Cell mediated immune response to the hepatitis C virus

Spred2 controls the severity of Concanavalin A-induced liver damage by limiting interferon-gamma production by CD4+ and CD8+ T cells

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Spred2^-/- mice developed exacerbated Con A-induced liver damage with increased IFNγ production.

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MEK/ERK inhibitor U0126 markedly inhibited the damage and reduced IFNγ production.

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Neutralization of IFNγ abolished the damage with down-regulated hepatic STAT1 activation.

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Depletion of CD4⁺/CD8⁺ T cells improved the damage with decreased IFNγ production.

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Transplantation of CD4⁺/CD8⁺ T cells into RAG1^-/- mice reproduced severe liver damage.

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Liver damage and IFNγ production were significantly lower in Spred2 transgenic mice.

Introduction

Mitogen-activated protein kinases (MAPKs) are involved in T cell-mediated liver damage. However, the inhibitory mechanism(s) that controls T cell-mediated liver damage remains unknown.

Objectives

We investigated whether Spred2 (Sprouty-related, EVH1 domain-containing protein 2) that negatively regulates ERK-MAPK pathway has a biological impact on T cell-mediated liver damage by using a murine model.

Methods

We induced hepatotoxicity in genetically engineered mice by intravenously injecting Concanavalin A (Con A) and analyzed the mechanisms using serum chemistry, histology, ELISA, qRT-PCR, Western blotting and flow cytometry.

Results

Spred2-deficient mice (Spred2^-/-) developed more sever liver damage than wild-type (WT) mice with increased interferon-γ (IFNγ) production. Hepatic ERK phosphorylation was enhanced in Spred2^-/- mice, and pretreatment of Spred2^-/- mice with the MAPK/ERK inhibitor U0126 markedly inhibited the liver damage and reduced IFNγ production. Neutralization of IFNγ abolished the damage with decreased hepatic Stat1 activation in Spred2^-/- mice. IFNγ was mainly produced from CD4⁺ and CD8⁺ T cells, and their depletion decreased liver damage and IFNγ production. Transplantation of CD4⁺ and/or CD8⁺ T cells from Spred2^-/- mice into RAG1^-/- mice deficient in both T and B cells caused more severe liver damage than those from WT mice. Hepatic expression of T cell attractants, CXCL9 and CXCL10, was augmented in Spred2^-/- mice as compared to WT mice. Conversely, liver damage, IFNγ production and the recruitment of CD4⁺ and CD8⁺ T cells in livers after Con A challenge were lower in Spred2 transgenic mice, and Spred2-overexpressing CD4⁺ and CD8⁺ T cells produced lower levels of IFNγ than WT cells upon stimulation with Con A in vitro.

Conclusion

We demonstrated, for the first time, that Spred2 functions as an endogenous regulator of T cell IFNγ production and Spred2-mediated inhibition of ERK-MAPK pathway may be an effective remedy for T cell-dependent liver damage.

New Epitope Peptides Derived from Hepatitis C Virus (HCV) 2a Which Have the Capacity to Induce Cytotoxic T Lymphocytes in HLA-A2+HCV-Infected Patients

Because cytotoxic T lymphocytes (CTLs) play an important role in the specific immunotherapy of hepatitis C virus (HCV) infection, a series of CTL epitopes has been defined from HCV genotype 1a or 1b protein. Here, we attempted to identify HCV2a-derived epitopes that are capable of inducing HLA-A2-restricted and peptide-specific CTLs. Peripheral blood mononuclear cells (PBMCs) of HLA-A2+ HCV2ainfected patients or healthy donors were stimulated in vitro with each of the HCV2a-derived peptides, which were prepared based on the HLA-A2-binding motif, and their peptide-specific and HLA-A2-restricted cytotoxicities were examined. The HCV2a 432-441, HCV2a 716-724, and HCV2a 2251-2260 peptides were found to efficiently induce peptide-specific CTLs from the PBMCs of HLA-A2+ HCV2ainfected patients. Cytotoxicity was mainly mediated by CD8+ T cells in a HLA class I-restricted manner. These results indicate that the HCV2a 432-441, HCV2a 716-724, and HCV2a 2251-2260 peptides might be applicable for peptide-based immunotherapy of HLA-A2+ HCV2a-infected patients.

