The diversity of costimulatory and inhibitory receptor pathways and the regulation of antiviral T cell responses

Effects of co-infection with Clonorchis sinensis on T cell exhaustion levels in patients with chronic hepatitis B

To investigate the effects of co-infection with Clonorchis sinensis (C. sinensis) on T cell exhaustion levels in patients with chronic hepatitis B, we enrolled clinical cases in this study, including the patients with concomitant C. sinensis and HBV infection. In this study, we detected inhibitory receptors and cytokine expression in circulating CD4+ and CD8+ T cells by flow cytometry. PD-1 and TIM-3 expression levels were significantly higher on CD4+ T and CD8+ T cells from co-infected patients than on those from the HBV patients. In addition, CD4+ T cells and CD8+ T cells function were significantly inhibited by C. sinensis and HBV co-infection compared with HBV single infection, secreting lower levels of Interferon gamma (IFN-γ), Interleukin-2 (IL-2), and TNF-α. Our current results suggested that C. sinensis co-infection could exacerbate T cell exhaustion in patients with chronic hepatitis B. PD-1 and TIM-3 could be novel biomarkers for T cell exhaustion in patients with Clonorchis sinensis and chronic hepatitis B co-infection. Furthermore, it may be one possible reason for the weaker response to antiviral therapies and the chronicity of HBV infection in co-infected patients. We must realize the importance of C. sinensis treatment for HBV-infected patients. It might provide useful information for clinical doctors to choose the right treatment plans.

Exploring the immune microenvironment of osteosarcoma through T cell exhaustion-associated gene expression: a study on prognosis prediction

Background

Osteosarcoma is a highly aggressive type of bone cancer with a poor prognosis. In the tumor immune microenvironment, T-cell exhaustion can occur due to various factors, leading to reduced tumor-killing ability. The purpose of this study was to construct a prognostic model based on T-cell exhaustion-associated genes in osteosarcoma.

Methods

Patient data for osteosarcoma were retrieved from the TARGET and GEO databases. Consensus clustering was employed to identify two novel molecular subgroups. The dissimilarities in the tumor immune microenvironment between these subgroups were evaluated using the "xCell" algorithm. GO and KEGG analyses were conducted to elucidate the underlying mechanisms of gene expression. Predictive risk models were constructed using the least absolute shrinkage and selection operator algorithm and Cox regression analysis. To validate the prognostic significance of the risk gene expression model at the protein level, immunohistochemistry assays were performed on osteosarcoma patient samples. Subsequently, functional analysis of the key risk gene was carried out through in vitro experimentation.

Results

Four gene expression signatures (PLEKHO2, GBP2, MPP1, and VSIG4) linked to osteosarcoma prognosis were identified within the TARGET-osteosarcoma cohort, categorizing patients into two subgroups. The resulting prognostic model showed strong predictive capability, with area under the receiver operating characteristic curve (AUC) values of 0.728/0.740, 0.781/0.658, and 0.788/0.642 for 1, 3, and 5-year survival in both training and validation datasets. Notably, patients in the low-risk group had significantly higher stromal, immune, and ESTIMATE scores compared to high-risk counterparts. Additionally, a nomogram was developed, exhibiting high accuracy in predicting the survival outcome of osteosarcoma patients. Immunohistochemistry, Kaplan-Meier, and time-dependent AUC analyses consistently supported the prognostic value of the risk model within our osteosarcoma patient cohort. In vitro experiments provided additional validation by demonstrating that the downregulation of GBP2 promoted the proliferation, migration, and invasion of osteosarcoma cells while inhibiting apoptosis.

Conclusion

The current study established a prognostic signature associated with TEX-related genes and elucidated the impact of the pivotal gene GBP2 on osteosarcoma cells via in vitro experiments. Consequently, it introduces a fresh outlook for clinical prognosis prediction and sets the groundwork for targeted therapy investigations in osteosarcoma.

The role of CD4+ T cells in tumor and chronic viral immune responses

Immunotherapies are mainly aimed to promote a CD8+ T cell response rather than a CD4+ T cell response as cytotoxic T lymphocytes (CTLs) can directly kill target cells. Recently, CD4+ T cells have received more attention due to their diverse roles in tumors and chronic viral infections. In antitumor and antichronic viral responses, CD4+ T cells relay help signals through dendritic cells to indirectly regulate CD8+ T cell response, interact with B cells or macrophages to indirectly modulate humoral immunity or macrophage polarization, and inhibit tumor blood vessel formation. Additionally, CD4+ T cells can also exhibit direct cytotoxicity toward target cells. However, regulatory T cells exhibit immunosuppression and CD4+ T cells become exhausted, which promote tumor progression and chronic viral persistence. Finally, we also outline immunotherapies based on CD4+ T cells, including adoptive cell transfer, vaccines, and immune checkpoint blockade. Overall, this review summarizes diverse roles of CD4+ T cells in the antitumor or protumor and chronic viral responses, and also highlights the immunotherapies based on CD4+ T cells, giving a better understanding of their roles in tumors and chronic viral infections.

The current state and future of T-cell exhaustion research

'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'.

Lymphocyte activation gene 3 is increased and affects cytokine production in rheumatoid arthritis

BACKGROUND

Lymphocyte activation gene-3 (LAG-3) inhibits T cell activation and interferes with the immune response by binding to MHC-II. As antigen presentation is central in rheumatoid arthritis (RA) pathogenesis, we studied aspects of LAG-3 as a serological marker and mediator in the pathogenesis of RA. Since Galectin-3 (Gal-3) is described as an additional binding partner for LAG-3, we also aimed to study the functional importance of this interaction.

METHODS

Plasma levels of soluble (s) LAG-3 were measured in early RA patients (eRA, n = 99) at baseline and after 12 months on a treat-to-target protocol, in self-reportedly healthy controls (HC, n = 32), and in paired plasma and synovial fluid (SF) from chronic RA patients (cRA, n = 38). Peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs) were examined for LAG-3 expression by flow cytometry. The binding and functional outcomes of LAG-3 and Gal-3 interaction were assessed with surface plasmon resonance (SPR) and in cell cultures using rh-LAG3, an antagonistic LAG-3 antibody and a Gal-3 inhibitor.

RESULTS

Baseline sLAG-3 in the plasma was increased in eRA compared to HC and remained significantly elevated throughout 12 months of treatment. A high level of sLAG-3 at baseline was associated with the presence of IgM-RF and anti-CCP as well as radiographic progression. In cRA, sLAG-3 was significantly increased in SF compared with plasma, and LAG-3 was primarily expressed by activated T cells in SFMCs compared to PBMCs. Adding recombinant human LAG-3 to RA cell cultures resulted in decreased cytokine secretion, whereas blocking LAG-3 with an antagonistic antibody resulted in increased cytokine secretion. By SPR, we found a dose-dependent binding between LAG-3 and Gal-3. However, inhibiting Gal-3 in cultures did not further change cytokine production.

CONCLUSIONS

sLAG-3 in the plasma and synovial fluid is increased in both early and chronic RA patients, particularly in the inflamed joint. High levels of sLAG-3 are associated with autoantibody seropositivity and radiographic progression in eRA, and LAG-3 plays a biologically active role in cRA by decreasing inflammatory cytokine production. This functional outcome is not affected by Gal-3 interference. Our results suggest that LAG-3 is a faceted regulator of inflammation in early and chronic RA.

Implications and Emerging Therapeutic Avenues of Inflammatory Response in HPV+ Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinomas (HNSCC) are a heterogeneous group of malignancies which have shown exponential incidence in the last two decades especially due to human papillomavirus (HPV) infection. The HPV family comprises more than 100 types of viruses with HPV16 and HPV18 being the most prevalent strains in HNSCC. Literature data reveal that the mutation profile as well as the response to chemotherapy and radiotherapy are distinct among HPV+ versus HPV-negative tumors. Furthermore, the presence of the virus induces activation of an immune response, in particular the recruitment of specific antiviral T lymphocytes to tumor sites. These T cells when activated produce soluble factors including cytokines and chemokines capable of modifying the local immune tumor microenvironment and impact on tumor response to the treatment. In this comprehensive review we investigated current knowledge on how the presence of an HPV can modify the inflammatory response systemically and within the tumor microenvironment's immunological responses, thereby impacting on disease prognosis and survival. We highlighted the research gaps and emerging approaches necessary to discover novel immunotherapeutic targets for HPV-associated HNSCC.

