Qualitative and Quantitative Differences in Peptides Bound to HLA-B27 in the Presence of Mouse versus Human Tapasin Define a Role for Tapasin as a Size-Dependent Peptide Editor

Antibody-Peptide Epitope Conjugates for Personalized Cancer Therapy

Antibody-peptide epitope conjugates (APEC) are a new class of modified antibody-drug conjugates that redirect T-cell viral immunity against tumor cells. APECs contain a tumor-specific protease cleavage site linked to a patient-specific viral epitope, resulting in presentation of viral epitopes on cancer cells and subsequent recruitment and killing by CD8+ T cells. Here we developed an experimental pipeline to create patient-specific APECs and identified new preclinical therapies for ovarian carcinoma. Using functional assessment of viral peptide antigen responses to common viruses like cytomegalovirus (CMV) in patients with ovarian cancer, a library of 192 APECs with distinct protease cleavage sequences was created using the anti-epithelial cell adhesion molecule (EpCAM) antibody. Each APEC was tested for in vitro cancer cell killing, and top candidates were screened for killing xenograft tumors grown in zebrafish and mice. These preclinical modeling studies identified EpCAM-MMP7-CMV APEC (EpCAM-MC) as a potential new immunotherapy for ovarian carcinoma. Importantly, EpCAM-MC also demonstrated robust T-cell responses in primary ovarian carcinoma patient ascites samples. This work highlights a robust, customizable platform to rapidly develop patient-specific APECs.

SIGNIFICANCE

This study develops a high-throughput preclinical platform to identify patient-specific antibody-peptide epitope conjugates that target cancer cells and demonstrates the potential of this immunotherapy approach for treating ovarian carcinoma.

The viral transcription group determines the HLA class I cellular immune response against human respiratory syncytial virus

The cytotoxic T-lymphocyte-mediated killing of virus-infected cells requires previous recognition of short viral antigenic peptides bound to human leukocyte antigen class I molecules that are exposed on the surface of infected cells. The cytotoxic T-lymphocyte response is critical for the clearance of human respiratory syncytial virus infection. In this study, naturally processed viral human leukocyte antigen class I ligands were identified with mass spectrometry analysis of complex human leukocyte antigen-bound peptide pools isolated from large amounts of human respiratory syncytial virus-infected cells. Acute antiviral T-cell response characterization showed that viral transcription determines both the immunoprevalence and immunodominance of the human leukocyte antigen class I response to human respiratory syncytial virus. These findings have clear implications for antiviral vaccine design.

HLA-A*01:03, HLA-A*24:02, HLA-B*08:01, HLA-B*27:05, HLA-B*35:01, HLA-B*44:02, and HLA-C*07:01 monochain transgenic/H-2 class I null mice: novel versatile preclinical models of human T cell responses

We have generated a panel of transgenic mice expressing HLA-A*01:03, -A*24:02, -B*08:01, -B*27:05, -B*35:01, -B*44:02, or -C*07:01 as chimeric monochain molecules (i.e., appropriate HLA α1α2 H chain domains fused with a mouse α3 domain and covalently linked to human β2-microglobulin). Whereas surface expression of several transgenes was markedly reduced in recipient mice that coexpressed endogenous H-2 class I molecules, substantial surface expression of all human transgenes was observed in mice lacking H-2 class I molecules. In these HLA monochain transgenic/H-2 class I null mice, we observed a quantitative and qualitative restoration of the peripheral CD8(+) T cell repertoire, which exhibited a TCR diversity comparable with C57BL/6 WT mice. Potent epitope-specific, HLA-restricted, IFN-γ-producing CD8(+) T cell responses were generated against known reference T cell epitopes after either peptide or DNA immunization. HLA-wise, these new transgenic strains encompass a large proportion of individuals from all major human races and ethnicities. In combination with the previously created HLA-A*02:01 and -B*07:02 transgenic mice, the novel HLA transgenic mice described in this report should be a versatile preclinical animal model that will speed up the identification and optimization of HLA-restricted CD8(+) T cell epitopes of potential interest in various autoimmune human diseases and in preclinical evaluation of T cell-based vaccines.