Overexpression of Regulatory T Cells Type 1 (Tr1) Specific Markers in a Patient with HCV-Induced Hepatocellular Carcinoma

Hepatitis C virus (HCV) is an important causative agent of liver disease, but factors that determine the resolution or progression of infection are poorly understood. In this study, we suggested that existence of immunosuppressive mechanisms, supported by regulatory T cells and especially the regulatory T cell 1 subset (Tr1), may explain the impaired immune response during infection and thus the fibrosis aggravation to hepatocellular carcinoma (HCC). Using quantitative real-time PCR, we investigated the intra-hepatic presence of Tr1 cells in biopsies from a genotype 1b infected patient followed for an 18-year period from cirrhosis to HCC. We described a significant increase of gene expression in particular for the cytokines IL-10, TGF-β, and their receptors that were perfectly correlated with an increased expression of the Tr1 specific markers (combined expression of CD4, CD18, and CD49b). This was strongly marked since the patient evolved in the pathology and could explain the failure of the treatment. In conclusion, evidence of regulatory T cell installation in the liver of chronically infected patient with cirrhosis and HCC suggests for the first time a key role for these cells in the course of HCV infection.

Characterization of antigenic variants of hepatitis C virus in immune evasion

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Chronic hepatitis C

The goal of antiviral therapy for patients with chronic hepatitis C virus (HCV) infection is to attain a sustained virologic response (SVR), which is defined as undetectable serum HCV-RNA levels at 6 months after the cessation of treatment. Major improvements in antiviral therapy for chronic hepatitis C have occurred in the past decade. The addition of ribavirin to interferon-alfa therapy and the introduction of pegylated interferon (PEG-IFN) have substantially improved SVR rates in patients with chronic hepatitis C. The optimization of HCV therapy with PEG-IFN and ribavirin continues to evolve. Studies are ongoing that use viral kinetics to tailor therapy to an individual's antiviral response and determine the ideal length of treatment to maximize the chance of SVR. Improved SVR can be achieved with new specific inhibitors that target the HCV NS3/4A protease and the NS5B polymerase. Several long-term follow-up studies have shown that SVR, when achieved, is associated with a very low risk of virologic relapse. Furthermore, antiviral therapy can reduce the morbidity and mortality rates associated with chronic hepatitis C by reducing fibrosis progression, the incidence of cirrhosis, and hepatocellular carcinoma.

Ethnic and geographical differences in HLA associations with the outcome of hepatitis C virus infection

Backgrounds

The association of human leukocyte antigen (HLA) genes with the outcome of hepatitis C virus (HCV) infection may be modified by ethnic and geographical differences.

Results

HLA-A, -C, -DRB1 and -DQB1 genotyping were performed in a Midwestern American cohort of 105 HCV infected subjects among which 49 cleared HCV infection and 56 had persistent viral infection. A new protective association of HLA-Cw*05 to HCV infection of all ethnic populations was identified (OR = 0.12, 95% CI = 0.01–0.97, P = 0.03). It was surprising that HLA-A*02 (P for interaction = 0.02) and HLA-DRB1*12 (P for interaction = 0.05) showed statistical interaction with race indicating opposite associations in Caucasians (OR = 2.74 for A*02 and 2.15 for DRB1*12) and non-Caucasians (OR = 0.41 for A*02 and 0.15 for DRB1*12). In addition, HLA-DRB1*01 (OR = 0.26), DQB1*05 (OR = 0.23) and the haplotype DRB1*01-DQB1*05 (OR = 0.19) showed strong associations with viral clearance in Caucasians. The protective associations of A*03 (OR = 0.20) and DQB1*03 (OR = 0.20) were exclusive to non-Caucasians. In contrast, DQB1*02 (OR = 2.56, 95% CI = 1.15–7.71, P = 0.02) and the haplotype DRB1*07-DQB1*02 (OR = 5.25, 95% CI = 1.04–26.6, P = 0.03) were risk markers in Caucasians.

Conclusion

The associations of HLA-A*02 and HLA-DRB1*12 with HCV infection are opposite with different races. HLA-A*03, Cw*05, DRB1*01, DQB1*03 and DQB1*05 are associated with viral clearance while HLA-DRB1*07 and DQB1*02 are risk markers for viral persistence of HCV infection in Midwestern Americans. These results reveal ethnically and geographically different distribution of HLA-genes which are associated with the outcome of HCV infection.