Inhibitory Immune Checkpoint Receptors and Ligands as Prognostic Biomarkers in COVID-19 Patients

Coronavirus disease 2019 (COVID-19) is caused by SARS-CoV-2. During T-cell activation, the immune system uses different checkpoint pathways to maintain co-inhibitory and co-stimulatory signals. In COVID-19, expression of immune checkpoints (ICs) is one of the most important manifestations, in addition to lymphopenia and inflammatory cytokines, contributing to worse clinical outcomes. There is a controversy whether upregulation of ICs in COVID-19 patients might lead to T-cell exhaustion or activation. This review summarizes the available studies that investigated IC receptors and ligands in COVID-19 patients, as well as their effect on T-cell function. Several IC receptors and ligands, including CTLA-4, BTLA, TIM-3, VISTA, LAG-3, TIGIT, PD-1, CD160, 2B4, NKG2A, Galectin-9, Galectin-3, PD-L1, PD-L2, LSECtin, and CD112, were upregulated in COVID-19 patients. Based on the available studies, there is a possible relationship between disease severity and increased expression of IC receptors and ligands. Overall, the upregulation of some ICs could be used as a prognostic biomarker for disease severity.

Clinical and prognostic implications of an immune-related risk model based on TP53 status in lung adenocarcinoma

TP53 mutation is the most widespread mutation in lung adenocarcinoma (LUAD). Meanwhile, p53 (encoded by TP53) has recently been implicated in immune responses. However, it is still unknown whether TP53 mutation remodels the tumour microenvironment to influence tumour progression and prognosis in LUAD. In this study, we developed a 6‐gene immune‐related risk model (IRM) to predict the survival of patients with LUAD in The Cancer Genome Atlas (TCGA) cohort based on TP53 status, and the predictive ability was confirmed in 2 independent cohorts. TP53 mutation led to a decreased immune response in LUAD. Further analysis revealed that patients in the high‐index group had observably lower relative infiltration of memory B cells and regulatory T cells and significantly higher relative infiltration of neutrophils and resting memory CD4⁺ T cells. Additionally, the IRM index positively correlated with the expression of critical immune checkpoint genes, including PDCD1 (encoding PD‐1) and CD274 (encoding PD‐L1), which was validated in the Nanjing cohort. Furthermore, as an independent prognostic factor, the IRM index was used to establish a nomogram for clinical application. In conclusion, this IRM may serve as a powerful prognostic tool to further optimize LUAD immunotherapy.

Not-so-opposite ends of the spectrum: CD8+ T cell dysfunction across chronic infection, cancer and autoimmunity

CD8⁺ T cells are critical mediators of cytotoxic effector function in infection, cancer and autoimmunity. In cancer and chronic viral infection, CD8⁺ T cells undergo a progressive loss of cytokine production and cytotoxicity, a state termed T cell exhaustion. In autoimmunity, autoreactive CD8⁺ T cells retain the capacity to effectively mediate the destruction of host tissues. Although the clinical outcome differs in each context, CD8⁺ T cells are chronically exposed to antigen in all three. These chronically stimulated CD8⁺ T cells share some common phenotypic features, as well as transcriptional and epigenetic programming, across disease contexts. A better understanding of these CD8⁺ T cell states may reveal novel strategies to augment clearance of chronic viral infection and cancer and to mitigate self-reactivity leading to tissue damage in autoimmunity.

LILRB4 suppresses immunity in solid tumors and is a potential target for immunotherapy

Immune receptors expressed on TAMs are intriguing targets for tumor immunotherapy. In this study, we found inhibitory receptor LILRB4 on a variety of intratumoral immune cell types in murine tumor models and human cancers, most prominently on TAMs. LILRB4, known as gp49B in mice, is a LILRB family receptor. Human and murine LILRB4 have two extracellular domains but differ in the number of intracellular ITIMs (three versus two). We observed a high correlation in LILRB4 expression with other immune inhibitory receptors. After tumor challenge, LILRB4^−/− mice and mice treated with anti-LILRB4 antibody showed reduced tumor burden and increased survival. LILRB4^−/− genotype or LILRB4 blockade increased tumor immune infiltrates and the effector (Teff) to regulatory (Treg) T cell ratio and modulated phenotypes of TAMs toward less suppressive, CD4⁺ T cells to Th1 effector, and CD8⁺ T cells to less exhausted. These findings reveal that LILRB4 strongly suppresses tumor immunity in TME and that alleviating that suppression provides antitumor efficacy.

Transcriptional regulatory network for the establishment of CD8+ T cell exhaustion

Chronic infection with persistent antigenic stimulation results in the generation of exhausted CD8⁺ T cells, which are considered defective effector CD8⁺ T cells, and thus compromises effective immune responses. However, recent studies have illustrated that exhausted CD8⁺ T cells may be purposely generated and maintained to provide mild immune responses against chronic infection or cancer, which can be safer over a long period of time than strong immune responses. Indeed, a specific population of exhausted CD8⁺ T cells that behaves similarly to self-renewing stem cells and provides a continuous supply of exhausted CD8⁺ T cells has been identified, indicating that this population can be considered progenitors of exhausted CD8⁺ T cells. Furthermore, several ground-breaking studies in the last few years have shed new light on the transcriptional regulatory network governing the generation and propagation of exhausted CD8⁺ T cells, which involves T cell receptor (TCR) signaling that leads to NFAT-TCF1 (nuclear factor of activated T cells-T cell factor 1) activity followed by activation of the TOX/NR4A axis. Elucidation of the intracellular signaling pathways will help to define the definitive developmental stages leading to exhausted CD8⁺ T cells, which can be exploited to advance our never-ending battle against cancer. This review will summarize the recent discoveries that have deepened our understanding of the exhaustion program of cytotoxic CD8⁺ T cells.

A type of T cell previously thought to be defective could actually provide long-term mild immune responses for combating cancer. The unique environment created during chronic infections gives rise to functionally inert T cells known as ‘exhausted’ cells, which were once thought to impede immune responses. Wooseok Seo and co-workers at Nagoya University and the National Cancer Center in Tokyo, Japan, have reviewed recent studies suggesting that exhausted T cells may be generated by the body to provide mild immune responses. Such responses are safer over the long term than strong inflammatory defense mechanisms, where T cells may be overstimulated, leading to uncontrolled tissue damage and induced T cell death. The signaling pathways that generate and propagate exhausted cells are being revealed, shedding light on the developmental stages that lead to this subtle but effective response to chronic conditions.

Transcriptional regulatory network for the establishment of CD8+ T cell exhaustion

Chronic infection with persistent antigenic stimulation results in the generation of exhausted CD8⁺ T cells, which are considered defective effector CD8⁺ T cells, and thus compromises effective immune responses. However, recent studies have illustrated that exhausted CD8⁺ T cells may be purposely generated and maintained to provide mild immune responses against chronic infection or cancer, which can be safer over a long period of time than strong immune responses. Indeed, a specific population of exhausted CD8⁺ T cells that behaves similarly to self-renewing stem cells and provides a continuous supply of exhausted CD8⁺ T cells has been identified, indicating that this population can be considered progenitors of exhausted CD8⁺ T cells. Furthermore, several ground-breaking studies in the last few years have shed new light on the transcriptional regulatory network governing the generation and propagation of exhausted CD8⁺ T cells, which involves T cell receptor (TCR) signaling that leads to NFAT-TCF1 (nuclear factor of activated T cells-T cell factor 1) activity followed by activation of the TOX/NR4A axis. Elucidation of the intracellular signaling pathways will help to define the definitive developmental stages leading to exhausted CD8⁺ T cells, which can be exploited to advance our never-ending battle against cancer. This review will summarize the recent discoveries that have deepened our understanding of the exhaustion program of cytotoxic CD8⁺ T cells.

A proportion of CD4+ T cells from patients with chronic Chagas disease undergo a dysfunctional process, which is partially reversed by benznidazole treatment

Background

Signs of senescence and the late stages of differentiation associated with the more severe forms of Chagas disease have been described in the Trypanosoma cruzi antigen-specific CD4⁺ T-cell population. However, the mechanisms involved in these functions are not fully known. To date, little is known about the possible impact of benznidazole treatment on the T. cruzi-specific functional response of CD4⁺ T cells.

Methodology/Principal findings

The functional capacity of CD4⁺ T cells was analyzed by cytometric assays in chronic Chagas disease patients, with indeterminate form (IND) and cardiac alterations (CCC) (25 and 15, respectively) before and after benznidazole treatment. An increase in the multifunctional capacity (expression of IFN-γ, IL-2, TNF-α, perforin and/or granzyme B) of the antigen-specific CD4⁺ T cells was observed in indeterminate versus cardiac patients, which was associated with the reduced coexpression of inhibitory receptors (2B4, CD160, CTLA-4, PD-1 and/or TIM-3). The functional profile of these cells shows statistically significant differences between IND and CCC (p<0.001), with a higher proportion of CD4⁺ T cells coexpressing 2 and 3 molecules in IND (54.4% versus 23.1% and 4.1% versus 2.4%, respectively). A significant decrease in the frequencies of CD4⁺ T cells that coexpress 2, 3 and 4 inhibitory receptors was observed in IND after 24–48 months of treatment (p<0.05, p<0.01 and p<0.05, respectively), which was associated with an increase in antigen-specific multifunctional activity. The IND group showed, at 9–12 months after treatment, an increase in the CD4⁺ T cell subset coproducing three molecules, which were mainly granzyme B⁺, perforin⁺ and IFN-γ⁺ (1.4% versus 4.5%).

