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.

BackgroundThe development of effective cancer vaccines still remains a challenge. Despite the crucial role of plasmacytoid dendritic cells (pDCs) in anti-tumor responses, their therapeutic potential has not yet been worked out. We explored the relevance of HLA-A*0201 matched allogeneic pDCs as vectors for immunotherapy.Methods and FindingsStimulation of PBMC from HLA-A*0201+ donors by HLA-A*0201 matched allogeneic pDCs pulsed with tumor-derived peptides triggered high levels of antigen-specific and functional cytotoxic T cell responses (up to 98% tetramer+ CD8 T cells). The pDC vaccine demonstrated strong anti-tumor therapeutic in vivo efficacy as shown by the inhibition of tumor growth in a humanized mouse model. It also elicited highly functional tumor-specific T cells ex-vivo from PBMC and TIL of stage I-IV melanoma patients. Responses against MelA, GP100, tyrosinase and MAGE-3 antigens reached tetramer levels up to 62%, 24%, 85% and 4.3% respectively. pDC vaccine-primed T cells specifically killed patients' own autologous melanoma tumor cells. This semi-allogeneic pDC vaccine was more effective than conventional myeloid DC-based vaccines. Furthermore, the pDC vaccine design endows it with a strong potential for clinical application in cancer treatment.ConclusionsThese findings highlight HLA-A*0201 matched allogeneic pDCs as potent inducers of tumor immunity and provide a promising immunotherapeutic strategy to fight cancer.

Several sources of evidence suggest that tumor-specific T cells have the potential to control melanoma tumors. Current active and adoptive therapeutic approaches to elicit such T cells are either not sufficiently clinically efficient or require fastidious processes that impede their extensive clinical use. As plasmacytoid dendritic cells (pDCs) have a crucial role in triggering antitumor immunity especially in melanoma, we explored their potential as a cell-based approach for melanoma immunotherapy. An irradiated human HLA-A(*)0201(+) pDC line loaded with peptides derived from the major melanoma tumor antigens, MelA/MART-1, gp100/pmel17, tyrosinase, and MAGE-A3, was used to trigger functional multi-specific T cells ex vivo from peripheral blood mononuclear cells and tumor-infiltrating lymphocytes from stage I-IV HLA-A(*)0201(+) melanoma patients. pDCs loaded with melanoma-derived peptides promptly induced high levels of melanoma tumor-specific T cells from both sources. pDC-primed central/effector memory antitumor T cells were highly functional as indicated by the specific IFNγ secretion and membrane CD107 expression upon stimulation. Cells also exhibited strong cytotoxicity toward semi-allogeneic melanoma cells and patient-derived tumor cells. The simple design and potent efficacy of this promising approach provides a preclinical basis for the development of a pDC-based vaccine and an alternative means to produce tumor-specific T cells for adoptive cellular immunotherapy in melanoma patients.