Methionine oxidation selectively enhances T cell reactivity against a melanoma antigen

The impact of the peptide amino acids side-chain modifications on the immunological recognition has been scarcely explored. We investigate here the effect of methionine oxidation on the antigenicity of the melanoma immunodominant peptide 369-YMDGTMSQV-377 (YMD). Using CD8⁺ T cell activation assays, we found that the antigenicity of the sulfoxide form is higher when compared to the YMD peptide. This is consistent with free energy computations performed on HLA-A∗02:01/YMD/TCR complex showing that this is lowered upon oxidation, paired with a steep increase in order at atomic level. Oxidized YMD forms were identified at the melanoma cell surface by LC-MS/MS analysis. These results demonstrate that methionine oxidation in the antigenic peptides may generate altered peptide ligands with increased antigenicity, and that this oxidation may occur in vivo, opening up the possibility that high-affinity CD8⁺ T cells might be naturally primed in the course of melanoma progression, as a result of immunosurveillance.

Melanoma, Melanin, and Melanogenesis: The Yin and Yang Relationship

Melanin pigment plays a critical role in the protection against the harmful effects of ultraviolet radiation and other environmental stressors. It is produced by the enzymatic transformation of L-tyrosine to dopaquinone and subsequent chemical and biochemical reactions resulting in the formation of various 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and 5,6-dihydroxyindole (DHI) oligomers-main constituents of eumelanin, and benzothiazine and benzothiazole units of pheomelanin. The biosynthesis of melanin is regulated by sun exposure and by many hormonal factors at the tissue, cellular, and subcellular levels. While the presence of melanin protects against the development of skin cancers including cutaneous melanoma, its presence may be necessary for the malignant transformation of melanocytes. This shows a complex role of melanogenesis in melanoma development defined by chemical properties of melanin and the nature of generating pathways such as eu- and pheomelanogenesis. While eumelanin is believed to provide radioprotection and photoprotection by acting as an efficient antioxidant and sunscreen, pheomelanin, being less photostable, can generate mutagenic environment after exposure to the short-wavelength UVR. Melanogenesis by itself and its highly reactive intermediates show cytotoxic, genotoxic, and mutagenic activities, and it can stimulate glycolysis and hypoxia-inducible factor 1-alpha (HIF-1α) activation, which, combined with their immunosuppressive effects, can lead to melanoma progression and resistance to immunotherapy. On the other hand, melanogenesis-related proteins can be a target for immunotherapy. Interestingly, clinicopathological analyses on advanced melanomas have shown a negative correlation between tumor pigmentation and diseases outcome as defined by overall survival and disease-free time. This indicates a "Yin and Yang" role for melanin and active melanogenesis in melanoma development, progression, and therapy. Furthermore, based on the clinical, experimental data and diverse effects of melanogenesis, we propose that inhibition of melanogenesis in advanced melanotic melanoma represents a realistic adjuvant strategy to enhance immuno-, radio-, and chemotherapy.

Engineering soluble T-cell receptors for therapy

Immunotherapy approaches that target peptide-human leukocyte antigen (pHLA) complexes are becoming highly attractive because of their potential to access virtually all foreign and cellular proteins. For this reason, there has been considerable interest in the development of the natural ligand for pHLA, the T-cell receptor (TCR), as a soluble drug to target disease-associated pHLA presented at the cell surface. However, native TCR stability is suboptimal for soluble drug development, and natural TCRs generally have weak affinities for pHLAs, limiting their potential to reach efficacious receptor occupancy levels as soluble drugs. To overcome these limitations and make full use of the TCR as a soluble drug platform, several protein engineering solutions have been applied to TCRs to enhance both their stability and affinity, with a focus on retaining target specificity and selectivity. Here, we review these advances and look to the future for the next generation of soluble TCR-based therapies that can target monomorphic HLA-like proteins presenting both peptide and nonpeptide antigens.

T-Cell Receptor Mimic Antibodies for Cancer Immunotherapy

Antibody-based immunotherapies show clinical effectiveness in various cancer types. However, the target repertoire is limited to surface or soluble antigens, which are a relatively small percentage of the cancer proteome. Most proteins of the human proteome are intracellular. Short peptides from intracellular targets can be presented by MHC class I (MHC-I) molecules on cell surface, making them potential targets for cancer immunotherapy. Antibodies can be developed to target these peptide/MHC complexes, similar to the recognition of such complexes by the T-cell receptor (TCR). These antibodies are referred to as T-cell receptor mimic (TCRm) or TCR-like antibodies. Ongoing preclinical and clinical studies will help us understand their mechanisms of action and selection of target epitopes for immunotherapy. The present review will summarize and discuss the selection of intracellular antigens, production of the peptide/MHC complexes, isolation of TCRm antibodies for therapeutic applications, limitations of TCRm antibodies, and possible ways to advance TCRm antibody-based approaches into the clinic.

Human dendritic cells adenovirally-engineered to express three defined tumor antigens promote broad adaptive and innate immunity

Dendritic cell (DC) immunotherapy has shown a promising ability to promote anti-tumor immunity in vitro and in vivo. Many trials have tested single epitopes and single antigens to activate single T cell specificities, and often CD8(+) T cells only. We previously found that determinant spreading and breadth of antitumor immunity correlates with improved clinical response. Therefore, to promote activation and expansion of polyclonal, multiple antigen-specific CD8(+) T cells, as well as provide cognate help from antigen-specific CD4(+) T cells, we have created an adenovirus encoding three full length melanoma tumor antigens (tyrosinase, MART-1 and MAGE-A6, "AdVTMM"). We previously showed that adenovirus (AdV)-mediated antigen engineering of human DC is superior to peptide pulsing for T cell activation, and has positive biological effects on the DC, allowing for efficient activation of not only antigen-specific CD8(+) and CD4(+) T cells, but also NK cells. Here we describe the cloning and testing of "AdVTMM2," an E1/E3-deleted AdV encoding the three melanoma antigens. This novel three-antigen virus expresses mRNA and protein for all antigens, and AdVTMM-transduced DC activate both CD8(+) and CD4(+) T cells which recognize melanoma tumor cells more efficiently than single antigen AdV. Addition of physiological levels of interferon-α (IFNα) further amplifies melanoma antigen-specific T cell activation. NK cells are also activated, and show cytotoxic activity. Vaccination with multi-antigen engineered DC may provide for superior adaptive and innate immunity and ultimately, improved antitumor responses.

