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LAG‐3 is a member of the immunoglobulin superfamily expressed on activated T cells, but also on other immune cells. It has significant homology to CD4. Both molecules have four extracellular Ig‐like domains with similar structural motifs but the sequence identity between LAG‐3 and CD4 is low. Furthermore, unlike CD4 LAG‐3 restrains T cell responses and antibodies targeting this receptor are emerging drugs in cancer immunotherapy. A combination of LAG‐3 and PD‐1 antibodies has already been approved for the treatment of metastatic melanoma. Despite this success, its biology is still not well understood. Here we summarize the current knowledge on expression, ligands, and function of LAG‐3. We point to the differences between LAG‐3 and other inhibitory immune checkpoints and describe obstacles to study the role of this receptor in T cell activation processes. Finally, we discuss future directions for scientific efforts to come to a more complete understanding of the biology of this eminent immune checkpoint. [ABSTRACT FROM AUTHOR]

The Epstein–Barr virus (EBV) is a ubiquitous gamma‐herpesvirus and a class 1 carcinogen that is closely associated with a series of malignant lymphomas and epithelial cell carcinomas. Although these EBV‐related cancers may exhibit different features in clinical symptoms and anatomical sites, they all have a characteristic immune‐suppressed tumor immune microenvironment (TIME) that is tightly correlated with an abundance of tumor‐infiltrating lymphocytes (TILs) that primarily result from the EBV infection. Overwhelming evidence indicates that an upregulation of immune‐checkpoint molecules is a powerful strategy employed by the EBV to escape immune surveillance. While previous studies have mainly focused on the therapeutic effects of PD‐1 and CTLA‐4 blockades in treating EBV‐associated tumors, several novel inhibitory receptors (e.g., CD47, LAG‐3, TIM‐3, VISTA, and DDR1) have recently been identified as potential targets for treating EBV‐associated malignancies (EBVaMs). This review retrospectively summarizes the biological mechanisms used for immune checkpoint evasion in EBV‐associated tumors. Its purpose is to update our current knowledge concerning the underlying mechanisms by which an immune checkpoint blockade triggers host antitumor immunity against EBVaMs. Additionally, this review may help investigators to more fully understand the correlation between EBV infection and tumor development and subsequently develop novel therapeutic strategies. [ABSTRACT FROM AUTHOR]

The interaction of myeloid-derived suppressor cells (MDSCs) with T cells within G-CSF-mobilized peripheral blood stem cell (PBSC) grafts in patients undergoing autologous or allogeneic hematopoietic stem cell transplantation remains to be elucidated. Through studying allo- and auto-PBSC grafts, we observed grafts containing large numbers of T cells and MDSCs with intergraft variability in their percentage and number. T cells from autologous grafts compared to allografts expressed relative higher percentages of inhibitory receptors PD-1, CTLA-4, TIM-3, LAG-3, TIGIT and BTLA. Autograft T cells had decreased cell proliferation and IFN-γ secretion, which supported the possible presence of T cell exhaustion. On the contrary, graft monocytic MDSCs (M-MDSCs) expressed multiple inhibitory receptor ligands, including PD-L1, CD86, Galectin-9, HVEM and CD155. The expression of inhibitory receptor ligands on M-MDSCs was correlated with their corresponding inhibitory receptors on T cells in the grafts. Isolated M-MDSCs had the ability to suppress T cell proliferation and IFN-γ secretion and/or promote Treg expansion. Blocking the PD-L1-PD-1 signaling pathway partially reversed the functions of M-MDSCs. Taken together, our data indicated that T cells and M-MDSCs in PBSC grafts express complementary inhibitory receptor–ligand pairing, which may impact the quality of immune recovery and clinical outcome post transplantation. [ABSTRACT FROM AUTHOR]

Natural Killer (NK) cells, integral components of the innate immune system, play a crucial role in the protection against intracellular threats. Their cytotoxic power requires that activation is tightly controlled, and in this, they take a unique position within the immune system. Rather than depending on the engagement of a single activating receptor, their activation involves a delicate balance between inhibitory and activating signals mediated through an array of surface molecules. Only when this cumulative balance surpasses a specific threshold do NK cells initiate their activity. Remarkably, the activation threshold of NK cells remains robust even when cells express vastly different repertoires of inhibitory and activating receptors. These threshold values seem to be influenced by NK cell interactions with their environment during development and after release from the bone marrow. Understanding how NK cells integrate this intricate pattern of stimuli is an ongoing area of research, particularly relevant for cellular therapies seeking to harness the anti-cancer potential of these cells by modifying surface receptor expression. In this review, we will explore some of the current dogmas regarding NK cell activation and discuss recent literature addressing advances in our understanding of this field. [ABSTRACT FROM AUTHOR]

Summary: Natural killer (NK) cells play a crucial role in controlling viral infections. The ability to kill infected cells without prior immunization, yet being tolerant to self, healthy cells, depends on the balance of germ-line encoded surface receptors. NK-cell receptors are divided into either activating, leading to activation of NK cell and its cytotoxic and pro-inflammatory activity, or inhibitory, providing tolerance for a target cell. The signals from inhibitory receptors dominate and NK-cell activation requires stimulation of activating receptors. In viral infections, NK-cell interaction with infected cells can result in activation, memory-like NK-cell differentiation, or NK-cell exhaustion, which constitutes one of the viral immune evasion mechanisms. All of these states are associated with the modulation of NK-cell receptor expression. In this review, we summarize the current knowledge of NK-cell receptors and their role in viral infection control, as well as the alterations of their expression observed in acute or chronic infections. We present recently discovered SARS-CoV-2-mediated modulation of NK-cell receptor expression and compare them with other human viral infections. Finally, since modulation of NK-cell receptor activation gives a promising addition to currently used antiviral therapies, we briefly discuss the clinical significance and future perspective of the application of agonists or antagonists of activating and inhibitory receptors, respectively. In sum, our review shows that although much is known about NK-cell receptor biology, a deeper understanding of NK-cell receptors role in viral infections is still needed. This review summarizes recent knowledge on NK cell receptor alterations mediated by viral infections, along with the mechanisms responsible for this modulation. We present recently discovered SARS-CoV-2-mediated modulation of NK cell receptor expression and compare them with other human viral infections. Graphical Abstract [ABSTRACT FROM AUTHOR]

T cell exhaustion occurs mostly in chronic infections, cancers and autoimmune diseases. Continuous antigenic stimulation leads to the generation of exhausted T cells, which is characterized by progressive loss of effector function, continuous high expression of inhibitory receptors, transcription and epigenetic changes, and metabolic disorders. The in-depth study of the specific mechanism of T cell exhaustion is providing new ideas for the immunotherapy of chronic infection, lung cancer and chronic airway inflammatory disease in respiratory diseases. This paper discussed the influencing factors and characteristics of T cell exhaustion and reviewed the current research status of T cell exhaustion and respiratory diseases. [ABSTRACT FROM AUTHOR]

Hemorrhagic fever with renal syndrome (HFRS) is a rodent-borne disease widespread in Europe and Asia. HFRS is caused by negative-sensed single-stranded RNA orthohantaviruses transmitted to humans through inhaling aerosolized excreta of infected rodents. Symptoms of HFRS include acute kidney injury, thrombocytopenia, hemorrhages, and hypotension. The immune response raised against viral antigens plays an important role in the pathogenesis of HFRS. Inhibitory co-receptors are essential in regulating immune responses, mitigating immunopathogenesis, and reducing tissue damage. Our research showed an increased soluble form of inhibitory co-receptors TIM-3, LAG-3, and PD-1 in HFRS patients associated with disease severity. Our study aimed to investigate the impact of HFRS on the concentrations of soluble forms of inhibitory receptors TIM-3, LAG-3, and PD-1 in the patient's serum and the potential correlation with key clinical parameters. Our study aimed to investigate the impact of HFRS on the concentrations of soluble forms of inhibitory receptors TIM-3, LAG-3, and PD-1 in the patient's serum and their possible association with relevant clinical parameters. Using multiplex immunoassay, we found elevated levels of TIM-3, LAG-3, and PD-1 proteins in the serum of HFRS patients. Furthermore, increased levels were associated with creatinine, urea, lactate dehydrogenase concentrations, and platelet count. These findings suggest that these proteins play a role in regulating the immune response and disease progression. [ABSTRACT FROM AUTHOR]

