Structural insight into T cell coinhibition by PD-1H (VISTA)

VISTA: A promising target for overcoming immune evasion in gynecologic cancers

Immune checkpoint blockade (ICB) therapy has revolutionized cancer treatment but has shown limited efficacy in gynecologic cancers. VISTA (V-domain Ig suppressor of T-cell activation), a member of the B7 family, is emerging as another checkpoint that regulates the anti-tumor immune responses within the tumor microenvironment. This paper reviews the structure, expression, and mechanism of action of VISTA. Furthermore, it highlights recent advances in VISTA-blocking therapies and their potential in improving outcomes for patients with gynecologic cancers. By understanding the role of VISTA in mediating the immune evasion of gynecologic tumors, we can develop more effective combinatory treatment strategies that could overcome resistance to current ICB therapies.

VISTA: A Novel Checkpoint for Cancer Immunotherapy

V-domain Ig suppressor of T cell activation (VISTA) is a recently identified member of the B7 family of immunoregulatory proteins. It is pivotal for maintaining T cell quiescence and exerts a significant regulatory influence on the immune response to tumors. Accumulating clinical evidence suggests that the influence of VISTA on tumor immunity is more nuanced than initially postulated. Although these revelations add layers of complexity to our understanding of the function of VISTA, they also offer novel avenues for scientific inquiry and potential therapeutic targets. In this review, we scrutinize the current literature pertaining to the expression of VISTA in various of malignancies, aiming to elucidate its intricate roles within the tumor microenvironment and in cancer immunotherapy.

VISTA nonredundantly regulates proliferation and CD69low γδ T cell accumulation in the intestine in murine sepsis

Sepsis is a dysregulated systemic immune response to infection i.e. responsible for ∼35% of in-hospital deaths at a significant fiscal healthcare cost. Our laboratory, among others, has demonstrated the efficacy of targeting negative checkpoint regulators (NCRs) to improve survival in a murine model of sepsis, cecal ligation and puncture (CLP). B7-CD28 superfamily member, V-domain immunoglobulin suppressor of T cell activation (VISTA), is an ideal candidate for strategic targeting in sepsis. VISTA is a 35 to 45 kDa type 1 transmembrane protein with unique biology that sets it apart from all other NCRs. We recently reported that VISTA-/- mice had a significant survival deficit post-CLP, which was rescued upon adoptive transfer of a VISTA-expressing pMSCV-mouse Foxp3-EF1α-GFP-T2A-puro stable Jurkat cell line (Jurkatfoxp3 T cells). Based on our prior study, we investigated the effector cell target of Jurkatfoxp3 T cells in VISTA-/- mice. γδ T cells are a powerful lymphoid subpopulation that require regulatory fine-tuning by regulatory T cells to prevent overt inflammation/pathology. In this study, we hypothesized that Jurkatfoxp3 T cells nonredundantly modulate the γδ T cell population post-CLP. We found that VISTA-/- mice have an increased accumulation of intestinal CD69low γδ T cells, which are not protective in murine sepsis. Adoptive transfer of Jurkatfoxp3 T cells decreased the intestinal γδ T cell population, suppressed proliferation, skewed remaining γδ T cells toward a CD69high phenotype, and increased soluble CD40L in VISTA-/- mice post-CLP. These results support a potential regulatory mechanism by which VISTA skews intestinal γδ T cell lineage representation in murine sepsis.

LRIG1 engages ligand VISTA and impairs tumor-specific CD8+ T cell responses

Immune checkpoint blockade is a promising approach to activate antitumor immunity and improve the survival of patients with cancer. V-domain immunoglobulin suppressor of T cell activation (VISTA) is an immune checkpoint target; however, the downstream signaling mechanisms are elusive. Here, we identify leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) as a VISTA binding partner, which acts as an inhibitory receptor by engaging VISTA and suppressing T cell receptor signaling pathways. Mice with T cell-specific LRIG1 deletion developed superior antitumor responses because of expansion of tumor-specific cytotoxic T lymphocytes (CTLs) with increased effector function and survival. Sustained tumor control was associated with a reduction of quiescent CTLs (TCF1+ CD62Lhi PD-1low) and a reciprocal increase in progenitor and memory-like CTLs (TCF1+ PD-1+). In patients with melanoma, elevated LRIG1 expression on tumor-infiltrating CD8+ CTLs correlated with resistance to immunotherapies. These results delineate the role of LRIG1 as an inhibitory immune checkpoint receptor and propose a rationale for targeting the VISTA/LRIG1 axis for cancer immunotherapy.