Specificity of bispecific T cell receptors and antibodies targeting peptide-HLA

Tumor-associated peptide-human leukocyte antigen complexes (pHLAs) represent the largest pool of cell surface-expressed cancer-specific epitopes, making them attractive targets for cancer therapies. Soluble bispecific molecules that incorporate an anti-CD3 effector function are being developed to redirect T cells against these targets using 2 different approaches. The first achieves pHLA recognition via affinity-enhanced versions of natural TCRs (e.g., immune-mobilizing monoclonal T cell receptors against cancer [ImmTAC] molecules), whereas the second harnesses an antibody-based format (TCR-mimic antibodies). For both classes of reagent, target specificity is vital, considering the vast universe of potential pHLA molecules that can be presented on healthy cells. Here, we made use of structural, biochemical, and computational approaches to investigate the molecular rules underpinning the reactivity patterns of pHLA-targeting bispecifics. We demonstrate that affinity-enhanced TCRs engage pHLA using a comparatively broad and balanced energetic footprint, with interactions distributed over several HLA and peptide side chains. As ImmTAC molecules, these TCRs also retained a greater degree of pHLA selectivity, with less off-target activity in cellular assays. Conversely, TCR-mimic antibodies tended to exhibit binding modes focused more toward hot spots on the HLA surface and exhibited a greater degree of crossreactivity. Our findings extend our understanding of the basic principles that underpin pHLA selectivity and exemplify a number of molecular approaches that can be used to probe the specificity of pHLA-targeting molecules, aiding the development of future reagents.

In silico prediction of tumor antigens derived from functional missense mutations of the cancer gene census

Antigen-specific immune responses against peptides derived from missense gene mutations have been identified in multiple cancers. The application of personalized peptide vaccines based on the tumor mutation repertoire of each cancer patient is a near-term clinical reality. These peptides can be identified for pre-validation by leveraging the results of massive gene sequencing efforts in cancer. In this study, we utilized NetMHC 3.2 to predict nanomolar peptide binding affinity to 57 human HLA-A and B alleles. All peptides were derived from 5,685 missense mutations in 312 genes annotated as functionally relevant in the Cancer Genome Project. Of the 26,672,189 potential 8-11 mer peptide-HLA pairs evaluated, 0.4% (127,800) display binding affinities < 50 nM, predicting high affinity interactions. These peptides can be segregated into two groups based on the binding affinity to HLA proteins relative to germline-encoded sequences: peptides for which both the mutant and wild-type forms are high affinity binders, and peptides for which only the mutant form is a high affinity binder. Current evidence directs the attention to mutations that increase HLA binding affinity, as compared with cognate wild-type peptide sequences, as these potentially are more relevant for vaccine development from a clinical perspective. Our analysis generated a database including all predicted HLA binding peptides and the corresponding change in binding affinity as a result of point mutations. Our study constitutes a broad foundation for the development of personalized peptide vaccines that hone-in on functionally relevant targets in multiple cancers in individuals with diverse HLA haplotypes.

Opportunities and Challenges for Antibodies against Intracellular Antigens

Therapeutic antibodies are one most significant advances in immunotherapy, the development of antibodies against disease-associated MHC-peptide complexes led to the introduction of TCR-like antibodies. TCR-like antibodies combine the recognition of intracellular proteins with the therapeutic potency and versatility of monoclonal antibodies (mAb), offering an unparalleled opportunity to expand the repertoire of therapeutic antibodies available to treat diseases like cancer. This review details the current state of TCR-like antibodies and describes their production, mechanisms as well as their applications. In addition, it presents an insight on the challenges that they must overcome in order to become commercially and clinically validated.

TCR-like antibodies in cancer immunotherapy

Cancer immunotherapy has been regarded as the most significant scientific breakthrough of 2013, and antibody therapy is at the core of this breakthrough. Despite significant success achieved in recent years, it is still difficult to target intracellular antigens of tumor cells with traditional antibodies, and novel therapeutic strategies are needed. T cell receptor (TCR)-like antibodies comprise a novel family of antibodies that can recognize peptide/MHC complexes on tumor cell surfaces. TCR-like antibodies can execute specific and significant anti-tumor immunity through several distinct molecular mechanisms, and the success of this type of antibody therapy in melanoma, leukemia, and breast, colon, and prostate tumor models has excited researchers in the immunotherapy field. Here, we summarize the generation strategy, function, and molecular mechanisms of TCR-like antibodies described in publications, focusing on the most significant discoveries.

Targeting the MHC Ligandome by Use of TCR-Like Antibodies

Monoclonal antibodies (mAbs) are valuable as research reagents, in diagnosis and in therapy. Their high specificity, the ease in production, favorable biophysical properties and the opportunity to engineer different properties make mAbs a versatile class of biologics. mAbs targeting peptide–major histocompatibility molecule (pMHC) complexes are often referred to as “TCR-like” mAbs, as pMHC complexes are generally recognized by T-cell receptors (TCRs). Presentation of self- and non-self-derived peptide fragments on MHC molecules and subsequent activation of T cells dictate immune responses in health and disease. This includes responses to infectious agents or cancer but also aberrant responses against harmless self-peptides in autoimmune diseases. The ability of TCR-like mAbs to target specific peptides presented on MHC allows for their use to study peptide presentation or for diagnosis and therapy. This extends the scope of conventional mAbs, which are generally limited to cell-surface or soluble antigens. Herein, we review the strategies used to generate TCR-like mAbs and provide a structural comparison with the analogous TCR in pMHC binding. We further discuss their applications as research tools and therapeutic reagents in preclinical models as well as challenges and limitations associated with their use.

