In such cases, thymus transplantation can be successful as a second procedure particularly if it is possible to use a thymus matching for any MHC alleles (also called human leukocyte antigen (HLA) alleles in humans) in the recipient which were mismatched with the original HSCT donor to reduce the risk that the procedure might facilitate graft-versus-host disease (GVHD) mediated by the HSCT donor cells (125). Here, HLA-C is linked to graft versus host disease.