Structural basis for the immune recognition and selectivity of the immune receptor PVRIG for ligand Nectin-2.

Nectin and nectin-like (Necl) co-receptor axis, comprised of receptors DNAM-1, TIGIT, CD96, PVRIG, and nectin/Necl ligands, is gaining prominence in immuno-oncology. Within this axis, the inhibitory receptor PVRIG recognizes Nectin-2 with high affinity, but the underlying molecular basis remains unknown. By determining the crystal structure of PVRIG in complex with Nectin-2, we identified a unique CC' loop in PVRIG, which complements the double-lock-and-key binding mode and contributes to its high affinity for Nectin-2. The association of the corresponding charged residues in the F-strands explains the ligand selectivity of PVRIG toward Nectin-2 but not for Necl-5. Moreover, comprehensive comparisons of the binding capacities between co-receptors and ligands provide innovative insights into the intra-axis immunoregulatory mechanism. Taken together, these findings broaden our understanding of immune recognition and regulation mediated by nectin/Necl co-receptors and provide a rationale for the development of immunotherapeutic strategies targeting the nectin/Necl axis.

Characterization of a novel anti-PVRIG antibody with Fc-competent function that exerts strong antitumor effects via NK activation in preclinical models.

Poliovirus receptor-related immunoglobulin domain-containing protein, or PVRIG, is a newly discovered immune checkpoint that has emerged as a promising target for cancer immunotherapy. It is primarily expressed on activated T and natural killer (NK) cells, and once engaged with its ligand, PVRL2, it induces inhibitory signaling in T cells, thereby promoting the functional exhaustion of tumor-infiltrating lymphocytes (TILs). Here, we characterized IBI352g4a, a novel humanized anti-PVRIG antibody with Fc-competent function, explored the mechanism of its antitumor activity in preclinical models, and systemically evaluated the contribution of FcrR engagement to PVRIG blockade-induced antitumor activity. IBI352g4a binds to the extracellular domain of human PVRIG with high affinity (Kd = 0.53 nM) and specificity, and fully blocks the interaction between PVRIG and its ligand PVRL2. Unlike other immune checkpoints, IBI352g4a significantly induced NK cell activation and degranulation, but had a minimal effect on T-cell activation in in vitro functional assays. IBI352g4a induced strong antitumor effect in several preclinic models, through in vivo mechanism analysis we found that both NK and T cells contribute to the antitumor effect, but NK cells play predominant roles. Specifically, a single dose of IBI352g4a induced significant NK cell activation in TILs, but T-cell activation was observed only after the second dose. Moreover, the Fc effector function is critical for both NK cell activation and treatment efficacy in vitro and in vivo. Our study, for the first time, demonstrates that both NK activation and FcrR engagement are required for antitumor efficacy induced by PVRIG blockade.

PVRIG Expression Is an Independent Prognostic Factor and a New Potential Target for Immunotherapy in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is a frequent and deadly cancer in need of new treatments. Immunotherapy has shown promising results in several solid tumors. The TIGIT/DNAM-1 axis gathers targets for new immune checkpoint inhibitors (ICIs). Here, we aimed at highlighting the potential of this axis as a new therapeutic option for HCC. For this, we built a large transcriptomic database of 683 HCC samples, clinically annotated, and 319 normal liver tissues. We interrogated this database for the transcriptomic expression of each member of the TIGIT/DNAM-1 axis and tested their prognostic value for survival. We then focused on the most discriminant one for these criteria, i.e., PVRIG, and analyzed the clinical characteristics, the disease-free and overall survivals, and biological pathways associated with PVRIG High tumors. Among all members of the TIGIT/DNAM-1 axis, PVRIG expression was higher in tumors than in normal liver, was heterogeneous across tumors, and was the only member with independent prognostic value for better survival. PVRIG High tumors were characterized by a higher lymphocytic infiltrate and enriched for signatures associated with tertiary lymphoid structures and better anti-tumor immune response. These results suggest that patients with PVRIG High tumors might be good candidates for immune therapy involving ICIs, notably ICIs targeting the TIGIT/DNAM-1 axis. Further functional and clinical validation is urgently required.

The CD112R/CD112 axis: a breakthrough in cancer immunotherapy.

