Imatinib mesylate neither reduces viability nor stimulates apoptosis in T cells. Unstimulated T cells and T cells stimulated with PHA were cultured for 72 hours without or with imatinib mesylate (5.0 μM). Then the cells were assayed for activated caspase 3 and for binding of annexin V. Shown are mean values ± SD. PHA stimulation increased the frequency of cells with activated caspase 3 and cells binding annexin V (P < .001 for both). Imatinib mesylate induced a decrease of activated caspase 3 levels (P = .03) but did not change the frequency of cells binding annexin V (P = .10).