Natural HLA-B*2705 protein ligands with glutamine as anchor motif: implications for HLA-B27 association with spondyloarthropathy

The presentation of short viral peptide antigens by human leukocyte antigen (HLA) class I molecules on cell surfaces is a key step in the activation of cytotoxic T lymphocytes, which mediate the killing of pathogen-infected cells or initiate autoimmune tissue damage. HLA-B27 is a well known class I molecule that is used to study both facets of the cellular immune response. Using mass spectrometry analysis of complex HLA-bound peptide pools isolated from large amounts of HLA-B*2705(+) cells, we identified 200 naturally processed HLA-B*2705 ligands. Our analyses revealed that a change in the position (P) 2 anchor motif was detected in the 3% of HLA-B*2705 ligands identified. B*2705 class I molecules were able to bind these six GlnP2 peptides, which showed significant homology to pathogenic bacterial sequences, with a broad range of affinities. One of these ligands was able to bind with distinct conformations to HLA-B27 subtypes differentially associated with ankylosing spondylitis. These conformational differences could be sufficient to initiate autoimmune damage in patients with ankylosing spondylitis-associated subtypes. Therefore, these kinds of peptides (short, with GlnP2, and similar low affinity to all HLA-B27 subtypes tested but with unlike conformations in differentially ankylosing spondylitis-associated subtypes) must not be excluded from future researches involving potential arthritogenic peptides.

Bare lymphocyte syndrome: an opportunity to discover our immune system

Bare lymphocyte syndrome (BLS) is a rare immunodeficiency disorder manifested by the partial or complete disappearance of major histocompatibility complex (MHC) proteins from the surface of the cells. Based on this specific feature, it is categorized into three different types depending on which type of MHC protein is affected. These proteins are mainly involved in generating the effective immune responses by differentiating 'self' from 'non-self' antigens through a process referred to as antigen presentation. Investigations on BLS have immensely contributed to our understanding of the transcriptional regulation of these molecules and have led to the discovery of several important proteins of the antigen presentation pathway. Reviews on this subject consistently project type II BLS, MHC II deficiency as BLS syndrome, although literatures' document cases of other types of BLS too. Therefore, in this article, we have assembled information on the BLS syndrome to produce a systematic narration while emphasizing the importance of BLS system in studying various aspects of immune biology.

From HLA-B27 to spondyloarthritis: a journey through the ER

Almost four decades of research into the role of human leukocyte antigen-B27 (HLA-B27) in susceptibility to spondyloarthritis has yet to yield a convincing answer. New results from an HLA-B27 transgenic rat model now demonstrate quite convincingly that CD8(+) T cells are not required for the inflammatory phenotype. Discoveries that the HLA-B27 heavy chain has a tendency to misfold during the assembly of class I complexes in the endoplasmic reticulum (ER) and to form aberrant disulfide-linked dimers after transport to the cell surface have forced the generation of new ideas about its role in disease pathogenesis. In transgenic rats, HLA-B27 misfolding generates ER stress and leads to activation of the unfolded protein response, which dramatically enhances the production of interleukin-23 (IL-23) in response to pattern recognition receptor agonists. These findings have led to the discovery of striking T-helper 17 cell activation and expansion in this animal model, consistent with results emerging from humans with spondyloarthritis and the discovery of IL23R as an additional susceptibility gene for ankylosing spondylitis. Together, these results suggest a novel link between HLA-B27 and the T-helper 17 axis through the consequences of protein misfolding and open new avenues of investigation as well as identifying new targets for therapeutic intervention in this group of diseases.

Design of a HIV-1-derived HLA-B07.02-restricted polyepitope construct

OBJECTIVE

To design a vaccine construct containing various but conserved HIV-1-derived epitopes and generating broad CD8 T cell responses.

METHODS

HLA-B7 transgenic H-2KD KO transgenic mice were used to identify potential new HLA-B07.02-restricted HIV-1-derived epitopes. Immunological recognition of these epitopes was confirmed by IFN-gamma ELISpot assays with PBMCs from HLA-B*0702 HIV-1-infected individuals. For these peptides as well as others previously identified, the capacity to induce cross-reactive responses against their frequent allelic variants was evaluated in the mouse model. A set of epitopes inducing strong T cell responses against various and conserved regions of HIV-1 was selected. A DNA vaccine was designed to express them as a unique antigen with or without a three amino acid ARY extension flanking each epitope. The spectrum of CD8 T responses generated by polyepitope constructs was tested in HLA-B7 transgenic mice.

