The relative importance of the resolution level of HLA typing has not been fully defined for related donor transplantation. To address this question, we retrospectively evaluated patients who underwent a first related hematopoietic stem cell transplantation (HSCT) from 2000 to 2011 from an HLA high-resolution matched (MRD, n=2,244), high-resolution 1 locus-mismatched (HR-MMRD, n=116), or low-resolution 1 locus-mismatched related donor (LR-MMRD, n=396) in the graft-versus-host direction at three loci (HLA A, B, and DRB1) using the database of the Japan Society for Hematopoietic Cell Transplantation. The median age was 40 years (0-74). The median follow-up duration of surviving patients was 950 days. Although the cumulative incidences of grade III-IV acute graft-versus-host disease (GVHD) in the HR-MMRD and LR-MMRD groups were significantly higher than those in the MRD group (HR-MMRD 19.8%, LR-MMRD 20.4%, and MRD 9.5%), there was no statistically significant difference between the HR-MMRD and LR-MMRD groups (P=0.65). Although both HR-MMRD and LR-MMRD were significantly associated with an increased risk of non-relapse mortality and a worse overall survival, there was no statistically significant difference between the HR-MMRD and LR-MMRD groups. In conclusion, LR-MM and HR-MM have a similar adverse impact on the outcome in related HSCT.
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