The CD4:CD8 ratio of activated T lymphocytes after exposure to cytarabine, ATRA and valproic acid alone or in combination. PBMCs derived from three healthy blood donors were activated by anti-CD3 plus anti-CD28 during 3 days of in vitro culture before flow cytometric analysis of the CD4:CD8 ratio. Cultures were prepared without drugs, with single drugs or with drug combinations. (A) The figure shows the gating strategy for estimation of CD4+CD5+ and CD8+CD5+ T cells lymphocytes in a representative experiment. (B) The overall results are presented as bar graph (mean ratio with SD) for the drugfree control cultures and cultures prepared with the indicated single drugs or drug combinations. 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).