For example, high resolution HLA typing has been shown to significantly improve outcome when stem cell transplant recipients and their unrelated donors are matched for both alleles at five of the classical HLA loci (HLA-A,-B,-C,-DRB1 and-DQB1, a 10/10 match) [25–28], as it is thought that disparity at these important compatibility loci can contribute to complications such as graft-versus-host disease and consequently, to mortality. Here, HLA-A is linked to graft versus host disease.