LAUSR

Although outcomes of hematopoietic stem cell transplantation from alternative donors have been improved, it has not yet challenged the precedence of HLA‐matched or a few loci‐mismatched donors. Because the availabilities of these donors among nonsibling relatives have been scarcely discussed, we analyzed them using a large Japanese dataset of HLA typing. Data set included HLA data from 2838 patients and their relatives, distributed in all parts of Japan. Antigen mismatches at the HLA‐A, ‐B, ‐DR loci and allele mismatches at the HLA‐A, ‐B, ‐C, ‐DRB1 loci were examined. The availabilities of 0 to 1/6 antigen‐mismatched donors among one parent‐candidate and one sibling‐candidate were 24.3% and 33.9%, and those of 0 to 2/8 allele‐mismatched donors were 18.6% and 32.1%, respectively. Additional HLA‐C antigen mismatches (18.1% vs 0.0%) along with the possession of 1 to 3/8 allele mismatches (31.3% vs 3.0%) were more frequently observed in parent‐candidates than in sibling‐candidate. Most multiple allele‐mismatched pairs had HLA‐B allele mismatches. In conclusion, expanding donor searches to include nonsibling relatives could widen the availability of conventional relative donors with 0 to 1/6 antigen mismatches or 0 to 2/8 allele mismatch to 20% to 30%. High‐resolution typing including HLA‐C locus examination should be performed, because additional mismatches at HLA‐C loci along with multiple allele mismatches were often observed, especially among nonsibling pairs.