Functional restoration of HCV-specific CD8 T cells by PD-1 blockade is defined by PD-1 expression and compartmentalization

Klebsiella pneumoniae emerging anti-immunology paradigms: from stealth to evasion

Klebsiella pneumoniae (KP) is a global threat to human health due to the isolation of multidrug-resistant strains. Despite advancements in understanding KP's population structure, antibiotic resistance mechanisms, and transmission patterns, a gap remains in how KP evades defenses, allowing the pathogen to flourish in tissues despite an activated immune system. KP infection biology has been shaped by the notion that the pathogen has evolved to shield from defenses more than actively suppress them. This review describes new paradigms of how KP exploits the coevolution with the innate immune system to hijack immune effectors and receptors to ablate signaling pathways and to counteract cell-intrinsic immunity, making apparent that KP can no longer be considered only as a stealth pathogen.

T Cell Exhaustion in Allergic Diseases and Allergen Immunotherapy: A Novel Biomarker?

PURPOSE OF REVIEW

This review explores the emerging role of T cell exhaustion in allergic diseases and allergen immunotherapy (AIT). It aims to synthesize current knowledge on the mechanisms of T cell exhaustion, evaluate its potential involvement in allergic inflammation, and assess its implications as a novel biomarker for predicting and monitoring AIT efficacy.

RECENT FINDINGS

Recent studies highlight that T cell exhaustion, characterized by co-expression of inhibitory receptors (e.g., PD-1, CTLA-4, TIM-3), diminished cytokine production, and altered transcriptional profiles, may suppress type 2 inflammation in allergic diseases. In allergic asthma, exhausted CD4 + T cells exhibit upregulated inhibitory receptors, correlating with reduced IgE levels and airway hyperreactivity. During AIT, prolonged high-dose allergen exposure drives allergen-specific Th2 and T follicular helper (Tfh) cell exhaustion, potentially contributing to immune tolerance. Notably, clinical improvements in AIT correlate with depletion of allergen-specific Th2 cells and persistent expression of exhaustion markers (e.g., PD-1, CTLA-4) during maintenance phases. Blockade of inhibitory receptors (e.g., PD-1) enhances T cell activation, underscoring their dual regulatory role in allergy. T cell exhaustion represents a double-edged sword in allergy: it may dampen pathological inflammation in allergic diseases while serving as a mechanism for AIT-induced tolerance. The co-expression of inhibitory receptors on allergen-specific T cells emerges as a promising biomarker for AIT efficacy. Future research should clarify the transcriptional and metabolic drivers of exhaustion in allergy, validate its role across diverse allergic conditions, and optimize strategies to harness T cell exhaustion for durable immune tolerance. These insights could revolutionize therapeutic approaches and biomarker development in allergy management.

Dysfunction and regulatory interplay of T and B cells in chronic hepatitis B: immunotherapy and emerging antiviral strategies

In the context of chronic hepatitis B virus (HBV) infection, the continuous replication of HBV within host hepatocytes is a characteristic feature. Rather than directly causing hepatocyte destruction, this replication leads to immune dysfunction and establishes a state of T-B immune tolerance. Successful clearance of the HBV virus is dependent on the close collaboration between humoral and cellular immunity. Humoral immunity, mediated by B-cell subpopulations, and cellular immunity, dominated by T-cell subpopulations show varying degrees of dysfunction during chronic hepatitis B (CHB). Notably, not all T- and B-cells produce positive immune responses. This review examine the most recent developments in the mutual regulation of T-B cells during chronic HBV infection. Our focus is on the prevailing immunotherapeutic strategies, such as T cell engineering, HBV-related vaccines, PD-1 inhibitors, and Toll-like receptor agonists. While nucleos(t)ide analogues (NUCs) and interferons have notable limitations, including inadequate viral suppression, drug resistance, and adverse reactions, several HBV entry inhibitors have shown promising clinical efficacy. To overcome the challenges posed by NUCs or monotherapy, the combination of immunotherapy and novel antiviral agents presents a promising avenue for future CHB treatment and potential cure.

PD-L1: From cancer immunotherapy to therapeutic implications in multiple disorders

The PD-L1/PD-1 signaling pathway is the gold standard for cancer immunotherapy. Therapeutic antibodies targeting PD-1, such as nivolumab (Opdivo) and pembrolizumab (Keytruda), and PD-L1, including atezolizumab (Tecentriq), durvalumab (Imfinzi), and avelumab (Bavencio) have received Food and Drug Administration approval and are currently being used to treat various cancers. Traditionally, PD-L1 is known as an immune checkpoint protein that binds to the PD-1 receptor on its surface to inhibit the activity of T cells, which are the primary effector cells in antitumor immunity. However, it also plays a role in cancer progression, which goes beyond traditional understanding. Here, we highlight the multifaceted mechanisms of action of PD-L1 in cancer cell proliferation, transcriptional regulation, and systemic immune suppression. Moreover, we consider the potential role of PD-L1 in the development and pathogenesis of diseases other than cancer, explore PD-L1-focused therapeutic approaches for these diseases, and assess their clinical relevance. Through this review, we hope to provide deeper insights into the PD-L1/PD-1 signaling pathway and present a broad perspective on potential therapeutic approaches for cancer and other diseases.

Stress from environmental change drives clearance of a persistent enteric virus

Persistent viral infections are associated with long-term health issues and prolonged transmission. How external perturbations after initial exposure affect the duration of infection is unclear. We discovered that murine astrovirus, an enteric RNA virus, persists indefinitely when mice remain unperturbed but is cleared rapidly after cage change. Besides eliminating the external viral reservoir, cage change also induced a transcriptional defense response in the intestinal epithelium. We further identified that displacing infected animals initially caused a temporary period of immune suppression through the stress hormone corticosterone, which was followed by an immune rebound characterized by an increase in CD8 T cells responsible for the epithelial antiviral responses. Our findings show how viral persistence can be disrupted by preventing re-exposure and activating immunity upon stress recovery, indicating that external factors can be manipulated to shorten the duration of a viral infection.

Targeting myeloid-derived suppressor cells promotes antiparasitic T-cell immunity and enhances the efficacy of PD-1 blockade (15 words)

Immune exhaustion corresponds to a loss of effector function of T cells that associates with cancer or chronic infection. Here, our objective was to decipher the mechanisms involved in the immune suppression of myeloid-derived suppressor cells (MDSCs) and to explore the potential to target these cells for immunotherapy to enhance checkpoint blockade efficacy in a chronic parasite infection. We demonstrated that programmed cell-death-1 (PD-1) expression was significantly upregulated and associated with T-cell dysfunction in advanced alveolar echinococcosis (AE) patients and in Echinococcus multilocularis-infected mice. PD-1 blockade ex vivo failed to reverse AE patients' peripheral blood T-cell dysfunction. PD-1/PD-L1 blockade or PD-1 deficiency had no significant effects on metacestode in mouse model. This was due to the inhibitory capacities of immunosuppressive granulocytic MDSCs (G-MDSCs), especially in the liver surrounding the parasite pseudotumor. MDSCs suppressed T-cell function in vitro in an indoleamine 2, 3 dioxygenase 1 (IDO1)-dependent manner. Although depleting MDSCs alone restored T-cell effector functions and led to some limitation of disease progression in E. multilocularis-infected mice, combination with PD-1 blockade was better to induce antiparasitic efficacy. Our findings provide preclinical evidence in support of targeting MDSC or combining such an approach with checkpoint blockade in patients with advanced AE. (200 words).

Biomarkers in Detection of Hepatitis C Virus Infection

The hepatitis C virus (HCV) infection affects 58 million people worldwide. In the United States, the incidence rate of acute hepatitis C has doubled since 2014; during 2021, this increased to 5% from 2020. Acute hepatitis C is defined by any symptom of acute viral hepatitis plus either jaundice or elevated serum alanine aminotransferase (ALT) activity with the detection of HCV RNA, the anti-HCV antibody, or hepatitis C virus antigen(s). However, most patients with acute infection are asymptomatic. In addition, ALT activity and HCV RNA levels can fluctuate, and a delayed detection of the anti-HCV antibody can occur among some immunocompromised persons with HCV infection. The detection of specific biomarkers can be of great value in the early detection of HCV infection at an asymptomatic stage. The high rate of HCV replication (which is approximately 1010 to 1012 virions per day) and the lack of proofreading by the viral RNA polymerase leads to enormous genetic diversity, creating a major challenge for the host immune response. This broad genetic diversity contributes to the likelihood of developing chronic infection, thus leading to the development of cirrhosis and liver cancer. Direct-acting antiviral (DAA) therapies for HCV infection are highly effective with a cure rate of up to 99%. At the same time, many patients with HCV infection are unaware of their infection status because of the mostly asymptomatic nature of hepatitis C, so they remain undiagnosed until the liver damage has advanced. Molecular mechanisms induced by HCV have been intensely investigated to find biomarkers for diagnosing the acute and chronic phases of the infection. However, there are no clinically verified biomarkers for patients with hepatitis C. In this review, we discuss the biomarkers that can differentiate acute from chronic hepatitis C, and we summarize the current state of the literature on the useful biomarkers that are detectable during acute and chronic HCV infection, liver fibrosis/cirrhosis, and hepatocellular carcinoma (HCC).

