Exogenous Addition of Minor H Antigen HA-1+ Dendritic Cells to Skin Tissues Ex Vivo Causes Infiltration and Activation of HA-1-Specific Cytotoxic T Cells

Minor histocompatibility antigens: past, present, and future

Minor histocompatibility (H) antigens are key molecules driving allo-immune responses in both graft-versus-host-disease (GvHD) and in graft-versus-leukemia (GvL) reactivity in human leukocyte antigen (HLA)-matched hematopoietic stem-cell transplantation (HSCT). Dissection of the dual function of minor H antigens became evident through their different modes of tissue and cell expression, i.e. hematopoietic system-restricted or broad. Broadly expressed minor H antigens can cause both GvHD and GvL effects, while hematopoietic system-restricted minor H antigens are more prone to induce GvL responses. This phenomenon renders the latter group of minor H antigens as curative tools for HSCT-based immunotherapy of hematological malignancies and disorders, in which minor H antigen-specific responses are enhanced in order to eradicate the malignant cells. This article describes the immunogenetics of minor H antigens and methods that have been developed to identify them. Moreover, it summarizes the clinical relevance of minor H antigens in transplantation, with special regards to allogeneic HSCT and solid-organ transplantation.

Predicting alloreactivity in transplantation

Human leukocyte Antigen (HLA) mismatching leads to severe complications after solid-organ transplantation and hematopoietic stem-cell transplantation. The alloreactive responses underlying the posttransplantation complications include both direct recognition of allogeneic HLA by HLA-specific alloantibodies and T cells and indirect T-cell recognition. However, the immunogenicity of HLA mismatches is highly variable; some HLA mismatches lead to severe clinical B-cell- and T-cell-mediated alloreactivity, whereas others are well tolerated. Definition of the permissibility of HLA mismatches prior to transplantation allows selection of donor-recipient combinations that will have a reduced chance to develop deleterious host-versus-graft responses after solid-organ transplantation and graft-versus-host responses after hematopoietic stem-cell transplantation. Therefore, several methods have been developed to predict permissible HLA-mismatch combinations. In this review we aim to give a comprehensive overview about the current knowledge regarding HLA-directed alloreactivity and several developed in vitro and in silico tools that aim to predict direct and indirect alloreactivity.

A novel recombinant Salmonella vaccine enhances the innate immunity of NK cells against acute myeloid leukaemia cells Kasumi-1 in vitro

Minor histocompatibility antigen HA-1-specific cytotoxic lymphocyte (CTL) clones have apparent anti-leukaemic efficacy, and the AML/ETO gene is a special fusion gene in leukaemic cells. Thus, we hypothesised that a vaccine targeting HA-1 and AML/ETO could stimulate NK cells to target leukaemia cells. Furthermore, we packaged the vaccine using attenuated Salmonella to enhance its immuno-activity. Expression of the NK cell-activating ligand ULBP2 was notably elevated upon packaging in a co-recombinant group. An AML/ETO single plasmid gave the weakest vaccine. The level of miR-182, which targets ULBP2, significantly decreased with increasing IFN-γ and granzyme B in a co-recombinant group. In summary, DNA vaccines including AML/ETO and HA-1 fragments significantly enhance the innate immunity of NK cells in vitro.

Multicenter analyses demonstrate significant clinical effects of minor histocompatibility antigens on GvHD and GvL after HLA-matched related and unrelated hematopoietic stem cell transplantation

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.

Regulatory T cells inhibit CD8(+) T-cell tissue invasion in human skin graft-versus-host reactions

BACKGROUND

Regulatory T cells (Tregs) effectively ameliorate graft-versus-host disease (GVHD). The mechanisms underlying Treg therapeutic effect on GVHD are not fully elucidated. This study investigates whether Treg prevention of GVH tissue damage is associated with blocking CD8 effector T-cell tissue invasion, a question not yet addressed in humans.

METHOD

Tissue-infiltrating T cells and histopathology scores were detected using an in vitro human GVHD skin explant model, together with immunohistochemistry, cytometric bead array, functional adhesion and migration assays, flow cytometry, and quantitative real-time polymerase chain reaction.

RESULTS

Treg intervention during priming significantly decreased effector T-cell infiltration into target tissue (P<0.01) resulting in a striking reduction in the histopathology score of tissue injury (P<0.0001). These results were coupled with reduced CXCR3 and cutaneous lymphocyte antigen expression by effector T cells, together with decreased CXCL10 and CXCL11 expression in target tissue. Treg intervention also impaired the functional interaction of CXCR3 and cutaneous lymphocyte antigen with their specific ligands (P<0.01) and suppressed the secretion of CXCL9, CXCL10, and interferon-γ (P<0.01, P<0.05, and P<0.001, respectively). Late addition of Tregs into the effector phase abolished their ability to suppress effector T-cell tissue invasion, resulting in a total loss of their ability to ameliorate GVH tissue damage.

CONCLUSION

Preventing effector T-cell tissue invasion is a critical mechanistic event leading to Treg attenuation of GVH tissue damage. This therapeutic effect is associated with a failure of CD8 T cells to increase tissue homing receptors after allo-stimulation, together with a breakdown of interferon-γ-induced chemoattractant expression in the target tissue.

Minor histocompatibility antigen typing by DNA sequencing for clinical practice in hematopoietic stem-cell transplantation

In HLA-matched stem-cell transplantation (SCT), minor H antigens are key molecules driving allo-immune responses in both graft-versus-host disease (GvHD) and in graft-versus-leukemia (GvL) reactivity. Dissection of the dual function of minor H antigens became evident through their different modes of tissue and cell expression, i.e., hematopoietic system restricted or broad. Broadly expressed minor H antigens are the targets of immune responses in both arms of graft-versus-host (GvH) responses, i.e., both GvHD and GvL, whereas the immune responses against the hematopoietic system-specific minor H antigens are restricted to the GvL arm of SCT. Evidently, it is this latter group of minor H antigens that can function as curative tools for stem-cell (SC)-based immunotherapy of hematological malignancies and disorders. The HLA-matched patient/donor combinations, incompatible for one of the hematopoietic-specific minor H antigens, are suitable for minor H antigen immunotherapy (Goulmy, Immunol Rev 157:125-140, 1997). Information on the minor H antigen phenotype is therefore needed. Hereto, genomic typing for minor H antigens has been implemented in many HLA laboratories. Here, we firstly summarize the relevance of minor H antigens particularly in hematopoietic SCT. Secondly, we describe a method for typing the various polymorphic minor H antigens molecularly identified to date by DNA sequencing.