VISTA checkpoint inhibition by pH-selective antibody SNS-101 with optimized safety and pharmacokinetic profiles enhances PD-1 response

VISTA, an inhibitory myeloid-T-cell checkpoint, holds promise as a target for cancer immunotherapy. However, its effective targeting has been impeded by issues such as rapid clearance and cytokine release syndrome observed with previous VISTA antibodies. Here we demonstrate that SNS-101, a newly developed pH-selective VISTA antibody, addresses these challenges. Structural and biochemical analyses confirmed the pH-selectivity and unique epitope targeted by SNS-101. These properties confer favorable pharmacokinetic and safety profiles on SNS-101. In syngeneic tumor models utilizing human VISTA knock-in mice, SNS-101 shows in vivo efficacy when combined with a PD-1 inhibitor, modulates cytokine and chemokine signaling, and alters the tumor microenvironment. In summary, SNS-101, currently in Phase I clinical trials, emerges as a promising therapeutic biologic for a wide range of patients whose cancer is refractory to current immunotherapy regimens.

PD-1H/VISTA mediates immune evasion in acute myeloid leukemia

Acute myeloid leukemia (AML) presents a pressing medical need in that it is largely resistant to standard chemotherapy as well as modern therapeutics, such as targeted therapy and immunotherapy, including anti-programmed cell death protein (anti-PD) therapy. We demonstrate that programmed death-1 homolog (PD-1H), an immune coinhibitory molecule, is highly expressed in blasts from the bone marrow of AML patients, while normal myeloid cell subsets and T cells express PD-1H. In studies employing syngeneic and humanized AML mouse models, overexpression of PD-1H promoted the growth of AML cells, mainly by evading T cell-mediated immune responses. Importantly, ablation of AML cell-surface PD-1H by antibody blockade or genetic knockout significantly inhibited AML progression by promoting T cell activity. In addition, the genetic deletion of PD-1H from host normal myeloid cells inhibited AML progression, and the combination of PD-1H blockade with anti-PD therapy conferred a synergistic antileukemia effect. Our findings provide the basis for PD-1H as a potential therapeutic target for treating human AML.

Immune Inhibitory Molecule PD-1 Homolog (VISTA) Colocalizes with CD11b Myeloid Cells in Melanoma and Is Associated with Poor Outcomes

Tumors evade immunity through the overexpression of immune inhibitory molecules in the tumor microenvironment such as PD-L1/B7-H1. An immune inhibitory molecule named PD-1 homolog (also known as V-domain Ig-containing suppressor of T cell activation [VISTA]) functions to control both T cells and myeloid cells. Current clinical trials using anti-VISTA-blocking agents for treatment of cancer are ongoing. We sought to determine the extent of VISTA expression in primary cutaneous melanomas (n = 190), identify the critical cell types expressing VISTA, and correlate its expression with PD-L1 expression using multiplexed quantitative immunofluorescence. Within the tumor subcompartments, VISTA is most highly expressed on CD11b myeloid cells, and PD-L1 is most highly expressed on CD68 myeloid cells in our melanoma cohort. There is little correlation between VISTA and PD-L1 expression intensity, suggesting that individual tumors have distinct immunosuppressive tumor microenvironments. High levels of VISTA expression on CD11b myeloid cells but not PD-L1 expression were associated with greater melanoma recurrence and greater all-cause mortality. Our findings suggest that cell-specific VISTA expression may be a negative prognostic biomarker for melanoma and a future potential therapeutic target.