The recent discovery of immune checkpoint inhibitors is a significant milestone in cancer immunotherapy research. However, some patients with primary or adaptive drug resistance might not benefit from the overall therapeutic potential of immunotherapy in oncology. Thus, it is becoming increasingly critical for oncologists to explore the availability of new immune checkpoint inhibitors. An emerging co-inhibitory receptor, CD112R (also called PVRIG), is most commonly expressed on natural killer (NK) and T cells. It binds to its ligand (CD112 or PVRL2/nectin-2) and inhibits the strength with which T cells and NK cells respond to cancer. Therefore, CD112R is being presented as a new immune checkpoint inhibitor with high potential in cancer immunotherapy. CD112 is easily detectable on antigen-presenting or tumor cells, and its high level of expression has been linked with tumor progression and poor outcomes in most cancer patients. This review explores the molecular and functional relationship between CD112R, TIGIT, CD96, and CD226 in T cell responses. In addition, this review comprehensively discusses the recent developments of CD112R/CD112 immune checkpoints in cancer immunotherapy and prognosis.

Blockade of checkpoint receptor PVRIG unleashes anti-tumor immunity of NK cells in murine and human solid tumors.

BACKGROUND: Although checkpoint-based immunotherapy has shown exciting results in the treatment of tumors, around 70% of patients have experienced unresponsiveness. PVRIG is a recently identified immune checkpoint receptor and blockade of which could reverse T cell exhaustion to treat murine tumor; however, its therapeutic potential via NK cells in mice and human remains seldom reported. METHODS: In this study, we used patient paraffin-embedded colon adenocarcinoma sections, various murine tumor models (MC38 colon cancer, MCA205 fibrosarcoma and LLC lung cancer), and human NK cell- or PBMC-reconstituted xenograft models (SW620 colon cancer) to investigate the effect of PVRIG on tumor progression. RESULTS: We found that PVRIG was highly expressed on tumor-infiltrating NK cells with exhausted phenotype. Furthermore, either PVRIG deficiency, early blockade or late blockade of PVRIG slowed tumor growth and prolonged survival of tumor-bearing mice by inhibiting exhaustion of NK cells as well as CD8+ T cells. Combined blockade of PVRIG and PD-L1 showed better effect in controlling tumor growth than using either one alone. Depletion of NK or/and CD8+ T cells in vivo showed that both cell types contributed to the anti-tumor efficacy of PVRIG blockade. By using Rag1-/- mice, we demonstrated that PVRIG blockade could provide therapeutic effect in the absence of adaptive immunity. Further, blockade of human PVRIG with monoclonal antibody enhanced human NK cell function and inhibited human tumor growth in NK cell- or PBMC-reconstituted xenograft mice. CONCLUSIONS: Our results reveal the importance of NK cells and provide novel knowledge for clinical application of PVRIG-targeted drugs in future.

COM902, a novel therapeutic antibody targeting TIGIT augments anti-tumor T cell function in combination with PVRIG or PD-1 pathway blockade.

Immune checkpoint inhibitors (ICIs) have emerged as promising therapies for the treatment of cancer. However, existing ICIs, namely PD-(L)1 and CTLA-4 inhibitors, generate durable responses only in a subset of patients. TIGIT is a co-inhibitory receptor and member of the DNAM-1 family of immune modulating proteins. We evaluated the prevalence of TIGIT and its cognate ligand, PVR (CD155), in human cancers by assessing their expression in a large set of solid tumors. TIGIT is expressed on CD4+ and CD8+ TILs and is upregulated in tumors compared to normal tissues. PVR is expressed on tumor cells and tumor-associated macrophages from multiple solid tumors. We explored the therapeutic potential of targeting TIGIT by generating COM902, a fully human anti-TIGIT hinge-stabilized IgG4 monoclonal antibody that binds specifically to human, cynomolgus monkey, and mouse TIGIT, and disrupts the binding of TIGIT with PVR. COM902, either alone or in combination with a PVRIG (COM701) or PD-1 inhibitor, enhances antigen-specific human T cell responses in-vitro. In-vivo, a mouse chimeric version of COM902 in combination with an anti-PVRIG or anti-PD-L1 antibody inhibited tumor growth and increased survival in two syngeneic mouse tumor models. In summary, COM902 enhances anti-tumor immune responses and is a promising candidate for the treatment of advanced malignancies.

