CD8A and graft versus host disease: GVHD is considered to be mediated by activated CD8+ cytotoxic T-cell (CTL) from the graft donor after these cells had met graft recipient alloantigens in the context of antigen presenting cells (APCs) in the subepithelial dome of gut Peyer’s patches, the major sites where immune response is set up against luminal antigens and microorganisms (Murai et al., 2003).