A highly potent anti-VISTA antibody KVA12123 - a new immune checkpoint inhibitor and a promising therapy against poorly immunogenic tumors

Background

Immune checkpoint therapies have led to significant breakthroughs in cancer patient treatment in recent years. However, their efficiency is variable, and resistance to immunotherapies is common. VISTA is an immune-suppressive checkpoint inhibitor of T cell response belonging to the B7 family and a promising novel therapeutic target. VISTA is expressed in the immuno-suppressive tumor microenvironment, primarily by myeloid lineage cells, and its genetic knockout or antibody blockade restores an efficient antitumor immune response.

Methods

Fully human monoclonal antibodies directed against VISTA were produced after immunizing humanized Trianni mice and single B cell sequencing. Anti-VISTA antibodies were evaluated for specificity, cross-reactivity, monocyte and T cell activation, Fc-effector functions, and antitumor efficacy using in vitro and in vivo models to select the KVA12123 antibody lead candidate. The pharmacokinetics and safety profiles of KVA12123 were evaluated in cynomolgus monkeys.

Results

Here, we report the development of a clinical candidate anti-VISTA monoclonal antibody, KVA12123. KVA12123 showed high affinity binding to VISTA through a unique epitope distinct from other clinical-stage anti-VISTA monoclonal antibodies. This clinical candidate demonstrated high specificity against VISTA with no cross-reactivity detected against other members of the B7 family. KVA12123 blocked VISTA binding to its binding partners. KVA12123 induced T cell activation and demonstrated NK-mediated monocyte activation. KVA12123 treatment mediated strong single-agent antitumor activity in several syngeneic tumor models and showed enhanced efficacy in combination with anti-PD-1 treatment. This clinical candidate was engineered to improve its pharmacokinetic characteristics and reduce Fc-effector functions. It was well-tolerated in preclinical toxicology studies in cynomolgus monkeys, where hematology, clinical chemistry evaluations, and clinical observations revealed no indicators of toxicity. No cytokines associated with cytokine release syndrome were elevated.

Conclusion

These results establish that KVA12123 is a promising drug candidate with a distinct but complementary mechanism of action of the first generation of immune checkpoint inhibitors. This antibody is currently evaluated alone and in combination with pembrolizumab in a Phase 1/2 open-label clinical trial in patients with advanced solid tumors.

Imatinib and M351-0056 enhance the function of VISTA and ameliorate the development of SLE via IFN-I and noncanonical NF-κB pathway

V-domain immunoglobulin suppressor of T-cell activation (VISTA), an important negative checkpoint protein, participates in immunoregulation. Systemic lupus erythematosus (SLE) is an autoimmune disease in which patients exhibit high levels of autoantibodies and multi-organ tissue injury, primarily involving the kidney and skin. In wild-type (WT) mice and Vsir-/- mice with pristane-induced lupus-like disease, we found that VISTA deficiency exacerbated the lupus-like disease in mice, possibly through aberrant activation of type I interferon (IFN-I) signaling, CD4+ T cell, and noncanonical nuclear factor-κB (NF-κB) pathway. Surface plasmon resonance results showed that imatinib, an FDA-approved tyrosine kinase inhibitor, may have a high affinity for human VISTA-ECD with a KD value of 0.2009 μM. The biological activities of imatinib and VISTA agonist M351-0056 were studied in monocytes and T cells and in lupus-like disease murine model of chronic graft-versus-host disease (cGVHD) and lupus-prone MRL/lpr mice. VISTA small-molecule agonist reduced the cytokine production of peripheral blood mononuclear cells (PBMCs) and Jurkat cells and inhibited PBMCs proliferation. Moreover, they attenuated the levels of autoantibodies, renal injury, inflammatory cytokines, chemokines, and immune cell expansion in the cGVHD mouse model and MRL/lpr mice. Our findings also demonstrated that VISTA small-molecule agonist ameliorated the development of SLE through improving aberrantly activated IFN-I signaling and noncanonical NF-κB pathway. In conclusion, VISTA has a protective effect on the development and progression of SLE. VISTA agonist M351-0056 and imatinib have been firstly demonstrated to attenuate SLE, suggesting interventions to enhance VISTA function may be effective in treating SLE. VISTA deficiency exacerbates pristane-induced lupus-like disease in mice by promoting activation of the IFN-I and noncanonical NF-κB pathway. Imatinib was screened as a small-molecule VISTA agonist by molecular docking, SPR, and cellular level experiments. VISTA agonists (M351-0056 and imatinib) alleviated lupus-like disease progression in the cGVHD mouse model and MRL/lpr mice by inhibiting activation of IFN-I and noncanonical NF-κB pathway.

