DNAM-1 ligand expression on Ag-stimulated T lymphocytes is mediated by ROS-dependent activation of DNA-damage response: relevance for NK–T cell interaction

Clinical response and pathway-specific correlates following TIGIT-LAG3 blockade in myeloma: the MyCheckpoint randomized clinical trial

Persons with myeloma were randomized to receive an anti-TIGIT (T cell immunoreceptor) or anti-LAG3 (lymphocyte activation gene) antibody followed by combination with pomalidomide and dexamethasone ( NCT04150965 ). Primary and secondary endpoints were safety and efficacy, respectively. Therapy was well tolerated without dose-limiting toxicity. Durable clinical responses were observed in both the anti-TIGIT(three of six participants) and the anti-LAG3 (two of six participants) arms. Anti-LAG3 responders had higher naive cluster of differentiation 4 (CD4)-positive T cells and lower programmed cell death protein 1-positive effector T cells. Anti-TIGIT responders had higher CD226 expression, natural killer cell activation and lower CD112 expression. These data demonstrate the clinical activity of TIGIT-LAG3 blockade and identify pathway-specific response correlates in myeloma.

The basic biology of NK cells and its application in tumor immunotherapy

Natural Killer (NK) cells play a crucial role as effector cells within the tumor immune microenvironment, capable of identifying and eliminating tumor cells through the expression of diverse activating and inhibitory receptors that recognize tumor-related ligands. Therefore, harnessing NK cells for therapeutic purposes represents a significant adjunct to T cell-based tumor immunotherapy strategies. Presently, NK cell-based tumor immunotherapy strategies encompass various approaches, including adoptive NK cell therapy, cytokine therapy, antibody-based NK cell therapy (enhancing ADCC mediated by NK cells, NK cell engagers, immune checkpoint blockade therapy) and the utilization of nanoparticles and small molecules to modulate NK cell anti-tumor functionality. This article presents a comprehensive overview of the latest advances in NK cell-based anti-tumor immunotherapy, with the aim of offering insights and methodologies for the clinical treatment of cancer patients.

The Nectin family ligands, PVRL2 and PVR, in cancer immunology and immunotherapy

In recent years, immunotherapy has emerged as a crucial component of cancer treatment. However, its efficacy remains limited across various cancer types, highlighting unmet needs. Poliovirus receptor-related 2 (PVRL2) and Poliovirus receptor (PVR) are members of the Nectin and Nectin-like Molecules family, known for their role as cell-cell adhesion molecules. With the development of immunotherapy, their involvement in tumor immune mechanisms as immune checkpoint factors has garnered significant attention. PVRL2 and PVR are predominantly expressed on tumor cells and antigen-presenting cells, binding to PVRIG and TIGIT, respectively, which are primarily found on T and NK cells, thereby suppressing antitumor immunity. Notably, gynecological cancers such as ovarian and endometrial cancers exhibit high expression levels of PVRL2 and PVR, with similar trends observed in various other solid and hematologic tumors. Targeting these immune checkpoint pathways offers a promising therapeutic avenue, potentially in combination with existing treatments. However, the immunomodulatory mechanism involving these bindings, known as the DNAM-1 axis, is complex, underscoring the importance of understanding it for developing novel therapies. This article comprehensively reviews the immunomodulatory mechanisms centered on PVRL2 and PVR, elucidating their implications for various cancer types.

CD155 is essential for skeletal muscle regeneration by regulating satellite cell proliferation and differentiation

CD155, a member of the immunoglobulin superfamily, is closely related to cell proliferation, adhesion, and migration. CD155 is overexpressed on the surface of cancer cells to promote cell proliferation and is upregulated in damaged tissues as a stress-induced molecule. The process of skeletal muscle regeneration after injury is complex and involves injurious stimulation and subsequent satellite cell proliferation. However, the role of CD155 in this process remains unelucidated. This study aimed to explore the role of CD155 in injured skeletal muscle regeneration and to clarify its effect on satellite cell proliferation and differentiation. Here, quantitative real-time polymerase chain reaction (RT-qPCR) and immunofluorescence results indicated that CD155 expression in satellite cells increased after skeletal muscle injury. CD155 knockout in mice impaired the regeneration of skeletal muscle. A bone marrow transplantation mouse model was constructed and revealed that CD155 on skeletal muscle tissues, not immune cells, affected muscle regeneration. In vitro, CD155 knockdown in myoblasts inhibited their proliferation and differentiation. The transcriptomic analysis also indicated that CD155 absence can impair the biological proliferation and differentiation process of myoblasts. Our research demonstrates that CD155 directly promotes injured muscle regeneration by regulating satellite cell proliferation and differentiation, which may be a potential therapeutic molecule for skeletal muscle injury.

Killer instincts: natural killer cells as multifactorial cancer immunotherapy

Natural killer (NK) cells integrate heterogeneous signals for activation and inhibition using germline-encoded receptors. These receptors are stochastically co-expressed, and their concurrent engagement and signaling can adjust the sensitivity of individual cells to putative targets. Against cancers, which mutate and evolve under therapeutic and immunologic pressure, the diversity for recognition provided by NK cells may be key to comprehensive cancer control. NK cells are already being trialled as adoptive cell therapy and targets for immunotherapeutic agents. However, strategies to leverage their naturally occurring diversity and agility have not yet been developed. In this review, we discuss the receptors and signaling pathways through which signals for activation or inhibition are generated in NK cells, focusing on their roles in cancer and potential as targets for immunotherapies. Finally, we consider the impacts of receptor co-expression and the potential to engage multiple pathways of NK cell reactivity to maximize the scope and strength of antitumor activities.

Balancing act: the complex role of NK cells in immune regulation

Natural killer (NK) cells, as fundamental components of innate immunity, can quickly react to abnormalities within the body. In-depth research has revealed that NK cells possess regulatory functions not only in innate immunity but also in adaptive immunity under various conditions. Multiple aspects of the adaptive immune process are regulated through NK cells. In our review, we have integrated multiple studies to illuminate the regulatory function of NK cells in regulating B cell and T cell responses during adaptive immune processes, focusing on aspects including viral infections and the tumor microenvironment (TME). These insights provide us with many new understandings on how NK cells regulate different phases of the adaptive immune response.

