The hepatitis C virus non-structural NS5A protein impairs both the innate and adaptive hepatic immune response in vivo

A short hepatitis C virus NS5A peptide expression by AAV vector modulates human T cell activation and reduces vector immunogenicity

Viral vector-mediated gene therapies have the potential to treat many human diseases; however, host immune responses against the vector and/or the transgene pose a safety risk to the patients and can negatively impact product efficacy. Thus, novel strategies to reduce vector immunogenicity are critical for the advancement of these therapies. T cell activation (TCA) is required for the development of immune responses during gene therapy. We hypothesized that modulation of TCA by incorporating a novel viral immunomodulatory factor into a viral vector may reduce unwanted TCA and immune responses during gene therapy. To test this hypothesis, we identified an immunomodulatory domain of the hepatitis C virus (HCV) NS protein 5A (NS5A) protein and studied the effect of viral vectors expressing NS5A peptide on TCA. Lentiviral vector-mediated expression of a short 20-mer peptide derived from the NS5A protein in human T cells was sufficient to inhibit TCA. Synthetic 20-mer NS5A peptide also inhibited TCA in primary human T cells. Mechanistically, the NS5A protein interacted with Lck and inhibited proximal TCR signaling. Importantly, NS5A peptide expression did not cause global T cell signaling dysfunction as distal T cell signaling was not inhibited. Finally, recombinant adeno-associated virus (AAV) vector expressing the 20-mer NS5A peptide reduced both the recall antigen and the TCR-mediated activation of human T cells and did not cause global T cell signaling dysfunction. Together, these data suggest that expression of a 20-mer NS5A peptide by an AAV vector may reduce unwanted TCA and may contribute to lower vector immunogenicity during gene therapy.

Hepatitis C Virus and Hepatocellular Carcinoma: When the Host Loses Its Grip

Chronic infection with hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma (HCC). Novel treatments with direct-acting antivirals achieve high rates of sustained virologic response; however, the HCC risk remains elevated in cured patients, especially those with advanced liver disease. Long-term HCV infection causes a persistent and accumulating damage of the liver due to a combination of direct and indirect pro-oncogenic mechanisms. This review describes the processes involved in virus-induced disease progression by viral proteins, derailed signaling, immunity, and persistent epigenetic deregulation, which may be instrumental to develop urgently needed prognostic biomarkers and as targets for novel chemopreventive therapies.

Interactions between Viperin, Vesicle-Associated Membrane Protein A, and Hepatitis C Virus Protein NS5A Modulate Viperin Activity and NS5A Degradation

The radical SAM enzyme, viperin, exerts a wide range of antiviral effects through both the synthesis of the antiviral nucleotide 3'-deoxy-3',4'-didehydro-CTP (ddhCTP) and through its interactions with various cellular and viral proteins. Here we investigate the interaction of viperin with hepatitis C virus nonstructural protein 5A (NS5A) and the host sterol regulatory protein, vesicle-associated membrane protein A (VAP-33). NS5A and VAP-33 form part of the viral replication complex that is essential for replicating the RNA genome of the hepatitis C virus. Using transfected enzymes in HEK293T cells, we show that viperin binds independently to both NS5A and the C-terminal domain of VAP-33 (VAP-33C) and that this interaction is dependent on the proteins being colocalized to the ER membrane. Coexpression of VAP-33C and NS5A resulted in changes to the catalytic activity of viperin that depended upon viperin being colocalized to the ER membrane. The viperin-NS5A-VAP-33C complex exhibited the lowest specific activity, indicating that NS5A may inhibit viperin's ability to synthesize ddhCTP. Coexpression of viperin with NS5A was also found to significantly reduce cellular NS5A levels, most likely by increasing the rate of proteasomal degradation. An inactive mutant of viperin, unable to bind the iron-sulfur cluster, was similarly effective at reducing cellular NS5A levels.

Immune-mediated effects targeting hepatitis C virus in a syngeneic replicon cell transplantation mouse model

OBJECTIVE

HCV is characterised by its ability to establish chronic infection in hepatocytes and to replicate in the presence of an inflammation. We mimicked this situation in vivo in immune-competent mice by syngeneic transplantation of HCV replicon-containing mouse hepatoma cells.

DESIGN

A total of 5 million H-2^b positive Hep56.1D cells, carrying a subgenomic genotype (gt) 2a replicon (HCV replicon cells) or stably expressing comparable levels of the HCV NS3/4A protease/helicase complex (NS3/4A hepatoma cells), were injected subcutaneously into syngeneic H-2^b-restricted mice. Kinetics of tumour growth, HCV RNA replication levels and HCV-specific immune responses were monitored. For immune monitoring, new H-2^b-restricted cytotoxic T cell epitopes within the gt2a NS3/4A region were mapped. Immune mice were generated by DNA-based vaccination.

