The Human Leukocyte Antigen (HLA) or the Major Histocompatibility Complex (MHC) is a highly polymorphic region of the human genome (on the short arm of chromosome 6) that is critically involved in the rejection and graft-versus-host disease (GVHD) of hematopoietic stem cell transplants [1,2], the pathogenesis of numerous autoimmune diseases [3-6], infectious diseases [7] and drug adverse reactions [8,9]. The gene discussed is HLA-C; the disease is graft versus host disease.