T cell responses must be balanced to ensure adequate protection against malignant transformation and an array of pathogens while also limiting damage to healthy cells and preventing autoimmunity. T cell exhaustion serves as a regulatory mechanism to limit the activity and effector function of T cells undergoing chronic antigen stimulation. Exhausted T cells exhibit poor proliferative potential; high inhibitory receptor expression; altered transcriptome, epigenome, and metabolism; and, most importantly, reduced effector function. While exhaustion helps to restrain damage caused by aberrant T cells in settings of autoimmune disease, it also limits the ability of cells to respond against persistent infection and cancer, leading to disease progression. Here we review the process of T cell exhaustion, detailing the key characteristics and drivers as well as highlighting our current understanding of the underlying transcriptional and epigenetic programming. We also discuss how exhaustion can be targeted to enhance T cell functionality in cancer. [ABSTRACT FROM AUTHOR]

Background: HBV-specific T lymphocytes are pivotal in eliminating the hepatitis B virus (HBV) and regulating intrahepatic inflammatory reactions. Effective T cell responses curtail HBV infection; however, compromised immunity can result in persistent infection. Beyond the acute phase, the continued presence of antigens and inflammation leads to the increased expression of various inhibitory receptors, such as PD-1, CTLA-4, Tim-3, LAG3, 2B4, CD160, BTLA, and TIGIT. This escalates the dysfunction of and diminishes the immune and proliferative abilities of T cells. Methods: In this study, we reviewed English-language literature from PubMed, Web of Science, and Scopus up to 9 July 2023. This paper aims to elucidate the inhibitory effects of these receptors on HBV-specific T lymphocytes and how immune function can be rejuvenated by obstructing the inhibitory receptor signaling pathway in chronic HBV patients. We also summarize the latest insights into related anti-HBV immunotherapy. Result: From 66 reviewed reports, we deduced that immunotherapy targeting inhibitory receptors on T cells is a reliable method to rejuvenate T cell immune responses in chronic HBV patients. However, comprehensive combination therapy strategies are essential for a functional cure. Conclusions: Targeting T cell suppressor receptors and combining immunotherapy with antiviral treatments may offer a promising approach towards achieving a functional cure, urging future research to prioritize effective combination therapeutic strategies for chronic HBV infection. [ABSTRACT FROM AUTHOR]

The interaction of myeloid-derived suppressor cells (MDSCs) with T cells within G-CSF-mobilized peripheral blood stem cell (PBSC) grafts in patients undergoing autologous or allogeneic hematopoietic stem cell transplantation remains to be elucidated. Through studying allo- and auto-PBSC grafts, we observed grafts containing large numbers of T cells and MDSCs with intergraft variability in their percentage and number. T cells from autologous grafts compared to allografts expressed relative higher percentages of inhibitory receptors PD-1, CTLA-4, TIM-3, LAG-3, TIGIT and BTLA. Autograft T cells had decreased cell proliferation and IFN-γ secretion, which supported the possible presence of T cell exhaustion. On the contrary, graft monocytic MDSCs (M-MDSCs) expressed multiple inhibitory receptor ligands, including PD-L1, CD86, Galectin-9, HVEM and CD155. The expression of inhibitory receptor ligands on M-MDSCs was correlated with their corresponding inhibitory receptors on T cells in the grafts. Isolated M-MDSCs had the ability to suppress T cell proliferation and IFN-γ secretion and/or promote Treg expansion. Blocking the PD-L1-PD-1 signaling pathway partially reversed the functions of M-MDSCs. Taken together, our data indicated that T cells and M-MDSCs in PBSC grafts express complementary inhibitory receptor–ligand pairing, which may impact the quality of immune recovery and clinical outcome post transplantation.

Natural Killer (NK) cells, integral components of the innate immune system, play a crucial role in the protection against intracellular threats. Their cytotoxic power requires that activation is tightly controlled, and in this, they take a unique position within the immune system. Rather than depending on the engagement of a single activating receptor, their activation involves a delicate balance between inhibitory and activating signals mediated through an array of surface molecules. Only when this cumulative balance surpasses a specific threshold do NK cells initiate their activity. Remarkably, the activation threshold of NK cells remains robust even when cells express vastly different repertoires of inhibitory and activating receptors. These threshold values seem to be influenced by NK cell interactions with their environment during development and after release from the bone marrow. Understanding how NK cells integrate this intricate pattern of stimuli is an ongoing area of research, particularly relevant for cellular therapies seeking to harness the anti-cancer potential of these cells by modifying surface receptor expression. In this review, we will explore some of the current dogmas regarding NK cell activation and discuss recent literature addressing advances in our understanding of this field.

The mortality rate of cervical cancer is the highest among female malignant tumors and seriously threatens women's lives and health. Persistent high-risk human papillomavirus (HPV) infection is the leading cause of cervical cancer, which provides the basis for immunotherapy. In recent years, owing to progress in targeted therapy and immunotherapy, the survival time of patients with cervical cancer has been significantly extended. However, effective treatments for advanced, recurrent, and metastatic cancers are lacking. "Tumor immunotherapy" has been described as a viable option for tumor therapy but the efficacy of immunotherapy for cervical cancer has only been demonstrated in phase I or II clinical trials. Immune checkpoint inhibitors (ICIs) have shown promising clinical results particularly for treating recurrent and advanced cervical cancer, however, they remain inadequate in some patients. Immune checkpoint is the target of immunotherapy. Therefore, the identification of novel therapeutic targets is essential. In this paper, the structure, expression, function, biological effect of immune inhibitory receptors (IRs) and related clinical studies were reviewed, in order to further explore the application potential of these immune checkpoints and apply them to the future clinical treatment of cervical cancer. [ABSTRACT FROM AUTHOR]

Hemorrhagic fever with renal syndrome (HFRS) is a rodent-borne disease widespread in Europe and Asia. HFRS is caused by negative-sensed single-stranded RNA orthohantaviruses transmitted to humans through inhaling aerosolized excreta of infected rodents. Symptoms of HFRS include acute kidney injury, thrombocytopenia, hemorrhages, and hypotension. The immune response raised against viral antigens plays an important role in the pathogenesis of HFRS. Inhibitory co-receptors are essential in regulating immune responses, mitigating immunopathogenesis, and reducing tissue damage. Our research showed an increased soluble form of inhibitory co-receptors TIM-3, LAG-3, and PD-1 in HFRS patients associated with disease severity. Our study aimed to investigate the impact of HFRS on the concentrations of soluble forms of inhibitory receptors TIM-3, LAG-3, and PD-1 in the patient’s serum and the potential correlation with key clinical parameters. Our study aimed to investigate the impact of HFRS on the concentrations of soluble forms of inhibitory receptors TIM-3, LAG-3, and PD-1 in the patient’s serum and their possible association with relevant clinical parameters. Using multiplex immunoassay, we found elevated levels of TIM-3, LAG-3, and PD-1 proteins in the serum of HFRS patients. Furthermore, increased levels were associated with creatinine, urea, lactate dehydrogenase concentrations, and platelet count. These findings suggest that these proteins play a role in regulating the immune response and disease progression.

