated– and one sample with cytarabine 44 μM). Cultures without anti-CD3 and anti-CD28 and thereby no proliferating cells were used as the negative gating control. (B) The overall results are presented as bar graphs for the control samples and samples exposed to the indicated single drugs or drug combinations. Results are presented as the mean percentages (with SD) of proliferative T cells. A repeated measure ANOVA with Dunnett’s Multiple Comparison Test was used to determine statistically significant differences (*p <0.05; **p <0.01; ***p <0.001).