A uniform genomic minor histocompatibility antigen typing methodology and database designed to facilitate clinical applications

An AS-qPCR-based method for the detection of Alzheimer's disease-related SNPs

Alzheimer's disease (AD) is one of the most serious neurodegenerative diseases in the world and has a strong genetic predisposition. At present, there is still no effective method for the early diagnosis and prevention of AD. Accumulating evidence shows the association of several loci with AD risk, such as apolipoprotein E (APOE) and translocase of outer mitochondrial membrane 40 (TOMM40). However, for routine disease diagnosis in clinics, genotype detection methods based on gene sequencing technology are time-consuming and excessively costly. Thus, in this study, we developed a high-sensitivity, low-cost, and convenient single nucleotide polymorphism (SNP) detection assay method based on allele-specific quantitative polymerase chain reaction (AS-qPCR) technology, which can be used to determine the SNP genotype in APOE and TOMM40. A total of 40 patients were recruited from the outpatient department of the memory clinic of Dongzhimen Hospital, Beijing University of Chinese Medicine. The SNP detection assay method includes three steps. First, positive plasmids with different genotypes (TT/CC/TC) in APOE rs429358, rs7412, and TOMM40 rs11556505 were prepared. Second, 3'-T/3'-C primers were designed to amplify these positive plasmids for each SNP site. Finally, we calculated the log10 of the copy number ratio for each positive plasmid, and the genotype interpretation interval was established. Based on this method, we investigated whether the SNPs in 40 patients could be accurately calculated using AS-qPCR technology. The accuracy of SNP detection was verified by PCR-Pooling sequencing. The results showed that SNP genotypes assessed by AS-qPCR technology corresponded perfectly to the results obtained by conventional DNA sequencing. We have developed a genotype detection method for AD based on AS-qPCR, which can be performed easily, rapidly, accurately, and at low cost. The method will contribute to the early diagnosis of patients with late-onset Alzheimer's and the detection of large clinical samples in the future.

Minor histocompatibility antigens HA-8 and PANE1 in the TUNISIAN population

BACKGROUND

Minor histocompatibility antigens (mHAgs) are endogenous immunogenic peptides initially identified due to complications detected in several contexts of HLA geno-identical hematopoietic stem cell transplantation (HSCT). In this study, we chose to examine the molecular polymorphism of the mHAgs HA-8 and PANE1 in the Tunisian population.

MATERIAL AND METHODS

This study was conducted on 150 healthy and unrelated individuals. The DNA extraction and Sequence-Specific Primers PCR (PCR-SSP) methods were used for the molecular genotyping of the selected SNPs: PUM3 (rs2173904) and CENPM (rs5758511).

RESULTS

Our results show that, 94% of Tunisians are carriers of the PANE1R allele (immunogenic variant of the PANE1 mHAg) and 68% of Tunisians are carriers of the HA-8R allele (immunogenic variant of the HA-8 mHAg). Furthermore, this study shows that about 5% of the Tunisians are carrier of the PANE1R antigen and its HLA molecule of presentation (the PANE1R/HLA-A*0301 combination). However, only 2% of Tunisians are carrier of the HA-8R/HLA-A*0201 combination, that is, the HA8 immunogenic variant and its specific HLA molecule of presentation.

CONCLUSION

Our results are close to those reported in Caucasian, Asiatic, and African populations, this may be explained by the historical events experienced by Tunisia for millennia. These results could be used for further clinical and anthropological studies.

Designing Allele-Specific Competitive-Extension PCR-Based Assays for High-Throughput Genotyping and Gene Characterization

Polymerase chain reaction (PCR) is a simple and rapid method that can detect nucleotide polymorphisms and sequence variation in basic research applications, agriculture, and medicine. Variants of PCR, collectively known as allele-specific PCR (AS-PCR), use a competitive reaction in the presence of allele-specific primers to preferentially amplify only certain alleles. This method, originally named by its developers as Kompetitive Allele Specific PCR (KASP), is an AS-PCR variant adapted for fluorescence-based detection of amplification results. We developed a bioinformatic tool for designing probe sequences for PCR-based genotyping assays. Probe sequences are designed in both directions, and both single nucleotide polymorphisms (SNPs) and insertion-deletions (InDels) may be targeted. In addition, the tool allows discrimination of up to four-allelic variants at a single SNP site. To increase both the reaction specificity and the discriminative power of SNP genotyping, each allele-specific primer is designed such that the penultimate base before the primer's 3' end base is positioned at the SNP site. The tool allows design of custom FRET cassette reporter systems for fluorescence-based assays. FastPCR is a user-friendly and powerful Java-based software that is freely available (http://primerdigital.com/tools/). Using the FastPCR environment and the tool for designing AS-PCR provides unparalleled flexibility for developing genotyping assays and specific and sensitive diagnostic PCR-based tests, which translates into a greater likelihood of research success.