ABSTRACTNatural killer/T-cell lymphoma (NKTCL) is an incurable aggressive T-cell lymphoma closely correlated with Epstein‒Barr virus (EBV) infection. Chronic and consistent viral infection induces T-cell exhaustion. Herein, we describe T-cell dysfunction in NKTCL patients for the first time. Peripheral blood mononuclear cells (PBMCs) from age-matched healthy donors (HDs) and NKTCL patients were collected, and lymphocyte distributions, multiple surface inhibitory receptors (IRs), effector cytokine production and cell proliferation were determined by flow cytometry. PBMCs from HDs were cocultured with NKTCL cell lines to verify the clinical findings. IR expression was further assessed in NKTCL tumor biopsies using multiplex immunohistochemistry (mIHC). NKTCL patients have higher frequencies than HDs of inhibitory T regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSCs). T-cell distribution also varies between NKTCL patients and HDs. T cells from NKTCL patients demonstrated higher expression levels of multiple IRs than HDs. Meanwhile, T-cell proliferation and interferon-γ production was significantly reduced in NKTCL patients. More importantly, the number of EBV-specific cytotoxic cells was lower in NTKCL patients, and these cells demonstrated upregulation of multiple IRs and secreted fewer effector cytokines. Interestingly, NKTCL cells caused normal PBMCs to acquire T-cell exhaustion phenotypes and induced generation of Tregs and MDSCs. In line with ex vivo finding, mIHC results showed that CD8+ T cells from NKTCL tumor biopsies expressed much higher level of IRs compared with reactive lymphoid hyperplasia individuals. The immune microenvironment of NKTCL patients exhibited T-cell dysfunction and accumulation of inhibitory cell components, which may contribute to impaired antitumor immunity.

Abstract Background CD6 is one of many cell surface receptors known to regulate signal transduction upon T cell activation. However, whether CD6 mediates costimulatory or inhibitory signals is controversial. When T cells engage with antigen presenting cells (APCs), CD6 interacts with its ligand CD166 at the cell–cell interface while the cytosolic tail assembles a complex signalosome composed of adaptors and effector enzymes, that may either trigger activating signaling cascades, or instead modulate the intensity of signaling. Except for a few cytosolic adaptors that connect different components of the CD6 signalosome, very little is known about the mechanistic effects of the cytosolic effectors that bind CD6. Methods Jurkat model T cells were transfected to express wild-type (WT) CD6, or a cytoplasmic truncation, signaling-disabled mutant, CD6Δcyt. The two resulting cell lines were directly activated by superantigen (sAg)-loaded Raji cells, used as APCs, to assess the net signaling function of CD6. The Jurkat cell lines were further adapted to express a FRET-based unimolecular HRas biosensor that reported the activity of this crucial GTPase at the immunological synapse. Results We show that deletion of the cytosolic tail of CD6 enhances T-cell responses, indicating that CD6 restrains T-cell activation. One component of the CD6-associated inhibitory apparatus was found to be the GTPase activating protein of Ras (RasGAP), that we show to associate with CD6 in a phosphorylation-dependent manner. The FRET HRas biosensor that we developed was demonstrated to be functional and reporting the activation of the T cell lines. This allowed to determine that the presence of the cytosolic tail of CD6 results in the down-regulation of HRas activity at the immunological synapse, implicating this fundamental GTPase as one of the targets inhibited by CD6. Conclusions This study provides the first description of a mechanistic sequence of events underlying the CD6-mediated inhibition of T-cell activation, involving the modulation of the MAPK pathway at several steps, starting with the coupling of RasGAP to the CD6 signalosome, the repression of the activity of Ras, and culminating in the reduction of ERK1/2 phosphorylation and of the expression of the T-cell activation markers CD69 and IL-2R α chain. Video abstract

Natural killer (NK) cells play a crucial role in the anti-tumor transaction through cytolytic activity with the help of proportionate expression of their activating receptors (ARs) and inhibitory receptors (IRs). The proliferation, differentiation, and effector's functions of NK cells were affected and regulated by CD4+CD25+ regulatory T (Treg) cells through the NKG2D receptor expressed on NK cells. It has not yet been established whether Treg cells also affects the expression and functions of other receptors of NK cell. Moreover, the effect of cyclophosphamide (CYP) treatment on the expression and functions of AR and IR receptors of NK cells regulated by Treg cells during cancer progression is not clearly understood. Therefore, we have used the metronomic dose of CYP and anti-CD25 and anti-TGF-β to inhibit the effects of Treg cells in DL-induced tumor microenvironment and analyze the expression of ARs and IRs on NK cells and the FoxP3 level on Treg cells. It was observed that treatment of CYP and blocking antibodies not only affects the functions of tumor-associated NK cells (TANK cells) by modulating the expression of ARs and IRs in DL-induced tumor microenvironment, but also downregulates the functions of Treg cells. The findings of our study supported and suggested that the use of CYP in combination with other therapeutic approaches will effectively reduce tumor growth directly and/or indirectly by modulating the NK cell-mediated immune response of the host. [ABSTRACT FROM AUTHOR]

The hepatitis B virus (HBV) continues to be a leading cause of morbidity and mortality worldwide. In developing countries, HBV is the most common etiology of those liver diseases such as chronic hepatitis B (CHB), acute hepatitis B (AHB), acute-on-chronic liver failure (ACLF), liver cirrhosis (LC), and hepatocellular carcinoma (HCC). CD8+ T cell exhaustion is a condition of T cell malfunction and reduction that plays a crucial role in the progression of HBV infection. This systematic review attempts to evaluate the main inhibitory mechanisms involved in CD8+ T cell exhaustion, in different clinical phases of HBV infection and relation to disease progression. A systematic search in PubMed, Web of Science, and Scopus was performed to identify articles published in English till October 2022. According to the numerous conducted studies, we conclude that CD8+ T cell exhaustion commonly occurs in the tumoral and chronic suppressive environment and CHB and HCC patients; furthermore, this phenomenon is less seen in AHB and ACLF patients. The emergence of surficial inhibitory receptors (IRs) on CD8+ T cells is the leading cause of exhaustion, and programmed cell death protein-1 (PD-1) has much importance among the others. [ABSTRACT FROM AUTHOR]

In response to prolonged stimulation by tumour antigens, T cells gradually become exhausted. There is growing evidence that exhausted T cells not only lose their potent effector functions but also express multiple inhibitory receptors. Checkpoint blockade (CPB) therapy can improve cancer by reactivating exhausted effector cell function, leading to durable clinical responses, but further improvements are needed given the limited number of patients who benefit from treatment, even with autoimmune complications. Here, we suggest, based on recent advances that tumour antigens are the primary culprits of exhaustion, followed by some immune cells and cytokines that also play an accomplice role in the exhaustion process, and we also propose that chronic stress-induced hypoxia and hormones also play an important role in promoting T-cell exhaustion. Understanding the classification of exhausted CD8+ T-cell subpopulations and their functions is important for the effectiveness of immune checkpoint blockade therapies. We mapped the differentiation of T-cell exhausted subpopulations by changes in transcription factors, indicating that T-cell exhaustion is a dynamic developmental process. Finally, we summarized the novel immune checkpoints associated with depletion in recent years and combined them with bioinformatics to construct a web of exhaustion-related immune checkpoints with the aim of finding novel therapeutic targets associated with T-cell exhaustion in malignant tumours, aiming to revive the killing ability of exhausted T cells and restore anti-tumour immunity through combined targeted immunotherapy. [ABSTRACT FROM AUTHOR]

Similar to immune cells, non‐hematopoietic cells recognize microbial and endogenous threats. Their response to these stimuli is dependent on the environmental context. For example, intact intestinal epithelium expresses pattern recognition receptors (PRRs) but should tolerate commensal bacteria, while damaged epithelium should respond promptly to initiate an immune response. This indicates that non‐hematopoietic cells possess mechanisms to sense environmental context and regulate their responses. Inhibitory receptors provide context sensing to immune cells. For instance, they raise the threshold for activation to prevent overzealous immune activation to harmless stimuli. Inhibitory receptors are typically studied on hematopoietic cells, but several of these receptors are expressed on non‐hematopoietic cells. Here, we review evidence for the regulation of non‐hematopoietic cells by inhibitory receptors, focusing on epithelial and endothelial cells. We explain that inhibitory receptors on these cells can sense a wide range of signals, including cell‐cell adhesion, cell‐matrix adhesion, and apoptotic cells. More importantly, they regulate various functions on these cells, including immune activation, proliferation, and migration. In conclusion, we propose that inhibitory receptors provide context to non‐hematopoietic cells by fine tuning their response to endogenous or microbial stimuli. These findings prompt to investigate the functions of inhibitory receptors on non‐hematopoietic cells more systematically. [ABSTRACT FROM AUTHOR]