Beyond αβ T cells: NK, iNKT, and γδT cell biology in leukemic patients and potential for off-the-shelf adoptive cell therapies for AML

Acute myeloid leukemia (AML) remains an elusive disease to treat, let alone cure, even after highly intensive therapies such as stem cell transplants. Adoptive cell therapeutic strategies based on conventional alpha beta (αβ)T cells are an active area of research in myeloid neoplasms given their remarkable success in other hematologic malignancies, particularly B-cell-derived acute lymphoid leukemia, myeloma, and lymphomas. Several limitations have hindered clinical application of adoptive cell therapies in AML including lack of leukemia-specific antigens, on-target-off-leukemic toxicity, immunosuppressive microenvironments, and leukemic stem cell populations elusive to immune recognition and destruction. While there are promising T cell-based therapies including chimeric antigen receptor (CAR)-T designs under development, other cytotoxic lymphocyte cell subsets have unique phenotypes and capabilities that might be of additional benefit in AML treatment. Of particular interest are the natural killer (NK) and unconventional T cells known as invariant natural killer T (iNKT) and gamma delta (γδ) T cells. NK, iNKT, and γδT cells exhibit intrinsic anti-malignant properties, potential for alloreactivity, and human leukocyte-antigen (HLA)-independent function. Here we review the biology of each of these unconventional cytotoxic lymphocyte cell types and compare and contrast their strengths and limitations as the basis for adoptive cell therapies for AML.

Complex interactions of cellular players in chronic Graft-versus-Host Disease

Chronic Graft-versus-Host Disease is a life-threatening inflammatory condition that affects many patients after allogeneic hematopoietic stem cell transplantation. Although we have made substantial progress in understanding disease pathogenesis and the role of specific immune cell subsets, treatment options are still limited. To date, we lack a global understanding of the interplay between the different cellular players involved, in the affected tissues and at different stages of disease development and progression. In this review we summarize our current knowledge on pathogenic and protective mechanisms elicited by the major involved immune subsets, being T cells, B cells, NK cells and antigen presenting cells, as well as the microbiome, with a special focus on intercellular communication of these cell types via extracellular vesicles as up-and-coming fields in chronic Graft-versus-Host Disease research. Lastly, we discuss the importance of understanding systemic and local aberrant cell communication during disease for defining better biomarkers and therapeutic targets, eventually enabling the design of personalized treatment schemes.

DNAM-1 chimeric receptor-engineered NK cells: a new frontier for CAR-NK cell-based immunotherapy

DNAM-1 is a major NK cell activating receptor and, together with NKG2D and NCRs, by binding specific ligands, strongly contributes to mediating the killing of tumor or virus-infected cells. DNAM-1 specifically recognizes PVR and Nectin-2 ligands that are expressed on some virus-infected cells and on a broad spectrum of tumor cells of both hematological and solid malignancies. So far, while NK cells engineered for different antigen chimeric receptors (CARs) or chimeric NKG2D receptor have been extensively tested in preclinical and clinical studies, the use of DNAM-1 chimeric receptor-engineered NK cells has been proposed only in our recent proof-of-concept study and deserves further development. The aim of this perspective study is to describe the rationale for using this novel tool as a new anti-cancer immunotherapy.

Development and Validation of a Prognostic Risk Model Based on Nature Killer Cells for Serous Ovarian Cancer

Nature killer (NK) cells are increasingly considered important in tumor microenvironment, but their role in predicting the prognosis of ovarian cancer has not been revealed. This study aimed to develop a prognostic risk model for ovarian cancer based on NK cells. Firstly, differentially expressed genes (DEGs) of NK cells were found by single-cell RNA-sequencing dataset analysis. Based on six NK-cell DEGs identified by univariable, Lasso and multivariable Cox regression analyses, a prognostic risk model for serous ovarian cancer was developed in the TCGA cohort. This model was then validated in three external cohorts, and evaluated as an independent prognostic factor by multivariable Cox regression analysis together with clinical characteristics. With the investigation of the underlying mechanism, a relation between a higher risk score of this model and more immune activities in tumor microenvironment was revealed. Furthermore, a detailed inspection of infiltrated immunocytes indicated that not only quantity, but also the functional state of these immunocytes might affect prognostic risk. Additionally, the potential of this model to predict immunotherapeutic response was exhibited by evaluating the functional state of cytotoxic T lymphocytes. To conclude, this study introduced a novel prognostic risk model based on NK-cell DEGs, which might provide assistance for the personalized management of serous ovarian cancer patients.

NK cells are never alone: crosstalk and communication in tumour microenvironments

Immune escape is a hallmark of cancer. The dynamic and heterogeneous tumour microenvironment (TME) causes insufficient infiltration and poor efficacy of natural killer (NK) cell-based immunotherapy, which becomes a key factor triggering tumour progression. Understanding the crosstalk between NK cells and the TME provides new insights for optimising NK cell-based immunotherapy. Here, we present new advances in direct or indirect crosstalk between NK cells and 9 specialised TMEs, including immune, metabolic, innervated niche, mechanical, and microbial microenvironments, summarise TME-mediated mechanisms of NK cell function inhibition, and highlight potential targeted therapies for NK-TME crosstalk. Importantly, we discuss novel strategies to overcome the inhibitory TME and provide an attractive outlook for the future.

T cell-derived interleukin-22 drives the expression of CD155 by cancer cells to suppress NK cell function and promote metastasis

Although T cells can exert potent anti-tumor immunity, a subset of T helper (Th) cells producing interleukin-22 (IL-22) in breast and lung tumors is linked to dismal patient outcome. Here, we examined the mechanisms whereby these T cells contribute to disease. In murine models of lung and breast cancer, constitutional and T cell-specific deletion of Il22 reduced metastases without affecting primary tumor growth. Deletion of the IL-22 receptor on cancer cells decreases metastasis to a degree similar to that seen in IL-22-deficient mice. IL-22 induced high expression of CD155, which bound to the activating receptor CD226 on NK cells. Excessive activation led to decreased amounts of CD226 and functionally impaired NK cells, which elevated the metastatic burden. IL-22 signaling was also associated with CD155 expression in human datasets and with poor patient outcomes. Taken together, our findings reveal an immunosuppressive circuit activated by T cell-derived IL-22 that promotes lung metastasis.

Discovery of a novel piperlongumine analogue as a microtubule polymerization inhibitor with potent anti-angiogenic and anti-metastatic efficacy

In an effort to discover anticancer agents with simultaneous effects on tubulin and angiogenesis, we designed and synthesized two series of piperlongumie (PL) derivatives by replacing of phenyl group with a variety of benzoheterocycle (series II) or cyclizing the C7-C8 olefin into an aromatic heterocycle (series I). Most of the new compounds showed better antiproliferative activities against six cancer cell lines than the parent drug PL. Compound II-14b had the best cytotoxic profile of these two series in cancer cells, whilst being relatively low cytotoxicity against normal human cells and high potency against drug-resistant cells. It disrupted cellular microtubule networks and inhibited tubulin assembly with an IC50 value of 5.8 μM. Further studies elucidated that II-14b showed antitumor activities through multiple mechanisms, including the pruduction of abundant ROS, the dissipation of mitochondrial membrane potential, the accumulation of DNA double-strand breaks, and the induction of cell cycle in G2/M phase. More importantly, we have observed that it possesses potential anti-angiogenesis capabilities, including suppression of HUVECs cell migration, invasion, and endothelial tube formation in vitro and in vivo. In vivo assessment indicated that II-14b inhibits the growth and metastasis of MGC-803 xenograft tumour in zebrafish. These findings show that II-14b is a high-efficacy and non-toxic antitumor agent.

