Tumor-associated E-cadherin mutations affect binding to the killer cell lectin-like receptor G1 in humans

KLRG1 is reduced on NK cells in SLE patients, inversely correlates with disease activity and is modulated by hydroxychloroquine in vitro

OBJECTIVES

Killer cell lectin-like receptor G 1 (KLRG1), a transmembrane receptor with inhibitory capacity expressed in human immune cells, emerged as a novel susceptibility gene for systemic lupus erythematosus (SLE). The aim of this study was to investigate the expression of KLRG1 in SLE patients compared to healthy controls (HC) on both NK and T cells and to evaluate its possible involvement in SLE pathogenesis.

METHODS

Eighteen SLE patients and twelve healthy controls were enrolled. Peripheral blood mononuclear cells (PBMCs) from these patients were phenotypically characterized by immunofluorescence and flow cytometry. The effect of the hydroxychloroquine (HCQ) in vitro on KLRG1 expression and its signaling mediated functions in NK cells were analyzed.

RESULTS

KLRG1 expression was significantly reduced on the analyzed immune cell populations in SLE patients compared to HC, especially on total NK cells. Moreover, expression of KLRG1 on total NK cells inversely correlated with the SLEDAI-2K. A direct association between KLRG1 expression on NK cells and patients' treatment with HCQ was observed. In vitro treatment with HCQ increased KLRG1 expression on NK cells. In HC, KLRG1+ NK cells showed reduced degranulation and IFNγ production, while in SLE patient, this inhibition occurred only for the IFNγ production.

CONCLUSION

With this study we revealed a reduced expression and an impaired function of KLRG1 on NK cells in SLE patients. These results suggest a possible role of KLRG1 in the pathogenesis of SLE and as a novel biomarker of this disease.

Emerging Nano-/Biotechnology Drives Oncolytic Virus-Activated and Combined Cancer Immunotherapy

Oncolytic viruses (OVs) as one promising antitumor methods have made important contributions to tumor immunotherapy, which arouse increasing attention. They provide the dual mechanisms including direct killing effect toward tumor cells and immune activation for elevating antitumor responses, which have been proved in many preclinical studies. Especially, natural or genetically modified viruses as clinical immune preparations have emerged as a new promising approach objective to oncology treatment. The approval of talimogene laherparepvec (T-VEC) by the U.S. Food and Drug Administration (FDA) for the therapy of advanced melanoma could be considered as a milestone achievement in the clinical translation of OV. In this review, we first discussed the antitumor mechanisms of OVs with an emphasis on targeting, replication, and propagation. We further outlined the state of the art of current OVs in tumor and underlined the activated biological effects especially including immunity. More significantly, the enhanced immune responses based on OVs were systematically discussed from different perspectives such as combination with immunotherapy, genetic engineering of OVs, integration with nanobiotechnology or nanoparticles, and antiviral response counteraction, where their principles were shed light on. The development of OVs in the clinics was also highlighted to analyze the actuality and concerns of different OV applications in clinical trials. At last, the future perspectives and challenges of OVs as an already widely accepted treatment means were discussed. This review will provide a systematic review and deep insight into OV development and also offer new opportunities and guidance pathways to drive the further clinical translation.

The Yin and Yang of Targeting KLRG1+ Tregs and Effector Cells

The literature surrounding KLRG1 has primarily focused on NK and CD8⁺ T cells. However, there is evidence that the most suppressive Tregs express KLRG1. Until now, the role of KLRG1 on Tregs has been mostly overlooked and remains to be elucidated. Here we review the current literature on KLRG1 with an emphasis on the KLRG1⁺ Treg subset role during cancer development and autoimmunity. KLRG1 has been recently proposed as a new checkpoint inhibitor target, but these studies focused on the effects of KLRG1 blockade on effector cells. We propose that when designing anti-tumor therapies targeting KLRG1, the effects on both effector cells and Tregs will have to be considered.

Genome-scale screens identify factors regulating tumor cell responses to natural killer cells

To systematically define molecular features in human tumor cells that determine their degree of sensitivity to human allogeneic natural killer (NK) cells, we quantified the NK cell responsiveness of hundreds of molecularly annotated 'DNA-barcoded' solid tumor cell lines in multiplexed format and applied genome-scale CRISPR-based gene-editing screens in several solid tumor cell lines, to functionally interrogate which genes in tumor cells regulate the response to NK cells. In these orthogonal studies, NK cell-sensitive tumor cells tend to exhibit 'mesenchymal-like' transcriptional programs; high transcriptional signature for chromatin remodeling complexes; high levels of B7-H6 (NCR3LG1); and low levels of HLA-E/antigen presentation genes. Importantly, transcriptional signatures of NK cell-sensitive tumor cells correlate with immune checkpoint inhibitor (ICI) resistance in clinical samples. This study provides a comprehensive map of mechanisms regulating tumor cell responses to NK cells, with implications for future biomarker-driven applications of NK cell immunotherapies.

Functions and clinical significance of KLRG1 in the development of lung adenocarcinoma and immunotherapy

BACKGROUND

As a marker of differentiation, Killer cell lectin like receptor G1 (KLRG1) plays an inhibitory role in human NK cells and T cells. However, its clinical role remains inexplicit. This work intended to investigate the predictive ability of KLRG1 on the efficacy of immune-checkpoint inhibitor in the treatment of lung adenocarcinoma (LUAD), as well as contribute to the possible molecular mechanisms of KLRG1 on LUAD development.

METHODS

Using data from the Gene Expression Omnibus, the Cancer Genome Atlas and the Genotype-Tissue Expression, we compared the expression of KLRG1 and its related genes Bruton tyrosine kinase (BTK), C-C motif chemokine receptor 2 (CCR2), Scm polycomb group protein like 4 (SCML4) in LUAD and normal lung tissues. We also established stable LUAD cell lines with KLRG1 gene knockdown and investigated the effect of KLRG1 knockdown on tumor cell proliferation. We further studied the prognostic value of the four factors in terms of overall survival (OS) in LUAD. Using data from the Gene Expression Omnibus, we further investigated the expression of KLRG1 in the patients with different responses after immunotherapy.

RESULTS

The expression of KLRG1, BTK, CCR2 and SCML4 was significantly downregulated in LUAD tissues compared to normal controls. Knockdown of KLRG1 promoted the proliferation of A549 and H1299 tumor cells. And low expression of these four factors was associated with unfavorable overall survival in patients with LUAD. Furthermore, low expression of KLRG1 also correlated with poor responses to immunotherapy in LUAD patients.