Background: Liver cancer is the sixth most common cancer worldwide and the third leading cause of cancer-related death. As a chronic liver disease, many studies have shown that the immune response plays a key role in the progression of liver cancer. Chronic hepatitis B virus (HBV) infection is one of the high-risk factors for HCC, accounting for 50%-80% of HCC cases worldwide, and little is known about the immune status of HBV associated hepatocellular carcinoma (HBV-HCC), therefore, we aimed to explore the changes in peripheral immunity in patients with HBV-HCC. Methods: In this study, patients with HBV-HCC (n=26), patients with hepatitis Brelated cirrhosis (HBV-LC) (n=31) and healthy volunteers (n=49) were included. The lymphocytes and their subpopulation phenotypes in peripheral blood were characterized. In addition, we explored the effect of viral replication on peripheral immunity in patients with HCC and analyzed the circulating immunophenotypic characteristics at different stages of HCC with flow cytometry. Results: Firstly, our results showed that the percentages of total αβ T cells in the peripheral blood of HBV-HCC patients was significantly decreased compared to healthy subjects. Secondly, we found that naïve CD4+ T cells in HBV-HCC patients were significantly reduced, terminally differentiated CD8+ T cells, homing memory CD8+ T cells and Th2 cells were increased in peripheral circulation in HBV-HCC patients. Moreover, in the peripheral blood of HBVHCC patients, expression of TIGIT on CD4+ T cells and PD-1 on the surface of Vd 1 T cells was increased. In addition, we found that sustained viral replication resulted in up-regulation of TIM3 expression on CD4+ T cells, and TIM3+ γδ T cells increased in peripheral circulation in patients with advanced HBV-HCC. Frontiers in. Conclusion: Our study showed that circulating lymphocytes in HBV-HCC patients exhibited features of immune exhaustion, especially in HCC patients with persistent viral replication and in patients with intermediate and advanced HBV-HCC, including decreased frequency of T cells and elevated expression of inhibitory receptors including TIGIT and TIM3 on CD4+ T cells and γδ T cells. Meanwhile, our research suggests that the combination of CD3+ T cell and CD8+HLADR+CD38+ T cell may be a potential diagnostic indicator for HBV-HCC. These findings could help us to better understand the immune characteristics of HBV-HCC and explore the immune mechanisms and immunotherapy strategies for HBV-HCC. [ABSTRACT FROM AUTHOR]

Simple Summary: It has been known for decades that immune T cells, especially due to their capacity for powerful antigen-directed cytotoxicity, have become a central focus for engaging the immune system in the fight against cancer. Interest in harnessing T cells for cancer immunotherapy is rapidly growing. The latest clinical research aims to effectively use immune checkpoint inhibitor (ICI) drugs to treat cancer patients. However, T cells can either establish a protective antitumor response, or, in contrast, induce severe dysfunction that promotes disease progression in the majority of chronic infection patients. The contradiction depends, to a large degree, on the interaction between immune T cells and other tumor infiltrating cells or inflammatory cytokines around the tumor microenvironment. This review aims to summarize the current knowledge and regulatory mechanisms of CD8+T cell exhaustion, since reversing T cell exhaustion will definitely become a biomarker of clinical tumor immunotherapy. CD8+T cell exhaustion is a state of T cell dysfunction during chronic infection and tumor progression. Exhausted CD8+T cells are characterized by low effector function, high expression of inhibitory receptors, unique metabolic patterns, and altered transcriptional profiles. Recently, advances in understanding and interfering with the regulatory mechanisms associated with T cell exhaustion in tumor immunotherapy have brought greater attention to the field. Therefore, we emphasize the typical features and related mechanisms of CD8+T cell exhaustion and particularly the potential for its reversal, which has clinical implications for immunotherapy. [ABSTRACT FROM AUTHOR]

The co-expression of inhibitory receptors (IRs) is a hallmark of CD8+ T-cell exhaustion (Tex) in people living with HIV-1 (PLWH). Understanding alterations of IRs expression in PLWH on long-term antiretroviral treatment (ART) remains elusive but is critical to overcoming CD8+ Tex and designing novel HIV-1 cure immunotherapies. To address this, we combine high-dimensional supervised and unsupervised analysis of IRs concomitant with functional markers across the CD8+ T-cell landscape on 24 PLWH over a decade on ART. We define irreversible alterations of IRs co-expression patterns in CD8+ T cells not mitigated by ART and identify negative associations between the frequency of TIGIT+ and TIGIT+ TIM-3+ and CD4+ T-cell levels. Moreover, changes in total, SEB-activated, and HIV-1-specific CD8+ T cells delineate a complex reshaping of memory and effector-like cellular clusters on ART. Indeed, we identify a selective reduction of HIV-1 specific-CD8+ T-cell memory-like clusters sharing TIGIT expression and low CD107a that can be recovered by mAb TIGIT blockade independently of IFNγ and IL-2. Collectively, these data characterize with unprecedented detail the patterns of IRs expression and functions across the CD8+ T-cell landscape and indicate the potential of TIGIT as a target for Tex precision immunotherapies in PLWH at all ART stages.

Systemic lupus erythematosus (SLE) is a severe autoimmune disease that displays considerable heterogeneity not only in its symptoms, but also in its environmental and genetic causes. Studies in SLE patients have revealed that many genetic variants contribute to disease development. However, often its etiology remains unknown. Existing efforts to determine this etiology have focused on SLE in mouse models revealing not only that mutations in specific genes lead to SLE development, but also that epistatic effects of several gene mutations significantly amplify disease manifestation. Genome-wide association studies for SLE have identified loci involved in the two biological processes of immune complex clearance and lymphocyte signaling. Deficiency in an inhibitory receptor expressed on B lymphocytes, Siglec-G, has been shown to trigger SLE development in aging mice, as have mutations in DNA degrading DNase1 and DNase1l3, that are involved in clearance of DNA-containing immune complexes. Here, we analyze the development of SLE-like symptoms in mice deficient in either Siglecg and DNasel or Siglecg and DNase1l3 to evaluate potential epistatic effects of these genes. We found that germinal center B cells and follicular helper T cells were increased in aging Siglecg-/- x Dnase1-/- mice. In contrast, anti-dsDNA antibodies and anti-nuclear antibodies were strongly increased in aging Siglecg-/- x Dnase1l3-/- mice, when compared to single-deficient mice. Histological analysis of the kidneys revealed glomerulonephritis in both Siglecg-/- x Dnase1-/- and Siglecg-/- x Dnase1l3-/- mice, but with a stronger glomerular damage in the latter. Collectively, these findings underscore the impact of the epistatic effects of Siglecg with DNase1 and Dnase1l3 on disease manifestation and highlight the potential combinatory effects of other gene mutations in SLE. [ABSTRACT FROM AUTHOR]

Summary: Neutrophils are the first leukocytes recruited from the circulation in response to invading pathogens or injured cells. To eradicate pathogens and contribute to tissue repair, recruited neutrophils generate and release a host of toxic chemicals that can also damage normal cells. To avoid collateral damage leading to tissue injury and organ dysfunction, molecular mechanisms evolved that tightly control neutrophil response threshold to activating signals, the strength and location of the response, and the timing of response termination. One mechanism of response control is interruption of activating intracellular signaling pathways by the 20 inhibitory receptors expressed by neutrophils. The two inhibitory C‐type lectin receptors expressed by neutrophils, CLEC12A and DCIR, exhibit both common and distinct molecular and functional mechanisms, and they are associated with different diseases. In this review, we use studies on CLEC12A as a model of inhibitory receptor regulation of neutrophil function and participation in disease. Understanding the molecular mechanisms leading to inhibitory receptor specificity offers the possibility of using physiologic control of neutrophil functions as a pharmacologic tool to control inflammatory diseases. [ABSTRACT FROM AUTHOR]