The pharmacological properties and corresponding mechanisms of farrerol: a comprehensive review

CONTEXT

Farrerol, a typical natural flavanone isolated from the traditional Chinese herb 'Man-shan-hong' [Rhododendron dauricum L. (Ericaceae)] with phlegm-reducing and cough-relieving properties, is widely used in China for treating bronchitis and asthma.

OBJECTIVE

To present the anti-inflammatory, antioxidant, vasoactive, antitumor, and antimicrobial effects of farrerol and its underlying molecular mechanisms.

METHODS

The literature was reviewed by searching PubMed, Medline, Web of Knowledge, Scopus, and Google Scholar databases between 2011 and May 2021. The following key words were used: 'farrerol,' 'flavanone,' 'anti-inflammatory,' 'antioxidant,' 'vasoactive,' 'antitumor,' 'antimicrobial,' and 'molecular mechanisms'.

RESULTS

Farrerol showed anti-inflammatory effects mainly mediated via the inhibition of interleukin (IL)-6/8, IL-1β, tumour necrosis factor(TNF)-α, NF-κB, NO, COX-2, JNK1/2, AKT, PI3K, ERK1/2, p38, Keap-1, and TGF-1β. Farrerol exhibited antioxidant effects by decreasing JNK, MDA, ROS, NOX4, Bax/Bcl-2, caspase-3, p-p38 MAPK, and GSK-3β levels and enhancing Nrf2, GSH, SOD, GSH-Px, HO-1, NQO1, and p-ERK levels. The vasoactive effects of farrerol were also shown by the reduced α-SMA, NAD(P)H, p-ERK, p-Akt, mTOR, Jak2, Stat3, Bcl-2, and p38 levels, but increased OPN, occludin, ZO-1, eNOS, CaM, IP3R, and PLC levels. The antitumor effects of farrerol were evident from the reduced Bcl-2, Slug, Zeb-1, and vimentin levels but increased p27, ERK1/2, p38, caspase-9, Bax, and E-cadherin levels. Farrerol reduced α-toxin levels and increased NO production and NF-κB activity to impart antibacterial activity.

CONCLUSIONS

This review article provides a theoretical basis for further studies on farrerol, with a view to develop and utilise farrerol for treating of vascular-related diseases in the future.

Genome integrity and inflammation in the nervous system

Preservation of genomic integrity is crucial for nervous system development and function. DNA repair deficiency results in several human diseases that are characterized by both neurodegeneration and neuroinflammation. Recent research has highlighted a role for compromised genomic integrity as a key factor driving neuropathology and triggering innate immune signaling to cause inflammation. Here we review the mechanisms by which DNA damage engages innate immune signaling and how this may promote neurological disease. We also consider the contributions of different neural cell types towards DNA damage-driven neuroinflammation. A deeper knowledge of genome maintenance mechanisms that prevent aberrant immune activation in neural cells will guide future therapies to ameliorate neurological disease.

A comprehensive analysis of the prognostic value and immune infiltration of low expression DBT in clear cell renal cell carcinoma

Background: Although DBT is strongly associated with human tumorigenesis and progression through a variety of pathways, the role of DBT in clear cell renal cell carcinoma (ccRCC) has not been well established.

Materials and methods: The Cancer Genome Atlas (TCGA)-Kidney renal clear cell carcinoma (KIRC) databset provides RNA sequencing data and clinicopathological information on ccRCC. The Gene Expression Omnibus (GEO) database was used to validate the DBT expression levels, and qPCR was used to examine the DBT expression in renal cancer cell lines and ccRCC tissue samples from our centre. In parallel, DBT protein expression was explored in the Human Protein Atlas (HPA) database, and western blotting and immunohistochemistry of renal cancer cell lines and ccRCC tissues validated the results. Additionally, the diagnostic and prognostic value of DBT was comprehensively evaluated by receiver operating characteristic (ROC) curves, univariate and multivariate Cox regression analyses, and Kaplan‒Meier survival analysis. The protein‒protein interaction (PPI) network based on the STRING website, Gene Ontology (GO) analysis, Kyoto Gene and Genome Encyclopedia (KEGG) analysis and gene set enrichment analysis (GSEA) further provided a landscape of the molecular mechanisms of DBT in ccRCC. Finally, the TIMER 2.0, GEPIA and TISIDB websites were used to understand the relationship between DBT and immune characteristics.

Results: The mRNA expression and protein expression of DBT were significantly downregulated in ccRCC tissues relative to normal tissues, which was associated with poor clinical outcomes. DBT has an encouraging discriminatory power for ccRCC and is an independent prognostic factor for ccRCC patients. Mechanistically, DBT is mainly involved in the regulation of immune-related signalling pathways in ccRCC; it is associated with a variety of immune infiltrating cells and immune checkpoints.

Conclusion: DBT is a tumour suppressor gene in ccRCC and could be used as a new biomarker for diagnostic and prognostic purposes, and it is associated with immune infiltration in ccRCC.

Enhanced natural killer cell anti-tumor activity with nanoparticles mediated ferroptosis and potential therapeutic application in prostate cancer

Ferroptosis provides an opportunity to overcome the cancer cell therapeutic resistance and modulate the immune system. Here an interaction between ferroptosis of cancer cells and natural killer (NK) cells was investigated with a clinical grade iron oxide nanoparticle (ferumoxytol) for potential synergistic anti-cancer effect of ferroptosis and NK cell therapy in prostate cancer. When ferumoxytol mediated ferroptosis of cancer cells was combined with NK cells, the NK cells' cytotoxic function was increased. Observed ferroptosis mediated NK cell activation was also confirmed with IFN-γ secretion and lytic degranulation. Upregulation of ULBPs, which is one of the ligands for NK cell activating receptor NKG2D, was observed in the co-treatment of ferumoxytol mediated ferroptosis and NK cells. Additionally, HMGB1 and PD-L1 expression of cancer cells were observed in the treatment of ferroptosis + NK cells. Finally, in vivo therapeutic efficacy of ferumoxytol mediated ferroptosis and NK cell therapy was observed with significant tumor volume regression in a prostate cancer mice model. These results suggest that the NK cells' function can be enhanced with ferumoxytol mediated ferroptosis.