Conclusions/Significance

A CD4⁺ T cell dysfunctional process was detected in chronic Chagas disease patients, being more exacerbated in those patients with cardiac symptoms. After short-term benznidazole treatment (9–12 months), indeterminate patients showed a significant increase in the frequency of multifunctional antigen-specific CD4⁺ T cells.

Trypanosoma cruzi infection triggers several immune mechanisms in the host that do not result in a total clearance of the parasite, the persistence of which leads to the chronicity of Chagas disease. The mechanisms by which some chronic patients remain asymptomatic or become symptomatic are not entirely clear. The aim of the present manuscript is to study the CD4⁺ T cell population and its functional capacity in patients with different forms of chronic disease. The obtained results indicate that cells from indeterminate patients have an enhanced multifunctional profile, which is associated with the reduced expression of inhibitory molecules. CD4⁺ T cells from chronic patients with cardiac alterations show lower functional activity against specific antigens of the parasite and increased coexpression of inhibitory molecules. After benznidazole treatment, antigen-specific CD4⁺ T cells, especially those from indeterminate patients, are more likely to show a multifunctional profile and a decline in the coexpression of inhibitory receptors. These results allow us to make progress in clarifying the mechanisms that may influence disease progression and to realize the importance of antiparasitic treatment for the enhancement of the activity of the immune system.

Platelet Induced Functional Alteration of CD4+ and CD8+ T Cells in HNSCC

Platelets (PLT) are the second most abundant cell type in human blood and exert various immune-regulatory functions under both physiological and pathological conditions. In fact, immune cell regulation via platelets has been demonstrated in several studies within the past decade. However, the exact mechanisms behind T cell regulation remain poorly understood. We questioned whether the formation of aggregates of platelets and T cells has an impact on T-cell functions. In the present study, we stimulated PBMC cultures with anti-CD3 and anti-CD28 mABs and cultured them at a PLT: PBMC ratio of 1:1 or 100:1. After 24, 48, and 72 h, PD-1, PD-L1 expression, and proliferation were analyzed on T cells using flow cytometry. Cytokine production was measured in PHA stimulated CD4 cells after 6 h. We found a significant platelet-mediated decrease in PD-1 and PD-L1 expression, proliferation, as well as IFN-γ and TNF-α production. Perturbations also at least partially remained after spatial separation of PLTs from PBMCs in Transwell-assays. T cell-platelet aggregates showed similar levels of activation markers, proliferation, and secreted cytokines as their non-complexed counterparts. Results indicate a platelet mediated regulation of T cells via direct and indirect contact, but only mediocre effects of the complex formation itself.

Exosomes Represent an Immune Suppressive T Cell Checkpoint in Human Chronic Inflammatory Microenvironments

Background: T cells present in chronic inflammatory tissues such as nasal polyps (from chronic rhinosinusitis patients) have been demonstrated to be hypo-responsive to activation via the TCR, similar to tumor-specific T cells in multiple different human tumor microenvironments. While immunosuppressive exosomes have been known to contribute to the failure of the tumor-associated T cells to respond optimally to activation stimuli, it is not known whether they play a similar role in chronic inflammatory microenvironments. In the current study, we investigate whether exosomes derived from chronic inflammatory microenvironments contribute to the immune suppression of T cells. Methods: Exosomes were isolated by ultracentrifugation and characterized by size and composition using nanoparticle tracking analysis, scanning electron microscopy, antibody arrays and flow exometry. Immunosuppressive ability of the exosomes was measured by quantifying its effect on activation of T cells, using nuclear translocation of NFκB as an activation endpoint. Results: Exosomes were isolated and characterized from two different types of chronic inflammatory tissues - nasal polyps from chronic rhinosinusitis patients and synovial fluid from rheumatoid arthritis patients. These exosomes arrest the activation of T cells stimulated via the TCR. This immune suppression, like that which is seen in tumor microenvironments, is dependent in part upon a lipid, ganglioside GD3, which is expressed on the exosomal surface. Conclusion: Immunosuppressive exosomes present in non-malignant chronic inflammatory tissues represent a new T cell checkpoint, and potentially represent a novel therapeutic target to enhance the response to current therapies and prevent disease recurrences.

ThymicPeptides Reverse Immune Exhaustion in Patients with Reactivated Human Alphaherpesvirus1 Infections

Recurrent infection with human alphaherpesvirus 1 (HHV-1) may be associated with immune exhaustion that impairs virus elimination. Thymic peptides enhance immune function and thus could overcome immune exhaustion. In this study, we investigated whether reactivation of herpes infections was associated with immune exhaustion. Moreover, we examined the impact of treatment with thymostimulin on the expression of programmed cell death protein 1 (PD-1) and its ligand (PD-L1) on T and B lymphocytes in patients suffering from recurrent HHV-1 reactivation. We also assessed the effector function of peripheral blood mononuclear cells (PBMCs) after stimulation with thymic peptides. We enrolled 50 women with reactivated HHV-1 infections and healthy volunteers. We measured the expression of various activation and exhaustion markers on the surface of PBMCs using flow cytometry. In ex vivo experiments, we measured the secretion of inflammatory cytokines by PBMCs cultured with thymostimulin. Compared with controls, patients with reactivated HHV-1 infections had increased percentages of CD3+ co-expressing CD25, an activation marker (p < 0.001). Moreover, these patients had increased percentages of CD4+ and CD8+ cells co-expressing the inhibitory markers PD-1 and PD-L1. In cultures of PBMCs from the patients, thymostimulin increased the secretion of interferon gamma (p < 0.001) and interleukin (IL)-2 (p = 0.023), but not IL-4 or IL-10.Two-month thymostimulin therapy resulted in no reactivation of HHV-1 infection during this period and the reduction of PD-1 and PD-L1 expression on the surface of T and B lymphocytes (p < 0.001). In conclusion, reactivation of herpes infection is associated with immune exhaustion, which could be reversed by treatment with thymic peptides.

Combination immunotherapy with anti-PD-L1 antibody and depletion of regulatory T cells during acute viral infections results in improved virus control but lethal immunopathology

Combination immunotherapy (CIT) is currently applied as a treatment for different cancers and is proposed as a cure strategy for chronic viral infections. Whether such therapies are efficient during an acute infection remains elusive. To address this, inhibitory receptors were blocked and regulatory T cells depleted in acutely Friend retrovirus-infected mice. CIT resulted in a dramatic expansion of cytotoxic CD4+ and CD8+ T cells and a subsequent reduction in viral loads. Despite limited viral replication, mice developed fatal immunopathology after CIT. The pathology was most severe in the gastrointestinal tract and was mediated by granzyme B producing CD4+ and CD8+ T cells. A similar post-CIT pathology during acute Influenza virus infection of mice was observed, which could be prevented by vaccination. Melanoma patients who developed immune-related adverse events under immune checkpoint CIT also presented with expanded granzyme-expressing CD4+ and CD8+ T cell populations. Our data suggest that acute infections may induce immunopathology in patients treated with CIT, and that effective measures for infection prevention should be applied.

Hepatitis B Virus: Advances in Prevention, Diagnosis, and Therapy

Currently, despite the use of a preventive vaccine for several decades as well as the use of effective and well-tolerated viral suppressive medications since 1998, approximately 250 million people remain infected with the virus that causes hepatitis B worldwide. Hepatitis C virus (HCV) and hepatitis B virus (HBV) are the leading causes of liver cancer and overall mortality globally, surpassing malaria and tuberculosis. Linkage to care is estimated to be very poor both in developing countries and in high-income countries, such as the United States, countries in Western Europe, and Japan. In the United States, by CDC estimates, only one-third of HBV-infected patients or less are aware of their infection. Some reasons for these low rates of surveillance, diagnosis, and treatment include the asymptomatic nature of chronic hepatitis B until the very late stages, a lack of curative therapy with a finite treatment duration, a complex natural history, and a lack of knowledge about the disease by both care providers and patients. In the last 5 years, more attention has been focused on the important topics of HBV screening, diagnosis of HBV infection, and appropriate linkage to care. There have also been rapid clinical developments toward a functional cure of HBV infection, with novel compounds currently being in various phases of progress. Despite this knowledge, many of the professional organizations provide guidelines focused only on specific questions related to the treatment of HBV infection. This focus leaves a gap for care providers on the other HBV-related issues, which include HBV's epidemiological profile, its natural history, how it interacts with other viral hepatitis diseases, treatments, and the areas that still need to be addressed in order to achieve HBV elimination by 2030. Thus, to fill these gaps and provide a more comprehensive and relevant document to regions worldwide, we have taken a global approach by using the findings of global experts on HBV as well as citing major guidelines and their various approaches to addressing HBV and its disease burden.

