Effect of HLA mismatching at HLA-A, -B, and -DRB1 for umbilical-cord blood transplantation in Taiwan

Unrelated cord blood transplantation has become a reliable alternative therapy for children and adults owing to that one or two antigen/allele mismatches between a patient and the cord blood donor are acceptable without occurrence of graft-versus-host disease. To investigate the relationship between the number and types of mismatches and relapse, we compared the number of mismatched and non-mismatched donor-recipient pairs, number of mismatched alleles, and number of mismatched antigens at each of the Human Leukocyte Antigen (HLA) -A, -B, and -DR loci, respectively. The result indicates that the number of mismatched antigens at the HLA-A locus was significantly associated with occurrence of relapse (X² P-value = 0.0243; RR = 1.49, 95% CI: 1.04–2.13). Additionally, the number of mismatched donor-recipient pairs and the number of mismatched alleles at the HLA-DR locus was negatively associated with risks of relapse (X² P-value = 0.0028; RR = 0.52, 95% CI: 0.31–0.89). In this study, we found that the mismatch at the HLA-A locus is associated with increased risk of relapse; while the mismatch at the HLA-DR locus is innocuous. Hence, we suggest that the well-matched HLA-A alleles were most critical for matching HLA alleles between umbilical-cord blood transplantation donors and recipients. In other words, cord blood transplantation requires less stringent HLA matching, if there are two 5/6 or 4/6 HLA matched donors, it's better to choose HLA-A matched donor at least.