The kinetics of inhibitory immune checkpoints during and post-COVID-19: the knowns and unknowns

The immune system is tightly regulated to prevent immune reactions to self-antigens and to avoid excessive immune responses during and after challenges from non-self-antigens. Inhibitory immune checkpoints (IICPs), as the major regulators of immune system responses, are extremely important for maintaining the homeostasis of cells and tissues. However, the high and sustained co-expression of IICPs in chronic infections, under persistent antigenic stimulations, results in reduced immune cell functioning and more severe and prolonged disease complications. Furthermore, IICPs-mediated interactions can be hijacked by pathogens in order to evade immune induction or effector mechanisms. Therefore, IICPs can be potential targets for the prognosis and treatment of chronic infectious diseases. This is especially the case with regards to the most challenging infectious disease of recent times, coronavirus disease-2019 (COVID-19), whose long-term complications can persist long after recovery. This article reviews the current knowledge about the kinetics and functioning of the IICPs during and post-COVID-19.

Combinatorial blockade for cancer immunotherapy: targeting emerging immune checkpoint receptors

The differentiation, survival, and effector function of tumor-specific CD8+ cytotoxic T cells lie at the center of antitumor immunity. Due to the lack of proper costimulation and the abundant immunosuppressive mechanisms, tumor-specific T cells show a lack of persistence and exhausted and dysfunctional phenotypes. Multiple coinhibitory receptors, such as PD-1, CTLA-4, VISTA, TIGIT, TIM-3, and LAG-3, contribute to dysfunctional CTLs and failed antitumor immunity. These coinhibitory receptors are collectively called immune checkpoint receptors (ICRs). Immune checkpoint inhibitors (ICIs) targeting these ICRs have become the cornerstone for cancer immunotherapy as they have established new clinical paradigms for an expanding range of previously untreatable cancers. Given the nonredundant yet convergent molecular pathways mediated by various ICRs, combinatorial immunotherapies are being tested to bring synergistic benefits to patients. In this review, we summarize the mechanisms of several emerging ICRs, including VISTA, TIGIT, TIM-3, and LAG-3, and the preclinical and clinical data supporting combinatorial strategies to improve existing ICI therapies.

The checkpoint inhibitor PD-1H/VISTA controls osteoclast-mediated multiple myeloma bone disease

Multiple myeloma bone disease is characterized by the development of osteolytic bone lesions. Recent work identified matrix metalloproteinase 13 as a myeloma-derived fusogen that induces osteoclast activation independent of its proteolytic activity. We now identify programmed death-1 homolog, PD-1H, as the bona fide MMP-13 receptor on osteoclasts. Silencing PD-1H or using Pd-1h^-/- bone marrow cells abrogates the MMP-13-enhanced osteoclast fusion and bone-resorptive activity. Further, PD-1H interacts with the actin cytoskeleton and plays a necessary role in supporting c-Src activation and sealing zone formation. The critical role of PD-1H in myeloma lytic bone lesions was confirmed using a Pd-1h^-/- myeloma bone disease mouse model wherein myeloma cells injected into Pd-1h^-/-Rag2^-/- results in attenuated bone destruction. Our findings identify a role of PD-1H in bone biology independent of its known immunoregulatory functions and suggest that targeting the MMP-13/PD-1H axis may represent a potential approach for the treatment of myeloma associated osteolysis.