Engineering Nanoparticles to Reprogram the Tumor Immune Microenvironment for Improved Cancer Immunotherapy

Immunotherapy is rapidly maturing towards extensive clinical use. However, it does not work well in large patient populations because of an immunosuppressed microenvironment and limited reinvigoration of antitumor immunity. The tumor microenvironment is a complex milieu in which the principles of physiology and anatomy are defied and which is considered an immune-privileged site promoting T cell exhaustion. Tremendous research interest exists in developing nanoparticle-based approaches to modulate antitumor immune responses. The increasing use of immunotherapies in the clinic requires robust programming of immune cells to boost antitumor immunity. This review summarizes recent advances in the engineering of nanoparticles for improved anticancer immunotherapy. It discusses emerging nanoparticle-based approaches for the modulation of tumor cells and immune cells, such as dendritic cells, T cells and tumor-associated macrophages, with the intention to overcome challenges currently faced in the clinic. Furthermore, this review describes potentially curative combination therapeutic approaches to provoke effective tumor antigen-specific immune responses. We foresee a future in which improvement in patient's surveillance will become a mainstream practice.

IL-2 Restores T-Cell Dysfunction Induced by Persistent Mycobacterium tuberculosis Antigen Stimulation

Tuberculosis (TB) is a chronic disease mainly caused by Mycobacterium tuberculosis. The function of T cells usually decreased and even exhausted in severe TB such as multiple drug resistant TB (MDR-TB), which might lead to the failure of treatment in return. The mechanism of T cell dysfunction in TB is still not clear. In this study we set up a mouse model of T cell dysfunction by persistent M. tuberculosis antigen stimulation and investigated the therapeutic role of interleukin 2 (IL-2) in it. C57BL/6 mice were primed with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) and boosted repeatedly with a combination of M. tuberculosis fusion proteins Mtb10.4-HspX (MH) plus ESAT6-Ag85B-MPT64 _<190-198>-Mtb8.4-Rv2626c (LT70) or MH plus ESAT6 and CFP10 with adjuvant of N, N'-dimethyl-N, N'-dioctadecylammonium bromide (DDA) plus polyinosinic-polycytidylic acid (Poly I:C). Following persistent antigen stimulation, the mice were treated with IL-2 and the therapeutic effects were analyzed. The results showed that compared with the mice that received transient antigen stimulation (boost twice), persistent antigen stimulation (boost more than 10 times) resulted in decrease of antigen specific IFN-γ and IL-2 production, reduction of memory CD8⁺ T cells, over-expression of immune checkpoint programmed cell death protein 1 (PD-1), and impaired the protective immunity against bacterial challenge. Treating the T cell functionally exhausted mice with IL-2 restored antigen-specific T cell responses and protective efficacy. In conclusion, persistent stimulation with M. tuberculosis antigens induced T cell dysfunction, which could be restored by complement of IL-2.

A dynamical motif comprising the interactions between antigens and CD8 T cells may underlie the outcomes of viral infections

Some viral infections culminate in very different outcomes in different individuals. They can be rapidly cleared in some, cause persistent infection in others, and cause mortality from immunopathology in yet others. The conventional view is that the different outcomes arise as a consequence of the complex interactions between a large number of different factors (virus, different immune cells, and cytokines). Here, we identify a simple dynamical motif comprising the essential interactions between antigens and CD8 T cells and posit it as predominantly determining the outcomes. Viral antigen can activate CD8 T cells, which in turn, can kill infected cells. Sustained antigen stimulation, however, can cause CD8 T-cell exhaustion, compromising effector function. Using mathematical modeling, we show that the motif comprising these interactions recapitulates all of the outcomes observed. The motif presents a conceptual framework to understand the variable outcomes of infection. It also explains a number of confounding experimental observations, including the variation in outcomes with the viral inoculum size, the evolutionary advantage of exhaustion in preventing lethal pathology, the ability of natural killer (NK) cells to act as rheostats tuning outcomes, and the role of the innate immune response in the spontaneous clearance of hepatitis C. Interventions that modulate the interactions in the motif may present routes to clear persistent infections or limit immunopathology.

Chronic stimulation drives human NK cell dysfunction and epigenetic reprograming

A population of Natural Killer (NK) cells expressing the activating receptor NKG2C and the maturation marker CD57 expands in response to human cytomegalovirus (HCMV) infection. CD3-CD56dimCD57+NKG2C+ NK cells are similar to CD8+ memory T cells with rapid and robust effector function upon re-stimulation, persistence, and epigenetic remodeling of the IFNG locus. Chronic antigen stimulation drives CD8+ memory T cell proliferation while also inducing genome-wide epigenetic reprograming and dysfunction. We hypothesized that chronic stimulation could similarly induce epigenetic reprograming and dysfunction in NK cells. Here we show that chronic stimulation of adaptive NK cells through NKG2C using plate-bound agonistic antibodies in combination with IL-15 drove robust proliferation and activation of CD3-CD56dimCD57+NKG2C+ NK cells while simultaneously inducing high expression of the checkpoint inhibitory receptors LAG-3 and PD-1. Marked induction of checkpoint inhibitory receptors was also observed on the surface of adaptive NK cells co-cultured with HCMV-infected endothelial cells. Chronically stimulated adaptive NK cells were dysfunctional when challenged with tumor targets. These cells exhibited a pattern of epigenetic reprograming, with genome-wide alterations in DNA methylation. Our study has important implications for cancer immunotherapy and suggest that exhausted NK cells could be targeted with inhibitory checkpoint receptor blockade.

CEACAM1 structure and function in immunity and its therapeutic implications

The type I membrane protein receptor carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) distinctively exhibits significant alternative splicing that allows for tunable functions upon homophilic binding. CEACAM1 is highly expressed in the tumor environment and is strictly regulated on lymphocytes such that its expression is restricted to activated cells where it is now recognized to function in tolerance pathways. CEACAM1 is also an important target for microbes which have co-opted these attributes of CEACAM1 for the purposes of invading the host and evading the immune system. These properties, among others, have focused attention on CEACAM1 as a unique target for immunotherapy in autoimmunity and cancer. This review examines recent structural information derived from the characterization of CEACAM1:CEACAM1 interactions and heterophilic modes of binding especially to microbes and how this relates to CEACAM1 function. Through this, we aim to provide insights into targeting CEACAM1 for therapeutic intervention.

Principles of Immunotherapy: Implications for Treatment Strategies in Cancer and Infectious Diseases

The advances in cancer biology and pathogenesis during the past two decades, have resulted in immunotherapeutic strategies that have revolutionized the treatment of malignancies, from relatively non-selective toxic agents to specific, mechanism-based therapies. Despite extensive global efforts, infectious diseases remain a leading cause of morbidity and mortality worldwide, necessitating novel, innovative therapeutics that address the current challenges of increasing antimicrobial resistance. Similar to cancer pathogenesis, infectious pathogens successfully fashion a hospitable environment within the host and modulate host metabolic functions to support their nutritional requirements, while suppressing host defenses by altering regulatory mechanisms. These parallels, and the advances made in targeted therapy in cancer, may inform the rational development of therapeutic interventions for infectious diseases. Although "immunotherapy" is habitually associated with the treatment of cancer, this review accentuates the evolving role of key targeted immune interventions that are approved, as well as those in development, for various cancers and infectious diseases. The general features of adoptive therapies, those that enhance T cell effector function, and ligand-based therapies, that neutralize or eliminate diseased cells, are discussed in the context of specific diseases that, to date, lack appropriate remedial treatment; cancer, HIV, TB, and drug-resistant bacterial and fungal infections. The remarkable diversity and versatility that distinguishes immunotherapy is emphasized, consequently establishing this approach within the armory of curative therapeutics, applicable across the disease spectrum.