CONCLUSION

Based on these findings, we inferred that KLRG1 had significant correlation with immunotherapy response. Meanwhile, KLRG1, BTK, CCR2 and SCML4 might serve as valuable prognostic biomarkers in LUAD.

Development of Antihuman Killer Cell Lectin-Like Receptor Subfamily G Member 1 Monoclonal Antibodies for Flow Cytometry

Killer cell lectin-like receptor subfamily G member 1 (KLRG1), a type II transmembrane protein, was identified as an inhibitory receptor expressed on natural killer (NK) cells and certain T cells. The protein regulates effector functions and developmental processes in these cells. In this study, we established a specific and sensitive monoclonal antibody (mAb) for human KLRG1 (hKLRG1), which is useful for flow cytometry, using a Cell-Based Immunization and Screening (CBIS) method. The established anti-hKLRG1 mAb, KLMab-1 (mouse IgG₁, kappa), reacted with overexpressed hKLRG1 in Chinese hamster ovary-K1 (CHO/hKLRG1) and human NK cells, which also expressed endogenous hKLRG1 as confirmed by flow cytometry. KLMab-1, which was established by the CBIS method, could be useful for elucidating the hKLRG1-related biological response by flow cytometry.

T cell markers recount the course of immunosenescence in healthy individuals and chronic kidney disease

Aging results in substantial changes in almost all cellular subpopulations within the immune system, including functional and phenotypic alterations. T lymphocytes, as the main representative population of cellular immunity, have been extensively studied in terms of modifications and adjustments during aging. Phenotypic alterations are attributed to three main mechanisms; a reduction of naïve T cell population with a shift to more differentiated forms, a subsequent oligoclonal expansion of naïve T cells characterized by repertoire restriction, and replicative insufficiency after repetitive activation. These changes and the subsequent phenotypic disorders are comprised in the term "immunosenescence". Similar changes seem to occur in chronic kidney disease, with T cells of young patients resembling those of healthy older individuals. A broad range of surface markers can be utilized to identify immunosenescent T cells. In this review, we will discuss the most important senescence markers and their potential connection with impaired renal function.

Advances and potential pitfalls of oncolytic viruses expressing immunomodulatory transgene therapy for malignant gliomas

Glioblastoma (GBM) is an immunosuppressive, lethal brain tumor. Despite advances in molecular understanding and therapies, the clinical benefits have remained limited, and the life expectancy of patients with GBM has only been extended to ~15 months. Currently, genetically modified oncolytic viruses (OV) that express immunomodulatory transgenes constitute a research hot spot in the field of glioma treatment. An oncolytic virus is designed to selectively target, infect, and replicate in tumor cells while sparing normal tissues. Moreover, many studies have shown therapeutic advantages, and recent clinical trials have demonstrated the safety and efficacy of their usage. However, the therapeutic efficacy of oncolytic viruses alone is limited, while oncolytic viruses expressing immunomodulatory transgenes are more potent inducers of immunity and enhance immune cell-mediated antitumor immune responses in GBM. An increasing number of basic studies on oncolytic viruses encoding immunomodulatory transgene therapy for malignant gliomas have yielded beneficial outcomes. Oncolytic viruses that are armed with immunomodulatory transgenes remain promising as a therapy against malignant gliomas and will undoubtedly provide new insights into possible clinical uses or strategies. In this review, we summarize the research advances related to oncolytic viruses that express immunomodulatory transgenes, as well as potential treatment pitfalls in patients with malignant gliomas.

Association of DNA-Methylation Profiles With Immune Responses Elicited in Breast Cancer Patients Immunized With a Carbohydrate-Mimicking Peptide: A Pilot Study

Immune response to a given antigen, particularly in cancer patients, is complex and is controlled by various genetic and environmental factors. Identifying biomarkers that can predict robust response to immunization is an urgent need in clinical cancer vaccine development. Given the involvement of DNA methylation in the development of lymphocytes, tumorigenicity and tumor progression, we aimed to analyze pre-vaccination DNA methylation profiles of peripheral blood mononuclear cells (PBMCs) from breast cancer subjects vaccinated with a novel peptide-based vaccine referred to as P10s-PADRE. This pilot study was performed to evaluate whether signatures of differentially methylated (DM) loci can be developed as potential predictive biomarkers for prescreening subjects with cancer who will most likely generate an immune response to the vaccine. Genomic DNA was isolated from PBMCs of eight vaccinated subjects, and their DNA methylation profiles were determined using Infinium^® MethylationEPIC BeadChip array from Illumina. A linear regression model was applied to identify loci that were differentially methylated with respect to anti-peptide antibody titers and with IFN-γ production. The data were summarized using unsupervised-learning methods: hierarchical clustering and principal-component analysis. Pathways and networks involved were predicted by Ingenuity Pathway Analysis. We observed that the profile of DM loci separated subjects in regards to the levels of immune responses. Canonical pathways and networks related to metabolic and immunological functions were found to be involved. The data suggest that it is feasible to correlate methylation signatures in pre-treatment PBMCs with immune responses post-treatment in cancer patients going through standard-of-care chemotherapy. Larger and prospective studies that focus on DM loci in PBMCs is warranted to develop pre-screening biomarkers before BC vaccination.

Clinical Trial Registration:www.ClinicalTrials.gov, Identifier: NCT02229084.

E-Cadherin in Pancreatic Ductal Adenocarcinoma: A Multifaceted Actor during EMT

Epithelial-to-mesenchymal transition (EMT) is a step-wise process observed in normal and tumor cells leading to a switch from epithelial to mesenchymal phenotype. In tumors, EMT provides cancer cells with a metastatic phenotype characterized by E-cadherin down-regulation, cytoskeleton reorganization, motile and invasive potential. E-cadherin down-regulation is known as a key event during EMT. However, E-cadherin expression can be influenced by the different experimental settings and environmental stimuli so that the paradigm of EMT based on the loss of E-cadherin determining tumor cell behavior and fate often becomes an open question. In this review, we aimed at focusing on some critical points in order to improve the knowledge of the dynamic role of epithelial cells plasticity in EMT and, specifically, address the role of E-cadherin as a marker for the EMT axis.

