Hepatitis C virus (HCV)-specific CD8+ cells produce transforming growth factor beta that can suppress HCV-specific T-cell responses

A multicentric and nationwide predictive study role of T cell sub-population in the prevalence and prognosis of cryoglobulinemia among genotype 4 chronic hepatitis C patients

The infection caused by the hepatitis C virus (HCV) is a significant global health concern. The prevailing genotype of HCV in Egypt is 4a, commonly referred to as GT-4a. A significant proportion exceeding 50% of patients infected with HCV experience extrahepatic manifestations (EHMs), encompassing a diverse range of clinical presentations. These manifestations, including essential mixed cryoglobulinemia (MC), can serve as initial and solitary indicators of the disease. The complete understanding of the pathogenesis of EHM remains unclear, with autoimmune phenomena being recognized as the primary causative factor. In this study, we examined the predictive significance of T-cell subpopulations in relation to the occurrence and prognosis of cryoglobulinemia in HCV patients. A total of 450 CHC genotype four treatment naïve patients were enrolled in this analytic cross-sectional study after thorough clinical, laboratory, and radiological examinations. All patients underwent laboratory investigations, including testing for cryoglobulin antibodies and measurements of CD4 and CD8 levels; two groups were described according to their test results: Group 1 consists of patients who have tested positive for cryoglobulin antibodies and Group 2 consists of patients who have tested negative for cryoglobulin antibodies. The exclusion criteria encompassed individuals with HIV infection or chronic HBV infection. Additionally, pelvi-abdominal ultrasonography was performed. Our study included 450 treatment naïve CHC patients (59% male, mean age 50.8 years). The patients were categorized according to their cryoglobulin antibodys test results into two groups: group A, CHC patients with cryoglobulin antibodies (Abs) negative (364 patients), and group B, CHC patients with cryoglobulin Ab positive (86 patients). Group B demonstrated a higher average age, elevated international normalized ratio, more prolonged duration of HCV infection, lower albumin, higher alanine aminotransferase, higher aspartate aminotransferase, higher bilirubin, lower CD8, lower CD4, and lower CD4:CD8 ratio. In contrast, 27 out of 86 (31.40%) patients in group B had symptoms; 85.8% had purpura and arthralgia, 74.3% had paresthesias, 86.7% had weakness, and 12.2% had non-Hodgkin's lymphoma. The levels of CD4 and CD8 were found to be decreased in chronic HCV patients with MC. T-cell subpopulation serves as a reliable indicator for assessing the prevalence and prognosis of MC in individuals with genotype 4 chronic hepatitis C. However, additional research is needed to further understand the development and spread of various emerging infectious diseases. Nevertheless, it is noteworthy that a critical threshold may exist beyond which EHM reaches a point of no return.

CD8+ T cells promote HIV latency by remodeling CD4+ T cell metabolism to enhance their survival, quiescence, and stemness

HIV infection persists during antiretroviral therapy (ART) due to a reservoir of latently infected cells that harbor replication-competent virus and evade immunity. Previous ex vivo studies suggested that CD8+ T cells from people with HIV may suppress HIV expression via non-cytolytic mechanisms, but the mechanisms responsible for this effect remain unclear. Here, we used a primary cell-based in vitro latency model and demonstrated that co-culture of autologous activated CD8+ T cells with HIV-infected memory CD4+ T cells promoted specific changes in metabolic and/or signaling pathways resulting in increased CD4+ T cell survival, quiescence, and stemness. Collectively, these pathways negatively regulated HIV expression and ultimately promoted the establishment of latency. As shown previously, we observed that macrophages, but not B cells, promoted latency in CD4+ T cells. The identification of CD8-specific mechanisms of pro-latency activity may favor the development of approaches to eliminate the viral reservoir in people with HIV.

BCHE as a Prognostic Biomarker in Endometrial Cancer and Its Correlation with Immunity

Background

In developed countries, the most common gynecologic malignancy is endometrial carcinoma (EC), making the identification of EC biomarkers extremely essential. As a natural enzyme, butyrylcholinesterase (BCHE) is found in hepatocytes and plasma. There is a strong correlation between BCHE gene mutations and cancers and other diseases. The aim of this study was to analyze the role of BCHE in patients with EC.

Methods

A variety of analyses were conducted on The Cancer Genome Atlas (TCGA) data, including differential expression analysis, enrichment analysis, immunity, clinicopathology, and survival analysis. The Gene Expression Omnibus (GEO) database was used to validate outcomes. Using R tools, Gene Set Enrichment Analysis (GSEA) and Gene Ontology (GO) analyses revealed the potential mechanisms of BCHE in EC. Sangerbox tools were used to delve into the relations between BCHE expression and tumor microenvironment, including microsatellite instability (MSI), tumor neoantigen count (TNC), and tumor mutation burden (TMB). BCHE's genetic alteration analysis was conducted by cBioPortal. In addition, the Human Protein Atlas (HPA) was used to validate the outcomes by immunohistochemistry, and an analysis of the protein-protein interaction network (PPI) was performed with the help of the STRING database.

Results

Based on our results, BCHE was a significant independent prognostic factor for patients with EC. The prognosis with EC was affected by age, stage, grade, histological type, and BCHE. GSEA showed that BCHE was closely related to pathways regulating immune response, including transforming growth factor-β (TGF-β) signaling pathways and cancer immunotherapy through PD1 blockade pathways. The immune analysis revealed that CD4+ regulatory T cells (Tregs) were negatively correlated with BCHE expression and the immune checkpoint molecules CD28, ADORA2A, BTNL2, and TNFRSF18 were all significantly related to BCHE. BCHE expression was also associated with TMB by genetic alteration analysis.

Conclusions

Identifying BCHE as a biomarker for EC might help predict its prognosis and could have important implications for immunotherapy.

The multi-faceted roles of TGF-β in regulation of immunity to infection

Transforming Growth Factor-β is a potent regulator of the immune system, acting at every stage from thymic differentiation, population of the periphery, control of responsiveness, tissue repair and generation of memory. It is therefore a central player in the immune response to infectious pathogens, but its contribution is often clouded by multiple roles acting on different cells in time and space. Hence, context is all-important in understanding when TGF-β is beneficial or detrimental to the outcome of infection. In this review, a full range of infectious agents from viruses to helminth parasites are explored within this framework, drawing contrasts and general conclusions about the importance of TGF-β in these diseases.

Epigenetic scars of CD8+ T cell exhaustion persist after cure of chronic infection in humans

T cell exhaustion is an induced state of dysfunction that arises in response to chronic infection and cancer. Exhausted CD8⁺ T cells acquire a distinct epigenetic state, but it is not known whether that chromatin landscape is fixed or plastic following the resolution of a chronic infection. Here we show that the epigenetic state of exhaustion is largely irreversible, even after curative therapy. Analysis of chromatin accessibility in HCV- and HIV-specific responses identifies a core epigenetic program of exhaustion in CD8⁺ T cells, which undergoes only limited remodeling before and after resolution of infection. Moreover, canonical features of exhaustion, including super-enhancers near the genes TOX and HIF1A, remain 'epigenetically scarred.' T cell exhaustion is therefore a conserved epigenetic state that becomes fixed and persists independent of chronic antigen stimulation and inflammation. Therapeutic efforts to reverse T cell exhaustion may require new approaches that increase the epigenetic plasticity of exhausted T cells.

Effects of Pegylated Interferon Alpha and Ribavirin (pegIFN-α/RBV) Therapeutic Approach on Regulatory T Cells in HCV-Monoinfected and HCV/HIV-Coinfected Patients

Approximately 25% of HIV-infected patients are co-infected with HCV. Notably, the burden of HCV infection (e.g., viral persistence, viral load, or HCV-related liver symptoms) is more pronounced in the presence of HIV co-infection. However, to date, the underlying immune mechanisms accounting for accelerated disease progression in HIV/HCV-coinfected individuals have not been described in sufficient detail. We hypothesized that regulatory T cells (Treg) bearing potent immunosuppressive capacities could not only play a substantial role in the pathogenesis of HCV/HIV coinfection but also modulate the response to the standard anti-viral therapy.

MATERIALS AND METHODS

To this end, we studied alterations in frequencies of Treg cells in correlation with other Treg-related and virus-related parameters in both HCV and HCV/HIV-infected patients subjected to standard pegIFN-α/RBV therapy.

