Soluble PD-1 Facilitates 4-1BBL–Triggered Antitumor Immunity against Murine H22 Hepatocarcinoma In vivo

Recombinant Newcastle disease viruses expressing immunological checkpoint inhibitors induce a pro-inflammatory state and enhance tumor-specific immune responses in two murine models of cancer

Introduction

Tumor microenvironments are immunosuppressive due to progressive accumulation of mutations in cancer cells that can drive expression of a range of inhibitory ligands and cytokines, and recruitment of immunomodulatory cells, including myeloid-derived suppressor cells (MDSC), tumor-associated macrophages, and regulatory T cells (Tregs).

Methods

To reverse this immunosuppression, we engineered mesogenic Newcastle disease virus (NDV) to express immunological checkpoint inhibitors anti-cytotoxic T lymphocyte antigen-4 and soluble programmed death protein-1.

Results

Intratumoral administration of recombinant NDV (rNDV) to mice bearing intradermal B16-F10 melanomas or subcutaneous CT26LacZ colon carcinomas led to significant changes in the tumor-infiltrating lymphocyte profiles. Vectorizing immunological checkpoint inhibitors in NDV increased activation of intratumoral natural killer cells and cytotoxic T cells and decreased Tregs and MDSCs, suggesting induction of a pro-inflammatory state with greater infiltration of activated CD8+ T cells. These notable changes translated to higher ratios of activated effector/suppressor tumor-infiltrating lymphocytes in both cancer models, which is a promising prognostic marker. Whereas all rNDV-treated groups showed evidence of tumor regression and increased survival in the CT26LacZ and B16-F10, only treatment with NDV expressing immunological checkpoint blockades led to complete responses compared to tumors treated with NDV only.

Discussion

These data demonstrated that NDV expressing immunological checkpoint inhibitors could reverse the immunosuppressive state of tumor microenvironments and enhance tumor-specific T cell responses.

Targeting alternative splicing as a new cancer immunotherapy-phosphorylation of serine arginine-rich splicing factor (SRSF1) by SR protein kinase 1 (SRPK1) regulates alternative splicing of PD1 to generate a soluble antagonistic isoform that prevents T cell exhaustion

BACKGROUND

Regulation of alternative splicing is a new therapeutic approach in cancer. The programmed cell death receptor 1 (PD-1) is an immunoinhibitory receptor expressed on immune cells that binds to its ligands, PD-L1 and PD-L2 expressed by cancer cells forming a dominant immune checkpoint pathway in the tumour microenvironment. Targeting this pathway using blocking antibodies (nivolumab and pembrolizumab) is the mainstay of anti-cancer immunotherapies, restoring the function of exhausted T cells. PD-1 is alternatively spliced to form isoforms that are either transmembrane signalling receptors (flPD1) that mediate T cell death by binding to the ligand, PD-L1 or an alternatively spliced, soluble, variant that lacks the transmembrane domain.

METHODS

We used PCR and western blotting on primary peripheral blood mononuclear cells (PBMCs) and Jurkat T cells, IL-2 ELISA, flow cytometry, co-culture of melanoma and cholangiocarcinoma cells, and bioinformatics analysis and molecular cloning to examine the mechanism of splicing of PD1 and its consequence.

RESULTS

The soluble form of PD-1, generated by skipping exon 3 (∆Ex3PD1), was endogenously expressed in PBMCs and T cells and prevents cancer cell-mediated T cell repression. Multiple binding sites of SRSF1 are adjacent to PD-1 exon 3 splicing sites. Overexpression of phosphomimic SRSF1 resulted in preferential expression of flPD1. Inhibition of SRSF1 phosphorylation both by SRPK1 shRNA knockdown and by a selective inhibitor, SPHINX31, resulted in a switch in splicing to ∆Ex3PD1. Cholangiocarcinoma cell-mediated repression of T cell IL-2 expression was reversed by SPHINX31 (equivalent to pembrolizumab).

CONCLUSIONS

These results indicate that switching of the splicing decision from flPD1 to ∆Ex3PD1 by targeting SRPK1 could represent a potential novel mechanism of immune checkpoint inhibition in cancer.

The Expression Levels and Concentrations of PD-1 and PD-L1 Proteins in Septic Patients: A Systematic Review

Sepsis is a series of life-threatening organ dysfunction caused by an impaired host response to infection. A large number of molecular studies of sepsis have revealed complex interactions between infectious agents and hosts that result in heterogeneous manifestations of sepsis. Sepsis can cause immunosuppression and increase the expression of checkpoint inhibitor molecules, including programmed death protein (PD-1) and programmed death ligand 1 (PD-L1), and thus PD-1 and PD-L1 are thought to be useful as diagnostic and prognostic tools for sepsis. PD-1 is an inhibitor of both adaptive and innate immune responses, and is expressed on activated T lymphocytes, natural killer (NK) cells, B lymphocytes, macrophages, dendritic cells (DCs), and monocytes, whereas PD-L1 is expressed on macrophages, some activated T and B cells, and mesenchymal stem cells as well as various non-hematopoietic cells. This systematic review aims to assess the PD-1 and PD-L1 protein expression levels and concentrations in septic and other infectious patients.

Increased Soluble PD-1 Predicts Response to Nivolumab plus Ipilimumab in Melanoma

BACKGROUND

Checkpoint inhibitors have revolutionized the treatment of metastatic melanoma, yielding long-term survival in a considerable proportion of the patients. Yet, 40-60% of patients do not achieve a long-term benefit from such therapy, emphasizing the urgent need to identify biomarkers that can predict response to immunotherapy and guide patients for the best possible treatment. Here, we exploited an unsupervised machine learning approach to identify potential inflammatory cytokine signatures from liquid biopsies, which could predict response to immunotherapy in melanoma.

METHODS

We studied a cohort of 77 patients diagnosed with unresectable advanced-stage melanoma undergoing treatment with first-line nivolumab plus ipilimumab or pembrolizumab. Baseline and on-treatment plasma samples were tested for levels of PD-1, PD-L1, IFNγ, IFNβ, CCL20, CXCL5, CXCL10, IL6, IL8, IL10, MCP1, and TNFα and analyzed by Uniform Manifold Approximation and Projection (UMAP) dimension reduction method and k-means clustering analysis.

RESULTS

Interestingly, using UMAP analysis, we found that treatment-induced cytokine changes measured as a ratio between baseline and on-treatment samples correlated significantly to progression-free survival (PFS). For patients treated with nivolumab plus ipilimumab we identified a group of patients with superior PFS that were characterized by significantly higher baseline-to-on-treatment increments of PD-1, PD-L1, IFNγ, IL10, CXCL10, and TNFα compared to patients with worse PFS. Particularly, a high PD-1 increment was a strong individual predictor for superior PFS (HR = 0.13; 95% CI 0.034-0.49; p = 0.0026). In contrast, decreasing levels of IFNγ and IL6 and increasing levels of CXCL5 were associated with superior PFS in the pembrolizumab group, although none of the cytokines were individually predictors for PFS.

CONCLUSIONS

In short, our study demonstrates that a high increment of PD-1 is associated with superior PFS in advanced-stage melanoma patients treated with nivolumab plus ipilimumab. In contrast, decreasing levels of IFNγ and IL6, and increasing levels of CXCL5 are associated with response to pembrolizumab. These results suggest that using serial samples to monitor changes in cytokine levels early during treatment is informative for treatment response.

Biological Characteristics and Clinical Significance of Soluble PD-1/PD-L1 and Exosomal PD-L1 in Cancer

The immune checkpoint pathway consisting of the cell membrane-bound molecule programmed death protein 1 (PD-1) and its ligand PD-L1 has been found to mediate negative regulatory signals that effectively inhibit T-cell proliferation and function and impair antitumor immune responses. Considerable evidence suggests that the PD-1/PD-L1 pathway is responsible for tumor immune tolerance and immune escape. Blockage of this pathway has been found to reverse T lymphocyte depletion and restore antitumor immunity. Antagonists targeting this pathway have shown significant clinical activity in specific cancer types. Although originally identified as membrane-type molecules, several other forms of PD-1/PD-L1 have been detected in the blood of cancer patients, including soluble PD-1/PD-L1 (sPD-1/sPD-L1) and exosomal PD-L1 (exoPD-L1), increasing the composition and functional complications of the PD-1/PD-L1 signaling pathway. For example, sPD-1 has been shown to block the PD-1/PD-L immunosuppressive pathway by binding to PD-L1 and PD-L2, whereas the role of sPD-L1 and its mechanism of action in cancer remain unclear. In addition, many studies have investigated the roles of exoPD-L1 in immunosuppression, as a biomarker for tumor progression and as a predictive biomarker for response to immunotherapy. This review describes the molecular mechanisms underlying the generation of sPD-1/sPD-L1 and exoPD-L1, along with their biological activities and methods of detection. In addition, this review discusses the clinical importance of sPD-1/sPD-L1 and exoPD-L1 in cancer, including their predictive and prognostic roles and the effects of treatments that target these molecules.