Vista of the Future: Novel Immunotherapy Based on the Human V-Set Immunoregulatory Receptor for Digestive System Tumors

While gastrointestinal tumors remain a multifactorial and prevalent group of malignancies commonly treated surgically in combination with chemotherapy and radiotherapy, advancements regarding immunotherapeutic approaches continue to occur. Entering a new era of immunotherapy focused on overcoming resistance to preceding therapies caused the emergence of new therapeutic strategies. A promising solution surfaces with a V-domain Ig suppressor of T-cell activation (VISTA), a negative regulator of a T-cell function expressed in hematopoietic cells. Due to VISTA's ability to act as both a ligand and a receptor, several therapeutic approaches can be potentially developed. A broad expression of VISTA was discovered on various tumor-growth-controlling cells, which proved to increase in specific tumor microenvironment (TME) conditions, thus serving as a rationale behind the development of new VISTA-targeting. Nevertheless, VISTA's ligands and signaling pathways are still not fully understood. The uncertain results of clinical trials suggest the need for future examining inhibitor agents for VISTA and implicating a double immunotherapeutic blockade. However, more research is needed before the breakthrough can be achieved. This review discusses perspectives and novel approaches presented in the current literature. Based on the results of the ongoing studies, VISTA might be considered a potential target in combined therapy, especially for treating gastrointestinal malignancies.

Transcriptome profiling reveals transcriptional regulation of VISTA in T cell activation

PURPOSE

V-domain immunoglobulin suppressor of T-cell activation (VISTA) is a novel type of immune checkpoint. This study was performed to explore the potential mechanism by which different domains of VISTA affect T-cell activation and search for potential interacting proteins.

METHODS

Stably transfected Jurkat cell lines were constructed to overexpress human VISTA (VISTA-FL), cytoplasmic domain deletion mutants (VISTA-ΔECD) and extracellular domain deletion mutants (VISTA- ΔCD). Empty vector (EV) control cell lines were constructed. Four stable cell lines were subjected to transcriptome sequencing after stimulation with PMA and PHA. The differentially expressed genes (DEGs) were analysed to explore the potential pathway by which VISTA inhibits T-cell activation. Proteinprotein interaction (PPI) network analysis was used to search for potential interacting proteins of VISTA.

RESULTS

In this study, 1256 DEGs were identified in Jurkat-VISTA-FL cells, 740 DEGs in Jurkat-VISTA-ΔCD cells, and 5605 DEGs in Jurkat-VISTA-ΔECD cells compared with Jurkat-EV cells. DEGs were mainly enriched in pathways related to T-cell differentiation, T-cell receptor signalling pathway and T-cell migration in Jurkat-VISTA-ΔECD cells; with cholesterol biosynthesis in Jurkat-VISTA-ΔCD cells; and with the inflammatory response in Jurkat-VISTA-FL cells. HHLA2 and CTH were identified as potential partners that interact directly with VISTA. The results also show an indirect interaction between VISTA and PSGL-1.

CONCLUSIONS

This study revealed the pathways by which VISTA is involved in T-cell activation and identified the potential binding partners of VISTA through RNA-seq, providing valuable resources for developing in-depth studies of the action mechanisms of VISTA as a potential target for cancer and inflammatory diseases.

Disrupting cancer angiogenesis and immune checkpoint networks for improved tumor immunity

Immune checkpoint inhibitors (ICIs) have advanced the field of cancer immunotherapy in patients by sustaining effector immune cell activity within the tumor microenvironment. However, the approach in general is still faced with issues related to ICI response duration/resistance, treatment eligibility, and safety, which indicates a need for further refinements. As immune checkpoint upregulation is inextricably linked to cancer-induced angiogenesis, newer clinical efforts have demonstrated the feasibility of disrupting both tumor-promoting networks to mediate enhanced immune-driven protection. This review focuses on such key evidence stipulating the necessity of co-applying ICI and anti-angiogenic strategies in cancer patients, with particular interest in highlighting newer engineered antibody approaches that may provide theoretically superior multi-pronged and safe therapeutic combinations.