LMP7 polymorphism may modify the presentation and clinical impact of minor histocompatibility antigens in matched related hematopoietic stem cell transplantation

Differential expression of minor histocompatibility antigens between the recipient and donor determines their disparity and can be modified by immunoproteasomes that regulate their processing and presentation. We examined the impact of HA-1 and HA-8 disparity, and immunoproteasome LMP7 polymorphism in 130 pairs. In multivariate analysis, HA-1 disparity showed a statistically significant association with an increased incidence of acute graft-versus-host disease (aGVHD) II-IV (p = 0.043, HR: 3.71, 95%CI = 1.04-13.26), while LMP7-Q/Q showed a trend toward increased incidence of aGVHD compared to LMP7-Q/K and K/K genotypes (p = 0.087, HR: 2.36, 95%CI = 0.88-6.31). All HA-1 and HA-8 disparate patients who developed aGVHD had the LMP7-Q/Q genotype. No significant association could be detected between HA-1, HA-8, or LMP7 and chronic GVHD, relapse-free survival (RFS), overall survival (OS), or transplant-related mortality (TRM). In conclusion, we suggested an association between the HA-1 disparity and the risk of developing aGVHD with a possible modifying effect of LMP7.

AScall - Automatic Allele-Specific qPCR Analysis

Minor histocompatibility antigens (MiHA) are critical elements for the immune response after allogeneic hematopoietic stem cell transplantation. They may cause both beneficial and detrimental effects in forms of graft-versus-tumor and graft-versus-host accordingly. MiHAs originate from donor-recipient discrepancies in single nucleotide polymorphisms, insertions, and deletions. To determine the genetic mismatches between a donor and a recipient, we have implemented a real-time PCR method in conjunction with allele-specific primers (AS-qPCR). The new approach allows for multiplexing up to 480 reactions per 96 well plate and differs from common qPCR based genotyping methods. Earlier, we have confirmed and published the AS-qPCR method, but standard software for qPCR analysis does not suit AS-qPCR data. Here we fill this gap and describe AScall - the interactive web application for the proposed genotyping method. With a convenient interface mimicking a regular qPCR machine interface, our tool allows batch qPCR data import via universal RDML format, amplification curves preprocessing, quality control, sample genotype calling, detailed results visualization, and report generation. We show the use of AScall for SNP and indel genotyping for the MiHA study, but anyone can use the application for an accordingly designed AS-qPCR experiment of their own. Genotyping was done manually and with AScall for 96 genomic DNA samples. AScall processed 4,800 qPCRs in 1.5 min, with only two genotype mismatches compared to manual analysis. It took 3 h for an experienced researcher for manual analysis. Source code is freely available for download at https://github.com/kablag/AScall. The tool is freely available on the web at the AScall server http://shtest.evrogen.net/AScall.

Minor Histocompatibility Antigen-Specific T Cells

Minor Histocompatibility (H) antigens are major histocompatibility complex (MHC)/Human Leukocyte Antigen (HLA)-bound peptides that differ between allogeneic hematopoietic stem cell transplantation (HCT) recipients and their donors as a result of genetic polymorphisms. Some minor H antigens can be used as therapeutic T cell targets to augment the graft-vs.-leukemia (GVL) effect in order to prevent or manage leukemia relapse after HCT. Graft engineering and post-HCT immunotherapies are being developed to optimize delivery of T cells specific for selected minor H antigens. These strategies have the potential to reduce relapse risk and thereby permit implementation of HCT approaches that are associated with less toxicity and fewer late effects, which is particularly important in the growing and developing pediatric patient. Most minor H antigens are expressed ubiquitously, including on epithelial tissues, and can be recognized by donor T cells following HCT, leading to graft-vs.-host disease (GVHD) as well as GVL. However, those minor H antigens that are expressed predominantly on hematopoietic cells can be targeted for selective GVL. Once full donor hematopoietic chimerism is achieved after HCT, hematopoietic-restricted minor H antigens are present only on residual recipient malignant hematopoietic cells, and these minor H antigens serve as tumor-specific antigens for donor T cells. Minor H antigen-specific T cells that are delivered as part of the donor hematopoietic stem cell graft at the time of HCT contribute to relapse prevention. However, in some cases the minor H antigen-specific T cells delivered with the graft may be quantitatively insufficient or become functionally impaired over time, leading to leukemia relapse. Following HCT, adoptive T cell immunotherapy can be used to treat or prevent relapse by delivering large numbers of donor T cells targeting hematopoietic-restricted minor H antigens. In this review, we discuss minor H antigens as T cell targets for augmenting the GVL effect in engineered HCT grafts and for post-HCT immunotherapy. We will highlight the importance of these developments for pediatric HCT.

Rapid Multiplex Genotyping of 20 HLA-A*02:01 Restricted Minor Histocompatibility Antigens

A subset of MHC-associated self-peptides presented by the recipient's cells and immunologically foreign to the donor can induce an allogeneic immune response after hematopoietic stem cell transplantation (HSCT). These immunogenic peptides originate from the genomic polymorphisms and are known as minor histocompatibility antigens (MiHA). MiHA mismatches trigger the post-transplant immune response, which could manifest in both the deleterious “graft-vs.-host” disease and the beneficial “graft-vs.-leukemia” effect. Importantly, some MiHAs are considered to be promising targets for posttransplant T-cell immunotherapy of hematopoietic malignancies. This creates a demand for a robust and fast approach to genotyping MiHA-encoding polymorphisms. We report a multiplex real-time PCR method for the genotyping of 20 polymorphisms that are encoding HLA-A^*02:01-restricted MiHAs. This method uses allele-specific primers and gene-specific hydrolysis probes. In 1 h it allows for the detection of MiHA mismatches in a donor-recipient pair without the need for electrophoresis, sequencing, or other time-consuming techniques. We validated the method with Sanger and NGS sequencing and demonstrated good performance over a wide range of DNA concentrations. We propose our protocol as a fast and accurate method of identifying mismatched MiHAs. The information on the MiHA mismatches is useful for studying the allogeneic immune response following HSCT and for selecting the targets for post-transplant T-cell therapy.

