The hepatitis C virus and immune evasion: non-structural 3/4A transgenic mice are resistant to lethal tumour necrosis factor alpha mediated liver disease

From viruses to cancer: exploring the role of the hepatitis C virus NS3 protein in carcinogenesis

Hepatitis C virus (HCV) chronically infects approximately 170 million people worldwide and is a known etiological agent of hepatocellular carcinoma (HCC). The molecular mechanisms of HCV-mediated carcinogenesis are not fully understood. This review article focuses on the oncogenic potential of NS3, a viral protein with transformative effects on cells, although the precise mechanisms remain elusive. Unlike the more extensively studied Core and NS5A proteins, NS3's roles in cancer development are less defined but critical. Research indicates that NS3 is implicated in several carcinogenic processes such as proliferative signaling, cell death resistance, genomic instability and mutations, invasion and metastasis, tumor-related inflammation, immune evasion, and replicative immortality. Understanding the direct impact of viral proteins such as NS3 on cellular transformation is crucial for elucidating HCV's role in HCC development. Overall, this review sheds light on the molecular mechanisms used by NS3 to contribute to hepatocarcinogenesis, and highlights its significance in the context of HCV-associated HCC, underscoring the need for further investigation into its specific molecular and cellular actions.

Preclinical animal models to evaluate therapeutic antiviral antibodies

Despite the availability of effective preventative vaccines and potent small-molecule antiviral drugs, effective non-toxic prophylactic and therapeutic measures are still lacking for many viruses. The use of monoclonal and polyclonal antibodies in an antiviral context could fill this gap and provide effective virus-specific medical interventions. In order to develop these therapeutic antibodies, preclinical animal models are of utmost importance. Due to the variability in viral pathogenesis, immunity and overall characteristics, the most representative animal model for human viral infection differs between virus species. Therefore, throughout the years researchers sought to find the ideal preclinical animal model for each virus. The most used animal models in preclinical research include rodents (mice, ferrets, …) and non-human primates (macaques, chimpanzee, ….). Currently, antibodies are tested for antiviral efficacy against a variety of viruses including different hepatitis viruses, human immunodeficiency virus (HIV), influenza viruses, respiratory syncytial virus (RSV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and rabies virus. This review provides an overview of the current knowledge about the preclinical animal models that are used for the evaluation of therapeutic antibodies for the abovementioned viruses.

Integrated analysis to study the interplay between post-translational modifications (PTM) in hepatitis C virus proteins and hepatocellular carcinoma (HCC) development

Many PTMs dysregulation is known to be the major cause of many cancers including HCV induced HCC. PTMs of hepatitis C virus (HCV) regions NS3/4A, NS5A and NS5B are crucial for proper protein functions and replication that directly affect the generation of infectious virus particles and completion of its life cycle. In this study, we have performed comprehensive analysis of PTMs within HCV non-structural proteins (NS3/4A, NS5A and NS5B) through bioinformatics analysis to examine post-translational crosstalk between phosphorylation, palmitoylation, methylation, acetylation and ubiquitination sites in selected viral proteins. Our analysis has revealed many highly putative PTMs sites that are also conserved among major genotypes conferring the importance of these sites. We have also analysed viral 3D structures in their modified and unmodified forms to address extent and signatures of structural changes upon PTM. This study provides evidence that PTMs induce significant conformational changes and make viral proteins more stable. To find the potential role of PTMs in HCV induced HCC, docking analysis between selected viral proteins and p38-MAPK has been performed which also confirms their strong association with HCV induced HCC. The major findings proposed that PTMs at specific sites of HCV viral proteins could dysregulate specific pathways that cause the development of HCC.

The Oncogenic Role of Hepatitis C Virus

Persistent infection with hepatitis C virus (HCV) is a major risk factor for hepatocellular carcinoma (HCC). Accumulating evidence suggests that not only inflammation and subsequent fibrosis but also HCV itself are associated with hepatocarcinogenesis. To date, studies using transgenic mouse and cell-culture models, in which HCV proteins are expressed, indicate the direct pathogenicity of HCV, including oncogenic activity. In particular, the core protein of HCV induces excessive oxidative stress by impairing the mitochondrial electron transfer system by disrupting the function of the molecular chaperone, prohibitin. HCV also modulates intracellular signaling pathways, including mitogen-activated protein kinase, promoting the proliferation of hepatocytes. In addition, HCV induces disorders in lipid and glucose metabolism, thereby accelerating the progression of liver fibrosis and the development of HCC. Due to the development of direct-acting antivirals, which was made possible by basic research, HCV can be eradicated from almost all infected patients. However, such patients can develop HCC long after eradication of HCV, suggesting the genetic and/or epigenetic changes induced by HCV may be persistent. These results enhance our understanding of the role of HCV in hepatocarcinogenesis and will facilitate the development of therapeutic and preventive strategies for HCV-induced HCC.

Advances in Transgenic Mouse Models to Study Infections by Human Pathogenic Viruses

Medical research is changing into direction of precision therapy, thus, sophisticated preclinical models are urgently needed. In human pathogenic virus research, the major technical hurdle is not only to translate discoveries from animals to treatments of humans, but also to overcome the problem of interspecies differences with regard to productive infections and comparable disease development. Transgenic mice provide a basis for research of disease pathogenesis after infection with human-specific viruses. Today, humanized mice can be found at the very heart of this forefront of medical research allowing for recapitulation of disease pathogenesis and drug mechanisms in humans. This review discusses progress in the development and use of transgenic mice for the study of virus-induced human diseases towards identification of new drug innovations to treat and control human pathogenic infectious diseases.

HCV modifies EGF signalling and upregulates production of CXCR2 ligands: Role in inflammation and antiviral immune response

BACKGROUND & AIMS

To affect immune response and inflammation, the hepatitis C virus (HCV) substantially influences intercellular communication pathways that are decisive for immune cell recruitment. The present study investigates mechanisms by which HCV modulates chemokine-mediated intercellular communication from infected cells.