In vivo single-cell high-dimensional mass cytometry analysis to track the interactions between Klebsiella pneumoniae and myeloid cells

In vivo single-cell approaches have transformed our understanding of the immune populations in tissues. Mass cytometry (CyTOF), that combines the resolution of mass spectrometry with the ability to conduct multiplexed measurements of cell molecules at the single cell resolution, has enabled to resolve the diversity of immune cell subsets, and their heterogeneous functionality. Here we assess the feasibility of taking CyTOF one step further to immuno profile cells while tracking their interactions with bacteria, a method we term Bac-CyTOF. We focus on the pathogen Klebsiella pneumoniae interrogating the pneumonia mouse model. Using Bac-CyTOF, we unveil the atlas of immune cells of mice infected with a K. pneumoniae hypervirulent strain. The atlas is characterized by a decrease in the populations of alveolar and monocyte-derived macrophages. Conversely, neutrophils, and inflammatory monocytes are characterized by an increase in the subpopulations expressing markers of less active cells such as the immune checkpoint PD-L1. These are the cells infected. We show that the type VI secretion system (T6SS) contributes to shape the lung immune landscape. The T6SS governs the interaction with monocytes/macrophages by shifting Klebsiella from alveolar macrophages to interstitial macrophages and limiting the infection of inflammatory monocytes. The lack of T6SS results in an increase of cells expressing markers of active cells, and a decrease in the subpopulations expressing PD-L1. By probing Klebsiella, and Acinetobacter baumannii strains with limited ability to survive in vivo, we uncover that a heightened recruitment of neutrophils, and relative high levels of alveolar macrophages and eosinophils and the recruitment of a characteristic subpopulation of neutrophils are features of mice clearing infections. We leverage Bac-CyTOF-generated knowledge platform to investigate the role of the DNA sensor STING in Klebsiella infections. sting-/- infected mice present features consistent with clearing the infection including the reduced levels of PD-L1. STING absence facilitates Klebsiella clearance.

The expression of CTLA-4 in hepatic alveolar echinococcosis patients and blocking CTLA-4 to reverse T cell exhaustion in Echinococcus multilocularis-infected mice

Alveolar echinococcosis (AE) is a zoonotic parasitic disease caused by the infection of Echinococcus multilocularis (E. multilocularis) larvae. Cytotoxic T-lymphocyte antigen 4 (CTLA-4) produces inhibitory signals and induces T cell exhaustion, thereby inhibiting the parasiticidal efficacy of the liver immune system. Therefore, the purpose of this study is to explore how T-cell exhaustion contributes to AE and whether blocking CTLA-4 could reverse T cell exhaustion. Here we discovered that the expression of CTLA-4 was increased in the infiltrating margin around the lesion of the liver from AE patients by using western blot and immunohistochemistry assay. Multiple fluorescence immunohistochemistry identified that CTLA-4 and CD4/CD8 molecules were co-localized. For in vitro experiments, it was found that the sustained stimulation of E. multilocularis antigen could induce T cell exhaustion, blocking CTLA-4-reversed T cell exhaustion. For in vivo experiments, the expression of CTLA-4 was increased in the liver of E. multilocularis-infected mice, and the CTLA-4 and CD4/CD8 molecules were co-localized. Flow cytometry analysis demonstrated that the percentages of both CD4+ T cells and CD8+ T cells in the liver and peripheral blood were significantly increased and induced T exhaustion. When the mice were treated with anti-CTLA-4 antibodies, the number and weight of the lesions decreased significantly. Meanwhile, the flow cytometry results suggested that blocking CTLA-4 could effectively reverse T cell exhaustion and reactivate immune function. Our work reveals that blocking CTLA-4 could effectively reverse the T cell exhaustion caused by E. multilocularis and could be used as a novel target for the treatment of AE.

Clinical implications of hepatitis B virus core antigen-mediated immunopathologic T cell responses in chronic hepatitis B

Hepatitis B virus (HBV) infection significantly impacts Asian populations. The influences of continuous HBV antigen and inflammatory stimulation to T cells in chronic hepatitis B (CHB) remain unclear. In this study, we first conducted bioinformatics analysis to assess T-cell signaling pathways in CHB patients. In a Taiwanese cohort, we examined the phenotypic features of HBVcore -specific T cells and their correlation with clinical parameters. We used core protein overlapping peptides from the Taiwan prevalent genotype B HBV to investigate the antiviral response and the functional implication of HBV-specific T cells. In line with Taiwanese dominant HLA-alleles, we also evaluated ex vivo HBVcore -specific T cells by pMHC-tetramers targeting epitopes within HBV core protein. Compared to healthy subjects, we disclosed CD8 T cells from CHB patients had higher activation marker CD38 levels but showed an upregulation in the inhibitory receptor PD-1. Our parallel study showed HBV-specific CD8 T cells were more activated with greater PD-1 expression than CMV-specific subset and bulk CD8 T cells. Moreover, our longitudinal study demonstrated a correlation between the PD-1 fluctuation pattern of HBVcore -specific CD8 T cells and liver inflammation in CHB patients. Our research reveals the HBV core antigen-mediated immunopathologic profile of CD8 T cells in chronic HBV infection. Our findings suggest the PD-1 levels of HBVcore -specific CD8 T cells can be used as a valuable indicator of personal immune response for clinical application in hepatitis management.

Blockade of BTLA alone or in combination with PD-1 restores the activation and proliferation of CD8+ T cells during in vitro infection with NCP BVDV

Bovine viral diarrhea virus (BVDV) infection can result in typical peripheral blood lymphopenia and immune dysfunction. However, the molecular mechanism underlying the onset of lymphopenia remains unclear. B and T lymphocyte attenuator (BTLA) is a novel immune checkpoint molecule that primarily inhibits activation and proliferation of T cells. Blockade of BTLA with antibodies can boost the proliferation and anti-viral immune functions of T cells. Nonetheless, the immunomodulatory effects of BTLA in CD8+ T cells during BVDV infection remain unknown. Therefore, BTLA expression was measured in bovine peripheral blood CD8+ T cells infected with BVDV in vitro. Furthermore, the effects of BTLA or PD-1 blockade on CD8+ T cell activation, proliferation, and anti-viral immunological activities were investigated, as well as expression of signaling molecules downstream of BTLA, both alone and in combination. The results demonstrated that BTLA and PD-1 mRNA and protein levels were considerably increased in CD8+ T cells infected with cytopathic and non-cytopathic (NCP) BVDV. Surprisingly, as compared to blockade of either BTLA or PD-1, blockade of both dramatically increased proliferation and expression of CD25 and p-EKR of CD8+ T cells infected with NCP BVDV. Furthermore, blockade of BTLA, but not PD-1, had no effect on BVDV replication or IFN-γ expression. These findings confirmed the immunomodulatory roles of BTLA during BVDV infection, as well as the synergistic role of BTLA and PD-1 in NCP BVDV infection, thereby providing new insights to promote activation and the anti-viral immunological activities of CD8+ T cells.

T-Cell Exhaustion in HIV-1/Hepatitis C Virus Coinfection Is Reduced After Successful Treatment of Chronic Hepatitis C

Background

T-cell responses during chronic viral infections become exhausted, which is reflected by upregulation of inhibitory receptors (iRs) and increased interleukin 10 (IL-10). We assessed 2 iRs-PD-1 (programmed cell death protein 1) and Tim-3 (T-cell immunoglobulin and mucin domain-containing protein 3)-and IL-10 mRNAs in peripheral blood mononuclear cells (PBMCs) and their soluble analogs (sPD-1, sTim-3, and IL-10) in plasma in chronic HIV-1/hepatitis C virus (HCV) coinfection and explored the effect of HCV treatment on these markers. We also aimed to establish whether iR expression may be determined by the HCV CD8+ T-cell immunodominant epitope sequence.

Methods

Plasma and PBMCs from 31 persons with chronic HIV-1/HCV coinfection from the Swiss HIV Cohort Study were collected before and after HCV treatment. As controls, 45 persons who were HIV-1 negative with chronic HCV infection were recruited. Exhaustion markers were assessed by enzyme-linked immunosorbent assay in plasma and by quantitative reverse transcription polymerase chain reaction in PBMCs. Analysis of an HCV epitope sequence was conducted by next-generation sequencing: HLA-A*02-restricted NS31073-1081 and NS31406-1415 and HLA-A*01-restricted NS31436-1444.

Results

The study revealed higher plasma sPD-1 (P = .0235) and IL-10 (P = .002) levels and higher IL-10 mRNA in PBMCs (P = .0149) in HIV-1/HCV coinfection. A decrease in plasma sPD-1 (P = .0006), sTim-3 (P = .0136), and IL-10 (P = .0003) and Tim-3 mRNA in PBMCs (P = .0210) was observed following successful HCV treatment. Infection with the HLA-A*01-restricted NS31436-1444 ATDALMTGY prototype variant was related to higher sTim-3 levels than infection with the ATDALMTGF escape variant (P = .0326).