RESULTS

HCV replicon and NS3/4A hepatoma cells generated solid tumours in vivo. Similar to what is seen in human HCV infection did HCV RNA replicate in the presence of inflammation. NS3/4A-specific CD8+ T cells seemed to transiently reduce HCV RNA levels. Both CD4+ and CD8+ T cells were required for protection against tumour growth. Vaccine-induced NS3/4A(gt2a)-specific T cells protected against HCV replicon tumours in wild-type, but not in HCV NS3/4A(gt1a)-transgenic mice with dysfunctional HCV-specific T cells. Importantly, as in human HCV infection, HCV replicon cells neither primed nor boosted a strong NS3/4A-specific T cell response.

CONCLUSION

Syngeneic transplantation of mouse HCV replicon cells into immune-competent animals mirrors many in vivo events in humans. This system is versatile and can be applied to any genetically modified H-2^b-restricted mouse strain.

Nonstructural 5A Protein of Hepatitis C Virus Interferes with Toll-Like Receptor Signaling and Suppresses the Interferon Response in Mouse Liver

The hepatitis C virus nonstructural protein NS5A is involved in resistance to the host immune response, as well as the viral lifecycle such as replication and maturation. Here, we established transgenic mice expressing NS5A protein in the liver and examined innate immune responses against lipopolysaccharide (LPS) in vivo. Intrahepatic gene expression levels of cytokines such as interleukin-6, tumor necrosis factor-α, and interferon-γ were significantly suppressed after LPS injection in the transgenic mouse liver. Induction of the C-C motif chemokine ligand 2, 4, and 5 was also suppressed. Phosphorylation of the signal transducer and activator of transcription 3, which is activated by cytokines, was also reduced, and expression levels of interferon-stimulated genes, 2’-5’ oligoadenylate synthase, interferon-inducible double-stranded RNA-activated protein kinase, and myxovirus resistance 1 were similarly suppressed. Since LPS binds to toll-like receptor 4 and stimulates the downstream pathway leading to induction of these genes, we examined the extracellular signal-regulated kinase and IκB-α. The phosphorylation levels of these molecules were reduced in transgenic mouse liver, indicating that the pathway upstream of the molecules was disrupted by NS5A. Further analyses revealed that the interaction between interleukin-1 receptor-associated kinase-1 and tumor necrosis factor receptor associated factor-6 was dispersed in transgenic mice, suggesting that NS5A may interfere with this interaction via myeloid differentiation primary response gene 88, which was shown to interact with NS5A. Since the gut microbiota, a source of LPS, is known to be associated with pathological conditions in liver diseases, our results suggest the involvement of NS5A in the pathogenesis of HCV infected-liver via the suppression of innate immunity.

Mapping the genomic diversity of HCV subtypes 1a and 1b: Implications of structural and immunological constraints for vaccine and drug development

Despite significant progress in hepatitis C (HCV) treatment, global viral eradication remains a challenge. An in-depth map of its genome diversity within the context of structural and immunological constraints could contribute to the design of pan-genotypic antivirals and preventive vaccines. For such analyses, extensive information is only available for the highly prevalent HCV genotypes (GT) 1a and 1b. Using 647 GT1a and 408 GT1b full-genome sequences obtained from the Los Alamos database, we found that respectively 3 per cent and 82 per cent of all codon positions are under positive and negative selective pressure, suggesting variation mainly accumulates due to random genetic drift. An association between conservation and both structured RNA and secondary protein structures confirmed the important role of structural elements at nucleotide and at amino acid level. Remarkably, CD8⁺ T-cell epitopes in HCV GT1a were significantly more conserved, while at the same time containing more sites under positive selection. Similarly, CD4⁺ T-cell epitopes were significantly more conserved in both HCV subtypes, but under less positive selective pressure in GT1b and more negative selective pressure in GT1a. In contrast, B-cell epitopes in both subtypes were less conserved and under less stringent negative selection. These findings argue against immune selective pressure as the main force of between-host diversifying evolution. Despite its high variability, HCV is under strict evolutionary constraints, most probably to keep its genes and proteins functional during the replication cycle. These are encouraging findings for vaccine and drug design, which could consider these newly established genetic diversity profiles.

Classical swine fever virus NS5A protein changed inflammatory cytokine secretion in porcine alveolar macrophages by inhibiting the NF-κB signaling pathway

Background

Classical swine fever (CSF) caused by CSF virus (CSFV) is a highly contagious disease of the pigs. A number of studies have suggested that CSFV non-structural (NS) 5A protein is involved in CSFV-associated pathogenesis, but its mechanism is still uncertain. The aim of this study was to investigate the roles of NS5A protein in CSFV-associated pathogenesis in cultured porcine alveolar macrophages (PAMs).

Methods

After PAMs cultured in vitro were transfected with CSFV NS5A, the alterations in IL-1β, IL-6 and TNF-α expression were determined by ELISA, the RIG-I signaling activity related to inflammatory cytokine secretion was investigated by Western blot and Immunofluorescent staining.