The E-Cadherin Cleavage Associated to Pathogenic Bacteria Infections Can Favor Bacterial Invasion and Transmigration, Dysregulation of the Immune Response and Cancer Induction in Humans

Once bound to the epithelium, pathogenic bacteria have to cross epithelial barriers to invade their human host. In order to achieve this goal, they have to destroy the adherens junctions insured by cell adhesion molecules (CAM), such as E-cadherin (E-cad). The invasive bacteria use more or less sophisticated mechanisms aimed to deregulate CAM genes expression or to modulate the cell-surface expression of CAM proteins, which are otherwise rigorously regulated by a molecular crosstalk essential for homeostasis. Apart from the repression of CAM genes, a drastic decrease in adhesion molecules on human epithelial cells can be obtained by induction of eukaryotic endoproteases named sheddases or through synthesis of their own (prokaryotic) sheddases. Cleavage of CAM by sheddases results in the release of soluble forms of CAM. The overexpression of soluble CAM in body fluids can trigger inflammation and pro-carcinogenic programming leading to tumor induction and metastasis. In addition, the reduction of the surface expression of E-cad on epithelia could be accompanied by an alteration of the anti-bacterial and anti-tumoral immune responses. This immune response dysfunction is likely to occur through the deregulation of immune cells homing, which is controlled at the level of E-cad interaction by surface molecules α_E integrin (CD103) and lectin receptor KLRG1. In this review, we highlight the central role of CAM cell-surface expression during pathogenic microbial invasion, with a particular focus on bacterial-induced cleavage of E-cad. We revisit herein the rapidly growing body of evidence indicating that high levels of soluble E-cad (sE-cad) in patients’ sera could serve as biomarker of bacterial-induced diseases.

Co-inhibitory T cell receptor KLRG1: human cancer expression and efficacy of neutralization in murine cancer models

Background

KLRG1 is a lymphocyte co-inhibitory, or immune checkpoint, receptor expressed predominantly on late-differentiated effector and effector memory CD8+ T and NK cells. Targeting of KLRG1 neutralization in murine cancer models has not previously been reported.

Methods

We studied KLRG1 expression in human blood and tumor samples from available genomic datasets. Anti-KLRG1 neutralizing antibody was studied in the murine 4T1 breast cancer as monotherapy, and in the MC38 colon cancer and B16F10 melanoma models as combination therapy with anti-PD-1 antibody.

Results

In human blood and tumor samples, KLRG1 expression is aligned with cytotoxic T and NK cell differentiation, and upregulated in human tumor samples after a variety of therapies, potentially contributing to adaptive resistance. In in vivo murine models, anti-KLRG1 antibody monotherapy in the 4T1 breast cancer model reduced lung metastases (decreased lung weights p=0.04; decreased nodule count p=0.002), while anti-KLRG1 + anti-PD-1 combination therapy in the MC38 colon cancer and B16F10 melanoma models produced synergistic benefit greater than anti-PD-1 alone for tumor volume (MC38 p=0.01; B16F10 p=0.007) and survival (MC38 p=0.02; B16F10 p=0.002).

Conclusions

These studies provide the first evidence that inhibition of the KLRG1 pathway enhances immune control of cancer in murine models, and provide target validation for KLRG1 targeting of human cancer. The mechanism of efficacy of KLRG1 blockade in murine models remains to be determined.

An oncolytic herpesvirus expressing E-cadherin improves survival in mouse models of glioblastoma

The efficacy of oncolytic herpes simplex virus (oHSV) is limited by rapid viral clearance by innate immune effector cells and poor intratumoral viral spread. We combine two approaches to overcome these barriers: inhibition of natural killer (NK) cells and enhancement of intratumoral viral spread. We engineered an oHSV to express CDH1, encoding E-cadherin, an adherent molecule and a ligand for KLRG1, an inhibitory receptor expressed on NK cells. In vitro, infection with this engineered virus, named OV-CDH1, induced high surface E-cadherin expression on infected glioblastoma (GBM) cells, which typically lack endogenous E-cadherin. Ectopically expressed E-cadherin enhanced the spread of OV-CDH1 by facilitating cell-to-cell infection and viral entry and reduced viral clearance by selectively protecting OV-CDH1-infected cells from KLRG1+ NK cell killing. In vivo, OV-CDH1 treatment substantially prolonged the survival in GBM-bearing mouse models, primarily because of improved viral spread rather than inhibition of NK cell activity. Thus, virus-induced overexpression of E-cadherin may be a generalizable strategy for improving cancer virotherapy.

Tumor immunotherapy: drug-induced neoantigens (xenogenization) and immune checkpoint inhibitors

More than 40 years ago, we discovered that novel transplantation antigens can be induced in vivo or in vitro by treating murine leukemia with dacarbazine. Years later, this phenomenon that we called “Chemical Xenogenization” (CX) and more recently, “Drug-Induced Xenogenization” (DIX), was reproduced by Thierry Boon with a mutagenic/carcinogenic compound (i.e. N-methyl-N’-nitro-N-nitrosoguanidine). In both cases, the molecular bases of DIX rely on mutagenesis induced by methyl adducts to oxygen-6 of DNA guanine. In the present review we illustrate the main DIX-related immune-pharmacodynamic properties of triazene compounds of clinical use (i.e. dacarbazine and temozolomide).

In recent years, tumor immunotherapy has come back to the stage with the discovery of immune checkpoint inhibitors (ICpI) that show an extraordinary immune-enhancing activity. Here we illustrate the salient biochemical features of some of the most interesting ICpI and the up-to-day status of their clinical use. Moreover, we illustrate the literature showing the direct relationship between somatic mutation burden and susceptibility of cancer cells to host’s immune responses.

When DIX was discovered, we were not able to satisfactorily exploit the possible presence of triazene-induced neoantigens in malignant cells since no device was available to adequately enhance host’s immune responses in clinical settings. Today, ICpI show unprecedented efficacy in terms of survival times, especially when elevated mutation load is associated with cancer cells. Therefore, in the future, mutation-dependent neoantigens obtained by appropriate pharmacological intervention appear to disclose a novel approach for enhancing the therapeutic efficacy of ICpI in cancer patients.