Conclusions

The results underscore the synergistic effect of coinfection on expression of exhaustion markers, their reduction following successful HCV treatment and imply that iR levels may operate on an epitope-specific manner.

Controlling viral inflammatory lesions by rebalancing immune response patterns

In this review, we discuss a variety of immune modulating approaches that could be used to counteract tissue-damaging viral immunoinflammatory lesions which typify many chronic viral infections. We make the point that in several viral infections the lesions can be largely the result of one or more aspects of the host response mediating the cell and tissue damage rather than the virus itself being directly responsible. However, within the reactive inflammatory lesions along with the pro-inflammatory participants there are also other aspects of the host response that may be acting to constrain the activity of the damaging components and are contributing to resolution. This scenario should provide the prospect of rebalancing the contributions of different host responses and hence diminish or even fully control the virus-induced lesions. We identify several aspects of the host reactions that influence the pattern of immune responsiveness and describe approaches that have been used successfully, mainly in model systems, to modulate the activity of damaging participants and which has led to lesion control. We emphasize examples where such therapies are, or could be, translated for practical use in the clinic to control inflammatory lesions caused by viral infections.

Polymorphisms Related to Iron Homeostasis Associate with Liver Disease in Chronic Hepatitis C

Dysregulation of iron metabolism in chronic hepatitis C (CHC) is a significant risk factor for hepatic cirrhosis and cancer. We studied if known genetic variants related to iron homeostasis associate with liver disease progression in CHC. Retrospective analysis included 249 CHC patients qualified for antiviral therapy between 2004 and 2014. For all patients, nine SNPs within HFE, TFR2, HDAC2, HDAC3, HDAC5, TMPRSS6, and CYBRD1 genes were genotyped. Expression of selected iron-related genes, was determined with qRT-PCR in 124 liver biopsies, and mRNA expression of co-inhibitory receptors (PD-1, Tim3, CTLA4) was measured in 79 liver samples. CYBRD1 rs884409, HDAC5 rs368328, TFR2 rs7385804, and TMPRSS6 rs855791 associated with histopathological changes in liver tissue at baseline. The combination of minor allele in HDAC3 rs976552 and CYBRD1 rs884409 linked with higher prevalence of hepatocellular carcinoma (HCC) during follow up (OR 8.1 CI 2.2-29.2; p = 0.001). Minor allele in HDAC3 rs976552 associated with lower hepatic expression of CTLA4. Tested polymorphisms related to iron homeostasis associate with histopathological changes in the liver. The presence of both HDAC3 rs976552 G and CYBRD1 rs884409 G alleles correlates with HCC occurrence, especially in the group of patients with elevated AST (>129 IU/L). rs976552 in HDAC3 could impact immunological processes associated with carcinogenesis in CHC.

Double Positive CD4+CD8+ (DP) T-Cells Display Distinct Exhaustion Phenotype in Chronic Hepatitis C

In chronic hepatitis C (CHC), characterized by exhaustion of T-cell function, increased frequencies of double-positive (DP) (CD4⁺CD8⁺) cells are present in peripheral blood. We compared the exhaustion phenotype between DP and single positive (SP) T-cells, including HCV-specific cells, and assessed the effect of successful HCV treatment on inhibitory receptors expression. Blood samples from 97 CHC patients were collected before and six months post-treatment. PD-1 (programmed cell death protein 1) and Tim-3 (T-cell immunoglobulin and mucin domain-containing molecule-3) expression was assessed by flow cytometry. DP T-cells displayed significantly higher PD-1 expression, lower Tim-3 expression than CD8⁺ SP T-cells and lower percentages of PD-1^-Tim-3^- cells than CD4⁺ SP T-cells, both before and after treatment. PD-1⁺Tim-3⁺ DP T-cells decreased following treatment. HCV-specific cells were more frequent among DP than SP T-cells, both before and after treatment. HCV-specific DP T-cells were characterized by lower PD-1 expression, higher PD-1 and Tim-3 co-expression, and lower percentages of PD-1^-Tim-3^- cells (both before and after treatment) and higher post-treatment Tim-3 than HCV-specific SP T-cells. Their percentages decreased following treatment, but the exhaustion phenotype remained unchanged. DP T-cells in CHC exhibit a distinct exhaustion phenotype from SP T-cells, and these changes mostly persist following successful treatment.

Lnc-AIFM2-1 promotes HBV immune escape by acting as a ceRNA for miR-330-3p to regulate CD244 expression

Chronic hepatitis B (CHB) virus infection is a major risk factor for cirrhosis and hepatocellular carcinoma (HCC). Hepatitis B virus (HBV) immune escape is regulated by the exhaustion of virus-specific CD8+ T cells, which is associated with abnormal expression of negative regulatory molecule CD244. However, the underlying mechanisms are unclear. To investigate the important roles of non-coding RNAs play in CD244 regulating HBV immune escape, we performed microarray analysis to determine the differential expression profiles of long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and mRNAs in patients with CHB and patients with spontaneous clearance of HBV. Competing endogenous RNA (ceRNA) was analyzed by bioinformatics methods and confirmed by the dual-luciferase reporter assay. Furthermore, gene silencing and overexpression experiments were used to further identify the roles of lncRNA and miRNA in HBV immune escape through CD244 regulation. The results showed that the expression of CD244 on the surface of CD8+ T cells was significantly increased in CHB patients and in the co-culture system of T cells and HBV-infected HepAD38 cells, which was accompanied by the reduction of miR-330-3p and the elevation of lnc-AIFM2-1. The down-regulated miR-330-3p induced the apoptosis of T cells by lifting the inhibition of CD244, which was reversed by miR-330-3p mimic or CD244-siRNA. Lnc-AIFM2-1 promotes the accumulation of CD244, which is mediated by decreased miR-330-3p, and then reduced the clearance ability of CD8+ T cells to HBV through regulated CD244 expression. And the injury in the ability of CD8+ T cells to clear HBV can be reversed by lnc-AIFM2-1-siRNA, miR-330-3p mimic, or CD244-siRNA. Collectively, our findings indicate that lnc-AIFM2-1 on CD244 by acting as a ceRNA of miR-330-3p contributes to HBV immune escape, which may provide novel insights into the roles of interaction networks among lncRNA, miRNA, and mRNA in HBV immune escape, highlighting potential applications of lnc-AIFM2-1 and CD244 for diagnosis and treatment in CHB.

Advanced development of biomarkers for immunotherapy in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common liver cancer and one of the leading causes of cancer-related deaths in the world. Mono-immunotherapy and combination therapy with immune checkpoint inhibitors (ICIs) and multitargeted tyrosine kinase inhibitors (TKIs) or anti-vascular endothelial growth factor (anti-VEGF) inhibitors have become new standard therapies in advanced HCC (aHCC). However, the clinical benefit of these treatments is still limited. Thus, proper biomarkers which can predict treatment response to immunotherapy to maximize clinical benefit while sparing unnecessary toxicity are urgently needed. Contrary to other malignancies, up until now, no acknowledged biomarkers are available to predict resistance or response to immunotherapy for HCC patients. Furthermore, biomarkers, which are established in other cancer types, such as programmed death ligand 1 (PD-L1) expression and tumor mutational burden (TMB), have no stable predictive effect in HCC. Thus, plenty of research focusing on biomarkers for HCC is under exploration. In this review, we summarize the predictive and prognostic biomarkers as well as the potential predictive mechanism in order to guide future research direction for biomarker exploration and clinical treatment options in HCC.

Modulating Immune Response in Viral Infection for Quantitative Forecasts of Drug Efficacy

The antiretroviral drug, the total level of viral production, and the effectiveness of immune responses are the main topics of this review because they are all dynamically interrelated. Immunological and viral processes interact in extremely complex and non-linear ways. For reliable analysis and quantitative forecasts that may be used to follow the immune system and create a disease profile for each patient, mathematical models are helpful in characterizing these non-linear interactions. To increase our ability to treat patients and identify individual differences in disease development, immune response profiling might be useful. Identifying which patients are moving from mild to severe disease would be more beneficial using immune system parameters. Prioritize treatments based on their inability to control the immune response and prevent T cell exhaustion. To increase treatment efficacy and spur additional research in this field, this review intends to provide examples of the effects of modelling immune response in viral infections, as well as the impact of pharmaceuticals on immune response.

