The structure, expression, and multifaceted role of immune-checkpoint protein VISTA as a critical regulator of anti-tumor immunity, autoimmunity, and inflammation

Non-Small Cell Lung Cancer: Challenge and Improvement of Immune Drug Resistance

Lung cancer is the leading cause of cancer deaths in the world. At present, immunotherapy has made a great breakthrough in lung cancer treatment. A variety of immune checkpoint inhibitors have been applied into clinical practice, including antibodies targeting the programmed cell death-1, programmed cell death-ligand 1, and cytotoxic T-lymphocyte antigen 4. However, in the actual clinical process, about 30%-50% of patients still do not receive long-term benefits. Abnormal antigen presentation, functional gene mutation, tumor microenvironment, and other factors can lead to primary or secondary resistance. In this paper, we reviewed the immune mechanism of immune checkpoint inhibitor resistance, various combination strategies, and prediction of biomarkers to overcome resistance in order to accurately screen out the advantageous population, expand the beneficiary population, and enable precise and individualized medicine.

VISTA facilitates phagocytic clearance of HIV infected CEM-SS T cells

Phagocytosis is a critical component of the innate immune response to viral infection, resulting in the clearance of infected cells while minimizing the exposure of uninfected cells. On the other hand, phagocytosis of HIV-infected T cells may cause phagocytes, such as macrophages and dendritic cells, to be infected, thus leading to HIV cell-to-cell transmission. V domain immunoglobulin suppressor of T cell activation (VISTA, gene Vsir, aliases Gi24, Dies-1, PD-1H, and DD1α) has been identified as an immune checkpoint molecule that possesses dual activities when expressed on APCs and T cells. Our study found that VISTA might play a significant role during the immune response to HIV infection via apoptosis upregulation and subsequent phagocytosis of infected CEM-SS T cells. HIV-induced apoptosis and monocytic cell engulfment were tested utilizing CEM-SS T cells as target cells and the monocytic cell line THP-1 as phagocytic cells. Cells were infected with a GFP-labeled HIV strain, NL4-3. HIV-infected CEM-SS T cells displayed greater apoptotic activity (approximately 18.0%) than mock-infected controls. Additionally, phagocytosis of HIV-infected CEM-SS T cells was increased approximately 4-fold. Expression of VISTA on infected CEM-SS T cells was detected in 16.7% of cells, which correlated with the increased phagocytosis observed. When an antagonistic antibody against VISTA was used, the number of phagocytosed cells was reduced by a factor of 2, which was replicated utilizing human stem cell-derived dendritic cells. Phagocytosis was also confirmed by the upregulation of IL-1β expression, which was 5-fold higher in infected cells than in control cells. We also found that VISTA overexpression on both phagocytes and HIV-infected CEM-SS T cells facilitated phagocytosis. Our study suggests that VISTA may act as a direct ligand in the phagocytosis of HIV-infected T cells.

Inhibition of lung tumorigenesis by a small molecule CA170 targeting the immune checkpoint protein VISTA

Expressed on cells of the myeloid and lymphoid lineages, V-domain Ig Suppressor of T cell Activation (VISTA) is an emerging target for cancer immunotherapy. Blocking VISTA activates both innate and adaptive immunity to eradicate tumors in mice. Using a tripeptide small molecule antagonist of VISTA CA170, we found that it exhibited potent anticancer efficacy on carcinogen-induced mouse lung tumorigenesis. Remarkably, lung tumor development was almost completely suppressed when CA170 was combined with an MHCII-directed KRAS peptide vaccine. Flow cytometry and single-cell RNA sequencing (scRNA-seq) revealed that CA170 increased CD8+ T cell infiltration and enhanced their effector functions by decreasing the tumor infiltration of myeloid-derived suppressor cells (MDSCs) and Regulatory T (Treg) cells, while the Kras vaccine primarily induced expansion of CD4+ effector T cells. VISTA antagonism by CA170 revealed strong efficacy against lung tumorigenesis with broad immunoregulatory functions that influence effector, memory and regulatory T cells, and drives an adaptive T cell tumor-specific immune response that enhances the efficacy of the KRAS vaccine.

New emerging targets in cancer immunotherapy: the role of VISTA

The immune surveillance system is complex and regulated by different actors. Programmed death protein-ligand 1 (PD-L1), the only approved biomarker in clinical practice, has proven to be imperfect in selecting patients to immune checkpoint inhibitors treatment. Therefore, new biomarkers, and new therapeutic targets, are needed to maximise the efficacy of immunotherapy. V-domain Ig Suppressor of T-cell Activation (VISTA) is a programmed death protein-1 (PD-1) homolog expressed on T cells and on antigen-presenting cells, which regulates processes of activation and repression of the immune system with not yet completely clarified mechanisms. Its blockage has demonstrated in vitro and in vivo antitumour activity. The clinical research of VISTA antagonists is ongoing. Particularly, CA-170, an orally delivered dual inhibitor of VISTA and PD-L1, has shown to have clinical efficacy in phase I and II clinical trials in different advanced solid tumour types. Further data are needed to define whether this drug class can become a new therapeutic option for patients with VISTA expressing cancers.

