Programmed death-1 affects suppressor of cytokine signaling-1 expression in T cells during hepatitis C infection

The role of SOCS proteins in the development of virus- induced hepatocellular carcinoma

Background

Liver cancer has become one of the most common cancers and has a high mortality rate. Hepatocellular carcinoma is one of the most common liver cancers, and its occurrence and development process are associated with chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections.

Main body

The serious consequences of chronic hepatitis virus infections are related to the viral invasion strategy. Furthermore, the viral escape mechanism has evolved during long-term struggles with the host. Studies have increasingly shown that suppressor of cytokine signaling (SOCS) proteins participate in the viral escape process. SOCS proteins play an important role in regulating cytokine signaling, particularly the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway. Cytokines stimulate the expression of SOCS proteins, in turn, SOCS proteins inhibit cytokine signaling by blocking the JAK-STAT signaling pathway, thereby achieving homeostasis. By utilizing SOCS proteins, chronic hepatitis virus infection may destroy the host’s antiviral responses to achieve persistent infection.

Conclusions

This review provides recent knowledge regarding the role of SOCS proteins during chronic hepatitis virus infection and provides some new ideas for the future treatment of chronic hepatitis.

Downregulation of SOCS gene expression can inhibit the formation of acute and persistent BDV infections

High expression of suppressors of cytokine signalling (SOCS) has been detected during various viral infections. As a negative feedback regulator, SOCS participates in the regulation of multiple signalling pathways. In this study, to study the related mechanism between SOCS and BDV and to explore the effect of SOCS on IFN pathways in nerve cells, downregulated of SOCS1/3 in oligodendroglial (OL) cells and OL cells persistently infected with BDV (OL/BDV) were constructed with RNA interference technology. An interferon inducer (poly I:C, PIC) and an IFN-α/β R1 antibody were used as stimulation in the SOCS1/3 low-expression cell models, qRT-PCR was used to detect type I IFN and BDV nucleic acid expression, Western blot was used to detect the expression of BDV P40 protein. After BDV acute infection with OL cells which with downregulated SOCS expression, the virus accounting was not detected, and the viral protein expression was lower than that of OL/BDV cells; the OL/BDV cells with downregulated SOCS expression had lower virus nucleic acid and protein expression than OL/BDV cells. Stimulated by IFN-α/β R1 antibody, the expression of type I interferon in OL/BDV cells decreased, and the content of BDV nucleic acid and protein increased, which was higher than that of OL/BDV cells. From the results, it was concluded that downregulating SOCS1/3 can inhibit the formation of acute BDV infection and virus replication in persistent BDV infection by promoting the expression of IFN-α/β and that SOCS can be used as a new target for antiviral therapy.

Transcriptomics and Targeted Proteomics Analysis to Gain Insights Into the Immune-control Mechanisms of HIV-1 Infected Elite Controllers

A small subset of HIV-1 infected individuals, the "Elite Controllers" (EC), can control viral replication and restrain progression to immunodeficiency without antiretroviral therapy (ART). In this study, a cross-sectional transcriptomics and targeted proteomics analysis were performed in a well-defined Swedish cohort of untreated EC (n=19), treatment naïve patients with viremia (VP, n=32) and HIV-1-negative healthy controls (HC, n=23). The blood transcriptome identified 151 protein-coding genes that were differentially expressed (DE) in VP compared to EC. Genes like CXCR6 and SIGLEC1 were downregulated in EC compared to VP. A definite distinction in gene expression between males and females among all patient-groups were observed. The gene expression profile between female EC and the healthy females was similar but did differ between male EC and healthy males. At targeted proteomics analysis, 90% (29/32) of VPs clustered together while EC and HC clustered separately from VP. Among the soluble factors, 33 were distinctive to be statistically significant (False discovery rate=0.02). Cell surface receptor signaling pathway, programmed cell death, response to cytokine and cytokine-mediated signaling seem to synergistically play an essential role in HIV-1 control in EC.