Hepatocytes infected with hepatitis C virus change immunological features in the liver microenvironment

Hepatitis C virus (HCV) infection is remarkably efficient in establishing viral persistence, leading to the development of liver cirrhosis and hepatocellular carcinoma (HCC). Direct-acting antiviral agents (DAAs) are promising HCV therapies to clear the virus. However, recent reports indicate potential increased risk of HCC development among HCV patients with cirrhosis following DAA therapy. CD8+ T-cells participate in controlling HCV infection. However, in chronic hepatitis C patients, severe CD4+ and CD8+ T-cell dysfunctions have been observed. This suggests that HCV may employ mechanisms to counteract or suppress the host T-cell responses. The primary site of viral replication is within hepatocytes where infection can trigger the expression of costimulatory molecules and the secretion of immunoregulatory cytokines. Numerous studies indicate that HCV infection in hepatocytes impairs antiviral host immunity by modulating the expression of immunoregulatory molecules. Hepatocytes expressing whole HCV proteins upregulate the ligands of programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), and transforming growth factor β (TGF-β) synthesis compared to those in hepatocytes in the absence of the HCV genome. Importantly, HCV-infected hepatocytes are capable of inducing regulatory CD4+ T-cells, releasing exosomes displaying TGF-β on exosome surfaces, and generating follicular regulatory T-cells. Recent studies report that the expression profile of exosome microRNAs provides biomarkers of HCV infection and HCV-related chronic liver diseases. A better understanding of the immunoregulatory mechanisms and identification of biomarkers associated with HCV infection will provide insight into designing vaccine against HCV to bypass HCV-induced immune dysregulation and prevent development of HCV-associated chronic liver diseases.

Immunomodulatory regulator blockade in a viral exacerbation model of severe asthma

Asthmatics are more susceptible to viral infections than healthy individuals and are known to have impaired innate anti-viral defences. Influenza A virus causes significant morbidity and mortality in this population. Immuno-modulatory regulators (IMRs) such as PD-1 are activated on T cells following viral infection as part of normal T cell activation responses, and then subside, but remain elevated in cases of chronic exposure to virus, indicative of T cell exhaustion rather than activation. There is evidence that checkpoint inhibition can enhance anti-viral responses during acute exposure to virus through enhancement of CD8+T cell function. Although elevated PD-1 expression has been described in pulmonary tissues in other chronic lung diseases, the role of IMRs in asthma has been relatively unexplored as the basis for immune dysfunction. We first assessed IMR expression in the peripheral circulation and then quantified changes in IMR expression in lung tissue in response to ex-vivo influenza infection. We found that the PD-1 family members are not significantly altered in the peripheral circulation in individuals with severe asthma but are elevated in pulmonary tissues following ex-vivo influenza infection. We then applied PD-1 Mab inhibitor treatment to bronchial biopsy tissues infected with influenza virus and found that PD-1 inhibition was ineffective in asthmatics, but actually increased infection rates in healthy controls. This study, therefore, suggests that PD-1 therapy would not produce harmful side-effects when applied in people with severe asthma, but could have important, as yet undescribed, negative effects on anti-viral responses in healthy individuals that warrant further investigation.

Cellular Senescence in Immunity against Infections

Cellular senescence is characterized by irreversible cell cycle arrest in response to different triggers and an inflammatory secretome. Although originally described in fibroblasts and cell types of solid organs, cellular senescence affects most tissues with advancing age, including the lymphoid tissue, causing chronic inflammation and dysregulation of both innate and adaptive immune functions. Besides its normal occurrence, persistent microbial challenge or pathogenic microorganisms might also accelerate the activation of cellular aging, inducing the premature senescence of immune cells. Therapeutic strategies counteracting the detrimental effects of cellular senescence are being developed. Their application to target immune cells might have the potential to improve immune dysfunctions during aging and reduce the age-dependent susceptibility to infections. In this review, we discuss how immune senescence influences the host's ability to resolve more common infections in the elderly and detail the different markers proposed to identify such senescent cells; the mechanisms by which infectious agents increase the extent of immune senescence are also reviewed. Finally, available senescence therapeutics are discussed in the context of their effects on immunity and against infections.

Bioinformatic analysis of PD-1 checkpoint blockade response in influenza infection

BACKGROUND

The programmed cell death 1 (PD-1)/PD-1 ligand 1 (PD-L1) signaling pathway is significantly upregulated in influenza virus infection, which impairs the antiviral response. Blocking this signaling pathway may reduce the damage, lower the virus titer in lung tissue, and alleviate the symptoms of infection to promote recovery. In addition to the enhanced viral immune response, using of immune checkpoint inhibitors in influenza virus infection is controversial, the aim of this study was to identify the key factors and regulatory mechanisms in the PD-1 checkpoint blockade response microenvironment in influenza infection.

METHODS

A BALB/c mouse model of influenza A/PR8(H1N1) infection was established then constructed, and whole-transcriptome sequencing including mRNAs, miRNAs (microRNAs), lncRNAs (long noncoding RNAs), and circRNAs (circular RNAs) of mice treated with PD-1 checkpoint blockade by antibody treatment and IgG2a isotype control before infection with A/PR8(H1N1) were performed. Subsequently, the differential expression of transcripts between these two groups was analyzed, followed by functional interaction prediction analysis to investigate gene-regulatory circuits.

RESULTS

In total, 84 differentially expressed dif-mRNAs, 36 dif-miRNAs, 90 dif-lncRNAs and 22 dif-circRNAs were found in PD-1 antagonist treated A/PR8(H1N1) influenza-infected lungs compared with the controls (IgG2a isotype control treated before infection). In spleens between the above two groups, 45 dif-mRNAs, 36 dif-miRNAs, 57 dif-lncRNAs, and 24 dif-circRNAs were identified. Direct function enrichment analysis of dif-mRNAs and dif-miRNAs showed that these genes were mainly involved in myocardial damage related to viral infection, mitogen activated protein kinase (MAPK) signaling pathways, RAP1 (Ras-related protein 1) signaling pathway, and Axon guidance. Finally, 595 interaction pairs were obtained for the lungs and 462 interaction pairs for the spleens were obtained in the competing endogenous RNA (ceRNA) complex network, in which the downregulated mmu-miR-7043-3p and Vps39-204 were enriched significantly in PD-1 checkpoint blockade treated A/PR8(H1N1) infection group.

CONCLUSIONS

The present study provided a basis for the identification of potential pathways and hub genes that might be involved in the PD-1 checkpoint blockade response microenvironment in influenza infection.

Immunological Characteristics of Patients Receiving Ultra-Short Treatment for Chronic Hepatitis C

Reducing the treatment duration for chronic hepatitis C could be an important tool in the effort to reach the elimination goals set by the World Health Organization. The current challenge is to predict the target group who will achieve sustained virological response at week 12 (SVR12) with shorter treatment duration. The aim of this exploratory study was to characterize immune subsets with focus on inhibitory receptors in patients who experienced SVR12 or virological relapse following four weeks treatment with glecaprevir/pibrentasvir with or without ribavirin. A total of 32 patients were included in this study of whom 21 achieved SVR12 and 11 had virological relapse. All available samples at baseline (n = 31) and end of treatment (EOT) (n = 30) were processed for flow cytometric analysis in order to measure the expression of PD-1, 2B4, BY55, CTLA-4, TIM-3 and LAG-3 on 12 distinct T cell subsets. At baseline, patients with SVR12 (n=21) had numerically lower frequencies of inhibitory receptors for 83% (60/72) of the investigated T-cell subtypes. The most significant difference observed between the two groups was a lower frequency of stem cell-like memory T-cells CD4⁺PD1⁺ in the SVR group (p = 0.007). Furthermore, we observed a significant positive correlation between baseline viral load and the expression of PD-1 on the total CD8⁺ T-cells and effector memory T-cells CD4⁺ and CD8⁺ for patients with virological relapse. This study suggests a measurable immunologic phenotype at baseline of patients achieving SVR12 after short treatment compared to patients with virological relapse.

CD8+ T-Cell Exhaustion Phenotype in Chronic Hepatitis C Virus Infection Is Associated With Epitope Sequence Variation

Background and Aims

During chronic hepatitis C virus (HCV) infection, CD8⁺ T-cells become functionally exhausted, undergoing progressive phenotypic changes, i.e., overexpression of “inhibitory” molecules such as PD-1 (programmed cell death protein 1) and/or Tim-3 (T-cell immunoglobulin and mucin domain-containing molecule-3). The extreme intrahost genetic diversity of HCV is a major mechanism of immune system evasion, facilitating epitope escape. The aim of the present study was to determine whether T-cell exhaustion phenotype in chronic HCV infection is related to the sequence repertoire of NS3 viral immunodominant epitopes.

Methods

The study population was ninety prospective patients with chronic HCV genotype 1b infection. Populations of peripheral blood CD8⁺ T-cells expressing PD-1/Tim-3 were assessed by multiparametric flow cytometry, including HCV-specific T-cells after magnetic-based enrichment using MHC-pentamer. Autologous epitope sequences were inferred from next-generation sequencing. The correction of sequencing errors and genetic variants reconstruction was performed using Quasirecomb.

Results

There was an interplay between the analyzed epitopes sequences and exhaustion phenotype of CD8⁺ T-cells. A predominance of NS3₁₄₀₆ epitope sequence, representing neither prototype KLSGLGLNAV nor cross-reactive variants (KLSSLGLNAV, KLSGLGINAV or KLSALGLNAV), was associated with higher percentage of HCV-specific CD8⁺PD-1⁺Tim-3⁺ T-cells, P=0.0102. Variability (at least two variants) of NS3₁₄₀₆ epitope sequence was associated with increased frequencies of global CD8⁺PD-1⁺Tim-3⁺ T-cells (P=0.0197) and lower frequencies of CD8⁺PD-1⁻Tim-3⁻ T-cells (P=0.0079). In contrast, infection with NS3₁₀₇₃ dominant variant epitope (other than prototype CVNGVCWTV) was associated with lower frequency of global CD8⁺PD-1⁺Tim-3⁺ T-cells (P=0.0054).