Detection of Immune Checkpoint Receptors - A Current Challenge in Clinical Flow Cytometry

Immunological therapy principles are increasingly determining modern medicine. They are used to treat diseases of the immune system, for tumors, but also for infections, neurological diseases, and many others. Most of these therapies base on antibodies, but small molecules, soluble receptors or cells and modified cells are also used. The development of immune checkpoint inhibitors is amazingly fast. T-cell directed antibody therapies against PD-1 or CTLA-4 are already firmly established in the clinic. Further targets are constantly being added and it is becoming increasingly clear that their expression is not only relevant on T cells. Furthermore, we do not yet have any experience with the long-term systemic effects of the treatment. Flow cytometry can be used for diagnosis, monitoring, and detection of side effects. In this review, we focus on checkpoint molecules as target molecules and functional markers of cells of the innate and acquired immune system. However, for most of the interesting and potentially relevant parameters, there are still no test kits suitable for routine use. Here we give an overview of the detection of checkpoint molecules on immune cells in the peripheral blood and show examples of a possible design of antibody panels.

VISTA: A Promising Target for Cancer Immunotherapy?

Agents targeting the B7 family co-inhibitory receptors cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed cell death protein-1 (PD-1), or its ligand (PD-L1), have a pivotal role in clinical practice. V-domain Ig suppressor of T-cell activation (VISTA) is a protein highly conserved between species, with a similar amino acid sequence to the B7 family members, characterized by a particularly structural homology to PD-1. It has been counted as an emerging target within the list of novel targetable immune checkpoints in oncology. Physiologically, VISTA exerts a regulatory function on the immune system at several levels, particularly by modulating T cells activation. Its altered activity plays a role in many autoimmune diseases, and its expression has been found to be prognostically implicated in different cancer types in preclinical models. We hereby present the main evidence on the value of VISTA as an immune checkpoint in solid and hematological malignancies. We also review its value as a potential target for cancer immunotherapy, by reporting the results of Phase I and II clinical trials assessing the use of drugs targeting VISTA. The complexity of its pathway, along with some unclear biological aspects concerning its molecular interactions, currently represent a limit to the applicability of VISTA as an effective biomarker for immunotherapy in oncology. A deeper characterization of this immune checkpoint may help defining its value within immune signatures of solid and hematological malignancies, and to design future therapeutic strategies.

Immunotherapeutic Approaches in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare and aggressive malignant disease affecting the mesothelium, commonly associated to asbestos exposure. The current therapeutic actions, based on cisplatin/pemetrexed treatment, are limited due to the late stage at which most patients are diagnosed and to the intrinsic chemo-resistance of the tumor. Another relevant point is the absence of approved therapies in the second line setting following progression of MPM after chemotherapy. Considering the poor prognosis of the disease and the fact that the incidence of this tumor is expected to increase in the next decade, novel therapeutic approaches are urgently needed. In the last few years, several studies have investigated the efficacy and safety of immune-checkpoint inhibitors (ICIs) in the treatment of unresectable advanced MPM, and a number of trials with immunotherapeutic agents are ongoing in both first line and second line settings. In this review, we describe the most promising emerging immunotherapy treatments for MPM (ICIs, engineered T cells to express chimeric antigen receptors (CARs), dendritic cells (DCs) vaccines), focusing on the biological and immunological features of this tumor as well as on the issues surrounding clinical trial design.

A data-driven approach for the discovery of biomarkers associated with thyroid eye disease

Background

Thyroid eye disease (TED) is the most common autoimmune disease and usually occurs in patients with hyperthyroidism. In this disease, eye-related tissue, such as eye muscles, eyelids, tear glands, etc., become inflated, which causes the eyes and eyelids to become red, swollen, and uncomfortable. The pathophysiology of this disease is still poorly known.

Aim

This study aims to discover potential biomarkers and regulatory pathways of TED which will not only help to diagnose the disease and understand orbital involvement in thyroid dysfunction but also provide an insight for better therapeutics.

Methods

We applied a data-driven approach by combining gene biomarkers both from published literature and computationally predicted from microarray gene expression data. Further, the DAVID tool is used for Gene Ontology-based enrichment analysis.

Results

We obtained a total of 22 gene biomarkers, including 18 semi-automatically curated from the literature and 4 predicted using data-driven approaches, involved in the pathogenesis of TED that can be used as potential information for therapeutic targets. Further, we constructed a regulatory pathway of TED biomarkers comprises of 310 connected components, and 1134 interactions using four prominent interaction databases.

Conclusion

This constructed pathway can be further utilized for disease dynamics and simulation studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-01903-9.

Combined Assessment of Immune Checkpoint Regulator VISTA on Tumor-Associated Immune Cells and Platelet-to-Lymphocyte Ratio Identifies Advanced Germ Cell Tumors with Higher Risk of Unfavorable Outcomes

Simple Summary

Testicular germ cell tumors (GCTs) are the most common malignancies in young males. The current treatment regimens are usually highly effective and curative. Nevertheless, a portion of patients presents with recurrence or succumbs due to the disease. There is an undoubtful necessity to investigate new prognostic markers to stratify the risk of such events. The current study aimed to evaluate the prognostic significance of markers of the tumor microenvironment and systemic inflammation markers in GCTs. We found that low expression of immune checkpoint proteins VISTA (V-domain Ig suppressor of T cell activation) and PD-L1 (programmed death-ligand 1) on tumor-associated immune cells and elevated inflammatory marker platelet-to-lymphocyte ratio are associated with a higher risk of events in testicular GCTs. It indicates a role of both local anti-tumor immune response and systemic inflammation in these tumors.