RESULTS

Five new epitopes were identified in accessory and regulatory HIV-1 proteins. Twelve HLA-B07.02-restricted epitopes were selected on the basis of their structural conservation and cross-reactive immunogenicity. The ARY N-terminal extension flanking each epitope markedly increases their affinity for TAP and the use of this flanking extension in polyepitope vaccine has a sizable advantage to induce CD8 T cell cytotoxic responses in mice following DNA immunization.

CONCLUSION

The HLA-B7 mouse model allows to rapidly identify various HIV-1-derived epitopes of vaccine interest. Grouped in a polyepitope construct designed to increase their processing, this vaccine may be suitable for inducing multiple and relevant HIV-1-specific CTL responses in humans.

Regulation of MHC class I assembly and peptide binding

Peptide binding to MHC class I molecules is a component of a folding and assembly process that occurs in the endoplasmic reticulum (ER) and uses both cellular chaperones and dedicated factors. The involvement of glycoprotein quality-control chaperones and cellular oxidoreductases in peptide binding has led to models that are gradually being refined. Some aspects of the peptide loading process (e.g., the biosynthesis and degradation of MHC class I complexes) conform to models of glycoprotein quality control, but other aspects (e.g., the formation of a stable disulfide-linked dimer between tapasin and ERp57) deviate from models of chaperone and oxidoreductase function. Here we review what is known about the intersection of glycoprotein folding, oxidative reactions, and MHC class I peptide loading, emphasizing events that occur in the ER and within the MHC class I peptide loading complex.

Peptide-based vaccines for cancer: realizing their potential

Advances in the engineering of peptides, adjuvants and delivery systems have renewed the enthusiasm for peptide-based vaccination regimens in the setting of cancer, and there are a variety of clinical trials being conducted by pharmaceutical companies based on the use of peptides. The challenges to successful cancer immunotherapy are common to all immunotherapeutic strategies and not unique to peptide-based vaccination regimens. This review will describe the advances in the identification, design and delivery of peptides, the challenges to successful immunotherapy and will discuss potential options for the future.

Molecular machinations of the MHC-I peptide loading complex

The acquisition of an optimal peptide ligand by MHC class I molecules is crucial for the generation of immunity to viruses and tumors. This process is orchestrated by a molecular machine known as the peptide loading complex (PLC) that consists of specialized and general ER-resident molecules. These proteins collaborate to ensure the loading of an optimal peptide ligand into the antigen binding cleft of class I molecules. The surprising diversity of peptides bound to MHC class I molecules and recapitulation of class I assembly in vitro have provided new insights into the molecular machinations of peptide loading. Coupled with the extraordinary polymorphism of class I molecules and their differential dependence on various components of the PLC for cell surface expression, a picture of peptide loading at the molecular level has recently emerged and will be discussed herein.

An extra molecule in addition to human tapsin is required for surface expression of β2m linked HLA-B4402 on murine cell

Murine MHC class I can be readily expressed on the surface of human cell lines, but human class I molecules are expressed on mouse cells at a reduced level. Both human beta-2-microglobulin (beta(2)m) and tapasin (Tpn) have been demonstrated to be required for proper human MHC class I surface expression. Here we report that besides beta(2)m and tapasin, an extra unidentified component is also critical for the expression of certain human class I alleles. By covalently linking HLA-B4402 heavy chain to beta(2)m (beta(2)m-B44) a pre-assembled class I molecule has been created, which can be efficiently expressed and travel to the surface in human cells. In spite of being able to express inside cells, the linked beta(2)m-B44 molecule does not express on the surface of a murine fibroblast. Further investigation shows that lack of appearance on the surface is not due to quick degradation of unloaded class I, since provision of HLA-B4402 binding peptide could not rescue impaired surface expression. Co-expression with human tapasin does not rescue the defect excluding tapasin as the critical component for expression and indicating that a novel component of human origin is required for efficient surface expression of beta(2)m-B44 in murine cells. Surprisingly, not only did the beta(2)m-B44 construct fail to express on murine cells but also the surface expression of native murine MHC class I Kb was greatly reduced in transfected cells. It is likely that the expressed linked chain competitively associates with a component of class I processing in murine cells, reducing the exit rate of assembled mouse class I molecules. The results together suggest an unknown mechanism, which leads to the trapping of class I molecules in the ER.