Development of Inhibitors Targeting the V-Domain Ig Suppressor of T Cell Activation Signal Pathway

Blockade of cytotoxic T lymphocyte antigen 4 (CTLA-4) and programmed cell death-1/programmed cell death-ligand 1 (PD-1/PD-L1) has produced considerable therapeutic effect, but only in a fraction of patients, so more targets are being investigated. VISTA (V-domain Ig suppressor of T cell activation) is a novel immune checkpoint that is broadly expressed within hematopoietic cells and multiple cancers (low expressing frequency on solid tumors), particularly those with a poor immunotherapy response rate. As a result, VISTA has been identified as an appealing target for immunotherapy, and several VISTA inhibitors are currently in clinical and preclinical trials. In this review, the structural features and binding partners of VISTA are summarized, and we describe the latest developments of monoclonal antibodies and small molecules targeting VISTA as well as possible future directions for development of therapies targeting VISTA.

IGSF11 and VISTA: a pair of promising immune checkpoints in tumor immunotherapy

Immunotherapy has become the major treatment for tumors in clinical practice, but some intractable problems such as the low response rate and high rates of immune-related adverse events still hinder the progress of tumor immunotherapy. Hence, it is essential to explore additional immunotherapy treatment targets. In this review, we focus on the structure, expression and expression-related mechanisms, interactions, biological functions and the progress in preclinical/clinical research of IGSF11 and VISTA in tumors. We cover the progress in recent research with this pair of immune checkpoints in tumor immune regulation, proliferation, immune resistance and predictive prognosis. Both IGSF11 and VISTA are highly expressed in tumors and are modulated by various factors. They co-participate in the functional regulation of immune cells and the inhibition of cytokine production. Besides, in the downregulation of IGSF11 and VISTA, both inhibit the growth of some tumors. Preclinical and clinical trials all emphasize the predictive role of IGSF11 and VISTA in the prognosis of tumors, and that the predictive role of the same gene varies from tumor to tumor. At present, further research is proving the enormous potential of IGSF11 and VISTA in tumors, and especially the role of VISTA in tumor immune resistance. This may prove to be a breakthrough to solve the current clinical immune resistance, and most importantly, since research has focused on VISTA but less on IGSF11, IGSF11 may be the next candidate for tumor immunotherapy.

Ablation of T cell-associated PD-1H enhances functionality and promotes adoptive immunotherapy

Programmed death-1 homolog (PD-1H) is a co-inhibitory molecule that negatively regulates T cell-mediated immune responses. In this study, we determined whether ablation of T cell-associated PD-1H could enhance adoptive T cell therapy in experimental tumor models. The expression of PD-1H is up-regulated in activated and tumor-infiltrating CD8+ T cells. Activated CD8+ T cells from PD-1H deficient (KO) mice exhibited increased cell proliferation, cytokine production and anti-tumor activity in vitro. Adoptive transfer of PD-1H-KO CD8+ T cells resulted in the regression of established syngeneic mouse tumors. Similar results were obtained when PD-1H was ablated in T cells by CRISPR/Cas9-mediated gene silencing. Furthermore, ablation of PD-1H in CAR-T cells significantly improved their anti-tumor activity against human xenografts in vivo. Our results indicate that T cell-associated PD-1H could suppress immunity in the tumor microenvironment and targeting PD-1H may improve T cell adoptive immunotherapy.

Immunotherapy for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is characterized by extensive tumor heterogeneity at both the pathologic and molecular levels, particularly accelerated aggressiveness, and terrible metastasis. It is responsible for the increased mortality of breast cancer patients. Due to the negative expression of estrogen receptors, progesterone receptors, and human epidermal growth factor receptor 2, the progress of targeted therapy has been hindered. Higher immune response in TNBCs than for other breast cancer types makes immunotherapy suitable for TNBC therapy. At present, promising treatments in immunotherapy of TNBC include immune checkpoints (ICs) blockade therapy, adoptive T-cell immunotherapy, and tumor vaccine immunotherapy. In addition, nanomedicines exhibit great potential in cancer therapy through the enhanced permeability and retention (EPR) effect. Immunotherapy-involved combination therapy may exert synergistic effects by combining with other treatments, such as traditional chemotherapy and new treatments, including photodynamic therapy (PTT), photodynamic therapy (PDT), and sonodynamic therapy (SDT). This review focuses on introducing the principles and latest development as well as progress in using nanocarriers as drug-delivery systems for the immunotherapy of TNBC.