Epithelial-mesenchymal transition leads to NK cell-mediated metastasis-specific immunosurveillance in lung cancer

During epithelial-mesenchymal transition (EMT) epithelial cancer cells transdifferentiate into highly motile, invasive, mesenchymal-like cells, giving rise to disseminating tumor cells. Few of these disseminated cells successfully metastasize. Immune cells and inflammation in the tumor microenvironment were shown to drive EMT, but few studies investigated the consequences of EMT for tumor immunosurveillance. In addition to initiating metastasis, we demonstrate that EMT confers increased susceptibility to natural killer (NK) cells and contributes, in part, to the inefficiency of the metastatic process. Depletion of NK cells allowed spontaneous metastasis without affecting primary tumor growth. EMT-induced modulation of E-cadherin and cell adhesion molecule 1 (CADM1) mediated increased susceptibility to NK cytotoxicity. Higher CADM1 expression correlates with improved patient survival in 2 lung and 1 breast adenocarcinoma patient cohorts and decreased metastasis. Our observations reveal a novel NK-mediated, metastasis-specific immunosurveillance in lung cancer and present a window of opportunity for preventing metastasis by boosting NK cell activity.

Immunological Consequences of Epithelial-Mesenchymal Transition in Tumor Progression

Microenvironments that tumor cells encounter are different during the stages of cancer progression-primary tumor, metastasis, and at the metastatic site. This suggests potential differences in immune surveillance of primary tumor and metastasis. Epithelial-mesenchymal transition (EMT) is a key reversible process in which cancer cells transition into highly motile and invasive cells for dissemination. Only a tiny proportion successfully metastasize, supporting the notion of metastasis-specific immune surveillance. EMT involves extensive molecular reprogramming of cells conferring many clinically relevant features to cancer cells and affects tumor cell interactions within the tumor microenvironment. We review the impact of tumor immune infiltrates on tumor cell EMT and the consequences of EMT in shaping the immune microenvironment of tumors. The usefulness of EMT as a model to investigate metastasis-specific immune surveillance mechanisms are also explored. Finally, we discuss potential implications of EMT for tumor immunogenicity, as well as current immunotherapies and future strategies.

E-cadherin roles in animal biology: A perspective on thyroid hormone-influence

The establishment, remodeling and maintenance of tissular architecture during animal development, and even across juvenile to adult life, are deeply regulated by a delicate interplay of extracellular signals, cell membrane receptors and intracellular signal messengers. It is well known that cell adhesion molecules (cell-cell and cell-extracellular matrix) play a critical role in these processes. Particularly, adherens junctions (AJs) mediated by E-cadherin and catenins determine cell-cell contact survival and epithelia function. Consequently, this review seeks to encompass the complex and prolific knowledge about E-cadherin roles during physiological and pathological states, particularly focusing on the influence exerted by the thyroid hormone (TH).

Structural basis for recognition of cellular and viral ligands by NK cell receptors

Natural killer (NK) cells are key components of innate immune responses to tumors and viral infections. NK cell function is regulated by NK cell receptors that recognize both cellular and viral ligands, including major histocompatibility complex (MHC), MHC-like, and non-MHC molecules. These receptors include Ly49s, killer immunoglobulin-like receptors, leukocyte immunoglobulin-like receptors, and NKG2A/CD94, which bind MHC class I (MHC-I) molecules, and NKG2D, which binds MHC-I paralogs such as the stress-induced proteins MICA and ULBP. In addition, certain viruses have evolved MHC-like immunoevasins, such as UL18 and m157 from cytomegalovirus, that act as decoy ligands for NK receptors. A growing number of NK receptor–ligand interaction pairs involving non-MHC molecules have also been identified, including NKp30–B7-H6, killer cell lectin-like receptor G1–cadherin, and NKp80–AICL. Here, we describe crystal structures determined to date of NK cell receptors bound to MHC, MHC-related, and non-MHC ligands. Collectively, these structures reveal the diverse solutions that NK receptors have developed to recognize these molecules, thereby enabling the regulation of NK cytolytic activity by both host and viral ligands.

Can exercise-related improvements in immunity influence cancer prevention and prognosis in the elderly?

Cancer incidence increases with advancing age. Over 60% of new cancers and 70% of cancer deaths occur in individuals aged 65 years or older. One factor that may contribute to this is immunosenescence - a canopy term that is used to describe age-related declines in the normal functioning of the immune system. There are multiple age-related deficits in both the innate and adaptive systems that may play a role in the increased incidence of cancer. These include decreased NK-cell function, impaired antigen uptake and presentation by monocytes and dendritic cells, an increase in 'inflammaging', a decline in the number of naïve T-cells able to respond to evolving tumor cells, and an increase in functionally exhausted senescent cells. There is consensus that habitual physical exercise can offer protection against certain types of cancer; however the evidence linking immunological mechanisms, exercise, and reduced cancer risk remain tentative. Multiple studies published over the last two decades suggest that exercise can mitigate the deleterious effects of age on immune function, thus increasing anti-cancer immunity. The potential ameliorative effect of exercise on these mechanisms include evidence that physical activity is able to stimulate greater NK-cell activity, enhance antigen-presentation, reduce inflammation, and prevent senescent cell accumulation in the elderly. Here we discuss the role played by the immune system in preventing and controlling cancer and how aging may retard these anti-cancer mechanisms. We also propose a pathway by which exercise-induced alterations in immunosenescence may decrease the incidence of cancer and help improve prognosis in cancer patients.

Mouse TIGIT inhibits NK-cell cytotoxicity upon interaction with PVR

The activity of natural killer (NK) cells is controlled by a balance of signals derived from inhibitory and activating receptors. TIGIT is a novel inhibitory receptor, recently shown in humans to interact with two ligands: PVR and Nectin2 and to inhibit human NK-cell cytotoxicity. Whether mouse TIGIT (mTIGIT) inhibits mouse NK-cell cytotoxicity is unknown. Here we show that mTIGIT is expressed by mouse NK cells and interacts with mouse PVR. Using mouse and human Ig fusion proteins we show that while the human TIGIT (hTIGIT) cross-reacts with mouse PVR (mPVR), the binding of mTIGIT is restricted to mPVR. We further demonstrate using surface plasmon resonance (SPR) and staining with Ig fusion proteins that mTIGIT binds to mPVR with higher affinity than the co-stimulatory PVR-binding receptor mouse DNAM1 (mDNAM1). Functionally, we show that triggering of mTIGIT leads to the inhibition of NK-cell cytotoxicity, that IFN-γ secretion is enhanced when mTIGIT is blocked and that the TIGIT-mediated inhibition is dominant over the signals delivered by the PVR-binding co-stimulatory receptors. Additionally, we identify the inhibitory motif responsible for mTIGIT inhibition. In conclusion, we show that TIGIT is a powerful inhibitory receptor for mouse NK cells.