Clinical significance of the immune cell landscape in hepatocellular carcinoma patients with different degrees of fibrosis.

BACKGROUND: The major causes of morbidity and mortality of patients with chronic liver disease are liver fibrosis and cirrhosis. Previous studies have been concerned with immune dysfunction in the pathogenesis of cirrhosis progress. However, the potential molecular mechanism of how the liver's fibrotic state favors tumor progression is still unclear. We attempted to reveal deviations of the immune cell landscape between various liver tissues and identify key biomarkers associated with patients' outcomes. METHOD: CIBERSORT was used for estimating the proportions of immune cells in various liver tissues. Comparative studies were carried out by Kruskal-Wallis test and Wilcoxon test. For survival analyses, the Cox proportional hazard regression model, Kaplan-Meier estimates, and log-rank test were used. RESULTS: Significantly different adaptive and innate immune cell types were selected, including T cells, plasma cells, and resting mast cells. Meanwhile, the immune cell landscapes in The Cancer Genome Atlas' (TCGA) hepatocellular carcinoma (HCC) patients with different degrees of fibrosis were also calculated. Comparative studies and survival analysis were carried out. Resting mast cell and activated NK cells in HCC patients with fibrosis was significantly lower than that in other HCC patients without fibrosis. Then, the potential genes involved in immune cells and significantly associated with patients' outcome were identified. These genes may be potential novel checkpoints for immunotherapy, including PVRIG related to NK resting/activated cells and T cell CD8+ infiltration which was recently targeted in breast cancer. Furthermore, Pearson correlation coefficient analysis suggested that PVRIG is significantly positively related to other checkpoint molecules and Teff gene signatures. CONCLUSIONS: Alternative treatments, including immunotherapies, are necessary and urgent for HCC. Although checkpoint inhibitors that block CTLA-4 and PD-1 have improved cancer immunotherapies, targeting additional checkpoint receptors may be required to broaden patient response to immunotherapy. Our studies may find possible ways to select novel targets and improve immunotherapy efficacy by disrupting their function and promoting immune infiltration in advanced HCC patients with higher fibrosis and even cirrhosis.

DNAM-1 and the TIGIT/PVRIG/TACTILE Axis: Novel Immune Checkpoints for Natural Killer Cell-Based Cancer Immunotherapy.

Natural killer (NK) cells are lymphocytes of the innate immune response characterized by their role in the destruction of tumor cells. Activation of NK cells depend on a fine balance between activating and inhibitory signals mediated by different receptors. In recent years, a family of paired receptors that interact with ligands of the Nectin/Nectin-like (Necl) family has attracted great interest. Two of these ligands, Necl-5 (usually termed CD155 or PVR) and Nectin-2 (CD112), frequently expressed on different types of tumor cells, are recognized by a group of receptors expressed on T and NK cells that exert opposite functions after interacting with their ligands. These receptors include DNAM-1 (CD226), TIGIT, TACTILE (CD96) and the recently described PVRIG. Whereas activation through DNAM-1 after recognition of CD155 or CD112 enhances NK cell-mediated cytotoxicity against a wide range of tumor cells, TIGIT recognition of these ligands exerts an inhibitory effect on NK cells by diminishing IFN-γ production, as well as NK cell-mediated cytotoxicity. PVRIG has also been identified as an inhibitory receptor that recognizes CD112 but not CD155. However, little is known about the role of TACTILE as modulator of immune responses in humans. TACTILE control of tumor growth and metastases has been reported in murine models, and it has been suggested that it negatively regulates the anti-tumor functions mediated by DNAM-1. In NK cells from patients with solid cancer and leukemia, it has been observed a decreased expression of DNAM-1 that may shift the balance in favor to the inhibitory receptors TIGIT or PVRIG, further contributing to the diminished NK cell-mediated cytotoxic capacity observed in these patients. Analysis of DNAM-1, TIGIT, TACTILE and PVRIG on human NK cells from solid cancer or leukemia patients will clarify the role of these receptors in cancer surveillance. Overall, it can be speculated that in cancer patients the TIGIT/PVRIG pathways are upregulated and represent novel targets for checkpoint blockade immunotherapy.