Results

It was suggested that, the stable expressed CSFV NS5A solely had no influence on the expressions of inflammatory cytokines IL-1β, IL-6 and TNF-α in PAMs Moreover, NS5A protein could suppressed IL-1β, IL-6 and TNF-α expression induced by poly(I:C). It was also showed that NS5A protein did not impair the expressions of RIG-I, MDA5, IPS-1, NF-κB and IkBα in cells without poly(I:C) stimulation. Protein expressions of RIG-I, MDA5, IPS-1, NF-κB were not disrupted by NS5A protein in poly(I:C)-stimulated cells, while poly(I:C)-induced NF-κB nuclear translocation and activity was obviously suppressed by this protein. A suppression in poly(I:C)-induced IkBα degradation in NS5A-expressing cells was also observed.

Conclusion

These data indicated that CSFV NS5A protein could inhibit the secretion of inflammatory cytokine induced by poly(I:C) through the suppression of the NF-κB signaling pathway, indicating the participation of CSFV NS5A protein in the pathogenesis of CSFV.

The Autophagosomal SNARE Protein Syntaxin 17 Is an Essential Factor for the Hepatitis C Virus Life Cycle

Syntaxin 17 is an autophagosomal SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein required for the fusion of autophagosomes with lysosomes to form autolysosomes and thereby to deliver the enclosed contents for degradation. Hepatitis C virus (HCV) induces autophagy. In light of the observation that the number of viral particles formed by HCV-infected cells is much greater than the number of infectious viral particles finally released by HCV-infected cells, the regulation of fusion between autophagosomes and lysosomes might fulfill a key function controlling the number of released virions. HCV-replicating cells possess a decreased amount of syntaxin 17 due to impaired expression and increased turnover of syntaxin 17. Overexpression of syntaxin 17 in HCV-replicating cells diminishes the number of released infectious viral particles and decreases the amount of intracellular retained viral particles by favoring the formation of autolysosomes, in which HCV particles are degraded. Inhibition of lysosomal acidification by bafilomycin rescues the decreased release of virions from syntaxin 17-overexpressing cells, while induction of autophagy by rapamycin enforces the impairment of release under these conditions. Vice versa, inhibition of syntaxin 17 expression by specific small interfering RNAs results in an elevated amount of intracellular retained viral particles and facilitates the release of HCV virions by impairment of autophagosome-lysosome fusion. HCV genome replication, however, is not affected by modulation of syntaxin 17 expression. These data identify syntaxin 17 to be a novel factor controlling the release of HCV. This is achieved by regulation of autophagosome-lysosome fusion, which affects the equilibrium between the release of infectious viral particles and lysosomal degradation of intracellular retained viral particles.

IMPORTANCE

Hepatitis C virus (HCV) induces autophagy. Syntaxin 17 is an autophagosomal SNARE protein required for the fusion of autophagosomes with lysosomes. In HCV-infected cells, a major fraction of the de novo-synthesized viral particles is not released but is intracellularly degraded. In this context, the effect of HCV on the amount and distribution of syntaxin 17 and the relevance of syntaxin 17 for the viral life cycle were investigated. This study demonstrates that the amount of syntaxin 17 decreased in HCV-replicating cells. In addition, syntaxin 17 is identified to be a novel factor controlling the release of HCV, and the relevance of autophagosome-lysosome fusion as a regulator of the amount of released viral particles is revealed. Taken together, these findings indicate that syntaxin 17 is involved in the regulation of autophagosome-lysosome fusion and thereby affects the equilibrium between the release of infectious viral particles and the lysosomal degradation of intracellularly retained viral particles.

Functional differences in hepatitis C virus nonstructural (NS) 3/4A- and 5A-specific T cell responses

The hepatitis C virus nonstructural (NS) 3/4A and NS5A proteins are major targets for the new direct-acting antiviral compounds. Both viral proteins have been suggested as modulators of the response to the host cell. We have shown that NS3/4A- and NS5A-specific T cell receptors confer different effector functions, and that killing of NS3/4A-expressing hepatocytes is highly dependent on IFN-γ. We here characterize the functional differences in the T cell responses to NS3/4A and NS5A. NS3/4A- and NS5A-specific T cells could be induced at various frequencies in wild-type-, NS3/4A-, and NS5A-transgenic mice. Priming of NS5A-specific T cells required a high DNA dose, and was unlike NS3/4A dependent on both CD4⁺ and CD8⁺ T cells, but less influenced by CD25⁺/GITR⁺ regulatory T cells. The presence of IL-12 greatly improved specific CD8⁺ T cell priming by NS3/4A but not by NS5A, suggesting a less dependence of IFN-γ for NS5A. This notion was supported by the observation that NS5A-specific T cells could eliminate NS5A-expressing hepatocytes also in the absence of IFN-γ-receptor-2. This supports that NS3/4A- and NS5A-specific T cells become activated and eliminate antigen expressing, or infected hepatocytes, by distinct mechanisms, and that NS5A-specific T cells show an overall less dependence of IFN-γ.