Conclusions

Our results indicate that PD-1/Tim-3 receptor expression is largely determined by viral epitope sequence and is evident for both HCV-specific and global CD8⁺ T-cells, pointing to the importance of evaluating autologous viral epitope sequences in the investigation of CD8⁺ T-cell exhaustion in HCV infection.

Innate and Adaptive Immunopathogeneses in Viral Hepatitis; Crucial Determinants of Hepatocellular Carcinoma

Viral hepatitis B (HBV) and hepatitis C (HCV) infections remain the most common risk factors for the development of hepatocellular carcinoma (HCC), and their heterogeneous distribution influences the global prevalence of this common type of liver cancer. Typical hepatitis infection elicits various immune responses within the liver microenvironment, and viral persistence induces chronic liver inflammation and carcinogenesis. HBV is directly mutagenic but can also cause low-grade liver inflammation characterized by episodes of intermittent high-grade liver inflammation, liver fibrosis, and cirrhosis, which can progress to decompensated liver disease and HCC. Equally, the absence of key innate and adaptive immune responses in chronic HCV infection dampens viral eradication and induces an exhausted and immunosuppressive liver niche that favors HCC development and progression. The objectives of this review are to (i) discuss the epidemiological pattern of HBV and HCV infections, (ii) understand the host immune response to acute and chronic viral hepatitis, and (iii) explore the link between this diseased immune environment and the development and progression of HCC in preclinical models and HCC patients.

B cell overexpression of FCRL5 and PD-1 is associated with low antibody titers in HCV infection

Antibodies targeting the hepatitis C virus (HCV) envelope glycoprotein E2 are associated with delayed disease progression, and these antibodies can also facilitate spontaneous clearance of infection in some individuals. However, many infected people demonstrate low titer and delayed anti-E2 antibody responses. Since a goal of HCV vaccine development is induction of high titers of anti-E2 antibodies, it is important to define the mechanisms underlying these suboptimal antibody responses. By staining lymphocytes with a cocktail of soluble E2 (sE2) glycoproteins, we detected HCV E2-specific (sE2+) B cells directly ex vivo at multiple acute infection timepoints in 29 HCV-infected subjects with a wide range of anti-E2 IgG titers, including 17 persistently infected subjects and 12 subjects with spontaneous clearance of infection. We performed multi-dimensional flow cytometric analysis of sE2+ and E2-nonspecific (sE2-) class-switched B cells (csBC). In sE2+ csBC from both persistence and clearance subjects, frequencies of resting memory B cells (rMBC) were reduced, frequencies of activated MBC (actMBC) and tissue-like MBC (tlMBC) were increased, and expression of FCRL5, an IgG receptor, was significantly upregulated. Across all subjects, plasma anti-E2 IgG levels were positively correlated with frequencies of sE2+ rMBC and sE2+ actMBC, while anti-E2 IgG levels were negatively correlated with levels of FCRL5 expression on sE2+ rMBC and PD-1 expression on sE2+ actMBC. Upregulation of FCRL5 on sE2+ rMBC and upregulation of PD-1 on sE2+ actMBC may limit anti-E2 antibody production in vivo. Strategies that limit upregulation of these molecules could potentially generate higher titers of protective antibodies against HCV or other pathogens.

Antiviral immunity relies on production of protective immunoglobulin G (IgG) by B cells, but many hepatitis C virus (HCV)-infected individuals have very low levels of HCV-specific IgG in their serum. Elucidating mechanisms underlying this suboptimal IgG expression remains paramount in guiding therapeutic and vaccine strategies. In this study, we developed a highly specific method to capture HCV-specific B cells and characterized their surface protein expression. Two proteins analyzed were Fc receptor-like protein 5 (FCRL5), a cell surface receptor for IgG, and programmed cell death protein-1 (PD-1), a marker of lymphocyte activation and exhaustion. We measured serum levels of anti-HCV IgG in these subjects and demonstrated that overexpression of FCRL5 and PD-1 on memory B cells was associated with reduced anti-E2 IgG levels. This study uses HCV as a viral model, but the findings may be applicable to many viral infections, and they offer new potential targets to enhance antiviral IgG production.

Emerging Role of PD-1/PD-L1 Inhibitors in Chronic Liver Diseases

Programmed cell death protein 1 (PD-1)/PD-ligand (L)1, the immune checkpoint inhibitors have emerged as a promising strategy for the treatment of various diseases including chronic liver diseases (CLDs) such as hepatitis, liver injury and hepatocellular carcinoma (HCC). The role of PD-1/PD-L1 has been widely inspected in the treatment of viral hepatitis and HCC. PD-1 is known to play a crucial role in inhibiting immunological responses and stimulates self-tolerance by regulating the T-cell activity. Further, it promotes apoptosis of antigen-specific T-cells while preventing apoptosis of Treg cells. PD-L1 is a trans-membrane protein which is recognized as a co-inhibitory factor of immunological responses. Both, PD-1 and PD-L1 function together to downregulate the proliferation of PD-1 positive cells, suppress the expression of cytokines and stimulate apoptosis. Owing to the importance of PD-1/PD-L1 signaling, this review aims to summarize the potential of PD-1/PD-L1 inhibitors in CLDs along with toxicities associated with them. We have enlisted some of the important roles of PD-1/PD-L1 in CLDs, the clinically approved products and the pipelines of drugs under clinical evaluation.

Inverted CD8 T-Cell Exhaustion and Co-Stimulation Marker Balance Differentiate Aviremic HIV-2-Infected From Seronegative Individuals

HIV-2 is less pathogenic compared to HIV-1. Still, disease progression may develop in aviremic HIV-2 infection, but the driving forces and mechanisms behind such development are unclear. Here, we aimed to reveal the immunophenotypic pattern associated with CD8 T-cell pathology in HIV-2 infection, in relation to viremia and markers of disease progression. The relationships between pathological differences of the CD8 T-cell memory population and viremia were analyzed in blood samples obtained from an occupational cohort in Guinea-Bissau, including HIV-2 viremic and aviremic individuals. For comparison, samples from HIV-1- or dually HIV-1/2-infected and seronegative individuals were obtained from the same cohort. CD8 T-cell exhaustion was evaluated by the combined expression patterns of activation, stimulatory and inhibitory immune checkpoint markers analyzed using multicolor flow cytometry and advanced bioinformatics. Unsupervised multidimensional clustering analysis identified a cluster of late differentiated CD8 T-cells expressing activation (CD38+, HLA-DR^int/high), co-stimulatory (CD226+/-), and immune inhibitory (2B4+, PD-1^high, TIGIT^high) markers that distinguished aviremic from viremic HIV-2, and treated from untreated HIV-1-infected individuals. This CD8 T-cell population displayed close correlations to CD4%, viremia, and plasma levels of IP-10, sCD14 and beta-2 microglobulin in HIV-2 infection. Detailed analysis revealed that aviremic HIV-2-infected individuals had higher frequencies of exhausted TIGIT+ CD8 T-cell populations lacking CD226, while reduced percentage of stimulation-receptive TIGIT-CD226+ CD8 T-cells, compared to seronegative individuals. Our results suggest that HIV-2 infection, independent of viremia, skews CD8 T-cells towards exhaustion and reduced co-stimulation readiness. Further knowledge on CD8 T-cell phenotypes might provide help in therapy monitoring and identification of immunotherapy targets.

Monitoring PD-1 Phosphorylation to Evaluate PD-1 Signaling during Antitumor Immune Responses

PD-1 expression marks activated T cells susceptible to PD-1-mediated inhibition but not whether a PD-1-mediated signal is being delivered. Molecular predictors of response to PD-1 immune checkpoint blockade (ICB) are needed. We describe a monoclonal antibody (mAb) that detects PD-1 signaling through the detection of phosphorylation of the immunotyrosine switch motif (ITSM) in the intracellular tail of mouse and human PD-1 (phospho-PD-1). We showed PD-1⁺ tumor-infiltrating lymphocytes (TILs) in MC38 murine tumors had high phosphorylated PD-1, particularly in PD-1⁺TIM-3⁺ TILs. Upon PD-1 blockade, PD-1 phosphorylation was decreased in CD8⁺ TILs. Phospho-PD-1 increased in T cells from healthy human donors after PD-1 engagement and decreased in patients with Hodgkin lymphoma following ICB. These data demonstrate that phosphorylation of the ITSM motif of PD-1 marks dysfunctional T cells that may be rescued with PD-1 blockade. Detection of phospho-PD-1 in TILs is a potential biomarker for PD-1 immunotherapy responses.

Viral infections and the efficacy of PD-(L)1 inhibitors in virus-related cancers: Head and neck squamous cell carcinoma and hepatocellular carcinoma

PURPOSE

This study aimed to test the interaction between viral infections and immune checkpoint inhibitor (ICI) efficacy for two virus-associated tumors, head and neck squamous carcinoma (HNSCC) and hepatocellular carcinoma (HCC), by conducting a systematic review and meta-analysis.