Senescence marker killer cell lectin-like receptor G1 (KLRG1) contributes to TNF-α production by interaction with its soluble E-cadherin ligand in chronically inflamed joints

OBJECTIVES

Killer cell lectin-like receptor G1 (KLRG1) is an NK cell marker also expressed on T cells showing an immunosenescent phenotype. KLRG1 binding to its ligand E-cadherin inhibits functional responses. It was recently shown that soluble E-cadherin (sE-cadherin) also influences KLRG1 signalling, although its involvement in arthritis is unknown. Our goal was to evaluate the contribution of KLRG1(+) T cells to synovitis.

METHODS

Paired peripheral blood (PB) and synovial fluid (SF) mononuclear cells from 21 patients with spondyloarthritis (SpA) or rheumatoid arthritis (RA), eight with crystal-induced arthritis and 10 controls were obtained. T cells were characterised for KLRG1 expression directly ex vivo, while TNF-α/IFN-γ production was assessed after polyclonal stimulation. Assays of chemotaxis response towards SF were conducted. Additionally, sE-cadherin levels in our paired samples were determined. Moreover, TNF-α/IFN-γ production by antigen-specific T cells was evaluated in the presence of sE-cadherin.

RESULTS

KLRG1(+) T cells were enriched in SF as opposed to PB of SpA and RA patients, which contrasts with results obtained in crystal-induced arthritides. KLRG1(+) T cells were more functionally active as opposed to KLRG1(-) T cells and migrated preferentially towards SpA and RA SF. sE-cadherin levels were higher in SF versus plasma. The presence of sE-cadherin enhanced the number of KLRG1(+) CD4(+) T cells able to produce TNF-α but not IFN-γ.

CONCLUSIONS

sE-cadherin contributes to the local proinflammatory environment in the joint by favouring TNF-α production by KLRG1(+) CD4(+) T cells. This pathway seems to be operational in both SpA and RA, but not in crystal-induced arthritis.

Killer cell lectin-like receptor G1 deficiency significantly enhances survival after Mycobacterium tuberculosis infection

The expression of T cell differentiation markers is known to increase during Mycobacterium tuberculosis infection, and yet the biological role of such markers remains unclear. We examined the requirement of the T cell differentiation marker killer cell lectin-like receptor G1 (KLRG1) during M. tuberculosis infection using mice deficient in KLRG1. KLRG1(-/-) mice had a significant survival extension after M. tuberculosis infection compared to wild-type controls, and maintained a significantly lower level of pulmonary M. tuberculosis throughout chronic infection. Improved control of M. tuberculosis infection was associated with an increased number of activated pulmonary CD4(+) T cells capable of secreting gamma interferon (IFN-γ). Our report is the first to show an in vivo impact of KLRG1 on disease control.

Different inhibitory capacities of human and mouse KLRG1 are linked to distinct disulfide-mediated oligomerizations

The killer cell lectin-like receptor G1 (KLRG1) is a cadherin-binding inhibitory receptor expressed by NK and T cells in humans and mice. Although structural and ligand-binding properties of human (h) and mouse (m) KLRG1 are very similar, KLRG1-mediated inhibition under physiological conditions is only observed with human lymphocytes. Using a well-defined in vitro system, we demonstrate here that mKLRG1 exhibits a significantly lower inhibitory capacity compared with the human homolog. Biochemical analyses further showed that mKLRG1 formed monomers and disulfide-linked dimers, trimers, and tetramers whereas hKLRG1 was exclusively present as disulfide-linked dimer. Mutational analysis revealed a crucial role of Cys(62) present in the stalk region of mKLRG1 but not of hKLRG1 for oligomer formation. Strikingly, mimicking hKLRG1 by replacement of Cys(62) in mKLRG1 by glutamine prevented tri- and tetramer formation and increased the inhibitory capacity. Furthermore, mutated mKLRG1 molecules that were unable to form disulfide-linked dimers at all or at a decreased level lacked inhibitory activity. These data indicate that only dimeric KLRG1 entities exhibit potent inhibitory capacities. The lower inhibitory capacity of mKLRG1 compared with hKLRG1 can thus be rationalized by a decreased proportion of dimeric entities, which can be pinpointed to a single amino acid.

IQGAP1: a regulator of intracellular spacetime relativity

Activating and inhibiting receptors of lymphocytes collect valuable information about their mikròs kósmos. This information is essential to initiate or to turn off complex signaling pathways. Irrespective of these advances, our knowledge on how these intracellular activation cascades are coordinated in a spatiotemporal manner is far from complete. Among multiple explanations, the scaffolding proteins have emerged as a critical piece of this evolutionary tangram. Among many, IQGAP1 is one of the essential scaffolding proteins that coordinate multiple signaling pathways. IQGAP1 possesses multiple protein interaction motifs to achieve its scaffolding functions. Using these domains, IQGAP1 has been shown to regulate a number of essential cellular events. This includes actin polymerization, tubulin multimerization, microtubule organizing center formation, calcium/calmodulin signaling, Pak/Raf/Mek1/2-mediated Erk1/2 activation, formation of maestrosome, E-cadherin, and CD44-mediated signaling and glycogen synthase kinase-3/adenomatous polyposis coli-mediated β-catenin activation. In this review, we summarize the recent developments and exciting new findings of cellular functions of IQGAP1.