PD-1/PD-L1 signal pathway participates in HCV F protein-induced T cell dysfunction in chronic HCV infection

Programmed cell death-1/programmed cell death-1 ligand 1 (PD-1/PD-L1) inhibitory signal pathway has been verified to be involved in the establishment of persistent viral infections. Blockade of PD-1/PD-L1 engagement to reinvigorate T cell activity is supposed to be a potential therapeutic scheme. Studies have verified the participation of PD-1/PD-L1 in hepatitis C virus (HCV) core protein-regulated immune response. To determine the roles of PD-1/PD-L1 signal pathway in HCV F protein-induced immunoreaction in chronic HCV infection, variations in T cells were examined. The results showed that PD-1 expression on CD8(+) and CD4(+) T cells was increased with HCV F stimulation in both chronic HCV patients and healthy controls, and could be reduced partly by PD-1/PD-L1 blocking. Additionally, by PD-1/PD-L1 blocking, HCV F-induced inhibition of T cell proliferation and promotion of cellular apoptosis were partly or even totally recovered. Furthermore, levels of both Th1 and Th2 cytokines were elevated in the presence of anti-PD-L1 antibody. All these results indicated that PD-1/PD-L1 signal pathway also participates in HCV F protein-induced immunoregulation. PD-1/PD-L1 blocking plays important roles in the restoration of effective functionality of the impaired T cells in chronic HCV patients.

Programmed death (PD)-1 attenuates macrophage activation and brain inflammation via regulation of fibrinogen-like protein 2 (Fgl-2) after intracerebral hemorrhage in mice

Neuroinflammation plays an important role in the recovery of brain injury in ICH. Macrophage is the major executor in the neuroinflammation and initiates neurological defects. Programmed death 1 (PD-1) delivers inhibitory signals that regulate the balance between T cell activation, tolerance, and immunopathology. PD-1 expression by macrophages plays a pathologic role in the innate inflammatory response. However, the exact role of PD-1 on inflammatory responses following ICH has not been well identified. In this experiment, PD-1 KO (PD-1 -/-) ICH mice and Wild-type (WT) ICH mice were caused by intracranial injection of type IV collagenase. The level of macrophage activation, inflammatory cytokines and fibrinogen-like protein 2 (Fgl-2) were detected using immunofluorescence staining and ELISA assays. In addition, brain edema and neurological scores of ICH mice were also measured. Our data demonstrated that ICH promoted PD-1 expression of macrophage and enhanced inflammatory cytokines and Fgl-2 concentrations. PD-1 -/- mice exhibited significantly higher expression of the inflammatory cytokines which initiate Fgl-2, than did their wild-type (WT) littermates. As a result, macrophage activation, cerebral edema and neurological deficit scores of PD-1 -/- mice were higher. In conclusion, our data demonstrate that PD-1 plays a vital role in brain inflammation via regulation of Fgl-2 after ICH, and that manipulation of PD-1 might be a promising therapeutical target in ICH.

Tim-3 suppression combined with TLR3 activation enhances antiviral immune response in patients with chronic HCV infection

OBJECTIVE

To investigate the regulation mechanism of T cell immunoglobulin and mucin domain-3 (Tim-3) combined with toll-like receptor 3 (TLR3) or TLR4 on antiviral immune and inflammatory response in patients with chronic hepatitis C virus (HCV) infection.

METHODS

Patients with chronic HCV infection and healthy control subjects were recruited. Patients received interferon (IFN)-α based therapy. Plasma galectin-9 (Gal-9) was quantitated. Peripheral blood mononuclear cells (PBMCs) were cultured with TLR3 or TLR4 agonists, alone or in combination with Tim-3 antagonist. Levels of IFN-α, TNF-α, and 2'-5' oligoadenylate synthetase (2'-5'OAS), myxovirus resistance protein A (MxA) and suppressor of cytokine 1 (SOCS1) RNA in PBMC cultures were evaluated.

RESULTS

Plasma Gal-9 levels were increased in patients (n = 52) compared with controls (n = 20) and significantly declined at treatment week 12 and 24 weeks post-treatment. IFN-α, 2'-5'OAS, MxA, TNF-α and SOCS1 were upregulated by TLR3 and TLR4 agonists. TNF-α and SOCS1 levels were suppressed by the addition of Tim-3 antagonist.

CONCLUSIONS

Tim-3 blockade in combination with TLR activation induces the expression of antiviral molecules without a significant increase in TNF-α or SOCS1.

