Background-The success of unrelated hematopoietic-cell transplantation (HCT) is limited by graft-versus-host disease (GVHD). A sequence dimorphism in exon one of HLA-B gives rise to

Hematopoietic cell transplantation from HLA-haploidentical related donors is increasingly used to treat hematologic cancers; however, characteristics of the optimal haploidentical donor have not been established. We studied the role of donor HLA mismatching in graft-versus-host disease (GVHD), disease recurrence and survival after haploidentical donor transplantation with post-transplantation cyclophosphamide (PTCy) for 1434 acute leukemia or myelodysplastic syndrome patients reported to the Center for International Blood and Marrow Transplant Research. The impact of mismatching in the graft-versus-host vector for HLA-A, -B, -C, -DRB1, and -DQB1 alleles, the HLA-B leader, and HLA-DPB1 T-cell epitope (TCE) were studied using multivariable regression methods. Outcome was associated with HLA (mis)matches at individual loci rather than the total number of HLA mismatches. HLA-DRB1 mismatches were associated with lower risk of disease recurrence. HLA-DRB1-mismatching with HLA-DQB1-matching correlated with improved disease-free survival. HLA-B leader matching and HLA-DPB1 TCE-non-permissive mismatching were each associated with improved overall survival. HLA-C matching lowered chronic GVHD risk, and the level of HLA-C expression correlated with transplant-related mortality. Matching status at the HLA-B leader and HLA-DRB1, -DQB1 and -DPB1 predicted disease-free survival, as did patient and donor CMV serostatus, patient age and co-morbidity index. A web-based tool was developed to facilitate selection of the best haploidentical related donor by calculating disease-free survival based on these characteristics. In conclusion, HLA factors influence the success of haploidentical transplantation with PTCy. HLA-DRB1 and -DPB1 mismatching and HLA-C, -B leader, and -DQB1 matching are favorable. Consideration of HLA factors may help to optimize the selection of haploidentical related donors.

PURPOSE The main aim of this study was to evaluate the significance of HLA-DPB1 expression in acute graft-versus-host disease (GVHD) after hematopoietic cell transplantation (HCT) from HLA-A, -B, -C, -DRB1, -DQB1–matched and –mismatched unrelated donors. PATIENTS AND METHODS Between January 1, 2017, and January 10, 2019, we assessed 19,136 patients who received HCT from an HLA-A, -B, -C, -DRB1, -DQB1–matched or –mismatched unrelated donor performed in Australia, the European Union, Japan, North America, and the United Kingdom between 1988 and 2016. Among transplant recipients with one HLA-DPB1 mismatch, the patient’s mismatched HLA-DPB1 allotype was defined as low or high expression. Multivariable regression models were used to assess risks of GVHD associated with high expression relative to low expression HLA-DPB1 mismatches. The effect of increasing numbers of HLA-DPB1 mismatches on clinical outcome was assessed in HLA-mismatched transplant recipients. RESULTS In HLA-A, -B, -C, -DRB1,-DQB1–matched transplant recipients, donor mismatching against one high-expression patient HLA-DPB1 increased moderate (odds ratio [OR], 1.36; P = .001) and severe acute GVHD (OR, 1.32; P = .0016) relative to low-expression patient mismatches, regardless of the expression level of the donor’s mismatched HLA-DPB1. Among transplant recipients with one HLA-A, -B, -C, -DRB1, or -DQB1 mismatch, the odds of acute GVHD increased with increasing numbers of HLA-DPB1 mismatches (OR, 1.23 for one; OR, 1.40 for two mismatches relative to zero mismatches for moderate GVHD; OR, 1.19 for one; OR, 1.40 for two mismatches relative to zero for severe GVHD), but not with the level of expression of the patient’s mismatched HLA-DPB1 allotype. CONCLUSION The level of expression of patient HLA-DPB1 mismatches informs the risk of GVHD after HLA-A, -B, -C, -DRB1, -DQB1–matched unrelated HCT, and the total number of HLA-DPB1 mismatches informs the risk of GVHD after HLA-mismatched unrelated HCT. Prospective consideration of HLA-DPB1 may help to lower GVHD risks after transplantation.

Hematopoietic-cell transplantation (HCT) from HLA-mismatched unrelated donors can cure life-threatening blood disorders but its success is limited by graft-versus-host disease (GVHD). HLA-B leaders encode methionine (M) or threonine (T) at position 2 and give rise to TT, MT or MM genotypes. The dimorphic HLA-B leader informs GVHD risk in HLA-B-mismatched HCT. If the leader influences outcome in other HLA-mismatched transplant settings, the success of HCT could be improved for future patients. We determined leader genotypes for 11872 patients transplanted between 1988 and 2016 from unrelated donors with one HLA-A -B,-C,-DRB1 or -DQB1 mismatch. Multivariate regression methods were used to evaluate risks associated with patient leader genotype according to the mismatched HLA locus and with HLA-A,-B,-C,-DRB1 or -DQB1 mismatching according to patient leader genotype. The impact of the patient leader genotype on acute GVHD and mortality varied across different mismatched HLA loci. Non-relapse mortality was higher among HLA-DQB1-mismatched MM patients compared to HLA-DQB1-mismatched TT patients (hazard ratio 1.35; P = .01). Grades III-IV GVHD risk was higher among HLA-DRB1-mismatched MM or MT patients compared to HLA-DRB1-mismatched TT patients (odds ratio 2.52 and 1.51, respectively). Patients tolerated a single HLA-DQB1 mismatch better than mismatches at other loci. Outcome after HLA-mismatched transplantation depends on the HLA-B leader dimorphism and the mismatched HLA locus. The patient's leader variant provides new information on the limits of HLA mismatching. The success of HLA-mismatched unrelated transplantation might be enhanced through the judicious selection of mismatched donors for a patient's given leader genotype.

HLA-DQ heterodimers increase the susceptibility to autoimmune diseases but their role in hematopoietic-cell transplantation is unknown. We tested the hypothesis that outcome after HLA-matched and HLA-DQ-mismatched hematopoietic-cell transplantation is influenced by HLA-DQ heterodimers. Heterodimers were defined in 5164 HLA-matched and 520 HLA-DQ-mismatched patients and their transplant donors according to well-established crystallographic criteria. Group 1 (G1) heterodimers are any DQA1*02/03/04/05/06α paired with any DQB1*02/03/04β. Group 2 (G2) heterodimers are DQA1*01α paired with any DQB1*05/06β. Multivariable models identified significantly higher relapse risk in G1G2 and G2G2 compared to G1G1 HLA-matched patients with malignant disease; risk increased with increasing numbers of G2-molecules. In HLA-DQ-mismatched transplantation for malignant diseases, matching or mismatching for G2 increased relapse risk. G2 lowered disease-free survival after both HLA-matched and HLA-DQ-mismatched transplantation. A paradigm based on HLA-DQ heterodimers provides a functional definition of the hematopoietic-cell transplantation barrier and a means to lower risks for future patients.