Human platelet alloantigen (HPA)-5a/b mismatch decreases disease-free survival in unrelated bone marrow transplantation

Matching of human platelet alloantigen (HPA) systems 2–6 was retrospectively investigated in 715 unrelated bone marrow transplantations. Of the five HPA systems studied, HPA‐5 mismatching was found to have a significant effect on the disease‐free survival rate of recipients following transplantation in the HLA‐A, ‐B, ‐C, and ‐DR allele‐matched donor‐recipient pairs. The effect of the HPA‐5 mismatch was most significant in the recipient group possessing the HLA haplotype A*2402‐B*5201, which is a highly frequent haplotype among the Japanese population. However, the probability of development of acute graft‐versus‐host disease (GVHD) was not increased significantly by the HPA‐5 mismatching. These findings suggest that the HPA‐5 mismatching decreases the recipient’s survival by a mechanism different from that in the case of mismatching of minor antigens found often in transplant recipients developing GVHD.