The relevance of Tim-3 polymorphisms and F protein to the outcomes of HCV infection

Hepatitis C virus (HCV) is one of the major causes of liver inflammation. The aim of this study was to investigate the associations of T-cell immunoglobulin and mucin domain-3 (Tim-3) polymorphisms and the alternate reading frame protein (F protein) with the outcomes of HCV infection. Three single-nucleotide polymorphisms (SNPs; rs10053538, rs12186731, and rs13170556) of Tim-3 were genotyped in this study, which included 203 healthy controls, 558 hepatitis C anti-F-positive patients, and 163 hepatitis C anti-F-negative patients. The results revealed that the rs12186731 CT and rs13170556 TC and CC genotypes were significantly less frequent in the anti-F-positive patients [odds ratio (OR) = 0.54, 95 % confidence interval (CI) = 0.35-0.83, p = 0.005; OR = 0.26, 95 % CI = 0.18-0.39, p < 0.001; and OR = 0.19, 95 % CI = 0.10-0.35, p < 0.001, respectively), and the rs13170556 TC genotype was more frequent in the chronic HCV (CHC) patients (OR = 1.70, 95 % CI = 1.20-2.40, p = 0.002). The combined analysis of the rs12186731 CT and rs13170556 TC/CC genotypes revealed a locus-dosage protective effect in the anti-F-positive patients (OR = 0.22, 95 % CI = 0.14-0.33, p trend < 0.001). Stratified analyses revealed that the frequencies of the rs12186731 (CT + TT) genotypes were significantly lower in the older (OR = 0.31, 95 % CI = 0.15-0.65, p = 0.002) and female (OR = 0.30, 95 % CI = 0.17-0.52, p < 0.001) subgroups, and rs13170556 (TC + CC) genotypes exhibited the same effect in all subgroups (all p < 0.001) in the anti-F antibody generations. Moreover, the rs13170556 (TC + CC) genotypes were significantly more frequent in the younger (OR = 1.86, 95 % CI = 1.18-2.94, p = 0.007) and female (OR = 2.38, 95 % CI = 1.48-3.83, p < 0.001) subgroups of CHC patients. These findings suggest that the rs12186731 CT and rs13170556 TC/CC genotypes of Tim-3 provide potential protective effects with the F protein in the outcomes of HCV infection and that these effects are related to sex and age.

The core of hepatitis C virus pathogenesis

Capsid proteins form protective shells around viral genomes and mediate viral entry. However, many capsid proteins have additional and important roles for virus infection and in modulating cellular response to infection, with important consequences on pathogenesis. Infection by the Hepatitis C virus (HCV) can lead to liver steatosis, cirrhosis, and hepatocellular carcinoma. Herein, we focus on the role in pathogenesis of Core, the capsid protein of the HCV.

Hepatitis C virus-associated B-cell non-Hodgkin's lymphomas: what do we know?

Epidemiological studies have shown an increased risk of developing B-cell lymphomas in patients with chronic hepatitis C virus (HCV) infection. There is, however, a great geographic variability and it remains unclear whether additional environmental and genetic factors are involved or whether the international discrepancies represent simply a consequence of the variable prevalence of HCV infection in different countries. Other confounding factors may affect the comparability of the different studies, including the method of HCV assessment, the selection of normal controls, the lymphoma classification used and the year of publication. The most convincing evidence for a causal relationship comes from the observation, mainly limited to some indolent subtypes, of B-cell lymphoma regressions after successful HCV eradication with antiviral treatment. Yet, the molecular mechanism of HCV-induced lymphomagenesis are mainly hypothetical. According to most plausible models, lymphoma growth is a consequence of continuous antigenic stimulation induced by the chronic viral infection. This review will summarize the current knowledge on HCV-associated lymphomas and their management.

T cells Exhibit Reduced Signal Transducer and Activator of Transcription 5 Phosphorylation and Upregulated Coinhibitory Molecule Expression After Kidney Transplantation

BACKGROUND

T-cell depletion therapy is associated with diminished interleukin (IL)-7/IL-15-dependent homeostatic proliferation resulting in incomplete T-cell repopulation. Furthermore, it is associated with impaired T-cell functions. We hypothesized that this is the result of impaired cytokine responsiveness of T cells, through affected signal transducer and activator of transcription (STAT)5 phosphorylation and upregulation of coinhibitory molecules.