METHODS

Chemokine expression was studied in HCV_cc-infected cell lines or cell lines harbouring a subgenomic replicon, as well as in serum samples from patients. Expression or activity of mediators and signalling intermediates was manipulated using knockdown approaches or specific inhibitors.

RESULTS

HCV enhances expression of CXCR2 ligands in its host cell via the induction of epidermal growth factor (EGF) production. Knockdown of EGF or of the p65 subunit of the NF-κB complex results in a substantial downregulation of HCV-induced CXCR2 ligand expression, supporting the involvement of an EGF-dependent mechanism as well as activation of NF-κB. Furthermore, HCV upregulates expression of CXCR2 ligands in response to EGF stimulation via downregulation of the T-cell protein tyrosine phosphatase (TC-PTP [PTPN2]), activation of NF-κB, and enhancement of EGF-inducible signal transduction via MEK1 (MAP2K1). This results in the production of a cytokine/chemokine pattern by the HCV-infected cell that can recruit neutrophils but not monocytes.

CONCLUSIONS

These data reveal a novel EGF-dependent mechanism by which HCV influences chemokine-mediated intercellular communication. We propose that this mechanism contributes to modulation of the HCV-induced inflammation and the antiviral immune response.

LAY SUMMARY

In most cases hepatitis C virus (HCV) results in chronic infection and persistent viral replication, taking decades until development of overt disease. To achieve such a course, the respective virus must have developed mechanisms to circumvent antiviral response, to modulate the inflammatory response and to utilise the infrastructure of its host with moderate effect on its viability. The present study provides novel data indicating that HCV induces epidermal growth factor production in its host cell, enhancing epidermal growth factor-inducible expression of chemokines that bind to the CXCR2 receptor and recruit neutrophile granulocytes. Importantly, chemokines are critical mediators determining the pattern of immune cells recruited to the site of injury and thereby the local inflammatory and immunological milieu. These data strongly suggest that HCV triggers mechanisms that enable the virus to influence the inflammatory and immunological processes of its host.

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.

Animal Models to Study Hepatitis C Virus Infection

With more than 71 million chronically infected people, the hepatitis C virus (HCV) is a major global health concern. Although new direct acting antivirals have significantly improved the rate of HCV cure, high therapy cost, potential emergence of drug-resistant viral variants, and unavailability of a protective vaccine represent challenges for complete HCV eradication. Relevant animal models are required, and additional development remains necessary, to effectively study HCV biology, virus–host interactions and for the evaluation of new antiviral approaches and prophylactic vaccines. The chimpanzee, the only non-human primate susceptible to experimental HCV infection, has been used extensively to study HCV infection, particularly to analyze the innate and adaptive immune response upon infection. However, financial, practical, and especially ethical constraints have urged the exploration of alternative small animal models. These include different types of transgenic mice, immunodeficient mice of which the liver is engrafted with human hepatocytes (humanized mice) and, more recently, immunocompetent rodents that are susceptible to infection with viruses that are closely related to HCV. In this review, we provide an overview of the currently available animal models that have proven valuable for the study of HCV, and discuss their main benefits and weaknesses.

Mouse Systems to Model Hepatitis C Virus Treatment and Associated Resistance

While addition of the first-approved protease inhibitors (PIs), telaprevir and boceprevir, to pegylated interferon (PEG-IFN) and ribavirin (RBV) combination therapy significantly increased sustained virologic response (SVR) rates, PI-based triple therapy for the treatment of chronic hepatitis C virus (HCV) infection was prone to the emergence of resistant viral variants. Meanwhile, multiple direct acting antiviral agents (DAAs) targeting either the HCV NS3/4A protease, NS5A or NS5B polymerase have been approved and these have varying potencies and distinct propensities to provoke resistance. The pre-clinical in vivo assessment of drug efficacy and resistant variant emergence underwent a great evolution over the last decade. This field had long been hampered by the lack of suitable small animal models that robustly support the entire HCV life cycle. In particular, chimeric mice with humanized livers (humanized mice) and chimpanzees have been instrumental for studying HCV inhibitors and the evolution of drug resistance. In this review, we present the different in vivo HCV infection models and discuss their applicability to assess HCV therapy response and emergence of resistant variants.

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.

A non-human hepadnaviral adjuvant for hepatitis C virus-based genetic vaccines

Human hepatitis B virus (HBV) core antigen (HBcAg) can act as an adjuvant in hepatitis C virus (HCV)-based DNA vaccines. Since two billion people are, or have been, in contact with HBV, one may question the use of human HBV sequences as adjuvant. We herein evaluated non-human stork hepatitis B virus core gene-sequences from stork as DNA vaccine adjuvants. Full-length and fragmented stork HBcAg gene-sequences were added to an HCV non-structural (NS) 3/4A gene (NS3/4A-stork-HBcAg). This resulted in an enhanced priming of HCV-specific IFN-γ and IL-2 responses in both wild-type (wt)- and NS3/4A-transgenic (Tg) mice, the latter with dysfunctional NS3/4A-specific T cells. The NS3/4A-stork-HBcAg vaccine primed NS3/4A-specific T cells in hepatitis B e antigen (HBeAg)-Tg mice with dysfunctional T cells to HBcAg and HBeAg. Repeated immunizations boosted expansion of IFN-γ and IL-2-producing NS3/4A-specific T cells in wt- and NS3/4A-Tg mice. Importantly, NS3/4A-stork-HBcAg-DNA induced in vivo long-term functional memory T cell responses, whose maintenance required CD4(+) T cells. Thus, avian HBcAg gene-sequences from stork can effectively act as a DNA vaccine adjuvant. This technology can most likely be universally expanded to other genetic vaccine antigens, as this completely avoids the use of sequences from a human virus where a pre-existing immunity may interfere with its adjuvant effect.

