HLA-B Leader Dimorphism Impacts on Outcomes of HLA-Matched Related/Unrelated Transplantation: Analysis of the Japanese Society for Transplantation and Cellular Therapy

Background: HLA-B leader encodes methionine (M) or threonine (T) at position 2 and gives rise to TT, MT, or MM genotype. HLA-B M leaders promote higher HLA-E expression than T leaders, enhancing T cell and natural killer (NK) cell recognition on HLA-E via NKG2A and NKG2C related to cytomegalovirus (CMV) recognition. The dimorphic HLA-B leader informs acute graft-versus-host disease (GVHD) risk in HLA 1 allele mismatched unrelated hematopoietic stem cell transplantation (HCT) (Petersdorf EW et al. Lancet Haematol. 2020 and Blood. 2020) and haploidentical HCT (Fuchs EJ et al. 62nd ASH Annual Meeting 2020). However, the impact of the HLA-B leader genotype in HLA-matched related/unrelated donor HCT from the viewpoints of CMV reactivation has not been elucidated fully yet. We performed this retrospective study to explore the significance of HLA-B leaders in HLA-matched related/unrelated HCT in the Japanese population.