RESULTS

Notably, we found that pegIFN-α/RBV therapy significantly increased levels of Treg cells in HCV-infected but not in HIV/HCV-coinfected individuals. Furthermore, HIV/HCV-coinfection was demonstrated to inhibit expansion of regulatory T cells during anti-viral treatment; thus, it might probably be responsible for viral persistence and HCV-related liver damage.

CONCLUSIONS

Therapy with pegIFN-α/RBV demonstrated a significant effect on regulatory T cells in the course of HIV and/or HCV infection indicating a crucial role in the anti-viral immune response.

Reversing T-cell exhaustion in immunotherapy: a review on current approaches and limitations

Introduction:T cell functions are altered during chronic viral infections and tumor development. This is mainly manifested by significant changes in T cells' epigenetic and metabolic landscapes, pushing them into an 'exhausted' state. Reversing this T cell exhaustion has been emerging as a 'game-changing' therapeutic approach against cancer and chronic viral infection.Areas covered:This review discusses the cellular pathways related to T cell exhaustion, and the clinical development and possible cellular targets that can be exploited therapeutically to reverse this exhaustion. We searched various databases (e.g. Google Scholar, PubMed, Elsevier, and other scientific database sites) using the keywords T cell exhaustion, T cell activation, co-inhibitory receptors, and reversing T cell exhaustion.Expert opinion:The discovery of the immune checkpoints pathways represents a significant milestone toward understanding and reversing T cell exhaustion. Antibodies that target these pathways have already demonstrated promising activities in reversing T cell exhaustion. Nevertheless, there are still many associated limitations. In this context, next-generation alternatives are on the horizon. This includes the use of small molecules to block the immune checkpoints' receptors, combining them with other treatments, and identifying novel, safer and more effective immunotherapeutic targets.

Natural Killer Cells and T Cells in Hepatocellular Carcinoma and Viral Hepatitis: Current Status and Perspectives for Future Immunotherapeutic Approaches

Natural killer (NK) cells account for 25–50% of the total number of hepatic lymphocytes, which implicates that NK cells play an important role in liver immunity. The frequencies of both circulating and tumor infiltrating NK cells are positively correlated with survival benefit in hepatocellular cancer (HCC) and have prognostic implications, which suggests that functional impairment in NK cells and HCC progression are strongly associated. In HCC, T cell exhaustion is accompanied by the interaction between immune checkpoint ligands and their receptors on tumor cells and antigen presenting cells (APC). Immune checkpoint inhibitors (ICIs) have been shown to interfere with this interaction and have altered the therapeutic landscape of multiple cancer types including HCC. Immunotherapy with check-point inhibitors, aimed at rescuing T-cells from exhaustion, has been applied as first-line therapy for HCC. NK cells are the first line effectors in viral hepatitis and play an important role by directly eliminating virus infected cells or by activating antigen specific T cells through IFN-γ production. Furthermore, chimeric antigen receptor (CAR)-engineered NK cells and T cells offer unique opportunities to create CAR-NK with multiple specificities learning from the experience gained with CAR-T cells with potentially less adverse effects. This review focus on the abnormalities of NK cells, T cells, and their functional impairment in patients with chronic viral hepatitis, which contributes to progression to hepatic malignancy. Furthermore, we discuss and summarize recent advances in the NK cell and T cell based immunotherapeutic approaches in HCC.

Tumor necrosis family receptor superfamily member 9/tumor necrosis factor receptor-associated factor 1 pathway on hepatitis C viral persistence and natural history

Hepatitis C virus (HCV) infection is an excellent immunological model for understanding the mechanisms developed by non-cytopathic viruses and tumors to evade the adaptative immune response. The antigen-specific cytotoxic T cell response is essential for keeping HCV under control, but during persistent infection, these cells become exhausted or even deleted. The exhaustion process is progressive and depends on the infection duration and level of antigenemia. During high antigenic load and long duration of infection, T cells become extremely exhausted and ultimately disappear due to apoptosis. The development of exhaustion involves the impairment of positive co-stimulation induced by regulatory cytokines, such as transforming growth factor beta 1. This cytokine downregulates tumor necrosis factor receptor (TNFR)-associated factor 1 (TRAF1), the signal transducer of the T cell co-stimulatory molecule TNFR superfamily member 9 (known as 4-1BB). This impairment correlates with the low reactivity of T cells and an exhaustion phenotype. Treatment with interleukin-7 in vitro restores TRAF1 expression and rescues T cell effector function. The process of TRAF1 loss and its in vitro recovery is hierarchical, and more affected by severe disease progression. In conclusion, TRAF1 dynamics on T cells define a new pathogenic model that describes some aspects of the natural history of HCV, and sheds light on novel immunotherapy strategies for chronic viral infections and cancer.

Association between Hepatitis C Virus Viremia and the rs12979860, rs2228145 and rs1800795 SNP (CT/AC/GG) Genotype in Saudi Kidney Transplant Recipients

Background:

Hepatitis C virus (HCV) is a major health problem, particularly in high-risk groups such as kidney transplant recipients, where it can adversely affect graft survival and increase the relative risk for mortality. Recently, the role of genetic variation among HCV patients in determining the outcome of infections has been under investigation.

Objective:

To investigate the association of single-nucleotide polymorphisms (SNPs) rs12979860 (located within the interleukin-28B locus), rs2228145 (interleukin-6 receptor) and rs1800795 (interleukin-6 promoter) with HCV viremia in renal transplant patients.

Materials and Methods:

In this analytical cross-sectional study, 149 kidney transplant recipients, 82 males (median age: 41 years) and 67 females (median age: 45 years), were screened for HCV RNA in blood using real-time polymerase chain reaction and genotyped by sequencing (rs12979860) and restriction fragment length polymorphism (rs2228145 and rs1800795).

Results:

HCV RNA was detected in 17 (11.41%) of the 149 patients. There was no statistically significant association between the studied SNPs and HCV viremia. However, a combination of the CT/AC/GG genotype was significantly associated with HCV viremia (odds ratio: 5.4). The genotype AA of rs2228145 in the IL-6 receptor was associated with viremia levels of >10⁵ copies/ml (odds ratio: 5.96).

Conclusion:

To the best of the authors' knowledge, this is the first study that has shown that the CT/AC/GG genotype has an impact on HCV viremia in kidney transplant patients. Therefore, such SNP genotypes may potentially be used to identify transplant patients at risk of HCV infection.

Transforming growth factor beta induces fibroblasts to express and release the immunomodulatory protein PD-L1 into extracellular vesicles

Transforming growth factor-beta (TGFβ) is an enigmatic protein with various roles in healthy tissue homeostasis/development as well as the development or progression of cancer, wound healing, fibrotic disorders, and immune modulation, to name a few. As TGFβ is causal to various fibroproliferative disorders featuring localized or systemic tissue/organ fibrosis as well as the activated stroma observed in various malignancies, characterizing the pathways and players mediating its action is fundamental. In the current study, we found that TGFβ induces the expression of the immunoinhibitory molecule Programed death-ligand 1 (PD-L1) in human and murine fibroblasts in a Smad2/3- and YAP/TAZ-dependent manner. Furthermore, PD-L1 knockdown decreased the TGFβ-dependent induction of extracellular matrix proteins, including collagen Iα1 (colIα1) and alpha-smooth muscle actin (α-SMA), and cell migration/wound healing. In addition to an endogenous role for PD-L1 in profibrotic TGFβ signaling, TGFβ stimulated-human lung fibroblast-derived PD-L1 into extracellular vesicles (EVs) capable of inhibiting T cell proliferation in response to T cell receptor stimulation and mediating fibroblast cell migration. These findings provide new insights and potential targets for a variety of fibrotic and malignant diseases.

