After HSCT, NKG2D-mediated co-stimulation of CD8+ T cells presumably contributes to both GVHD and graft-versus-leukemia (GVL) reactions and similarly, NKG2D-mediated NK-cell activation potentially contributes to GVL effects and to protection against pathogens such as cytomegalovirus (Leung, 2011). This evidence concerns the gene CD8A and leukemia.