The hepatitis C virus protein NS3 suppresses TNF-α-stimulated activation of NF-κB by targeting LUBAC

The transcription factor nuclear factor κB (NF-κB) is crucial for innate immune defense against viral infections, and its activation requires the ubiquitylation of upstream proteins, including the adaptor protein NEMO (NF-κB essential modulator). Many infectious pathogens, including hepatitis C virus (HCV), inhibit NF-κB signaling in host cells, which promotes pathogen survival. Frequently, HCV-infected individuals develop a chronic infection, which suggests that HCV can subvert host antiviral responses. We found that HCV infection and replication inhibited the activation of NF-κB by the inflammatory cytokine tumor necrosis factor-α (TNF-α), which was mediated by the viral protein NS3 and, to a lesser extent, NS5B. NS3 directly interacted with linear ubiquitin chain assembly complex (LUBAC), competed with NEMO for binding to LUBAC, and inhibited the LUBAC-mediated linear ubiquitylation of NEMO and the subsequent activation of NF-κB. Together, our results highlight an immune evasion strategy adopted by HCV to modulate host antiviral responses and enhance virus survival and persistence.

Hepatitis C Virus Nonstructural 3/4A Protein Dampens Inflammation and Contributes to Slow Fibrosis Progression during Chronic Fibrosis In Vivo

HCV infection typically induces liver injury and inflammation, which appears to be responsible for the associated fibrogenesis. To date, the mechanism underlying the different rates of disease progression remains unclear. The aim of the study is to understand the possible role of the HCV non-structural (NS) 3/4A protein in the fibrosis progression. We used NS3/4A-expressing transgenic mice (NS3/4A-Tg) to accomplish the goals of the study. Different stages of liver fibrosis were induced in wild-type and NS3/4A-Tg mice by single carbon tetrachloride (acute) or multiple injections for 4 (intermediate) or 8 (chronic) weeks. Fibrotic parameters, inflammatory responses and hepatocyte turnover were extensively examined. Hepatic expression of HCV NS3/4A did not induce spontaneous liver damage. However, NS3/4A expression exerted contrasting effects during acute and chronic liver damage. During early fibrogenesis and intermediate fibrosis (4 weeks), NS3/4A-Tg mice exhibited enhanced liver damage whereas reduced fibrosis was observed in NS3/4A-Tg during chronic liver fibrosis (8 weeks). Furthermore, attenuated inflammation was observed in NS3/4A-Tg during chronic fibrosis with increase in M2 macrophages, hepatocyte proliferation, decreased hepatocyte apoptosis and decreased ductular reaction. In conclusion, during early fibrogenesis, HCV NS3/4A contributes to liver damage. While, during chronic liver fibrosis, NS3/4A dampens inflammation and induces hepatocyte regeneration thereby contributing to slow fibrosis progression to promote its survival or persistence.

HCV animal models and liver disease

The development and evaluation of effective therapies and vaccines for the hepatitis C virus (HCV) and the study of its interactions with the mammalian host have been hindered for a long time by the absence of suitable small animal models. Due to the narrow host tropism of HCV, the development of mice that can be robustly engrafted with human hepatocytes was a major breakthrough since they recapitulate the complete HCV life cycle. This model has been useful to investigate many aspects of the HCV life cycle, including antiviral interventions. However, studies of cellular immunity, immunopathogenesis and resulting liver diseases have been hampered by the lack of a small animal model with a functional immune system. In this review, we summarize the evolution of in vivo models for the study of HCV.

Establishment of a novel triple-transgenic mouse: conditionally and liver-specifically expressing hepatitis C virus NS3/4A protease

It is well known that NS3/4A protein plays crucial roles in the hepatitis C virus (HCV) replication. NS3/4A protein also results to virus-mediated immune evasion and persistence of infection through the interaction with host proteins. However, the lack of a suitable animal model hampers studies of HCV NS3/4A protein interaction with host proteins, which impacts immunopathology due to infection. Here, transgenic vector containing transcriptional regulation and Fluc reporter gene was constructed to conditionally express NS3/4A protein under the dual control of Tet-On regulatory system and Cre/LoxP gene-knockout system. NS3/4A transgenic founder mice were continuously crossed with Lap transgenic mice expressing reverse tetracycline-controlled transcriptional activator (rtTA), the NS3/4A/Lap double transgenic mouse lines with liver-specifically and conditionally expressing reporter (luciferase Fluc) under control of Tet-On system were established. The NS3/4A/Lap double transgenic mouse are mated with Lap/LC-1 double transgenic mouse with liver-specifically and conditionally expressing Cre recombinase under control of Tet-On system, NS3/4A/Lap/LC-1 triple transgenic mouse were generated. In vivo bioluminescent imaging, western blotting and immunohistochemical staining (IHS) was used to confirm that NS3/4A protein was strictly expressed in the liver of Doxycycline-induced triple transgenic mice. The results show that we established a triple-transgenic mouse model conditionally expressing the HCV NS3/4A protein under strict control of the Tet-On regulatory system and Cre/loxP system. This novel transgenic mouse model expressing NS3/4A in a temporally and spatially-specific manner will be useful for studying interactions between HCV NS3/4A protein and the host, also for evaluating NS3/4A protease inhibitors.