Intracellular Pathogens: Host Immunity and Microbial Persistence Strategies

Infectious diseases caused by pathogens including viruses, bacteria, fungi, and parasites are ranked as the second leading cause of death worldwide by the World Health Organization. Despite tremendous improvements in global public health since 1950, a number of challenges remain to either prevent or eradicate infectious diseases. Many pathogens can cause acute infections that are effectively cleared by the host immunity, but a subcategory of these pathogens called "intracellular pathogens" can establish persistent and sometimes lifelong infections. Several of these intracellular pathogens manage to evade the host immune monitoring and cause disease by replicating inside the host cells. These pathogens have evolved diverse immune escape strategies and overcome immune responses by residing and multiplying inside host immune cells, primarily macrophages. While these intracellular pathogens that cause persistent infections are phylogenetically diverse and engage in diverse immune evasion and persistence strategies, they share common pathogen type-specific mechanisms during host-pathogen interaction inside host cells. Likewise, the host immune system is also equipped with a diverse range of effector functions to fight against the establishment of pathogen persistence and subsequent host damage. This article provides an overview of the immune effector functions used by the host to counter pathogens and various persistence strategies used by intracellular pathogens to counter host immunity, which enables their extended period of colonization in the host. The improved understanding of persistent intracellular pathogen-derived infections will contribute to develop improved disease diagnostics, therapeutics, and prophylactics.

A changing paradigm: management and treatment of the HCV/HIV-co-infected patient

Hepatitis C virus (HCV) treatment in HIV/HCV co-infected individuals has renewed relevance given the ongoing opioid crisis and rise of new HIV and HCV infections associated with injection drug use. Patients co-infected with HIV and HCV demonstrate increased rates of hepatic fibrosis, progression to liver failure, and liver-related mortality. HIV co-infection does not impact outcomes of current HCV treatments, and patients should be treated the same as HCV mono-infected persons, though attention to drug:drug interactions is required. In this review, we discuss the mechanisms mediating injury to the liver in HIV mono-infection and HIV/HCV co-infection, and present the landmark trials of HCV treatment in HIV-infected individuals.

Description of CD8+ Regulatory T Lymphocytes and Their Specific Intervention in Graft-versus-Host and Infectious Diseases, Autoimmunity, and Cancer

Gershon and Kondo described CD8⁺ Treg lymphocytes as the first ones with regulating activity due to their tolerance ability to foreign antigens and their capacity to inhibit the proliferation of other lymphocytes. Regardless, CD8⁺ Treg lymphocytes have not been fully described-unlike CD4⁺ Treg lymphocytes-because of their low numbers in blood and the lack of specific and accurate population markers. Still, these lymphocytes have been studied for the past 30 years, even after finding difficulties during investigations. As a result, studies have identified markers that define their subpopulations. This review is focused on the expression of cell membrane markers as CD25, CD122, CD103, CTLA-4, CD39, CD73, LAG-3, and FasL as well as soluble molecules such as FoxP3, IFN-γ, IL-10, TGF-β, IL-34, and IL-35, in addition to the lack of expression of cell activation markers such as CD28, CD127 CD45RC, and CD49d. This work also underlines the importance of identifying some of these markers in infections with several pathogens, autoimmunity, cancer, and graft-versus-host disease as a strategy in their prevention, monitoring, and cure.

Identification of IL-10-secreting CD8+CD28-PD-1+ regulatory T cells associated with chronic hepatitis C virus infection

CD8⁺CD28^- regulatory T cells (Tregs) play important roles in chronic viral infections. Programmed death 1 (PD-1) is highly expressed on hepatitis C virus (HCV)-specific CTLs. However, little is known regarding the role of CD8⁺CD28-PD1⁺ T cells in hepatitis C. Herein, we found that the frequency of CD8⁺CD28^-PD1⁺, but not CD8⁺CD28^-PD1^- T cells, correlated with markers of chronic hepatitis C virus (HCV) infection and the response to treatment. Our results showed that CD8⁺CD28-PD1⁺ T cells were significantly elevated in chronic HCV-infected patients and there was a distinct correlation between the frequency of CD8⁺CD28-PD1⁺ T cells and serum levels of HCV RNA. During a 48-week course of treatment with peg-IFN-a2a plus ribavirin, dynamic changes in the frequencies of CD8⁺CD28-PD1⁺ T cells were observed, associated with the virologic response. IL-10 secretion may explain the suppressive function of CD8⁺CD28-PD1⁺ T cells in chronic HCV-infected patients. Overall, our study demonstrates that PD-1 is an important marker of CD8⁺CD28^- Tregs in chronic HCV infection. Thus, the frequency and regulatory function of CD8⁺CD28-PD1⁺ T cells play vital roles in HCV infection and the response to treatment.

The role of regulatory T cells in immunopathogenesis and immunotherapy of viral infections

Two hepatotropic viruses hepatitis C virus (HCV) and hepatitis B virus (HBV) have been considered as the main cause of chronic viral infections. In addition, human immunodeficiency virus (HIV) attacks the immune system by eradication of some white blood cell (T-helper cell). The role of Tregs in HCV, HBV and HIV infections ranges from suppressing antiviral T cell responses to protecting tissues as liver and immune cells from immune mediated injury. In this review, we discuss the influence of regulatory T cells in immunopathology of specific viral infections including HCV, HBV and HIV by focusing on targeting Tregs as novel approach in vaccinology against viral infections.

According to Hepatitis C Virus (HCV) Infection Stage, Interleukin-7 Plus 4-1BB Triggering Alone or Combined with PD-1 Blockade Increases TRAF1low HCV-Specific CD8+ Cell Reactivity

Hepatitis C virus (HCV)-specific CD8⁺ T cells suffer a progressive exhaustion during persistent infection (PI) with HCV. This process could involve the positive immune checkpoint 4-1BB/4-1BBL through the loss of its signal transducer, TRAF1. To address this issue, peripheral HCV-specific CD8⁺ T cells (pentamer-positive [pentamer⁺]/CD8⁺ T cells) from patients with PI and resolved infection (RI) after treatment were studied. The duration of HCV infection and the liver fibrosis progression rate inversely correlated with the likelihood of detection of peripheral pentamer⁺/CD8⁺ cells. In PI, pentamer⁺/CD8⁺ cells had impaired antigen-specific reactivity that worsened when these cells were not detectable ex vivo Short/midduration PI was characterized by detectable peripheral PD-1⁺ CD127^low TRAF1^low cells. After triggering of T cell receptors (TCR), the TRAF1 level positively correlated with the levels of CD127, Mcl-1, and CD107a expression and proliferation intensity but negatively with PD-1 expression, linking TRAF1^low to exhaustion. In vitro treatment with interleukin-7 (IL-7) upregulated TRAF1 expression, while treatment with transforming growth factor-β1 (TGF-β1) did the opposite, suggesting that the IL-7/TGF-β1 balance, besides TCR stimulation, could be involved in TRAF1 regulation. In fact, the serum TGF-β1 concentration was higher in patients with PI than in patients with RI, and it negatively correlated with TRAF1 expression. In line with IL-7 increasing the level of TRAF1 expression, IL-7 plus 4-1BBL treatment in vitro enhanced T cell reactivity in patients with short/midduration infection. However, in patients with long-lasting PI, anti-PD-L1, in addition to the combination of IL-7 and 4-1BBL, was necessary to reestablish T cell proliferation in individuals with slowly progressing liver fibrosis (slow fibrosers) but had no effect in rapid fibrosers. In conclusion, a peripheral hyporeactive TRAF1^low HCV-specific CD8⁺ T cell response, restorable by IL-7 plus 4-1BBL treatment, characterizes short/midduration PI. In long-lasting disease, HCV-specific CD8⁺ T cells are rarely detectable ex vivo, but treatment with IL-7, 4-1BBL, and anti-PD-L1 recovers their reactivity in vitro in slow fibrosers.IMPORTANCE Hepatitis C virus (HCV) infects 71 million people worldwide. Two-thirds develop a chronic disease that can lead to cirrhosis and hepatocellular carcinoma. Direct-acting antivirals clear the infection, but there are still patients who relapse. In these cases, additional immunotherapy could play a vital role. A successful anti-HCV immune response depends on virus-specific CD8⁺ T cells. During chronic infection, these cells are functionally impaired, which could be due to the failure of costimulation. This study describes exhausted specific T cells, characterized by low levels of expression of the signal transducer TRAF1 of the positive costimulatory pathway 4-1BB/4-1BBL. IL-7 upregulated TRAF1 expression and improved T cell reactivity in patients with short/midduration disease, while in patients with long-lasting infection, it was also necessary to block the negative PD-1/PD-L1 checkpoint. When the results are taken together, this work supports novel ways of restoring the specific CD8⁺ T cell response, shedding light on the importance of TRAF1 signaling. This could be a promising target for future immunotherapy.