NK-cells have an impaired response to acute exercise and a lower expression of the inhibitory receptors KLRG1 and CD158a in humans with latent cytomegalovirus infection

NK-cells and γδ T-cells are cytotoxic effectors of the immune system that are preferentially mobilized into the blood compartment in response to acute stress and exercise. While infection history is known to alter the phenotype and exercise-responsiveness of CD8+ T-cells, the influence of latent cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infections on the phenotypes and exercise-responsiveness of NK-cells and γδ T-cells are unknown. Twenty healthy males (age: 28.4±5.4 years) cycled for 30 min at 85% peak power. Blood lymphocytes isolated before, immediately after, and 1 h after exercise were surface stained for CD3, CD4, CD8, CD56, CD57, CD158a, KLRG1, and γδ-TCR antigens by four-color flow cytometry. CMV and EBV serostatus (pos/neg) was determined by ELISA. CMVpos had lower proportions of NK-cells expressing inhibitory receptors (KLRG1+ and CD158a+) and higher proportions of terminally differentiated NK-cells (KLRG1-/CD57+) compared to CMVneg. CMVpos mobilized far fewer (132 cells/μL vs. 245 cells/μL) NK-cells in response to exercise despite having similar baseline NK-cell counts and physiological responses to exercise as CMVneg, although terminally differentiated NK-cells were equally responsive to exercise regardless of CMV serostatus (p=0.658). EBVpos had higher proportions of CD8+ NK-cells, but cellular responses to exercise were not influenced by EBV. The frequency and exercise-responsiveness of γδ T-cells was not affected by CMV or EBV serostatus (p>0.05). In conclusion, latent CMV infection is associated with lowered numbers of NK-cells expressing inhibitory receptors and a blunted mobilization of NK-cells in response to acute exercise. This may indicate a compromised immune response to "fight-or-flight" situations in those infected with CMV.

Regulation and function of the E-cadherin/catenin complex in cells of the monocyte-macrophage lineage and DCs

E-cadherin is best characterized as adherens junction protein, which through homotypic interactions contributes to the maintenance of the epithelial barrier function. In epithelial cells, the cytoplasmic tail of E-cadherin forms a dynamic complex with catenins and regulates several intracellular signal transduction pathways, including Wnt/β-catenin, PI3K/Akt, Rho GTPase, and NF-κB signaling. Recent progress uncovered a novel and critical role for this adhesion molecule in mononuclear phagocyte functions. E-cadherin regulates the maturation and migration of Langerhans cells, and its ligation prevents the induction of a tolerogenic state in bone marrow-derived dendritic cells (DCs). In this respect, the functionality of β-catenin could be instrumental in determining the balance between immunogenicity and tolerogenicity of DCs in vitro and in vivo. Fusion of alternatively activated macrophages and osteoclasts is also E-cadherin-dependent. In addition, the E-cadherin ligands CD103 and KLRG1 are expressed on DC-, T-, and NK-cell subsets and contribute to their interaction with E-cadherin-expressing DCs and macrophages. Here we discuss the regulation, function, and implications of E-cadherin expression in these central orchestrators of the immune system.

E-cadherin expression on human carcinoma cell affects trastuzumab-mediated antibody-dependent cellular cytotoxicity through killer cell lectin-like receptor G1 on natural killer cells

Trastuzumab is a recombinant antibody drug that is widely used for the treatment of HER2-overexpressing breast carcinoma. Despite encouraging clinical results, many HER2-overexpressing carcinomas are primarily resistant to trastuzumab. We attempted to explain trastuzumab resistance and search for solutions. Since the killer cell lectin-like receptor G1 (KLRG1), an inhibitory receptor expressed on subsets of natural killer (NK) cells recognizes E-cadherin as ligands and may inhibit immune responses by regulating the effector function of NK cells, we used HER2-overexpressing carcinoma cells which were expressing E-cadherin to investigate the role of antibody-dependent cellular cytotoxicity (ADCC) through KLRG1 on NK cells in vitro and vivo. The results indicated that HER2-overexpressing carcinoma cells were killed by trastuzumab-mediated ADCC and the ADCC activity was reflected the degree of E-cadherin expression on carcinoma cells. We found that expression of E-cadherin was shown to be a predictor of response to trastuzumab-based treatment for HER2-overexpressing carcinomas, furthermore, trastuzumab-mediated ADCC was markedly enhanced by KLRG1-negative peripheral blood mononuclear cells (PBMCs(KLRG1(-))).

Down-regulation of mast cell responses through ITIM containing inhibitory receptors

The multiple cell types that comprise the immune system provide an efficient defense system against invading pathogens and micro-organisms. In general, immune cells are activated for disparate functions, such as proliferation, production and release of mediators and chemotaxis, as a result of interactions between ligands and their matching immunoreceptors. This in turn leads to the recruitment and activation of a cascade of second messengers, via their regulators/adaptors, that determine the net effect of the initial response. However, activation of cells of the immune system must be tightly regulated by a finely tuned interplay between activation and inhibition to avoid excessive or inappropriate responsiveness and to maintain homeostasis. Loss of inhibitory signals may disrupt this balance, leading to various pathological processes such as allergic and auto-immune diseases. In this chapter, we will discuss down-regulating mechanisms of mast cells focusing on immunoreceptor tyrosine-based inhibition motifs (ITIM)-containing inhibitory receptors (IR).

Comparative study of tumorigenesis and tumor immunity in invertebrates and nonmammalian vertebrates

Despite intense study in mammals, the different roles played by the immune system in detecting (immunosurveillance), controlling and remodeling (immunoediting) neoplasia, and perhaps in metastasis are not fully understood. In this review, I will present evidence of neoplasia and invasive malignancy, as well as tumor immunity in invertebrates and nonmammalian vertebrates. I will also present a comparative and evolutionary view of the complex interactions between neoplasia and the host immune system. Overall, I wish to go beyond the too simplistic dichotomy between invertebrates with innate immunity that are only affected with benign neoplasia and vertebrates with adaptive immunity that are affected by metastatic malignancies or cancer.

The NK receptor KLRG1 is dispensable for virus-induced NK and CD8+ T-cell differentiation and function in vivo

The killer cell lectin-like receptor G1 (KLRG1) is expressed by NK and T-cell subsets and recognizes members of the classical cadherin family. KLRG1 is widely used as a lymphocyte differentiation marker in both humans and mice but the physiological role of KLRG1 in vivo is still unclear. Here, we generated KLRG1-deficient mice by homologous recombination and used several infection models for their characterization. The results revealed that KLRG1 deficiency did not affect development and function of NK cells examined under various conditions. KLRG1 was also dispensable for normal CD8+ T-cell differentiation and function after viral infections. Thus, KLRG1 is a marker for distinct NK and T-cell differentiation stages but it does not play a deterministic role in the generation and functional characteristics of these lymphocyte subsets. In addition, we demonstrate that E-cadherin expressed by K562 target cells inhibited NK-cell reactivity in transgenic mice over-expressing KLRG1 but not in KLRG1-deficient or WT mice. Hence, the inhibitory potential of KLRG1 in mice is rather weak and strong activation signals during viral infections may override the inhibitory signal in vivo.