Therapeutic Antibodies against Intracellular Tumor Antigens

Monoclonal antibodies are among the most clinically effective drugs used to treat cancer. However, their target repertoire is limited as there are relatively few tumor-specific or tumor-associated cell surface or soluble antigens. Intracellular molecules represent nearly half of the human proteome and provide an untapped reservoir of potential therapeutic targets. Antibodies have been developed to target externalized antigens, have also been engineered to enter into cells or may be expressed intracellularly with the aim of binding intracellular antigens. Furthermore, intracellular proteins can be degraded by the proteasome into short, commonly 8-10 amino acid long, peptides that are presented on the cell surface in the context of major histocompatibility complex class I (MHC-I) molecules. These tumor-associated peptide-MHC-I complexes can then be targeted by antibodies known as T-cell receptor mimic (TCRm) or T-cell receptor (TCR)-like antibodies, which recognize epitopes comprising both the peptide and the MHC-I molecule, similar to the recognition of such complexes by the TCR on T cells. Advances in the production of TCRm antibodies have enabled the generation of multiple TCRm antibodies, which have been tested in vitro and in vivo, expanding our understanding of their mechanisms of action and the importance of target epitope selection and expression. This review will summarize multiple approaches to targeting intracellular antigens with therapeutic antibodies, in particular describing the production and characterization of TCRm antibodies, the factors influencing their target identification, their advantages and disadvantages in the context of TCR therapies, and the potential to advance TCRm-based therapies into the clinic.

Development of a T-cell Receptor Mimic Antibody against Wild-Type p53 for Cancer Immunotherapy

The tumor suppressor p53 is widely dysregulated in cancer and represents an attractive target for immunotherapy. Because of its intracellular localization, p53 is inaccessible to classical therapeutic monoclonal antibodies, an increasingly successful class of anticancer drugs. However, peptides derived from intracellular antigens are presented on the cell surface in the context of MHC I and can be bound by T-cell receptors (TCR). Here, we report the development of a novel antibody, T1-116C, that acts as a TCR mimic to recognize an HLA-A*0201-presented wild-type p53 T-cell epitope, p5365-73(RMPEAAPPV). The antibody recognizes a wide range of cancers, does not bind normal peripheral blood mononuclear cells, and can activate immune effector functions to kill cancer cells in vitroIn vivo, the antibody targets p5365-73 peptide-expressing breast cancer xenografts, significantly inhibiting tumor growth. This represents a promising new agent for future cancer immunotherapy. Cancer Res; 77(10); 2699-711. ©2017 AACR.

Opportunities and challenges for TCR mimic antibodies in cancer therapy

INTRODUCTION

Monoclonal antibodies (mAbs) are potent cancer therapeutic agents, but exclusively recognize cell-surface targets whereas most cancer-associated proteins are found intracellularly. Hence, potential cancer therapy targets such as over expressed self-proteins, activated oncogenes, mutated tumor suppressors, and translocated gene products are not accessible to traditional mAb therapy. An emerging approach to target these epitopes is the use of TCR mimic mAbs (TCRm) that recognize epitopes similar to those of T cell receptors (TCR).

AREAS COVERED

TCRm antigens are composed of a linear peptide sequence derived from degraded proteins and presented in the context of cell-surface MHC molecules. We discuss how the nature of the TCRm epitopes provides both advantages (absolute tumor specificity and access to a new universe of important targets) and disadvantages (low density, MHC restriction, MHC down-regulation, and cross-reactive linear epitopes) to conventional mAb therapy. We will also discuss potential solutions to these obstacles.

EXPERT OPINION

TCRm combine the specificity of TCR recognition with the potency, pharmacologic properties, and versatility of mAbs. The structure and presentation of a TCRm epitope has important consequences related to the choice of targets, mAb design, available peptides and MHC subtype restrictions, possible cross-reactivity, and therapeutic activity.

Immunogenic peptide discovery in cancer genomes

As immunotherapies to treat malignancy continue to diversify along with the tumor types amenable to treatment, it will become very important to predict which treatment is most likely to benefit a given patient. Tumor neoantigens, novel peptides resulting from somatic tumor mutations and recognized by the immune system as foreign, are likely to contribute significantly to the efficacy of immunotherapy. Multiple in silico methods have been developed to predict whether peptides, including tumor neoantigens, will be presented by the major histocompatibility complex (MHC) Class I or Class II, and interact with the T cell receptor (TCR). The methods for neoantigen prediction will be reviewed here, along with the most important examples of their use in the field of oncology.

Specific increase in potency via structure-based design of a TCR

Adoptive immunotherapy with Ag-specific T lymphocytes is a powerful strategy for cancer treatment. However, most tumor Ags are nonreactive "self" proteins, which presents an immunotherapy design challenge. Recent studies have shown that tumor-specific TCRs can be transduced into normal PBLs, which persist after transfer in ∼30% of patients and effectively destroy tumor cells in vivo. Although encouraging, the limited clinical responses underscore the need for enrichment of T cells with desirable antitumor capabilities prior to patient transfer. In this study, we used structure-based design to predict point mutations of a TCR (DMF5) that enhance its binding affinity for an agonist tumor Ag-MHC (peptide-MHC [pMHC]), Mart-1 (27L)-HLA-A2, which elicits full T cell activation to trigger immune responses. We analyzed the effects of selected TCR point mutations on T cell activation potency and analyzed cross-reactivity with related Ags. Our results showed that the mutated TCRs had improved T cell activation potency while retaining a high degree of specificity. Such affinity-optimized TCRs have demonstrated to be very specific for Mart-1 (27L), the epitope for which they were structurally designed. Although of somewhat limited clinical relevance, these studies open the possibility for future structural-based studies that could potentially be used in adoptive immunotherapy to treat melanoma while avoiding adverse autoimmunity-derived effects.