Regulation of the Immune Response by TGF-β: From Conception to Autoimmunity and Infection

Transforming growth factor β (TGF-β) is a pleiotropic cytokine involved in both suppressive and inflammatory immune responses. After 30 years of intense study, we have only begun to elucidate how TGF-β alters immunity under various conditions. Under steady-state conditions, TGF-β regulates thymic T-cell selection and maintains homeostasis of the naïve T-cell pool. TGF-β inhibits cytotoxic T lymphocyte (CTL), Th1-, and Th2-cell differentiation while promoting peripheral (p)Treg-, Th17-, Th9-, and Tfh-cell generation, and T-cell tissue residence in response to immune challenges. Similarly, TGF-β controls the proliferation, survival, activation, and differentiation of B cells, as well as the development and functions of innate cells, including natural killer (NK) cells, macrophages, dendritic cells, and granulocytes. Collectively, TGF-β plays a pivotal role in maintaining peripheral tolerance against self- and innocuous antigens, such as food, commensal bacteria, and fetal alloantigens, and in controlling immune responses to pathogens.

Regulatory T Cells in Hepatitis B and C Virus Infections

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are hepatotropic viruses that establish chronic persistent infection by effectively escaping the host immune response and can cause immune-mediated liver injury. It has recently become apparent that regulatory T (Treg) cells, specifically CD4+CD25+Foxp3+ Treg cells, modulate viral diseases by suppressing antiviral immune responses and regulating inflammatory host injury. The roles of Treg cells in HBV and HCV infections range from suppressing antiviral T cell responses to protecting the liver from immune-mediated damage. This review describes Treg cells and subpopulations and focuses on the roles of these cells in HBV and HCV infections.

Molecular and Cellular Characterization of Human CD8 T Suppressor Cells

Bidirectional interactions between dendritic cells and Ag-experienced T cells initiate either a tolerogenic or immunogenic pathway. The outcome of these interactions is of crucial importance in malignancy, transplantation, and autoimmune diseases. Blockade of costimulation results in the induction of T helper cell anergy and subsequent differentiation of antigen-specific CD8⁺ T suppressor/regulatory cells (Ts). Ts, primed in the presence of inhibitory signals, exert their inhibitory function in an antigen-specific manner, a feature with tremendous clinical potential. In transplantation or autoimmunity, antigen-specific Ts can enforce tolerance to auto- or allo-antigens, while otherwise leaving the immune response to pathogens uninhibited. Alternatively, blockade of inhibitory receptors results in the generation of cytolytic CD8⁺ T cells, which is vital toward defense against tumors and viral diseases. Because CD8⁺ T cells are MHC Class I restricted, they are able to recognize HLA-bound antigenic peptides presented not only by APC but also on parenchymal cells, thus eliciting or suppressing auto- or allo-immune reactions.

TGFβ1-Mediated SMAD3 Enhances PD-1 Expression on Antigen-Specific T Cells in Cancer

Programmed death-1 (PD-1) is a coinhibitory receptor that downregulates the activity of tumor-infiltrating lymphocytes (TIL) in cancer and of virus-specific T cells in chronic infection. The molecular mechanisms driving high PD-1 expression on TILs have not been fully investigated. We demonstrate that TGFβ1 enhances antigen-induced PD-1 expression through SMAD3-dependent, SMAD2-independent transcriptional activation in T cells in vitro and in TILs in vivo The PD-1^hi subset seen in CD8⁺ TILs is absent in Smad3-deficient tumor-specific CD8⁺ TILs, resulting in enhanced cytokine production by TILs and in draining lymph nodes and antitumor activity. In addition to TGFβ1's previously known effects on T-cell function, our findings suggest that TGFβ1 mediates T-cell suppression via PD-1 upregulation in the tumor microenvironment (TME). They highlight bidirectional cross-talk between effector TILs and TGFβ-producing cells that upregulates multiple components of the PD-1 signaling pathway to inhibit antitumor immunity.

SIGNIFICANCE

Engagement of the coinhibitory receptor PD-1 or its ligand, PD-L1, dramatically inhibits the antitumor function of TILs within the TME. Our findings represent a novel immunosuppressive function of TGFβ and demonstrate that TGFβ1 allows tumors to evade host immune responses in part through enhanced SMAD3-mediated PD-1 expression on TILs. Cancer Discov; 6(12); 1366-81. ©2016 AACRThis article is highlighted in the In This Issue feature, p. 1293.

Role of regulatory T-cells during hepatitis C infection: From the acute phase to post-transplantation recurrence

Hepatitis C viral infection persists and becomes chronic in a majority of affected individuals. Numerous factors have been described to explain how the virus manages to escape the host immune system. One important escape mechanism is the increase in regulatory T cells induced by the virus. In this review, we will focus on the status of regulatory T cells throughout the natural history of hepatitis C infection and after liver transplantation. The molecular mechanisms involved in increasing the number of regulatory T cells are also discussed, as are data regarding the impact of regulatory T-cells on hepatic fibrosis in the context of hepatitis C viral infection.

Innate and Adaptive Immune Regulation During Chronic Viral Infections

Chronic viral infections represent a unique challenge to the infected host. Persistently replicating viruses outcompete or subvert the initial antiviral response, allowing the establishment of chronic infections that result in continuous stimulation of both the innate and adaptive immune compartments. This causes a profound reprogramming of the host immune system, including attenuation and persistent low levels of type I interferons, progressive loss (or exhaustion) of CD8(+) T cell functions, and specialization of CD4(+) T cells to produce interleukin-21 and promote antibody-mediated immunity and immune regulation. Epigenetic, transcriptional, posttranscriptional, and metabolic changes underlie this adaptation or recalibration of immune cells to the emerging new environment in order to strike an often imperfect balance between the host and the infectious pathogen. In this review we discuss the common immunological hallmarks observed across a range of different persistently replicating viruses and host species, the underlying molecular mechanisms, and the biological and clinical implications.

The host HLA-A*02 allele is associated with the response to pegylated interferon and ribavirin in patients with chronic hepatitis C virus infection

Human leukocyte antigen (HLA) alleles are associated with both the progression of chronic hepatitis C (CHC) and the sustained virological response (SVR) to antiviral therapy. HLA-A*02 is the most common HLA allele in people of European/Caucasian descent and the Chinese and Japanese population. Therefore, we investigated whether HLA-A*02 expression is associated with disease outcome in Chinese CHC patients. Three hundred thirty-one treatment-naïve CHC patients were recruited in this study. The expression of HLA-A*02 was tested by FACS and LABType SSO assays. All patients were treated weekly with pegylated interferon plus ribavirin (PEG-IFN/RBV) according to a standard protocol. Virological response was assessed by TaqMan assay at the 4th, 12th, 24th, and 48th week of therapy, and again at the 24th week post-therapy. By the end of the study, 293 CHC patients, including 144 HLA-A*02-positive patients and 149 HLA-A*02-negative patients, were evaluable for analysis. There were no statistical differences in clinicopathological parameters between HLA-A*02-positive and negative patients before antiviral therapy (P > 0.05). The HLA-A*02-positive patients had a higher rapid virological response (RVR, 74.3 % versus 62.4 %, P = 0.03) and SVR (78.5 % versus 64.4 %, P = 0.01) and a lower relapse rate (4.2 % versus 11.9 %, P = 0.03) than HLA-A*02-negative patients. Multivariable logistic regression analysis showed that HLA-A*02 expression, liver fibrosis stages Collapse

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MESH Headings

• Adult
• Alleles
• Antiviral Agents/therapeutic use
• Asian People/genetics
• China
• Drug Therapy, Combination
• Female
• HLA-A Antigens/genetics
• Hepacivirus/drug effects
• Hepacivirus/genetics
• Hepacivirus/physiology
• Hepatitis C, Chronic/drug therapy
• Hepatitis C, Chronic/genetics
• Humans
• Interferon alpha-2
• Interferon-alpha/therapeutic use
• Middle Aged
• Polyethylene Glycols/therapeutic use
• Prospective Studies
• Recombinant Proteins/therapeutic use
• Ribavirin/therapeutic use
• Treatment Outcome