METHODS

We searched databases from inception until December 30, 2020 to identify phase 2 or 3 randomized clinical trials involving ICI treatments with data on hazard ratios (HRs) for survival according to viral infection status. We evaluated the heterogeneity between patients with and without viral infections using an interaction test. Subgroup analyses were conducted to explore variations in the efficacy of immunotherapy according to viral infection status.

RESULTS

Six phase 3 trials with 3672 patients (1382 with viral infections [38%] and 2115 without viral infections [57%]) were included. Among these patients, the pooled HR for survival was 0.69 (95% confidence interval [CI], 0.60-0.79) for those with viral infections and 0.84 (95% CI, 0.77-0.91) for those without infections after ICI treatment. Patients with viral infections achieved a better prognosis after ICI therapy than those without infections (P = 0.018). This was evident in patients with hepatitis B virus-associated HCC (P = 0.016), but not in patients with hepatitis C virus-associated HCC (P = 0.081) or in patients with human papillomavirus-positive HNSCC (P = 0.67).

CONCLUSION

Patients with advanced HNSCC and HCC, regardless of viral infection status, could benefit from ICI treatment. Patients with hepatitis B virus-associated HCC were more likely to benefit from ICI treatment than patients without viral infections.

REGISTRATION

Our systematic review protocol was registered with the International Prospective Register of Systematic Reviews on March 27, 2020 (registration number CRD42020155326).

Co-infections as Modulators of Disease Outcome: Minor Players or Major Players?

Human host and pathogen interaction is dynamic in nature and often modulated by co-pathogens with a functional role in delineating the physiological outcome of infection. Co-infection may present either as a pre-existing pathogen which is accentuated by the introduction of a new pathogen or may appear in the form of new infection acquired secondarily due to a compromised immune system. Using diverse examples of co-infecting pathogens such as Human Immunodeficiency Virus, Mycobacterium tuberculosis and Hepatitis C Virus, we have highlighted the role of co-infections in modulating disease severity and clinical outcome. This interaction happens at multiple hierarchies, which are inclusive of stress and immunological responses and together modulate the disease severity. Already published literature provides much evidence in favor of the occurrence of co-infections during SARS-CoV-2 infection, which eventually impacts the Coronavirus disease-19 outcome. The availability of biological models like 3D organoids, mice, cell lines and mathematical models provide us with an opportunity to understand the role and mechanism of specific co-infections. Exploration of multi-omics-based interactions across co-infecting pathogens may provide deeper insights into their role in disease modulation.

A Review of Hepatitis B Virus and Hepatitis C Virus Immunopathogenesis

Despite the advances in therapy, hepatitis B virus (HBV) and hepatitis C virus (HCV) still represent a significant global health burden, both as major causes of cirrhosis, hepatocellular carcinoma, and death worldwide. HBV is capable of incorporating its covalently closed circular DNA into the host cell's hepatocyte genome, making it rather difficult to eradicate its chronic stage. Successful viral clearance depends on the complex interactions between the virus and host's innate and adaptive immune response. One encouraging fact on hepatitis B is the development and effective distribution of the HBV vaccine. This has significantly reduced the spread of this virus. HCV is a RNA virus with high mutagenic capacity, thus enabling it to evade the immune system and have a high rate of chronic progression. High levels of HCV heterogeneity and its mutagenic capacity have made it difficult to create an effective vaccine. The recent advent of direct acting antivirals has ushered in a new era in hepatitis C therapy. Sustained virologic response is achieved with DAAs in 85-99% of cases. However, this still leads to a large population of treatment failures, so further advances in therapy are still needed. This article reviews the immunopathogenesis of HBV and HCV, their properties contributing to host immune system avoidance, chronic disease progression, vaccine efficacy and limitations, as well as treatment options and common pitfalls of said therapy.

Gamma-Chain Receptor Cytokines & PD-1 Manipulation to Restore HCV-Specific CD8+ T Cell Response during Chronic Hepatitis C

Hepatitis C virus (HCV)-specific CD8⁺ T cell response is essential in natural HCV infection control, but it becomes exhausted during persistent infection. Nowadays, chronic HCV infection can be resolved by direct acting anti-viral treatment, but there are still some non-responders that could benefit from CD8⁺ T cell response restoration. To become fully reactive, T cell needs the complete release of T cell receptor (TCR) signalling but, during exhaustion this is blocked by the PD-1 effect on CD28 triggering. The T cell pool sensitive to PD-1 modulation is the progenitor subset but not the terminally differentiated effector population. Nevertheless, the blockade of PD-1/PD-L1 checkpoint cannot be always enough to restore this pool. This is due to the HCV ability to impair other co-stimulatory mechanisms and metabolic pathways and to induce a pro-apoptotic state besides the TCR signalling impairment. In this sense, gamma-chain receptor cytokines involved in memory generation and maintenance, such as low-level IL-2, IL-7, IL-15, and IL-21, might carry out a positive effect on metabolic reprogramming, apoptosis blockade and restoration of co-stimulatory signalling. This review sheds light on the role of combinatory immunotherapeutic strategies to restore a reactive anti-HCV T cell response based on the mixture of PD-1 blocking plus IL-2/IL-7/IL-15/IL-21 treatment.

DGKA Mediates Resistance to PD-1 Blockade

Immunologic checkpoint blockade has been proven effective in a variety of malignancies. However, high rates of resistance have substantially hindered its clinical use. Understanding the underlying mechanisms may lead to new strategies for improving therapeutic efficacy. Although a number of signaling pathways have been shown to be associated with tumor cell-mediated resistance to immunotherapy, T cell-intrinsic resistant mechanisms remain elusive. Here, we demonstrated that diacylglycerol kinase alpha (Dgka) mediated T-cell dysfunction during anti-PD-1 therapy by exacerbating the exhaustion of reinvigorated tumor-specific T cells. Pharmacologic ablation of Dgka postponed T-cell exhaustion and delayed development of resistance to PD-1 blockade. Dgka inhibition also enhanced the efficacy of anti-PD-1 therapy. We further found that the expression of DGKA in cancer cells promoted tumor growth via the AKT signaling pathway, suggesting that DGKA might be a target in tumor cells as well. Together, these findings unveiled a molecular pathway mediating resistance to PD-1 blockade and provide a potential therapeutic strategy with combination immunotherapy.

Antigen shedding into the circulation contributes to tumor immune escape

Tumors employ various mechanisms to escape elimination by the immune system. In addition to the local induction of immunosuppressive cell types such as regulatory T cells or myeloid derived suppressor cells, tumor antigen shedding into the circulation may suppress antitumor CD8⁺ T-cell function via tolerogenic liver sinusoidal endothelial cells.

T-Cell Immunity against the Hepatitis C Virus: A Persistent Research Priority in an Era of Highly Effective Therapy

Approximately 70% of acute hepatitis C virus (HCV) infections become chronic, indicating that the virus is exceptionally well adapted to persist in humans with otherwise normal immune function. Robust, lifelong replication of this small RNA virus does not require a generalized failure of immunity. HCV effectively subverts innate and adaptive host defenses while leaving immunity against other viruses intact. Here, the role of CD4⁺ and CD8⁺ T-cell responses in control of HCV infection and their failure to prevent virus persistence in most individuals are reviewed. Two issues of practical importance remain priorities in an era of highly effective antiviral therapy for chronic hepatitis C. First, the characteristics of successful T-cell responses that promote resolution of HCV infection are considered, as they will underpin development of vaccines that prevent HCV persistence. Second, defects in T-cell immunity that facilitate HCV persistence and whether they are reversed after antiviral cure to provide protection from reinfection are also addressed.

Chronic genotype 1 hepatitis C along with cirrhosis drives a persistent imprint in virus-specific CD8+ T cells after direct-acting antiviral therapies

Chronic hepatitis C virus (HCV) infection impairs HCV CD8⁺ T-cell responses, while it could influence immune responses towards unrelated viruses/vaccines (e.g. cytomegalovirus, CMV, and influenza, Flu). The aim of our study was to delineate whether restoration of these virus-specific CD8⁺ T cells occurs after direct-acting antiviral (DAA) therapies and particularly in patients with cirrhosis. We performed longitudinal analysis (baseline, week 4, follow-up [FU] 12 and FU48) of virus-specific CD8⁺ T cells by multicolour flow cytometry in HCV-cirrhotic patients undergoing DAA therapy (n = 26) after in vitro expansion with immunodominant HCV, CMV and Flu epitopes restricted by HLA-A*02. HCV noncirrhotic patients (n = 9) and healthy individuals (n = 10) served as controls. We found that the proliferative capacity of HCV-specific CD8⁺ T cells increased from baseline up to FU48 in a significant proportion of cirrhotic and noncirrhotic patients. Nevertheless, these cells remained poor cytokine producers in both patient groups, regardless of the down-regulation of inhibitory co-regulatory receptors in HCV-cirrhotic patients at FU48. Likewise, high expression levels of these exhaustion markers were detected in CMV-/Flu-specific CD8⁺ T cells in HCV-cirrhotic patients at all time points, albeit without affecting their proliferative capacity or cytokine production. We conclude that DAA therapies induce restoration of the proliferative capacity of HCV-specific CD8⁺ T cells. However, these cells remain phenotypically and functionally impaired. Contrarily, the 'exhausted' phenotype in CMV-/Flu-specific CD8⁺ T cells in HCV-cirrhotic patients did not associate with their functions. Larger studier with longer follow-up may elucidate whether this complex interplay influences the outcome of cirrhotic patients.