The oncogenic role of hepatitis C virus

Persistent infection with hepatitis C virus (HCV) is a major risk toward development of hepatocellular carcinoma (HCC). However, it remains controversial in the pathogenesis of HCC associated with HCV whether the virus plays a direct or an indirect role. The observation that chronic hepatitis C patients with sustained high levels of serum alanine aminotransferase are prone to develop HCC suggests the significance of inflammation in hepatocarcinogenesis in hepatitis C. However, the rare development of HCC in patients with autoimmune hepatitis, which is accompanied by robust inflammation, even after the progress into cirrhosis, implies a possibility of the direct role of HCV in HCC development. What is the role of HCV, a simple plus-stranded RNA virus, whose genome is never integrated into the host genome, in hepatocarcinogenesis? The studies using transgenic mouse and cultured cell models, in which the HCV proteins are expressed, indicate the direct pathogenicity of HCV, including oncogenic activities. In particular, the core protein of HCV induces overproduction of oxidative stress by impairing the mitochondrial electron transfer system, through insulting the function of molecular chaperon, prohibitin. HCV also modulates the intracellular signaling pathways including mitogen-activated protein kinase, leading to the acquisition of growth advantage by hepatocytes. In addition, HCV induces disorders in lipid and glucose metabolisms, thereby accelerating the progression of liver fibrosis and HCC development. These results would provide a clue for further understanding of the role of HCV in pathogenesis of persistent HCV infection including hepatocarcinogenesis.

Cleavage of the T cell protein tyrosine phosphatase by the hepatitis C virus nonstructural 3/4A protease induces a Th1 to Th2 shift reversible by ribavirin therapy

Ribavirin has proven to be a key component of hepatitis C therapies both involving IFNs and new direct-acting antivirals. The hepatitis C virus-mediated interference with intrahepatic immunity by cleavage of mitochondrial antiviral signaling protein (MAVS) and T cell protein tyrosine phosphatase (TCPTP) suggests an avenue for compounds that may counteract these effects. We therefore studied the effects of ribavirin, with or without inhibition of the nonstructural (NS)3/4A protease, on intrahepatic immunity. The intrahepatic immunity of wild-type and NS3/4A-transgenic mice was determined by Western blot, ELISA, flow cytometry, and survival analysis. Various MAVS or TCPTP constructs were injected hydrodynamically to study their relevance. Ribavirin pretreatment was performed in mice expressing a functional or inhibited NS3/4A protease to analyze its effect on NS3/4A-mediated changes. Intrahepatic NS3/4A expression made mice resistant to TNF-α-induced liver damage and caused an alteration of the intrahepatic cytokine (IFN-γ and IL-10) and chemokine (CCL3, CCL17, CCL22, CXCL9, and CXCL11) profiles toward an anti-inflammatory state. Consistent with this, the number of intrahepatic Th1 cells and IFN-γ(+) T cells in NS3/4A-transgenic mice decreased, whereas the amount of Th2 cells increased. These effects could be reversed by injection of uncleavable TCPTP but not uncleavable MAVS and were absent in a mouse expressing a nonfunctional NS3/4A protease. Importantly, the NS3/4A-mediated effects were reversed by ribavirin treatment. Thus, cleavage of TCPTP by NS3/4A induces a shift of the intrahepatic immune response toward a nonantiviral Th2-dominated immunity. These effects are reversed by ribavirin, supporting that ribavirin complements the effects of direct-acting antivirals as an immunomodulatory compound.

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.

Liver immune-pathogenesis and therapy of human liver tropic virus infection in humanized mouse models

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infect and replicate primarily in human hepatocytes. Few reliable and easy accessible animal models are available for studying the immune system's contribution to the liver disease progression during hepatitis virus infection. Humanized mouse models reconstituted with human hematopoietic stem cells (HSCs) have been developed to study human immunology, human immunodeficiency virus 1 infection, and immunopathogenesis. However, a humanized mouse model engrafted with both human immune and human liver cells is needed to study infection and immunopathogenesis of HBV/HCV infection in vivo. We have recently developed the humanized mouse model with both human immune and human liver cells (AFC8-hu HSC/Hep) to study immunopathogenesis and therapy of HCV infection in vivo. In this review, we summarize the current models of HBV/HCV infection and their limitations in immunopathogenesis. We will then present our recent findings of HCV infection and immunopathogenesis in the AFC8-hu HSC/Hep mouse, which supports HCV infection, human T-cell response and associated liver pathogenesis. Inoculation of humanized mice with primary HCV isolates resulted in long-term HCV infection. HCV infection induced elevated infiltration of human immune cells in the livers of HCV-infected humanized mice. HCV infection also induced HCV-specific T-cell immune response in lymphoid tissues of humanized mice. Additionally, HCV infection induced liver fibrosis in humanized mice. Anti-human alpha smooth muscle actin (αSMA) staining showed elevated human hepatic stellate cell activation in HCV-infected humanized mice. We discuss the limitation and future improvements of the AFC8-hu HSC/Hep mouse model and its application in evaluating novel therapeutics, as well as studying both HCV and HBV infection, human immune responses, and associated human liver fibrosis and cancer.

HCV-induced miR-21 contributes to evasion of host immune system by targeting MyD88 and IRAK1

Upon recognition of viral components by pattern recognition receptors, such as the toll-like receptors (TLRs) and retinoic acid-inducible gene I (RIG-I)-like helicases, cells are activated to produce type I interferon (IFN) and proinflammatory cytokines. These pathways are tightly regulated by the host to prevent an inappropriate cellular response, but viruses can modulate these pathways to proliferate and spread. In this study, we revealed a novel mechanism in which hepatitis C virus (HCV) evades the immune surveillance system to proliferate by activating microRNA-21 (miR-21). We demonstrated that HCV infection upregulates miR-21, which in turn suppresses HCV-triggered type I IFN production, thus promoting HCV replication. Furthermore, we demonstrated that miR-21 targets two important factors in the TLR signaling pathway, myeloid differentiation factor 88 (MyD88) and interleukin-1 receptor-associated kinase 1 (IRAK1), which are involved in HCV-induced type I IFN production. HCV-mediated activation of miR-21 expression requires viral proteins and several signaling components. Moreover, we identified a transcription factor, activating protein-1 (AP-1), which is partly responsible for miR-21 induction in response to HCV infection through PKCε/JNK/c-Jun and PKCα/ERK/c-Fos cascades. Taken together, our results indicate that miR-21 is upregulated during HCV infection and negatively regulates IFN-α signaling through MyD88 and IRAK1 and may be a potential therapeutic target for antiviral intervention.