Specific targeting of a naturally presented osteosarcoma antigen, papillomavirus binding factor peptide, using an artificial monoclonal antibody

Osteosarcoma is a rare but highly malignant tumor occurring most frequently in adolescents. The prognosis of non-responders to chemotherapy is still poor, and new treatment modalities are needed. To develop peptide-based immunotherapy, we previously identified autologous cytotoxic T lymphocyte-defined osteosarcoma antigen papillomavirus binding factor (PBF) in the context of HLA-B55 and the cytotoxic T lymphocyte epitope (PBF A2.2) presented by HLA-A2. PBF and HLA class I are expressed in ∼90 and 70% of various sarcomas, respectively. However, the expression status of peptide PBF A2.2 presented by HLA-A2 on osteosarcoma cells has remained unknown because it is difficult to generate a specific probe that reacts with the HLA·peptide complex. For detection and qualification of the HLA-A*02:01·PBF A2.2 peptide complex on osteosarcoma cells, we tried to isolate a single chain variable fragment (scFv) antibody directed to the HLA-*A0201·PBF A2.2 complex using a naïve scFv phage display library. As a result, scFv clone D12 with high affinity (KD = 1.53 × 10(-9) M) was isolated. D12 could react with PBF A2.2 peptide-pulsed T2 cells and HLA-A2+PBF+ osteosarcoma cell lines and simultaneously demonstrated that the HLA·peptide complex was expressed on osteosarcoma cells. In conclusion, scFv clone D12 might be useful to select candidate patients for PBF A2.2 peptide-based immunotherapy and develop antibody-based immunotherapy.

Galectin 9 and PINCH, novel immunotherapy targets of renal cell carcinoma: a rationale to find potential tumour antigens and the resulting cytotoxic T lymphocytes induced by the derived peptides

OBJECTIVE

To analyse and then generalize the mechanism by which partial or complete response is achieved among a limited number of patients with metastatic renal cell carcinoma (RCC) treated with interferon or interleukin-2.

MATERIALS AND METHODS

An expression library of RCC (clear-cell carcinoma) was screened using the sera of patients with metastatic RCC who benefited from partial or complete response to cytokine therapy, the postulation being that those remarkable responders obtained specific cellular immunity against RCC with the antibodies to react with the cancer antigen. Peripheral blood mononuclear-cells (PBMCs) from healthy volunteers were stimulated with the antigen-derived peptides to induce specific cytotoxic T lymphocytes (CTLs). Specific activities of CTLs were measured by ⁵¹Cr-releasing assay.

RESULTS

Among 15 positive clones isolated, two novel genes, galectin 9 and PINCH, were expressed at much higher levels in cancerous lesions than in normal tissues in all the patients with clear-cell carcinoma who were examined. Both HLA-A*2402-restricted and HLA-A*0201-restricted CTLs were induced by each antigen-derived peptide to exhibit specific and highly cytotoxic activities towards RCC cells. Specific CTLs were induced abundantly, as shown by flow cytometry analysis of the CTLs labelled with fluorescein isothiocyanate anti-CD107a and APC anti-CD8. The clonal expansion of the CTLs was shown by the clonality of T-cell receptor Vβ repertoires.

CONCLUSION

A novel approach based on clinical observations yielded promising tumour antigens as immunotherapy targets of RCC.

Function and Potentials of M. tuberculosis Epitopes

Study of the function of epitopes of Mycobacterium tuberculosis antigens contributed significantly toward better understanding of the immunopathogenesis and to efforts for improving infection and disease control. Characterization of genetically permissively presented immunodominant epitopes has implications for the evolution of the host–parasite relationship, development of immunodiagnostic tests, and subunit prophylactic vaccines. Knowledge of the determinants of cross-sensitization, relevant to other pathogenic or environmental mycobacteria and to host constituents has advanced. Epitope-defined IFNγ assay kits became established for the specific detection of infection with tubercle bacilli both in humans and cattle. The CD4 T-cell epitope repertoire was found to be more narrow in patients with active disease than in latently infected subjects. However, differential diagnosis of active TB could not be made reliably merely on the basis of epitope recognition. The mechanisms by which HLA polymorphism can influence the development of multibacillary tuberculosis (TB) need further analysis of epitopes, recognized by Th2 helper cells for B-cell responses. Future vaccine development would benefit from better definition of protective epitopes and from improved construction and formulation of subunits with enhanced immunogenicity. Epitope-defined serology, due to its operational advantages is suitable for active case finding in selected high disease incidence populations, aiming for an early detection of infectious cases and hence for reducing the transmission of infection. The existing knowledge of HLA class I binding epitopes could be the basis for the construction of T-cell receptor-like ligands for immunotherapeutic application. Continued analysis of the functions of mycobacterial epitopes, recognized by T cells and antibodies, remains a fertile avenue in TB research.

Antigen-dependent integration of opposing proximal TCR-signaling cascades determines the functional fate of T lymphocytes

T cell anergy is a key tolerance mechanism to mitigate unwanted T cell activation against self by rendering lymphocytes functionally inactive following Ag encounter. Ag plays an important role in anergy induction where high supraoptimal doses lead to the unresponsive phenotype. How T cells "measure" Ag dose and how this determines functional output to a given antigenic dose remain unclear. Using multiparametric phospho-flow and mass cytometry, we measured the intracellular phosphorylation-dependent signaling events at a single-cell resolution and studied the phosphorylation levels of key proximal human TCR activation- and inhibition-signaling molecules. We show that the intracellular balance and signal integration between these opposing signaling cascades serve as the molecular switch gauging Ag dose. An Ag density of 100 peptide-MHC complexes/cell was found to be the transition point between dominant activation and inhibition cascades, whereas higher Ag doses induced an anergic functional state. Finally, the neutralization of key inhibitory molecules reversed T cell unresponsiveness and enabled maximal T cell functions, even in the presence of very high Ag doses. This mechanism permits T cells to make integrated "measurements" of Ag dose that determine subsequent functional outcomes.