2B4 Mediates Inhibition of CD8+ T Cell Responses via Attenuation of Glycolysis and Cell Division

We recently showed that 2B4 expression on memory T cells in human renal transplant recipients was associated with reduced rates of rejection. To investigate whether 2B4 functionally underlies graft acceptance during transplantation, we established an experimental model in which 2B4 was retrogenically expressed on donor-reactive murine CD8+ T cells (2B4rg), which were then transferred into naive recipients prior to skin transplantation. We found that constitutive 2B4 expression resulted in significantly reduced accumulation of donor-reactive CD8+ T cells following transplantation and significantly prolonged graft survival following transplantation. This marked reduction in alloreactivity was due to reduced proliferation of CD8+ Thy1.1+ 2B4rg cells as compared with control cells, underpinned by extracellular flux analyses demonstrating that 2B4-deficient (2B4KO) CD8+ cells activated in vitro exhibited increased glycolytic capacity and upregulation of gene expression profiles consistent with enhanced glycolytic machinery as compared with wild type controls. Furthermore, 2B4KO CD8+ T cells primed in vivo exhibited significantly enhanced ex vivo uptake of a fluorescent glucose analogue. Finally, the proliferative advantage associated with 2B4 deficiency was only observed in the setting of glucose sufficiency; in glucose-poor conditions, 2B4KO CD8+ T cells lost their proliferative advantage. Together, these data indicate that 2B4 signals function to alter T cell glucose metabolism, thereby limiting the proliferation and accumulation of CD8+ T cells. Targeting 2B4 may therefore represent a novel therapeutic strategy to attenuate unwanted CD8+ T cell responses.

Immunomodulatory effects of Tim-3 and PD-1 on chronic hepatitis B virus infection

In patients with chronic hepatitis B virus (HBV) infection, the immune cells are dysfunctional, and the immune function cannot work normally. T-cell immunoglobulin mucin-3 (Tim-3) and programmed death receptor-1 (PD-1) are overexpressed on the surface of immune cells, such as cluster of differentiation (CD)4+, CD8+ T-lymphocytes, and natural killer (NK) cells. Many studies indicate that this phenomenon is closely related to the persistence, occurrence, development, and prognosis of HBV. Tim-3 and PD-1 may be used as new immune targets for the treatment of chronic hepatitis B.

Mechanisms of PD-1/PD-L1 expression and prognostic relevance in non-Hodgkin lymphoma: a summary of immunohistochemical studies

Immune checkpoint blockade therapeutics, notably antibodies targeting the programmed death 1 (PD-1) receptor and its PD-L1 and PD-L2 ligands, are currently revolutionizing the treatment of cancer. For a sizeable fraction of patients with melanoma, lung, kidney and several other solid cancers, monoclonal antibodies that neutralize the interactions of the PD-1/PD-L1 complex allow the reconstitution of long-lasting antitumor immunity. In hematological malignancies this novel therapeutic strategy is far less documented, although promising clinical responses have been seen in refractory and relapsed Hodgkin lymphoma patients. This review describes our current knowledge of PD-1 and PD-L1 expression, as reported by immunohistochemical staining in both non-Hodgkin lymphoma cells and their surrounding immune cells. Here, we discuss the multiple intrinsic and extrinsic mechanisms by which both T and B cell lymphomas up-regulate the PD-1/PD-L1 axis, and review current knowledge about the prognostic significance of its immunohistochemical detection. This body of literature establishes the cell surface expression of PD-1/PD-L1 as a critical determinant for the identification of non-Hodgkin lymphoma patients eligible for immune checkpoint blockade therapies.

Bright-field in situ hybridization detects gene alterations and viral infections useful for personalized management of cancer patients

INTRODUCTION

Bright-field in situ hybridization (ISH) methods detect gene alterations that may improve diagnostic precision and personalized management of cancer patients. Areas covered: This review focuses on some bright-field ISH techniques for detection of gene amplification or viral infection that have already been introduced in tumor pathology, research and diagnostic practice. Other emerging ISH methods, for the detection of translocation, mRNA and microRNA have recently been developed and need both an optimization and analytical validation. The review also deals with their clinical applications and implications on the management of cancer patients. Expert commentary: The technology of bright-field ISH applications has advanced significantly in the last decade. For example, an automated dual-color assay was developed as a clinical test for selecting cancer patients that are candidates for personalized therapy. Recently an emerging bright-field gene-protein assay has been developed. This method simultaneously detects the protein, gene and centromeric targets in the context of tissue morphology, and might be useful in assessing the HER2 status particularly in equivocal cases or samples with heterogeneous tumors. The application of bright-field ISH methods has become the gold standard for the detection of tumor-associated viral infection as diagnostic or prognostic factors.

N-acetyl cysteine protects anti-melanoma cytotoxic T cells from exhaustion induced by rapid expansion via the downmodulation of Foxo1 in an Akt-dependent manner

Therapeutic outcomes for adoptive cell transfer (ACT) therapy are constrained by the quality of the infused T cells. The rapid expansion necessary to obtain large numbers of cells results in a more terminally differentiated phenotype with decreased durability and functionality. N-acetyl cysteine (NAC) protects against activation-induced cell death (AICD) and improves anti-tumor efficacy of Pmel-1 T cells in vivo. Here, we show that these benefits of NAC can be extended to engineered T cells and significantly increases T-cell survival within the tumor microenvironment. The addition of NAC to the expansion protocol of human TIL13838I TCR-transduced T cells that are under evaluation in a Phase I clinical trial, demonstrated that findings in murine cells extend to human cells. Expansion of TIL13838I TCR-transduced T cells in NAC also increased their ability to kill target cells in vitro. Interestingly, NAC did not affect memory subsets, but diminished up-regulation of senescence (CD57) and exhaustion (PD-1) markers and significantly decreased expression of the transcription factors EOMES and Foxo1. Pharmacological inhibition of the PI3K/Akt pathway ablates the decrease in Foxo1 induced by NAC treatment of activated T cells. This suggests a model in which NAC through PI3K/Akt activation suppresses Foxo1 expression, thereby impacting its transcriptional targets EOMES, PD-1, and granzyme B. Taken together, our results indicate that NAC exerts pleiotropic effects that impact the quality of TCR-transduced T cells and suggest that the addition of NAC to current clinical protocols should be considered.

Towards predictive biomarkers for immunotherapy response in breast cancer patients

Immunotherapy using anti-PD(L)1 has revolutionized treatment for various tumor types. Early data have shown durable responses in a small subgroup of breast cancer patients. So far, the response rates appear higher for breast tumors that are triple negative, PDL1-positive and/or harbor high levels of immune cells. Both comprehensive analyses of the breast tumor microenvironment and exploiting research on biomarkers in other cancer types, such as melanoma and lung cancer, may contribute to the discovery of accurate biomarkers to select breast cancer patients for immunotherapy. Here we summarize key features of the breast tumor microenvironment as well as putative predictive biomarkers established in other tumor types. Insights from both fields can guide future studies to enable personalized breast cancer immunotherapy.

miR-28 modulates exhaustive differentiation of T cells through silencing programmed cell death-1 and regulating cytokine secretion

T cell exhaustion is a state of T cell dysfunction that arises during many cancer. miRNAs are one of major gene regulators which result in translational inhibition and/or mRNA degradation. We hypothesized that miRNAs exist that can silence PD1 and act as a modulator in vitro to revert exhaustive status of T cells. We demonstrated that the exhausted T cells with inhibitory receptors (IRs) are significantly increased in the melanoma-bearing mice. Meanwhile, the differentiated miRNA profiles in PD1+ exhaustive T cells were identified using a miRNA array; 11 miRNAs were observed with significant altered levels in the exhausted T cells isolated from melanoma-bearing mice. Among those identified miRNA candidates, miR-28 was capable of binding to multiple IRs based on an in silico analysis and subsequently silencing PD1, as demonstrated by a dual luciferase assay. Moreover, the expression of PD1 was attenuated after transfection with miR-28 mimic. The ability of miR-28 in regulating T cell exhaustion was further evidenced by the fact that the expression of PD1, TIM3 and BTLA of exhausted T cells was increased by the inhibitor of miR28. On the other hand, miR-28 also regulated the PD1+ Foxp3+ and TIM3+ Foxp3+ exhaustive Treg cells in vitro. miR-28 regulating T cell exhaustion was also observed by its ability in reinstalling impaired secretion of cytokines IL-2 and TNF-α by exhausted T cells. This study is the first to discover the effect of miR-28 on T cell exhaustion, providing novel targets with potential use as therapeutic markers in cancer immunotherapy.