Seven mysteries of LAG-3: a multi-faceted immune receptor of increasing complexity

Despite three decades of research to its name and increasing interest in immunotherapies that target it, LAG-3 remains an elusive co-inhibitory receptor in comparison to the well-established PD-1 and CTLA-4. As such, LAG-3 targeting therapies have yet to achieve the clinical success of therapies targeting other checkpoints. This could, in part, be attributed to the many unanswered questions that remain regarding LAG-3 biology. Of these, we address: (i) the function of the many LAG-3-ligand interactions, (ii) the hurdles that remain to acquire a high-resolution structure of LAG-3, (iii) the under-studied LAG-3 signal transduction mechanism, (iv) the elusive soluble form of LAG-3, (v) the implications of the lack of (significant) phenotype of LAG-3 knockout mice, (vi) the reports of LAG-3 expression on the epithelium, and (vii) the conflicting reports of LAG-3 expression (and potential contributions to pathology) in the brain. These mysteries which surround LAG-3 highlight how the ever-evolving study of its biology continues to reveal ever-increasing complexity in its role as an immune receptor. Importantly, answering the questions which shroud LAG-3 in mystery will allow the maximum therapeutic benefit of LAG-3 targeting immunotherapies in cancer, autoimmunity and beyond.

Feedback regulation of antioxidant transcription factor NFE2L1 and immunostimulatory factor 41BBL mediates the crosstalk between oxidative stress and tumor immunity

Targeting the immune checkpoint to inhibit tumor immune escape, which is one of the fundamental causes of cancer, has become an important strategy for cancer treatment. The molecular mechanism of tumor immune escape involved in the process of spontaneous hepatocellular carcinoma after specifically knocking out NFE2L1, the core regulator of redox homeostasis, in the mouse liver is still unclear. Transcriptome data showed that the immunostimulatory TNFSF9/41BBL was significantly reduced in NFE2L1 knockdown hepatocarcinoma HepG2 cells, and this suggests that 41BBL may be an oxidative stress-responsive immune checkpoint. The results of the promoter activity experiment showed that NFE2L1 can promote 41BBL gene transcription activation through the ARE element in the promoter region. In addition, cell biology experiments have found that overexpression of 41BBL can inhibit cell proliferation and promote senescence. Importantly, reactive oxygen species in cells significantly increased after overexpression of 41BBL, whereas NFE2L1 was inhibited, indicating that 41BBL has the effect of feedback regulating oxidative stress in cells. In conclusion, in this study, the transcriptional activation effect of NFE2L1 on 41BBL and the feedback inhibition relationship of 41BBL on NFE2L1 was clarified. The NFE2L1/41BBL axis might be an important pathway that mediates the crosstalk between oxidative stress and the tumor immune response.

Development and Verification of an Immune-Related Gene Pairs Prognostic Signature in Hepatocellular Carcinoma

With the increasing prevalence of Hepatocellular carcinoma (HCC) and the poor prognosis of immunotherapy, reliable immune-related gene pairs (IRGPs) prognostic signature is required for personalized management and treatment of patients. Gene expression profiles and clinical information of HCC patients were obtained from the TCGA and ICGC databases. The IRGPs are constructed using immune-related genes (IRGs) with large variations. The least absolute shrinkage and selection operator (LASSO) regression analysis was used to construct IRGPs signature. The IRGPs signature was verified through the ICGC cohort. 1,309 IRGPs were constructed from 90 IRGs with high variability. We obtained 50 IRGPs that were significantly connected to the prognosis and constructed a signature that included 17 IRGPs. In the TCGA and ICGC cohorts, patients were divided into high and low-risk patients by the IRGPs signature. The overall survival time of low-risk patients is longer than that of high-risk patients. After adjustment for clinical and pathological factors, multivariate analysis showed that the IRGPs signature is an independent prognostic factor. The Receiver operating characteristic (ROC) curve confirmed the accuracy of the signature. Besides, gene set enrichment analysis (GSEA) revealed that the signature is related to immune biological processes, and the immune microenvironment status is distinct in different risk patients. The proposed IRGPs signature can effectively assess the overall survival of HCC, and provide the relationship between the signature and the reactivity of immune checkpoint therapy and the sensitivity of targeted drugs, thereby providing new ideas for the diagnosis and treatment of the disease.

Soluble B7-CD28 Family Inhibitory Immune Checkpoint Proteins and Anti-Cancer Immunotherapy

Co-inhibitory B7-CD28 family member proteins negatively regulate T cell responses and are extensively involved in tumor immune evasion. Blockade of classical CTLA-4 (cytotoxic T lymphocyte-associated antigen-4) and PD-1 (programmed cell death protein-1) checkpoint pathways have become the cornerstone of anti-cancer immunotherapy. New inhibitory checkpoint proteins such as B7-H3, B7-H4, and BTLA (B and T lymphocyte attenuator) are being discovered and investigated for their potential in anti-cancer immunotherapy. In addition, soluble forms of these molecules also exist in sera of healthy individuals and elevated levels are found in chronic infections, autoimmune diseases, and cancers. Soluble forms are generated by proteolytic shedding or alternative splicing. Elevated circulating levels of these inhibitory soluble checkpoint molecules in cancer have been correlated with advance stage, metastatic status, and prognosis which underscore their broader involvement in immune regulation. In addition to their potential as biomarker, understanding their mechanism of production, biological activity, and pathological interactions may also pave the way for their clinical use as a therapeutic target. Here we review these aspects of soluble checkpoint molecules and elucidate on their potential for anti-cancer immunotherapy.

Correlation of sPD1 with Procalcitonin and C-Reactive Protein Levels in Patients with Sepsis

Objective

Sepsis results from dysregulated host responses to infection, and it is a major cause of mortality in the world. Co-inhibitory molecules, such as PD-1, play a critical role in this process. Considering the lack of information on the relation between sPD1 and sepsis, the present study aimed to examine the sPD1 level in septic patients and evaluate its correlation with procalcitonin (PCT) and C-reactive protein (CRP) levels.

Materials and Methods

This descriptive cross-sectional study consisted of three groups, including septic patients (n=15), suspected of sepsis (n=15), and healthy subjects (n=15). White blood cells (WBCs) and platelet (PLT) counts are evaluated. The serum levels of CRP, PCT, and sPD1 were measured by immunoturbidimetric assay, electro- chemiluminescence technology, and the enzyme-linked immunosorbent assay (ELISA), respectively.

Results

Our study indicated that there was a significant difference in WBC and PLT counts between the septic group compared to suspected and control groups (P<0.001, P<0.01, respectively). The CRP level was significantly higher in septic compared to suspected and control groups (P<0.001). There was also a significant difference between the PCT level in septic and suspected groups in comparison with the controls (P<0.001, P<0.01). The sPD1 level was significantly higher in septic patients compared to suspected and control groups (P<0.001). In septic patients, sPD1 levels were correlated positively with the CRP and PCT levels.

Conclusion

Overall, sPD1 correlation with inflammatory markers, might propose it as a potential biomarker to sepsis diagnosis. However, the clinical application of serum sPD-1 testing in patients with sepsis requires further investigation.

Soluble PD-1: Predictive, Prognostic, and Therapeutic Value for Cancer Immunotherapy

Programmed death protein 1 (PD-1) interaction with PD-L1 deliver immunosuppressive environment for tumor growth, and its blockade with directed monoclonal antibodies (anti-PD-1/anti-PD-L1) has shown remarkable clinical outcome. Lately, their soluble counterparts, sPD-1 and sPD-L1, have been detected in plasma, and elevated levels have been associated with advanced disease, clinical stages, and worst prognosis for cancer patients. Elevated plasma levels of sPD-L1 have been correlated with worst prognosis in several studies and has displayed a persistent outlook. On the other hand, sPD-1 levels have been inconsistent in their predictive and prognostic ability. Pretherapeutic higher sPD-1 plasma levels have shown to predict advanced disease state and to a lesser extent worst prognosis. Any increase in sPD-1 plasma level post therapeutically have been correlated with improved survival for various cancers. In vitro and in vivo studies have shown sPD-1 ability to bind PD-L1 and PD-L2 and block PD-1/PD-L1 interaction. Local delivery of sPD-1 in cancer tumor microenvironment through local gene therapy have demonstrated an increase in tumor specific CD8+ T cell immunity and tumor growth reduction. It had also exhibited enhancement of T cell immunity induced by vaccination and other gene therapeutic agents. Furthermore, it may also lessen the inhibitory effect of circulating sPD-L1 and enhance the effects of mAb-based immunotherapy. In this review, we highlight various aspects of sPD-1 role in cancer prediction, prognosis, and anti-cancer immunity, as well as, its therapeutic value for local gene therapy or systemic immunotherapy in blocking the PD-1 and PD-L1 checkpoint interactions.