Immune Checkpoints in Viral Infections

As evidence has mounted that virus-infected cells, such as cancer cells, negatively regulate the function of T-cells via immune checkpoints, it has become increasingly clear that viral infections similarly exploit immune checkpoints as an immune system escape mechanism. Although immune checkpoint therapy has been successfully used in cancer treatment, numerous studies have suggested that such therapy may also be highly relevant for treating viral infection, especially chronic viral infections. However, it has not yet been applied in this manner. Here, we reviewed recent findings regarding immune checkpoints in viral infections, including COVID-19, and discussed the role of immune checkpoints in different viral infections, as well as the potential for applying immune checkpoint blockades as antiviral therapy.

PD-L1 Checkpoint Inhibition Narrows the Antigen-Specific T Cell Receptor Repertoire in Chronic Lymphocytic Choriomeningitis Virus Infection

Checkpoint inhibitors are effective in restoring exhausted CD8⁺ T cell responses in persistent viral infections or tumors. Several compounds are in clinical use for different malignancies, but trials in patients with chronic viral infections have also been conducted. In a mouse model of persistent lymphocytic choriomeningitis virus (LCMV) infection, it was shown that checkpoint inhibitor treatment increased T cell proliferation and functionality, but its influence on the antigen-specific T cell receptor (TCR) repertoire is unknown. NP396-specific CD8⁺ T cells dominate during acute LCMV infection and are predominantly exhausted during chronic infection. Next-generation sequencing of NP396-specific TCRs showed that exhaustion corresponds with a significantly reduced NP396-specific TCR repertoire diversity: Shannon indices of 4 in immunized mice to 2.6 in persistently infected mice. Anti-PD-L1 treatment during persistent LCMV infection restored NP396-specific T cell responses and reduced viral titers. Nevertheless, anti-PD-L1-treated mice showed an even more narrowed TCR repertoire, with reduced TCR diversity compared to that of persistently infected control mice (Shannon indices of 2.1 and 2.6, respectively). Interestingly, anti-PD-L1 treatment-induced narrowing of the TCR repertoire negatively correlates with functional and physical restoration of the antigen-specific T cell response. Further, we found that private, hyperexpanded TCR clonotypes dominated the T cell response after anti-PD-L1 treatment. Although being private, these top clonotypes from anti-PD-L1-treated mice revealed a more closely related CDR3 motif than those of top clonotypes from persistently infected control mice. In conclusion, although targeting the PD-1/PD-L1 pathway reinvigorates exhausted CD8⁺ T cells, it fails to restore T cell repertoire diversity.IMPORTANCE Checkpoint inhibitors are effective immunotherapeutics to restore cancer- and virus-induced exhausted CD8⁺ T cells, by enhancing the quality and survival of immune responses. Although checkpoint inhibitors are already used as therapy against various cancers, not much is known about their multifaceted impact on the exhausted CD8⁺ T cell receptor (TCR) repertoire. This report describes for the first time the evolvement of an exhausted antigen-specific CD8⁺ TCR repertoire under checkpoint inhibitor treatment. By using a well-established virus model, we were able to show major shifts toward oligoclonality of the CD8⁺ TCR repertoire response against a massively exhausted lymphocytic choriomeningitis virus (LCMV) epitope. While supporting viral control in the LCMV model, oligoclonality and more private of TCR repertoires may impact future pathogenic challenges and may promote viral escape. Our results may explain the ongoing problems of viral escapes, unpredictable autoimmunity, and heterogeneous responses appearing as adverse effects of checkpoint inhibitor treatments.

Adaptive Immune Response against Hepatitis C Virus

A functional adaptive immune response is the major determinant for clearance of hepatitis C virus (HCV) infection. However, in the majority of patients, this response fails and persistent infection evolves. Here, we dissect the HCV-specific key players of adaptive immunity, namely B cells and T cells, and describe factors that affect infection outcome. Once chronic infection is established, continuous exposure to HCV antigens affects functionality, phenotype, transcriptional program, metabolism, and the epigenetics of the adaptive immune cells. In addition, viral escape mutations contribute to the failure of adaptive antiviral immunity. Direct-acting antivirals (DAA) can mediate HCV clearance in almost all patients with chronic HCV infection, however, defects in adaptive immune cell populations remain, only limited functional memory is obtained and reinfection of cured individuals is possible. Thus, to avoid potential reinfection and achieve global elimination of HCV infections, a prophylactic vaccine is needed. Recent vaccine trials could induce HCV-specific immunity but failed to protect from persistent infection. Thus, lessons from natural protection from persistent infection, DAA-mediated cure, and non-protective vaccination trials might lead the way to successful vaccination strategies in the future.

Upregulation of Multiple CD8+ T Cell Exhaustion Pathways Is Associated with Recurrent Ocular Herpes Simplex Virus Type 1 Infection

A large proportion of the world's population harbors latent HSV type 1 (HSV-1). Cross-talk between antiviral CD8⁺ T cells and HSV-1 appear to control latency/reactivation cycles. We found that compared with healthy asymptomatic individuals, in symptomatic (SYMP) patients, the CD8⁺ T cells with the same HLA-A*0201-restricted HSV-1 epitope specificities expressed multiple genes and proteins associated to major T cell exhaustion pathways and were dysfunctional. Blockade of immune checkpoints with anti-LAG-3 and anti-PD-1 antagonist mAbs synergistically restored the frequency and function of antiviral CD8⁺ T cells, both 1) ex vivo, in SYMP individuals and SYMP HLA-A*0201 transgenic mice; and 2) in vivo in HSV-1-infected SYMP HLA-A*0201 transgenic mice. This was associated with a significant reduction in virus reactivation and recurrent ocular herpetic disease. These findings confirm antiviral CD8⁺ T cell exhaustion during SYMP herpes infection and pave the way to targeting immune checkpoints to combat recurrent ocular herpes.

Programmed cell death protein 1 (PD-1) in infection

Exhausted and dysfunctional T cells triggered by infection and cancer render the immune system unable to eliminate these pathogens. Pharmacologic blockade of the surface receptors that inhibit T-cell function has shown remarkable success in patients with various malignancies. In this Review, we discuss the emerging evidence of inhibiting checkpoint pathways as a potential role in controlling or clearing infectious diseases. Though interesting tendencies, much work is still needed in order to develop safe strategies that can be translated into clinically relevant outcomes in patients with infections.

JAK/STAT signaling is involved in IL-35-induced inhibition of hepatitis B virus antigen-specific cytotoxic T cell exhaustion in chronic hepatitis B

AIMS

Interleukin-35 (IL-35) is a new member of the interleukin-12 family and is composed of the P35 and EB virus-inducible gene 3 subunits. The aims of this study were to examine the roles of IL-35 in the exhaustion of HBV-specific CTLs, as little as known on the subject.

MAIN METHODS

The relative levels of serum HBV markers were detected using automated biochemical techniques. The HBV DNA copies were measured by RT-qPCR. The expression of inhibitory receptors and the cell cytokines on the surface of CTLs were determined by flow cytometry. The pSTAT1-pSTAT4 protein levels expression was determined by flow cytometry, confocal microscopy and Western blot.

KEY FINDINGS

Our results showed that IL-35 can activate the Janus kinase 1 (JAK1)/tyrosine kinase 2 (TYK2)/signal transducer and activator of transcription 1 (STAT1)/STAT4 pathway in CTLs in vitro. Interferon-γ and tumor necrosis alpha-α expression increased in CTLs in the presence of a JAK/STAT-pathway blocker. In addition, we evaluated the expression of the exhaustion-associated molecules programmed death-1, cytotoxic T lymphocyte-associated protein-4, and lymphocyte activation gene-3 in CTLs after adding the JAK-STAT inhibitor The results showed that the expression of exhaustion-associated molecules on the CTL surface decreased after blocking the JAK-STAT pathway. IL-35 inhibited the function of HBV-specific CTLs through the JAK1/TYK2/STAT1/STAT4 pathway, and the function of CTLs was recovered after blocking the JAK/STAT pathway.

SIGNIFICANCE

These data provide a new experimental basis for immunotherapy for chronic hepatitis B.

