The finding that keratinocytes overexpressing a self-antigen can also activate naive CD8+ T cells directly and induce a local GVHD-like inflammation (80) suggests the possibility that allogeneic T cells entering the skin can potentially be regulated by multiple cell types via cognate interactions; in this case, the outcome of the interaction could be specific to the T cell clone or to the antigen involved. This evidence concerns the gene CD8A and graft versus host disease.