Abstract

In the current study, we aimed to investigate whether expression of immune checkpoint proteins (V-domain Ig suppressor of T cell activation (VISTA) and programmed death-ligand 1 (PD-L1)) and markers of systemic inflammation could predict progression/relapse and death in the cohort of 180 patients with testicular germ-cell tumors (GCTs). Expression of PD-L1 and VISTA was assessed by immunohistochemistry utilizing tissue microarrays. To estimate systemic inflammation neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR), and platelet-to-lymphocyte ratio (PLR) were calculated. We found high PD-L1 and VISTA expression on tumor-associated immune cells (TAICs) in 89 (49.44%) and 63 (37.22%) of GCTs, respectively, whereas tumor cells besides trophoblastic elements were almost uniformly negative. High PD-L1 was associated with seminomatous histology and lower stage. Relapses in stage I patients occurred predominantly in cases with low numbers of PD-L1 and VISTA-expressing TAICs. In stage II/III disease, the combination of low VISTA-expressing TAICs and high PLR was identified as predictor of shorter event-free survival (HR 4.10; 1.48–11.36, p = 0.006) and overall survival (HR 15.56, 95% CI 1.78–135.51, p = 0.001) independently of tumor histology and location of metastases. We demonstrated that the assessment of immune checkpoint proteins on TAICs may serve as a valuable prognostic factor in patients with high-risk testicular GCTs. Further study is warranted to explore the predictive utility of these biomarkers in GCTs.

V-domain Ig suppressor of T cell activation (VISTA) inhibition is a new approach to cancer therapy: a Bibliometric study

V-domain Ig suppressor of T cell activation (VISTA) is a transmembrane protein that plays a crucial role in the regulation of antitumor immunity. Therapeutic intervention that inhibits the VISTA pathway constitutes a new approach in the treatment of cancer. The aim of the present study was to provide a bibliometric literature review of VISTA research in the field of cancer. Published articles on the topic were retrieved from the Web of Science Core Collection Database of Hassan II University from the beginning of the database to November 14, 2019. The articles were analyzed and a lot of information was available on the Web of Science, such as the number of citations, the names of the authors, country, publication year, Web of Science categories, and journal. A total of 76 papers (research and review articles) were retrieved from the Web of Science Core Collection Database to introduce VISTA research in cancer topic. All of the articles were published in English during the period between 2011 and 2019; the annual publications number has increased from 1 in 2011 to 22 in 2019. Cancer immunology immunotherapy journal, Cancer immunology research journal, and Cancer research journal, each one has published 3 articles (3.9% of the total publications), the impact factors of the journals ranged from 2.34 to 10.19. The author who has published high number of articles was Noelle RJ with 11 articles; according to the keyword co-occurrence, VISTA was the most frequent keyword with a frequency of 42.1%, followed by immune (36.8%). This is the first work that treats the application of bibliometric methods in VISTA research in the oncology field and represents an important bibliographic source for future studies on the role of VISTA in cancer and immunotherapy of cancer.

The Functional Crosstalk between Myeloid-Derived Suppressor Cells and Regulatory T Cells within the Immunosuppressive Tumor Microenvironment

Simple Summary

Immunotherapy improved the therapeutic landscape for patients with advanced cancer diseases. However, many patients do not benefit from immunotherapy. The bidirectional crosstalk between myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg) contributes to immune evasion, limiting the success of immunotherapy by checkpoint inhibitors. This review aims to outline the current knowledge of the role and the immunosuppressive properties of MDSC and Treg within the tumor microenvironment (TME). Furthermore, we will discuss the importance of the functional crosstalk between MDSC and Treg for immunosuppression, issuing particularly the role of cell adhesion molecules. Lastly, we will depict the impact of this interaction for cancer research and discuss several strategies aimed to target these pathways for tumor therapy.

Abstract

Immune checkpoint inhibitors (ICI) have led to profound and durable tumor regression in some patients with metastatic cancer diseases. However, many patients still do not derive benefit from immunotherapy. Here, the accumulation of immunosuppressive cell populations within the tumor microenvironment (TME), such as myeloid-derived suppressor cells (MDSC), tumor-associated macrophages (TAM), and regulatory T cells (Treg), contributes to the development of immune resistance. MDSC and Treg expand systematically in tumor patients and inhibit T cell activation and T effector cell function. Numerous studies have shown that the immunosuppressive mechanisms exerted by those inhibitory cell populations comprise soluble immunomodulatory mediators and receptor interactions. The latter are also required for the crosstalk of MDSC and Treg, raising questions about the relevance of cell–cell contacts for the establishment of their inhibitory properties. This review aims to outline the current knowledge on the crosstalk between these two cell populations, issuing particularly the potential role of cell adhesion molecules. In this regard, we further discuss the relevance of β2 integrins, which are essential for the differentiation and function of leukocytes as well as for MDSC–Treg interaction. Lastly, we aim to describe the impact of such bidirectional crosstalk for basic and applied cancer research and discuss how the targeting of these pathways might pave the way for future approaches in immunotherapy.

Dual roles of myeloid-derived suppressor cells induced by Toll-like receptor signaling in cancer

Myeloid-derived suppressor cells (MDSCs) are one of the major components of the tumor microenvironment (TME), and are the main mediators of tumor-induced immunosuppression. Recent studies have reported that the survival, differentiation and immunosuppressive activity of MDSCs are affected by the Toll-like receptor (TLR) signaling pathway. However, the regulatory effect of TLR signaling on MDSCs remains controversial. TLR-induced MDSC can acquire different immunosuppressive activities to influence the immune response that can be either beneficial or detrimental to cancer immunotherapy. The present review summarizes the effects of TLR signals on the number, phenotype and inhibitory activity of MDSCs, and their role in cancer immunotherapy, which cannot be ignored if effective cancer immunotherapies are to be developed for the immunosuppression of the TME.