Increased Coexpression of PD-1, TIGIT, and KLRG-1 on Tumor-Reactive CD8+ T Cells During Relapse after Allogeneic Stem Cell Transplantation

Allogeneic stem cell transplantation (allo-SCT) can be a curative treatment for patients with a hematologic malignancy due to alloreactive T cell responses recognizing minor histocompatibility antigens (MiHA). Yet tumor immune escape mechanisms can cause failure of T cell immunity, leading to relapse. Tumor cells display low expression of costimulatory molecules and can up-regulate coinhibitory molecules that inhibit T cell functionality on ligation with their counter-receptors on the tumor-reactive T cells. The aim of this explorative study was to evaluate immune checkpoint expression profiles on T cell subsets and on cytomegalovirus (CMV)- and/or MiHA-reactive CD8⁺ T cells of allo-SCT recipients using a 13-color flow cytometry panel, and to correlate these expression patterns to clinical outcomes. MiHA-reactive CD8⁺ T cells exhibited an early differentiated CD27⁺⁺/CD28⁺⁺ phenotype with low KLRG-1 and CD57 expression. These T cells also displayed increased expression of PD-1, TIM-3, and TIGIT compared with total effector memory T cells and CMV-specific CD8⁺ T cells in healthy donors and allo-SCT recipients. Remarkably, high coexpression of PD-1, TIGIT, and KLRG-1 on MiHA-reactive CD8⁺ T cells was associated with relapse after allo-SCT. Taken together, these findings indicate that MiHA-specific CD8⁺ T cells of relapsed patients have a distinctive coinhibitory expression signature compared with patients who stay in remission. This phenotype may serve as a potential monitoring tool in patients. Moreover, these findings suggest that PD-1 and TIGIT play important roles in regulating T cell-mediated tumor control, providing a rationale for immunotherapy with blocking antibodies to treat relapse after allo-SCT.

Single step multiple genotyping by MALDI-TOF mass spectrometry, for evaluation of minor histocompatibility antigens in patients submitted to allogeneic stem cell transplantation from HLA-matched related and unrelated donor

The outcome of patients underwent to allogeneic stem cell transplantation (allo- SCT) is closely related to graft versus host disease (GvHD) and graft versus leukemia (GvL) effects which can be mediated by mHAgs. 23 mHAgs have been identified and reported to be differently correlated with GVHD or GVL and the aim of this work was develop a method to genotype the mHAgs described so far. For this study we used MALDI-TOF iPLEX Gold Mass Array technology. We tested 46 donor/recipient matched pairs that underwent allo-SCT because of Philadelphia positive (Ph+) chronic myeloid leukemia (n=29) or Ph+ acute lymphoblastic leukemia (n=17). Our data show that sibling pairs had a lesser number of mHAgs mismatches compared to MUD pairs. Notably, donor/recipient genomic mismatch on DPH1 was correlated with an increased risk of acute GvHD and LB-ADIR-1R mismatch on graft versus host direction was correlated with a better RFS with no increase of GvHD risk. Our work provides a simple, accurate and highly automatable method for mHAgs genotyping and suggest the role of mHAgs in addressing the immune reaction between donor and host.

Human Microtumors Generated in 3D: Novel Tools for Integrated In Situ Studies of Cancer Immunotherapies

Cellular immunotherapy targeting human tumor antigens is a promising strategy to treat solid tumors. Yet clinical results of cellular immunotherapy are disappointing. Moreover, the currently available in vitro human tumor models are not designed to study the optimization of T-cell therapies of solid tumors. Here, we describe a novel assay for multiparametric in situ analysis of therapeutic effects on individual human three-dimensional (3D) tumors. In this assay, tumors of several millimeter diameter are generated from human cancer cell lines of different tumor entities in a collagen type I microenvironment. A newly developed approach for efficient morphological analysis reveals that these in vitro tumors resemble many characteristics of the corresponding clinical cancers such as histological features, immunohistochemical staining patterns, distinct tumor growth compartments and heterogeneous protein expression. To assess the response to therapy with tumor antigen specific T-cells, standardized protocols are described to determine T-cell infiltration and tumor destruction by monitoring soluble factors and tumor growth. Human tumors engineered in 3D collagen scaffolds are excellent in vitro surrogates for avascular tumor stages allowing integrated analyses of the antitumor efficacy of cancer specific immunotherapy in situ.

