Taken together, data summarized in Figures 1 and 2 demonstrate that transfer of an unfractionated donor splenocyte inoculum containing 5 x 106 CD8 T cells is sufficient to induce near maximal reductions in host B cell populations for B6→F1 acute GVHD and >200% increase in several splenic subsets in D2→F1 chronic GVHD mice. This evidence concerns the gene CD8A and acute graft versus host disease.