Cardiotoxicity of immune checkpoint inhibitors: An updated review

The immune checkpoint molecules are involved in the regulation of T cells in order to prevent them from attacking to sell tissues and play a role in the immune response homeostasis. Application of the immune checkpoint inhibitors (ICIs) has provided a promising therapeutic approach in pathologies where the immune system is suppressed. The extended utilization of ICIs in several cancers has caused immune-related side effects in the cardiovascular system like cardiomyopathy and myocarditis. Cardiac toxicity, one of the main side effects of the ICIs based therapeutic approach has less been concerned; however, during the last years, many cases of fatal heart failure and myocarditis have been reported in patients treated with ICIs. In this review article, we attempted to discuss the cardiac adverse effects of inhibiting different immune checkpoint molecules. This article is protected by copyright. All rights reserved.

PD-1H (VISTA)-mediated suppression of autoimmunity in systemic and cutaneous lupus erythematosus

Systemic lupus erythematosus (SLE) and discoid lupus erythematosus (DLE) of the skin are autoimmune diseases characterized by inappropriate immune responses against self-proteins; the key elements that determine disease pathogenesis and progression are largely unknown. Here, we show that mice lacking immune inhibitory receptor VISTA or programmed death-1 homolog (PD-1H KO) on a BALB/c background spontaneously develop cutaneous and systemic autoimmune diseases resembling human lupus. Cutaneous lupus lesions of PD-1H KO mice have clustering of plasmacytoid dendritic cells (pDCs) similar to human DLE. Using mass cytometry, we identified proinflammatory neutrophils as critical early immune infiltrating cells within cutaneous lupus lesions of PD-1H KO mice. We also found that PD-1H is highly expressed on immune cells in human SLE, DLE lesions, and cutaneous lesions of MRL/lpr mice. A PD-1H agonistic monoclonal antibody in MRL/lpr mice reduces cutaneous disease, autoantibodies, inflammatory cytokines, chemokines, and immune cell expansion. Furthermore, PD-1H on both T cells and myeloid cells including neutrophils and pDCs could transmit inhibitory signals, resulting in reduced activation and function, establishing PD-1H as an inhibitory receptor on T cells and myeloid cells. On the basis of these findings, we propose that PD-1H is a critical element in the pathogenesis and progression of lupus, and PD-1H activation could be effective for treatment of systemic and cutaneous lupus.

Discovery and Optimization of Small-Molecule Ligands for V-Domain Ig Suppressor of T-Cell Activation (VISTA)

V-domain Ig suppressor of T-cell activation (VISTA) is an immune checkpoint that affects the ability of T-cells to attack tumors. A FRET-based high throughput screening identified NSC622608 as the first small-molecule ligand for VISTA. Investigation of the interaction of NSC622608 with VISTA using STD NMR and molecular modeling enabled the identification of a potential binding site in VISTA for NSC622608. Screening NSC622608 against a library of single-point VISTA mutants revealed the key residues in VISTA interacting with NSC622608. Further structural optimization resulted in a lead with submicromolar VISTA binding affinity. The lead compound blocked VISTA signaling in vitro, enhanced T-cell proliferation, and restored T-cell activation in the presence of VISTA-expressing cancer cell lines. This work would enable future development of small molecules targeting VISTA as immunomodulators and imaging probes.

Mechanisms of resistance to immune checkpoint inhibitors

The emergence of immune checkpoint inhibitors in recent years has transformed cancer treatment in many tumor types. Durable clinical responses in refractory cancer types have been observed. However, despite these promising long-term responses, the majority of patients fail to respond to immune checkpoint blockade, demonstrating primary resistance. In addition, some of those who initially respond to treatment eventually experience relapse secondary to acquired resistance. Both primary and acquired resistance is a result of complex and constantly evolving interactions between cancer cells and the immune system. Some mechanisms of resistance have been characterized to date, and more continue to be uncovered. The tumor microenvironment, tumor immunogenicity, and oncologic pathways play roles in response and resistance to immune checkpoint blockade. By elucidating and targeting mechanisms of resistance, treatments can be guided to improve clinical outcomes. Combination treatment strategies with immune checkpoint inhibitors are being tested in clinical trials, with several already in clinical use. This review will discuss the different resistance mechanisms and potential therapeutic strategies to overcome resistance.

Small molecules as antagonists of co-inhibitory pathways for cancer immunotherapy: a patent review (2018-2019)

INTRODUCTION

Therapeutic antibodies blocking co-inhibitory pathways do not attack tumor cells directly, but instead bind to their targeted proteins and mobilize the immune system to eradicate tumors. However, only a small fraction of patients with certain cancer types can benefit from the antibodies. Additionally, antibodies have shown serious immune-related adverse events in certain patients. Small-molecule antagonists may be a complementary and potentially synergistic approach to antibodies for patients with various cancers.

AREAS COVERED

The authors review the small molecules as antagonists of co-inhibitory pathway proteins, summarize their preliminary SARs, discuss biochemistry assays used in patents for the development of small molecules as novel antagonists.