UGT2B17 minor histocompatibility mismatch and clinical outcome after HLA-identical sibling donor stem cell transplantation

Minor histocompatibility Ags (mHags) have been implicated in the pathogenesis of GVHD after allogeneic hematopoietic stem cell transplantation (HSCT). Uridine diphospho-glucuronosyltransferase 2B17 (UGT2B17) gene deletion may act as a mHag and its association with acute GVHD (aGVHD) has been described. We retrospectively studied the clinical impact of a UGT2B17 mismatch in a cohort of 1127 patients receiving a HSCT from an HLA-identical sibling donor. UGT2B17 mismatch was present in 69 cases (6.1%). Incidence of severe aGVHD was higher in the UGT2B17 mismatched pairs (22.7% vs 14.6%), but this difference was not statistically significant (P: 0.098). We did not detect differences in chronic GVHD, overall survival, relapse-free survival, transplant-related mortality or relapse. Nevertheless, when we analyzed only those patients receiving grafts from a male donor (616 cases), aGVHD was significantly higher in the UGT2B17 mismatched group (25.1% vs 12.8%; P: 0.005) and this association was confirmed by the multivariate analysis (P: 0.043; hazard ratio: 2.16, 95% confidence interval: 1.03-4.57). Overall survival was worse for patients mismatched for UGT2B17 (P: 0.005). We conclude that UGT2B17 mismatch has a negative clinical impact in allogeneic HSCT from HLA-identical sibling donors only when a male donor is used. These results should be confirmed by other studies.

Possible role of minor h antigens in the persistence of donor chimerism after stem cell transplantation; relevance for sustained leukemia remission

Persistent complete donor chimerism is an important clinical indicator for remissions of hematological malignancies after HLA-matched allogeneic stem cell transplantation (SCT). However, the mechanisms mediating the persistence of complete donor chimerism are poorly understood. The frequent coincidence of complete donor chimerism with graft-versus-leukemia effects and graft-versus-host disease suggests that immune responses against minor histocompatibility antigens (mHags) are playing an important role in suppressing the host hematopoiesis after allogeneic SCT. Here, we investigated a possible relationship between donor immune responses against the hematopoiesis-restricted mHag HA-1 and the long-term kinetics of host hematopoietic chimerism in a cohort of 10 patients after allogeneic HLA-matched, HA-1 mismatched SCT. Functional HA-1 specific CTLs (HA-1 CTLs) were detectable in 6/10 patients lysing host-type hematopoietic cells in vitro. Presence of HA-1 CTLs in the peripheral blood coincided with low host hematopoiesis levels quantified by highly sensitive mHag specific PCR. Additionally, co-incubation of host type CD34⁺ cells with HA-1 CTLs isolated after allogeneic SCT prevented progenitor and cobblestone area forming cell growth in vitro and human hematopoietic engraftment in immunodeficient mice. Conversely, absence or loss of HA-1 CTLs mostly coincided with high host hematopoiesis levels and/or relapse. In summary, in this first study, presence of HA-1 CTLs paralleled low host hematopoiesis levels. This coincidence might be supported by the capacity of HA-1 CTLs isolated after allogeneic SCT to specifically eliminate host type hematopoietic stem/progenitor cells. Additional studies involving multiple mismatched mHags in more patients are required to confirm this novel characteristic of mHag CTLs as factor for the persistence of complete donor chimerism and leukemia remission after allogeneic SCT.

Molecular typing methods for minor histocompatibility antigens

Minor histocompatibility (H) antigen mismatching leads to clinically relevant alloimmune reactivity. Depending on the tissue expression pattern of the involved minor H antigens, the immune response may either cause graft-versus-host disease and a graft-versus-tumor effect or lead to only a graft-versus-leukemia effect. Thus, identification of recipient-donor pairs with minor H antigen mismatches has clinical importance. This chapter describes molecular typing methods for molecular typing of minor H antigens.

Rejection of leukemic cells requires antigen-specific T cells with high functional avidity

In a context where injection of antigen (Ag)-specific T cells probably represents the future of leukemia immunotherapy, identification of optimal target Ags is crucial. We therefore sought to discover a reliable marker for selection of the most potent Ags. To this end, (1) we immunized mice against 8 individual Ags: 4 minor histocompatibility Ags (miHAs) and 4 leukemia-associated Ags (LAAs) that were overexpressed on leukemic relative to normal thymocytes; (2) we assessed their ability to reject EL4 leukemic cells; and (3) we correlated the properties of our Ags (and their cognate T cells) with their ability to induce protective antileukemic responses. Overall, individual miHAs instigated more potent antileukemic responses than LAAs. Three features had no influence on the ability of primed T cells to reject leukemic cells: (1) MHC-peptide affinity; (2) the stability of MHC-peptide complexes; and (3) epitope density at the surface of leukemic cells, as assessed using mass spectrometry. The cardinal feature of successful Ags is that they were recognized by high-avidity CD8 T cells that proliferated extensively in vivo. Our work suggests that in vitro evaluation of functional avidity represents the best criterion for selection of Ags, which should be prioritized in clinical trials of leukemia immunotherapy.

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.