Profiles of serum soluble programmed death-1 and programmed death-ligand 1 levels in chronic hepatitis B virus-infected patients with different disease phases and after anti-viral treatment

BACKGROUND

Soluble programmed death-1 (sPD-1) and soluble programmed death-ligand 1 (sPD-L1) play a role in immune regulation of chronic hepatitis B virus (HBV) infection.

AIM

To investigate the profiles of serum sPD-1 and sPD-L1 in chronic HBV-infected patients with different disease phases and after anti-viral treatment.

METHODS

A total of 99 chronic HBV-infected patients were enrolled and divided into HBeAg-positive chronic HBV infection (EPI) group, HBeAg-positive chronic hepatitis B (EPH) group, HBeAg-negative chronic hepatitis B (ENH) group and HBeAg-negative chronic HBV infection (ENI) group. Eleven healthy subjects were included as healthy controls (HCs). Thirty-two EPH patients received anti-viral treatment with nucleos(t)ide analogues and were followed up to 5 years. Serum sPD-1 and sPD-L1 levels were detected by Multiplex Immunoassays.

RESULTS

Serum sPD-1 and sPD-L1 levels of chronic HBV infected patients were significantly higher than that of HCs (P < 0.01). Patients in EPH, ENH and EPI groups had higher serum sPD-1 and sPD-L1 levels than that in HCs (P < 0.01). After anti-viral treatment, serum sPD-1 and sPD-L1 levels declined rapidly. EPH patients with HBeAg clearance after 2 years of anti-viral treatment showed lower baseline HBeAg and sPD-1 levels compared to those without HBeAg clearance.

CONCLUSIONS

Serum sPD-1 and sPD-L1 levels varied among chronic HBV infected patients with different disease phases. Lower baseline sPD-1 levels were associated with HBeAg clearance after 2 years of anti-viral treatment in EPH patients.

Prognostic value of programmed cell death ligand 1 (PD-L1) for hepatocellular carcinoma: a meta-analysis

The prognostic role of programmed death ligand-1 (PD-L1) expression in hepatocellular carcinoma (HCC) has been widely studied but the results are controversial. In this comprehensive meta-analysis, we elucidated the clinical value of PD-L1 in HCC. Relevant studies were systematically searched in the Cochrane Library, EMBASE, and PubMed until June 27, 2019. Eligible studies were validated for the prognostic effect of PD-L1 on the overall survival (OS), disease-free survival (DFS), and relapse-free survival (RFS) in HCC using a hazard ratio (HR) and its 95% confidence interval (95% CI). Twenty-three studies with 3529 patients were involved in this meta-analysis. The pooled results revealed that high membrane-bound PD-L1 (mPD-L1) expression was associated with poor OS (HR: 1.42; 95% CI: 1.12-1.80; P = 0.004) and had no significant correlation with RFS (HR: 1.14; 95% CI: 0.85-1.54; P = 0.39), and DFS (HR: 1.36; 95% CI: 0.81-2.28; P = 0.25). The results also indicated that high soluble PD-L1 (sPD-L1) levels were associated with worse OS (HR: 2.93; 95% CI: 2.20-3.91; P < 0.00001). In addition, high mPD-L1 expression was associated with high alpha-fetoprotein levels (AFP; OR = 1.46; 95% CI: 1.16-1.84; P = 0.001), hepatitis (OR = 0.72; 95% CI: 0.54-0.98; P = 0.03), poor tumor differentiation (OR = 0.68; 95% CI: 0.55-0.84; P = 0.03), and tumor-infiltrating lymphocytes (OR = 3.39; 95% CI: 1.06-10.91; P = 0.04). The mPD-L1 expression had no significant correlation with age, number of tumors, gender, tumor size, liver cirrhosis, vascular invasion, tumor encapsulation, or TNM stage. The study revealed that high mPD-L1 expression in the tumor tissue and high sPD-L1 levels were associated with shorter OS in HCC. Moreover, overexpression of mPD-L1 was significantly associated with poor tumor differentiation, hepatitis, AFP elevation, and tumor-infiltrating lymphocytes.

Single droplet detection of immune checkpoints on a multiplexed electrohydrodynamic biosensor

Monitoring soluble immune checkpoints in circulating fluids has the potential for minimally-invasive diagnostics and personalised therapy in precision medicine. Yet, the sensitive detection of multiple immune checkpoints from small volumes of liquid biopsy samples is challenging. In this study, we develop a multiplexed immune checkpoint biosensor (MICB) for parallel detection of soluble immune checkpoints PD-1, PD-L1, and LAG-3. MICB integrates a microfluidic sandwich immunoassay using engineered single chain variable fragments and alternating current electrohydrodynamic in situ nanofluidic mixing for promoting biosensor-target interaction and reducing non-specific non-target binding. MICB provides advantages of simultaneous analysis of up to 28 samples in <2 h, requires as little as a single sample drop (i.e., 20 μL) per target immune checkpoint, and applies high-affinity yeast cell-derived single chain variable fragments as a cost-effective alternative to monoclonal antibodies. We investigate the assay performance of MICB and demonstrate its capability for accurate immune checkpoint detection in simulated patient serum samples at clinically-relevant levels. MICB provides a dynamic range of 5 to 200 pg mL-1 for PD-1 and PD-L1, and 50 to 1000 pg mL-1 for LAG-3 with a coefficient of variation <13.8%. Sensitive immune checkpoint detection was achieved with limits of detection values of 5 pg mL-1 for PD-1, 5 pg mL-1 for PD-L1, and 50 pg mL-1 for LAG-3. The multiplexing capability, sensitivity, and relative assay simplicity of MICB make it capable of serving as a bioanalytical tool for immune checkpoint therapy monitoring.

Expression of costimulatory and inhibitory receptors in FoxP3+ regulatory T cells within the tumor microenvironment: Implications for combination immunotherapy approaches

The unprecedented success of immune checkpoint inhibitors has given rise to a rapidly growing number of immuno-oncology agents undergoing preclinical and clinical development and an exponential increase in possible combinations. Defining a clear rationale for combinations by identifying synergies between immunomodulatory pathways has therefore become a high priority. Immunosuppressive regulatory T cells (Tregs) within the tumor microenvironment (TME) represent a major roadblock to endogenous and therapeutic tumor immunity. However, Tregs are also essential for the maintenance of immunological self-tolerance, and share many molecular pathways with conventional T cells including cytotoxic T cells, the primary mediators of tumor immunity. Hence the inability to specifically target and neutralize Tregs within the TME of cancer patients without globally compromising self-tolerance poses a significant challenge. Here we review recent advances in the characterization of tumor-infiltrating Tregs with a focus on costimulatory and inhibitory receptors. We discuss receptor expression patterns, their functional role in Treg biology and mechanistic insights gained from targeting these receptors in preclinical models to evaluate their potential as clinical targets. We further outline a framework of parameters that could be used to refine the assessment of Tregs in cancer patients and increase their value as predictive biomarkers. Finally, we propose modalities to integrate our increasing knowledge on Treg phenotype and function for the rational design of checkpoint inhibitor-based combination therapies. Such combinations have great potential for synergy, as they could concomitantly enhance cytotoxic T cells and inhibit Tregs within the TME, thereby increasing the efficacy of current cancer immunotherapies.

HBV and HIV/HBV Infected Patients Have Distinct Immune Exhaustion and Apoptotic Serum Biomarker Profiles

Background:

Hepatitis B virus (HBV) infection is a leading cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma worldwide. Due to their shared routes of transmission, approximately 10% of HIV-infected patients worldwide are chronically coinfected with HBV. Additionally, liver disease has become a major cause of morbidity and mortality in HBV/HIV coinfected patients due to prolonged survival with the success of antiretroviral therapy. The relationship between immune exhaustion markers (PD-1/PD-L1) and apoptotic markers such as Fas/FasL, TGFβ1, TNF-α, and Th1/Th2 cytokines are not clearly delineated in HBV/HIV coinfection.

Methods:

Levels of soluble Fas/FasL, TGFβ1, TNF-α, and sPD-1/sPD-L1 as well as Th1 and Th2 cytokines were evaluated in the sera of HBV-monoinfected (n = 30) and HBV/HIV-coinfected (n = 15) patients and compared to levels in healthy controls (n = 20).