EXPERT OPINION

The disclosed pharmacophores of small molecules as co-inhibitory pathway antagonists are represented by biphenyl derivatives, biaryl derivatives, teraryl derivatives, quateraryl derivatives, and oxadiazole/thiadiazole derivatives. However, these antagonists are still inferior to therapeutic antibodies in their inhibitory activities due to relatively flat of human co-inhibitory pathways proteins. Allosteric modulators may be an alternative approach. The more safety and efficacy evaluation trials of small-molecule antagonists targeting co-inhibitory pathways should be performed to demonstrate the proof-of-principle that small-molecule antagonists can result in sustained safety and antitumor response in the near future.

Mechanism-based treatment of cancer with immune checkpoint inhibitor therapies

Immune checkpoints are cell surface molecules that initiate regulatory pathways which have powerful control of CD8+ cytolytic T cell activity. Antagonistic and agonistic antibodies engaging these molecules have demonstrated profound impact on immune activation and have entered clinical use for the treatment of a variety of diseases. Over the past decade, antagonistic antibodies known as immune checkpoint inhibitors have become a new pillar of cancer treatment and have reshaped the therapeutic landscape in oncology. These agents differ in their mechanism of action and toxicity profiles compared to more traditional systemic cancer treatments such as chemo- and targeted therapies. This article reviews the pharmacology of this new class of agents.

Targeting NK Cell Checkpoint Receptors or Molecules for Cancer Immunotherapy

Checkpoint blockade therapy, for example using antibodies against CTLA-4 and PD-1/PD-L1, relieves T cells from the suppression by inhibitory checkpoints in the tumor microenvironment; thereby achieving good outcomes in the treatment of different cancer types. Like T cells, natural killer (NK) cell inhibitory receptors function as checkpoints for NK cell activation. Upon interaction with their cognate ligands on infected cells, tumor cells, dendritic cells and regulatory T cells, signals from these receptors severely affect NK cells' activation and effector functions, resulting in NK cell exhaustion. Checkpoint inhibition with antagonistic antibodies (Abs) can rescue NK cell exhaustion and arouse their robust anti-tumor capacity. Most notably, the response to anti-PD-1 therapy can be enhanced by the increased frequency and activation of NK cells, thereby increasing the overall survival of patients with multiple types of cancer. In addition, rescue of NK cell activity could enhance adaptive T cells' anti-tumor activity. Some antagonistic Abs (e.g., anti-TIGIT and anti-NKG2A monoclonal Abs) have extraordinary potential in cancer therapy, as evidenced by their induction of potent anti-tumor immunity through recovering both NK and T cell function. In this review, we summarize the dysfunction of NK cells in the tumor microenvironment and the key NK cell checkpoint receptors or molecules that control NK cell function. We particularly focus on recent advances in the most promising strategies through blockade of NK cell checkpoints or their combination with other approaches to more effectively reject tumors.

Cross-Species Single-Cell Analysis Reveals Divergence of the Primate Microglia Program

Microglia, the brain-resident immune cells, are critically involved in many physiological and pathological brain processes, including neurodegeneration. Here we characterize microglia morphology and transcriptional programs across ten species spanning more than 450 million years of evolution. We find that microglia express a conserved core gene program of orthologous genes from rodents to humans, including ligands and receptors associated with interactions between glia and neurons. In most species, microglia show a single dominant transcriptional state, whereas human microglia display significant heterogeneity. In addition, we observed notable differences in several gene modules of rodents compared with primate microglia, including complement, phagocytic, and susceptibility genes to neurodegeneration, such as Alzheimer's and Parkinson's disease. Our study provides an essential resource of conserved and divergent microglia pathways across evolution, with important implications for future development of microglia-based therapies in humans.

Immune Checkpoints Contribute Corneal Immune Privilege: Implications for Dry Eye Associated with Checkpoint Inhibitors

The eye is provided with immune protection against pathogens in a manner that greatly reduces the threat of inflammation-induced vision loss. Immune-mediated inflammation and allograft rejection are greatly reduced in the eye, a phenomenon called 'immune privilege'. Corneal tissue has inherent immune privilege properties with underlying three mechanisms: (1) anatomical, cellular, and molecular barriers in the cornea; (2) an immunosuppressive microenvironment; and (3) tolerance related to regulatory T cells and anterior chamber-associated immune deviation. This review describes the molecular mechanisms of the immunosuppressive microenvironment and regulatory T cells in the cornea that have been elucidated from animal models of ocular inflammation, especially those involving corneal transplantation, it also provides an update on immune checkpoint molecules in corneal and systemic immune regulation, and its relevance for dry eye associated with checkpoint inhibitor therapy.

Overcoming resistance to anti-PD1 and anti-PD-L1 treatment in gastrointestinal malignancies

In the last few years, the unprecedented results of immune checkpoint inhibitors have led to a paradigm shift in clinical practice for the treatment of several cancer types. However, the vast majority of patients with gastrointestinal cancer do not benefit from immunotherapy. To date, microsatellite instability high and DNA mismatch repair deficiency are the only robust predictive biomarkers of response to immune checkpoint inhibitors. Unfortunately, these patients comprise only 5%-10% of all gastrointestinal cancers. Several mechanisms of both innate and adaptive resistance to immunotherapy have been recognized that may be at least in part responsible for the failure of immune checkpoint inhibitors in this population of patients. In the first part of this review article, we provide an overview of the main clinical trials with immune checkpoint inhibitors in patients with gastrointestinal cancer and the role of predictive biomarkers. In the second part, we discuss the actual body of knowledge in terms of mechanisms of resistance to immunotherapy and the most promising approach that are currently under investigation in order to expand the population of patients with gastrointestinal cancer who could benefit from immune checkpoint inhibitors.