VISTA Is a Diagnostic Biomarker and Immunotherapy Target of Aggressive Feline Mammary Carcinoma Subtypes

Simple Summary

Mammary tumors are common in cats, showing aggressive behavior and few therapeutic options. Recently, feline mammary carcinomas have become a reliable cancer model for human breast cancer studies, due to the similarities between the two species. Thus, the identification of new tumor biomarkers and therapeutic targets to improve cat’s prognosis is needed. VISTA is an important immune checkpoint protein that has gained importance over the past few years in women’s cancers. In this study, the serum VISTA levels and tumor expression were analyzed in cats with mammary tumors, being correlated with other immune checkpoints. In the diseased animals, VISTA is overexpressed in more aggressive tumor subtypes (HER2-positive and triple-negative), showing a positive correlation with the expression of VISTA in tumor-infiltrating lymphocytes, and is associated with an immunosuppressive status, suggesting that VISTA could be a promising non-invasive prognostic biomarker and therapeutic target in cats with mammary carcinomas, as reported in humans.

Abstract

Feline mammary carcinoma (FMC) is a common neoplasia, showing aggressive clinicopathological features, without viable therapeutic options. The study of tumor microenvironment has gained importance, due to the ability to control tumor progression by regulating the immune response. Considering the lack of knowledge, feline serum VISTA levels from cats with mammary carcinoma were compared with healthy controls, and with serum levels of PD-1/PD-L1, CTLA-4, LAG-3, IL-6, and TNF-α. In parallel, VISTA tumor expression was evaluated in FMC samples. The obtained data revealed that serum VISTA levels were significantly higher in cats presenting HER2-positive (p = 0.0025) or triple-negative subtypes (p = 0.0019), with higher serum levels in luminal A (p = 0.0025) correlated to the presence of metastasis (p = 0.0471). Furthermore, in HER2-positive or triple-negative tumors, correlations were obtained between serum VISTA levels and the serum levels of the above-mentioned molecules. In tumors, VISTA expression revealed a stronger intensity in cancer cells, when compared to TILs (p < 0.0001). Stratifying the samples by subtypes, a higher number of VISTA-positive TILs was observed in the HER2-positive subtype, compared with triple-negative tumors (p = 0.0138). In conclusion, results support the development of therapeutic strategies for HER2-positive and triple-negative FMC subtypes, reinforcing the use of cats as a human oncology model.

VISTA inhibitors in cancer immunotherapy: a short perspective on recent progresses

V-domain immunoglobulin (Ig) suppressor of T cell activation (VISTA) is a novel negative checkpoint regulator that mediates T cell proliferation and cytokine production. The VISTA signaling pathway blockade has been proved as a promising strategy for cancer immunotherapy. Recent VISTA sequence analysis and crystal structure investigations have revealed its independent and unique function as compared with B7 family members, such as PD-1. This review will discuss VISTA binding partners and compare the structural differences between VISTA and other B7 family members, focusing on VISTA functions in immune activation and maintaining T cell quiescence. Recent progress and the therapeutic potential of biomacromolecules, such as monoclonal antibodies (mAbs) and small molecules targeting VISTA, are also discussed. Among these, a first-in-class small-molecule antagonist, CA-170, is highlighted.

Immune functions as a ligand or a receptor, cancer prognosis potential, clinical implication of VISTA in cancer immunotherapy

Since cancer immunotherapy with immune checkpoint inhibitors of PD/PDL-1 and CTLA-4 limited efficacy to the patients due to resistance during the current decade, novel target is required for customized treatment due to tumor heterogeneity. V-domain Ig-containing suppressor of T cell activation (VISTA), a programmed death protein-1(PD-1) homolog expressed on T cells and on antigen presenting cells(APC), has emerged as a new target in several cancers. Though VISTA inhibitors including CA-170 are considered attractive in cancer immunotherapy to date, the information on VISTA as a potent biomarker of cancer prognosis and its combination therapy is still lacking to date. Thus, in this review, we discussed extracellular domain, ligands, expression, immune functions and clinical implications of VISTA and finally suggested conclusion and perspectives.