Examining the presentation of tumor-associated antigens on peptide-pulsed T2 cells

Peptide-pulsed T2 cells are routinely used to study T-cell activation by MHC-restricted peptides derived from tumor-associated antigens (TAAs). Nevertheless, the capacity of T2 cells to present antigenic epitopes remains to be precisely quantified, primarily due to the detection limits imposed by available methods. Since naturally-processed TAA-derived epitopes have been shown to be displayed at levels as low as 10–150 copies per cell, highly sensitive detection and quantification techniques are essential to assess the natural degree of T-cell sensitivity. Here, we report the use of soluble, high-affinity T-cell receptors (TCRs) coupled with single-molecule fluorescence microscopy to quantify three reported TAA-derived epitopes on peptide-pulsed T2 cells, dissecting the relationship between concentration of exogenous peptide, number of epitopes presented, and activation of epitope-specific T cells. Our findings indicate that peptide concentrations in the low nanomolar range are required for T2 cells to present TAAs in extents that are comparable to those of malignant cells.

Antigen-specific immunomodulation for type 1 diabetes by novel recombinant antibodies directed against diabetes-associates auto-reactive T cell epitope

The trimolecular complex composed of autoreactive T-cell receptor, MHC class II, and an autoantigenic peptide plays a central role in the activation of pathogenic Islet-specific CD4+ T cells in type 1 diabetes (T1D). We isolated and characterized novel antibodies against autoreactive T-cell epitopes associated with T1D. Our antibodies mimic the specificity of the T-cell receptor (TCR), while binding MHC class II/peptide complexes in an autoantigen peptide specific, MHC-restricted manner. The isolated TCR-like antibodies were directed against the minimal T-cell epitope GAD-555-567 in the context of the HLA-DR4-diabetic-associated molecule. A representative high-affinity TCR-like antibody clone (G3H8) enabled the detection of intra- and extra-cellular DR4/GAD-555-567 complexes in antigen presenting cells. I561M single mutation at the central position (P5) of the GAD-555-567 peptide abolished the binding of G3H8 to the DR4/GAD complex, demonstrating its high fine TCR-like specificity. The G3H8 TCR-like antibody significantly inhibited GAD-555-567 specific, DR4 restricted T-cell response in vitro and in vivo in HLA-DR4 transgenic mice. Our findings constitute a proof-of-concept for the utility of TCR-like antibodies as antigen-specific immunomodulation agents for regulating pathogenic T-cells and suggest that TCR-like antibodies targeting autoreactive MHC class II epitopes are valuable research tools that enable studies related to antigen presentation as well as novel therapeutic agents that may be used to modulate autoimmune disorders such as T1D.

A constructed HLA-A2-restricted pMAGE-A1(278-286) tetramer detects specific cytotoxic T lymphocytes in tumour tissues in situ

OBJECTIVE

To construct a human leucocyte antigen (HLA)-A2-restricted peptide 278-286 of melanoma-associated antigen family A, 1 (pMAGE-A1(278-286)) tetramer to analyse the distribution of cytotoxic T lymphocytes (CTLs) in tumour tissue and tumour-adjacent normal tissue.

METHODS

A HLA-A2-pMAGE-A1(278-286) tetramer was constructed. The distribution of pMAGE-A1(278-286)-specific CTLs was investigated in tumour tissues and tumour-adjacent normal tissues from patients with hepatocellular carcinoma using in situ HLA-A2-pMAGE-A1(278-286) tetramer staining.

RESULTS

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis indicated that HLA-A2 heavy and light chain proteins were successfully obtained. The successful construction of the HLA-A2-pMAGE-A1(278-286) monomer was confirmed with Western blot analysis using W6/32 antibody. Flow cytometry confirmed the specific binding of HLA-A2-pMAGE-A1(278-286) tetramer to pMAGE-A1(278-286)-specific CTLs. In situ HLA-A2-pMAGE-A1(278-286) tetramer staining demonstrated that the number of pMAGE-A1(278-286)-specific CTLs in tumour tissues was significantly higher than in tumour-adjacent normal tissues.

CONCLUSIONS

The HLA-A2-pMAGE-A1(278-286) tetramer was useful for the detection of pMAGE-A1(278-286)-specific CTLs in both tumour tissues and tumour-adjacent normal tissues. In situ tetramer staining is a powerful tool for investigating the distribution of pMAGE-A1278-286-specific CTLs in the tumour microenvironment.

Recent progress in canine tumor vaccination: potential applications for human tumor vaccines

Tumor vaccination holds great promise for the treatment of cancer and research concerning tumor vaccination in dogs is of great interest for veterinary as well as human medicine. Indeed, cancer is the leading cause of death in adult dogs and companion animals are acknowledged as excellent preclinical models for human oncology. The license of the veterinary melanoma vaccine (Oncept™) and Provenge® for the treatment of prostate cancer in men established tumor vaccination as a valid treatment modality for cancer. Although the results with this and other vaccines are promising, there are still some hurdles to overcome. In this article, preclinical and clinical trials with tumor vaccines in dogs are discussed, as well as the surplus value of canine cancer patients for human medicine.

Kinetics of antigen expression and epitope presentation during virus infection

Current knowledge about the dynamics of antigen presentation to T cells during viral infection is very poor despite being of fundamental importance to our understanding of anti-viral immunity. Here we use an advanced mass spectrometry method to simultaneously quantify the presentation of eight vaccinia virus peptide-MHC complexes (epitopes) on infected cells and the amounts of their source antigens at multiple times after infection. The results show a startling 1000-fold range in abundance as well as strikingly different kinetics across the epitopes monitored. The tight correlation between onset of protein expression and epitope display for most antigens provides the strongest support to date that antigen presentation is largely linked to translation and not later degradation of antigens. Finally, we show a complete disconnect between the epitope abundance and immunodominance hierarchy of these eight epitopes. This study highlights the complexity of viral antigen presentation by the host and demonstrates the weakness of simple models that assume total protein levels are directly linked to epitope presentation and immunogenicity.