Characterization of α-taxilin as a novel factor controlling the release of hepatitis C virus

Although it is well established that the release of HCV (hepatitis C virus) occurs through the secretory pathway, many aspects concerning the control of this process are not yet fully understood. α-Taxilin was identified as a novel binding partner of syntaxin-4 and of other members of the syntaxin family, which are part of SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) complexes and so are involved in intracellular vesicle traffic. Since α-taxilin prevents t-SNARE (target SNARE) formation by binding exclusively to free syntaxin-4, it exerts an inhibitory effect on the vesicular transport. HCV-replicating Huh7.5 cells and HCV-infected primary human hepatocytes and liver samples of patients suffering from chronic HCV contain significantly less α-taxilin compared with the controls. HCV impairs the expression of α-taxilin via NS5A-dependent interruption of the Raf/MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase] signal transduction cascade. Moreover, the half-life of α-taxilin is significantly reduced in HCV-replicating cells. Whereas modulation of α-taxilin expression does not significantly affect genome replication, the overexpression of α-taxilin prevents the release of HCV. In contrast with this, silencing of α-taxilin expression leads to increased release of infectious viral particles. This is due to the negative effect of α-taxilin on t-SNARE formation that leads to impaired vesicular trafficking. Accordingly, overexpression of the t-SNARE component syntaxin-4 increases release of HCV, whereas silencing leads to an impaired release. These data identify α-taxilin as a novel factor that controls the release of HCV and reveal the mechanism by which HCV controls the activity of α-taxilin.

Resistance-Associated NS5A Variants of Hepatitis C Virus Are Susceptible to Interferon-Based Therapy

BACKGROUND & AIMS

The presence of resistance-associated variants (RAVs) of hepatitis C virus (HCV) attenuates the efficacy of direct acting antivirals (DAAs). The objective of this study was to characterize the susceptibility of RAVs to interferon-based therapy.

METHODS

Direct and deep sequencing were performed to detect Y93H RAV in the NS5A region. Twenty nine genotype 1b patients with detectable RAV at baseline were treated by a combination of simeprevir, pegylated interferon and ribavirin. The longitudinal changes in the proportion of Y93H RAV during therapy and at breakthrough or relapse were determined.

RESULTS

By direct sequencing, Y93H RAV became undetectable or decreased in proportion at an early time point during therapy (within 7 days) in 57% of patients with both the Y93H variant and wild type virus at baseline when HCV RNA was still detectable. By deep sequencing, the proportion of Y93H RAV against Y93 wild type was 52.7% (5.8%- 97.4%) at baseline which significantly decreased to 29.7% (0.16%- 98.3%) within 7 days of initiation of treatment (p = 0.023). The proportion of Y93H RAV was reduced in 21 of 29 cases (72.4%) and a marked reduction of more than 10% was observed in 14 cases (48.7%). HCV RNA reduction was significantly greater for Y93H RAV (-3.65±1.3 logIU/mL/day) than the Y93 wild type (-3.35±1.0 logIU/mL/day) (p<0.001).

CONCLUSION

Y93H RAV is more susceptible to interferon-based therapy than the Y93 wild type.

Therapeutic DNA vaccination using in vivo electroporation followed by standard of care therapy in patients with genotype 1 chronic hepatitis C

Clearance of infections caused by the hepatitis C virus (HCV) correlates with HCV-specific T cell function. We therefore evaluated therapeutic vaccination in 12 patients with chronic HCV infection. Eight patients also underwent a subsequent standard-of-care (SOC) therapy with pegylated interferon (IFN) and ribavirin. The phase I/IIa clinical trial was performed in treatment naive HCV genotype 1 patients, receiving four monthly vaccinations in the deltoid muscles with 167, 500, or 1,500 μg codon-optimized HCV nonstructural (NS) 3/4A-expressing DNA vaccine delivered by in vivo electroporation (EP). Enrollment was done with 2 weeks interval between patients for safety reasons. Treatment was safe and well tolerated. The vaccinations significantly improved IFN-γ-producing responses to HCV NS3 during the first 6 weeks of therapy. Five patients experienced 2-10 weeks 0.6-2.4 log10 reduction in serum HCV RNA. Six out of eight patients starting SOC therapy within 1-30 months after the last vaccine dose were cured. This first-in-man therapeutic HCV DNA vaccine study with the vaccine delivered by in vivo EP shows transient effects in patients with chronic HCV genotype 1 infection. The interesting result noted after SOC therapy suggests that therapeutic vaccination can be explored in a combination with SOC treatment.