Hepatitis C virus (HCV), a major cause of chronic hepatitis, end-stage cirrhosis, and hepatocellular carcinoma, has chronically infected 200 million people worldwide and 3–4 million more each year. When triggered by viral infection, host cells produce type I interferon (IFN) and proinflammatory cytokines to antagonize the virus. Despite extensive research, the mechanism underlying HCV immune system evasion remains elusive. Our results provided the first direct evidence that microRNA-21 (miR-21) feedback inhibits type I IFN signaling when cells are challenged with HCV, thus promoting the infection. MicroRNA is a kind of endogenous non-coding small RNA that regulates a wide range of biological processes and participate in innate and adaptive immune responses through complementarily pairing with target mRNA, which can regulate its expression or translation. Currently, miRNAs have intrigued many scientists as potent targets or therapeutic agents for diseases. In our study, the targets of miR-21, myeloid differentiation factor 88 (MyD88) and interleukin-1 receptor-associated kinase 1 (IRAK1), which are important for HCV-induced type I IFN production, have also been found. Moreover, we identified a transcription factor, AP-1, which is partly responsible for miR-21 induction in response to HCV infection. Taken together, our research has provided new insights into understanding the effects of miRNA on host-virus interactions, and revealed a potential therapeutic target for antiviral intervention.

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.

Interplay between Hepatitis C Virus and Redox Cell Signaling

Hepatitis C virus (HCV) infects approximately 3% of the world’s population. Currently licensed treatment of HCV chronic infection with pegylated-interferon-α and ribavirin, is not fully effective against all HCV genotypes and is associated to severe side effects. Thus, development of novel therapeutics and identification of new targets for treatment of HCV infection is necessary. Current opinion is orienting to target antiviral drug discovery to the host cell pathways on which the virus relies, instead of against viral structures. Many intracellular signaling pathways manipulated by HCV for its own replication are finely regulated by the oxido-reductive (redox) state of the host cell. At the same time, HCV induces oxidative stress that has been found to affect both virus replication as well as progression and severity of HCV infection. A dual role, positive or negative, for the host cell oxidized conditions on HCV replication has been reported so far. This review examines current information about the effect of oxidative stress on HCV life cycle and the main redox-regulated intracellular pathways activated during HCV infection and involved in its replication.

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.

Limited effect on NS3-NS4A protein cleavage after alanine substitutions within the immunodominant HLA-A2-restricted epitope of the hepatitis C virus genotype 3a non-structural 3/4A protease

It has been well established that immunological escape mutations within the hepatitis C virus genotype (gt) 1a non-structural (NS) 3/4A protease are partly prevented by a reduction in viral protease fitness. Surprisingly little is known about whether similar mutations affect proteases from other genotypes. In the present study, we assessed both the HLA-A2-restricted CTL response and gt3a NS3/4A protease fitness. Similar to gt1, the 1073-1081 epitope was immunodominant within the gt3a-specific HLA-A2-restricted CTL response, despite sequence similarity of only 56 % between the gt1a and gt3a genes. However, unlike the gt1a NS3/4A protease, all residues within the gt3a 1073-1081 epitope could be replaced sequentially by alanine while retaining protease activity, at least in part.

Animal models in the study of hepatitis C virus-associated liver pathologies

It is estimated that more than 170 million individuals worldwide are chronically infected with hepatitis C virus (HCV), with approximately 20% of the cases developing cirrhosis. Each year, between 1 and 4% of patients exhibiting cirrhosis develop hepatocellular carcinoma. Chronic HCV infection is also linked with the development of several metabolic disorders, including hepatic steatosis and insulin resistance. Research into HCV-related pathologies is hampered by a relative paucity of small animal models. As a result, little is known about the molecular mechanisms involved, and much of our current knowledge is drawn by inference from in vitro studies using overexpressed proteins. In this article, we will review the currently available animal models for the study of HCV pathogenesis, with an emphasis on murine models. Then, we will provide an overview of how these models have contributed to the deciphering of the molecular mechanisms underlying dysregulated lipid metabolism and hepatocellular carcinoma during HCV infection.

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.

Aberrant transcription and post-transcriptional processing of hepatitis C virus non-structural genes in transgenic mice

Hepatitis C virus (HCV) infection is a leading cause of chronic liver disease worldwide. Since several aspects of the infection remain unresolved, there is a pressing need for a convenient animal model that can mimic the clinical disease and aid the evaluation of treatment strategies. Although some success has been achieved in transgenic approaches for development of rodent models of HCV, transgenic expression of the complete HCV polyprotein or an entire set of the viral non-structural (NS) proteins continues to be a serious challenge. Using northern blot and 5' rapid amplification of cDNA ends (RACE), we unraveled two possible mechanisms that can impede HCV NS transgene expression in the mouse liver. Several truncated transcripts are produced from alternate transcription start sites along the HCV NS sequence within the murine environment, in vivo. Translation of these shorter transcripts is blocked either by the positioning of a contextual stop codon or through a shift in the reading frame. In addition, the complete NS transcript undergoes trans-splicing through 5' recombination with a non-transgene-derived, spliced leader sequence that appends a potential stop codon upstream of the translation start. These findings thus demonstrate that HCV NS-derived transgenes are subject to aberrant transcriptional initiation and post-transcriptional processing in the nucleus of a mouse host. Strategies to prevent such aberrant transcription start/RNA processing might be key to the development of a successful HCV transgenic mouse model.