CD155 in tumor progression and targeted therapy

CD155, also known as the poliovirus receptor (PVR), has received considerable attention in recent years because of its intrinsic and extrinsic roles in tumor progression. Although barely expressed in host cells, CD155 is upregulated in tumor-infiltrating myeloid cells. High expression of CD155 in tumor cells across multiple cancer types is common and associated with poor patient outcomes. The intrinsic functions of CD155 in tumor cells promote tumor progression and metastasis, whereas its extrinsic immunoregulatory functions in the tumor microenvironment (TME) involve interaction with the upregulated inhibitory immune cell receptor and checkpoint TIGIT, suggesting that CD155 and CD155 pathways are promising tumor immunotherapy targets. Preclinical studies demonstrate that targeting CD155 and its receptor (anti-TIGIT) using a single treatment or in combination with anti-PD-1 can improve immune-mediated tumor control. However, there is still a limited understanding of CD155 and its associated targeting strategies, especially antibody and immune cell editing-related strategies of CD155 in cancer. Here, we review the role of CD155 in host and tumor cells in controlling tumor progression and discuss the potential of targeting CD155 for tumor therapy.

CD155 promotes radioresistance and malignancy of esophageal cancer by regulating Hippo-YAP pathway

The expression of CD155 has been observed to increase in various human cancers, but its role in the development of esophageal cancer (EC) is unclear. Radiotherapy is one of the primary therapeutic options for EC. However, radioresistance is still a severe issue in EC treatment. In this study, Oncomine database mining, immunohistochemistry, and survival analysis showed that higher expression of CD155 in patients with EC than in healthy controls. In vitro and in vivo, we found for the first time that irradiation increased the expression of CD155 in EC cells. CD155 knockdown inhibited cell proliferation and migration and tumor formation, and significantly increased radiosensitivity in EC. The in vivo model with high CD155 expression significantly promoted the proliferation and migration of EC cells. Furthermore, increased CD155 expression was associated with poor prognosis in patients with EC. CD155 regulated the Hippo-Yap pathway, influencing cell proliferation and migration. Therefore, CD155 is essential for the proliferation, migration, and radioresistance of EC. CD155 inhibition may be a viable strategy for improving radiation treatment efficacy in individuals with EC.

Emergence of the CD226 Axis in Cancer Immunotherapy

In recent years, a set of immune receptors that interact with members of the nectin/nectin-like (necl) family has garnered significant attention as possible points of manipulation in cancer. Central to this axis, CD226, TIGIT, and CD96 represent ligand (CD155)-competitive co-stimulatory/inhibitory receptors, analogous to the CTLA-4/B7/CD28 tripartite. The identification of PVRIG (CD112R) and CD112 has introduced complexity and enabled additional nodes of therapeutic intervention. By virtue of the clinical progression of TIGIT antagonists and emergence of novel CD96- and PVRIG-based approaches, our overall understanding of the 'CD226 axis' in cancer immunotherapy is starting to take shape. However, several questions remain regarding the unique characteristics of, and mechanistic interplay between, each receptor-ligand pair. This review provides an overview of the CD226 axis in the context of cancer, with a focus on the status of immunotherapeutic strategies (TIGIT, CD96, and PVRIG) and their underlying biology (i.e., cis/trans interactions). We also integrate our emerging knowledge of the immune populations involved, key considerations for Fc gamma (γ) receptor biology in therapeutic activity, and a snapshot of the rapidly evolving clinical landscape.

Natural Killer Cells in Multiple Sclerosis: Entering the Stage

Studies investigating the immunopathology of multiple sclerosis (MS) have largely focused on adaptive T and B lymphocytes. However, in recent years there has been an increased interest in the contribution of innate immune cells, amongst which the natural killer (NK) cells. Apart from their canonical role of controlling viral infections, cell stress and malignancies, NK cells are increasingly being recognized for their modulating effect on the adaptive immune system, both in health and autoimmune disease. From different lines of research there is now evidence that NK cells contribute to MS immunopathology. In this review, we provide an overview of studies that have investigated the role of NK cells in the pathogenesis of MS by use of the experimental autoimmune encephalomyelitis (EAE) animal model, MS genetics or through ex vivo and in vitro work into the immunology of MS patients. With the advent of modern hypothesis-free technologies such as single-cell transcriptomics, we are exposing an unexpected NK cell heterogeneity, increasingly blurring the boundaries between adaptive and innate immunity. We conclude that unravelling this heterogeneity, as well as the mechanistic link between innate and adaptive immune cell functions will lay the foundation for the use of NK cells as prognostic tools and therapeutic targets in MS and a myriad of other currently uncurable autoimmune disorders.

Contribution of immune cells to bone metastasis pathogenesis

Bone metastasis is closely related to the survival rate of cancer patients and reduces their quality of life. The bone marrow microenvironment contains a complex immune cell component with a local microenvironment that is conducive to tumor formation and growth. In this unique immune environment, a variety of immune cells, including T cells, natural killer cells, macrophages, dendritic cells, and myeloid-derived suppressor cells, participate in the process of bone metastasis. In this review, we will introduce the interactions between immune cells and cancer cells in the bone microenvironment, obtain the details of their contributions to the implications of bone metastasis, and discuss immunotherapeutic strategies targeting immune cells in cancer patients with bone metastasis.

Tanshinone IIA derivatives induced S-phase arrest through stabilizing c-myc G-quadruplex DNA to regulate ROS-mediated PI3K/Akt/mTOR pathway

Herein, a derivate from tanshinone IIA, 1,6,6-trimethyl-11-phenyl-7,8,9,10-tetrahydro-6H-furo[2',3':1,2]phenanthro[3,4-d]imidazole (TA25), has been synthesized and investigated as potential inhibitor against the proliferation, migration and invasion of lung cancer cells. MTT assay and cell colony formation assay results showed that TA25 exhibits acceptable inhibitory effect against the proliferation of lung cancer A549 cells, and the value of IC₅₀ was about 17.9 μM. This result was further confirmed by the inhibition of TA25 against the growth of xenograft lung cancer cells on zebrafish bearing tumor (A549 lung cancer cells). The results of wound-healing assay and FITC-gelatin invasion assay displayed that TA25 could inhibit the migration and invasion of lung cancer A549 cells. Moreover, the studies on the binding properties of TA25 interact with c-myc G-quadruplex DNA suggested that TA25 can bind in the G-quarter plane formed from G7, G11, G16 and G20 with c-myc G-quadruplex DNA through π-π stacking. Further study of the potential anti-cancer mechanism indicated that TA25 can induce S-phase arrest in lung cancer A549 cells, and this phenomenon resulted from the promotion of the production of reactive oxygen species and DNA damage in A549 cells under the action of TA25. Further research revealed that TA25 could inhibit the PI3K/Akt/mTOR signal pathway and increase the expression of p53 protein. Overall, TA25 can be developed into a promising inhibitor against the proliferation, migration and invasion of lung cancer cells and has potential clinical application in the near future.

