In HLA-identical allogeneic stem cell transplantation (SCT), alloreactive CD8+ T cells specific for minor histocompatibility antigens (MiHA) play a pivotal role in graft rejection, graft-versus-host disease (GVHD) and the curative graft-versus-tumor (GVT) response. The gene discussed is XIAP; the disease is graft versus host disease.