In order to determine the impact of each HLA allele mismatch combination in inducing acute GvHD, Kavase et al. analyzed a total of 5210 donor/recipient pairs who underwent HSCT through Japan Marrow Donor Program, typing retrospectively all the HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1 alleles. The gene discussed is HLA-A; the disease is graft versus host disease.