Abstract • 77

Interleukin (IL)-2 has recently been used for induction of a Graft versus Leukemia effect (GvL) following allogeneic bone marrow transplantation (BMT). The simultaneously induced severe graft versus host disease (GvHD), however, somewhat limits the therapeutic width of IL-2 treatment. Since distinct cytokine patterns appear to be responsible for GvL and GvHD, here the regulation of IL-2 induced T-1 and T-2 related cytokine production was investigated by cytoplasmic staining for IFN-γ and IL-4 and FACS analysis. IL-2 induced a significant activation of T-cells expressing IFN-γ alone(T-1), IL-4 alone (T-2) and (IL-4+IFN-γ) double positive T-cells(T-O). Blockade of CD40 ligand (CD40L)/CD40 interaction or inhibition of endogenous IL-12 significantly reduced the activation of T-O and T-1 cells, whereas T-2 cells was only marginally affected. In addition, IL-10 suppressed the cytokine production by T-0 and T-1, but not by T-2 cells. The inhibitory effect of IL-10 was overcome by addition of exogenous IL-12. In conclusion, different mechanisms are involved in the IL-2 mediated activation of human T-cells which might allow a selective stimulation of T-1 and T-2 cells. These observations might be of relevance for immunotherapy after allogeneic BMT.