Results:

HBV-monoinfected patients had significantly lower levels of the anti-inflammatory cytokine IL-4 (P < 0.05) and higher levels of apoptotic markers sFas, sFasL, and TGFβ-1 (P < 0.001) compared to healthy controls. Coinfection with HIV was associated with higher levels of sFas, TNF-α, and sPD-L1 (P < 0.005), and higher levels of the pro-inflammatory cytokines IL-6, IL-8, and IL-12p70 (P < 0.05) compared to healthy controls. Patients with HBV infection had a unique biomarker clustering profile comprised of IFN-γ, IL12p70, IL-10, IL-6, and TNF-α that was distinct from the profile of the healthy controls, and the unique HIV/HBV profile comprised GM-CSF, IL-4, IL-2, IFN-γ, IL12p70, IL-7, IL-10, and IL-1β. In HBV monoinfection a significant correlation between sFasL and PD1(r = 0.46, P = < 0.05) and between sFas and PDL1 (r = 0.48, P = <0.01) was observed.

Conclusion:

HBV-infected and HBV/HIV-coinfected patients have unique apoptosis and inflammatory biomarker profiles that distinguish them from each other and healthy controls. The utilization of those unique biomarker profiles for monitoring disease progression or identifying individuals who may benefit from novel immunotherapies such as anti-PD-L1 or anti-PD-1 checkpoint inhibitors appears promising and warrants further investigation.

Soluble immune checkpoints in cancer: production, function and biological significance

Immune checkpoints play important roles in immune regulation, and blocking immune checkpoints on the cell membrane is a promising strategy in the treatment of cancer. Based on this, monoclonal antibodies are having much rapid development, such as those against CTLA-4 (cytotoxic T lymphocyte antigen 4) and PD-1 (programmed cell death protein 1).But the cost of preparation of monoclonal antibodies is too high and the therapeutic effect is still under restrictions. Recently, a series of soluble immune checkpoints have been found such as sCTLA-4 (soluble CTLA-4) and sPD-1 (soluble PD-1). They are functional parts of membrane immune checkpoints produced in different ways and can be secreted by immune cells. Moreover, these soluble checkpoints can diffuse in the serum. Much evidence has demonstrated that these soluble checkpoints are involved in positive or negative immune regulation and that changes in their plasma levels affect the development, prognosis and treatment of cancer. Since they are endogenous molecules, they will not induce immunological rejection in human beings, which might make up for the deficiencies of monoclonal antibodies and enhance the utility value of these molecules. Therefore, there is an increasing need for investigating novel soluble checkpoints and their functions, and it is promising to develop relevant therapies in the future. In this review, we describe the production mechanisms and functions of various soluble immune checkpoint receptors and ligands and discuss their biological significance in regard to biomarkers, potential candidate drugs, therapeutic targets, and other topics.

Soluble PD-1-based vaccine targeting MUC1 VNTR and survivin improves anti-tumor effect

Soluble PD-1 (sPD1) can bind with ligands PD-L1/PD-L2 on the surface of dendritic cells (DCs). Therefore, a sPD1 vaccine fused with an immunogen can increase T cell activation against cancer. Here, we constructed a MUC1 and survivin (MS) combination gene tumor vaccine expressing MS fused with soluble PD-1 (sPD1/MS). To investigate whether the sPD1/MS fusion vaccine could enhance tumor-specific immune responses, its immunogenicity and anti-tumor activity were examined after intramuscular immunization in mice. Compared with the MS DNA vaccine, the specific cytolysis rate of the sPD1/MS fusion DNA vaccine was increased from 21.64% to 34.77%. Moreover, the sPD1/MS vaccine increased the tumor suppression rate from 17.18% to 30.96% and prolonged survival from 6.96% to 19.44% in a murine colorectal cancer model. Combining the sPD1/MS vaccine with oxaliplatin improved the tumor suppression rate to 74.71% in the murine colorectal cancer model. The sPD1/MS vaccine could also exert a good anti-tumor effect, increasing the tumor infiltrated CD8⁺ T cells by 6.5-fold (from 0.10% to 0.65%) in the murine lung cancer model. In conclusion, the sPD1/MS vaccine showed good immunogenicity and anti-tumor effect by activating lymphocytes effectively.

Circulating soluble programmed death-1 levels may differentiate immune-tolerant phase from other phases and hepatocellular carcinoma from other clinical diseases in chronic hepatitis B virus infection

Programmed death-1 (PD-1) is involved in the immune dysfunction of hepatitis B virus (HBV) infection and hepatocellular carcinoma (HCC). This study analyzed the association of circulating soluble PD-1 (sPD-1) levels with the phases and clinical diseases in chronic HBV infection. Serum sPD-1 levels were determined by enzyme linked immunosorbent assay in patients with different phases and liver diseases of chronic HBV infection. The sPD-1 levels in patients with chronic HBV infection were significantly elevated compared with HBV infection resolvers or healthy controls. According to phases, sPD-1 level in immune-tolerant phase (IT) was significantly lower than in other phases. Multivariate analysis showed that sPD-1 was an independent factor associated with IT. Area under the receiver operating characteristic (ROC) curves (AUC) showed that sPD-1 was significantly discriminative of IT from other phases with a cut-off of 1.535 ng/mL (AUC, 0.984; P<0.001). According to clinical diseases, sPD-1 level in HBV-related HCC was significantly higher than in other clinical diseases. Multivariate analysis showed that sPD-1 was an independent factor associated with HCC. The sPD-1 was significantly discriminative of HCC from other clinical diseases with a cut-off of 6.058 ng/mL (AUC, 0.962; P<0.001). The sPD-1 levels were significantly associated with HCC patients’ overall survival. HCC resection resulted in remarkable reduction in sPD-1 levels. These results demonstrate the involvement of sPD-1 in the disease course of chronic HBV infection and indicate the potential to apply sPD-1 as a biomarker for differentiating IT from other phases and HCC from other disease conditions in chronic HBV infection.

Immunotherapy for hepatocellular carcinoma patients: is it ready for prime time?

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and the second most common cause of cancer death worldwide. Current treatment options for patients with intermediate and advanced HCC are limited, and there is an unmet need for novel therapeutic approaches. HCC is an attractive target for immunomodulation therapy, since it arises in an inflammatory milieu due to hepatitis B and C infections and cirrhosis. However, a major barrier to the development and success of immunotherapy in patients with HCC is the liver's inherent immunosuppressive function. Recent advances in the field of cancer immunology allowed further characterization of immune cell subsets and function, and created new opportunities for therapeutic modulation of the immune system. In this review, we present the different immune cell subsets involved in potential immune modulation of HCC, discuss their function and clinical relevance, review the variety of immune therapeutic agents currently under investigation in clinical trials, and outline future research directions.

[Soluble PD-1 over-expression enhances the anti-tumor effect of senescence tumor cell vaccine against breast cancer cell growth in tumor-bearing mice]

OBJECTIVE

To investigate whether soluble PD-1 overexpression in 4T1 senescence tumor cells enhances the antitumor effect of senescence tumor cell vaccine (STCV) against breast tumor cells in a tumor-bearing mouse model.

METHODS

4T1 cells were treated with interferon-γ (IFN-γ) and the expression of PD-L1 was detected by flow cytometry. CCK8 assay was used to compare the cell proliferation activity between 4T1 cells and 4T1 cells infected by a lentiviral vector of sPD-1 (4T1/sPD-1 cells), and the expressions of sPD-1 mRNA and protein in 4T1/sPD-1 cells were detected using qPCR and Western blotting. The culture supernatant of 4T1/sPD-1 cells was added in 4T1 cells pre-treated with IFN-γ, and PD-1-positive 4T1 cells were detected with flow cytometry. Senescence β-galactosidase staining kit was used to detect the senescent 4T1 and 4T1/sPD-1 cells following exposure to X-ray radiation and Veliparib. Balb/c mice bearing subcutaneous 4T1 tumor xenografts were treated with injections of PBS, 4T1 STCV, or 4T1/sPD-1 STCV, and tumor growth was observed.

RESULTS

Stimulation with IFN-γ concentration-dependently up-regulated PD-L1 expression by as much as (84.80 ± 1.03)% in 4T1 cells (P < 0.001). sPD-1 overexpression in 4T1 cells did not significantly affect the cell proliferation. Treatment of 4T1 cells with 4T1/sPD-1 cell culture supernatant significantly increased the proportion of PD-1 + cells from (6.893 ± 0.271)% to (55.450 ± 0.555)% (P < 0.001). X-ray irradiation combined with Veliparib caused obvious senescence in 4T1 and 4T1/sPD-1 cells. In the tumor-preventing experiment, tumor formation occurred in all the mice in PBS group; 28.787% of the mice in 4T1 STCV group and 55.556% in 4T1/sPD-1 STCV group showed no tumor formation. In the tumor treatment experiment, tumor formation occurred in all the mice in PBS groups while in 4T1 STCV and 4T1/sPD-1 STCV groups, 11.111% and 38.89% of the mice were tumor-free during the observation period, respectively.

CONCLUSIONS

Senescence tumor cells vaccine has antitumor effect against breast cancer in mice, and sPD-1 overexpression can enhance this effect of the vaccine.