Anti-tumor necrosis factor α treatment promotes apoptosis and prevents liver regeneration in a transgenic mouse model of chronic hepatitis C

Tumor necrosis factor α (TNFα) has been implicated in a variety of inflammatory diseases, and anti-TNFα has been shown to improve therapy when added to standard of care in chronic hepatitis C virus (HCV) infection. In addition, patients with chronic HCV have increased serum levels of TNFα and the macrophage-attracting chemokine (C-C motif) ligand 2 (CCL2). A mouse model of chronic HCV with hepatic nonstructural (NS) 3/4A protein expression mimics the human infection through a reduced response to double-stranded RNA and cleavage of the T cell protein tyrosine phosphatase. The mice also display a resistance to TNFα in vivo. We therefore analyzed the relationship between NS3/4A and TNFα. Wild-type and NS3/4A-transgenic (Tg) mice were treated with TNFα/D-galactosamine (D-galN), acting through the TNF receptor 1 on hepatocytes and macrophages, or lipopolysaccharide (LPS)/D-galN, acting through Toll-like receptor 4 on sinusoidal endothelial cells, macrophages, and dendritic cells. Mice were analyzed for hepatic signaling, liver damage, TNFα, and CCL2. Similar to HCV-infected humans, NS3/4A-Tg mice displayed elevated basal levels of TNFα and CCL2. Treatment of NS3/4A-Tg mice with TNFα/D-galN or LPS/D-galN led to increased hepatic nuclear factor kappa B (NFκB) activation, increased TNFα and CCL2 levels, decreased apoptosis, and increased hepatocyte regeneration. Importantly, blocking NFκB activation (bortezomib) or administering anti-TNFα (infliximab) 4 hours after LPS/D-galN injection reversed the resistance of NS3/4A-Tg mice to TNFα-induced liver injury.

CONCLUSION

Resistance to TNFα seen in NS3/4A-Tg mice is explained by a hepatoprotective effect of NFκB and TNFα. Hence, anti-TNFα agents block these effects and are antiviral by promoting hepatocyte apoptosis and preventing hepatocyte regeneration.

Advances in understanding the role of HCV proteins in the pathogenesis of HCV-induced liver diseases in animal models

Hepatitis C virus (HCV) is closely associated with the occurrence of hepatitis, cirrhosis and liver cancer. As HCV naturally infects only humans and higher primates, few animal models of HCV infection have been established. As a result, limited knowledge on the pathophysiology of and host immune responses to HCV infection is obtained. Gene transfer approaches have been used to establish relevant animal models to investigate the molecular basis of HCV-induced liver diseases. This paper focuses on providing an overview of the recent advances in understanding the role of HCV proteins in the pathogenesis of HCV-induced liver diseases in animal models.

Effects of HCV proteins in current HCV transgenic models

Hepatits C virus (HCV) is an enveloped virus with positive-sense single-stranded RNA genome that causes both acute and persistent infections associated with chronic hepatitis, cirrhosis and hepatocellular carcinoma, which needs fully functional human hepatocytes for its development. Due to the strict human tropism of HCV, only human and higher primates such as chimpanzees have been receptive to HCV infection and development, cognition about pathophysiololgy and host immune responses of HCV infection is limited by lacking of simple laboratory models of infection for a long time. During the past decade, gene transfer approaches have been helpful to the understanding of the molecular basis of human disease. Transgenic cell lines, chimeric and transgenic animal models were developed and had been demonstrated their invaluable benefits. This review focuses on the existing HCV transgenic models and summarize the relative results about probable pathophysical changes induced by HCV proteins.

Animal models for hepatitis C and related liver disease

Persistent infection with hepatitis C virus (HCV) is a major risk toward development of hepatocellular carcinoma (HCC). The elucidation of pathogenesis of HCV-associated liver disease is hampered by the absence of appropriate animal models: there has been no animal model for HCV infection/pathogenesis except for the chimpanzee. In contrast, a number of transgenic mouse lines carrying the cDNA of the HCV genome have been established and evaluated in the study of HCV pathogenesis. The studies using transgenic mouse models, in which the HCV proteins such as the core protein are expressed, indicate the direct pathogenicity of HCV, including oncogenic activities. HCV transgenic mouse models also show a close relationship between HCV and some hepatic and extrahepatic manifestations such as hepatic steatosis, insulin resistance or Sjögren's syndrome. A crucial role of hepatic steatosis and insulin resistance in the pathogenesis of liver disease in HCV infection has been demonstrated, implying hepatitis C to be a metabolic disease. Besides the data connecting liver fibrosis progression and the disturbance in lipid and glucose metabolisms in hepatitis C patients, a series of evidence was found showing the association between these two conditions and HCV infection, chiefly using transgenic mouse carrying the HCV genome. Furthermore, the persistent activation of peroxisome proliferator-activated receptor (PPAR)-alpha has recently been found, yielding dramatic changes in the lipid metabolism and oxidative stress overproduction in cooperation with the mitochondrial dysfunction. These results would provide a clue for further understanding of the role of lipid metabolism in pathogenesis of hepatitis C including liver injury and hepatocarcinogenesis.

HCV animal models: a journey of more than 30 years

In the 1970s and 1980s it became increasingly clear that blood transfusions could induce a form of chronic hepatitis that could not be ascribed to any of the viruses known to cause liver inflammation. In 1989, the hepatitis C virus (HCV) was discovered and found to be the major causative agent of these infections. Because of its narrow tropism, the in vivo study of this virus was, especially in the early days, limited to the chimpanzee. In the past decade, several alternative animal models have been created. In this review we review these novel animal models and their contribution to our current understanding of the biology of HCV.