Minor histocompatibility antigens as determinants for graft-versus-host disease after allogeneic haematopoietic stem cell transplantation

Minor histocompatibility antigens (minor H antigens) are genetically polymorphic peptides that have been shown to elicit immune response when mismatched between donor and recipient of haematopoietic stem cell transplantation (HSCT). Depending on the expression profiles, mismatches in these genes may either lead to harmful graft-versus-host (GvH) reaction or desired graft-versus-leukaemia (GvL) effect. We analysed retrospectively the effect of HLA-restricted matching 11 established autosomal minor H antigens on the risk of graft-versus-host disease and relapse in 311 HLA-matched sibling HSCT of a single centre. Increased incidence of chronic GvH disease was shown to be associated with mismatches in the HA-8 and ACC-1. The mRNA expression profiles in a large set of healthy and malignant tissue samples of minor H antigen genes demonstrated in silico that the expression profiles of HA-8 and ACC-1 were surprisingly different: HA-8 gene was expressed in practically all tissues, whereas ACC-1 gene had a restricted profile. The results demonstrated that mismatches in minor H antigens HA-8 and ACC-1 predisposed to chronic graft-versus-host disease (GvHD).

Occurrence and Impact of Minor Histocompatibility Antigens' Disparities on Outcomes of Hematopoietic Stem Cell Transplantation from HLA-Matched Sibling Donors

We have examined the alleles of eleven minor histocompatibility antigens (MiHAs) and investigated the occurrence of immunogenic MiHA disparities in 62 recipients of allogeneic hematopoietic cell transplantation (allo-HCT) with myeloablative conditioning performed between 2000 and 2008 and in their HLA-matched sibling donors. Immunogenic MiHA mismatches were detected in 42 donor-recipient pairs: in 29% MiHA was mismatched in HVG direction, in another 29% in GVH direction; bidirectional MiHA disparity was detected in 10% and no MiHA mismatches in 32%. Patients with GVH-directed HY mismatches had lower both overall survival and disease-free survival at 3 years than patients with compatible HY; also higher incidence of both severe acute GvHD and extensive chronic GVHD was observed in patients with GVH-directed HY mismatch. On contrary, GVH-directed mismatches of autosomally encoded MiHAs had no negative effect on overall survival. Results of our study help to understand why posttransplant courses of allo-HCT from siblings may vary despite the complete high-resolution HLA matching of a donor and a recipient.

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.

Towards effective and safe immunotherapy after allogeneic stem cell transplantation: identification of hematopoietic-specific minor histocompatibility antigen UTA2-1

Donor T cells directed at hematopoietic system-specific minor histocompatibility antigens (mHags) are considered important cellular tools to induce therapeutic graft-versus-tumor (GvT) effects with low risk of graft-versus-host disease after allogeneic stem cell transplantation. To enable the clinical evaluation of the concept of mHag-based immunotherapy and subsequent broad implementation, the identification of more hematopoietic mHags with broad applicability is imperative. Here we describe novel mHag UTA2-1 with ideal characteristics for this purpose. We identified this antigen using genome-wide zygosity-genotype correlation analysis of a mHag-specific CD8⁺ cytotoxic T lymphocyte (CTL) clone derived from a multiple myeloma patient who achieved a long-lasting complete remission after donor lymphocyte infusion from an human leukocyte antigen (HLA)-matched sibling. UTA2-1 is a polymorphic peptide presented by the common HLA molecule HLA-A*02:01, which is encoded by the bi-allelic hematopoietic-specific gene C12orf35. Tetramer analyses demonstrated an expansion of UTA2-1-directed T cells in patient blood samples after several donor T-cell infusions that mediated clinical GvT responses. More importantly, UTA2-1-specific CTL effectively lysed mHag⁺ hematopoietic cells, including patient myeloma cells, without affecting non-hematopoietic cells. Thus, with the capacity to induce relevant immunotherapeutic CTLs, it's HLA-A*02 restriction and equally balanced phenotype frequency, UTA2-1 is a highly valuable mHag to facilitate clinical application of mHag-based immunotherapy.

HDAC inhibition and graft versus host disease

Histone deacetylase (HDAC) inhibitors are currently used clinically as anticancer drugs. Recent data have demonstrated that some of these drugs have potent antiinflammatory or immunomodulatory effects at noncytotoxic doses. The immunomodulatory effects have shown potential for therapeutic benefit after allogeneic bone marrow transplantation in several experimental models of graft versus host disease (GVHD). These effects, at least in part, result from the ability of HDAC inhibitors (HDACi) to suppress the function of host antigen presenting cells such as dendritic cells (DC). HDACi reduce the dendritic cell (DC) responses, in part, by enhancing the expression of indoleamine 2,3-dioxygenase (IDO) in a signal transducer and activator of transcription-3 (STAT-3) dependent manner. They also alter the function of other immune cells such as T regulatory cells and natural killer (NK) cells, which also play important roles in the biology of GVHD. Based on these observations, a clinical trial has been launched to evaluate the impact of HDAC inhibitors on clinical GVHD. The experimental, mechanistic studies along with the brief preliminary observations from the ongoing clinical trial are discussed in this review.

Minor histocompatibility antigens: presentation principles, recognition logic and the potential for a healing hand

PURPOSE OF REVIEW

There is ample evidence indicating a pathologic role for minor histocompatibility antigens in inciting graft-versus-host disease in major histocompatibility complex (MHC)-matched bone marrow transplantation and rejection of solid organ allografts. Here we review the current knowledge of the genetic and biochemical bases for the cause of minor histoincompatibility and the structural basis for the recognition of the resulting alloantigens by the T-cell receptor.