The Role of V-Domain Ig Suppressor of T Cell Activation (VISTA) in Cancer Therapy: Lessons Learned and the Road Ahead

Immune checkpoints (ICs) have pivotal roles in regulating immune responses. The inhibitory ICs in the tumor microenvironment (TME) have been implicated in the immune evasion of tumoral cells. Therefore, identifying and targeting these inhibitory ICs might be critical for eliminating tumoral cells. V-domain immunoglobulin suppressor of T cell activation (VISTA) is a novel inhibitory IC that is expressed on myeloid cells, lymphoid cells, and tumoral cells; therefore, VISTA can substantially regulate innate and adaptive anti-tumoral immune responses. Besides, growing evidence indicates that VISTA blockade can enhance the sensitivity of tumoral cells to conventional IC-based immunotherapy, e.g., cytotoxic T lymphocyte antigen 4 (CTLA-4) inhibitors. In this regard, the current study aimed to review the current evidence about the structure and expression pattern of VISTA, its role in TME, the clinicopathological significance of VISTA, and its prognostic values in various cancers. Besides, this review intended to collect the lessons from the recent pre-clinical and clinical studies and propose a strategy to overcome tumor immune-resistance states.

Terminating Cancer by Blocking VISTA as a Novel Immunotherapy: Hasta la vista, baby

VISTA is an up-and-coming immune checkpoint molecule that can become the target of new cancer immunotherapy treatments. Immune cells in the tumor microenvironment can largely influence the progression of cancer through inhibitory and stimulatory pathways. Indeed, VISTA is expressed on many immune cells, including T cells, myeloid-derived suppressor cells, tumor-associated macrophages, and dendritic cells. VISTA has predominantly been shown to act in an immune-suppressing manner that enables cancer progression. This review will delve into results from preclinical murine studies of anti-VISTA monoclonal antibody treatments, bring together recent studies that detect VISTA expression on immune cells from patient tumors of various cancers, and discuss ongoing clinical trials involving VISTA.

VISTA: A Mediator of Quiescence and a Promising Target in Cancer Immunotherapy

V-domain Ig suppressor of T cell activation (VISTA) is a B7 family member that maintains T cell and myeloid quiescence and is a promising target for combination cancer immunotherapy. During inflammatory challenges, VISTA activity reprograms macrophages towards reduced production of proinflammatory cytokines and increased production of interleukin (IL)-10 and other anti-inflammatory mediators. The interaction of VISTA with its ligands is regulated by pH, and the acidic pH ~6.0 in the tumor microenvironment (TME) facilitates VISTA binding to P-selectin glycoprotein ligand 1 (PSGL-1). Targeting intratumoral pH might be a way to reduce the immunoinhibitory activity of the VISTA pathway and enhance antitumor immune responses. We review differences among VISTA therapeutics under development as candidate immunotherapies, focusing on VISTA binding partners and the unique structural features of this interaction.

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.

Revisiting Immunotherapy: A Focus on Prostate Cancer

Therapeutic interventions to harness the immune system against tumor cells have provided mixed results in the past for several solid tumors and hematologic malignancies. However, immunotherapy has advanced considerably over the last decade and is becoming an integral combination for treating patients with advanced solid tumors. In particular, prostate cancer immunotherapy has shown modest efficacy for patients in the past. With several key discoveries on immune mechanisms and advanced molecular diagnostic platforms recently, immunotherapy is re-emerging as a viable option for prostate cancer, especially castration-resistant prostate cancer (CRPC), to stimulate antitumor immunity. Combination of patient-tailored immunotherapy and immune checkpoint blockers with conventional cytotoxic agents and androgen receptor-targeted therapies should move the field forward. With a recent adaptation that the application of immune checkpoint inhibitors has been successful in the treatment of more than a dozen solid tumors, including melanoma, lymphoma, liver, cervical, gastrointestinal, and breast cancers, it is a timely endeavor to harness immunotherapy for prostate cancer. Here, we provide an account on the progression of immunotherapy with new discoveries and precision approaches for tumors, in particular CRPC, from mechanistic standpoint to emerging limitations and future directions.