A major mechanism for the detection of virus infection is the recognition by T cells of short peptide fragments (epitopes) derived from the degradation of intracellular proteins presented at the cell surface in a complex with class I MHC. Whilst the mechanics of antigen degradation and the loading of peptides onto MHC are now well understood, the kinetics of epitope presentation have only been studied for individual model antigens. We addressed this issue by studying vaccinia virus, best known as the smallpox vaccine, using advanced mass spectrometry. Precise and simultaneous quantification of multiple peptide-MHC complexes showed that the surface of infected cells provides a surprisingly dynamic landscape from the point of view of anti-viral T cells. Further, concurrent measurement of virus protein levels demonstrated that in most cases, peak presentation of epitopes occurs at the same time or precedes the time of maximum protein build up. Finally, we found a complete disconnect between the abundance of epitopes on infected cells and the size of the responding T cell populations. These data provide new insights into how virus infected cells are seen by T cells, which is crucial to our understanding of anti-viral immunity and development of vaccines.

Limited induction of tumor cross-reactive T cells without a measurable clinical benefit in early melanoma patients vaccinated with human leukocyte antigen class I-modified peptides

PURPOSE

The progressive immune dysfunctions that occur in patients with advanced melanoma make them unlikely to efficiently respond to cancer vaccines. A multicenter randomized phase II trial was conducted to test whether immunization with modified HLA class I tumor peptides in the context of adjuvant therapy results in better immunologic responses and improved clinical outcomes in patients with early melanoma (stages IIB/C-III).

EXPERIMENTAL DESIGN

Forty-three patients were enrolled to undergo vaccination (n = 22) or observation (n = 21). The vaccine included four HLA-A*0201-restricted modified peptides (Melan-A/MART-1([27L]), gp100([210M]), NY-ESO-1([165V]), and Survivin([97M])) emulsified in Montanide ISA51 and injected subcutaneously in combination with cyclophosphamide (300 mg/m(2)) and low-dose IL-2 (3 × 10(6) IU). The immune responses were monitored using ex vivo IFN-γ-ELISpot, HLA/multimer staining, and in vitro short-term peptide sensitization assays.

RESULTS

Vaccination induced a rapid and persistent increase in specific effector memory CD8(+) T cells in 75% of the patients. However, this immunization was not associated with any significant increase in disease-free or overall survival as compared with the observation group. An extensive immunologic analysis revealed a significantly reduced cross-recognition of the corresponding native peptides and, most importantly, a limited ability to react to melanoma cells.

CONCLUSIONS

Adjuvant setting is an appealing approach for testing cancer vaccines because specific CD8(+) T cells can be efficiently induced in most vaccinated patients. However, the marginal antitumor activity of the T cells induced by modified peptides in this study largely accounts for the observed lack of benefit of vaccination. These findings suggest reconsidering this immunization strategy, particularly in early disease.

T cell receptor-like recognition of tumor in vivo by synthetic antibody fragment

A major difficulty in treating cancer is the inability to differentiate between normal and tumor cells. The immune system differentiates tumor from normal cells by T cell receptor (TCR) binding of tumor-associated peptides bound to Major Histocompatibility Complex (pMHC) molecules. The peptides, derived from the tumor-specific proteins, are presented by MHC proteins, which then serve as cancer markers. The TCR is a difficult protein to use as a recombinant protein because of production issues and has poor affinity for pMHC; therefore, it is not a good choice for use as a tumor identifier outside of the immune system. We constructed a synthetic antibody-fragment (Fab) library in the phage-display format and isolated antibody-fragments that bind pMHC with high affinity and specificity. One Fab, fE75, recognizes our model cancer marker, the Human Epidermal growth factor Receptor 2 (HER2/neu) peptide, E75, bound to the MHC called Human Leukocyte Antigen-A2 (HLA-A2), with nanomolar affinity. The fE75 bound selectively to E75/HLA-A2 positive cancer cell lines in vitro. The fE75 Fab conjugated with ⁶⁴Cu selectively accumulated in E75/HLA-A2 positive tumors and not in E75/HLA-A2 negative tumors in an HLA-A2 transgenic mouse as probed using positron emission tomography/computed tomography (PET/CT) imaging. Considering that hundreds to thousands of different peptides bound to HLA-A2 are present on the surface of each cell, the fact that fE75 arrives at the tumor at all shows extraordinary specificity. These antibody fragments have great potential for diagnosis and targeted drug delivery in cancer.

Tyrosinase degradation is prevented when EDEM1 lacks the intrinsically disordered region

EDEM1 is a mannosidase-like protein that recruits misfolded glycoproteins from the calnexin/calreticulin folding cycle to downstream endoplasmic reticulum associated degradation (ERAD) pathway. Here, we investigate the role of EDEM1 in the processing of tyrosinase, a tumour antigen overexpressed in melanoma cells. First, we analyzed and modeled EDEM1 major domains. The homology model raised on the crystal structures of human and Saccharomyces cerevisiae ER class I α1,2-mannosidases reveals that the major mannosidase domain located between aminoacids 121-598 fits with high accuracy. We have further identified an N-terminal region located between aminoacids 40-119, predicted to be intrinsically disordered (ID) and susceptible to adopt multiple conformations, hence facilitating protein-protein interactions. To investigate these two domains we have constructed an EDEM1 deletion mutant lacking the ID region and a triple mutant disrupting the glycan-binding domain and analyzed their association with tyrosinase. Tyrosinase is a glycoprotein partly degraded endogenously by ERAD and the ubiquitin proteasomal system. We found that the degradation of wild type and misfolded tyrosinase was enhanced when EDEM1 was overexpressed. Glycosylated and non-glycosylated mutants co-immunoprecipitated with EDEM1 even in the absence of its intact mannosidase-like domain, but not when the ID region was deleted. In contrast, calnexin and SEL 1L associated with the deletion mutant. Our data suggest that the ID region identified in the N-terminal end of EDEM1 is involved in the binding of glycosylated and non-glycosylated misfolded proteins. Accelerating tyrosinase degradation by EDEM1 overexpression may lead to an efficient antigen presentation and enhanced elimination of melanoma cells.