Transient and Local Expression of Chemokine and Immune Checkpoint Traps To Treat Pancreatic Cancer

Pancreatic tumors are known to be resistant to immunotherapy due to the extensive immune suppressive tumor microenvironment (TME). We hypothesized that CXCL12 and PD-L1 are two key molecules controlling the immunosuppressive TME. Fusion proteins, called traps, designed to bind with these two molecules with high affinity (K_d = 4.1 and 0.22 nM, respectively) were manufactured and tested for specific binding with the targets. Plasmid DNA encoding for each trap was formulated in nanoparticles and intravenously injected to mice bearing orthotopic pancreatic cancer. Expression of traps was mainly seen in the tumor, and secondarily, accumulations were primarily in the liver. Combination trap therapy shrunk the tumor and significantly prolonged the host survival. Either trap alone only brought in a partial therapeutic effect. We also found that CXCL12 trap allowed T-cell penetration into the tumor, and PD-L1 trap allowed the infiltrated T-cells to kill the tumor cells. Combo trap therapy also significantly reduced metastasis of the tumor cells to other organs. We conclude that the trap therapy significantly modified the immunosuppressive TME to allow the host immune system to kill the tumor cells. This can be an effective therapy in clinical settings.

The risk stratification and prognostic evaluation of soluble programmed death-1 on patients with sepsis in emergency department

OBJECTIVE

To evaluate the efficacy of soluble programmed death-1 (sPD-1) for risk stratification and prediction of 28-day mortality in patients with sepsis, we compared serum sPD-1 with procalcitonin (PCT), C-reactive protein (CRP), and the Mortality in Emergency Department Sepsis (MEDS) score.

METHODS

A total of 60 healthy volunteers and 595 emergency department (ED) patients were recruited for this prospective cohort study. According to the severity of their condition on ED arrival, the patients were allocated to the systemic inflammatory response syndrome group (130 cases), sepsis group (276 cases), severe sepsis group (121 cases), and septic shock group (68 cases). In addition, all patients with sepsis were also divided into the survivor group (349 cases) and nonsurvivor group (116 cases) according to the 28-day outcomes.

RESULTS

When the severity of sepsis increased, the levels of sPD-1 gradually increased. The levels of sPD-1, PCT, CRP and the MEDS score were also higher in the nonsurvivor group compared to the survivor group. Logistic regression suggested that sPD-1, PCT, and the MEDS score were independent risk factors for 28-day mortality of patients with sepsis. Area under the curve (AUC) of sPD-1, PCT and the MEDS score for 28-day mortality was 0.725, 0.693, and 0.767, respectively, and the AUC was improved when all 3 factors were combined (0.843).

CONCLUSION

Serum sPD-1 is positively correlated with the severity of sepsis, and it is valuable for risk stratification of patients and prediction of 28-day mortality. Combining sPD-1 with PCT and the MEDS score improves the prognostic evaluation.

Soluble PD-1 and PD-L1: predictive and prognostic significance in cancer

The membrane-bound molecules programmed death 1 (PD-1) and its ligand PD-L1 (PD-1/PD-L1) belong to the immune checkpoint pathway. PD-1 pathway downregulates effector T cells in immune response, thereby causing immune suppression. Recent studies have revealed that membrane-bound PD-1 and PD-L1 also have soluble forms. These soluble forms increase the complexity and diversity of the composition and function of the PD-1/PD-L1 signaling pathway. However, the exact roles of these molecules remain unknown. The objective of this systematic review was to elucidate the biological significance of soluble PD-1/PD-L1 in human cancers and evaluate whether they are potential diagnostic, therapeutic, or prognostic biomarkers. We expect to provide new clues for future research on soluble PD-1/PD-L1 pathway in human malignant tumors.

Soluble programmed death-1 levels are associated with disease activity and treatment response in patients with autoimmune hepatitis

PURPOSE

Autoimmune hepatitis (AIH) is a chronic liver disease caused by impaired immune regulation. Programmed death-1 (PD-1) is an inhibitory receptor mainly expressed by T cells and with its ligands, PD-L1 and PD-L2 present on antigen-presenting cells. We hypothesised the PD-1 axis to be impaired in AIH and investigated systemic levels of soluble(s) PD-1 and T cells ability to up-regulate PD-1 following in vitro activation in AIH patients.

MATERIALS AND METHODS

We included 67 AIH patients; 9 with active disease, 31 responders and 27 incomplete-responders to standard therapy. Forty-seven healthy controls (HC) were included for comparison. Soluble PD-1 was measured by enzyme-linked immunosorbent assay. The PD-1 expression on T cells was measured using flow cytometry before and after 48-h stimulation in vitro with CD3/CD28 in 13 AIH patients and 10 HC.

RESULTS

Soluble PD-1 was significantly elevated in AIH patients with active disease [0.24 ng/mL (range 0.16-0.28)] and in incomplete responders to standard therapy [0.17 (0.11-0.22)] compared with responders [0.11 (0.08-0.16), p = .008 and p = .01, respectively] and HC [0.12 (0.05-0.16), p = .02, both]. Following in vitro activation, PD-1 was significantly up-regulated (3.3-fold) on CD4⁺ T cells from AIH patients compared with HC (1.5-fold) (p = .0006).

CONCLUSIONS

AIH patients with active disease and incomplete response to standard treatment have similarly increased sPD-1 levels. Further, AIH patients have increased ability to up-regulate PD-1 following in vitro activation. Together these data suggests an impaired PD-1 axis in AIH.

4-1BB agonism: adding the accelerator to cancer immunotherapy

The success of checkpoint inhibitors has validated immunomodulatory agents as a valuable class of anticancer therapeutics. A promising co-stimulatory immunologic target is 4-1BB, or CD137, a member of the tumor necrosis factor receptor superfamily. Ligation of 4-1BB induces an activating signal in CD8(+) T cells and natural killer cells, resulting in increased pro-inflammatory cytokine secretion, cytolytic function, and antibody-dependent cell-mediated cytotoxicity. Targeting 4-1BB with agonistic monoclonal antibody (mAb) therapy demonstrated potent antitumor effects in murine tumor models. While anti-4-1BB mAbs have entered clinical trials, optimal efficacy of 4-1BB-targeted agents will inevitably come from combination therapeutic strategies. Checkpoint blockade is a compelling combination partner for 4-1BB agonism. This novel immunotherapeutic approach has the potential to active antitumor immune effectors by a complementary mechanism: simultaneously "removing the brakes" via blocking inhibitory signaling and "stepping on the accelerator" via co-stimulation. While important considerations should be given to 4-1BB-mediated toxicities, the current understanding of 4-1BB biology suggests it may play a key role in advancing the capabilities of cancer combination therapy.

4-1BB Agonists: Multi-Potent Potentiators of Tumor Immunity

Immunotherapy is a rapidly expanding field of oncology aimed at targeting, not the tumor itself, but the immune system combating the cancerous lesion. Of the many approaches currently under study to boost anti-tumor immune responses; modulation of immune co-receptors on lymphocytes in the tumor microenvironment has thus far proven to be the most effective. Antibody blockade of the T cell co-inhibitory receptor cytotoxic T lymphocyte antigen-4 (CTLA-4) has become the first FDA approved immune checkpoint blockade; however, tumor infiltrating lymphocytes express a diverse array of additional stimulatory and inhibitory co-receptors, which can be targeted to boost tumor immunity. Among these, the co-stimulatory receptor 4-1BB (CD137/TNFSF9) possesses an unequaled capacity for both activation and pro-inflammatory polarization of anti-tumor lymphocytes. While functional studies of 4-1BB have focused on its prominent role in augmenting cytotoxic CD8 T cells, 4-1BB can also modulate the activity of CD4 T cells, B cells, natural killer cells, monocytes, macrophages, and dendritic cells. 4-1BB’s expression on both T cells and antigen presenting cells, coupled with its capacity to promote survival, expansion, and enhanced effector function of activated T cells, has made it an alluring target for tumor immunotherapy. In contrast to immune checkpoint blocking antibodies, 4-1BB agonists can both potentiate anti-tumor and anti-viral immunity, while at the same time ameliorating autoimmune disease. Despite this, 4-1BB agonists can trigger high grade liver inflammation which has slowed their clinical development. In this review, we discuss how the underlying immunobiology of 4-1BB activation suggests the potential for therapeutically synergistic combination strategies in which immune adverse events can be minimized.

