These studies indicate that NK cells generated from centromeric-B KIR motif carriers are strongly reactive and may; 1) protect against graft versus host disease (GvHD) by depleting host antigen presenting cells; 2) facilitate engraftment by elimination of host immune barriers; 3) kill residual host tumor to protect against relapse, and; 4) decrease infectious complications. The gene discussed is KIR3DL1; the disease is neoplasm.