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Grants Collapse

Affiliation(s)

Meng Wang Department of Gastroenterology, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
Jian-Sheng Li
Yu Ping
Zhi-Qin Li
Li-Ping Wang
Qian Guo
Zhen Zhang
Dong-Li Yue
Fei Wang
Teng-Fei Zhang
Mohammad Serajul Islam
Yi Zhang

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T-cell exhaustion in chronic hepatitis B infection: current knowledge and clinical significance

Hepatitis B virus (HBV) infection is the major cause of inflammatory liver disease, of which the clinical recovery and effective anti-viral therapy is associated with the sustained viral control of effector T cells. In humans, chronic HBV infection often shows weak or absent virus-specific T-cell reactivity, which is described as the ‘exhaustion' state characterized by poor effector cytotoxic activity, impaired cytokine production and sustained expression of multiple inhibitory receptors, such as programmed cell death-1 (PD-1), lymphocyte activation gene-3, cytotoxic T lymphocyte-associated antigen-4 and CD244. As both CD4⁺ and CD8⁺ T cells participate in the immune responses against chronic hepatitis virus through distinct manners, compelling evidences have been proposed, which restore the anti-viral function of these exhausted T cells by blocking those inhibitory receptors with its ligand and will pave the way for the development of more effective immunotherapeutic and prophylactic strategies for the treatment of chronic infectious diseases. A large number of studies have stated the essentiality of T-cell exhaustion in virus-infected diseases, such as LCMV, hepatitis C virus (HCV), human immunodeficiency virus infections and cancers. Besides, the functional restoration of HCV- and HIV-specific CD8⁺ T cells by PD-1 blockade has already been repeatedly verified, and also for the immunological control of tumors in humans, blocking the PD-1 pathway could be a major immunotherapeutic strategy. Although the specific molecular pathways of T-cell exhaustion remain ambiguous, several transcriptional pathways have been implicated in T-cell exhaustion recently; among them Blimp-1, T-bet and NFAT2 were able to regulate exhausted T cells during chronic viral infection, suggesting a distinct lineage fate for this sub-population of T cells. This paper summarizes the current literature relevant to T-cell exhaustion in patients with HBV-related chronic hepatitis, the options for identifying new potential therapeutic targets to treat HBV infection and highlights priorities for further study.

T cell exhaustion during persistent viral infections

Although robust and highly effective anti-viral T cells contribute to the clearance of many acute infections, viral persistence is associated with the development of functionally inferior, exhausted, T cell responses. Exhaustion develops in a step-wise and progressive manner, ranges in severity, and can culminate in the deletion of the anti-viral T cells. This disarming of the response is consequential as it compromises viral control and potentially serves to dampen immune-mediated damage. Exhausted T cells are unable to elaborate typical anti-viral effector functions. They are characterized by the sustained upregulation of inhibitory receptors and display a gene expression profile that distinguishes them from prototypic effector and memory T cell populations. In this review we discuss the properties of exhausted T cells; the virological and immunological conditions that favor their development; the cellular and molecular signals that sustain the exhausted state; and strategies for preventing and reversing exhaustion to favor viral control.

Adaptive immune response during hepatitis C virus infection

Hepatitis C virus (HCV) infection affects about 170 million people worldwide and it is a major cause of liver cirrhosis and hepatocellular carcinoma. HCV is a hepatotropic non-cytopathic virus able to persist in a great percentage of infected hosts due to its ability to escape from the immune control. Liver damage and disease progression during HCV infection are driven by both viral and host factors. Specifically, adaptive immune response carries out an essential task in controlling non-cytopathic viruses because of its ability to recognize infected cells and to destroy them by cytopathic mechanisms and to eliminate the virus by non-cytolytic machinery. HCV is able to impair this response by several means such as developing escape mutations in neutralizing antibodies and in T cell receptor viral epitope recognition sites and inducing HCV-specific cytotoxic T cell anergy and deletion. To impair HCV-specific T cell reactivity, HCV affects effector T cell regulation by modulating T helper and Treg response and by impairing the balance between positive and negative co-stimulatory molecules and between pro- and anti-apoptotic proteins. In this review, the role of adaptive immune response in controlling HCV infection and the HCV mechanisms to evade this response are reviewed.

MicroRNA-155 controls Toll-like receptor 3- and hepatitis C virus-induced immune responses in the liver

The hepatitis C virus (HCV) establishes persistent infections despite strong activation of the innate immune system through TLR3 and other sensors. Therefore, we analysed regulatory mechanisms of TLR3-induced immune responses in nonparenchymal liver cells (NPCs). Effects of Interleukin-10 (IL-10), transforming growth factor beta (TGF-β) and immunoregulatory miR-155 on poly I:C-activated murine (C57BL/6) Kupffer cells (KC) and sinusoidal endothelial cells (LSEC) were assessed in vitro. NPCs were assayed for inflammatory and antiviral cytokines and T-cell (Balb/c)-activating factors. Gene expression of miR-155, IL-10, TGF-β and interferon sensitive genes (ISGs) in biopsies of patients with HCV was determined by qrt-PCR. TLR3-induced antiviral activity in murine NPCs was potently suppressed by IL-10 and TGF-β which correlated with decreased TLR3 expression and inhibition of NF-κB and IRF-3 activation. T-cell activation, induced by TLR3-activated NPCs, was also suppressed by IL-10 and TGF-β, which was associated with a down-regulation of CD80 and CD86. Pretreatment with IL-10 or TGF-β suppressed TLR3-induced miR-155 expression, which itself positively regulated poly I:C-mediated immune responses, thus counteracting IL-10 or TGF-β-induced immunosuppression. In addition, hepatic expression of miR-155 was elevated in chronically infected patients with HCV, was associated with an IL-28B SNP (rs12979860) and was inversely correlated with HCV serum load and ISG expression levels. As miR-155 is a key regulator of anti-inflammatory mechanisms that control innate and adaptive hepatic immune responses during HCV infection, miR-155 based therapies may represent a novel mechanism to control HCV in the future.

CD4+ primary T cells expressing HCV-core protein upregulate Foxp3 and IL-10, suppressing CD4 and CD8 T cells

Adaptive T cell responses are critical for controlling HCV infection. While there is clinical evidence of a relevant role for regulatory T cells in chronic HCV-infected patients, based on their increased number and function; mechanisms underlying such a phenomena are still poorly understood. Accumulating evidence suggests that proteins from Hepatitis C virus can suppress host immune responses. We and others have shown that HCV is present in CD4+ lymphocytes from chronically infected patients and that HCV-core protein induces a state of unresponsiveness in the CD4+ tumor cell line Jurkat. Here we show that CD4+ primary T cells lentivirally transduced with HCV-core, not only acquire an anergic phenotype but also inhibit IL-2 production and proliferation of bystander CD4+ or CD8+ T cells in response to anti-CD3 plus anti-CD28 stimulation. Core-transduced CD4+ T cells show a phenotype characterized by an increased basal secretion of the regulatory cytokine IL-10, a decreased IFN-γ production upon stimulation, as well as expression of regulatory T cell markers, CTLA-4, and Foxp3. A significant induction of CD4+CD25+CD127(low)PD-1(high)TIM-3(high) regulatory T cells with an exhausted phenotype was also observed. Moreover, CCR7 expression decreased in HCV-core expressing CD4+ T cells explaining their sequestration in inflamed tissues such as the infected liver. This work provides a new perspective on de novo generation of regulatory CD4+ T cells in the periphery, induced by the expression of a single viral protein.

Pathogenesis of chronic viral hepatitis: differential roles of T cells and NK cells

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections account for 57% of cases of liver cirrhosis and 78% of cases of primary liver cancer worldwide and cause a million deaths per year. Although HBV and HCV differ in their genome structures, replication strategies and life cycles, they have common features, including their noncytopathic nature and their capacity to induce chronic liver disease, which is thought to be immune mediated. However, the rate of disease progression from chronic hepatitis to cirrhosis varies greatly among infected individuals, and the factors that regulate it are largely unknown. This review summarizes our current understanding of the roles of antigen-specific and nonspecific immune cells in the pathogenesis of chronic hepatitis B and C and discusses recent findings that identify natural killer cells as regulators of T cell function and liver inflammation.