TIGIT blockade enhances NK cell activity against autologous HIV-1-infected CD4+ T cells

Objectives

During chronic human immunodeficiency virus (HIV)‐1 infection, inhibitory molecules upregulated on lymphocytes contribute to effector cell dysfunction and immune exhaustion. People living with HIV (PLWH) are at greater risk for age‐related morbidities, an issue magnified by human cytomegalovirus (CMV) coinfection. As CMV infection modifies natural killer (NK) cell properties and NK cells contribute to protection against HIV‐1 infection, we considered the role of T‐cell immunoreceptor with immunoglobulin and intracellular tyrosine inhibitory motif domains (TIGIT) in NK cell‐based HIV‐1 immunotherapy and elimination strategies.

Methods

We measured TIGIT expression on immune cell subsets of 95 PLWH and assessed its impact on NK cell function, including elimination of autologous CD4⁺ T cells infected through reactivation of endogenous HIV‐1.

Results

TIGIT was expressed on CD4⁺ T cells, CD8⁺ T cells and NK cells from PLWH. Although TIGIT levels on T cells correlated with HIV‐1 disease progression, the extent of TIGIT expression on NK cells more closely paralleled adaptation to CMV. TIGIT interacts with its predominant ligand, poliovirus receptor (PVR), to inhibit effector cell functions. Circulating CD4⁺ T cells from PLWH more frequently expressed PVR than HIV‐seronegative controls, and PVR expression was enriched in CD4⁺ T cells replicating HIV‐1 ex vivo. Treatment with anti‐TIGIT monoclonal antibodies increased NK cell HIV‐1‐specific antibody‐dependent cytotoxicity in vitro and ex vivo.

Conclusion

Blocking TIGIT may be an effective strategy to invigorate antibody‐dependent NK cell activity against HIV‐1 activated in cellular reservoirs for cure or treatment strategies.

TIGIT Can Exert Immunosuppressive Effects on CD8+ T Cells by the CD155/TIGIT Signaling Pathway for Hepatocellular Carcinoma In Vitro

Supplemental Digital Content is available in the text.

The efficacy of adoptive cellular immunotherapy against cancer cells is limited due to the presence of immunosuppressive cells within the solid tumor microenvironment. The upregulation of certain coinhibitory receptors may lead to exhaustion of the immune effector cells. T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) is an immune inhibitory receptor expressed by regulatory T cells and activated T cells and natural killer cells. The aim of this study was to determine the immunosuppressive effects of CD155/TIGIT signaling on CD8⁺ T cells of adoptive cellular immunotherapy in hepatocellular carcinoma (HCC). Our studies found that CD155 was overexpressed in HCC, and CD155^hi HCC cells upregulated TIGIT on CD8⁺ T cells, which decreased the secretion of interferon-γ, tumor necrosis factor-α, and interleukin-17A and increased that of interleukin-10 from the effector cells. However, TIGIT blockade or CD155-knockdown reversed the inhibitory effect of HCC cells on CD8⁺ T-cell effector function. These results indicate that TIGIT can exert an immunosuppressive effect on CD8 T cells by modulating cytokine production through CD155, and is a promising target to optimize adoptive cellular immunotherapy against HCC.

Generation of hypoimmunogenic T cells from genetically engineered allogeneic human induced pluripotent stem cells

Avoiding the immune rejection of transplanted T cells is central to the success of allogeneic cancer immunotherapies. One solution to protecting T-cell grafts from immune rejection involves the deletion of allogeneic factors and of factors that activate cytotoxic immune cells. Here we report the generation of hypoimmunogenic cancer-antigen-specific T cells derived from induced pluripotent stem cells (iPSCs) lacking β₂-microglobulin, the class-II major histocompatibility complex (MHC) transactivator and the natural killer (NK) cell-ligand poliovirus receptor CD155, and expressing single-chain MHC class-I antigen E. In mouse models of CD20-expressing leukaemia or lymphoma, differentiated T cells expressing a CD20 chimeric antigen receptor largely escaped recognition by NKG2A⁺ and DNAM-1⁺ NK cells and by CD8 and CD4 T cells in the allogeneic recipients while maintaining anti-tumour potency. Hypoimmunogenic iPSC-derived T cells may contribute to the creation of off-the-shelf T cell immunotherapies.

Effects of advanced glycation end products on neutrophil migration and aggregation in diabetic wounds

Increased accumulation of advanced glycation end products (AGEs) in diabetic skin is closely related to delayed wound healing. Studies have shown that the concentration of AGEs is elevated in the skin tissues and not subcutaneous tissues in refractory diabetic wounds, which suggests there may be a causal relationship between the two. In the present study, in vitro experiments revealed that AGEs activated neutrophils, and the migratory and adhesive functions of neutrophils decreased once AGE levels reached a certain threshold. Different levels of AGE expression differentially affected the function of neutrophils. Messenger RNA (mRNA) sequencing analysis combined with real-time polymerase chain reaction (PCR) showed that poliovirus receptor (PVR/CD155) and CTNND1, which play a role in migration- and adhesion-related signaling pathways, were decreased following AGE stimulation. Consequently, neutrophils cannot effectively stimulate the formation of the inflammatory belt needed to remove necrotic tissues and defend against foreign microorganisms within diabetic chronic wounds. In addition, this phenomenon may be related to the differential accumulation of AGEs in different layers of the skin.

CD155 on Tumor Cells Drives Resistance to Immunotherapy by Inducing the Degradation of the Activating Receptor CD226 in CD8+ T Cells

The activating receptor CD226 is expressed on lymphocytes, monocytes, and platelets and promotes anti-tumor immunity in pre-clinical models. Here, we examined the role of CD226 in the function of tumor-infiltrating lymphocytes (TILs) and resistance to immunotherapy. In murine tumors, a large proportion of CD8⁺ TILs had decreased surface expression of CD226 and exhibited features of dysfunction, whereas CD226^hi TILs were highly functional. This correlation was seen also in TILs isolated from HNSCC patients. Mutation of CD226 at tyrosine 319 (Y319) led to increased CD226 surface expression, enhanced anti-tumor immunity and improved efficacy of immune checkpoint blockade (ICB). Mechanistically, tumor-derived CD155, the ligand for CD226, initiated phosphorylation of Y319 by Src kinases, thereby enabling ubiquitination of CD226 by CBL-B, internalization, and proteasomal degradation. In pre-treatment samples from melanoma patients, CD226⁺CD8⁺ T cells correlated with improved progression-free survival following ICB. Our findings argue for the development of therapies aimed at maintaining the expression of CD226.