Discovery of New Immune Checkpoints: Family Grows Up

The first generation of immune checkpoint inhibitors (ICIs) including anti-CTLA-4 and anti-PD-1/anti-PD-L1 has achieved profound and great success. Till 2019 Q1, there are nine ICIs landing the oncology market: Ipilimumab (anti-CTLA-4, Bristol-Myers Squibb), Nivolumab (anti-PD-1, Bristol-Myers Squibb), Pembrolizumab (anti-PD-1, Merck), Atezolizumab (anti-PD-L1, Roche/Genentech), Durvalumab (anti-PD-L1, Astra Zeneca), Tremelimumab (anti-CTLA-4, Astra Zeneca), Cemiplimab (anti-PD-1, Sanofi/Regeneron), Toripalimab (anti-PD-1, Junshi), and Sintilimab (anti-PD-1, Innovent), which have covered the majority of hematologic and solid malignancies' indication. Beyond the considerable benefits for the patients, frustrated boundary still exists: limited response rate in monotherapy in late-stage population, poor effectiveness in neoplasms with immune desert and immune excluded types, and immune-related toxicities, some are life-threatened and with higher incidence in I-O combination regiment. Moreover, clinicians observed some cases switching to progression after achieving partial or complete response, indicating treatment failure or drug resistance. So people begin looking for the next generation of immune checkpoint members.

VISTA Is Crucial for Corneal Allograft Survival and Maintenance of Immune Privilege

Purpose

V-domain immunoglobulin suppressor of T cell activation (VISTA) is a novel immune checkpoint receptor and ligand for regulating T cell proliferation and cytokine production. The purpose of the present study was to determine the role of VISTA in the immune privilege of corneal allografts.

Methods

Expression of VISTA mRNA in mouse eyes was assessed with reverse-transcription PCR. Corneas of C57BL/6 mice were orthotopically transplanted into the eyes of BALB/c wild-type recipients treated with anti-VISTA mAb, and graft survival was assessed. A separate set of BALB/c mice treated with anti-VISTA mAb or rat IgG received injection of C57BL/6 splenocytes into the anterior chamber, and induction of allospecific anterior chamber-associated immune deviation (ACAID) was assessed. CD4+ and CD8+ T cells in the spleen were assessed with flow cytometry.

Results

VISTA mRNA was constitutively expressed in the cornea, and the expression of VISTA was localized to CD11b+ cells on the corneal stroma. Survival of allografts treated with anti-VISTA mAb was less than that of the control. ACAID was induced less efficiently in BALB/c mice treated with VISTA mAb. The proportions of CD8+ T cells and CD8+ CD103+ T cells (CD8+ T regulatory cells) in the spleen of BALB/c mice treated with anti-VISTA mAb were significantly lower than those of the control.

Conclusions

VISTA may play an essential role in the acceptance of corneal allografts via involvement with allospecific ACAID, which suppresses T cell infiltration into the cornea.

Immunological Targets for Immunotherapy: Inhibitory T Cell Receptors

Tumor development is characterized by the accumulation of mutational and epigenetic changes that transform normal cells and survival pathways into self-sustaining cells capable of untrammeled growth. Although multiple modalities including surgery, radiation, and chemotherapy are available for the treatment of cancer, the benefits conferred are often limited. The immune system is capable of specific, durable, and adaptable responses. However, cancers hijack immune mechanisms such as negative regulatory checkpoints that have evolved to limit inflammatory and immune responses to thwart effective antitumor immunity. The development of monoclonal antibodies against inhibitory receptors expressed by immune cells has produced durable responses in a broad array of advanced malignancies and heralded a new dawn in the cancer armamentarium. However, these remarkable responses are limited to a minority of patients and indications, highlighting the need for more effective and novel approaches. Preclinical and clinical studies with immune checkpoint blockade are exploring the therapeutic potential antibody-based therapy targeting multiple inhibitory receptors. In this chapter, we discuss the current understanding of the structure, ligand specificities, function, and signaling activities of various inhibitory receptors. Additionally, we discuss the current development status of various immune checkpoint inhibitors targeting these negative immune receptors and highlight conceptual gaps in knowledge.

Kidney residency of VISTA-positive macrophages accelerates repair from ischemic injury

Tissue-resident macrophages have unique tissue-specific functions in maintaining homeostasis and resolving inflammation. However, the repair role and relevant molecules of kidney-resident macrophages after ischemic injury remain unresolved. To this end, mice without kidney-resident R1 macrophages but containing infiltrating monocyte-derived R2 macrophages were generated using differential cellular kinetics following clodronate liposome treatment. When ischemia-reperfusion injury was induced in these mice, late phase repair was reduced. Transcriptomic and flow cytometric analyses identified that V-domain Ig suppressor of T cell activation (VISTA), an inhibitory immune checkpoint molecule, was constitutively expressed in kidney-resident R1 macrophages, but not in other tissue-resident macrophages. Here, VISTA functioned as a scavenger of apoptotic cells and served as a checkpoint to control kidney-infiltrating T cells upon T cell receptor-mediated stimulation. Together these functions improved the repair process after ischemia-reperfusion injury. CD14⁺ CD33⁺ mononuclear phagocytes of human kidney also expressed VISTA, which has similar functions to the mouse counterpart. Thus, VISTA is upregulated in kidney macrophages in a tissue-dependent manner and plays a repair role during ischemic injury.