Simple Summary: Boosting effector T cell anti-tumor response remains a challenge, in part owing to the expression of immune checkpoints and their ligands, such as NKG2A and HLA-E. Targeting NKG2A by gene knockout or blocking antibodies improves the cytotoxicity of Vδ2 T cells, a specific subset of human unconventional γδ T lymphocytes. Thus, a suitable selection of NKG2A+ or NKG2A− Vδ2 T cells for expansion or engineering could help to narrow the Vδ2 T cell population according to the expression of HLA-E on tumor cells. With this emerging knowledge, approaches to target NKG2A in Vδ2 T cells might be a promising step forward to boosting Vδ2 T cell-based cancer immunotherapies. Immune regulation has revolutionized cancer treatment with the introduction of T-cell-targeted immune checkpoint inhibitors (ICIs). This successful immunotherapy has led to a more complete view of cancer that now considers not only the cancer cells to be targeted and destroyed but also the immune environment of the cancer cells. Current challenges associated with the enhancement of ICI effects are increasing the fraction of responding patients through personalized combinations of multiple ICIs and overcoming acquired resistance. This requires a complete overview of the anti-tumor immune response, which depends on a complex interplay between innate and adaptive immune cells with the tumor microenvironment. The NKG2A was revealed to be a key immune checkpoint for both Natural Killer (NK) cells and T cells. Monalizumab, a humanized anti-NKG2A antibody, enhances NK cell activity against various tumor cells and rescues CD8 αβ T cell function in combination with PD-1/PD-L1 blockade. In this review, we discuss the potential for targeting NKG2A expressed on tumor-sensing human γδ T cells, mostly on the specific Vδ2 T cell subset, in order to emphasize its importance and potential in the development of new ICI-based therapeutic approaches. [ABSTRACT FROM AUTHOR]

Natural killer/T-cell lymphoma (NKTCL) is an incurable aggressive T-cell lymphoma closely correlated with Epstein‒Barr virus (EBV) infection. Chronic and consistent viral infection induces T-cell exhaustion. Herein, we describe T-cell dysfunction in NKTCL patients for the first time. Peripheral blood mononuclear cells (PBMCs) from age-matched healthy donors (HDs) and NKTCL patients were collected, and lymphocyte distributions, multiple surface inhibitory receptors (IRs), effector cytokine production and cell proliferation were determined by flow cytometry. PBMCs from HDs were cocultured with NKTCL cell lines to verify the clinical findings. IR expression was further assessed in NKTCL tumor biopsies using multiplex immunohistochemistry (mIHC). NKTCL patients have higher frequencies than HDs of inhibitory T regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSCs). T-cell distribution also varies between NKTCL patients and HDs. T cells from NKTCL patients demonstrated higher expression levels of multiple IRs than HDs. Meanwhile, T-cell proliferation and interferon-γ production was significantly reduced in NKTCL patients. More importantly, the number of EBV-specific cytotoxic cells was lower in NTKCL patients, and these cells demonstrated upregulation of multiple IRs and secreted fewer effector cytokines. Interestingly, NKTCL cells caused normal PBMCs to acquire T-cell exhaustion phenotypes and induced generation of Tregs and MDSCs. In line with ex vivo finding, mIHC results showed that CD8+ T cells from NKTCL tumor biopsies expressed much higher level of IRs compared with reactive lymphoid hyperplasia individuals. The immune microenvironment of NKTCL patients exhibited T-cell dysfunction and accumulation of inhibitory cell components, which may contribute to impaired antitumor immunity. [ABSTRACT FROM AUTHOR]

CD8+ T cells play a crucial role in anti‐tumour immunity, but they often undergo exhaustion, which affects the anti‐tumour activity of CD8+ T cells. The effect and mechanism of exhausted CD8+ T cells have become the focus of anti‐tumour immunity research. Recently, a large number of studies have confirmed that long‐term antigen exposure can induce exhaustion. Cytokines previously have identified their effects (such as IL‐2 and IL‐10) may play a dual role in the exhaustion process of CD8+ T cells, suggesting a new mechanism of inducing exhaustion. This review just focuses our current understanding of the biology of exhausted CD8+ T cells, including differentiation pathways, cellular characteristics and signalling pathways involved in inducing exhaustion, and summarizes how these can be applied to tumour immunotherapy. [ABSTRACT FROM AUTHOR]

'Exhaustion' is a term used to describe a state of native and redirected T-cell hypo-responsiveness resulting from persistent antigen exposure during chronic viral infections or cancer. Although a well-established phenotype across mice and humans, exhaustion at the molecular level remains poorly defined and inconsistent across the literature. This is, in part, due to an overreliance on surface receptors to define these cells and explain exhaustive behaviours, an incomplete understanding of how exhaustion arises, and a lack of clarity over whether exhaustion is the same across contexts, e.g. chronic viral infections versus cancer. With the development of systems-based genetic approaches such as single-cell RNA-seq and CRISPR screens applied to in vivo data, we are moving closer to a consensus view of exhaustion, although understanding how it arises remains challenging given the difficulty in manipulating the in vivo setting. Accordingly, producing and studying exhausted T-cells ex vivo are burgeoning, allowing experiments to be conducted at scale up and with high throughput. Here, we first review what is currently known about T-cell exhaustion and how it's being studied. We then discuss how improvements in their method of isolation/production and examining the impact of different microenvironmental signals and cell interactions have now become an active area of research. Finally, we discuss what the future holds for the analysis of this physiological condition and, given the diversity of ways in which exhausted cells are now being generated, propose the adoption of a unified approach to clearly defining exhaustion using a set of metabolic-, epigenetic-, transcriptional-, and activation-based phenotypic markers, that we call 'M.E.T.A'. [ABSTRACT FROM AUTHOR]

Systemic lupus erythematosus (SLE) is a severe autoimmune disease that displays considerable heterogeneity not only in its symptoms, but also in its environmental and genetic causes. Studies in SLE patients have revealed that many genetic variants contribute to disease development. However, often its etiology remains unknown. Existing efforts to determine this etiology have focused on SLE in mouse models revealing not only that mutations in specific genes lead to SLE development, but also that epistatic effects of several gene mutations significantly amplify disease manifestation. Genome-wide association studies for SLE have identified loci involved in the two biological processes of immune complex clearance and lymphocyte signaling. Deficiency in an inhibitory receptor expressed on B lymphocytes, Siglec-G, has been shown to trigger SLE development in aging mice, as have mutations in DNA degrading DNase1 and DNase1l3, that are involved in clearance of DNA-containing immune complexes. Here, we analyze the development of SLE-like symptoms in mice deficient in either Siglecg and DNase1 or Siglecg and DNase1l3 to evaluate potential epistatic effects of these genes. We found that germinal center B cells and follicular helper T cells were increased in aging Siglecg-/- x Dnase1-/- mice. In contrast, anti-dsDNA antibodies and anti-nuclear antibodies were strongly increased in aging Siglecg-/- x Dnase1l3-/- mice, when compared to single-deficient mice. Histological analysis of the kidneys revealed glomerulonephritis in both Siglecg-/- x Dnase1-/- and Siglecg-/- x Dnase1l3-/- mice, but with a stronger glomerular damage in the latter. Collectively, these findings underscore the impact of the epistatic effects of Siglecg with DNase1 and Dnase1l3 on disease manifestation and highlight the potential combinatory effects of other gene mutations in SLE.