DNA vaccine therapy for chronic hepatitis C virus (HCV) infection: immune control of a moving target

The use of DNA plasmids for DNA vaccination was first described in the early 1990 s. DNA vaccinations were successful in small animal models but in larger animals and humans problems appeared. One major obstacle, effective delivery, has been partly overcome by new delivery techniques, such as transdermal delivery with the gene gun, and in vivo electroporation. We are entering a new era of DNA vaccination, where such techniques can be tested in humans. DNA vaccination may be a useful therapy for chronic hepatitis C virus (HCV) infections. Patients with these infections have a reduced T cell response to the invading virus. The genetic variability of HCV, its immunomodulatory properties and high replication rate contribute to chronicity. By providing the correct stimulus T cells may be activated to clear the infection. The vaccination is intended to induce a coordinated immune-based attack on the continuously moving HCV target. If effective, this should help in clearing the infection.

Cellular models for the screening and development of anti-hepatitis C virus agents

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible, reliable and consistent manner. Many different models based on different forms of virions and hepatoma or other cell types have been described including virus-like particles, pseudotyped particles, subgenomic and full length replicons, virion productive replicons, immortalised hepatocytes, fetal and adult primary human hepatocytes. This review focuses on these different cellular models, their advantages and disadvantages at the biological and experimental levels, and their respective use for evaluating the effect of antiviral molecules on different steps of HCV biology including virus entry, replication, particles generation and excretion, as well as on the modulation by the virus of the host cell response to infection.

Nonstructural 3/4A protease of hepatitis C virus activates epithelial growth factor-induced signal transduction by cleavage of the T-cell protein tyrosine phosphatase

The hepatitis C virus (HCV) is a worldwide major cause of chronic liver disease with a high tendency to establish a persistent infection. To permit persistent replication of viral genomes through the cellular translation machinery without affecting host cell viability, viruses must have developed mechanisms to control cellular cascades required for sufficient viral replication, on the one hand, and to adapt viral replication to the cellular requirements on the other hand. The present study aimed to further elucidate mechanisms by which HCV targets growth factor signaling of the host cell and their implications for viral replication. The study describes a novel mechanism by which HCV influences the activation of the epithelial growth factor receptor/Akt pathway through a nonstructural (NS)3/4A-dependent down-regulation of the ubiquitously expressed tyrosine phosphatase T cell protein tyrosine phosphatase (TC-PTP). NS3/4A is demonstrated to cleave TC-PTP protease-dependently in vitro at two cleavage sites. The in vivo relevance of this finding is supported by the fact that down-regulation of TC-PTP protein expression could also be demonstrated in HCV-infected individuals and in transgenic mice with intrahepatic expression of NS3/4A.

CONCLUSION

This down-regulation of TC-PTP results in an enhancement of epithelial growth factor (EGF)-induced signal transduction and increases basal activity of Akt, which is demonstrated to be essential for the maintenance of sufficient viral replication. Hence, therapeutic targeting of NS3/4A may not only disturb viral replication by blocking the processing of the viral polyprotein but also exerts unforeseen indirect antiviral effects, further diminishing viral replication.

Cleavage of the IPS-1/Cardif/MAVS/VISA does not inhibit T cell-mediated elimination of hepatitis C virus non-structural 3/4A-expressing hepatocytes

BACKGROUND

Hepatitis C virus (HCV) effectively establishes persistent infection in human livers. The non-structural (NS) 3/4A complex participates in this process by cleavage of interferon beta (IFN beta) promoter stimulator-1 (IPS-1; also termed Cardif/MAVS/VISA), which inhibits responses to double stranded (ds) RNA. However, it is not known whether this effect extends beyond innate responses.

AIMS

To test if HCV NS3/4A affects innate and adaptive immune responses in vivo.

METHODS

NS3 levels were semi-quantified in human liver biopsies, transfected cells, and in transgenic (Tg) mouse livers by western blot. The effect of NS3/4A on dsRNA-mediated signalling and on the integrity of IPS-1 was analysed using in vitro translation, transfected cells and Tg mice. Cytotoxic T cell (CTL)-mediated clearance of transient firefly luciferase (FLuc)- and/or NS3/4A-Tg hepatocytes was determined using in vivo imaging and western blot.

RESULTS

NS3 protein levels were in a comparable range (0.1-49 microg/g tissue) in infected human livers and Tg mouse livers. Importantly, these levels of NS3/4A reduced murine innate responses to synthetic dsRNA in vivo, supporting the possibility that this occurs also in infected humans. The likely explanation for this was the NS3/4A-mediated cleavage of mouse IPS-1, albeit less efficiently than human IPS-1. Despite this, FLuc- and/or NS3/4A-expressing murine hepatocytes were effectively eliminated by hepatic CTLs, utilising the classical molecules for virus-infected cell lysis, including CD8, IFN gamma, perforin and FasL.

CONCLUSIONS

Although HCV NS3/4A inhibits the innate immunity, this does not prevent CTL-mediated clearance of NS3/4A-expressing hepatocytes in vivo. Thus, other HCV proteins are most likely responsible for interfering with the adaptive immunity.

Cellular and molecular interactions in coinfection with hepatitis C virus and human immunodeficiency virus

Coinfection with hepatitis C virus (HCV) and human immunodeficiency virus (HIV) is associated with increased HCV replication and a more rapid progression to severe liver disease, including the development of cirrhosis and hepatocellular carcinoma. In this review, we discuss the current understanding of the pathogenesis of HCV/HIV coinfection and the cellular and molecular mechanisms associated with the accelerated course of liver disease. The strength and breadth of HCV-specific T-cell responses are reduced in HCV/HIV-coinfected patients compared with those infected with HCV alone, suggesting that the immunosuppression induced by HIV compromises immune responses to HCV. HCV is not directly cytopathic, but many of the pathological changes observed in the liver of infected patients are a direct result of the intrahepatic antiviral immune responses. Apoptosis also has a role in HCV-mediated liver damage through the induction of apoptotic pathways involving the host immune response and HCV viral proteins. This review summarises the evidence correlating the role of cell-mediated immune responses and apoptosis with liver disease progression in HCV/HIV-coinfected patients.