Viral determinants of resistance to treatment in patients with hepatitis C

Chronic hepatitis C virus (HCV) infection affects more than 170 million persons worldwide and is responsible for the development of liver cirrhosis in many cases. Standard treatment with pegylated alpha interferon (IFN-alpha) in combination with the nucleoside analogue ribavirin leads to a sustained virologic response in approximately half of the patients. IFN-alpha is classified as an indirect treatment, as it interacts with the host's immune response. The mechanism of action of ribavirin is still unknown. The benefit of triple therapy by adding other antiviral agents, e.g., amantadine, is controversial. Currently, new direct antiviral drugs (HCV protease/polymerase inhibitors) are being evaluated in phase 1/phase 2 trials. Phenotypic resistance to antiviral therapy has been attributed to amino acid variations within distinct regions of the HCV polyprotein. While sensitivity to IFN-alpha-based antiviral therapy in vivo is clearly correlated with the number of mutations within the HCV NS5A protein, the underlying functional mechanisms for this association are unknown. In turn, in vitro, several mechanisms to circumvent the host immune defense or to block treatment-induced antiviral activities have been described for different HCV proteins. By the introduction of direct antiviral drugs, hepatitis C therapy now is entering a new era in which the development of resistance may become the most important parameter for treatment success or failure.

Monocyte-derived dendritic cell function in chronic hepatitis C is impaired at physiological numbers of dendritic cells

Monocyte-derived dendritic cells (MoDCs) are a promising cellular adjuvant for effector immune responses against tumours and chronic viral infections, including hepatitis C virus (HCV). If autologous DC therapeutic approaches are to be applied in persistent HCV infections in patients, it is important to have an unambiguous understanding of the functional status of the cell type used, namely MoDCs from patients with chronic hepatitis C (CHC) infection. Because of conflicting published reports of either impaired or normal MoDC function in CHC infection, we re-examined the ability of MoDCs from CHC and normal healthy donors (NHD) to mature to an inflammatory stimulus [tumour necrosis factor (TNF)-alpha] and their subsequent functional capabilities. Expression of maturation-associated phenotypic markers [human leucocyte antigen (HLA)-DR, CD83, CD86, CD40], allostimulatory capacity in mixed lymphocyte reactions (MLRs) and CD40-ligand-induced cytokine and chemokine generation were compared in CHC- versus NHD-MoDCs. TNF-alpha-stimulated CHC-MoDCs up-regulated phenotypic markers, but to significantly lower levels than NHD-MoDCs. At physiological ratios of DCs to T cells, CHC-MoDCs were less allostimulatory than NHD-MoDCs, but not when DC numbers were substantially increased. CHC- and NHD-MoDCs generated equivalent amounts of cytokines [TNF-alpha, interleukin (IL)-1beta, IL-6, IL-12p70, IL-15, IL-10] and chemokines [interferon-inducible protein (IP)-10, macrophage inflammatory protein (MIP)-1alpha, regulated upon activation, normal T expressed and secreted (RANTES)] after CD40 ligation. Because the functional defect was not apparent at high MoDC : T cell ratios, autologous MoDC therapy with sufficiently high numbers of DCs could, in theory, overcome any impairment of MoDC function in CHC.

Impaired NFAT nuclear translocation results in split exhaustion of virus-specific CD8+ T cell functions during chronic viral infection

In persistent viral infections, the host's immune system is challenged by the constant exposure to antigen, potentially causing continuous activation of CD8(+) T cells with subsequent immunopathology. Here we demonstrate, for experimental chronic lymphocytic choriomeningitis virus and human HIV infection, that upon prolonged in vivo exposure to antigen, TCR-triggered Ca(2+) flux, degranulation, and cytotoxicity are maintained on a cellular level, whereas cytokine production is severely impaired because of a selective defect in activation-induced NFAT nuclear translocation. During chronic infection, this differential regulation of pathways leading to diverse effector functions may allow CD8(+) T cells to sustain some degree of local viral control by direct cytotoxicity while limiting systemic immune pathology by silencing cytokine production.

Immunity and protection by adoptive transfer of dendritic cells transfected with hepatitis C NS3/4A mRNA