Animal models for hepatitis C

Hepatitis C remains a global epidemic. Approximately 3 % of the world's population suffers from chronic hepatitis C, which is caused by hepatitis C virus (HCV)-a positive sense, single-stranded RNA virus of the Flaviviridae family. HCV has a high propensity for establishing a chronic infection. If untreated chronic HCV carriers can develop severe liver disease including fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Antiviral treatment is only partially effective, costly, and poorly tolerated. A prophylactic or therapeutic vaccine for HCV does not exist. Mechanistic studies of virus-host interactions, HCV immunity, and pathogenesis as well as the development of more effective therapies have been hampered by the lack of a suitable small animal model. Besides humans, chimpanzees are the only species that is naturally susceptible to HCV infection. While experimentation in these large primates has yielded valuable insights, ethical considerations, limited availability, genetic heterogeneity, and cost limit their utility. In search for more tractable small animal models, numerous experimental approaches have been taken to recapitulate parts of the viral life cycle and/or aspects of viral pathogenesis that will be discussed in this review. Exciting new models and improvements in established models hold promise to further elucidate our understanding of chronic HCV infection.

Methods for monitoring gene gun-induced HBV- and HCV-specific immune responses in mouse models

The hepatitis B and C viruses (HBV/HCV) are major causes for chronic liver disease globally. For HBV new antiviral compounds can suppress the viral replication for years, but off-therapy responses are rare. Current therapies based on interferon and ribavirin can cure 45-85% of the treated HCV-infected patients largely depending on the viral genotype. New regimens including protease inhibitors will be introduced during 2011 and these will increase the cure rates for the hardest to treat HCV genotype 1 from 45 to 65%. Here a major need is to replace the immunomodulatory effects of interferon and/or ribavirin. Thus, therapeutic vaccines have a place in both chronic HBV and HCV infection. Unfortunately, none of these viruses can infect mice whereby substitute models are needed. We have used several types of murine models to predict the clinical efficacy of therapeutic vaccines for chronic HBV and HCV infections. In this chapter we describe transdermal delivery of genetic vaccines using the Helios Gene Gun device. A central role is that the model should have generally functional immune response, but with selective defects towards HBV and/or HCV. Thus, mice with stable integrated transgenes are useful. However, as a simple model to study the hepatic entry and functionality of a HBV- and/or HCV-specific immune responses other models are needed, where a killed transgenic hepatocyte is replaced by a healthy non-transgenic hepatocyte. Here we can effectively apply a technique termed hydrodynamic injection, which makes 10-30% of hepatocytes transiently transgenic for any plasmid. Within this chapter the methods used to characterize transiently transgenic mice are described. The main methods are the hydrodynamic injection technique, detection of transgene expression by immuno-precipitation, western blot, and immunohistochemistry. Finally, the in vivo functionality of T cells can be determined by using stably transfected syngeneic tumor cell lines expressing HBV and/or HCV proteins. The tumor challenge model enables studies of in vivo T cell function, whereas the cytotoxicity assay is used to determine T cell function in vitro. Overall, these models effectively reveal the efficiency by which various vaccine technologies, including biolistic DNA vaccination can kill the "infected" hepatocyte.

A synthetic codon-optimized hepatitis C virus nonstructural 5A DNA vaccine primes polyfunctional CD8+ T cell responses in wild-type and NS5A-transgenic mice

The hepatitis C virus (HCV) nonstructural (NS) 5A protein has been shown to promote viral persistence by interfering with both innate and adaptive immunity. At the same time, the HCV NS5A protein has been suggested as a target for antiviral therapy. In this study, we performed a detailed characterization of HCV NS5A immunogenicity in wild-type (wt) and immune tolerant HCV NS5A-transgenic (Tg) C57BL/6J mice. We evaluated how efficiently HCV NS5A-based genetic vaccines could activate strong T cell responses. Truncated and full-length wt and synthetic codon-optimized NS5A genotype 1b genes were cloned into eukaryotic expression plasmids, and the immunogenicity was determined after i.m. immunization in combination with in vivo electroporation. The NS5A-based genetic vaccines primed high Ab levels, with IgG titers of >10(4) postimmunization. With respect to CD8(+) T cell responses, the coNS5A gene primed more potent IFN-γ-producing and lytic cytotoxic T cells in wt mice compared with NS5A-Tg mice. In addition, high frequencies of NS5A-specific CD8(+) T cells were found in wt mice after a single immunization. To test the functionality of the CTL responses, the ability to inhibit growth of NS5A-expressing tumor cells in vivo was analyzed after immunization. A single dose of coNS5A primed tumor-inhibiting responses in both wt and NS5A-Tg mice. Finally, immunization with the coNS5A gene primed polyfunctional NS5A-specific CD8(+) T cell responses. Thus, the coNS5A gene is a promising therapeutic vaccine candidate for chronic HCV infections.