Boosters of a therapeutic HIV-1 vaccine induce divergent T cell responses related to regulatory mechanisms

Therapeutic human immunodeficiency virus (HIV) vaccines aim to reduce disease progression by inducing HIV-specific T cells. Vacc-4x are peptides derived from conserved domains within HIV-1 p24 Gag. Previously, Vacc-4x induced T cell responses in 90% of patients which were associated with reduced viral loads. Here we evaluate the effects of Vacc-4x boosters on T cell immunity and immune regulation seven years after primary immunization. Twenty-five patients on effective antiretroviral therapy received two Vacc-4x doses four weeks apart and were followed for 16 weeks. Vacc-4x T cell responses were measured by proliferation (CFSE), INF-γ, CD107a, Granzyme B, Delayed-Type Hypersensitivity test (DTH) and cytokines and chemokines (Luminex). Functional regulation of Vacc-4x-specific T cell proliferation was estimated in vitro using anti-IL-10 and anti-TGF-ß monoclonal antibodies. Vacc-4x-specific CD8(+) T cell proliferation increased in 80% after either the first (64%) or second (16%) booster. Only 40% remained responders after two boosters with permanently increased Vacc-4x-specific proliferative responses (p=0.005) and improved CD8(+) T cell degranulation, IFN-γ production and DTH. At baseline, responders had higher CD8(+) T cell degranulation (p=0.05) and CD4(+) INF-γ production (p=0.01), whereas non-responders had higher production of proinflammatory TNF-α, IL-1α and IL-1ß (p<0.045) and regulatory IL-10 (p=0.07). Notably, IL-10 and TGF-ß mediated downregulation of Vacc-4x-specific CD8(+) T cell proliferation increased only in non-responders (p<0.001). Downregulation during the study correlated to higher PD-1 expression on Vacc-4x-specific CD8(+) T cells (r=0.44, p=0.037), but was inversely correlated to changes in Vacc4x-specific CD8(+) T cell proliferation (r=-0.52, p=0.012). These findings show that Vacc-4x boosters can improve T cell responses in selected patients, but also induce vaccine-specific downregulation of T cell responses in others. Broad surveillance of T cell functions during immunization may help to individualize boosting, where assessment of vaccine-related immune regulation should be further explored as a potential new parameter.

Negative regulation of type I IFN expression by OASL1 permits chronic viral infection and CD8⁺ T-cell exhaustion

The type I interferons (IFN-Is) are critical not only in early viral control but also in prolonged T-cell immune responses. However, chronic viral infections such as those of human immunodeficiency virus (HIV) and hepatitis C virus (HCV) in humans and lymphocytic choriomeningitis virus (LCMV) in mice overcome this early IFN-I barrier and induce viral persistence and exhaustion of T-cell function. Although various T-cell-intrinsic and -extrinsic factors are known to contribute to induction of chronic conditions, the roles of IFN-I negative regulators in chronic viral infections have been largely unexplored. Herein, we explored whether 2'-5' oligoadenylate synthetase-like 1 (OASL1), a recently defined IFN-I negative regulator, plays a key role in the virus-specific T-cell response and viral defense against chronic LCMV. To this end, we infected Oasl1 knockout and wild-type mice with LCMV CL-13 (a chronic virus) and monitored T-cell responses, serum cytokine levels, and viral titers. LCMV CL-13-infected Oasl1 KO mice displayed a sustained level of serum IFN-I, which was primarily produced by splenic plasmacytoid dendritic cells, during the very early phase of infection (2-3 days post-infection). Oasl1 deficiency also led to the accelerated elimination of viremia and induction of a functional antiviral CD8 T-cell response, which critically depended on IFN-I receptor signaling. Together, these results demonstrate that OASL1-mediated negative regulation of IFN-I production at an early phase of infection permits viral persistence and suppresses T-cell function, suggesting that IFN-I negative regulators, including OASL1, could be exciting new targets for preventing chronic viral infection.

Role of T cell immunity in hepatitis C virus infections

Chronic infections with the hepatitis C virus (HCV) are a major global health issue. Viral replication is restricted to hepatocytes, and occurs for decades at high replication rates. Over the last decade, it became accepted that HCV-specific CD4(+) and CD8(+) T cells are crucial for protective immunity to HCV. However, a characteristic feature of persistent HCV infection is the dysfunctional T cell response, and over recent years enormous progress has been made in understanding the mechanisms that dampen the antiviral T cell responses in blood and liver of chronic HCV patients and also impact disease progression.

T-cell responses in hepatitis B and C virus infection: similarities and differences

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection are global health problems affecting 600 million people worldwide. Indeed, HBV and HCV are hepatotropic viruses that can cause acute and chronic liver disease progressing to liver cirrhosis and even hepatocellular carcinoma. Furthermore, co-infections of HBV and HCV with HIV are emerging worldwide. These co-infections are even more likely to develop persistent infection and are difficult to treat. There is growing evidence that virus-specific CD4⁺ and CD8⁺ T-cell responses play a central role in the outcome and pathogenesis of HBV and HCV infection. While virus-specific T-cell responses are able to successfully clear the virus in a subpopulation of patients, failure of these T-cell responses is associated with the development of viral persistence. In this review article, we will discuss similarities and differences in HBV- and HCV-specific T-cell responses that are central in determining viral clearance, persistence and liver disease.

Acute hepatitis C virus infection in a nurse trainee following a needlestick injury

Hepatitis C virus (HCV) infection after biological accident (needlestick injury) is a rare event. This report describes the first case of acute HCV infection after a needlestick injury in a female nursing student at Padua University Hospital. The student nurse was injured on the second finger of the right hand when recapping a 23-gauge needle after taking a blood sample. The patient who was the source was a 72-year-old female with weakly positive anti-HCV test results. Three months after the injury, at the second step of follow-up, a relevant increase in transaminases with a low viral replication activity (350 IU/mL) was observed in the student, indicating HCV infection. The patient tested positive for the same genotype (1b) of HCV as the injured student. A rapid decline in transaminases, which was not accompanied by viral clearance, and persistently positive HCV-RNA was described 1 mo later. Six months after testing positive for HCV, the student was treated with pegylated interferon plus ribavirin for 24 wk. A rapid virological response was observed after 4 wk of treatment, and a sustained virological response (SVR) was evident 6 mo after therapy withdrawal, confirming that the patient was definitively cured. Despite the favourable IL28B gene (rs12979860) CC- polymorphism observed in the patient, which is usually predictive of a spontaneous clearance and SVR, spontaneous viral clearance did not take place; however, infection with this genotype was promising for a sustained virological response after therapy.

Adaptive immune responses in hepatitis C virus infection

The adaptive immune response plays a central role in the outcome of hepatitis C virus (HCV) infection. Indeed, spontaneous viral clearance is associated with an early neutralizing antibody response as well as vigorous and sustained HCV-specific CD4+ and CD8+ T cell responses. In persistent HCV infection, however, all three components of the antiviral adaptive immune response fail due to different viral evasion strategies. In this chapter, we will describe the components of a successful immune response against HCV and summarize the mechanisms of immune failure. We will also highlight characteristics of protective CD8+ T cell responses which is the key factor to the design of an efficacious vaccine.

Hepatitis C virus-specific T-cell-derived transforming growth factor beta is associated with slow hepatic fibrogenesis

Hepatitis C virus (HCV)-specific immune effector responses can cause liver damage in chronic infection. Hepatic stellate cells (HSC) are the main effectors of liver fibrosis. TGFβ, produced by HCV-specific CD8(+) T cells, is a key regulatory cytokine modulating HCV-specific effector T cells. Here we studied TGFβ as well as other factors produced by HCV-specific intrahepatic lymphocytes (IHL) and peripheral blood cells in hepatic inflammation and fibrogenesis. This was a cross-sectional study of two well-defined groups of HCV-infected subjects with slow (≤ 0.1 Metavir units/year, n = 13) or rapid (n = 6) liver fibrosis progression. HCV-specific T-cell responses were studied using interferon-gamma (IFNγ)-ELISpot ±monoclonal antibodies (mAbs) blocking regulatory cytokines, along with multiplex, enzyme-linked immunosorbent assay (ELISA) and multiparameter fluorescence-activated cell sorting (FACS). The effects of IHL stimulated with HCV-core peptides on HSC expression of profibrotic and fibrolytic genes were determined. Blocking regulatory cytokines significantly raised detection of HCV-specific effector (IFNγ) responses only in slow fibrosis progressors, both in the periphery (P = 0.003) and liver (P = 0.01). Regulatory cytokine blockade revealed HCV-specific IFNγ responses strongly correlated with HCV-specific TGFβ, measured before blockade (R = 0.84, P = 0.0003), with only a trend to correlation with HCV-specific IL-10. HCV-specific TGFβ was produced by CD8 and CD4 T cells. HCV-specific TGFβ, not interleukin (IL)-10, inversely correlated with liver inflammation (R = -0.63, P = 0.008) and, unexpectedly, fibrosis (R = -0.46, P = 0.05). In addition, supernatants from HCV-stimulated IHL of slow progressors specifically increased fibrolytic gene expression in HSC and treatment with anti-TGFβ mAb abrogated such expression.

