The aim of the study was to characterize effects of exogenous cytokines on T lymphocytes derived from acute leukemia patients with chemotherapy-induced leukopenia. We investigated the cytokine responsiveness of long-term expanded CD4+ and CD8+ T cell clones and the effects of exogenous cytokines on anti-CD3-stimulated polyclonal T cell responses. After mitogenic activation in the presence of acute myelogenous leukemia (AML) blasts, most CD4+ and CD8+ clones proliferated in response to interleukin-2 (IL-2). Although a majority of the IL-2-responsive clones could also proliferate in the presence of exogenous IL-4, IL-7, IL-9, IL-10, IL-12, and IL-15, only IL-15 responses were equal to or exceeded the corresponding IL-2 responses. Exogenous cytokines were also added during T cell activation with phytohemagglutinin (PHA) + accessory leukemia cells derived from different AML patients, and all the cytokines then had divergent effects that depended on both differences between clones and differences between AML patients. However, for most of these T cell clone/AML blast combinations, IL-2 and IL-15 caused enhanced T cell proliferation. IL-2 and IL-15 also enhanced anti-CD3-stimulated polyclonal responses of nonexpanded T cells derived from cytopenic patients, whereas other cytokines had only minor effects. Our results demonstrate that cytokine-responsive T cells remain in the circulation during chemotherapy-induced cytopenia, and combination therapy including intensive chemotherapy and T cell-targeting cytokine therapy should, therefore, be possible in AML.