RECENT FINDINGS

Recent evidence indicates that we as independently conceived individuals are genetically unique, thus, offering a mechanism for minor histoincompatibility between MHC-identical donor-recipient pairs. Furthermore, advances in delineating the mechanisms underlying antigen cross-presentation by MHC class I molecules and a critical role for autophagy in presenting cytoplasmic antigens by MHC class II molecules have been made. These new insights coupled with the X-ray crystallographic solution of several peptide/MHC-T-cell receptor structures have revealed mechanisms of histoincompatibility.

SUMMARY

On the basis of these new insights, ways to test for allograft compatibility and concoction of immunotherapies are discussed.

New perspectives on the biology of acute GVHD

The use of allogeneic hematopoietic cell transplantation (HCT) has increased as new techniques have been developed for transplantation in patients who previously would not have been considered HCT candidates. However, its efficacy continued to be limited by the development of frequent and severe acute GVHD. The complex and intricate pathophysiology of acute GVHD is a consequence of interactions between the donor and host innate and adaptive immune responses. Multiple inflammatory molecules and cell types are implicated in the development of GVHD that can be categorized as: (1) triggers that initiate GVHD by therapy-induced tissue damage and the antigen disparities between host and graft tissue; (2) sensors that detect the triggers, that is, process and present alloantigens; (3) mediators such as T-cell subsets (naive, memory, regulatory, Th17 and natural killer T cells) and (4) the effectors and amplifiers that cause damage of the target organs. These multiple inflammatory molecules and cell types that are implicated in the development of GVHD have been described with models that use stepwise cascades. Herein, we provide a novel perspective on the immunobiology of acute GVHD and briefly discuss some of the outstanding questions and limitations of the model systems.

Immunomonitoring of graft-versus-host minor histocompatibility antigen correlates with graft-versus-host disease and absence of relapse after graft

BACKGROUND

After HLA-identical hematopoietic stem cell transplantation, minor histocompatibility (mH) antigen alloreactivity plays a dominant role in the development of graft-versus-host disease (GVHD) and graft versus leukemia (GVL).

STUDY DESIGN AND METHODS

We have analyzed the mH alloreactivity (enzyme-linked immunospot [ELISpot] for interferon-gamma[IFN-gamma] assay) from 24 donor/recipient pairs over a period of 2 years of follow-up and correlated such alloreactivity with the development of GVHD or absence of relapse. Circulating specific T cells anti-mH with multimer HLA-peptides were also studied.

RESULTS

We show by ELISpot IFN-gamma assay that alloreactivity during the first 3 months from donor versus recipient or donor versus mismatched identified mH antigens is associated with acute GVHD and GVL effect. In addition, we demonstrate that the donor-versus-recipient reactivity observed after the third month is highly associated with chronic GVHD and GVL (p = 0.0007). Finally, we show by multimer HLA-peptide assay that mH epitope-specific T cells present after 3 months are statistically related to the GVL effect.

CONCLUSIONS

Our results provide a robust method to monitor mH antigen graft-versus-host reaction and suggest that current identified mH have predictive value on GVHD and GVL.

The relevance of minor histocompatibility antigens in solid organ transplantation

PURPOSE OF REVIEW

Disparities in minor histocompatibility antigens between HLA-matched organ and hematopoietic stem cell donors and recipients create the risks of graft failure and graft-versus-host disease (GvHD) respectively. A decade ago, technical advances combined with genomic information resulted in the identification of the chemical nature of the first series of minor histocompatibility antigens, facilitating their molecular typing. A new era of research had begun in exploring the role of minor histocompatibility antigens in physiological and nonphysiological settings. Here we summarize, to the best of our knowledge, human studies on the relevance of minor histocompatibility antigens in solid organ transplantation with a main focus on renal allografting.

RECENT FINDINGS

The minor histocompatibility antigen HY is associated with acute rejection, and male grafts in female recipients have reduced graft survival; both cellular and humoral responses are observed. Studies on autosomal minor histocompatibility antigens on graft rejection are less conclusive; their role in transplant tolerance, however, offers perspective.

SUMMARY

Information on the clinical relevance of minor histocompatibility antigen allo-immune responses in solid organ allografting is still scarce. The possible implications of the minor histocompatibility allo-immune responses for future clinical practice in solid organ transplantation are discussed in relation to their possible detrimental or beneficial effects on the host.

Non-HLA T-cell reactivity during the first year after HLA-identical living-related kidney transplantation

BACKGROUND

It has been reported that donor-reactive T-cell responses may decrease during the first year after HLA-mismatched organ transplantation. We wondered whether donor-reactive T-cell responses directed to minor histocompatibility antigens (mHAgs) or other non-HLA antigens also decrease after HLA-identical living-related (LR) kidney transplantation.

METHODS

We studied donor-reactive T-cell responses by IFN-gamma and granzyme B (GrB) Elispot assays in 15 HLA-identical LR kidney transplant recipients before, six months and one yr after transplantation. Third-party reactivity was used as control. Patient and donor peripheral blood mononuclear cells were typed for 11 known mHAgs.