KLRG1--more than a marker for T cell senescence

The co-inhibitory receptor killer-cell lectin like receptor G1 (KLRG1) is expressed on NK cells and antigen-experienced T cells and has been postulated to be a marker of senescence. Whilst KLRG1 has frequently been used as a marker of cellular differentiation, data are emerging indicating that KLRG1 plays an inhibitory role. In this review we examine evidence highlighting this view of KLRG1 with emphasis on the functional defects that arise during T cell differentiation with age that may, in part, be actively maintained by inhibitory receptor signalling.

Simultaneous infiltration of polyfunctional effector and suppressor T cells into renal cell carcinomas

Renal cell carcinoma is frequently infiltrated by cells of the immune system. This makes it important to understand interactions between cancer cells and immune cells so they can be manipulated to bring clinical benefit. Here, we analyze subsets and functions of T lymphocytes infiltrating renal cell tumors directly ex vivo following mechanical disaggregation and without any culture step. Subpopulations of memory and effector CD4(+) Th1, Th2, and Th17 and CD8(+) Tc1 cells were identified based on surface phenotype, activation potential, and multicytokine production. Compared with the same patient's peripheral blood, T lymphocytes present inside tumors were found to be enriched in functional CD4(+) cells of the Th1 lineage and in effector memory CD8(+) cells. Additionally, several populations of CD4(+) and CD8(+) regulatory T cells were identified that may synergize to locally dampen antitumor T-cell responses.

Immunoregulatory functions of KLRG1 cadherin interactions are dependent on forward and reverse signaling

KLRG1 is an inhibitory receptor expressed on a subset of mature T and NK cells. Recently, E-, N-, and R-cadherin have been identified as ligands for KLRG1. Cadherins are a large family of transmembrane or membrane-associated glycoproteins that were thought to only bind specifically to other cadherins to mediate specific cell-to-cell adhesion in a Ca(2+)-dependent manner. The consequences of cadherin KLRG1 molecular interactions are not well characterized. Here, we report that the first 2 extracellular domains of cadherin are sufficient to initiate a KLRG1-dependent signaling. We also demonstrate that KLRG1 engagement inhibits cadherin-dependent cellular adhesion and influences dendritic cell secretion of inflammatory cytokines, thereby exerting immunosuppressive effects. Consistent with this, engagement of cadherin by KLRG1 molecule induces cadherin tyrosine phosphorylation. Therefore, KLRG1/cadherin interaction leads to the generation of a bidirectional signal in which both KLRG1 and cadherin activate downstream signaling cascades simultaneously. Taken together, our results provide novel insights on how KLRG1 and E-cadherin interactions are integrated to differentially regulate not only KLRG1(+) cells, but also E-cadherin-expressing cells, such as dendritic cells.

Alternatively activated macrophages engage in homotypic and heterotypic interactions through IL-4 and polyamine-induced E-cadherin/catenin complexes

Alternatively activated macrophages (AAMs), triggered by interleukin-4 (IL-4) and IL-13, play a modulating role during Th2 cytokine-driven pathologies, but their molecular armament remains poorly characterized. Here, we established E-cadherin (Cdh1) as a selective marker for IL-4/IL-13-exposed mouse and human macrophages, which is STAT6-dependently induced during polarized Th2 responses associated with Taenia crassiceps helminth infections or allergic airway inflammation. The IL-4-dependent, arginase-1/ornithine decarboxylase-mediated production of polyamines is important for maximal Cdh1 induction, unveiling a novel mechanism for IL-4-dependent gene transcription. At the macrophage surface, E-cadherin forms a functional complex with the catenins that accumulates at sites of cell contact. Macrophage-specific deletion of the Cdh1 gene illustrates the implication of E-cadherin in IL-4-driven macrophage fusion and heterotypic interactions with CD103(+) and KLRG1(+) T cells. This study identifies the E-cadherin/catenin complex as a discriminative, partly polyamine-regulated feature of IL-4/IL-13-exposed alternatively activated macrophages that contributes to homotypic and heterotypic cellular interactions.

Structure of natural killer cell receptor KLRG1 bound to E-cadherin reveals basis for MHC-independent missing self recognition

The cytolytic activity of natural killer (NK) cells is regulated by inhibitory receptors that detect the absence of self molecules on target cells. Structural studies of missing self recognition have focused on NK receptors that bind MHC. However, NK cells also possess inhibitory receptors specific for non-MHC ligands, notably cadherins, which are downregulated in metastatic tumors. We determined the structure of killer cell lectin-like receptor G1 (KLRG1) in complex with E-cadherin. KLRG1 mediates missing self recognition by binding to a highly conserved site on classical cadherins, enabling it to monitor expression of several cadherins (E-, N-, and R-) on target cells. This site overlaps the site responsible for cell-cell adhesion but is distinct from the integrin alpha(E)beta(7) binding site. We propose that E-cadherin may coengage KLRG1 and alpha(E)beta(7) and that KLRG1 overcomes its exceptionally weak affinity for cadherins through multipoint attachment to target cells, resulting in inhibitory signaling.

Molecular basis for E-cadherin recognition by killer cell lectin-like receptor G1 (KLRG1)

The killer cell lectin-like receptor G1, KLRG1, is a cell surface receptor expressed on subsets of natural killer (NK) cells and T cells. KLRG1 was recently found to recognize E-cadherin and thus inhibit immune responses by regulating the effector function and the developmental processes of NK and T cells. E-cadherin is expressed on epithelial cells and exhibits Ca(2+)-dependent homophilic interactions that contribute to cell-cell junctions. However, the mechanism underlying the molecular recognition of KLRG1 by E-cadherin remains unclear. Here, we report structural, binding, and functional analyses of this interaction using multiple methods. Surface plasmon resonance demonstrated that KLRG1 binds the E-cadherin N-terminal domains 1 and 2 with low affinity (K(d) approximately 7-12 microm), typical of cell-cell recognition receptors. NMR binding studies showed that only a limited N-terminal region of E-cadherin, comprising the homodimer interface, exhibited spectrum perturbation upon KLRG1 complex formation. It was confirmed by binding studies using a series of E-cadherin mutants. Furthermore, killing assays using KLRG1(+)NK cells and reporter cell assays demonstrated the functional significance of the N-terminal region of E-cadherin. These results suggest that KLRG1 recognizes the N-terminal homodimeric interface of domain 1 of E-cadherin and binds only the monomeric form of E-cadherin to inhibit the immune response. This raises the possibility that KLRG1 detects monomeric E-cadherin at exposed cell surfaces to control the activation threshold of NK and T cells.

