Imatinib mesylate suppresses cytokine synthesis by activated CD4 T cells of patients with chronic myelogenous leukemia

Although imatinib mesylate (IM) is highly effective at inducing complete cytogenetic remission in patients with chronic myelogenous leukemia (CML), it is known to suppress T-cell proliferation in vitro. As cytokines are required for T-cell proliferation, we investigated the effects of IM on cytokine synthesis by T cells of CML patients by assessing cytokine synthesis by activated CD4(+) and CD8(+) T cells in vitro. The activation of T cells in the whole blood of IM-treated patients (CML-IM) with Staphylococcus enterotoxin B resulted in significantly lower percentages of CD4(+) T cells that synthesized interleukin 2 (P = 0.017), interferon-gamma (P = 0.010), and tumor necrosis factor-alpha (P = 0.009) than did the activated T cells of control subjects. The addition of exogenous IM to the cultures of peripheral blood mononuclear cells of CML-IM patients reduced Th1 cytokine synthesis by the CD4(+) T cells. Furthermore, IM therapy at clinical doses suppressed the tyrosine phosphorylation of ZAP70. These findings suggest that inhibition of ZAP70 signaling pathway and suppression of Th1 cytokine synthesis by CD4(+) T cells required the presence of IM at the time of T-cell activation through the T-cell receptor.