RESULTS

During the study period, 60% and 36% of the patients demonstrated donor-reactive IFN-gamma and GrB producing cells (pc), respectively. The number of donor-reactive IFN-gamma and GrB pc was significantly lower than the number of third-party reactive IFN-gamma and GrB pc. After transplantation, donor-reactivity and third-party reactivity were comparable to pre-transplant values. No relation was found in mHAg mismatches between donor and recipient and donor-reactive T-cell response.

CONCLUSIONS

Donor-reactivity could be detected before and after HLA-identical LR kidney transplantation, but was not related with the number of mHAg mismatches, and did not decrease after transplantation.

Naturally acquired tolerance and sensitization to minor histocompatibility antigens in healthy family members

Bidirectional cell transfer during pregnancy frequently leads to postpartum persistence of allogeneic cells and alloimmune responses in both the mother and in her offspring. The life-long consequences of naturally acquired alloimmune reactivity are probably of importance for the outcome of allogeneic stem cell transplantation. We investigated the presence of CD8(pos) minor histocompatibility (H) antigen-specific cytotoxic T lymphocytes (T(CTL)) and CD8(pos) minor H antigen-specific T regulator cells (T(REG)) in peripheral blood cells obtained from 17 minor H antigen-disparate mother-offspring pairs. Absence of minor H antigen-specific T(REG), as marked by the feasibility to expand T(CTL) from isolated tetramer(pos) populations, was observed in 6 mothers and 1 son. The presence of minor H alloantigen-specific T(REG) was observed in 4 mothers and 5 sons. These T(REG) were detected within isolated tetramer(dim) staining fractions and functioned in a CTLA-4-dependent fashion. Our study indicates that both T(CTL) and T(REG) mediated alloimmunity against minor H antigens may be present in healthy female and male hematopoietic stem cell donors, potentially influencing graft-versus-host reactivity in different ways.

Hypomethylating drugs convert HA-1-negative solid tumors into targets for stem cell-based immunotherapy

Clinical responses of solid tumors after allogeneic human leukocyte antigen-matched stem cell transplantation (SCT) often coincide with severe graft-versus-host disease (GVHD). Targeting minor histocompatibility antigens (mHags) with hematopoiesis- and cancer-restricted expression, for example, HA-1, may allow boosting the antitumor effect of allogeneic SCT without risking severe GVHD. The mHag HA-1 is aberrantly expressed in cancers of most entities. However, an estimated 30% to 40% of solid tumors do not express HA-1 (ie, are HA-1(neg)) and cannot be targeted by HA-1-specific immunotherapy. Here, we investigated the transcriptional regulation of HA-1 gene expression in cancer. We found that DNA hypermethylation in the HA-1 promoter region is closely associated with the absence of HA-1 gene expression in solid tumor cell lines. Moreover, we detected HA-1 promoter hypermethylation in primary cancers. The hypomethylating agent 5-aza-2'-deoxycytidine induced HA-1 expression only in HA-1(neg) tumor cells and sensitized them for recognition by HA-1-specific cytotoxic T lymphocytes. Contrarily, the histone deacetylation inhibitor trichostatin A induced HA-1 expression both in some HA-1(neg) tumor cell lines and in normal nonhematopoietic cells. Our data suggest that promoter hypermethylation contributes to the HA-1 gene regulation in tumors. Hypomethylating drugs might extend the safe applicability of HA-1 as an immunotherapeutic target on solid tumors after allogeneic SCT.

Immunogenic disparities of 11 minor histocompatibility antigens (mHAs) in HLA-matched unrelated allogeneic hematopoietic SCT

We determined the alleles of 11 mHAs and investigated the association of immunogenic mHA mismatches between a donor and a recipient with a course of allogeneic hematopoietic SCT (allo-HSCT) from 10/10 alleles HLA-matched unrelated donors in 92 recipients after myeloablative conditioning between 2004 and 2006. The frequency analysis of mHA alleles, genotypes and phenotypes accompanied by appropriate restriction HLA Ags allowed for an estimation of the probability of immunogenic mismatches, which was the highest for HA-1, HA-8 and HY. GVH-directed disparity of mHAs with broad tissue distribution, especially of the sex-related HY Ag, influenced the results of allo-HSCT from HLA-matched unrelated donors by not only increasing the probability of chronic GVHD (cGVHD) but also by decreasing the relapse rate.

Targeting a single mismatched minor histocompatibility antigen with tumor-restricted expression eradicates human solid tumors

Regressions of metastatic solid tumors after allogeneic human leukocyte antigen (HLA)–matched stem cell transplantation (SCT) are often associated with detrimental graft-versus-host disease (GVHD). The graft-versus-host reaction of the HLA-matched donor is directed mainly against the multiple mismatched minor histocompatibility antigens (mHags) of the patient. mHags are strong HLA-restricted alloantigens with differential tissue distribution. Ubiquitously expressed mHags are the prime in situ targets of GVHD. The mHag HA-1 is hematopoiesis restricted, but displays additionally an aberrant expression on solid tumors. Thus, HA-1 might be an excellent target to boost the anti–solid tumor effect of allogeneic SCT without inducing severe GVHD. Here, we show that cytotoxic T lymphocytes (CTLs) solely targeting the human mHag HA-1 are capable of eradicating 3-dimensional human solid tumors in a highly mHag-specific manner in vitro, accompanied by interferon-γ release. In vivo, HA-1–specific CTLs distribute systemically and prevent human breast cancer metastases in immunodeficient mice. Moreover, HA-1–specific CTLs infiltrate and inhibit the progression of fully established metastases. Our study provides the first proof for the efficacy of a clinically applicable concept to exploit single mismatched mHags with hematopoiesis- and solid tumor–restricted expression for boosting the anti–solid tumor effect of allogeneic SCT.

