To assess the effects of IL-17 produced by donor-derived Th17 cells in acute GVHD, we compared the outcome of experimental acute GVHD induced by adoptive transfer of allogeneic CD4+ T cells from wild type (WT) or Il7af-/- donors [5] using C57BL/6 donors and lethally irradiated BALB/c recipients. The gene discussed is CD4; the disease is graft versus host disease.