Although both CD4 and CD8 T cells were found to be protective against GVHD induced by DLI in established MCs, the development of significantly more severe GVHD in CD8KO MCs than in CD4KO MCs suggests that donor BM-derived CD8 T cells provide more potent protection than donor BM-derived CD4 T cells. This evidence concerns the gene CD8A and graft versus host disease.