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Minor histocompatibility (H) antigens are allogeneic target molecules having significant roles in alloimmune responses after human leukocyte antigen–matched solid organ and stem cell transplantation (SCT). Minor H antigens are instrumental in the processes of transplant rejection, graft-versus-host disease, and in the curative graft-versus-tumor effect of SCT. The latter characteristic enabled the current application of selected minor H antigens in clinical immunotherapeutic SCT protocols. No information exists on the global phenotypic distribution of the currently identified minor H antigens. Therefore, an estimation of their overall impact in human leukocyte antigen–matched solid organ and SCT in the major ethnic populations is still lacking. For the first time, a worldwide phenotype frequency analysis of ten autosomal minor H antigens was executed by 31 laboratories and comprised 2,685 randomly selected individuals from six major ethnic populations. Significant differences in minor H antigen frequencies were observed between the ethnic populations, some of which appeared to be geographically correlated.

The effect of minor H antigen mismatching on the occurrence of graft-versus-host disease (GvHD) and graft-versus-leukemia (GvL) after HLA-matched hematopoietic stem cell transplantation (HSCT) has mainly been demonstrated in single-center studies. Yet, the International Histocompatibility and Immunogenetics Workshops (IHIW) provide a collaborative platform to execute crucial large studies. In collaboration with 20 laboratories of the IHIW, the roles of 10 autosomal and 10 Y chromosome-encoded minor H antigens were investigated on GvHD and relapse incidence in 639 HLA-identical related donor (IRD) and 210 HLA-matched unrelated donor (MUD) HSCT recipients. Donor and recipient DNA samples were genotyped for the minor H antigens HA-1, HA-2, HA-3, HA-8, HB-1, ACC-1, ACC-2, SP110, PANE1, UGT2B17, and HY. The correlations with the primary outcomes GvHD (acute or chronic GvHD), survival, and relapse were statistically analyzed. The results of these multicenter analyses show that none of the HLA class I-restricted HY antigens were found to be associated with any of the primary outcomes. Interestingly, of the HLA class II-restricted HY antigens analyzed, HLA-DQ5 positive recipients showed a significantly increased GvHD-free survival in female-to-male HSCT compared with male-to-female HSCT (P = .013). Yet, analysis of the overall gender effect, thus independent of the known HY antigens, between the gender groups demonstrated an increased GvHD incidence in the female-to-male transplantations (P < .005) and a decreased GvHD-free survival in the female-to-male transplantations (P < .001). Of all autosomally encoded minor H antigens, only mismatching for the broadly expressed minor H antigen HA-8 increased the GvHD incidence in IRD HSCT (Hazard ratio [HR] = 5.28, P < .005), but not in MUD HSCT. Most striking was the influence of hematopoietic restricted minor H antigens on GvL as mismatching for hematopoietic minor H antigens correlated with lower relapse rates (P = .078), higher relapse-free survival (P = .029), and higher overall survival (P = .032) in recipients with GvHD, but not in those without GvHD. In conclusion, the significant GvHD effect of the broadly expressed minor H antigen HA-8 favors matching for HA-8 in IRD, but not in MUD, patient/donor pairs. The GvHD-GvL association demonstrating a significant lower relapse in hematopoietic minor H antigen mismatched patient/donor pairs underlines their clinical applicability for adoptive immunotherapy, enhancing the GvL effect in a GvHD controllable manner.

The online version of this article has a Supplementary Appendix. BackgroundAn alternative reduced-toxicity conditioning regimen for allogeneic transplantation, based on treosulfan and fludarabine, has recently been identified. The rationale for this study was to investigate the efficacy and safety of this regimen prospectively in patients with a primary myelodysplastic syndrome. Design and MethodsA total of 45 patients with primary myelodysplastic syndromes were conditioned with 3¥14 g/m² treosulfan and 5¥30 mg/m² fludarabine followed by allogeneic hematopoietic stem cell transplantation. Subtypes of myelodysplastic syndromes were refractory anemia with excess blasts-2 (44%), refractory cytopenia with multilineage dysplasia (27%), refractory anemia (9%), refractory anemia with ringed sideroblasts (4%), refractory cytopenia with multilineage dysplasia and ringed sideroblasts (4%), refractory anemia with excess blasts-1 (2%), and myelodysplastic syndrome with isolated del (5q) (2%). The myelodysplastic syndrome was unclassified in 7% of the patients. Forty-seven percent of the patients had a favorable karyotype, 29% an unfavorable one, and 18% an intermediate karyotype. Patients were evaluated for engraftment, adverse events, graft-versus-host disease, non-relapse mortality, relapse incidence, overall survival and disease-free survival. ResultsAll but one patient showed primary engraftment of neutrophils after a median of 17 days. Nonhematologic adverse events of grade III-IV in severity included mainly infections and gastrointestinal symptoms (80% and 22% of the patients, respectively). Acute graft-versus-host disease grade II-IV developed in 24%, and extensive chronic graft-versus-host disease in 28% of the patients. After a median follow-up of 780 days, the 2-year overall and disease-free survival estimates were 71% and 67%, respectively. The 2-year cumulative incidences of non-relapse mortality and relapse were 17% and 16%, respectively. ConclusionsOur safety and efficacy data suggest that treosulfan-based conditioning therapy is a promising treatment option for patients with myelodysplastic syndromes. clinicaltrials.gov identifier: NCT01062490