MATERIALS AND METHODS

Patients were treated with T cell-depleting rabbit antithymocyte globulin (rATG) (6 mg/kg, n = 17) or nondepleting, anti-CD25 antibody (basiliximab, 2 × 40 mg, n = 25) induction therapy, in combination with tacrolimus, mycophenolate mofetil, and steroids. Before and the first year after transplantation, IL-7 and IL-2 induced STAT5 phosphorylation, and the expression of the coinhibitory molecules programmed cell death protein 1 (PD-1), T cell immunoglobulin mucin-3 (TIM-3), lymphocyte activation gene-3 (LAG-3), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), cluster of differentiation (CD) 160, and CD244 was measured by flow cytometry.

RESULTS

The first year after rATG, CD4+, and CD8+ T cells were affected in their IL-7-dependent phosphorylation of STAT5 (pSTAT5) which was most outspoken in the CD8+ memory population. The capacity of CD4+ and CD8+ T cells to pSTAT5 in response to IL-2 decreased after both rATG and basiliximab therapy. After kidney transplantation, the percentage of TIM-3+, PD-1+, and CD160+CD4+ T cells and the percentage of CD160+ and CD244+CD8+ T cells increased, with no differences in expression between rATG- and basiliximab-treated patients. The decrease in pSTAT5 capacity CD8+ T cells and the increase in coinhibitory molecules were correlated.

CONCLUSIONS

We show that memory T cells in kidney transplant patients, in particular after rATG treatment, have decreased cytokine responsiveness by impaired phosphorylation of STAT5 and have increased expression of coinhibitory molecules, processes which were correlated in CD8+ T cells.

Dendritic cells: The warriors upfront-turned defunct in chronic hepatitis C infection

Hepatitis C virus (HCV) infection causes tremendous morbidity and mortality with over 170 million people infected worldwide. HCV gives rise to a sustained, chronic disease in the majority of infected individuals owing to a failure of the host immune system to clear the virus. In general, an adequate immune response is elicited by an efficient antigen presentation by dendritic cells (DCs), the cells that connect innate and adaptive immune system to generate a specific immune response against a pathogen. However, HCV seems to dysregulate the activity of DCs, making them less proficient antigen presenting cells for the optimal stimulation of virus-specific T cells, hence interfering with an optimal anti-viral immune response. There are discordant reports on the functional status of DCs in chronic HCV infection (CHC), from no phenotypic or functional defects to abnormal functions of DCs. Furthermore, the molecular mechanisms behind the impairment of DC function are even so not completely elucidated during CHC. Understanding the mechanisms of immune dysfunction would help in devising strategies for better management of the disease at the immunological level and help to predict the prognosis of the disease in the patients receiving antiviral therapy. In this review, we have discussed the outcomes of the interaction of DCs with HCV and the mechanisms of DC impairment during HCV infection with its adverse effects on the immune response in the infected host.

Hepatitis C virus-induced reduction in miR-181a impairs CD4(+) T-cell responses through overexpression of DUSP6

T cells play a crucial role in viral clearance or persistence; however, the precise mechanisms that control their responses during viral infection remain incompletely understood. MicroRNA (miR) has been implicated as a key regulator controlling diverse biological processes through posttranscriptional repression. Here, we demonstrate that hepatitis C virus (HCV)-mediated decline of miR-181a expression impairs CD4(+) T-cell responses through overexpression of dual specific phosphatase 6 (DUSP6). Specifically, a significant decline of miR-181a expression along with overexpression of DUSP6 was observed in CD4(+) T cells from chronically HCV-infected individuals compared to healthy subjects, and the levels of miR-181a loss were found to be negatively associated with the levels of DUSP6 overexpression in these cells. Importantly, reconstitution of miR-181a or blockade of DUSP6 expression in CD4(+) T cells led to improved T-cell responses including enhanced CD25 and CD69 expression, increased interleukin-2 expression, and improved proliferation of CD4(+) T cells derived from chronically HCV-infected individuals.

CONCLUSION

Since a decline of miR-181a concomitant with DUSP6 overexpression is the signature marker for age-associated T-cell senescence, these findings provide novel mechanistic insights into HCV-mediated premature T-cell aging through miR-181a-regulated DUSP6 signaling and reveal new targets for therapeutic rejuvenation of impaired T-cell responses during chronic viral infection.