MHC class I antigen processing distinguishes endogenous antigens based on their translation from cellular vs. viral mRNA

To better understand the generation of MHC class I-associated peptides, we used a model antigenic protein whose proteasome-mediated degradation is rapidly and reversibly controlled by Shield-1, a cell-permeant drug. When expressed from a stably transfected gene, the efficiency of antigen presentation is ~2%, that is, one cell-surface MHC class I-peptide complex is generated for every 50 folded source proteins degraded upon Shield-1 withdrawal. By contrast, when the same protein is expressed by vaccinia virus, its antigen presentation efficiency is reduced ~10-fold to values similar to those reported for other vaccinia virus-encoded model antigens. Virus infection per se does not modify the efficiency of antigen processing. Rather, the efficiency difference between cellular and virus-encoded antigens is based on whether the antigen is synthesized from transgene- vs. virus-encoded mRNA. Thus, class I antigen-processing machinery can distinguish folded proteins based on the precise details of their synthesis to modulate antigen presentation efficiency.

Melanoma cells present high levels of HLA-A2-tyrosinase in association with instability and aberrant intracellular processing of tyrosinase

Short-lived protein translation products are proposed to be a major source of substrates for major histocompatibility complex (MHC) class I antigen processing and presentation; however, a direct link between protein stability and the presentation level of MHC class I-peptide complexes has not been made. We have recently discovered that the peptide Tyr((369-377)) , derived from the tyrosinase protein is highly presented by HLA-A2 on the surface of melanoma cells. To examine the molecular mechanisms responsible for this presentation, we compared characteristics of tyrosinase in melanoma cells lines that present high or low levels of HLA-A2-Tyr((369-377)) complexes. We found no correlation between mRNA levels and the levels of HLA-A2-Tyr((369-377)) presentation. Co-localization experiments revealed that, in cell lines presenting low levels of HLA-A2-Tyr((369-377)) complexes, tyrosinase co-localizes with LAMP-1, a melanosome marker, whereas in cell lines presenting high HLA-A2-Tyr((369-377)) levels, tyrosinase localizes to the endoplasmic reticulum. We also observed differences in tyrosinase molecular weight and glycosylation composition as well as major differences in protein stability (t(1/2) ). By stabilizing the tyrosinase protein, we observed a dramatic decrease in HLA-A2-tyrosinase presentation. Our findings suggest that aberrant processing and instability of tyrosinase are responsible for the high presentation of HLA-A2-Tyr((369-377)) complexes and thus shed new light on the relationship between intracellular processing, stability of proteins, and MHC-restricted peptide presentation.

T-cell-receptor-like antibodies - generation, function and applications

Tumour and virus-infected cells are recognised by CD8+ cytotoxic T cells that, in response, are activated to eliminate these cells. In order to be activated, the clonotypic T-cell receptor (TCR) needs to encounter a specific peptide antigen presented by the membrane surface major histocompatibility complex (MHC) molecule. Cells that have undergone malignant transformation or viral infection present peptides derived from tumour-associated antigens or viral proteins on their MHC class I molecules. Therefore, disease-specific MHC-peptide complexes are desirable targets for immunotherapeutic approaches. One such approach transforms the unique fine specificity but low intrinsic affinity of TCRs to MHC-peptide complexes into high-affinity soluble antibody molecules endowed with a TCR-like specificity towards tumour or viral epitopes. These antibodies, termed TCR-like antibodies, are being developed as a new class of immunotherapeutics that can target tumour and virus-infected cells and mediate their specific killing. In addition to their therapeutic capabilities, TCR-like antibodies are being developed as diagnostic reagents for cancer and infectious diseases, and serve as valuable research tools for studying MHC class I antigen presentation.

Retargeting NK92 cells using an HLA-A2-restricted, EBNA3C-specific chimeric antigen receptor

Advances in adoptive cell immunotherapy have led to several promising options for cancer patients. Single-chain variable fragments (scFvs) were isolated from a human phage display library by panning on recombinant human leukocyte antigen (HLA)-A2-peptide complexes. A scFv (EBNA Clone 315) specific for HLA-A2 carrying a 10 amino acid peptide (LLDFVRFMGV) derived from the Epstein-Barr virus latent protein EBNA3C was fully characterized. EBNA Clone 315 displayed exquisite specificity toward its targeted T-cell epitope (TCE) and did not cross-react with the free peptide, HLA-A2 complexes, which carried irrelevant peptides, or HLA-A2(-) cells. Furthermore, after engineering into a scFv-Fc fusion protein, we were able to determine its affinity, detection sensitivity, and ability to induce antibody-dependent cellular cytotoxicity (ADCC). As a proof-of-principle, a chimeric antigen receptor (CAR) version of EBNA Clone 315 was used to reprogram NK92MI cells. CAR-expressing NK92MI cells showed highly specific and potent cytotoxicity toward the targeted TCE, with detection sensitivity of approximately 25 molecules and cytolytic capacity threefold greater than scFv-Fc-mediated ADCC. For the first time, we show the successful reprogramming of non-T cells toward a specific TCE using a CAR.

DRiPs solidify: progress in understanding endogenous MHC class I antigen processing

Defective ribosomal products (DRiPs) are a subset of rapidly degraded polypeptides that provide peptide ligands for major histocompatibility complex (MHC) class I molecules. Here, recent progress in understanding DRiP biogenesis is reviewed. These findings place DRiPs at the center of the MHC class I antigen processing pathway, linking immunosurveillance of viruses and tumors to mechanisms of specialized translation and cellular compartmentalization. DRiPs enable the immune system to rapidly detect alterations in cellular gene expression with great sensitivity.

Properties and applications of single-chain major histocompatibility complex class I molecules

Stable major histocompatibility complex (MHC) class I molecules at the cell surface consist of three separate, noncovalently associated components: the class I heavy chain, the β(2)-microglobulin light chain, and a presented peptide. These three components are assembled inside cells via complex pathways involving many other proteins that have been studied extensively. Correct formation of disulfide bonds in the endoplasmic reticulum is central to this process of MHC class I assembly. For a single specific peptide to be presented at the cell surface for possible immune recognition, between hundreds and thousands of peptide-containing precursor polypeptides are required, so the overall process is relatively inefficient. To increase the efficiency of antigen presentation by MHC class I molecules, and for possible therapeutic purposes, single-chain molecules have been developed in which the three, normally separate components have been joined together via flexible linker sequences in a single polypeptide chain. Remarkably, these single-chain MHC class I molecules fold up correctly, as judged by functional recognition by cells of the immune system, and more recently by X-ray crystallographic structural data. This review focuses on the interesting properties and potential of this new type of engineered MHC class I molecule.