HCV NS5A and IRF9 compete for CypA binding

BACKGROUND & AIMS

Cyclophilin A (CypA) is vital for HCV replication. Cyp inhibitors successfully decrease viral loads in HCV-infected patients. However, their mechanisms of action remain unknown. Since interferon (IFN) can also suppress HCV replication, we asked whether a link between CypA and the IFN response exists.

METHODS

We used cellular and recombinant pulldown approaches to investigate the possibility of a specific association of CypA with host ligands.

RESULTS

We found for the first time that CypA binds to a major component of the IFN response - the IFN regulatory factor 9 (IRF9). IRF9 is the DNA-binding component of the transcriptional IFN-stimulated gene factor 3 (ISGF3). CypA binds directly to IRF9 via its peptidyl-prolyl isomerase (PPIase) pocket. Cyp inhibitors such as cyclosporine A (CsA) or non-immunosuppressive derivates such as alisporivir and SCY-635, prevent IRF9-CypA complex formation. CypA binds to the C-terminal IRF-association-domain (IAD), but not to the DNA-binding or linker domains of IRF9. Remarkably, CypA associates with the multimeric ISGF3 complex. We also obtained evidence that CypA neutralization enhances IFN-induced transcription. Interestingly, the hepatitis C virus (HCV) non-structural 5A (NS5A) protein, which is known to modulate the IFN response, competes with IRF9 for CypA binding and can prevent the formation of IRF9-CypA complexes.

CONCLUSIONS

This study demonstrates for the first time that CypA binds specifically to a component of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, IRF9. This study also reveals a novel opportunity of HCV to modulate the IFN response via NS5A.

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.

Early transcriptional programming links progression to hepatitis C virus-induced severe liver disease in transplant patients

Liver failure resulting from chronic hepatitis C virus (HCV) infection is a major cause for liver transplantation worldwide. Recurrent infection of the graft is universal in HCV patients after transplant and results in a rapid progression to severe fibrosis and end-stage liver disease in one third of all patients. No single clinical variable, or combination thereof, has, so far, proven accurate in identifying patients at risk of hepatic decompensation in the transplant setting. A combination of longitudinal, dimensionality reduction and categorical analysis of the transcriptome from 111 liver biopsy specimens taken from 57 HCV-infected patients over time identified a molecular signature of gene expression of patients at risk of developing severe fibrosis. Significantly, alterations in gene expression occur before histologic evidence of liver disease progression, suggesting that events that occur during the acute phase of infection influence patient outcome. Additionally, a common precursor state for different severe clinical outcomes was identified.

CONCLUSION

Based on this patient cohort, incidence of severe liver disease is a process initiated early during HCV infection of the donor organ. The probable cellular network at the basis of the initial transition to severe liver disease was identified and characterized.

A cell-permeable hairpin peptide inhibits hepatitis C viral nonstructural protein 5A-mediated translation and virus production

NS5A is a key regulator of the hepatitis C virus (HCV) life cycle including RNA replication, assembly, and translation. We and others have shown that NS5A augments HCV internal ribosomal entry site (IRES)-mediated translation. Furthermore, Quercetin treatment and heat shock protein (HSP) 70 knockdown inhibit the NS5A-driven augmentation of IRES-mediated translation and infectious virus production. We have also coimmunoprecipitated HSP70 with NS5A and demonstrated cellular colocalization, leading to the hypothesis that the NS5A/HSP70 complex formation is important for IRES-mediated translation. Here, we have identified the NS5A region responsible for complex formation through in vitro deletion analyses. Deletion of NS5A domains II and III failed to reduce HSP70 binding, whereas domain I deletion eliminated complex formation. NS5A domain I alone also bound HSP70. Deletion mapping of domain I identified the C-terminal 34 amino acids (C34) as the interaction site. Furthermore, addition of C34 to domains II and III restored complex formation. C34 expression significantly reduced intracellular viral protein levels, in contrast to same-size control peptides from other NS5A domains. C34 also competitively inhibited NS5A-augmented IRES-mediated translation, whereas controls did not. Triple-alanine scan mutagenesis determined that an exposed beta-sheet hairpin in C34 was primarily responsible for NS5A-augmented IRES-mediated translation. Moreover, treatment with a 10-amino acid peptide derivative of C34 suppressed NS5A-augmented IRES-mediated translation and significantly inhibited intracellular viral protein synthesis, with no associated cytotoxicity.

CONCLUSION

These results support the hypothesis that the NS5A/HSP70 complex augments viral IRES-mediated translation, identify a sequence-specific hairpin element in NS5A responsible for complex formation, and demonstrate the functional significance of C34 hairpin-mediated NS5A/HSP70 interaction. Identification of this element may allow for further interrogation of NS5A-mediated IRES activity, sequence-specific HSP recognition, and rational drug design. (HEPATOLOGY 2012;55:1662-1672).