KLRG1 signaling induces defective Akt (ser473) phosphorylation and proliferative dysfunction of highly differentiated CD8+ T cells

Highly differentiated CD8+CD28-CD27- T cells have short telomeres, defective telomerase activity, and reduced capacity for proliferation, indicating that they are close to replicative senescence. In addition, these cells express increased levels of the senescence-associated inhibitory receptor KLRG1 and have poor capacity for IL-2 synthesis and defective Akt (ser(473)) phosphorylation after activation. It is not known whether signaling via KLRG1 contributes to any of the attenuated differentiation-related functional changes in CD8+ T cells. To address this, we blocked KLRG1 signaling during T-cell receptor activation using antibodies against its major ligand, E-cadherin. This resulted in a significant enhancement of Akt (ser(473)) phosphorylation and T-cell receptor-induced proliferative activity of CD8+CD28-CD27- T cells. Furthermore, the increase of proliferation was directly linked to the Akt-mediated induction of cyclin D and E and reduction in the cyclin inhibitor p27 expression. In contrast, the reduced telomerase activity in highly differentiated CD8+CD28(-)CD27- T cells was not altered by KLRG1 blockade, indicating the involvement of other mechanisms. This is the first demonstration of a functional role for KLRG1 in primary human CD8+ T cells and highlights that certain functional defects that arise during progressive T-cell differentiation toward replicative senescence are maintained actively by inhibitory receptor signaling.

Interferon-gamma down-regulates NKG2D ligand expression and impairs the NKG2D-mediated cytolysis of MHC class I-deficient melanoma by natural killer cells

NKG2D operates as an activating receptor on natural killer (NK) cells and costimulates the effector function of alphabeta CD8(+) T cells. Ligands of NKG2D, the MHC class I chain-related (MIC) and UL16 binding protein (ULBP) molecules, are expressed on a variety of human tumors, including melanoma. Recent studies in mice demonstrated that NKG2D mediates tumor immune surveillance, suggesting that antitumor immunity in humans could be enhanced by therapeutic manipulation of NKG2D ligand (NKG2DL) expression. However, signals and mechanisms regulating NKG2DL expression still need to be elucidated. Here, we asked whether the proinflammatory cytokine Interferon-gamma (IFN-gamma) affects NKG2DL expression in melanoma. Cell lines, established from MHC class I-negative and -positive melanoma metastases, predominantly expressed MICA and ULBP2 molecules on their surface. Upon IFN-gamma treatment, expression of MICA, in some cases, also of ULBP2 decreased. Besides melanoma, this observation was made also for glioma cells. Down-regulation of NKG2DL surface expression was dependent on the cytokine dose and the duration of treatment, but was neither due to an intracellular retention of the molecules nor to an increased shedding of ligands from the tumor cell surface. Instead, quantitative RT-PCR revealed a decrease of MICA-specific mRNA levels upon IFN-gamma treatment and siRNA experiments pointed to an involvement of STAT-1 in this process. Importantly, IFN-gamma-treated MHC class I-negative melanoma cells were less susceptible to NKG2D-mediated NK cell cytotoxicity. Our study suggests that IFN-gamma, by down-regulating ligand expression, might facilitate escape of MHC class I-negative melanoma cells from NKG2D-mediated killing by NK cells.

Senescent T-lymphocytes are mobilised into the peripheral blood compartment in young and older humans after exhaustive exercise

Senescent T-lymphocytes are antigen-experienced cells that express the killer-cell lectin-like receptor G1 (KLRG1) and/or CD57; fail to clonally expand following further antigenic stimulation and prevail in the resting blood of older adults compared to the young. Physical exercise mobilises T-lymphocytes into the bloodstream and is therefore a model with which to compare age-related phenotypes of blood-resident T-cells with those T-cells entering the blood from peripheral lymphoid compartments. Eight young (Y; Age: 21+/-3 years) and 8 older (O; Age: 56+/-3 years) healthy males completed a maximal treadmill exercise protocol. Blood lymphocytes isolated before, immediately after and 1h after exercise were assessed for cell surface expression of KLRG1, CD57, CD28, CD45RA, CD45RO, CD62L and lymphocyte subset markers using three-colour flow cytometry. Lymphocyte subset numbers (CD3+, CD3+/CD4+, CD3+/CD8 and CD3-/CD56+) increased with exercise (p<0.05) but were not different between Y and O. At rest and immediately after exercise, the percentage of CD3+/CD8+ T-lymphocytes expressing KLRG1 and CD45RO was greater in O than Y, whereas Y had a greater expression of CD45RA and CD62L than O. The percentage of all CD3+/CD8+ and CD3+/CD4+ T-lymphocytes expressing KLRG1 and CD57 increased after exercise, but the magnitude of change was not age-dependent. In conclusion, there is a greater proportion of senescent CD3+/CD8+ T-lymphocytes in the blood of older adults compared to young at rest and immediately after exhaustive exercise, indicating that the greater frequency of KLRG1+/CD8+ T-lymphocytes in older humans is ubiquitous and not localised to the peripheral blood.

Characterization of a subset of antigen-specific human central memory CD4+ T lymphocytes producing effector cytokines

CCR7(+ )central memory (T(CM)) CD4(+) T cells play a central role in long-term immunological memory. Recent reports indicate that a proportion of CD4(+) T(CM) is able to produce effector cytokines. The phenotype and the role of this subset remain unknown. We characterized cytokine-producing human CD4(+) T(CM) specific for cleared protein and persistent viral Ag. Our results demonstrate that the type of Ag stimulation is a major determinant of CD4(+) T(CM) differentiation. CMV-specific T(CM) were significantly more differentiated than protein Ag-specific T(CM) and included higher proportions of IFN-gamma-producing cells. The expression of killer cell lectin-like receptor G1 (KLRG1) by protein Ag- and CMV-specific T(CM) was associated with increased production of effector cytokines. KLRG1(+) T(CM) expressed high levels of CD127, suggesting that they can survive long term under the influence of IL-7. The induction of KLRG1(+) T(CM) may therefore represent an important target of vaccination against pathogens controlled by cellular immune responses.