Cancer Immunotherapy and the Nectin Family

It is increasingly clear that the nectin family and its immunoreceptors shape the immune response to cancer through several pathways. Yet, even as antibodies against TIGIT, CD96, and CD112R advance into clinical development, biological and therapeutic questions remain unanswered. Here, we review recent progress, prospects, and challenges to understanding and tapping this family in cancer immunotherapy.

Targeting novel inhibitory receptors in cancer immunotherapy

T cells play a critical role in promoting tumor regression in both experimental models and humans. Yet, T cells that are chronically exposed to tumor antigen during cancer progression can become dysfunctional/exhausted and fail to induce tumor destruction. Such tumor-induced T cell dysfunction may occur via multiple mechanisms. In particular, immune checkpoint inhibitory receptors that are upregulated by tumor-infiltrating lymphocytes in many cancers limit T cell survival and function. Overcoming this inhibitory receptor-mediated T cell dysfunction has been a central focus of recent developments in cancer immunotherapy. Immunotherapies targeting inhibitory receptor pathways such as programmed cell death 1 (PD-1)/programmed death ligand 1 and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), alone or in combination, confer significant clinical benefits in multiple tumor types. However, many patients with cancer do not respond to immune checkpoint blockade, and dual PD-1/CTLA-4 blockade may cause serious adverse events, which limits its indications. Targeting novel non-redundant inhibitory receptor pathways contributing to tumor-induced T cell dysfunction in the tumor microenvironment may prove efficacious and non-toxic. This review presents preclinical and clinical findings supporting the roles of two key pathways-T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) and T cell immunoreceptor with Ig and ITIM domain (TIGIT)/CD226/CD96/CD112R-in cancer immunotherapy.

Altered oxidative stress markers in relation to T cells, NK cells & killer immunoglobulin receptors that are associated with disease activity in SLE patients

Systemic Lupus Erythematosus is an autoimmune disease with symptoms pervasive to all organ systems. It affects more females as compared to males (in the ratio 9:1). Oxidative stress plays a major role in the pathogenesis of SLE and other autoimmune diseases. In order to understand the relationship between cell specific oxidative stress and the severity of SLE, this research study involving the estimation of intracellular ROS accumulation in T and NK cell was conducted on SLE patients of North Indian Population. At the same time, to estimate anti-oxidant defense, Keap1 and Nrf2 levels were estimated in these cell types. The relationship between the expression of Killer immunoglobulin receptors i.e., KIR2DL4 & KIR3DL1 and oxidative stress was also evaluated as these receptors are imperative for the function and self-tolerance of NK cells.Oxidative stress was raised along with Keap1 and Nrf2 in T and NK cell subsets in SLE patients. The expression of KIR2DL4 was raised and that of KIR3DL1 was reduced in the NK cells of patients. The intensity of change in expression and its significance varied among the subsets. Nrf2 expression was raised in these species against oxidative stress as the antioxidant defense mechanism pertaining to Keap1-Nrf2 pathway, but the adequacy of response needs to be understood in further studies. The expression of KIR2DL4 and KIR3DL1 varied among the patient and healthy controls and the expression of the latter was found to have a significant positive relationship with plasma Glutathione(reduced) concentration.

TIGIT in cancer immunotherapy

Tumors evade immune-mediated recognition through multiple mechanisms of immune escape. On chronic tumor antigen exposure, T cells become dysfunctional/exhausted and upregulate various checkpoint inhibitory receptors (IRs) that limit T cells' survival and function. During the last decade, immunotherapies targeting IRs such as programmed cell death receptor 1 (PD-1) and anticytotoxic T lymphocyte-associated antigen 4 (CTLA-4) have provided ample evidence of clinical benefits in many solid tumors. Beyond CTLA-4 and PD-1, multiple other IRs are also targeted with immune checkpoint blockade in the clinic. Specifically, T cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT) is a promising new target for cancer immunotherapy. TIGIT is upregulated by immune cells, including activated T cells, natural killer cells, and regulatory T cells. TIGIT binds to two ligands, CD155 (PVR) and CD112 (PVRL2, nectin-2), that are expressed by tumor cells and antigen-presenting cells in the tumor microenvironment. There is now ample evidence that the TIGIT pathway regulates T cell-mediated and natural killer cell-mediated tumor recognition in vivo and in vitro. Dual PD-1/TIGIT blockade potently increases tumor antigen-specific CD8+ T cell expansion and function in vitro and promotes tumor rejection in mouse tumor models. These findings support development of ongoing clinical trials with dual PD-1/TIGIT blockade in patients with cancer.

Recent Advances in the Role of Natural Killer Cells in Acute Kidney Injury

Growing evidence is revealing a central role for natural killer (NK) cells, cytotoxic cells belonging to the broad family of innate lymphoid cells (ILCs), in acute and chronic forms of renal disease. NK cell effector functions include both the recognition and elimination of virus-infected and tumor cells and the capability of sensing pathogens through Toll-like receptor (TLR) engagement. Notably, they also display immune regulatory properties, exerted thanks to their ability to secrete cytokines/chemokines and to establish interactions with different innate and adaptive immune cells. Therefore, because of their multiple functions, NK cells may have a major pathogenic role in acute kidney injury (AKI), and a better understanding of the molecular mechanisms driving NK cell activation in AKI and their downstream interactions with intrinsic renal cells and infiltrating immune cells could help to identify new potential biomarkers and to select clinically valuable novel therapeutic targets. In this review, we discuss the current literature regarding the potential involvement of NK cells in AKI.

Cytotoxicity of Donor Natural Killer Cells to Allo-Reactive T Cells Are Related With Acute Graft-vs.-Host-Disease Following Allogeneic Stem Cell Transplantation

Objectives: The mechanism and immunoregulatory role of human natural killer (NK) cells in acute graft-vs.-host-disease (aGVHD) remains unclear. This study quantitatively analyzed the cytotoxicity of donor NK cells toward allo-reactive T cells, and investigated their relationship with acute GVHD (aGVHD).