Regulatory T cells and Th17 cells in viral infections: implications for multiple sclerosis and myocarditis

In immune-mediated diseases, Treg and proinflammatory Th17 cells have been suggested to play either suppressor (beneficial) or effector (detrimental) roles, respectively. Tissue damage in viral infections can be caused by direct viral replication or immunopathology. Viral replication can be enhanced by anti-inflammatory responses and suppressed by proinflammatory responses. However, Tregs could suppress proinflammatory responses, reducing immunopathology, while Th17 cell-induced inflammation may enhance immunopathology. Here, the roles of Treg and Th17 cells depend on whether tissue damage is caused by direct virus replication or immunopathology, which differ depending on the virus, disease stage and host immune background. Although the precise mechanisms of tissue damage in multiple sclerosis and myocarditis are unclear, both viral replication and immune effector cells have been proposed to cause pathogenesis. Personalized medicine that alters the balance between Treg and Th17 cells may ameliorate viral pathology during infections.

Viral interference with innate immunity by preventing NF-κB activity

Viruses are the most abundant and diverse pathogens challenging the host immune system, and as such are a severe threat to human health. To this end, viruses have evolved multiple strategies to evade and subvert the host immune response. Host-pathogen interactions are usually initiated via recognition of pathogen-associated molecular patterns (PAMPs) by host sensors known as pattern recognition receptors (PRRs), which include, Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), NOD-like receptors (NLRs) and DNA receptors. Effective sensing of PAMPs rapidly triggers host immune responses, via activation of complex signalling pathways that culminates in the induction of inflammatory responses and the eradication of pathogens. Activation of the nuclear factor-κB (NF-κB) transcription pathway is crucial for the immediate early step of immune activation. This review discusses the recent evidence describing a variety of viral effectors that have been shown to prevent NF-κB signalling. Most of these viral effectors can be broadly classified into three categories based on the site of inhibition within the NF-κB pathway, that is, at the (i) TLRs, (ii) IKK complex or (iii) the transcriptional level.

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.

Prospects for prophylactic and therapeutic vaccines against the hepatitis C viruses

Encouraging efficacy data have been obtained in the hepatitis C virus (HCV) chimpanzee model using prophylactic vaccines comprising adjuvanted recombinant envelope gpE1/gpE2 glycoproteins or prime/boost immunization regimens using defective adenoviruses and plasmid DNA expressing non-structural genes. While usually not resulting in sterilizing immunity after experimental challenge, the progression to chronic, persistent infection (which is responsible for HCV-associated pathogenicity in human) is inhibited. These and other vaccine candidates are in clinical development for both prophylactic as well as possible therapeutic applications. Given that other vaccines tested in the chimpanzee model may be possibly increasing the rate of chronicity, it is very important that this model continues to be available and used prior to initiation of clinical development. Several vaccine monotherapy trials in chronically infected HCV patients are resulting in small declines in viral load, suggesting that in future, combining vaccination with antiviral drug treatment may be beneficial.

New advances in the development of experimental models of hepatitis C virus infection

Hepatitis C virus (HCV) infection is another common cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma after hepatitis B virus. It is very difficult to study the variety and replication of HCV and interplay between HCV and the host and to develop new antiviral drugs and vaccines against HCV infection because of lack of susceptible hosts and stable and convenient experimental models of HCV infection. In this paper, we review recent advances in the development of experimental models of HCV infection.

Dendritic cells in hepatitis C infection: can they (help) win the battle?

Infection with hepatitis C virus (HCV) is a public health problem; it establishes a chronic course in ~85% of infected patients and increases their risk for developing liver cirrhosis, hepatocellular carcinoma, and significant extrahepatic manifestations. The mechanisms of HCV persistence remain elusive and are largely related to inefficient clearance of the virus by the host immune system. Dendritic cells (DCs) are the most efficient inducers of immune responses; they are capable of triggering productive immunity and maintaining the state of tolerance to self- and non-self antigens. During the past decade, multiple research groups have focused on DCs, in hopes of unraveling an HCV-specific DC signature or DC-dependent mechanisms of antiviral immunity which would lead to a successful HCV elimination strategy. This review incorporates the latest update in the current status of knowledge on the role of DCs in anti-HCV immunity as it relates to several challenging questions: (a) the phenotype and function of diverse DC subsets in HCV-infected patients; (b) the characteristics of non-human HCV infection models from the DCs' point of view; (c) how can in vitro systems, ranging from HCV protein- or peptide-exposed DC to HCV protein-expressing DCs, and in vivo systems, ranging from HCV protein-expressing transgenic mice to HCV-infected non-human primates, be employed to dissect the role of DCs in triggering/maintaining a robust antiviral response; and (d) the prospect of DC-based strategy for managing and finding a cure for HCV infection.