Frontline Science: Anti-PD-L1 protects against infection with common bacterial pathogens after burn injury

Burn patients are susceptible to infections due, in part, to immune dysfunction. Upregulation of programmed death-1 (PD-1) receptor on T cells and programmed cell death ligand-1 (PD-L1) on myeloid cells contribute to immune dysfunction in nonburn-related sepsis. We hypothesized that PD-1/PDL1 interactions contribute to immune dysfunction after burn injury. To determine the impact of burn injury and infection on PD-L1, PD-1 and costimulatory receptor expression by leukocytes and its relationship to T cell functions. The efficacy of anti-PD-L1 antibody was evaluated in a clinically relevant mouse model of burn injury and bacterial infection. Mice underwent 35% scald burn followed by Pseudomonas aeruginosa or Staphylococcus aureus infection on day 4 postburn. Anti-PD-L1 was administered on day 3 postburn. Numbers and phenotype of leukocytes, plasma cytokine concentrations, bacterial clearance, organ injury, and survival were assessed. Burn injury and infection with P. aeruginosa caused a significant upregulation of PD-L1 on myeloid cells, along with a decrease in T cell numbers and function, significant multiorgan injury, and decreased survival. Treatment with anti-PD-L1 antibody improved bacterial clearance, reduced organ injury, and enhanced survival during Pseudomonas burn wound infection. Furthermore, anti-PD-L1 effectively protected against multiorgan injury, and improved bacterial clearance and survival following systemic S. aureus infection after burn injury. Blockade of PD-1/PD-L1 interactions might represent a viable treatment to improve outcomes among critically ill burn-injured subjects and increased leukocyte PD-L1 expression could serve as a valuable biomarker to select appropriate patients for such treatment.

Dichotomous Roles of Programmed Cell Death 1 on HIV-Specific CXCR5+ and CXCR5- CD8+ T Cells during Chronic HIV Infection

Background

CXCR5⁺CD8⁺ T cells have been demonstrated to play an important role in the control of chronic viral replication; however, the relationship between CXCR5⁺CD8⁺ T cells, HIV disease progression, and programmed cell death 1 (PD-1) expression profile on CXCR5⁺CD8⁺ T cells during HIV infection remain poorly understood.

Methods

We enrolled a total of 101 HIV patients, including 62 typical progressors, 26 complete responders (CRs), and 13 immune non-responders (INRs). Flow cytometric analysis, immunohistochemical staining, and relative function (i.e., cytokine secretion and PD-1 blockade) assays were performed to analyze the properties of CXCR5⁺CD8⁺ T cells.

Results

HIV-specific CXCR5⁺CD8⁺ T cells in the peripheral blood and distribution of CXCR5⁺CD8⁺ T cells in the lymph node (LN) were negatively correlated with disease progression during chronic HIV infection. PD-1 was highly expressed on CXCR5⁺CD8⁺ T cells and positively associated with peripheral CD4⁺ T cell counts. Functionally, IFN-γ and TNF-α production of CXCR5⁺CD8⁺ T cells were reduced by PD-1 pathway blockade, but the production of IFN-γ and TNF-α from CXCR5^-CD8⁺ T cells increased in response to TCR stimulation. Interestingly, PD-1 expression was constantly retained on CXCR5⁺CD8⁺ T cells while significantly decreased on CXCR5^-CD8⁺ T cells after successful antiretroviral treatment in chronic HIV-infected patients.

Conclusion

PD-1⁺CXCR5⁺CD8⁺ T cells are functional cytotoxic T cells during chronic HIV infection. PD-1⁺CXCR5⁺CD8⁺ T cells may represent a novel therapeutic strategy for the disease.

Targeting Immune Cell Checkpoints during Sepsis

Immunosuppression is increasingly being recognized as one of the causes of increased morbidity and mortality during sepsis. Both innate and adaptive immune system dysfunction have been shown to cause an impaired ability to eradicate the primary infection and also lead to frequent occurrence of secondary opportunistic infections. Pre-clinical and clinical studies have shown that inhibitory immune checkpoint molecules, including programmed death-1 (PD-1), programmed death ligand-1 (PD-L1), cytotoxic T lymphocyte antigen-4 (CTLA-4), T cell membrane protein-3 (TIM-3), Lymphocyte activation-gene-3 (LAG-3) and 2B4, are upregulated during the course of sepsis. Engagement of these inhibitory molecules on various immune cells has been consistently shown to inhibit innate immune cell functions (e.g., phagocytosis, cytokine production and pathogen clearance) and also lead to impaired T cell competence. In numerous pre-clinical models of sepsis, therapeutic agents aimed at blocking engagement of inhibitory immune checkpoints on immune cells have been shown to improve innate and adaptive immune cell functions, increase host resistance to infection and significantly improve survival. Therefore, immunotherapy with immune cell checkpoint inhibitors holds significant potential for the future of sepsis therapy and merits further investigation.

Exhaustion of T lymphocytes in the tumor microenvironment: Significance and effective mechanisms

T lymphocytes play crucial roles in adaptive immune responses to tumors. However, due to different tolerance mechanisms and inhibitory effects of the tumor microenvironment (TME) on T cells, responses to tumors are insufficient. In fact, cellular and molecular suppressive mechanisms repress T cell responses in the TME, resulting in senescent, anergic and exhausted lymphocytes. Exhaustion is a poor responsive status of T cells, with up-regulated expression of inhibitory receptors, decreased production of effective cytokines, and reduced cytotoxic activity. Low immunogenicity of tumor antigens and inadequate presentation of tumor-specific antigens results in inappropriate activation of naive T lymphocytes against tumor antigens. Moreover, when effector cytotoxic T cells enter TME, they encounter a complicated network of cells and cytokines that suppress their effectiveness and turn them into exhausted T cells. Thus, the mechanism of T cell exhaustion in cancer is different from that in chronic infections. In this review we will discuss the main components such as inhibitory receptors, inflammatory cells, stromal cells, cytokine milieu as well as environmental and metabolic conditions in TME which play role in development of exhaustion. Furthermore, recent therapeutic methods available to overcome exhaustion will be discussed.

Prostaglandin E2 and PD-1 mediated inhibition of antitumor CTL responses in the human tumor microenvironment

Accumulating evidence indicates that inflammation plays a critical role in cancer development; however, mechanisms of immunosuppression hinder productive anti-tumor immunity to limit immunopathology. Tumor-specific cytotoxic T lymphocyte (CTL) dysfunction or exhaustion by upregulating inhibitory receptors such as programmed cell death 1 (PD-1) in tumor-bearing hosts is one such mechanism. Identification and blockade of the pathways that induce CTL dysfunction has been shown to partially restore CTL function in tumor-bearing hosts. Cyclooxygenase-2 (COX-2) is a rate-limiting enzyme for prostanoid biosynthesis, including prostaglandin E₂ (PGE₂), and plays a key role in both inflammation and cancer. The disruption of COX2/PGE2 signaling using COX₂ inhibitors or PGE2 receptors EP2 and EP4 antagonists, combined with anti-PD-1 blockade was therapeutic in terms of improving eradication of tumors and augmenting the numbers of functional tumor-specific CTLs. Thus, COX2/PGE2 axis inhibition is a promising adjunct therapy to PD-1 blockade for immune-based therapies in cancer.

Costimulatory and Coinhibitory Receptor Pathways in Infectious Disease

Costimulatory and inhibitory receptors play a key role in regulating immune responses to infections. Recent translation of knowledge about inhibitory receptors such as CTLA-4 and PD-1 into the cancer clinic highlights the opportunities to manipulate these pathways to treat human disease. Studies in infectious disease have provided key insights into the specific roles of these pathways and the effects of their manipulation. Here, recent studies are discussed that have addressed how major inhibitory and costimulatory pathways play a role in regulating immune responses during acute and chronic infections. Mechanistic insights from studies of infectious disease provide opportunities to further expand our toolkit to treat cancer and chronic infections in the clinic.

Functional differences between PD-1+ and PD-1- CD4+ effector T cells in healthy donors and patients with glioblastoma multiforme

Immune checkpoint inhibitors targeting programmed cell death protein 1 (PD-1) have been highly successful in the treatment of cancer. While PD-1 expression has been widely investigated, its role in CD4+ effector T cells in the setting of health and cancer remains unclear, particularly in the setting of glioblastoma multiforme (GBM), the most aggressive and common form of brain cancer. We examined the functional and molecular features of PD-1+CD4+CD25-CD127+Foxp3-effector cells in healthy subjects and in patients with GBM. In healthy subjects, we found that PD-1+CD4+ effector cells are dysfunctional: they do not proliferate but can secrete large quantities of IFNγ. Strikingly, blocking antibodies against PD-1 did not rescue proliferation. RNA-sequencing revealed features of exhaustion in PD-1+ CD4 effectors. In the context of GBM, tumors were enriched in PD-1+ CD4+ effectors that were similarly dysfunctional and unable to proliferate. Furthermore, we found enrichment of PD-1+TIM-3+ CD4+ effectors in tumors, suggesting that co-blockade of PD-1 and TIM-3 in GBM may be therapeutically beneficial. RNA-sequencing of blood and tumors from GBM patients revealed distinct differences between CD4+ effectors from both compartments with enrichment in multiple gene sets from tumor infiltrating PD-1-CD4+ effectors cells. Enrichment of these gene sets in tumor suggests a more metabolically active cell state with signaling through other co-receptors. PD-1 expression on CD4 cells identifies a dysfunctional subset refractory to rescue with PD-1 blocking antibodies, suggesting that the influence of immune checkpoint inhibitors may involve recovery of function in the PD-1-CD4+ T cell compartment. Additionally, co-blockade of PD-1 and TIM-3 in GBM may be therapeutically beneficial.