Background: CD6 is one of many cell surface receptors known to regulate signal transduction upon T cell activation. However, whether CD6 mediates costimulatory or inhibitory signals is controversial. When T cells engage with antigen presenting cells (APCs), CD6 interacts with its ligand CD166 at the cell–cell interface while the cytosolic tail assembles a complex signalosome composed of adaptors and effector enzymes, that may either trigger activating signaling cascades, or instead modulate the intensity of signaling. Except for a few cytosolic adaptors that connect different components of the CD6 signalosome, very little is known about the mechanistic effects of the cytosolic effectors that bind CD6. Methods: Jurkat model T cells were transfected to express wild-type (WT) CD6, or a cytoplasmic truncation, signaling-disabled mutant, CD6Δcyt. The two resulting cell lines were directly activated by superantigen (sAg)-loaded Raji cells, used as APCs, to assess the net signaling function of CD6. The Jurkat cell lines were further adapted to express a FRET-based unimolecular HRas biosensor that reported the activity of this crucial GTPase at the immunological synapse. Results: We show that deletion of the cytosolic tail of CD6 enhances T-cell responses, indicating that CD6 restrains T-cell activation. One component of the CD6-associated inhibitory apparatus was found to be the GTPase activating protein of Ras (RasGAP), that we show to associate with CD6 in a phosphorylation-dependent manner. The FRET HRas biosensor that we developed was demonstrated to be functional and reporting the activation of the T cell lines. This allowed to determine that the presence of the cytosolic tail of CD6 results in the down-regulation of HRas activity at the immunological synapse, implicating this fundamental GTPase as one of the targets inhibited by CD6. Conclusions: This study provides the first description of a mechanistic sequence of events underlying the CD6-mediated inhibition of T-cell activation, involving the modulation of the MAPK pathway at several steps, starting with the coupling of RasGAP to the CD6 signalosome, the repression of the activity of Ras, and culminating in the reduction of ERK1/2 phosphorylation and of the expression of the T-cell activation markers CD69 and IL-2R α chain. 9f2SuWv7Lo8KDpPx-hd1D5 Video abstract [ABSTRACT FROM AUTHOR]

Abstract Background Recently, allogeneic natural killer (NK) cells have gained considerable attention as promising immunotherapeutic tools due to their unique biological functions and characteristics. Although many NK expansion strategies have been reported previously, a deeper understanding of cryopreserved allogeneic NK cells is needed for specific therapeutic approaches. Methods We isolated CD3−CD56+ primary natural killer (pNK) cells from healthy donors and expanded them ex vivo using a GMP-compliant method without any feeder to generate large volumes of therapeutic pNK cells and cryopreserved stocks. After validation for high purity and activating phenotypes, we performed RNA sequencing of the expanded and cryopreserved pNK cells. The pNK cells were used against various cancer cell lines in 7-AAD/CFSE cytotoxicity assay. For in vivo efficacy study, NSG mice bearing subcutaneous cisplatin-resistant A2780cis xenografts were treated with our pNK cells or cisplatin. Antitumor efficacy was assessed by measuring tumor volume and weight. Results Compared to the pNK cells before expansion, pNK cells after expansion showed 2855 upregulated genes, including genes related to NK cell activation, cytotoxicity, chemokines, anti-apoptosis, and proliferation. Additionally, the pNK cells showed potent cytolytic activity against various cancer cell lines. Interestingly, our activated pNK cells showed a marked increase in NKp44 (1064-fold), CD40L (12,018-fold), and CCR5 (49-fold), and did not express the programmed cell death protein 1(PD-1). We also demonstrated the in vitro and in vivo efficacies of pNK cells against cisplatin-resistant A2780cis ovarian cancer cells having a high programmed death-ligand 1(PD-L1) and low HLA-C expression. Conclusions Taken together, our study provides the first comprehensive genome wide analysis of ex vivo-expanded cryopreserved pNK cells. It also indicates the potential use of expanded and cryopreserved pNK cells as a highly promising immunotherapy for anti-cancer drug resistant patients.

Non-invasive, immuno-dynamic, biomarkers positioned in cancer patient’s blood milieu with immuno-oncological applications are rare. We recently established a “first-in-class” serum functional immunodynamics status (sFIS) assay, wherein in vitro assessment of serum-induced myeloid NFkB and/or interferon (IFN) response-signaling can be performed to “mimic” in situ patient’s serum immune-biology. This modality has clear implications for anticipating patient prognosis and immunotherapy-relevant stratification.

Natural Killer (NK) cells are known for their high intrinsic cytotoxic capacity, and the possibility to be applied as ‘off-the-shelf’ product makes them highly attractive for cell-based immunotherapies. In patients with multiple myeloma (MM), an elevated number of NK cells has been correlated with higher overall-survival rate. However, NK cell function can be impaired by upregulation of inhibitory receptors, such as the immune checkpoint NKG2A. Here, we developed a CRISPR-Cas9-based gene editing protocol that allowed us to knockout about 80% of the NKG2A-encoding killer cell lectin like receptor C1 (KLRC1) locus in primary NK cells. In-depth phenotypic analysis confirmed significant reduction in NKG2A protein expression. Importantly, the KLRC1-edited NK cells showed significantly increased cytotoxicity against primary MM cells isolated from a small cohort of patients, and maintained the NK cell-specific cytokine production. In conclusion, KLRC1-editing in primary NK cells has the prospect of overcoming immune checkpoint inhibition in clinical applications.

Citrullination of proteins plays an important role in protein function and it has recently become clear that citrullinated proteins play a role in immune responses. In this study we examined how citrullinated collagen, an extracellular matrix protein, affects T-cell function during the development of autoimmune arthritis. Using an HLA-DR1 transgenic mouse model of rheumatoid arthritis, mice were treated intraperitoneally with either native type I collagen (CI), citrullinated CI (cit-CI), or phosphate buffered saline (PBS) prior to induction of autoimmune arthritis. While the mice given native CI had significantly less severe arthritis than controls administered PBS, mice receiving cit-CI had no decrease in the severity of autoimmune arthritis. Using Jurkat cells expressing the inhibitory receptor leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1), Western blot analysis indicated that while CI and cit-CI bound to LAIR-1 with similar affinity, only CI induced phosphorylation of the LAIR ITIM tyrosines; cit-CI was ineffective. These data suggest that cit-CI acts as an antagonist of LAIR-1 signaling, and that the severity of autoimmune arthritis can effectively be altered by targeting T cells with citrullinated collagen. [ABSTRACT FROM AUTHOR]