Induction and evasion of innate antiviral responses by hepatitis C virus

Persistent hepatitis C virus infection is associated with progressive hepatic fibrosis and liver cancer. Acute infection evokes several distinct innate immune responses, but these are partially or completely countered by the virus. Hepatitis C virus proteins serve dual functions in replication and immune evasion, acting to disrupt cellular signaling pathways leading to interferon synthesis, subvert Jak-STAT signaling to limit expression of interferon-stimulated genes, and block antiviral activities of interferon-stimulated genes. The net effect is a multilayered evasion of innate immunity, which negatively influences the subsequent development of antigen-specific adaptive immunity, thereby contributing to virus persistence and resistance to therapy.

In hepatic fibrosis, liver sinusoidal endothelial cells acquire enhanced immunogenicity

The normal liver is characterized by immunologic tolerance. Primary mediators of hepatic immune tolerance are liver sinusoidal endothelial cells (LSECs). LSECs block adaptive immunogenic responses to Ag and induce the generation of T regulatory cells. Hepatic fibrosis is characterized by both intense intrahepatic inflammation and altered hepatic immunity. We postulated that, in liver fibrosis, a reversal of LSEC function from tolerogenic to proinflammatory and immunogenic may contribute to both the heightened inflammatory milieu and altered intrahepatic immunity. We found that, after fibrotic liver injury from hepatotoxins, LSECs become highly proinflammatory and secrete an array of cytokines and chemokines. In addition, LSECs gain enhanced capacity to capture Ag and induce T cell proliferation. Similarly, unlike LSECs in normal livers, in fibrosis, LSECs do not veto dendritic cell priming of T cells. Furthermore, whereas in normal livers, LSECs are active in the generation of T regulatory cells, in hepatic fibrosis LSECs induce an immunogenic T cell phenotype capable of enhancing endogenous CTLs and generating potent de novo CTL responses. Moreover, depletion of LSECs from fibrotic liver cultures mitigates the proinflammatory milieu characteristic of hepatic fibrosis. Our findings offer a critical understanding of the role of LSECs in modulating intrahepatic immunity and inflammation in fibro-inflammatory liver disease.

Hepatitis C virus NS5A activates the mammalian target of rapamycin (mTOR) pathway, contributing to cell survival by disrupting the interaction between FK506-binding protein 38 (FKBP38) and mTOR

Hepatitis C virus (HCV) often establishes a persistent infection that most likely involves a complex host-virus interplay. We previously reported that the HCV nonstructural protein 5A (NS5A) bound to cellular protein FKBP38 and resulted in apoptosis suppression in human hepatoma cell line Huh7. In the present research we further found that NS5A increased phosphorylation levels of two mTOR-targeted substrates, S6K1 and 4EBP1, in Huh7 in the absence of serum. mTOR inhibitor rapamycin or NS5A knockdown blocked S6K1 and 4EBP1 phosphorylation increase in NS5A-Huh7 and HCV replicon cells, suggesting that NS5A specifically regulated mTOR activation. Overexpression of NS5A and FKBP38 mutants or FKBP38 knockdown revealed this mTOR activation was dependent on NS5A-FKBP38 interaction. Phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 treatment in NS5A-Huh7 showed that the mTOR activation was independent of PI3K. Moreover, NS5A suppressed caspase 3 and poly(ADP-ribose) polymerase activation, which was abolished by NS5A knockdown or rapamycin, indicating NS5A inhibited apoptosis specifically through the mTOR pathway. Further analyses suggested that apoptotic inhibition exerted by NS5A via mTOR also required NS5A-FKBP38 interaction. Glutathione S-transferase pulldown and co-immunoprecipitation showed that NS5A disrupted the mTOR-FKBP38 association. Additionally, NS5A or FKBP38 mutants recovered the mTOR-FKBP38 interaction; this indicated that the impairment of mTOR-FKBP38 association was dependent on NS5A-FKBP38 binding. Collectively, our data demonstrate that HCV NS5A activates the mTOR pathway to inhibit apoptosis through impairing the interaction between mTOR and FKBP38, which may represent a pivotal mechanism for HCV persistence and pathogenesis.

Immune response of cytotoxic T lymphocytes and possibility of vaccine development for hepatitis C virus infection

Immune responses of cytotoxic T lymphocytes (CTLs) are implicated in viral eradication and the pathogenesis of hepatitis C. Weak CTL response against hepatitis C virus (HCV) may lead to a persistent infection. HCV infection impairs the function of HCV-specific CTLs; HCV proteins are thought to actively suppress host immune responses, including CTLs. Induction of a strong HCV-specific CTL response in HCV-infected patients can facilitate complete HCV clearance. Thus, the development of a vaccine that can induce potent CTL response against HCV is strongly expected. We investigated HCV-specific CTL responses by enzyme-linked immuno-spot assay and/or synthetic peptides and identified over 40 novel CTL epitopes in the HCV protein. Our findings may contribute to the development of the HCV vaccine. In this paper, we describe the CTL responses in HCV infection and the attempts at vaccine development based on recent scientific articles.