Production and pathogenicity of hepatitis C virus core gene products

Hepatitis C virus (HCV) is a major cause of chronic liver diseases, including steatosis, cirrhosis and hepatocellular carcinoma, and its infection is also associated with insulin resistance and type 2 diabetes mellitus. HCV, belonging to the Flaviviridae family, is a small enveloped virus whose positive-stranded RNA genome encoding a polyprotein. The HCV core protein is cleaved first at residue 191 by the host signal peptidase and further cleaved by the host signal peptide peptidase at about residue 177 to generate the mature core protein (a.a. 1-177) and the cleaved peptide (a.a. 178-191). Core protein could induce insulin resistance, steatosis and even hepatocellular carcinoma through various mechanisms. The peptide (a.a. 178-191) may play a role in the immune response. The polymorphism of this peptide is associated with the cellular lipid drop accumulation, contributing to steatosis development. In addition to the conventional open reading frame (ORF), in the +1 frame, an ORF overlaps with the core protein-coding sequence and encodes the alternative reading frame proteins (ARFP or core+1). ARFP/core+1/F protein could enhance hepatocyte growth and may regulate iron metabolism. In this review, we briefly summarized the current knowledge regarding the production of different core gene products and their roles in viral pathogenesis.

PD-1 deletion restores susceptibility to experimental autoimmune encephalomyelitis in miR-155-deficient mice

MiR-155 (-/-) mice are highly resistant to experimental autoimmune encephalomyelitis (EAE), while Pdcd1 (-/-) mice develop a more severe form of the disease. To determine the conflicting roles of these two molecules in the disease, we generated miR-155 (-/-) Pdcd1 (-/-) double knockout (DKO) mice. We found that ablation of programmed cell death protein 1 (PD-1) expression in miR-155-deficient mice restored the susceptibility to EAE. The increased severity of the disease in DKO mice was accompanied by an enhanced T-cell infiltration into the brain as well as an increased production of pro-inflammatory cytokines IFN-γ and IL-17. Furthermore, the major contribution of the DKO to EAE was T-cell intrinsic since adoptive transfer of CD4(+) T cells from DKO donors promoted the disease in lymphopenic recipients. These results define PD-1 deficiency in miR-155 (-/-) mice as a promoting factor of autoimmune inflammation by increasing antigen-driven T-cell expansion and infiltration.

Immune exhaustion and immune senescence: two distinct pathways for HBV vaccine failure during HCV and/or HIV infection

Given the shared risk factors for transmission, co-infection of hepatitis B virus (HBV) with hepatitis C virus (HCV) and/or human immunodeficiency virus (HIV) is quite common, and may lead to increases in morbidity and mortality. As such, HBV vaccine is recommended as the primary means to prevent HBV super-infection in HCV- and/or HIV-infected individuals. However, vaccine response (sero-conversion with a hepatitis B surface antibody titer >10 IU/L) in this setting is often blunted, with poor response rates to standard HBV vaccinations in virally infected individuals when compared with the healthy subjects. This phenomenon also occurs to other vaccines in adults, such as pneumococcal and influenza vaccines, in other immunocompromised hosts who are really at risk for opportunistic infections, such as individuals with hemodialysis, transplant, and malignancy. In this review, we summarize the underlying mechanisms involving vaccine failure in these conditions, focusing on immune exhaustion and immune senescence--two distinct signaling pathways regulating cell function and fate. We raise the possibility that blocking these negative signaling pathways might improve success rates of immunizations in the setting of chronic viral infection.

Tim-3 alters the balance of IL-12/IL-23 and drives TH17 cells: role in hepatitis B vaccine failure during hepatitis C infection

Hepatitis B virus (HBV) vaccination is recommended for individuals with hepatitis C virus (HCV) infection given their shared risk factors and increased liver-related morbidity and mortality upon super-infection. Vaccine responses in this setting are often blunted, with poor response rates to HBV vaccinations in chronically HCV-infected individuals compared to healthy subjects. In this study, we investigated the role of T cell immunoglobulin mucin domain-3 (Tim-3)-mediated immune regulation in HBV vaccine responses during HCV infection. We found that Tim-3, a marker for T cell exhaustion, was over-expressed on monocytes, leading to a differential regulation of IL-12/IL-23 production which in turn TH17 cell accumulation, in HCV-infected HBV vaccine non-responders compared to HCV-infected HBV vaccine responders or healthy subjects (HS). Importantly, ex vivo blockade of Tim-3 signaling corrected the imbalance of IL-12/IL-23 as well as the IL-17 bias observed in HBV vaccine non-responders during HCV infection. These results suggest that Tim-3-mediated dysregulation of innate to adaptive immune responses is involved in HBV vaccine failure in individuals with chronic HCV infection, raising the possibility that blocking this negative signaling pathway might improve the success rate of HBV immunization in the setting of chronic viral infection.