• NB-T cells are more subjected to exhaustion conversion upon restimulation. • TOX is involved in the regulation of NB-T cells exhaustion at multiple levels. • DNA methylation program of the TOX gene may be involved in the remodeling of NB-T cells exhaustion by regulating TOX expression. T-cell exhaustion is one of the key reasons for attenuated T-cell cytotoxicity against tumours. At both the expression and epigenetic levels, a number of genes, including the transcription factor TOX, are believed to be implicated in regulating T-cell exhaustion. In the present study, we found that in NB patients, the ratio of exhausted T cells, featuring upregulated PD-1 and Tim-3, was increased. Meanwhile, the expression of inhibitory surface receptors, including Lag-3, CD160, VISTA and KLRG1, was also increased, but this was accompanied by a reduced ability to release the effector molecules IL-2, IFN-γ, TNF-α and Granzyme B in CD3+ T cells from NB patients. It is noteworthy that NB-derived memory T cells (Tm) showed more obvious exhausted characteristics than other T cells. Moreover, the T cells from NB patients possessed a higher potential for exhaustion conversion upon in vitro TCR stimulation in our time-course culture experiment. In NB patients, T-cell exhaustion was demonstrated to correlate with the elevated expression of TOX in freshly sorted CD3+ T cells as well as in anti-CD3 stimulated PBMCs. Most importantly, our data supported the idea that the hypomethylation of the TOX promoter may be one of the initiators that regulates TOX expression and enables TOX to play a crucial role in T-cell exhaustion reprogramming in NB patients. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells are important effectors of the innate immune system and participate in the first line of defense against infections and tumors. Prior to being functional, these lymphocytes must be educated or licensed through interactions of their major histocompatibility complex class I molecules with self-specific inhibitory receptors that recognize them. In the absence of such contacts, caused by either the lack of expression of the inhibitory receptors or a very low level of major histocompatibility complex class I (MHC class I) proteins, NK cells are hypo-reactive at baseline (ex vivo). After stimulation (assessed through plate-bound antibodies against activating receptors or culture in the presence of cytokines such as interleukin (IL)-2 or IL-15) however, they can become cytotoxic and produce cytokines. This is particularly the case in transporter associated with antigen processing (TAP)-deficient mice, which we investigated in the present study. Transporter associated with antigen processing transports endogenous peptides from the cytosol to the endoplasmic reticulum, where they are loaded on nascent MHC class I molecules, which then become stable and expressed at the cell surface. Consequently, TAP-KO mice have very low levels of MHC class I expression. We present a study about phenotypic and functional aspects of NK cells in two mouse strains, C57BL/6 wildtype and TAP1-KO in spleen and lung. We observed that in both types of mice, on the same genetic background, the initial pattern of education, conferred to the cells via the inhibitory receptors Ly49C/I and NKG2A, was maintained even after a strong stimulation by the cytokines interleukin-2, interleukin-12, interleukin-15 and interleukin-18. Furthermore, the percentages of activated NK cells expressing Ly49C/I and Ly49I were strongly downmodulated under these conditions. We completed our investigations with phenotypic studies of NK cells from these mice. [ABSTRACT FROM AUTHOR]

Natural killer cells are innate lymphocytes with the ability to lyse tumour cells depending on the balance of their activating and inhibiting receptors. Growing numbers of clinical trials show promising results of NK cell-based immunotherapies. Unlike T cells, NK cells can lyse tumour cells independent of antigen presentation, based simply on their activation and inhibition receptors. Various strategies to improve NK cell-based therapies are being developed, all with one goal: to shift the balance to activation. In this review, we discuss the current understanding of ways NK cells can lyse tumour cells and all the inhibitory signals stopping their cytotoxic potential. [ABSTRACT FROM AUTHOR]

Inhibitory receptors have been extensively described for their importance in regulating immune responses in chronic infections and cancers. Blocking the function of inhibitory receptors such as PD-1, CTLA-4, 2B4, Tim-3, and LAG-3 has shown promise for augmenting CD8 T cell activity and boosting pathogen-specific immunity. However, the prevalence of inhibitory receptors on CD4 T cells and their relative influence on CD4 T cell functionality in chronic HIV infection remains poorly described. We therefore determined and compared inhibitory receptor expression patterns of 2B4, CTLA-4, LAG-3, PD-1, and Tim-3 on virus-specific CD4 and CD8 T cells in relation to their functional T cell profile. In chronic HIV infection, inhibitory receptor distribution differed markedly between cytokine-producing T cell subsets with, gamma interferon (IFN-γ)- and tumor necrosis factor alpha (TNF-α)-producing cells displaying the highest and lowest prevalence of inhibitory receptors, respectively. Blockade of inhibitory receptors differentially affected cytokine production by cells in response to staphylococcal enterotoxin B stimulation. CTLA-4 blockade increased IFN-γ and CD40L production, while PD-1 blockade strongly augmented IFN-γ, interleukin-2 (IL-2), and TNF-α production. In a Friend retrovirus infection model, CTLA-4 blockade in particular was able to improve control of viral replication. Together, these results show that inhibitory receptor distribution on HIV-specific CD4 T cells varies markedly with respect to the functional subset of CD4 T cells being analyzed. Furthermore, the differential effects of receptor blockade suggest novel methods of immune response modulation, which could be important in the context of HIV vaccination or therapeutic strategies.IMPORTANCE Inhibitory receptors are important for limiting damage by the immune system during acute infections. In chronic infections, however, their expression limits immune system responsiveness. Studies have shown that blocking inhibitory receptors augments CD8 T cell functionality in HIV infection, but their influence on CD4 T cells remains unclear. We assessed the expression of inhibitory receptors on HIV-specific CD4 T cells and their relationship with T cell functionality. We uncovered differences in inhibitory receptor expression depending on the CD4 T cell function. We also found differences in functionality of CD4 T cells following blocking of different inhibitory receptors, and we confirmed our results in a Friend virus retroviral model of infection in mice. Our results show that inhibitory receptor expression on CD4 T cells is linked to CD4 T cell functionality and could be sculpted by blockade of specific inhibitory receptors. These data reveal exciting possibilities for the development of novel treatments and immunotherapeutics.

Natural killer (NK) cells are important effectors of the innate immune system and participate in the first line of defense against infections and tumors. Prior to being functional, these lymphocytes must be educated or licensed through interactions of their major histocompatibility complex class I molecules with self-specific inhibitory receptors that recognize them. In the absence of such contacts, caused by either the lack of expression of the inhibitory receptors or a very low level of major histocompatibility complex class I (MHC class I) proteins, NK cells are hypo-reactive at baseline (ex vivo). After stimulation (assessed through plate-bound antibodies against activating receptors or culture in the presence of cytokines such as interleukin (IL)-2 or IL-15) however, they can become cytotoxic and produce cytokines. This is particularly the case in transporter associated with antigen processing (TAP)-deficient mice, which we investigated in the present study. Transporter associated with antigen processing transports endogenous peptides from the cytosol to the endoplasmic reticulum, where they are loaded on nascent MHC class I molecules, which then become stable and expressed at the cell surface. Consequently, TAP-KO mice have very low levels of MHC class I expression. We present a study about phenotypic and functional aspects of NK cells in two mouse strains, C57BL/6 wildtype and TAP1-KO in spleen and lung. We observed that in both types of mice, on the same genetic background, the initial pattern of education, conferred to the cells via the inhibitory receptors Ly49C/I and NKG2A, was maintained even after a strong stimulation by the cytokines interleukin-2, interleukin-12, interleukin-15 and interleukin-18. Furthermore, the percentages of activated NK cells expressing Ly49C/I and Ly49I were strongly down-modulated under these conditions. We completed our investigations with phenotypic studies of NK cells from these mice.

Relatlimab (rela; anti-LAG-3) plus nivolumab (nivo; anti-PD-1) is safe and effective for treatment of advanced melanoma. We designed a trial (NCT03743766) where advanced melanoma patients received rela, nivo, or rela+nivo to interrogate the immunologic mechanisms of rela+nivo. Analysis of biospecimens from this ongoing trial demonstrated that rela+nivo led to enhanced capacity for CD8+ T cell receptor signaling and altered CD8+ T cell differentiation, leading to heightened cytotoxicity despite the retention of an exhaustion profile. Co-expression of cytotoxic and exhaustion signatures was driven by PRDM1, BATF, ETV7 , and TOX. Effector function was upregulated in clonally expanded CD8+ T cells that emerged after rela+nivo. A rela+nivo intratumoral CD8+ T cell signature was associated with a favorable prognosis. This intratumoral rela+nivo signature was validated in peripheral blood as an elevated frequency of CD38+TIM3+CD8+ T cells. Overall, we demonstrated that cytotoxicity can be enhanced despite the retention of exhaustion signatures, which will inform future therapeutic strategies. [Display omitted] • Rela+nivo enhances response to T cell receptor and IFN-γ signaling in CD8+ T cells • Cytotoxic and exhaustion gene modules are co-expressed following rela+nivo • PRDM1, BATF, ETV7 , and TOX drive rela+nivo cytotoxicity and exhaustion profile • Cytotoxicity and exhaustion profile is associated with clinical benefit Analysis of biospecimens from a phase 2 study of advanced melanoma shows that combined blockade of LAG-3 and PD-1 modulates the differentiation of CD8+ T cells by enhancing responses to T cell receptor and IFN-γ signaling, leading to enhanced effector functions despite the retention of an exhaustion profile. [ABSTRACT FROM AUTHOR]

CD8+T cell exhaustion is a state of T cell dysfunction during chronic infection and tumor progression. Exhausted CD8+T cells are characterized by low effector function, high expression of inhibitory receptors, unique metabolic patterns, and altered transcriptional profiles. Recently, advances in understanding and interfering with the regulatory mechanisms associated with T cell exhaustion in tumor immunotherapy have brought greater attention to the field. Therefore, we emphasize the typical features and related mechanisms of CD8+T cell exhaustion and particularly the potential for its reversal, which has clinical implications for immunotherapy.