Methods: We evaluated NK dose, subgroup, and receptor expression in allografts from 98 patients who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT). A CD107a degranulating assay was used as a quantitative detection method for the cytotoxic function of donor NK cells to allo-reactive T cells. In antibody-blocking assay, NK cells were pre-treated with anti-DNAM-1(CD226), anti-NKG2D, anti-NKP46, or anti-NKG-2A monoclonal antibodies (mAbs) before the degranulating assay.

Results: NK cells in allografts effectively inhibited auto-T cell proliferation following alloantigen stimulation, selectively killing alloantigen activated T cells. NKG2A⁻ NK cell subgroups showed higher levels of CD107a degranulation toward activated T cells, when compared with NKG2A⁻ subgroups. Blocking NKG2D or CD226 (DNAM-1) led to significant reductions in degranulation, whereas NKG2A block resulted in increased NK degranulation. Donor NK cells in the aGVHD group expressed lower levels of NKG2D and CD226, higher levels of NKG2A, and showed higher CD107a degranulation levels when compared with NK cells in the non-aGVHD group. Using univariate analysis, higher NK degranulation activities in allografts (CD107a^high) were correlated with a decreased risk in grade I–IV aGVHD (hazard risk [HR] = 0.294; P < 0.0001), grade III–IV aGVHD (HR = 0.102; P < 0.0001), and relapse (HR = 0.157; P = 0.015), and improved overall survival (HR = 0.355; P = 0.028) after allo-HSCT. Multivariate analyses showed that higher NK degranulation activities (CD107a^high) in allografts were independent risk factors for grades, I–IV aGVHD (HR = 0.357; P = 0.002), and grades III–IV aGVHD (HR = 0.13; P = 0.009).

Conclusions: These findings reveal that the degranulation activity of NK in allografts toward allo-activated T cells was associated with the occurrence and the severity of aGVHD, after allogeneic stem cell transplantation. This suggested that cytotoxicity of donor NK cells to allo-reactive T cells have important roles in aGVHD regulation.

CD226: An Emerging Role in Immunologic Diseases

CD226, a member of the immunoglobulin superfamily, is a functional protein initially expressed on natural killer and T cells. In recent years, the function of CD226 has been increasingly realized and researched. Accumulating evidence shows that CD226 is closely related to the occurrence of autoimmune diseases, infectious diseases, and tumors. Because of the CD226’s increasing importance, the author herein discusses the structure, mechanism of action, and role of CD226 in various pathophysiological environments, allowing for further understanding of the function of CD226 and providing the basis for further research in related diseases.

Synthesis, docking studies and antitumor activity of phenanthroimidazole derivatives as promising c-myc G-quadruplex DNA stabilizers

Phenanthroimidazole derivatives containing phenanthroline and imidazole heterocyclic aromatic rings are effective agents to inhibit tumor cell growth. Herein, halogen element-modified imidazo[4,5f][1,10]phenanthroline derivatives 1-6 (1, 4-fluorophenyl; 2, 4-chlorophenyl; 3, 4-bromobenyl; 4, 2,3-dichlorophenyl; 5, 3,4-dichlorophenyl; and 6, 2,4-dichlorophenyl) were synthesized, and their antitumor activities were investigated. All of the compounds, especially 4, exhibited an excellent inhibitory effect against nasopharyngeal carcinoma CNE-1 cells. This effect was better than that of doxorubicin. Compound 4 also markedly blocked the proliferation of the CNE-1 cells in a zebrafish xenograft model. The antitumor mechanisms might be attributed to apoptosis induction, which triggered ROS-mediated DNA damage and generated mitochondrial dysfunction by stabilizing c-myc G-quadruplex DNA structure. Results indicated that phenanthroimidazole derivatives could act as promising anticancer agents.

Killers 2.0: NK cell therapies at the forefront of cancer control

Natural killer (NK) cells are innate cytotoxic lymphocytes involved in the surveillance and elimination of cancer. As we have learned more and more about the mechanisms NK cells employ to recognize and eliminate tumor cells, and how, in turn, cancer evades NK cell responses, we have gained a clear appreciation that NK cells can be harnessed in cancer immunotherapy. Here, we review the evidence for NK cells' critical role in combating transformed and malignant cells, and how cancer immunotherapies potentiate NK cell responses for therapeutic purposes. We highlight cutting-edge immunotherapeutic strategies in preclinical and clinical development such as adoptive NK cell transfer, chimeric antigen receptor-expressing NK cells (CAR-NKs), bispecific and trispecific killer cell engagers (BiKEs and TriKEs), checkpoint blockade, and oncolytic virotherapy. Further, we describe the challenges that NK cells face (e.g., postsurgical dysfunction) that must be overcome by these therapeutic modalities to achieve cancer clearance.

TIGIT Blockade: A Multipronged Approach to Target the HIV Reservoir

During chronic human immunodeficiency virus type 1 (HIV-1) infection, upregulation of inhibitory molecules contributes to effector cell dysfunction and exhaustion. This, in combination with the ability of HIV-1 to reside dormant in cellular reservoirs and escape immune recognition, makes the pathway to HIV-1 cure particularly challenging. An idealized strategy to achieve HIV-1 cure proposes combined viral and immune activation by "shock"ing HIV-1 out of latency and into an immunologically visible state to be recognized and "kill"ed by immune effector cells. Here we outline the potential for blockade of the inhibitory immune checkpoint T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT) to overcome natural killer (NK) cell and T cell inhibition associated with HIV-1 infection and invigorate antiviral effector cell responses against HIV-1 reactivated from the latent cellular reservoir.

Prognostic significance of tumor poliovirus receptor and CTLA4 expression in patients with surgically resected non-small-cell lung cancer

INTRODUCTION

Poliovirus receptor (PVR) is a tumor promoter and a regulatory checkpoint that enhances immunosuppression. We investigated PVR expression by applying immunohistochemistry (IHC) staining. A positive association existed between PVR expression and cytotoxic T lymphocyte-associated antigen 4 (CTLA4) expression in patients with surgically resected non-small-cell lung cancer (NSCLC). PVR expression is a prognosis predictor of lung adenocarcinoma.

PURPOSE

To investigate the prognostic significance of PVR expression and CTLA4 expression for surgically resected NSCLC.

PATIENTS AND METHODS

The medical records of 108 Chinese patients with primary NSCLC who underwent surgery were retrospectively reviewed. The expression of PVR and CTLA4 were measured through IHC. Clinical characteristics, the association between PVR and CTLA4, and the prognostic significance of PVR were analyzed.