Novel Checkpoints and Cosignaling Molecules in Cancer Immunotherapy

The recent demonstration of the antitumor efficacy of checkpoint protein inhibition has resulted in the approval of blocking antibodies against the programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway in multiple different histologic findings. Therapeutic successes with PD-1/PD-L1 antibodies in melanoma and lung cancer have been followed by approvals in bladder, renal, and head and neck cancers and Hodgkin lymphoma, with others undoubtedly to come. However, PD-1 is only one of many checkpoints and agonistic regulatory molecules expressed on T cells by which maintenance of the balance between costimulatory and coinhibitory signaling pathways is perturbed in cancer. The manipulation of many of these molecules in cancer patients might be associated with clinical benefit. The majority of the T-cell cosignaling receptors belong to either the immunoglobulin superfamily or the tumor necrosis factor receptor superfamily. A total of 29 immunoglobulin superfamily and 26 tumor necrosis factor receptor superfamily cosignaling receptors have been identified that are expressed on T cells, providing fertile ground for development of inhibitory or agonistic antibodies and small molecules as cancer therapeutics. In the current work, we focus on some of the most promising new checkpoints and agonistic or cosignaling molecules that are in early clinical development as single agents or in combinations with PD-1/PD-L1, cytotoxic T-lymphocyte-associated protein 4 blockade, or chemotherapy with an emphasis on those that have reached the clinic and on important targets that are in late preclinical development.

Efficient control of chronic LCMV infection by a CD4 T cell epitope-based heterologous prime-boost vaccination in a murine model

CD4⁺ T cells are essential for sustaining CD8⁺ T cell responses during a chronic infection. The adoptive transfer of virus-specific CD4⁺ T cells has been shown to efficiently rescue exhausted CD8⁺ T cells. However, the question of whether endogenous virus-specific CD4⁺ T cell responses can be enhanced by certain vaccination strategies and subsequently reinvigorate exhausted CD8⁺ T cells remains unexplored. In this study, we developed a CD4⁺ T cell epitope-based heterologous prime-boost immunization strategy and examined the efficacy of this strategy using a mouse model of chronic lymphocytic choriomeningitis virus (LCMV) infection. We primed chronically LCMV-infected mice with a Listeria monocytogenes vector that expressed the LCMV glycoprotein-specific I-A^b-restricted CD4⁺ T cell epitope GP61-80 (LM-GP61) and subsequently boosted the primed mice with an influenza virus A (PR8 strain) vector that expressed the same CD4⁺ T cell epitope (IAV-GP61). This heterologous prime-boost vaccination strategy elicited strong anti-viral CD4⁺ T cell responses, which further improved both the quantity and quality of the virus-specific CD8⁺ T cells and led to better control of the viral loads. The combination of this strategy and the blockade of the programmed cell death-1 (PD-1) inhibitory pathway further enhanced the anti-viral CD8⁺ T cell responses and viral clearance. Thus, a heterologous prime-boost immunization that selectively induces virus-specific CD4⁺ T cell responses in conjunction with blockade of the inhibitory pathway may represent a promising therapeutic approach to treating patients with chronic viral infections.

Noncoding RNAs and immune checkpoints-clinical implications as cancer therapeutics

A major mechanism of tumor development and progression is silencing of the patient's immune response to cancer-specific antigens. Defects in the so-called cancer immunity cycle may occur at any stage of tumor development. Within the tumor microenvironment, aberrant expression of immune checkpoint molecules with activating or inhibitory effects on T lymphocytes induces immune tolerance and cellular immune escape. Targeting immune checkpoint molecules such as programmed cell death protein 1 (PD-1) and its ligand PD-L1 with specific antibodies has proven to be a major advance in the treatment of several types of cancer. Another way to therapeutically influence the tumor microenvironment is by modulating the levels of microRNAs (miRNAs), small noncoding RNAs that shuttle bidirectionally between malignant and tumor microenvironmental cells. These small RNA transcripts have two features: (a) their expression is quite specific to distinct tumors, and (b) they are involved in early regulation of immune responses. Consequently, miRNAs may be ideal molecules for use in cancer therapy. Many miRNAs are aberrantly expressed in human cancer cells, opening new opportunities for cancer therapy, but the exact functions of these miRNAs and their interactions with immune checkpoint molecules have yet to be investigated. This review summarizes recently reported findings about miRNAs as modulators of immune checkpoint molecules and their potential application as cancer therapeutics in clinical practice.

Future anti-HBV strategies

Although current oral antivirals can maintain viral suppression and reduce the risk of liver-related complications, lifelong therapy is associated with high cost, risk of breakthrough and potential toxicity. There is a need to develop a finite course of treatment which can provide sustained off-treatment virological and clinical response. The likely marker of such a clinical HBV CURE would be HBsAg clearance, but in addition cccDNA elimination would be required to prevent future reactivation (ie complete HBV cure). Chronic HBV infection is characterised by high viral and antigen burden and inadequate host immune responses, both of which will need to be overcome to achieve HBV CURE. Innovative approaches to restore innate and adaptive immune responses against HBV currently in clinical development include therapeutic vaccines, TLR-7 and TLR-8 agonists. In future, strategies to reverse T-cell exhaustion such as checkpoint inhibitors may be feasible. Currently, the only antivirals in clinical use are the HBV polymerase inhibitors. However, many other steps of HBV virion life cycle can be targeted by small molecules, including inhibitors of HBV entry, nucleocapsid formation and virion assembly and release. siRNAs could inhibit many different steps by blocking multiple HBV transcripts. But, the ultimate goal will be to successfully eradicate or silence cccDNA. It is likely that successful HBV cure will require combination of immunomodulatory, antiviral and cccDNA silencing strategies. Efficacy, safety, route of administration and cost will ultimately determine the impact of these new regimens on the burden of HBV.

Increasing LAG-3 expression suppresses T-cell function in chronic hepatitis B: A balance between immunity strength and liver injury extent

Weak or absent virus-specific CD8 T-cell responses to hepatitis B virus (HBV) infection are thought to be responsible for persistent HBV infection. Previous studies have indicated that multiple inhibitory receptors, including lymphocyte activation gene-3 (LAG-3), can suppress the CD8 T-cell response in chronic viral infection. This study aimed to detect LAG-3 expression and to investigate the manner in which the immune response is regulated to balance the strength of the response with the extent of liver injury in chronic HBV infection. The results showed that LAG-3 expression levels were significantly higher in CD8 T cells from chronic hepatitis B patients in the immune-active phase compared with chronic asymptomatic HBV carriers and healthy controls. CD8 T-cell function was suppressed in cells with high LAG-3 expression, and these cells exhibited reduced interferon-γ (IFN-γ) secretion. Furthermore, IFN-γ secretion was restored in CD8 T cells that were treated with a specific antibody to LAG-3. Taken together, liver injury was prominent in the immune-active phase, but suppressing T-cell function could mitigate this damage. Importantly, the inhibitory function of LAG-3 can be blocked using a LAG-3-specific antibody, and this can restore the activity of non-functional T cells.

PTPN22 contributes to exhaustion of T lymphocytes during chronic viral infection

The protein encoded by the autoimmune-associated protein tyrosine phosphatase nonreceptor type 22 gene, PTPN22, has wide-ranging effects in immune cells including suppression of T-cell receptor signaling and promoting efficient production of type I interferons (IFN-I) by myeloid cells. Here we show that mice deficient in PTPN22 resist chronic viral infection with lymphocytic choriomeningitis virus clone 13 (LCMV cl13). The numbers and function of viral-specific CD4 T lymphocytes is greatly enhanced, whereas expression of the IFNβ-induced IL-2 repressor, cAMP-responsive element modulator (CREM) is reduced. Reduction of CREM expression in wild-type CD4 T lymphocytes prevents the loss of IL-2 production by CD4 T lymphocytes during infection with LCMV cl13. These findings implicate the IFNβ/CREM/IL-2 axis in regulating T-lymphocyte function during chronic viral infection.