SOCS proteins in infectious diseases of mammals

As for most biological processes, the immune response to microbial infections has to be tightly controlled to remain beneficial for the host. Inflammation is one of the major consequences of the host's immune response. For its orchestration, this process requires a fine-tuned interplay between interleukins, endothelial cells and various types of recruited immune cells. Suppressors of cytokine signalling (SOCS) proteins are crucially involved in the complex control of the inflammatory response through their actions on various signalling pathways including the JAK/STAT and NF-κB pathways. Due to their cytokine regulatory functions, they are frequent targets for exploitation by infectious agents trying to escape the host's immune response. This review article aims to summarize our current knowledge regarding SOCS family members in the different mammalian species studied so far, and to display their complex molecular interactions with microbial pathogens.

Tim-3 pathway controls regulatory and effector T cell balance during hepatitis C virus infection

Hepatitis C virus (HCV) is remarkable at disrupting human immunity to establish chronic infection. Upregulation of inhibitory signaling pathways (such as T cell Ig and mucin domain protein-3 [Tim-3]) and accumulation of regulatory T cells (Tregs) play pivotal roles in suppressing antiviral effector T cell (Teff) responses that are essential for viral clearance. Although the Tim-3 pathway has been shown to negatively regulate Teffs, its role in regulating Foxp3(+) Tregs is poorly explored. In this study, we investigated whether and how the Tim-3 pathway alters Foxp3(+) Treg development and function in patients with chronic HCV infection. We found that Tim-3 was upregulated, not only on IL-2-producing CD4(+)CD25(+)Foxp3(-) Teffs, but also on CD4(+)CD25(+)Foxp3(+) Tregs, which accumulate in the peripheral blood of chronically HCV-infected individuals when compared with healthy subjects. Tim-3 expression on Foxp3(+) Tregs positively correlated with expression of the proliferation marker Ki67 on Tregs, but it was inversely associated with proliferation of IL-2-producing Teffs. Moreover, Foxp3(+) Tregs were found to be more resistant to, and Foxp3(-) Teffs more sensitive to, TCR activation-induced cell apoptosis, which was reversible by blocking Tim-3 signaling. Consistent with its role in T cell proliferation and apoptosis, blockade of Tim-3 on CD4(+)CD25(+) T cells promoted expansion of Teffs more substantially than Tregs through improving STAT-5 signaling, thus correcting the imbalance of Foxp3(+) Tregs/Foxp3(-) Teffs that was induced by HCV infection. Taken together, the Tim-3 pathway appears to control Treg and Teff balance through altering cell proliferation and apoptosis during HCV infection.

Apoptosis - an Ubiquitous T cell Immunomodulator

Apoptosis is a natural process where cells that are no longer required can be eliminated in a highly regulated, controlled manner. Apoptosis is important in maintaining the mammalian immune system and plays a significant role in immune response, positive and negative T cell selection, and cytotoxic death of target cells. When the apoptotic pathways are impaired or are not tightly regulated, autoimmune diseases, inflammatory diseases, viral and bacterial infections and cancers ensue. An imbalance in the anti-apoptotic and pro-apoptotic factors has been implicated in these diseases. Moreover, current therapies directed towards these diseases focus on the modulation of the apoptotic death pathways to regulate the immune response. In this review, we will focus on the process of T cell activation and apoptosis in autoimmune reactions, in response to tumor progression as well as in response to bacterial and viral infections.

Advances in hepatitis C virus vaccines, Part one: Advances in basic knowledge for hepatitis C virus vaccine design

INTRODUCTION

Around 3% of the world population is infected with HCV, with 3 - 4 million newly infected subjects added to this reservoir every year. At least 10% of these people will develop liver cirrhosis or cancer over time, while no approved vaccine against HCV infection is available to date.