TCRs used in cancer gene therapy cross-react with MART-1/Melan-A tumor antigens via distinct mechanisms

T cells engineered to express TCRs specific for tumor Ags can drive cancer regression. The first TCRs used in cancer gene therapy, DMF4 and DMF5, recognize two structurally distinct peptide epitopes of the melanoma-associated MART-1/Melan-A protein, both presented by the class I MHC protein HLA-A*0201. To help understand the mechanisms of TCR cross-reactivity and provide a foundation for the further development of immunotherapy, we determined the crystallographic structures of DMF4 and DMF5 in complex with both of the MART-1/Melan-A epitopes. The two TCRs use different mechanisms to accommodate the two ligands. Although DMF4 binds the two with a different orientation, altering its position over the peptide/MHC, DMF5 binds them both identically. The simpler mode of cross-reactivity by DMF5 is associated with higher affinity toward both ligands, consistent with the superior functional avidity of DMF5. More generally, the observation of two diverging mechanisms of cross-reactivity with the same Ags and the finding that TCR-binding orientation can be determined by peptide alone extend our understanding of the mechanisms underlying TCR cross-reactivity.

Enhanced stimulation of anti-ovarian cancer CD8(+) T cells by dendritic cells loaded with nanoparticle encapsulated tumor antigen

PROBLEM

Dendritic cell (DC)-based cancer therapies are favored approaches to stimulate anti-tumor T-cell responses. Unfortunately, tolerance to tumor antigens is difficult to overcome. Biodegradable poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NP) are effective reagents in the delivery of drugs and tumor-associated antigens (TAA). In this study, we assessed the capacity of a PLGA NP-based delivery system to augment CD8 T-cell responses to ovarian cancer TAA.

METHOD OF STUDY

Human DC were generated from blood monocytes by conventional in vitro differentiation and loaded with either soluble tumor lysate or NP/lysate conjugates (NPL). These antigen-loaded DC were then used to stimulate autologous CD8(+) T cells. Cytokine production and activation markers were evaluated in the CD8(+) T cells.

RESULTS

DC loading with NPL increased cytokine production by stimulated CD8 T cells and induced T-cell expression of cell surface co-stimulatory molecules, typical of anti-tumor immune responses. In contrast, delivery of naked tumor lysate antigens preferentially induced a T-cell profile characteristic of tolerization/exhaustion.

CONCLUSION

These findings indicate that delivery of TAA in NP enables DC to efficiently activate anti-tumor CD8(+) T cells. PLGA NP encapsulation of tumor-derived lysate protein antigens is an encouraging new preparative methodology for DC-based vaccination meriting clinical testing.

TCR-like antibodies distinguish conformational and functional differences in two- versus four-domain auto reactive MHC class II-peptide complexes

Antigen-presenting cell-associated four-domain MHC class II (MHC-II) molecules play a central role in activating autoreactive CD4(+) T cells involved in multiple sclerosis (MS) and type 1 diabetes (T1D). In contrast, two-domain MHC-II structures with the same covalently attached self-peptide (recombinant T-cell receptor ligands (RTLs)) can regulate pathogenic CD4(+) T cells and reverse clinical signs of experimental autoimmune diseases. RTL1000, which is composed of the β1α1 domains of human leukocyte antigen (HLA)-DR2 linked to the encephalitogenic human myelin oligodendrocyte glycoprotein (MOG)-35-55 peptide, was recently shown to be safe and well tolerated in a phase I clinical trial in MS. To evaluate the opposing biological effects of four- versus two-domain MHC-II structures, we screened phage Fab antibodies (Abs) for the neutralizing activity of RTL1000. Five different TCR-like Abs were identified that could distinguish between the two- versus four-domain MHC-peptide complexes while the cognate TCR was unable to make such a distinction. Moreover, Fab detection of native two-domain HLA-DR structures in human plasma implies that there are naturally occurring regulatory MHC-peptide complexes. These results demonstrate for the first time distinct conformational determinants characteristic of activating versus tolerogenic MHC-peptide complexes involved in human autoimmunity.

MART-1-specific melanoma tumor-infiltrating lymphocytes maintaining CD28 expression have improved survival and expansion capability following antigenic restimulation in vitro

We determined how CD8(+) melanoma tumor-infiltrating lymphocytes (TILs) isolated from two distinct phases of expansion in preparation for adoptive T cell therapy respond to melanoma Ag restimulation. We found that TILs isolated after the rapid expansion protocol (REP) phase, used to generate the final patient TIL infusion product, were hyporesponsive to restimulation with MART-1 peptide-pulsed dendritic cells, with many CD8(+) T cells undergoing apoptosis. Telomere length was shorter post-REP, but of sufficient length to support further cell division. Phenotypic analysis revealed that cell-surface CD28 expression was significantly reduced in post-REP TILs, whereas CD27 levels remained unchanged. Tracking post-REP TIL proliferation by CFSE dilution, as well as sorting for CD8(+)CD28(+) and CD8(+)CD28(-) post-REP subsets, revealed that the few CD28(+) TILs remaining post-REP had superior survival capacity and proliferated after restimulation with MART-1 peptide. An analysis of different supportive cytokine mixtures during the REP found that a combination of IL-15 and IL-21 facilitated comparable expansion of CD8(+) TILs as IL-2, but prevented the loss of CD28 expression with improved responsiveness to antigenic restimulation post-REP. These results suggest that current expansion protocols using IL-2 for melanoma adoptive T cell therapy yields largely CD8(+) T cells unable to persist and divide in vivo following Ag contact. The few CD8(+)CD28(+) T cells that remain may be the only CD8(+) TILs that ultimately survive to repopulate the host and mediate long-term tumor control. A REP protocol using IL-15 and IL-21 may greatly increase the number of CD28(+) TILs capable of long-term persistence.