HLA disparity between hematopoietic stem cell donors and recipients is one of the most important factors influencing transplant outcomes.HLA mismatching was determined by comparing the peptide sequences encoded by the exons that were used for HLA typing using a sequence database for the human MHC Low resolution HLA mismatches were defined as differences in the first two digits of the HLA types. The primary endpoint for this analysis was overall survival which was defined as the time from graft infusion to death from any cause.