NK Cell Dysfunction and Checkpoint Immunotherapy

NK cells play important roles in the innate immune responses against tumors. The effector function of NK cells relies on the integration of activating and inhibitory signals. Emerging checkpoint receptors and molecules are being revealed to mediate NK cell dysfunction in the tumor microenvironment. Inhibition of some NK cell surface checkpoint receptors has displayed the potential to reverse NK cell dysfunction in tumors, and to boost anti-tumor immunity, both in clinical trials (anti-KIR and anti-NKG2A), and in preclinical studies (e.g., anti-TIGIT, and anti-CD96). To fully exploit the potential of NK-based checkpoint immunotherapy, more understanding of the regional features of NK cells in the tumor microenvironment is required. This will provide valuable information regarding the dynamic nature of NK cell immune response against tumors, as well as novel checkpoints or pathways to be targeted. In this Review, we discuss recent advances in the understanding of NK cell dysfunction in tumors, as well as emerging strategies of NK-based checkpoint immunotherapy for tumors.

Immune-Checkpoint Protein VISTA Regulates Antitumor Immunity by Controlling Myeloid Cell-Mediated Inflammation and Immunosuppression

Immune-checkpoint protein V-domain immunoglobulin suppressor of T-cell activation (VISTA) controls antitumor immunity and is a valuable target for cancer immunotherapy. This study identified a role of VISTA in regulating Toll-like receptor (TLR) signaling in myeloid cells and controlling myeloid cell-mediated inflammation and immunosuppression. VISTA modulated the polyubiquitination and protein expression of TRAF6. Consequently, VISTA dampened TLR-mediated activation of MAPK/AP-1 and IKK/NF-κB signaling cascades. At cellular levels, VISTA regulated the effector functions of myeloid-derived suppressor cells and tolerogenic dendritic cell (DC) subsets. Blocking VISTA augmented their ability to produce proinflammatory mediators and diminished their T cell-suppressive functions. These myeloid cell-dependent effects resulted in a stimulatory tumor microenvironment that promoted T-cell infiltration and activation. We conclude that VISTA is a critical myeloid cell-intrinsic immune-checkpoint protein and that the reprogramming of tolerogenic myeloid cells following VISTA blockade promotes the development of T cell-mediated antitumor immunity.

Decreased Expression of Negative Immune Checkpoint VISTA by CD4+ T Cells Facilitates T Helper 1, T Helper 17, and T Follicular Helper Lineage Differentiation in GCA

Loss of immune checkpoint (IC) Programmed Death-1 (PD-1) and PD-Ligand1 (PD-L1) expression has been implicated in the immunopathology of Giant Cell Arteritis (GCA). The contribution of the negative immune checkpoint V-domain Immunoglobulin-containing suppressor of T cell activation (VISTA) to GCA pathology has not yet been studied. The aim of our study was to investigate if expression of VISTA and other IC molecules by peripheral blood (PB) immune cells is modulated in GCA and at the site of vascular inflammation. In addition, we assessed the effect of VISTA-Ig engagement on in vitro CD4+ T helper (Th) lineage differentiation. To this end, frequencies of monocytes expressing CD80/86, PD-L1, PD-L2, and VISTA were determined in blood samples from 30 GCA patients and 18 matched healthy controls by flow cytometry. In parallel, frequencies of CD4+ cells expressing CD28, Cytotoxic T-Lymphocyte-associated antigen-4 (CTLA-4), PD-1, and VISTA were determined. Immunohistochemistry was employed to detect VISTA, PD-1, and PD-L1-expressing cells in temporal artery biopsies (TABs) diagnostic of GCA. Furthermore, the effect of VISTA-Ig on in vitro CD4+ Th lineage differentiation in patients and controls was determined. Our study shows that frequencies of CD80/CD86+ and VISTA+ monocytes were decreased in treated GCA patients only. Moreover, proportions of PD-1+ and VISTA+ Th cells were significantly decreased in GCA patients. Clear infiltration of VISTA+, PD1+, and PD-L1+ cells was seen in GCA TABs. Finally, VISTA-Ig engagement failed to suppress Th1, Th17, and Tfh lineage development in GCA. Our results indicate that decreased expression of VISTA may facilitate development of pathogenic Th1 and Th17 cells in GCA.

Immune inhibitory proteins and their pathogenic and therapeutic implications in autoimmunity and autoimmune hepatitis

Key inhibitory proteins can blunt immune responses to self-antigens, and deficiencies in this repertoire may promote autoimmunity. The goals of this review are to describe the key immune inhibitory proteins, indicate their possible impact on the development of autoimmune disease, especially autoimmune hepatitis, and encourage studies to clarify their pathogenic role and candidacy as therapeutic targets. English abstracts were identified in PubMed by multiple search terms. Full length articles were selected for review, and secondary and tertiary bibliographies were developed. Cytotoxic T lymphocyte antigen-4 impairs ligation of CD28 to B7 ligands on antigen presenting cells and inhibits the adaptive immune response by increasing anti-inflammatory cytokines, generating regulatory T cells, and reducing T cell activation and proliferation. Programed cell death antigen-1 inhibits T cell selection, activation, and proliferation by binding with two ligands at different phases and locations of the immune response. A soluble alternatively spliced variant of this protein can dampen the inhibitory signal. Autoimmune hepatitis has been associated with polymorphisms of the cytotoxic T lymphocyte antigen-4 gene, reduced hepatic expression of a ligand of programed cell death antigen-1, an interfering soluble variant of this key inhibitory protein, and antibodies against it. Findings have been associated with laboratory indices of liver injury and suboptimal treatment response. Abatacept, belatacept, CD28 blockade, and induction of T cell exhaustion are management considerations that require scrutiny. In conclusion, deficiencies in key immune inhibitory proteins may promote the occurrence of autoimmune diseases, such as autoimmune hepatitis, and emerging interventions may overcome these deficiencies. Investigations should define the nature, impact and management of these inhibitory disturbances in autoimmune hepatitis.