RESULTS

A significant positive association was observed between PVR and CTLA4 expression in NSCLC (P = 0.016). PVR had a high positive rate among females, nonsmokers, and patients with adenocarcinoma and advanced lung cancer. The overall survival (OS) of patients with negative PVR expression was significantly longer than that of patients with positive PVR expression (P = 0.049), especially among females (P = 0.03) and nonsmokers (P = 0.025). Multivariate analysis results showed that advanced tumor stage and PVR expression were independent prognosis predictors of poor OS.

CONCLUSION

PVR can potentially serve as a prognostic predictor and biomarker for NSCLC and cancer anti-CTLA4 immunotherapy response.

CD155 contributes to the mesenchymal phenotype of triple-negative breast cancer

Patients with triple-negative breast cancer (TNBC) lack molecular targets and have an unfavorable outcome. CD155 is overexpressed in human cancers, but whether it plays a role in TNBC is unexplored. Here we found that CD155 was enriched in both TNBC cell lines and tumor tissues. High CD155 expression was related to poor prognosis of breast cancer patients. CD155 was associated with a mesenchymal phenotype. CD155 knockdown induced a mesenchymal-epithelial transition in TNBC cells, and suppressed TNBC cell migration, invasion and metastasis in vitro and in vivo. Mechanistically, CD155 cross-talked with oncogenic IL-6/Stat3 and TGF-β/Smad3 pathways. Moreover, CD155 knockdown inhibited TNBC cell growth and survival. Taken together, these data indicate that CD155 contributes to the aggressive behavior of TNBC; targeting CD155 may be beneficial to these patients.

Tumor intrinsic and extrinsic immune functions of CD155

CD155 (PVR/necl5/Tage4), a member of the nectin-like family of adhesion molecules, is highly upregulated on tumor cells across multiple cancer types and has been associated with worse patient outcomes. In addition to well described cell-intrinsic roles promoting tumor progression and metastasis, CD155 has now been implicated in immune regulation. The role of CD155 as a potent immune ligand with diverse cell-extrinsic functions is now being defined. CD155 signaling to immune cells is mediated through interactions with the co-stimulatory immune receptor CD226 (DNAM-1) and the inhibitory checkpoint receptors TIGIT and CD96, which are differentially regulated at the cell surface on T cells and NK cells. The integration of signals from CD155 cognate receptors modifies the activity of tumor-infiltrating lymphocytes in a context-dependent manner, making CD155 an attractive target for immune-oncology. Preclinical studies suggest that targeting this axis can improve immune-mediated tumor control, particularly when combined with existing anti-PD-1 checkpoint therapies. In this review, we discuss the roles of CD155 on host and tumor cells in controlling tumor progression and discuss the possibility of targeting CD155 for cancer therapy.

The Good and the Bad of Natural Killer Cells in Virus Control: Perspective for Anti-HBV Therapy

Immune modulatory therapies are widely believed to represent potential therapeutic strategies for chronic hepatitis B infection (CHB). Among the cellular targets for immune interventions, Natural Killer (NK) cells represent possible candidates because they have a key role in anti-viral control by producing cytokines and by exerting cytotoxic functions against virus-infected cells. However, in patients with chronic hepatitis B, NK cells have been described to be more pathogenic than protective with preserved cytolytic activity but with a poor capacity to produce anti-viral cytokines. In addition, NK cells can exert a regulatory activity and possibly suppress adaptive immune responses in the setting of persistent viral infections. Consequently, a potential drawback of NK-cell targeted modulatory interventions is that they can potentiate the suppressive NK cell effect on virus-specific T cells, which further causes impairment of exhausted anti-viral T cell functions. Thus, clinically useful NK-cell modulatory strategies should be not only suited to improve positive anti-viral NK cell functions but also to abrogate T cell suppression by NK cell-mediated T cell killing. This review outlines the main NK cell features with a particular focus on CHB infection. It describes different mechanisms involved in NK-T cell interplay as well as how NK cells can have positive anti-viral effector functions and negative suppressive effects on T cells activity. This review discusses how modulation of their balance can have potential therapeutic implications.

CD155 downregulation synergizes with adriamycin to induce breast cancer cell apoptosis

CD155 has been implicated in migration, invasion, proliferation and apoptosis of human cancer cells, and DNA damage response caused by chemotherapeutic agents or reactive oxygen species has been shown to attribute to CD155 induction. Adriamycin (Adr) is one of the most common chemotherapeutic drugs used to treat breast cancer. Here we reported that treatment with Adr upregulated CD155 expression on several in vitro cultured breast cancer cells and in breast cancer cell 4T1 xenografts. We also found that CD155 knockdown or Adr treatment induced apoptosis of in vitro cultured cancer cells and cancer cells in 4T1 xenografts, and a combination of CD155 knockdown with Adr treatment induced more cell death than either of them. Furthermore, we revealed that the combination of CD155 knockdown with Adr treatment suppressed the growth of 4T1 xenografts more significantly than them alone. In summary, our results demonstrate that CD155 downregulation synergizes with Adr to induce breast cancer cell apoptosis, thereby to suppress tumor growth. Our results also suggest that CD155 upregulation may be a mechanism underlying Adr resistance by breast cancer cells.

DNAM-1 Activating Receptor and Its Ligands: How Do Viruses Affect the NK Cell-Mediated Immune Surveillance during the Various Phases of Infection?

Natural Killer (NK) cells play a critical role in host defense against viral infections. The mechanisms of recognition and killing of virus-infected cells mediated by NK cells are still only partially defined. Several viruses induce, on the surface of target cells, the expression of molecules that are specifically recognized by NK cell-activating receptors. The main NK cell-activating receptors involved in the recognition and killing of virus-infected cells are NKG2D and DNAM-1. In particular, ligands for DNAM-1 are nectin/nectin-like molecules involved also in mechanisms allowing viral infection. Viruses adopt several immune evasion strategies, including those affecting NK cell-mediated immune surveillance, causing persistent viral infection and the development of virus-associated diseases. The virus's immune evasion efficacy depends on molecules differently expressed during the various phases of infection. In this review, we overview the molecular strategies adopted by viruses, specifically cytomegalovirus (CMV), human immunodeficiency virus (HIV-1), herpes virus (HSV), Epstein-Barr virus (EBV) and hepatitis C virus (HCV), aiming to evade NK cell-mediated surveillance, with a special focus on the modulation of DNAM-1 activating receptor and its ligands in various phases of the viral life cycle. The increasing understanding of mechanisms involved in the modulation of activating ligands, together with those mediating the viral immune evasion strategies, would provide critical tools leading to design novel NK cell-based immunotherapies aiming at viral infection control, thus improving cure strategies of virus-associated diseases.

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.