Immune homeostasis is achieved by balancing the activating and inhibitory signal transduction pathways mediated via cell surface receptors. Activation allows the host to mount an immune response to endogenous and exogenous antigens; suppressive modulation via inhibitory signaling protects the host from excessive inflammatory damage. The checkpoint regulation of myeloid cells during immune homeostasis raised their profile as important cellular targets for treating allergy, cancer and infectious disease. This review focuses on the structure and signaling of inhibitory receptors on myeloid cells, with particular attention placed on how the interplay between viruses and these receptors regulates antiviral immunity. The status of targeting inhibitory receptors on myeloid cells as a new therapeutic approach for antiviral treatment will be analyzed. [ABSTRACT FROM AUTHOR]

Objectives: This study aimed to clarify the dynamic changes of exhaustion features in T cells during oral carcinogenesis. Materials and Methods: Mice were randomly divided into 4NQO group and control group. The exhaustion features of CD4+ and CD8+ T cells of both groups were detected by flow cytometry. Furthermore, multiplex immunohistochemistry was used to evaluate the expression of inhibitory receptors in human normal, dysplastic, and carcinogenesis tissues. Finally, anti‐PD‐1 antibody treatment was performed at the early premalignant phase of oral carcinogenesis. Results: The proportion of naive T cells in 4NQO group was lower than those in control group, while the proportion of effector memory T cells was higher in 4NQO group. The expression of inhibitory receptors on CD4+ and CD8+ T cells increased gradually during carcinogenesis. In contrast, the secretion of cytokines by CD4+ and CD8+ T cells decreased gradually with the progression stage. Strikingly, those changes occurred before the onset of oral carcinogenesis. The expression of inhibitory receptors on T cells increased gradually as the human tissues progressed from normal, dysplasia to carcinoma. Interestingly, PD‐1 blockade at the early premalignant phase could reverse carcinogenesis progression by restoring T cell function. Conclusions: T‐cell dysfunction was established at the early premalignant phase of oral carcinogenesis; PD‐1 blockade at the early premalignant phase can effectively reverse T‐cell exhaustion features and then prevent carcinogenesis progression. [ABSTRACT FROM AUTHOR]

Chronic viruses and cancers thwart immune responses in humans by inducing T cell dysfunction. Using a murine chronic virus that models human infections, we investigated the function of the adhesion molecule, P-selectin glycoprotein ligand-1 (PSGL-1), that is upregulated on responding T cells. PSGL-1-deficient mice cleared the virus due to increased intrinsic survival of multifunctional effector T cells that had downregulated PD-1 as well as other inhibitory receptors. Notably, this response resulted in CD4(+)-T-cell-dependent immunopathology. Mechanistically, PSGL-1 ligation on exhausted CD8(+) T cells inhibited T cell receptor (TCR) and interleukin-2 (IL-2) signaling and upregulated PD-1, leading to diminished survival with TCR stimulation. In models of melanoma cancer in which T cell dysfunction occurs, PSGL-1 deficiency led to PD-1 downregulation, improved T cell responses, and tumor control. Thus, PSGL-1 plays a fundamental role in balancing viral control and immunopathology and also functions to regulate T cell responses in the tumor microenvironment.

The pathophysiological mechanism underlying Graves' disease (GD) remains incompletely understood. Inhibitory receptors on B cells are critical for humoral immunity, which plays a key role in GD pathogenesis. This study aimed to investigate B cell subsets distribution and inhibitory receptor expression on these subsets in GD patients. Peripheral blood was drawn from 41 healthy controls and 46 GD patients (21 patients with moderate GD, 25 patients with severe GD). B cell subset distribution and CD22, CD32b and CD72 expression on B cells were analyzed by flow cytometry. Serum cytokines were examined by enzyme-linked immunosorbent assay (ELISA). Compared with healthy controls, the naïve B cell percentage was increased, while the preswitched memory and conventional memory B cell percentages were decreased. The inhibitory receptors expression, especially CD32b, on B cell subsets was significantly decreased in patients with GD. In addition, the inhibitory receptors expression on B cell subsets from severe GD patients exhibited a decreasing trend compared with those from moderate GD patients. These results suggest that abnormal B cell subset distribution occurs in GD. Impaired inhibitory receptors, in particular CD32b, play a crucial role in GD pathogenesis and might be a therapeutic target to rebuild self-immune tolerance in GD. [ABSTRACT FROM AUTHOR]

Overwhelming activation of T cells in acute malaria is associated with severe outcomes. Thus, counter‐regulation by anti‐inflammatory mechanisms is indispensable for an optimal resolution of disease. Using Plasmodium berghei ANKA (PbA) infection of C57BL/6 mice, we performed a comprehensive analysis of co‐inhibitory molecules expressed on CD4+ and CD8+ T cells using an unbiased cluster analysis approach. We identified similar T cell clusters co‐expressing several co‐inhibitory molecules like programmed cell death protein 1 (PD‐1) and lymphocyte activation gene 3 (LAG‐3) in the CD4+ and the CD8+ T cell compartment. Interestingly, despite expressing co‐inhibitory molecules, which are associated with T cell exhaustion in chronic settings, these T cells were more functional compared to activated T cells that were negative for co‐inhibitory molecules. However, T cells expressing high levels of PD‐1 and LAG‐3 also conferred suppressive capacity and thus resembled type I regulatory T cells. To our knowledge, this is the first description of malaria‐induced CD8+ T cells with suppressive capacity. Importantly, we found an induction of T cells with a similar co‐inhibitory rich phenotype in Plasmodium falciparum‐infected patients. In conclusion, we demonstrate that malaria‐induced T cells expressing co‐inhibitory molecules are not exhausted, but acquire additional suppressive capacity, which might represent an immune regulatory pathway to prevent further activation of T cells during acute malaria. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells represent a subset of CD3- CD7+ CD56+/dim lymphocytes with cytotoxic and suppressor activity against virus-infected cells and cancer cells. The overall potential of NK cells has brought them to the spotlight of targeted immunotherapy in solid and hematological malignancies, including multiple myeloma (MM). Nonetheless, NK cells are subjected to a variety of cancer defense mechanisms, leading to impaired maturation, chemotaxis, target recognition, and killing. This review aims to summarize the available and most current knowledge about cancer-related impairment of NK cell function occurring in MM. [ABSTRACT FROM AUTHOR]

Natural Killer (NK) cells are known for their high intrinsic cytotoxic capacity, and the possibility to be applied as 'off-the-shelf' product makes them highly attractive for cell-based immunotherapies. In patients with multiple myeloma (MM), an elevated number of NK cells has been correlated with higher overall-survival rate. However, NK cell function can be impaired by upregulation of inhibitory receptors, such as the immune checkpoint NKG2A. Here, we developed a CRISPR-Cas9-based gene editing protocol that allowed us to knockout about 80% of the NKG2A-encoding killer cell lectin like receptor C1 (KLRC1) locus in primary NK cells. In-depth phenotypic analysis confirmed significant reduction in NKG2A protein expression. Importantly, the KLRC1-edited NK cells showed significantly increased cytotoxicity against primary MM cells isolated from a small cohort of patients, and maintained the NK cell-specific cytokine production. In conclusion, KLRC1-editing in primary NK cells has the prospect of overcoming immune checkpoint inhibition in clinical applications. [ABSTRACT FROM AUTHOR]