Short-term clinical outcomes after HLA 1-locus mismatched uPBSCT are similar to that after HLA-matched uPBSCT and uBMT.

In Japan, use of unrelated peripheral blood stem cell transplantation (uPBSCT) from HLA-mismatched unrelated donors has recently been approved. We compared outcomes between HLA-matched and 1-locus mismatched uPBSCT, as well as the impact of HLA disparity in uPBSCT and in unrelated bone marrow transplantation (uBMT). In total, 5862 uBMT recipients and 234 uPBSCT recipients were included. In terms of HLA allele disparity, 185 uPBSCT patients (79.1%) had no HLA mismatch, and 49 (20.9%) had 1-locus mismatch; in comparison, 3585 uBMT patients (61.2%) had no HLA mismatch, and 2277 (38.8%) had 1-locus mismatch. The impact of 1-locus mismatch as compared with match in uPBSCT was not significantly higher than in uBMT [hazard ratio (HR) = 1.02 and 1.27 for grade III-IV acute graft-versus-host disease, HR = 0.98 and 1.14 for non-relapse mortality, and HR = 0.87 and 1.06 for overall survival, respectively]. In conclusion, the impact of single-locus mismatch on short-term outcomes was comparable in uPBSCT and uBMT. Larger studies with longer follow-up are needed to assess long-term outcomes.