Impaired functional responses in follicular lymphoma CD8+TIM-3+ T lymphocytes following TCR engagement

Upregulation of T cell immunoglobulin-3 (TIM-3) has been associated with negative regulation of the immune response in chronic infection and cancer, including lymphoma. Here, we investigated the possible correlation between TIM-3 expression by ex vivo cytotoxic T cells (CTL) from follicular lymphoma (FL) biopsies and their functional unresponsiveness that could limit the favorable impact of CTL on disease progression. We report a high percentage of CD8⁺TIM-3⁺T cells in lymph nodes of FL patients. When compared to their CD8⁺TIM-3^- counterparts, CD8⁺TIM-3⁺ T cells exhibited defective cytokine production following TCR engagement. Furthermore, CD8⁺TIM-3⁺ T cells display ex vivo markers of lytic granule release and remain unresponsive to further TCR-induced activation of the lytic machinery. Although confocal microscopy showed that TIM-3 expression on CD8⁺ T cells correlated with minor alterations of immunological synapse, a selective reduction of ERK signaling in CD8⁺TIM-3⁺T cells was observed by phospho-flow analysis. Finally, short relapse-free survival despite rituximab(R)-chemotherapy was observed in patients with high content of TIM-3⁺ cells and a poor infiltrate of granzyme B⁺ T cells in FL lymph nodes. Together, our data indicate that, besides selective TCR early signaling defects, TIM-3 expression correlates with unresponsiveness of ex vivo CD8⁺ T cells in FL. They show that scores based on the combination of exhaustion and cytolytic markers in FL microenvironment might be instrumental to identify patients at early risk of relapses following R-chemotherapy.

Immunotherapy: A promising approach to reverse sepsis-induced immunosuppression

Sepsis is defined as life-threatening organ dysfunction caused by dysregulated host responses to infection (Third International Consensus definition for Sepsis and septic shock). Despite decades of research, sepsis remains the leading cause of death in intensive care units. More than 40 clinical trials, most of which have targeted the sepsis-associated pro-inflammatory response, have failed. Thus, antibiotics and fluid resuscitation remain the mainstays of supportive care and there is intense need to discover and develop novel, targeted therapies to treat sepsis. Both pre-clinical and clinical studies over the past decade demonstrate unequivocally that sepsis not only causes hyper-inflammation, but also leads to simultaneous adaptive immune system dysfunction and impaired antimicrobial immunity. Evidences for immunosuppression include immune cell depletion (T cells most affected), compromised T cell effector functions, T cell exhaustion, impaired antigen presentation, increased susceptibility to opportunistic nosocomial infections, dysregulated cytokine secretion, and reactivation of latent viruses. Therefore, targeting immunosuppression provides a logical approach to treat protracted sepsis. Numerous pre-clinical studies using immunomodulatory agents such as interleukin-7, anti-programmed cell death 1 antibody (anti-PD-1), anti-programmed cell death 1 ligand antibody (anti-PD-L1), and others have demonstrated reversal of T cell dysfunction and improved survival. Therefore, identifying immunosuppressed patients with the help of specific biomarkers and administering specific immunomodulators holds significant potential for sepsis therapy in the future. This review focusses on T cell dysfunction during sepsis and discusses the potential immunotherapeutic agents to boost T cell function during sepsis and improve host resistance to infection.

CD28 family of receptors on T cells in chronic HBV infection: Expression characteristics, clinical significance and correlations with PD-1 blockade

The aim of the present study was to investigate the overall clinical expression characteristics of the cluster of differentiation (CD)28 family receptors [CD28, inducible T-cell co-stimulator, programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated protein 4 and B- and T-lymphocyte attenuator] on T cells in patients with chronic hepatitis B (CHB), analyze the correlations among these receptors and the clinical parameters, and to investigate the effects of PD-1 blockade on the receptor expression profiles, T-cell function and other biological effects. The expression characteristics of the CD28 family of receptors, the effects of PD-1 blockade on the receptor expression profiles and the levels of interferon (IFN)-γ were investigated in the T cells of patients with CHB. In addition, the transcription factor, T-box 21 (T-bet) and GATA binding protein 3 (GATA-3) mRNA expression levels were investigated in the peripheral blood mononuclear cells (PBMCs) of patients with CHB. The expression levels of the CD28 family receptors in the T cells of patients with CHB demonstrated distinct characteristics, for example levels of PD-1 and CTLA-4 on CD4 T cells and ICOS, PD-1, and BTLA on CD8 T cells were increased in cells from patients with CHB compared with those from the healthy individuals. A significant positive correlation was demonstrated among the serum HBV DNA titers and the levels of PD-1 on CD8⁺ T cells with the highest expression of PD-1 corresponding to viral levels >10⁶ IU/ml. A significant positive correlation was observed between the serum HBV DNA titers and the expression levels of BTLA on CD8⁺ T cells with the highest expression of BTLA corresponding to viral levels >10⁶ IU/ml. PD-1 blockade altered the expression profiles of CD28 family receptors in the T cells of patients with CHB, partly enhanced T cell function and increased the ratio of T-bet/GATA-3 mRNA in PBMCs. Thus, CD28 family receptors are potential clinical indicators for the rapid monitoring of changes in T cell function during CHB treatment. Furthermore, PD-1 blockade has a therapeutic potential that may be enhanced by modulating the expression of co-stimulatory and -inhibitory receptors of the CD28 family.

Fine-tuning of CD8(+) T-cell effector functions by targeting the 2B4-CD48 interaction

Polyfunctionality and cytotoxic activity dictate CD8(+) T-cell efficacy in the eradication of infected and malignant cells. The induction of these effector functions depends on the specific interaction between the T-cell receptor (TCR) and its cognate peptide-MHC class I complex, in addition to signals provided by co-stimulatory or co-inhibitory receptors, which can further regulate these functions. Among these receptors, the role of 2B4 is contested, as it has been described as either co-stimulatory or co-inhibitory in modulating T-cell functions. We therefore combined functional, transcriptional and epigenetic approaches to further characterize the impact of disrupting the interaction of 2B4 with its ligand CD48, on the activity of human effector CD8(+) T-cell clones. In this setting, we show that the 2B4-CD48 axis is involved in the fine-tuning of CD8(+) T-cell effector function upon antigenic stimulation. Blocking this interaction resulted in reduced CD8(+) T-cell clone-mediated cytolytic activity, together with a subtle drop in the expression of genes involved in effector function regulation. Our results also imply a variable contribution of the 2B4-CD48 interaction to the modulation of CD8(+) T-cell functional properties, potentially linked to intrinsic levels of T-bet expression and TCR avidity. The present study thus provides further insights into the role of the 2B4-CD48 interaction in the fine regulation of CD8(+) T-cell effector function upon antigenic stimulation.

T cells from patients with Candida sepsis display a suppressive immunophenotype

BACKGROUND

Despite appropriate therapy, Candida bloodstream infections are associated with a mortality rate of approximately 40%. In animal models, impaired immunity due to T cell exhaustion has been implicated in fungal sepsis mortality. The purpose of this study was to determine potential mechanisms of fungal-induced immunosuppression via immunophenotyping of circulating T lymphocytes from patients with microbiologically documented Candida bloodstream infections.

METHODS

Patients with blood cultures positive for any Candida species were studied. Non-septic critically ill patients with no evidence of bacterial or fungal infection were controls. T cells were analyzed via flow cytometry for cellular activation and for expression of positive and negative co-stimulatory molecules. Both the percentages of cells expressing particular immunophenotypic markers as well as the geometric mean fluorescence intensity (GMFI), a measure of expression of the number of receptors or ligands per cell, were quantitated.

RESULTS

Twenty-seven patients with Candida bloodstream infections and 16 control patients were studied. Compared to control patients, CD8 T cells from patients with Candidemia had evidence of cellular activation as indicated by increased CD69 expression while CD4 T cells had decreased expression of the major positive co-stimulatory molecule CD28. CD4 and CD8 T cells from patients with Candidemia expressed markers typical of T cell exhaustion as indicated by either increased percentages of or increased MFI for programmed cell death 1 (PD-1) or its ligand (PD-L1).

CONCLUSIONS

Circulating immune effector cells from patients with Candidemia display an immunophenotype consistent with immunosuppression as evidenced by T cell exhaustion and concomitant downregulation of positive co-stimulatory molecules. These findings may help explain why patients with fungal sepsis have a high mortality despite appropriate antifungal therapy. Development of immunoadjuvants that reverse T cell exhaustion and boost host immunity may offer one way to improve outcome in this highly lethal disorder.