CONCLUSION

Although TGFβ is considered a major profibrogenic cytokine, local production of TGFβ by HCV-specific T cells appeared to have a protective role in HCV-infected liver, together with other T-cell-derived factors, ameliorating HCV liver disease progression.

Negative regulation of hepatitis C virus specific immunity is highly heterogeneous and modulated by pegylated interferon-alpha/ribavirin therapy

Specific inhibitory mechanisms suppress the T-cell response against the hepatitis C virus (HCV) in chronically infected patients. However, the relative importance of suppression by IL-10, TGF-β and regulatory T-cells and the impact of pegylated interferon-alpha and ribavirin (PegIFN-α/ribavirin) therapy on these inhibitory mechanisms are still unclear. We revealed that coregulation of the HCV-specific T-cell responses in blood of 43 chronic HCV patients showed a highly heterogeneous pattern before, during and after PegIFN-α/ribavirin. Prior to treatment, IL-10 mediated suppression of HCV-specific IFN-γ production in therapy-naive chronic HCV patients was associated with higher HCV-RNA loads, which suggests that protective antiviral immunity is controlled by IL-10. In addition, as a consequence of PegIFN-α/ribavirin therapy, negative regulation of especially HCV-specific IFN-γ production by TGF-β and IL-10 changed dramatically. Our findings emphasize the importance of negative regulation for the dysfunctional HCV-specific immunity, which should be considered in the design of future immunomodulatory therapies.

CD4⁺ and CD8⁺ regulatory T cells (Tregs) are elevated and display an active phenotype in patients with chronic HCV mono-infection and HIV/HCV co-infection

The aim of this study was to examine regulatory T cells (Tregs) in peripheral blood and liver tissue in patients with chronic hepatitis C virus (HCV) mono-infection and in patients with HIV/HCV co-infection. In a cross-sectional study were included 51 patients with chronic HCV infection, 24 patients with HIV/HCV co-infection and 24 healthy individuals. CD4⁺ and CD8⁺ Tregs were determined using flow cytometry. Fibrosis was examined by transient elastography. Inflammation, fibrosis and Tregs were determined in liver biopsies from 12 patients. Increased frequency of CD4⁺ and CD8⁺ Tregs was found in HIV/HCV co-infected patients [median: 6.4% (IQR: 5.7-6.9) and 1.0% (0.7-1.2), respectively] compared to HCV mono-infected patients [5.6% (4.2-6.3), P = 0.01 and 0.5% (0.3-0.7), P < 0.001, respectively]. Furthermore, HCV mono-infected patients had increased frequencies of Tregs compared with healthy controls (P < 0.05). However, no associations between the frequency of Tregs and fibrosis were found. Furthermore, characterization of CD4⁺ Tregs using CD45RA demonstrated a higher frequency of activated Tregs in both HCV mono-infected and HIV/HCV co-infected patients compared with healthy controls. Finally, number of intrahepatic Tregs was associated with both peripheral CD8⁺ Tregs and intrahepatic inflammation. In conclusion, HCV mono-infected patients and particularly HIV/HCV co-infected patients have increased the frequency of CD4⁺ and CD8⁺ Tregs compared with healthy controls. Furthermore, CD4⁺ Tregs in infected patients displayed an active phenotype. Tregs were not associated with fibrosis, but a positive correlation between intrahepatic Tregs and inflammation was found. Taken together, these results suggest a role for Tregs in the pathogenesis of chronic HCV infection.

Hepatitis C virus-mediated modulation of cellular immunity

The hepatitis C virus (HCV) is a major cause of chronic liver disease globally. A chronic infection can result in liver fibrosis, liver cirrhosis, hepatocellular carcinoma and liver failure in a significant ratio of the patients. About 170 million people are currently infected with HCV. Since 80 % of the infected patients develop a chronic infection, HCV has evolved sophisticated escape strategies to evade both the innate and the adaptive immune system. Thus, chronic hepatitis C is characterized by perturbations in the number, subset composition and/or functionality of natural killer cells, natural killer T cells, dendritic cells, macrophages and T cells. The balance between HCV-induced immune evasion and the antiviral immune response results in chronic liver inflammation and consequent immune-mediated liver injury. This review summarizes our current understanding of the HCV-mediated interference with cellular immunity and of the factors resulting in HCV persistence. A profound knowledge about the intrinsic properties of HCV and its effects on intrahepatic immunity is essential to be able to design effective immunotherapies against HCV such as therapeutic HCV vaccines.

Immunology of hepatitis C virus infections

The immune response in patients chronically infected with HCV plays a unique role during the infection because of its potential to contribute not only to viral clearance and, in some cases, protective immunity, but also to liver injury. A detailed understanding of the immunological mechanisms involved in persistence to HCV is essential to fully appreciate the complexity of the disease. In recent years, enormous progress has been made to characterize the dysfunctional natural killer cells and T cells during the chronic phase of infection. This information is important to further optimize treatment strategies based on the strengthening antiviral and immunomodulatory activities in patients chronically infected with HCV.

Peginterferon-α does not improve early peripheral blood HBV-specific T-cell responses in HBeAg-negative chronic hepatitis

BACKGROUND & AIMS

The effect of IFN-α therapy on HBV-specific T-cell responses in HBeAg-negative, genotype D, chronic hepatitis B is largely undefined. Understanding to what extent IFN-α can modulate HBV-specific T-cells is important to define strategies to optimize IFN efficacy and to identify immunological parameters to predict response to therapy.

METHODS

HBV-specific T-cell responses were analyzed longitudinally ex vivo and after expansion in vitro in 15 patients with genotype D, HBeAg-negative chronic hepatitis B treated with peginterferon-α-2a. HBV proteins and synthetic peptides were used to stimulate T-cell responses. Analysis of the CD4 and CD8 T-cell functions was performed by ELISPOT, intracellular cytokine and tetramer staining. The effect of anti-PD-L1 on T-cell functions was also analyzed.

RESULTS

Ex vivo IFN-γ production by total HBV-specific T-cells was significantly greater before therapy in patients who showed HBV DNA <50 IU/ml at weeks 24 and/or 48 of therapy. No significant improvement of T-cell proliferation, Th1 cytokine production and cytotoxicity was observed during IFN therapy by both ex vivo and in vitro analysis. PD-1/PD-L1 blockade showed a modest improvement of cytokine production in a total of 15% of T-cell lines.

CONCLUSIONS

IFN-α did not improve peripheral blood HBV-specific T-cell responses in the first 24 weeks of treatment, consistent either with a predominant antiviral/antiproliferative effect or with an immunomodulatory activity on other arms of the immune system which were not analyzed in our study. A better pre-treatment ex vivo IFN-γ production was associated with better chances to control HBV replication during therapy and represents a promising predictor of IFN efficacy.

Lack of TGF-β production by hepatitis C virus-specific T cells during HCV acute phase is associated with HCV clearance in HIV coinfection

BACKGROUND & AIMS

Immunity and genetic factors govern the recovery from acute hepatitis C virus (HCV) infection. No predictive factors have been yet identified in patients coinfected with the human immunodeficiency virus (HIV). We investigated whether early T cell responses to HCV producing transforming-growth-factor beta (TGF-β) predict the outcome of acute HCV coinfection, independently of the IL-28B gene polymorphism.