More than one reason to rethink the use of peptides in vaccine design

The use of peptides as therapeutics is experiencing renewed enthusiasm owing to advances in delivery, stability and design. Moreover, there is a growing emphasis on the use of peptides in vaccine design as insights into tissue-specific processing of the immunogenic epitopes of proteins and the discovery of unusually long cytotoxic T-lymphocyte epitopes broaden the range of targets and give clues to enhancing peptide immunogenicity. Peptides can also be synthesized with known post-translational modifications and/or deliberately introduced protease-resistant peptide bonds to regulate their processing independent of tissue-specific proteolysis and to stabilize these compounds in vivo. We discuss the potential of peptide-based vaccines for the treatment of chronic viral diseases and cancer, and review recent developments in the field of peptide-based vaccines.

HLA-B*2704, an Allotype Associated with Ankylosing Spondylitis, Is Critically Dependent on Transporter Associated with Antigen Processing and Relatively Independent of Tapasin and Immunoproteasome for Maturation, Surface Expression, and T Cell Recognition: Relationship to B*2705 and B*2706

B*2704 is strongly associated to ankylosing spondylitis in Asian populations. It differs from the main HLA-B27 allotype, B*2705, in three amino acid changes. We analyzed the influence of tapasin, TAP, and immunoproteasome induction on maturation, surface expression, and T cell allorecognition of B*2704 and compared some of these features with B*2705 and B*2706, allotypes not associated to disease. In the tapasin-deficient .220 cell line, this chaperone significantly influenced the extent of folding of B*2704 and B*2705, but not their egress from the endoplasmic reticulum. In contrast, B*2706 showed faster folding and no accumulation in the endoplasmic reticulum in the absence of tapasin. Surface expression of B*2704 was more tapasin dependent than B*2705. However, expression of free H chain decreased in the presence of this chaperone for B*2705 but not B*2704, suggesting that more suboptimal ligands were loaded on B*2705 in the absence of tapasin. Despite its influence on surface expression, tapasin had little effect on allorecognition of B*2704. Both surface expression and T cell recognition of B*2704 were critically dependent on TAP, as established with TAP-deficient and TAP-proficient T2 cells. Both immunoproteasome and surface levels of B*2704 were induced by IFN-gamma, but this had little effect on allorecognition. Thus, except for the differential effects of tapasin on surface expression, the tapasin, TAP, and immunoproteasome dependency of B*2704 for maturation, surface expression, and T cell recognition are similar to B*2705, indicating that basic immunological features are shared by the two major HLA-B27 allotypes associated to ankylosing spondylitis in human populations.

Consistent patterns of expression of HLA class I free heavy chains in healthy individuals and raised expression in spondyloarthropathy patients point to physiological and pathological roles

OBJECTIVES

Major histocompatibility complex class I (MHC-I) proteins exist at the cell surface in antigen presenting forms and as beta2m-independent free heavy chains (FHCs). FHCs have been implicated in spondyloarthritis, but little is known about their expression in healthy individuals. We studied FHC expression on various human cell types, comparing spondyloarthropathy patients with healthy and rheumatoid arthritis (RA) patient controls.

METHODS

MHC-I expression was analysed by flow cytometry. FHC levels were normalized for overall MHC-I to generate a relative expression level. Relative FHC levels were analysed for peripheral blood and trophoblast samples from healthy volunteers, RA and spondyloarthropathy patients. Macrophages and dendritic cells were cultured in vitro to analyse changes following activation. Peripheral blood leucocytes from patients with ankylosing spondylitis (AS) and RA were treated with inflammatory stimuli and subsequent alterations in their relative FHC levels were analysed.

RESULTS

We found consistent patterns of differential relative FHC expression across lymphocyte subpopulations and particularly high expression on extravillous trophoblast. FHCs were present at higher levels in a reactive arthritis (ReA) population than in healthy controls and RA patients; differences not merely due to the presence of Human Leucocyte Antigen (HLA) B27. Treatment of leucocytes from arthritic patients with bacterial lipopolysaccharide resulted in significant up-regulation of FHC compared with an HLA B27+ control population.

CONCLUSIONS

Our findings define normal levels and tissue expression of FHCs, and support the hypothesis that disregulation of heavy chain expression may play a pathogenic role in spondyloarthropathy.