Soluble co-signaling molecules predict long-term graft outcome in kidney-transplanted patients

Co-signaling molecules are responsible for full T-cell activation after solid organ transplantation. Their increased expression can lead to the release of a soluble form that can modulate the immune response post-transplantation. We analyzed the presence of co-signaling molecules (sCD30, sCD40, sCD137, sCTLA-4, sCD80, sCD28, sCD40L, sPD-1, and sPD-L1) in serum from kidney-transplanted patients (n = 59) obtained at different times (before transplantation, and 15 days, 3 months and 1 year post-transplantation) and their contribution to graft outcome was evaluated using principal component analysis. Before transplantation, high levels of soluble co-signaling molecules (mainly sCD30, sCD137 and sCD40) were detected in all patients. These molecules were modulated soon after receiving an allograft but never attained similar levels to those of healthy controls. A signature based on the determination of six soluble co-stimulatory (sCD30, sCD40, sCD137 and sCD40L) and co-inhibitory (sPD-1 and sPD-L1) molecules at 3 months post-transplantation allowed a group of patients to be identified (27.12%) with a worse long-term graft outcome. Patients with high levels of soluble molecules showed a progressive and gradual deterioration of kidney function (increased creatinine and proteinuria levels and decreased estimated glomerular filtration rate) over time and a higher risk of graft loss at 6 years post-transplantation than patients with low levels of these molecules (62.55% versus 5.14%, p<0.001). Thus, our data show an aberrant expression of soluble co-signaling molecules in kidney-transplanted patients whose quantification at 3 months post-transplantation might be a useful biomarker of immune status and help to predict long-term graft evolution.

Circulating programmed death-1 as a marker for sustained high hepatitis B viral load and risk of hepatocellular carcinoma

OBJECTIVE

Recent evidence indicates a crucial role of the immunoinhibitory receptor programmed death-1 (PD-1) in enforcing T-cell dysfunction during chronic viral infection and cancer. We assessed the impact of circulating soluble PD-1 (sPD-1) levels on long-term dynamics of hepatitis B virus (HBV) load and hepatocellular carcinoma (HCC) risk.

METHODS

In a case-cohort study on longitudinal analysis of viral load within a cohort of 2903 men chronically infected with HBV, followed up from baseline (1989-1992) through 2010, we determined sPD-1 levels in baseline plasma with enzyme-linked immunosorbent assay from 126 men who subsequently developed HCC and 1155 men who did not develop HCC. To evaluate whether patients' characteristics involved the use of sPD-1 as a biomarker, sPD-1 was also tested in 614 newly-diagnosed patients with HBV-related HCC recruited from a multicenter study for comparison with the 1155 noncases in the case-cohort study.

RESULTS

Plasma quartile levels of sPD-1 were positively associated with HCC risk for men in the case-cohort analysis (vs. quartile 1: adjusted odds ratios [95% confidence intervals] for quartile 2-quartile 4 were 1.51 [0.75-3.03], 2.15 [1.12-4.13], and 2.29 [1.20-4.38], respectively), and in the case-control study regardless of age-of-onset and clinical stage. Furthermore, we found longitudinal effect of elevated sPD-1 levels to maintain higher viral load for 4 or more years, with greater and more prolonged effect among HBV genotype C- vs. non-C-infected participants. High levels of viral load and sPD-1 (vs. absence of both) was associated with a 6.29-fold increase in risk of HCC, and combining both conditions with HBV genotype C yielded an odds ratio of 30.47 with significant additive interaction (relative excess risk due to interaction: 27.08 [95% confidence interval = 8.76-45.41]).

CONCLUSIONS

Our data suggest plasma sPD-1 as an important immune-related marker for assessment of HBV activity and HCC risk.

The PD-1/PD-Ls pathway and autoimmune diseases

The programmed death (PD)-1/PD-1 ligands (PD-Ls) pathway, is a new member of the B7/CD28 family, and consists of the PD-1 receptor and its ligands PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273). Recently, it is reported that PD-1, PD-L1 and PD-L2 also have soluble forms aside from their membrane bound forms. The soluble forms increase the diversity and complexity of PD-1/PD-Ls pathway in both composition and function. The PD-1/PD-Ls pathway is broadly expressed and exerts a wider range of immunoregulatory roles in T-cell activation and tolerance compared with other B7/CD28 family members. Studies show that the PD-1/PD-Ls pathway regulates the induction and maintenance of peripheral tolerance and protects tissues from autoimmune attack in physiological conditions. In addition, it is also involved in various diseases mediated by T cells, such as autoimmunity, tumor immunity, chronic viral infections, and transplantation immunity. In this review, we will summarize the relevance of the soluble forms and the latest researches on the role of PD-1/PD-Ls pathway in autoimmune diseases.

PD-1 blockade and OX40 triggering synergistically protects against tumor growth in a murine model of ovarian cancer

The co-inhibitory receptor Programmed Death-1 (PD-1) curtails immune responses and prevent autoimmunity, however, tumors exploit this pathway to escape from immune destruction. The co-stimulatory receptor OX40 is upregulated on T cells following activation and increases their clonal expansion, survival and cytokine production when engaged. Although antagonistic anti-PD-1 or agonistic anti-OX40 antibodies can promote the rejection of several murine tumors, some poorly immunogenic tumors were refractory to this treatment. In the present study, we evaluated the antitumor effects and mechanisms of combinatorial PD-1 blockade and OX40 triggering in a murine ID8 ovarian cancer model. Although individual anti-PD-1 or OX40 mAb treatment was ineffective in tumor protection against 10-day established ID8 tumor, combined anti-PD-1/OX40 mAb treatment markedly inhibited tumor outgrowth with 60% of mice tumor free 90 days after tumor inoculation. Tumor protection was associated with a systemic immune response with memory and antigen specificity and required CD4(+) cells and CD8(+) T cells. The anti-PD-1/OX40 mAb treatment increased CD4(+) and CD8(+) cells and decreased immunosuppressive CD4(+)FoxP3(+) regulatory T (Treg) cells and CD11b(+)Gr-1(+) myeloid suppressor cells (MDSC), giving rise to significantly higher ratios of both effector CD4(+) and CD8(+) cells to Treg and MDSC in peritoneal cavity; Quantitative RT-PCR data further demonstrated the induction of a local immunostimulatory milieu by anti-PD-1/OX40 mAb treatment. The splenic CD8(+) T cells from combined mAb treated mice produced high levels of IFN-γ upon tumor antigen stimulation and exhibited antigen-specific cytolytic activity. To our knowledge, this is the first study testing the antitumor effects of combined anti-PD-1/OX40 mAb in a murine ovarian cancer model, and our results provide a rationale for clinical trials evaluating ovarian cancer immunotherapy using this combination of mAb.

Eomesodermin is required for antitumor immunity mediated by 4-1BB-agonist immunotherapy

CD8⁺ T cells in progressing tumors frequently fail to mount an effective antitumor response often in association with the expression of inhibitory receptors, including programmed cell death-1 (PD-1) and lymphocyte-activation gene 3 (Lag3). Using a lymphoma tumor model, we demonstrate that tumor-infiltrating CD8⁺ T cells from growing tumors co-express inhibitory receptors and co-stimulatory receptors, including 4-1BB (TNFRSF9) as well as high levels of 2 transcription factors, Eomesodermin (Eomes) and T-bet (Tbx21), critical determinants of CD8⁺ T cell fate. Immunotherapy with an agonistic anti-4–1-BB antibody altered the ratio of Eomes to T-bet expression in tumor-infiltrating CD8⁺ T cells by increasing Eomes and decreasing T-bet expression. 4-1BB-agonist immunotherapy was also associated with downregulated expression of the inhibitory receptors PD-1 and Lag3 on tumor-infiltrating CD8⁺ T cells, a molecular phenotype associated with subsequent attenuation of tumor growth. Furthermore, 4-1BB-agonist immunotherapy failed to effect tumor progression in mice with Eomes deficient T cells. However, upon resumption of tumor growth, tumor-infiltrating CD8⁺ T cells from treated animals continued to express high levels of Eomes as well as elevated levels of the inhibitory receptors PD-1 and Lag3. Our data suggest that tumor-infiltrating CD8⁺ T cells are poised between activation and inhibition as dictated by expression of both co-stimulatory receptors and inhibitory receptors and demonstrate that T cell expression of Eomes is necessary, but not sufficient, for efficacious 4-1BB-agonist-mediated immunotherapy.

Combined PD-1 blockade and GITR triggering induce a potent antitumor immunity in murine cancer models and synergizes with chemotherapeutic drugs

BACKGROUND

The coinhibitory receptor Programmed Death-1 (PD-1) inhibits effector functions of activated T cells and prevents autoimmunity, however, cancer hijack this pathway to escape from immune attack. The costimulatory receptor glucocorticoid-induced TNFR related protein (GITR) is up-regulated on activated T cells and increases their proliferation, activation and cytokine production. We hypothesize that concomitant PD-1 blockade and GITR triggering would synergistically improve the effector functions of tumor-infiltrating T cells and increase the antitumor immunity. In present study, we evaluated the antitumor effects and mechanisms of combined PD-1 blockade and GITR triggering in a clinically highly relevant murine ID8 ovarian cancer model.