AREAS COVERED

This paper includes a detailed and correlated patent (selected by HCAPLUS search database) and literature (searched by PubMed) review on the HCV genome, proteins and key epitopes (including underestimated HCV proteins, alternate reading frame proteins), HCV immunology, immunosuppressive mechanisms and protective correlations of immunity in acute and chronic states of infection (features for prophylactic and therapeutic HCV vaccine design), recent HCV cell culture systems (HCV/JFH1) and animal models. In part two of this review, advances in HCV vaccine formulations and modalities as well as a detailed list of the current trials for HCV vaccine and discussion of the pros and cones of different strategies will be provided.

EXPERT OPINION

By using the advanced basic knowledge and tools obtained about HCV vaccinology in recent years and the application of novel formulations and modalities, at least partially effective vaccines will become available in the near future to prevent (or treat) the chronic (if not the acute) state of HCV infection. A few of such vaccines are already in clinical trials.

Tim-3 negatively regulates IL-12 expression by monocytes in HCV infection

T cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) is a newly identified negative immunomodulator that is up-regulated on dysfunctional T cells during viral infections. The expression and function of Tim-3 on human innate immune responses during HCV infection, however, remains poorly characterized. In this study, we report that Tim-3 is constitutively expressed on human resting CD14⁺ monocyte/macrophages (M/M_Ø) and functions as a cap to block IL-12, a key pro-inflammatory cytokine linking innate and adaptive immune responses. Tim-3 expression is significantly reduced and IL-12 expression increased upon stimulation with Toll-like receptor 4 (TLR4) ligand - lipopolysaccharide (LPS) and TLR7/8 ligand - R848. Notably, Tim-3 is over-expressed on un-stimulated as well as TLR-stimulated M/M_Ø, which is inversely associated with the diminished IL-12 expression in chronically HCV-infected individuals when compared to healthy subjects. Up-regulation of Tim-3 and inhibition of IL-12 are also observed in M/M_Ø incubated with HCV-expressing hepatocytes, as well as in primary M/M_Ø or monocytic THP-1 cells incubated with HCV core protein, an effect that mimics the function of complement C1q and is reversible by blocking the HCV core/gC1qR interaction. Importantly, blockade of Tim-3 signaling significantly rescues HCV-mediated inhibition of IL-12, which is primarily expressed by Tim-3 negative M/M_Ø. Tim-3 blockade reduces HCV core-mediated expression of the negative immunoregulators PD-1 and SOCS-1 and increases STAT-1 phosphorylation. Conversely, blocking PD-1 or silencing SOCS-1 gene expression also decreases Tim-3 expression and enhances IL-12 secretion and STAT-1 phosphorylation. These findings suggest that Tim-3 plays a crucial role in negative regulation of innate immune responses, through crosstalk with PD-1 and SOCS-1 and limiting STAT-1 phosphorylation, and may be a novel target for immunotherapy to HCV infection.

Impaired hepatitis B vaccine responses during chronic hepatitis C infection: involvement of the PD-1 pathway in regulating CD4(+) T cell responses

Vaccination for hepatitis B virus (HBV) in the setting of hepatitis C virus (HCV) infection is recommended, but responses to vaccination are blunted when compared to uninfected populations. The mechanism for this failure of immune response in HCV-infected subjects remains unknown but is thought to be a result of lymphocyte dysfunction during chronic viral infection. We have recently demonstrated that PD-1, a novel negative immunomodulator for T cell receptor (TCR) signaling, is involved in T and B lymphocyte dysregulation during chronic HCV infection. In this report, we further investigated the role of the PD-1 pathway in regulation of CD4(+) T cell responses to HBV vaccination in HCV-infected individuals. In a prospective HCV infected cohort, a poor response rate to HBV vaccination as assayed by seroconversion was observed in HCV-infected subjects (53%), while a high response rate was observed in healthy or spontaneously HCV-resolved individuals (94%). CD4(+) T cell responses to ex vivo stimulations of anti-CD3/CD28 antibodies or hepatitis B surface antigen (HBsAg) were found to be lower in HBV vaccine non-responders compared to those responders in HCV-infected individuals who had received a series of HBV immunizations. PD-1 expression on CD4(+) T cells was detected at relatively higher levels in these HBV vaccine non-responders than those who responded, and this was inversely associated with the cell activation status. Importantly, blocking the PD-1 pathway improved T cell activation and proliferation in response to ex vivo HBsAg or anti-CD3/CD28 stimulation in HBV vaccine non-responders. These results suggest that PD-1 signaling may be involved in impairing CD4(+) T cell responses to HBV vaccination in subjects with HCV infection, and raise the possibility that blocking this negative signaling pathway might improve success rates of immunization in the setting of chronic viral infection.