The Role of PD-1 in Acute and Chronic Infection

PD-1 as an immune checkpoint molecule down-regulates T cell activity during immune responses in order to prevent autoimmune tissue damage. In chronic infections or tumors, lasting antigen-exposure leads to permanent PD-1 expression that can limit immune-mediated clearance of pathogens or degenerated cells. Blocking PD-1 can enhance T cell function; in cancer treatment PD-1 blockade is already used as a successful therapy. However, the role of PD-1 expression and blocking in the context of acute and chronic infections is less defined. Building on its success in cancer therapy leads to the hypothesis that blocking PD-1 in infectious diseases is also beneficial in acute or chronic infections. This review will focus on the role of PD-1 expression in acute and chronic infections with virus, bacteria, and parasites, with a particular focus on recent studies regarding PD-1 blockade in infectious diseases.

PD-1-Mediated PI3K/Akt/mTOR, Caspase 9/Caspase 3 and ERK Pathways Are Involved in Regulating the Apoptosis and Proliferation of CD4+ and CD8+ T Cells During BVDV Infection in vitro

Acute infection of bovine viral diarrhea virus (BVDV) is associated with immune dysfunction and can cause peripheral blood lymphopenia and lymphocyte apoptosis. Our previous study has confirmed that programmed death-1 (PD-1) blockade inhibits peripheral blood lymphocyte (PBL) apoptosis and restores proliferation and anti-viral immune functions of lymphocytes after BVDV infection in vitro. However, the immunomodulatory effects of PD-1 pathway on major PBL subsets are unclear and their underlying molecular mechanisms need to be further studied. Therefore, in this study, we examined PD-1 expression in bovine PBL subsets after BVDV infection in vitro and analyzed the effects of PD-1 blockade on the apoptosis and proliferation of CD4⁺ and CD8⁺ T cells and expression of PD-1 downstream signaling molecules. The results showed that PD-1 expression was enhanced on CD4⁺ and CD8⁺ T cells, but not on CD21⁺ B cells after cytopathic (CP) BVDV (strain NADL) and non-cytopathic (NCP) BVDV (strain KD) infection in vitro and PD-1 blockade significantly reduced the apoptosis of CD4⁺ and CD8⁺ T cells after these two strains infection. Remarkably, PD-1 blockade significantly increased the proliferation of CD4⁺ and CD8⁺ T cells after CP BVDV infection, but only significantly increased the proliferation of CD4⁺ T cells after NCP BVDV infection. In addition, we confirmed that PD-1-mediated PI3K/Akt/mTOR, caspase 9/caspase 3 and ERK pathways are involved in regulating the apoptosis and proliferation of CD4⁺ and CD8⁺ T cells during BVDV infection in vitro. Notably, ERK is involved in the regulation mechanism PD-1 mediated only when the cells are infected with CP BVDV. Our findings provide a scientific basis for exploring the molecular mechanism of immune dysfunction caused by acute BVDV infection.

Use of Mass Cytometry to Profile Human T Cell Exhaustion

Mass cytometry has become an important technique for the deep analysis of single cell protein expression required for precision systems immunology. The ability to profile more than 40 markers per cell is particularly relevant for the differentiation of cell types for which low parametric characterization has proven difficult, such as exhausted CD8⁺ T cells (T_EX). T_EX with limited effector function accumulate in many chronic infections and cancers and are subject to inhibitory signaling mediated by several immune checkpoints (e.g., PD-1). Of note, T_EX represent considerable targets for immune-stimulatory therapies and are beginning to be recognized as a major correlate of successful checkpoint blockade approaches targeting the PD-1 pathway. T_EX exhibit substantial functional, transcriptomic and epigenomic differences compared to canonical functional T cell subsets [such as naïve (T_N), effector (T_EFF) and memory T cells (T_MEM)]. However, phenotypic distinction of T_EX from T_EFF and T_MEM can often be challenging since many molecules expressed by T_EX can also be expressed by effector and memory T cell populations. Moreover, significant heterogeneity of T_EX has been described, such as subpopulations of exhausted T cells with progenitor-progeny relationships or populations with different degrees of exhaustion or homeostatic potential that may directly inform about disease progression. In addition, T_EX subsets have essential clinical implications as they differentially respond to antiviral and checkpoint therapies. The precise assessment of T_EX thus requires a high-parametric analysis that accounts for differences to canonical T cell populations as well as for T_EX subset heterogeneity. In this review, we discuss how mass cytometry can be used to reveal the role of T_EX subsets in humans by combining exhaustion-directed phenotyping with functional profiling. Mass cytometry analysis of human T_EX populations is instrumental to gain a better understanding of T_EX in chronic infections and cancer. It has important implications for immune monitoring in therapeutic settings aiming to boost T cell immunity, such as during cancer immunotherapy.

Safety and efficacy of immune checkpoint inhibitors in patients with HBV/HCV infection and advanced-stage cancer: A systematic review

BACKGROUND

Cancer patients with hepatitis B or C virus (HBV/HCV) infection are commonly seen in clinical practice, however, the data of safety and efficacy of immune checkpoint inhibitors (ICIs) among them are sparse, because active HBV/HCV infected patients were generally excluded by clinical trials and the correlation between previous infection and treatment-related adverse events was rarely reported. This review is the first to summarize the results on the safety and efficacy of immune checkpoint inhibitors (ICIs) in HBV/HCV infected cancer patients.

METHOD

We searched literature and conference abstracts in PubMed and Embase followed the PRISMA guideline, using the keywords hepatitis B, hepatitis C, immune checkpoint inhibitor, ipilimumab, nivolumab, pembrolizumab, atezolizumab, durvalumab, avelumab, tremelimumab. Studies described patients with HBV/HCV infection treated with ICIs for advanced stage cancer were included.

FINDINGS

One hundred eighty six patients were identified from 14 articles (8 case reports, 4 case series, 2 trials). Eighty nine patients had HBV infection and 98 had HCV infection (1 both had HBV and HCV). The majority of patients were treated with PD-1 inhibitor monotherapy (140 of 186, 75.3%) and anti-CTLA-4 monotherapy (36 of 186, 19.4%). No treatment-related death was reported. The incidence of grade 3 or 4 hepatic transaminase elevating (HTE) in HBV and HCV infected patients were 3.4% (3/89) and 17.3% (17/98), respectively. 2.8% patients without antivirus therapy experienced virus load increasing, and 1.9% presented virus-related hepatitis. In terms of efficacy, 22 of 118 (18.6%) patients with liver cancer, 11 of 34 (32.4%) with melanoma, 1 of 6 (16.7%) with NSCLC showed objective responses (CR and PR) to ICIs in spite of lines of therapies.

CONCLUSION

ICIs is considered to be safe and effective in advanced cancer patients with hepatitis B or C infection, but still has possibilities to reactive hepatitis virus due to uncertain mechanisms. We recommend that those with viral hepatitis be monitored closely and treated with antiviral therapy if indicated before or during ICIs treatment.

Elimination of hepatitis C virus has limited impact on the functional and mitochondrial impairment of HCV-specific CD8+ T cell responses

BACKGROUND & AIMS

Hepatitis C virus (HCV)-specific CD8+ T cells are functionally impaired in chronic hepatitis C. Even though HCV can now be rapidly and sustainably cleared from chronically infected patients, the repercussions of HCV clearance on virus-specific CD8+ T cells remain elusive. Here, we aimed to investigate if HCV clearance by direct-acting antivirals (DAAs) could restore the functionality of exhausted HCV-specific CD8+ T cell responses.

METHODS

HCV-specific CD8+ T cells in peripheral blood were obtained from 40 patients with chronic HCV infection, during and 6 months following IFN-free DAA therapy. These cells were analyzed for comprehensive phenotypes, proliferation, cytokine production, mitochondrial fitness and response to immune-checkpoint blockade.

RESULTS

We show that, unlike activation markers that decreased, surface expression of multiple co-regulatory receptors on exhausted HCV-specific CD8+ T cells remained unaltered after clearance of HCV. Likewise, cytokine production by HCV-specific CD8+ T cells remained impaired following HCV clearance. The proliferative capacity of HCV multimer-specific CD8+ T cells was not restored in the majority of patients. Enhanced in vitro proliferative expansion of HCV-specific CD8+ T cells during HCV clearance was more likely in women, patients with low liver stiffness and low alanine aminotransferase levels in our cohort. Interestingly, HCV-specific CD8+ T cells that did not proliferate following HCV clearance could preferentially re-invigorate their proliferative capacity upon in vitro immune-checkpoint inhibition. Moreover, altered mitochondrial dysfunction exhibited by exhausted HCV-specific CD8+ T cells could not be normalized after HCV clearance.

CONCLUSION

Taken together, our data implies that exhausted HCV-specific CD8+ T cells remain functionally and metabolically impaired at multiple levels following HCV clearance in most patients with chronic hepatitis C. Our results might have implications in cases of re-infection with HCV and for HCV vaccine development.

LAY SUMMARY

Direct-acting antiviral therapy results in cure of hepatitis C virus (HCV) in almost all treated patients. However, the impacts of HCV cure on immune responses remain controversial. Whether immune responses to HCV recover is important in cases of re-exposure, or for the resolution of extrahepatic manifestations. The main finding of our study was that HCV-specific T cells remain functionally impaired despite HCV clearance. This finding could explain the fact that HCV cure does not lead to protective immunity and that re-infections have frequently been observed.

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.