METHODS

Intracellular cytokine staining assays against HCV-core, E1, NS2, and NS4 overlapping peptides were used for the analysis of peripheral HCV-specific TGF-β-producing T cells. Patients were genotyped for IL-28B polymorphisms. Healthy donors' samples were tested as controls. Twenty-four acute hepatitis C-HIV+ patients were followed-up for 15 months defining two groups: (A) Recovered (n=16, 5 spontaneous recoveries, 11 sustained virologic response after treatment), (B) Chronic HCV (n=8, 4 spontaneous chronic course, 4 therapeutic failures).

RESULTS

During the acute pretreatment phase, core/NS2-specific TGF-β-producing CD4+ and/or CD8+ T cells were detected in 8/24 (33%) patients. Lack of anti-HCV TGF-β+ cells was characteristic of healthy donors and Group A, except for 2 cases, with frequencies significantly lower than in Group B (p=0.04 and 0.01), and was associated with recovery in 14/16 cases. Presence of anti-HCV TGF-β+ cells was associated with persistent viremia in 6/8 cases (p=0.005). This profile remained stable over time. Such TGF-β production was independent of the rs129679860 SNP (p=1.0) which was not associated with recovery (p=1.0).

CONCLUSIONS

During acute hepatitis C, pre-therapeutic HCV-specific TGF-β-producing T cells are a new marker independent of the IL-28B gene polymorphism, predicting the lack of spontaneous or therapeutic HCV clearance.

Development and function of murine RORγt+ iNKT cells are under TGF-β signaling control

Invariant natural killer T (iNKT) cells have the ability to rapidly secret cytokines in response to diverse stimuli, and therefore influence numerous immune reactions. Although IFN-γ and IL-4 are thought to dominate iNKT cytokine production, a distinct subset of iNKT cells, expressing RORγt and producing IL-17, has now been identified in both mice and humans. Although a role in pathogen and allergic responses has been assigned to the RORγt(+) iNKT subset, factors controlling their development and function remain illusive. Here, we demonstrate that RORγt(+) iNKT-cell differentiation obeys transforming growth factor-β (TGF-β) signaling control, different from that described for conventional iNKT cells. We reveal that TGF-β signaling, and particularly its SMAD4-dependent pathway, is required for both the survival of RORγt(+) iNKT cells during their development and IL-17 production at the periphery. Moreover, constitutive TGF-β signaling in RORγt(+) iNKT cells drives higher peripheral numbers and increased tissue distribution. Finally, we found that SMAD4-dependent TGF-β signaling is mandatory for the peripheral expansion of the RORγt(+) iNKT cells responding to inflammatory signals. Thus, this work demonstrates that both the development and responsiveness of the newly described IL-17-producing iNKT cell subset is under the control of a dedicated TGF-β signaling pathway.

Mechanism of T cell exhaustion in a chronic environment

T cell exhaustion develops under conditions of antigen-persistence caused by infection with various chronic pathogens, such as human immunodeficiency virus (HIV) and mycobacterium tuberculosis (TB), or by the development of cancer. T cell exhaustion is characterized by stepwise and progressive loss of T cell function, which is probably the main reason for the failed immunological control of chronic pathogens and cancers. Recent observations have detailed some of the intrinsic and extrinsic factors that influence the severity of T cell exhaustion. Duration and magnitude of antigenic activation of T cells might be associated with up-regulation of inhibitory receptors, which is a major intrinsic factor of T cell exhaustion. Extrinsic factors might include the production of suppressive cytokines, T cell priming by either non-professional antigen-presenting cells (APCs) or tolerogenic dendritic cells (DCs), and alteration of regulatory T (Treg) cells. Further investigation of the cellular and molecular processes behind the development of T cell exhaustion can reveal therapeutic targets and strategies for the treatment of chronic infections and cancers. Here, we report the properties and the mechanisms of T cell exhaustion in a chronic environment.

Immunopathogenesis of HIV/hepatitis C virus coinfection

As a result of shared infection routes, approximately 25% of individuals infected with HIV in North America are also infected with hepatitis C virus (HCV). In the setting of HIV coinfection, the course of HCV disease is more aggressive, resulting in higher HCV viral loads and a more rapid progression of liver pathology. With the success of HAART, HCV-related end-stage liver disease has become a leading cause of morbidity and mortality in HIV/HCV-coinfected patients. In this article, we will discuss recent studies examining the immune response during HIV and HCV coinfection, focusing on alterations or dysfunctions in virus-specific T-cell responses that may play a role in the immunopathogenesis of HIV/HCV coinfection. Summarizing the impact of HIV coinfection on HCV-specific T-cell immunity and highlighting some of the proposed mechanisms of T-cell dysfunction in HIV/HCV-coinfected individuals may uncover information that could lead to new treatment strategies for these patients experiencing accelerated liver disease and generally poorer outcomes than their HCV-monoinfected counterparts.

Characterization of antigenic variants of hepatitis C virus in immune evasion

BACKGROUND

Antigenic variation is an effective way by which viruses evade host immune defense leading to viral persistence. Little is known about the inhibitory mechanisms of viral variants on CD4 T cell functions.

RESULTS

Using sythetic peptides of a HLA-DRB1*15-restricted CD4 epitope derived from the non-structural (NS) 3 protein of hepatitis C virus (HCV) and its antigenic variants and the peripheral blood mononuclear cells (PBMC) from six HLA-DRB1*15-positive patients chronically infected with HCV and 3 healthy subjects, the in vitro immune responses and the phenotypes of CD4+CD25+ cells of chronic HCV infection were investigated. The variants resulting from single or double amino acid substitutions at the center of the core region of the Th1 peptide not only induce failed T cell activation but also simultaneously up-regulate inhibitory IL-10, CD25-TGF-β+ Th3 and CD4+IL-10+ Tr1 cells. In contrast, other variants promote differentiation of CD25+TGF-β+ Th3 suppressors that attenuate T cell proliferation.

CONCLUSIONS

Naturally occuring HCV antigenic mutants of a CD4 epitope can shift a protective peripheral Th1 immune response into an inhibitory Th3 and/or Tr1 response. The modulation of antigenic variants on CD4 response is efficient and extensive, and is likely critical in viral persistence in HCV infection.

T cell exhaustion

T cell exhaustion is a state of T cell dysfunction that arises during many chronic infections and cancer. It is defined by poor effector function, sustained expression of inhibitory receptors and a transcriptional state distinct from that of functional effector or memory T cells. Exhaustion prevents optimal control of infection and tumors. Recently, a clearer picture of the functional and phenotypic profile of exhausted T cells has emerged and T cell exhaustion has been defined in many experimental and clinical settings. Although the pathways involved remain to be fully defined, advances in the molecular delineation of T cell exhaustion are clarifying the underlying causes of this state of differentiation and also suggest promising therapeutic opportunities.

Suppressive CD8+ T cells arise in the absence of CD4 help and compromise control of persistent virus

There is an urgent need to develop novel therapies for controlling chronic virus infections in immunocompromised patients. Disease associated with persistent γ-herpesvirus infection (EBV, human herpesvirus 8) is a significant problem in AIDS patients and transplant recipients, and clinical management of these conditions is difficult. Immune surveillance failure followed by γ-herpesvirus recrudescence can be modeled using murine γ-herpesvirus (MHV)-68 in mice lacking CD4(+) T cells. In contrast with other chronic infections, no obvious defect in the functional capacity of the viral-specific CD8(+) T cell response was detected. We show in this article that adoptive transfer of MHV-68-specific CD8(+) T cells was ineffective at reducing the viral burden. Together, these indicate the potential presence of T cell extrinsic suppressive factors. Indeed, CD4-depleted mice infected with MHV-68 express increased levels of IL-10, a cytokine capable of suppressing the function of both APCs and T cells. CD4-depleted mice developed a population of CD8(+) T cells capable of producing IL-10 that suppressed viral control. Although exhibiting cell surface markers indicative of activation, the IL-10-producing cells expressed increased levels of programmed death-1 but were not enriched in the MHV-68-specific compartment, nor were they uniformly CD44(hi). Therapeutic administration of an IL-10R blocking Ab enhanced control of the recrudescent virus. These data implicate IL-10 as a promising target for the restoration of immune surveillance against chronic γ-herpesvirus infection in immunosuppressed individuals.