Phenotype frequencies of autosomal minor histocompatibility antigens display significant differences among populations

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.

Peptides from cellular proteins evoking alloimmune responses in human leukocyte antigen–identical transplantation are called minor histocompatibility (H) antigens. Upon hematopoietic stem cell transplantation (HSCT) for hematological malignancies or for solid tumors, responses to minor H antigens may have detrimental effects, e.g., graft-versus-host-disease and graft rejection, but can also significantly contribute to the eradication of the tumor cells. We designated the latter antigens as “tumor” minor H antigens. Current clinical trials aim at using these tumor minor H antigens to boost the graft-versus-tumor response. So far, it is unclear how frequently the HSCT recipient and donor differ in their minor H antigens and thus how many cancer patients are eligible for minor H antigen-based treatment. Therefore, worldwide 31 laboratories joined forces to determine the genotype and phenotype frequencies of ten autosomally encoded minor H antigens in six ethnic populations. The frequencies vary depending upon ethnic background and geographic location of the population, implying that the potential applicability of the tumor minor H antigens differs from one population to another. Depending on the population, the current theoretical percentages of clinical application of the eight tumor minor H antigens in HLA-matched combinations is estimated at 12% to 34%.

Pathophysiology of acute graft-versus-host disease: recent advances

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for many malignant and nonmalignant hematologic diseases. Donor T cells from the allografts are critical for the success of this effective therapy. Unfortunately these T cells not only recognize and attack the disease cells/tissues but also the other normal tissues of the recipient as "foreign" or "nonself" and cause severe, immune-mediated toxicity, graft-versus-host disease (GVHD). Several insights into the complex pathophysiology of GVHD have been gained from recent experimental observations, which show that acute GVHD is a consequence of interactions between both the donor and the host innate and adaptive immune systems. These insights have identified a role for a variety of cytokines, chemokines, novel T-cell subsets (naĩve, memory, regulatory, and NKT cells) and for non-T cells of both the donor and the host (antigen presenting cells, delta T cells, B cells, and NK cells) in modulating the induction, severity, and maintenance of acute GVHD. This review will focus on the immunobiology of experimental acute GVHD with an emphasis on the recent observations.

Minor histocompatibility antigens as targets for immunotherapy using allogeneic immune reactions

Minor histocompatibility antigens (mHag) were originally identified as antigens causing graft rejection or graft-versus-host disease in human leukocyte antigen (HLA)-matched allogeneic transplantation. Molecular identification has revealed most to be major histocompatibility complex (MHC)-bound short peptide fragments encoded by genes which are polymorphic due to single nucleotide polymorphisms (SNP). Genotypic disparity of SNP between transplantation donors and recipients gives rise to mHag as non-self antigens for both the donor and the recipient. Subsequently, mHag have been explored as immunotherapeutic antigens for use against recurring hematological malignancies after allogeneic hematopoietic cell transplantation (HCT), because mHag expressed only on hematopoietic cells are considered to augment graft-versus-leukemia/lymphoma (GVL) effects without increasing the risk of life-threatening graft-versus-host disease (GVHD). Accumulating evidence suggests that T-cell responses to mHag aberrantly expressed on solid tumor cells are also involved in the eradication of sensitive tumors such as renal cell carcinomas following HCT. Over the past decade, the number of putative GVL-directed mHag has increased to a level that covers more than 30% of the Japanese patient population, so that clinical trials may now be executed in the setting of either vaccination or adoptive immunotherapy. As it is expected that immune responses to alloantigens are more powerful than to tumor antigens mostly derived from overexpressed self-proteins, mHag-based immunotherapy may lead to a new treatment modality for high-risk malignancies following allogeneic HCT.

Risk assessment in haematopoietic stem cell transplantation: minor histocompatibility antigens

Minor histocompatibility (H) antigens are key molecules in graft-versus-host disease (GvHD) and the graft-versus-tumour effect after allogeneic stem-cell transplantation (SCT). Today, molecular typing methods allow an easy assessment of differences in minor H antigens between patient and donors, so that the GvHD risk in individual patients can be estimated. However, the large number of minor H antigens prevents matching for them to avoid GvHD. Interestingly, mismatching for minor H antigens might improve the outcome of allogeneic SCT. Some minor H antigens are expressed mainly by malignant cells and can therefore serve as excellent targets for cancer immunotherapy. Thus, mismatching for tumour-expressed minor H antigens allows boosting of the curative effect of allogeneic SCT. Current research is elucidating the impact of e.g. donor immunization, immunodominance, or functional expression of minor H antigens on the extent of the GvH response.