As acute GVHD can be inhibited by the addition of neutralizing anti-IL-2 monoclonal antibodies (mAbs) and is not induced by perforin-deficient donor T cells [10,11], acute GVHD is associated with increased Th1-mediated immune responses and with perforin expression on donor T cells. The gene discussed is PRF1; the disease is acute graft versus host disease.