METHODS

Mice with 7 days-established peritoneal ID8 ovarian cancer were treated intraperitoneally (i.p.) with either control, anti-PD-1, anti-GITR or anti-PD-1/GITR monoclonal antibody (mAb) and their survival was evaluated; the phenotype and function of tumor-associated immune cells in peritoneal cavity of treated mice was analyzed by flow cytometry, and systemic antigen-specific immune response was evaluated by ELISA and cytotoxicity assay.

RESULTS

Combined anti-PD-1/GITR mAb treatment remarkably inhibited peritoneal ID8 tumor growth with 20% of mice tumor free 90 days after tumor challenge while treatment with either anti-PD-1 or anti-GITR mAb alone exhibited little antitumor effect. The durable antitumor effect was associated with a memory immune response and conferred by CD4⁺ cells and CD8⁺ T cells. The treatment of anti-PD-1/GITR mAb increased the frequencies of interferon-γ-producing effector T cells and decreased immunosuppressive regulatory T cells and myeloid-derived suppressor cells, shifting an immunosuppressive tumor milieu to an immunostimulatory state in peritoneal cavity. In addition, combined treatment of anti-PD-1/GITR mAb mounted an antigen-specific immune response as evidenced by antigen-specific IFN-γ production and cytolytic activity of spleen cells from treated mice. More importantly, combined treatment of anti-PD-1/GITR mAb and chemotherapeutic drugs (cisplatin or paclitaxel) further increased the antitumor efficacy with 80% of mice obtaining tumor-free long-term survival in murine ID8 ovarian cancer and 4 T1 breast cancer models.

CONCLUSIONS

Combined anti-PD-1/GITR mAb treatment induces a potent antitumor immunity, which can be further promoted by chemotherapeutic drugs. A combined strategy of anti-PD-1/GITR mAb plus cisplatin or paclitaxel should be considered translation into clinic.

Combinatorial PD-1 blockade and CD137 activation has therapeutic efficacy in murine cancer models and synergizes with cisplatin

There is an urgent need for improved therapy for advanced ovarian carcinoma, which may be met by administering immune-modulatory monoclonal antibodies (mAbs) to generate a tumor-destructive immune response. Using the ID8 mouse ovarian cancer model, we investigated the therapeutic efficacy of various mAb combinations in mice with intraperitoneal (i.p.) tumor established by transplanting 3 × 10⁶ ID8 cells 10 days previously. While most of the tested mAbs were ineffective when given individually or together, the data confirm our previous finding that 2 i.p. injections of a combination of anti-CD137 with anti-PD-1 mAbs doubles overall survival. Mice treated with this mAb combination have a significantly increased frequency and total number of CD8⁺ T cells both in the peritoneal lavage and spleens, and these cells are functional as demonstrated by antigen-specific cytolytic activity and IFN-γ production. While administration of anti-CD137 mAb as a single agent similarly increases CD8⁺ T cells, these have no functional activity, which may be attributed to up-regulation of co-inhibitory PD-1 and TIM-3 molecules induced by CD137. Addition of the anti-cancer drug cisplatin to the 2 mAb combination increased overall survival >90 days (and was probably curative) by a mechanism which included a systemic CD8⁺ T cell response with tumor specificity and immunological memory. Strikingly, combined treatment of cisplatin and CD137/PD-1 mAb also gave rise to the long-term survival of mice with established TC1 lung tumors. A similar combination of the 2 mAbs and cisplatin should be considered for clinical ‘translation’.

Reconstructed adeno-associated virus with the extracellular domain of murine PD-1 induces antitumor immunity

BACKGROUND

The negative signaling provided by interactions of the co-inhibitory molecule, programmed death-1 (PD-1), and its ligands, B7-H1 (PD-L1) and B7-DC (PD-L2), is a critical mechanism contributing to tumor evasion; blockade of this pathway has been proven to enhance cytotoxic activity and mediate antitumor therapy. Here we evaluated the anti-tumor efficacy of AAV-mediated delivery of the extracellular domain of murine PD-1 (sPD-1) to a tumor site.

MATERIAL AND METHODS

An rAAV vector was constructed in which the expression of sPD-1, a known negative regulator of TCR signals, is driven by human cytomegalovirus immediate early promoter (CMV-P), using a triple plasmid transfection system. Tumor-bearing mice were then treated with the AAV/sPD1 construct and expression of sPD-1 in tumor tissues was determined by semi quantitative RT-PCR, and tumor weights and cytotoxic activity of splenocytes were measured.

RESULTS

Analysis of tumor homogenates revealed sPD-1 mRNA to be significantly overexpressed in rAAV/sPD-1 treated mice as compared with control levels. Its use for local gene therapy at the inoculation site of H22 hepatoma cells could inhibit tumor growth, also enhancing lysis of tumor cells by lymphocytes stimulated specifically with an antigen. In addition, PD-1 was also found expressed on the surfaces of activated CD8+ T cells.

CONCLUSION

This study confirmed that expression of the soluble extracellular domain of PD-1 molecule could reduce tumor microenvironment inhibitory effects on T cells and enhance cytotoxicity. This suggests that it might be a potential target for development of therapies to augment T-cell responses in patients with malignancies.

Enhanced function of cytotoxic T lymphocytes induced by dendritic cells modified with truncated PSMA and 4-1BBL

Interactions between costimulatory molecules and their receptors are vital for Ag-presenting dendritic cells (DCs) to initiate T cells activation, expansion and their antitumor immune responses. Augmentation of costimulatory signal due to the interaction of DCs and T cells may amplify, sustain and drive diversity of cytotoxic T lymphocytes (CTLs) and consequently enhance the antitumor response. 4-1BBL/4-1BB is such a pair of costimulatory ligand and receptor, playing an important role in the co-stimulation of CTLs. Previously, we demonstrated that DCs transduced with recombinant adenovirus encoding truncated PSMA (tPSMA) and m4-1BBL could induce prostate cancer regression in mouse models. In the present study, we further explored the adjuvant role of 4-1BBL in modulating CTLs activation induced by tPSMA gene-pulsed DCs. The apoptosis and cytotoxicity against tPSMA expressing RM-1 cells of CTLs were determined. Results showed that tPSMA gene-pulsed DCs effectively induced T lymphocyte activation and cytotoxicity, which was enhanced by upregulated expression of 4-1BBL, displaying better cell viability, lower CTLs apoptosis, higher expression anti-apoptotic protein of Bcl-xL and phosphorylation of P38, enhanced NF-κB activation, as well as more IFN-γ production. These results demonstrated that 4-1BBL may play a significant role in the co-stimulation pathway for Ag-presenting DCs-mediated CTLs activity, which might be a beneficial adjuvant factor for DCs-based cancer immunotherapy.

T-cell intrinsic effects of GITR and 4-1BB during viral infection and cancer immunotherapy

GITR [glucocorticoid inducible tumor necrosis factor receptor (TNFR)-related protein] and 4-1BB are costimulatory TNFR family members that are expressed on regulatory and effector T cells as well as on other cells of the immune system. Here we discuss the role of GITR and 4-1BB on T cells during viral infections and in cancer immunotherapy. Systemic treatment with agonistic anti-4-1BB antibody leads to a number of immune system abnormalities, and clinical trials of anti-4-1BB have been terminated. However, other modes of 4-1BB ligation may be less toxic. To date, similar toxicities have not been reported for anti-GITR treatment of mice, although anti-GITR antibodies can exacerbate mouse autoimmune models. Intrinsic effects of GITR and 4-1BB on effector T cells appear to predominate over their effects on other cell types in some models. Despite their similarities in enhancing T-cell survival, 4-1BB and GITR are clearly not redundant, and both pathways are required for maximal CD8(+) T-cell responses and mouse survival following severe respiratory influenza infection. GITR uses TNFR-associated factor (TRAF) 2 and TRAF5, whereas 4-1BB recruits TRAF1 and TRAF2 to mediate survival signaling in T cells. The differential use of signaling adapters combined with their differential expression may explain the non-redundant roles of GITR and 4-1BB in the immune system.

Combination immunotherapy with 4-1BBL and CTLA-4 blockade for the treatment of prostate cancer

Immune regulation has been shown to be involved in the progressive growth of some murine tumours. Interruption of immune regulatory pathways via activation of 4-1BB or cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) blockade appears to be a promising strategy for cancer immunotherapy. In this study, we examined the effectiveness of 4-1BBL-expressing tumor cell vaccine in combination with CTLA-4 blockade on rejection of murine prostate cancer RM-1. We found that the combination of both a vaccine consisting of 4-1BBL-expressing RM-1 cells and CTLA-4 blockade resulted in regression of RM-1 tumors and a significant increase in survival of the tumour cell recipients, compared to that of either treatment alone. The combined vaccination resulted in higher CTL against RM-1 cells and increased secretion of IFN-γ, TNF-α, and IL-2 in the mix-cultured supernatant. These results suggest that combining activation of 4-1BB and blockade of CTLA-4 may offer a new strategy for prostate cancer immunotherapy.