Circulating Tregs correlate with viral load reduction in chronic HBV-treated patients with tenofovir disoproxil fumarate

Limited response to current hepatitis B virus (HBV) drugs is possibly due to inadequate host cytotoxic cellular responses. Circulating Tregs have been shown to be associated with chronicity of HBV infection, but their profile during antiviral therapy has not been studied. We analyzed the frequency and effect of Tregs on cellular immune responses against HBV in 35 chronic hepatitis B eAg-ve and eAg+ve patients treated with tenofovir 300 mg/day. Frequency of Tregs and their modulatory role in cytokine-secreting cells were determined after stimulation with HBsAg or HBcAg in the absence or presence of Tregs and after blockage of PD-1/PDL-1 in peripheral blood mononuclear cells (PBMCs). Prior to therapy, eAg-ve patients had lower HBV DNA levels, reduced CD8 T cells, increased Tregs, and T cells expressing PD1. After 12 weeks of therapy, >2 log HBV viral reduction was observed in both groups, along with an increase frequencies of CD8 T cells in eAg-ve patients and increased expression of chemokine receptors/Toll-like receptors in both groups. PD-1 expression on CD8 cells in PBMCs was decreased in both groups during therapy but not on Tregs. In eAg-ve group, sustained increase of Tregs was observed till week 12, which declined at week 24. In both groups, after 24 weeks, depletion of CD4(+)CD25(+) Tregs from PBMCs enhanced HBV-specific T cell responses, and blockage of PD-1/PDL1 pathway did enhance pro-inflammatory cytokine production in eAg+ve patients but not in eAg-ve. We conclude that Tregs induced by HBV replication in vivo are expanded in eAg-ve patients more. Reduction in HBV DNA by tenofovir partially restored adaptive immune responses and also reduced the Tregs. Blockage of PD-1/PDL1, enhanced cytokine production in eAg+ve patients but not in eAg-ve, suggests that distinctly different immunologic mechanisms are involved in eAg+ve and eAg-ve patients.

Cross-talk between programmed death-1 and suppressor of cytokine signaling-1 in inhibition of IL-12 production by monocytes/macrophages in hepatitis C virus infection

Hepatitis C virus (HCV) dysregulates innate immune responses and induces persistent viral infection. We previously demonstrated that HCV core protein impairs IL-12 expression by monocytes/macrophages (M/M(Φ)s) through interaction with a complement receptor gC1qR. Because HCV core-mediated lymphocyte dysregulation occurs through the negative immunomodulators programmed death-1 (PD-1) and suppressor of cytokine signaling-1 (SOCS-1), the aim of this study was to examine their role in HCV core-mediated IL-12 suppression in M/M(Φ)s. We analyzed TLR-stimulated, primary CD14(+) M/M(Φ)s from chronically HCV-infected and healthy subjects or the THP-1 cell line for PD-1, SOCS-1, and IL-12 expression following HCV core treatment. M/M(Φ)s from HCV-infected subjects at baseline exhibited comparatively increased PD-1 expression that significantly correlated with the degree of IL-12 inhibition. M/M(Φ)s isolated from healthy and HCV-infected individuals and treated with HCV core protein displayed increased PD-1 and SOCS-1 expression and decreased IL-12 expression, an effect that was also observed in cells treated with gC1qR's ligand, C1q. Blocking gC1qR rescued HCV core-induced PD-1 upregulation and IL-12 suppression, whereas blocking PD-1 signaling enhanced IL-12 production and decreased the expression of SOCS-1 induced by HCV core. Conversely, silencing SOCS-1 expression using small interfering RNAs increased IL-12 expression and inhibited PD-1 upregulation. PD-1 and SOCS-1 were found to associate by coimmunoprecipitation studies, and blocking PD-1 or silencing SOCS-1 in M/M(Φ) led to activation of STAT-1 during TLR-stimulated IL-12 production. These data suggested that HCV core/gC1qR engagement on M/M(Φ)s triggers the expression of PD-1 and SOCS-1, which can associate to deliver negative signaling to TLR-mediated pathways controlling expression of IL-12, a key cytokine linking innate and adaptive immunity.