Mouse models for the study of HCV infection and virus-host interactions

Hepatitis C virus (HCV) is a major cause of chronic liver disease including steatosis, cirrhosis and hepatocellular carcinoma. The development of transgenic mice expressing HCV proteins and the successful repopulation of SCID/Alb-uPA mice with human hepatocytes provides an important tool for unraveling virus-host interactions in vivo. Several of these mouse models exhibit aspects of HCV-related liver disease. Thus, these in vivo models play an important role to further understand the pathogenesis of HCV infection and to evaluate the pre-clinical safety and efficacy of new antiviral compounds against HCV. This review summarizes the most important mouse models currently used to study HCV pathogenesis and infection. Finally, the perspective of these models for future HCV research as well as the design of novel small animal models is discussed.

In Vivo Electroporation Enhances the Immunogenicity of Hepatitis C Virus Nonstructural 3/4A DNA by Increased Local DNA Uptake, Protein Expression, Inflammation, and Infiltration of CD3+ T Cells

The mechanisms by which in vivo electroporation (EP) improves the potency of i.m. DNA vaccination were characterized by using the hepatitis C virus nonstructural (NS) 3/4A gene. Following a standard i.m. injection of DNA with or without in vivo EP, plasmid levels peaked immediately at the site of injection and decreased by 4 logs the first week. In vivo EP did not promote plasmid persistence and, depending on the dose, the plasmid was cleared or almost cleared after 60 days. In vivo imaging and immunohistochemistry revealed that protein expression was restricted to the injection site despite the detection of significant levels of plasmid in adjacent muscle groups. In vivo EP increased and prolonged NS3/4A protein expression levels as well as an increased infiltration of CD3+ T cells at the injection site. These factors most likely additively contributed to the enhanced and broadened priming of NS3/4A-specific Abs, CD4+ T cells, CD8+ T cells, and gamma-IFN production. The primed CD8+ responses were functional in vivo, resulting in elimination of hepatitis C virus NS3/4A-expressing liver cells in transiently transgenic mice. Collectively, the enhanced protein expression and inflammation at the injection site following in vivo EP contributed to the priming of in vivo functional immune responses. These localized effects most likely help to insure that the strength and duration of the responses are maintained when the vaccine is tested in larger animals, including rabbits and humans. Thus, the combined effects mediated by in vivo EP serves as a potent adjuvant for the NS3/4A-based DNA vaccine.

Differential requirements of NS4A for internal NS3 cleavage and polyprotein processing of hepatitis C virus

The NS3 protein of hepatitis C virus (HCV) possesses protease activity responsible for the proteolytic cleavage of the viral polyprotein at the junctions of nonstructural proteins downstream of NS3. The NS3 protein was also found to be internally cleaved. In this study, we demonstrated that internal cleavages occurred on the NS3 protein of genotype 1b in the presence of NS4A, both in culture cells and with a mouse model system. No internal cleavage products were detected with the NS3 and NS4A proteins of genotype 2a. Three potential cleavage sites were detected in the NS3 protein (genotype 1b), with IPT(402)|S being the major one. The internal cleavage requires the polyprotein processing activity of NS3 protease, but when supplemented in trans, the internal cleavage efficiency is reduced. In addition, several mutations in NS4A disrupted the internal cleavage of NS3 but did not affect polyprotein processing, indicating that NS4A contributes differently to these two proteolytic activities. Furthermore, Ile-25, Val-26, and Ile-29 of the NS4A protein, important for the NS4A-dependent internal cleavages, were also shown to be critical for the transforming activity of NS3, but mutations at these critical residues resulted only in a slight increase of HCV replicating efficiency. The internal cleavage-associated enhancement of the transforming activity of NS3 was reduced when a T402A substitution at the major internal cleavage site was introduced. The multiple roles of NS4A in viral multiplication and pathogenesis make NS4A an ideal molecular target for HCV therapy.

New animal models for hepatitis C viral infection and pathogenesis studies

Hepatitis C virus (HCV) is a major cause of chronic liver disease, cirrhosis and hepatocellular carcinoma (HCC). In man, the pathobiological changes associated with HCV infection have been attributed to both the immune system and direct viral cytopathic effects. Until now, the lack of simple culture systems to infect and propagate the virus has hampered progress in understanding the viral life cycle and pathogenesis of HCV infection, including the molecular mechanisms implicated in HCV-induced HCC. This clearly demonstrates the need to develop small animal models for the study of HCV-associated pathogenesis. This review describes and discusses the development of new HCV animal models to study viral infection and investigate the direct effects of viral protein expression on liver disease.

Agonistic antibodies to Fas induce a breach in the endothelial lining of the liver and a breakdown in B cell tolerance

Liver disease can be associated with a breakdown in self-tolerance and the production of autoantibodies such as rheumatoid factors (RF), which bind to IgG. Here we investigated whether primary, non-infectious liver damage was sufficient to induce autoantibody production. We established a model of targeted liver damage induced by weekly sublethal injections of pro-apoptotic anti-Fas (CD95) antibodies. Liver damage, monitored by measurements of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, was minimal 1 week after anti-Fas injection. However, the sublethal Fas stimulation was sufficient to trigger significant haemorrhage in the liver, as assessed by Evans Blue dye leakage into the organ 5 h after anti-Fas antibody injection. We observed an induction of RF in response to the weekly injections of sublethal anti-Fas antibodies but not of isotype control antibodies, indicating a breakdown of self-tolerance induced by Fas engagement. RF induction was unlikely to be due to direct activation of B cells, as splenocytes stimulated with anti-Fas antibodies in vitro did not produce RF. These studies show that sublethal damage to the liver by Fas engagement leads to liver haemorrhage and is sufficient to trigger the breakdown of self-tolerance.