Inhibition of allogeneic islet graft rejection by VISTA-conjugated liposome

The Ig superfamily member V-domain Ig-containing suppressor of T-cell activation (VISTA) is a negative regulator with broad-spectrum activities and has reported that blockade of VISTA or combination with other negative checkpoint receptors sufficiently break tumor tolerance. However, it remains unclear whether VISTA could induce allogeneic T-cell hyporesponsiveness and inhibit allograft rejection. Here we found VISTA treatment significantly inhibited lymphocyte proliferation and activation in allogeneic MLR assay through impairing SYK-VAV pathway. Interestingly, though neither VISTA protein nor VISTA-Fc fusion protein administration exerted satisfactory immunosuppressive effect on allograft survival due to their short half-life in circulation, this problem was solved by conjugating VISTA protein on liposome by biotin-streptavidin system, which markedly prolonged its circulating half-life to 60 h. With islet transplant model, administration of VISTA-conjugated liposome could markedly prolong allograft survival by inhibition of SYK-VAV pathway, thus maintained the normal blood glucose level of recipients during treatment period. The results indicate VISTA is a promising therapeutic target to treat allograft rejection of islet transplantation.

The expression of the immune checkpoint regulator VISTA correlates with improved overall survival in pT1/2 tumor stages in esophageal adenocarcinoma

Immune checkpoint modulation in cancer has been demonstrated as a high-value therapeutic strategy in many tumor entities. VISTA is an immune checkpoint receptor regulating T-cell function. To the best of our knowledge, nothing is known about the expression and prognostic impact of VISTA on tumor infiltrating lymphocytes (TILs) in the tumor microenvironment of esophageal adenocarcinoma (EAC). We analyzed in total 393 EACs within a test-cohort (n = 165) and a validation-cohort (n = 228) using a monoclonal antibody (clone D1L2G). These data were statistically correlated with clinical as well as molecular data. 22.2% of the tumor cohort presented with a VISTA expression on TILs. These patients demonstrated an improved median overall survival compared to patients without VISTA expression (202.2 months vs. 21.6 months; p < 0.0001). The favorable outcome of VISTA positive tumors is significant in the entire cohort but mainly driven by the general better prognosis of T1/T2 tumors. However, in the pT1/2 group, VISTA positive tumors show a tremendous survival benefit compared to VISTA negative tumors revealing real long-term survivors in this particular subgroup. The survival difference is independent of the T-stage. This unique characteristic could influence neoadjuvant therapy concepts for EAC, since a profit of therapy could be reduced in the already favorable subgroup of VISTA positive tumors. VISTA emerges as a prognostic biomarker for long-term survival especially in the group of early TNM-stages. Future studies have to show the relevance of VISTA positive TILs within a tumor concerning response to specific immune checkpoint inhibition.

Emerging predictors of the response to the blockade of immune checkpoints in cancer therapy

Checkpoint blockade-based immunotherapy offers new options and powerful weapons for the treatment of cancer, but its efficacy varies greatly among different types of cancer and across individual patients. Thus, the development of the right tools that can be used to identify patients who could benefit from this therapy is of utmost importance in order to maximize the therapeutic benefit, minimize risk of toxicities, and guide combination approaches. Multiple predictors have emerged that are based on checkpoint receptor ligand expression, tumor mutational burden, neoantigen and microsatellite instability, tumor-infiltrating immune cells, and peripheral blood biomarkers. In this review, we discuss the current state and progress of predictors as aids in checkpoint blockade-based immunotherapy in cancer.

Distinct contribution of PD-L1 suppression by spatial expression of PD-L1 on tumor and non-tumor cells

Programmed cell death receptor 1 (PD-1) and its ligand, PD-L1, are important immune checkpoint proteins. Although antibodies that block PD-1/PD-L1 have shown promising clinical efficacy in a subset of cancer patients, the detailed cellular and molecular mechanisms behind anti-PD-1 and anti-PD-L1 immunotherapy are not well defined. Specifically, the way in which PD-L1 contributes to immune suppression on tumor and non-tumor cells remains controversial. By selectively blocking PD-L1 on either tumor or non-tumor cells, we demonstrated that PD-L1 from both sources suppressed the anti-tumor T-cell response. Blocking PD-L1 on either tumor cells or non-tumor cells inhibited tumor growth and enhanced immune cell infiltration, as well as the tumor-specific T-cell response. Further, simultaneously blocking tumor- and non-tumor-derived PD-L1 maximized anti-tumor T-cell responses and demonstrated synergy. In addition, the relative contribution of PD-L1 on tumor and non-tumor cells to immune suppression depended on the PD-L1 expression level. Lastly, we found that the F4/80 receptor was involved in the anti-tumor effect of PD-L1 blockade. Taken together, our data indicate that PD-L1 on both tumor and non-tumor cells is critical for T-cell inhibition, which provides new directions for the optimization of PD-L1-blocking antibodies and the development of clinical biomarker strategies.