Identification Of Minor Histocompatibility Antigens Research Articles

Personal tumor antigens in blood malignancies: genomics-directed identification and targeting.

Hematological malignancies have long been at the forefront of the development of novel immune-based treatment strategies. The earliest successful efforts originated from the extensive body of work in the field of allogeneic hematopoietic stem cell transplantation. These efforts laid the foundation for the recent exciting era of cancer immunotherapy, which includes immune checkpoint blockade, personal neoantigen vaccines, and adoptive T cell transfer. At the heart of the specificity of these novel strategies is the recognition of target antigens presented by malignant cells to T cells. Here, we review the advances in systematic identification of minor histocompatibility antigens and neoantigens arising from personal somatic alterations or recurrent driver mutations. These exciting efforts pave the path for the implementation of personalized combinatorial cancer therapy.

S890 NEW WHOLE GENOME ASSOCIATION SCANNING APPROACH FOR THE DISCOVERY OF HLA CLASS I‐RESTRICTED MINOR HISTOCOMPATIBILITY ANTIGENS

Background:Patients that undergo allogeneic stem cell transplantation (SCT) as treatment for hematological diseases face the risk of relapse as well as Graft‐versus‐Host Disease (GvHD). GvHD as well as the favorable Graft‐versus‐Leukemia effect are mediated by donor T cells. These T cells recognize minor histocompatibility antigens: polymorphic peptides, which are presented on the cell surface by HLA molecules and are caused by genetic differences in single nucleotide polymorphisms (SNPs) between patient and donor. Knowledge about mismatched minor histocompatibility antigens may enable a more directed donor search as well as better prediction and measurement of the Graft‐versus‐Leukemia effect and GvHD for personalized treatment after transplantation, thereby contributing to a better outcome for patients treated with allogeneic SCT.Aims:Identification of minor histocompatibility antigens has been a laborious process in the past. Therefore, whole genome association scanning was developed in our laboratory. However, this method was restricted to two HLAs and screening of one million SNPs. The aim of this study is to develop and use an optimized method to identify the dominant repertoire of minor histocompatibility antigens in common HLA class I alleles.Methods:Donor T‐cells isolated from patients after allogeneic SCT are tested for recognition of a new panel of 191 selected B‐cell lines, which are sequenced in the 1000 Genome Project. This panel enables the inclusion of seven common HLAs and increases SNP coverage to 12 million (MAF > 0.01). SNPs that strongly associate with T‐cell recognition are subsequently validated to encode minor histocompatibility antigens.Results:A total of 19 novel minor histocompatibility antigens have been identified that are presented in seven common HLA class I alleles, showing the potential of this optimized approach. Besides conventional antigens, cryptic peptides were found as well as peptides restricted to HLAs that were not primarily targeted.Summary/Conclusion:This improved approach for whole genome association scanning has been successfully applied in rapidly discovering new minor histocompatibility antigens. The new method surpasses previous methods in its rapidness and coverage of HLAs and SNPs across the human genome, which additionally allows for identification of cryptic peptides. With the increasing number of patients that are analyzed in this study, T‐cells recognizing known minor histocompatibility antigens are more often isolated, indicating that the repertoire of minor histocompatibility antigens is limited. Our optimized method is expected to discover the majority of unknown antigens in this repertoire, thereby contributing essential knowledge for new strategies to improve clinical outcome after allogeneic SCT.

Identification of minor histocompatibility antigens based on the 1000 Genomes Project.

Minor histocompatibility antigens are highly immunogeneic polymorphic peptides playing crucial roles in the clinical outcome of HLA-identical allogeneic stem cell transplantation. Although the introduction of genome-wide association-based strategies significantly has accelerated the identification of minor histocompatibility antigens over the past years, more efficient, rapid and robust identification techniques are required for a better understanding of the immunobiology of minor histocompatibility antigens and for their optimal clinical application in the treatment of hematologic malignancies. To develop a strategy that can overcome the drawbacks of all earlier strategies, we now integrated our previously developed genetic correlation analysis methodology with the comprehensive genomic databases from the 1000 Genomes Project. We show that the data set of the 1000 Genomes Project is suitable to identify all of the previously known minor histocompatibility antigens. Moreover, we demonstrate the power of this novel approach by the identification of the new HLA-DP4 restricted minor histocompatibility antigen UTDP4-1, which despite extensive efforts could not be identified using any of the previously developed biochemical, molecular biological or genetic strategies. The 1000 Genomes Project-based identification of minor histocompatibility antigens thus represents a very convenient and robust method for the identification of new targets for cancer therapy after allogeneic stem cell transplantation.

High-Throughput Identification of Potential Minor Histocompatibility Antigens by MHC Tetramer-Based Screening: Feasibility and Limitations

T-cell recognition of minor histocompatibility antigens (MiHA) plays an important role in the graft-versus-tumor (GVT) effect of allogeneic stem cell transplantation (allo-SCT). However, the number of MiHA identified to date remains limited, making clinical application of MiHA reactive T-cell infusion difficult. This study represents the first attempt of genome-wide prediction of MiHA, coupled to the isolation of T-cell populations that react with these antigens. In this unbiased high-throughput MiHA screen, both the possibilities and pitfalls of this approach were investigated. First, 973 polymorphic peptides expressed by hematopoietic stem cells were predicted and screened for HLA-A2 binding. Subsequently a set of 333 high affinity HLA-A2 ligands was identified and post transplantation samples from allo-SCT patients were screened for T-cell reactivity by a combination of pMHC-tetramer-based enrichment and multi-color flow cytometry. Using this approach, 71 peptide-reactive T-cell populations were generated. The isolation of a T-cell line specifically recognizing target cells expressing the MAP4K1IMA antigen demonstrates that identification of MiHA through this approach is in principle feasible. However, with the exception of the known MiHA HMHA1, none of the other T-cell populations that were generated demonstrated recognition of endogenously MiHA expressing target cells, even though recognition of peptide-loaded targets was often apparent.Collectively these results demonstrate the technical feasibility of high-throughput analysis of antigen-specific T-cell responses in small patient samples. However, the high-sensitivity of this approach requires the use of potential epitope sets that are not solely based on MHC binding, to prevent the frequent detection of T-cell responses that lack biological relevance.

Rapid Identification of Clinical Relevant Minor Histocompatibility Antigens via Genome-Wide Zygosity-Genotype Correlation Analysis

Identification of minor histocompatibility antigens (mHag) with classic methods often requires sophisticated technologies, determination, and patience. We here describe and validate a nonlaborious and convenient genetic approach, based on genome-wide correlations of mHag zygosities with HapMap single-nucleotide polymorphism genotypes, to identify clinical relevant mHags within a reasonable time frame. Using this approach, we sought for the mHag recognized by a HLA-DRB1*1501-restricted T-cell clone, isolated from a multiple myeloma patient during a strong graft-versus-tumor effect associated with acute graft-versus-host disease grade 3. In a period of 3 months, we determined the mHag phenotype of 54 HapMap individuals, deduced the zygosity of 20 individuals, defined the mHag locus by zygosity-genotype correlation analyses, tested the putative mHag peptides from this locus, and finally showed that the mHag is encoded by the arginine (R) allele of a nonsynonymous single-nucleotide polymorphism in the SLC19A1 gene. We conclude that this powerful and convenient strategy offers a broadly accessible platform toward rapid identification of mHags associated with graft-versus-tumor effect and graft-versus-host disease.