Effects of 4-1BB signaling on the biological function of murine dendritic cells

4-1BB signaling has profound effects on the T cell-induced cell immune response, but its biological function in dendritic cells (DCs) has remained largely uncharacterized. In this study, we investigated the function of 4-1BB in murine DCs with an agonistic mAb to 4-1BB. Interleukin (IL)-6 and IL-12 production was assessed by an enzyme-linked immunosorbent assay (ELISA). Co-stimulatory molecules (CD80 and CD86) in DCs were analyzed by flow cytometry. The results showed that 4-1BB was strongly expressed in DCs during the maturation process. Triggering 4-1BB increased the secretion of IL-6 and IL-12 and the upregulation of co-stimulatory molecules (CD80 and CD86) from DCs, indicating that agonistic mAb to 4-1BB directly improves the activation of DCs. Moreover, triggering 4-1BB induced a higher survival rate of DCs compared to that of hamster IgG isotype control, due to the upregulated expression of Bcl-2 and Bcl-xL. To further assess the role of 4-1BB on DCs stimulating T-cell proliferation, allogeneic mixed lymphocyte reactions were analyzed. The agonistic anti-4-1BB mAb induced a higher T-cell proliferation. These results suggest that 4-1BB affects the duration, DC-T interaction and immunogenicity of DCs.

The change of immunoactivity of dendritic cells induced by mouse 4-1BBL recombinant adenovirus

PURPOSE

The purpose of this study is to construct a recombinant adenovirus vector carrying mouse 4-1BBL and observe its effects in dendritic cells.

MATERIALS AND METHODS

Mouse 4-1BBL cDNA was taken from the plasmid pcDNA3-m4- 1BBL and subcloned into adenovirus shuttle plasmid pAdTrack-CMV, and then transformed into competent BJ5183 with plasmid pAdEasy-1. After recombination in E.coli, Ad-4-1BBL was packaged and amplified in HEK 293 cells. The expression of 4-1BBL in Ad-4-1BBL-transfected mouse prostate cancer cell line RM-1 was detected by reverse transcription polymerase chain reaction (RT-PCR) and Western blot. After the co-culture of dendritic cells (DCs) with Ad-4-1BBL-transfected RM-1 cells, interleukin (IL)-6 and IL-12 production were assessed by enzyme-linked immunosorbent assay (ELISA) and co-stimulatary molecules (CD80 and CD86) on DCs were analyzed by flow cytometry.

RESULTS

The levels of IL-6 (3,960 pg/mL) and IL-12 (249 pg/mL) production in Ad-m4-1BBL-pulsed DCs were more than those in none-pulsed DCs. The differences were statistically significant (p < 0.05). The expression of co-stimulatary molecules (CD80 and CD86) was up-regulated in Ad-m4-1BBL-pulsed DCs.

CONCLUSION

The results indicated the recombinant mouse 4-1BBL can effectively activate DCs.

Soluble B and T lymphocyte attenuator possesses antitumor effects and facilitates heat shock protein 70 vaccine-triggered antitumor immunity against a murine TC-1 cervical cancer model in vivo

B and T lymphocyte attenuator (BTLA)-herpesvirus entry mediator (HVEM) signaling coinhibitory pathway is believed to impair antitumor immune competences. An intriguing unresolved question is whether blockade of BTLA-HVEM guides an effective therapeutic tool against established tumors. To address this issue, we constructed a eukaryotic expression plasmid (psBTLA) that expressed the extracellular domain of murine BTLA (soluble form of BTLA), which could bind HVEM, the ligand of BTLA, and block BTLA-HVEM interactions. The data in this study showed that treatment by injection of psBTLA resulted in down-regulation of IL-10 and TGF-beta and promotion of dendritic cell function by increasing the expression of B7-1 and IL-12, but the adaptive antitumor immune responses achieved by psBTLA administration alone were limited and could not eradicate the tumor effectively. Next, we evaluated the immunotherapeutic efficacy and mechanism of combination therapy of heat shock protein 70 (HSP70) vaccine/psBTLA by using murine TC-1 cervical cancer mice as an ectopic tumor model. Our in vivo studies revealed that treatment with HSP70 vaccine alone did not lead to satisfactory tumor growth inhibition, whereas cotreatment with psBTLA significantly improved antitumor immunity and compensated the deficiency of HSP70 vaccine by increasing the expression of Th1 cytokines, IL-2, and IFN-gamma and decreasing transcription levels of IL-10, TGF-beta, and Foxp3 in the tumor microenvironment. Taken together, our findings indicate that blocking the BTLA-HVEM interaction with sBTLA enhances antitumor efficacy and results in a significant synergistic effect against existent tumor cells in vivo when combined with the HSP70 vaccine.

Anti-tumor immune response induced by dendritic cells transduced with truncated PSMA IRES 4-1BBL recombinant adenoviruses

Up-regulation of receptor-ligand pairs during interaction of a peptide-bound MHC complex on dendritic cells (DCs) with cognate TCR may amplify, sustain, and drive diversity in the ensuing T cell immune response. Members of the TNF ligand superfamily and the TNFR superfamily contribute to this costimulatory molecule signaling. In the present study, we used replication deficient adenoviruses to introduce a tumor-associated Ag (a truncated human prostate-specific membrane antigen (tPSMA)) and the T cell costimulatory molecule 4-1BBL into murine DCs, and observed the ability of these recombinant DCs to elicit tPSMA-directed T-cell responses in vitro and anti-tumor immunity to RM-1-tPSMA in a murine tumor model. Infection of DCs with Ad-tPSMA-IRES-m4-1BBL induced tPSMA-specific proliferative responses and up-regulated CD80 and CD86 s signaling molecules. The cytotoxic T lymphocytes activated by the Ad-tPSMA-IRES-m4-1BBL-transfected DCs showed significantly higher IFN-gamma production and cytotoxicity against the RM-1 cells transfected with tPSMA. Moreover, vaccination of mice with Ad-tPSMA-IRES-m4-1BBL-transfected DCs induced a potent protective and therapeutic anti-tumor immunity to RM-1-tPSMA in a tumor model. These results demonstrated that development of DCs engineered to express tPSMA and 4-1BBL by recombinant adenovirus-mediated gene transfer may offer a new strategy for prostate cancer immunotherapy.

Autophagy facilitates major histocompatibility complex class I expression induced by IFN-γ in B16 melanoma cells

The reduction or loss of MHC-I antigen surface expression in human and murine tumor cells is partly attributable to the dysregulation of various components of the MHC-I antigen-processing machinery. Accumulating evidence suggests that autophagy, besides its vital role in maintaining the cellular homeostasis, plays an important role in MHC-II surface expression. Here, we report that autophagy is a negative regulator of MHC-I antigen expression in B16 melanoma cells; however, in the presence of IFN-γ, it is converted to a positive regulator. We show that autophagy not only participates in the degradation of MHC-I antigen but also plays a role in the generation of MHC-I-binding peptides. For these two processes, IFN-γ interferes with MHC-I antigen degradation, rather than affecting peptide generation. Using B16 melanoma mouse model, we further show that autophagy may enhance the cytolysis of CTL to melanoma cells at the early stage of melanoma, but impairs the cytolysis at the late stage. Such different consequences may be explained by the different levels of IFN-γ during tumor progression. Taken together, our findings demonstrate that autophagy is involved in the regulation of MHC-I antigen expression, through which autophagy can play different roles in tumor immunity.

Echinoside A, a new marine-derived anticancer saponin, targets topoisomerase2alpha by unique interference with its DNA binding and catalytic cycle

BACKGROUND

Echinoside A was isolated from sea cucumber. This study demonstrates its anticancer effects and its mechanisms of action.

MATERIALS AND METHODS

Anticancer effects of echinoside A were evaluated in vitro and in vivo. TUNEL and DNA fragmentation assays were applied to examine its ability to induce apoptosis. A series of biochemical assays were applied to investigate the inhibition of echinoside A on topoisomerase2alpha (Top2alpha). Molecular docking analyses were used to demonstrate the direct interaction between echinoside A and Top2alpha.

RESULTS

Echinoside A inhibited the growth of tumors in mouse models and human prostate carcinoma xenografts in nude mouse models. Echinoside A shows the unique characteristics of inhibiting the noncovalent binding of Top2alpha to DNA by competing with DNA for the DNA-binding domain of the enzyme and of interfering predominantly with the Top2alpha-mediated prestrand passage cleavage/religation equilibrium over with the poststrand passage one. These features distinguish echinoside A from other known Top2alpha inhibitors. As a result, echinoside A induced DNA double-strand breaks in a Top2-dependent manner.

CONCLUSION

Echinoside A targets Top2alpha by unique interference with the binding of Top2 to DNA and by imparing the Top2-mediated DNA cleavage and religation, exerting potent in vitro and in vivo antitumor activities.