In this study, we tested the hypothesis that adoptive transfer of dendritic cells (DCs) transfected ex vivo with mRNA encoding hepatitis C virus (HCV) NS3/4A would initiate potent HCV-specific protective immune responses in vivo. Murine DCs were transfected with NS3/4A mRNA or eGFP mRNA using either electroporation or Transmessenger Transfection Reagent and then used for adoptive transfer. Electroporation resulted in higher transfection efficiency but lower levels of eGFP and NS3/4A expression when compared to transfection with Transmessenger. The murine NS3/4A mRNA-transfected DCs were functional in T cell activation in vitro. Adoptive transfer of NS3/4A mRNA-transfected DCs resulted in migration to regional lymph nodes, strong cellular immune responses and protection from challenge with vaccinia virus expressing NS3/NS4/NS5 in mice. Furthermore, although Transmessenger mediated transfection was less efficient than electroporation in terms of number of transfected cells, the DCs transfected with NS3/4A mRNA and Transmessenger expressed higher levels of protein and induced stronger immune responses and protection than DCs transfected with NS3/4A mRNA by electroporation. Since no study has explored the in vivo efficacy of mRNA-transfected DC-mediated vaccination against viral diseases, including hepatitis C, our study provided a novel vaccination strategy against hepatitis C as well as other pathogens.

Induction of hepatitis C virus (HCV)-specific T cells by needle stick injury in the absence of HCV-viraemia

BACKGROUND

The risk of hepatitis C virus (HCV) infection after occupational exposure is low with seroconversion rates between 0 and 5%. However, factors associated with natural resistance against HCV after needle stick injury are poorly defined. HCV-specific T-cell responses have been described in cross-sectional studies of exposed HCV-seronegative individuals.

MATERIALS AND METHODS

In this study, we prospectively followed 10 healthcare professionals who experienced an injury with an HCV-contaminated needle. Blood samples were taken on the day or the day after the event and at different time points during follow-up for up to 32 months. HCV-specific T-cell responses were investigated directly ex vivo and in T-cell lines.

RESULTS

None of the individuals became positive for HCV-RNA in serum tested with the highly sensitive transcription-mediated amplification (TMA)-assay or in peripheral blood mononuclear cells (PBMC). All of them remained anti-HCV negative throughout follow-up. At the time of injury, HCV-specific CD4+ T-cell responses were already detectable in two individuals and became detectable thereafter in three additional persons. Transient HCV-specific CD8+ T-cell responses developed in two HLA-A2 positive patients, which became negative until the most recent follow-up after 5 and 17 months, respectively.

CONCLUSION

We demonstrate the development of HCV-specific T cells in HCV-exposed individuals after needle stick injury indicating subinfectious exposure to HCV. T-cell immunity against HCV may contribute to the low prevalence of HCV in medical healthcare professionals in Western countries.

Hepatitis C virus: virology and experimental systems

Over the past several years, significant progress has been made toward the understanding of hepatitis C virus, especially the development of in vitro cell culture models. The scientific community now has the tools to gain a better understanding of the virus, which should translate into better clinical therapeutic modalities. Many new drugs are currently being evaluated, and a few are already undergoing clinica trials. This article focuses on the current advances in hepatitis C virus virology.

The role of virus-induced regulatory T cells in immunopathology

In recent years, regulatory T cells have received increased attention for their role in immune responses to microbial infections. The list of microbial pathogens associated with regulatory T cell responses is growing rapidly and includes bacteria, viruses, parasites, and fungi. As the biology of regulatory T cells is revealed, we are discovering that their induction during infection is a normal aspect of immunity, necessary to limit collateral damage from inflammatory responses and aggressive immunological effectors. Thus, these cells play a critical role in maintaining the delicate balance between preventing immunopathology and allowing the immune response to clear infections. While generally successful, there are notable exceptions where regulatory T cell-mediated suppression appears to be responsible for allowing certain viruses to establish and maintain a persistent state. In this review, we will discuss our current understanding of what virus-induced regulatory T cells are, how they are induced, and what mechanisms they use to suppress immunity. The complex role of Tregs in regulating immunity to viral infections, and the consequences their activity has on disease is illustrated by a review of specific viral infections including hepatitis C virus and human immunodeficiency virus.

Identification of a hepatitis C virus-reactive T cell receptor that does not require CD8 for target cell recognition

Hepatitis C virus (HCV) has been reported to elicit B and T cell immunity in infected patients. Despite the presence of antiviral immunity, many patients develop chronic infections leading to cirrhosis, hepatocellular carcinoma, and liver failure that can require transplantation. We have previously described the presence of HLA-A2-restricted, HCV NS3-reactive cytotoxic T lymphocytes (CTL) in the blood of HLA-A2- liver transplantation patients that received an HLA-A2+ liver allograft. These T cells are analogous to the "allospecific" T cells that have been described in hematopoietic stem cell transplantation patients. It has been speculated that allospecific T cells express high-affinity T cell receptors (TCRs). To determine if our HCV-reactive T cells expressed TCRs with relatively high affinity for antigen, we identified and cloned a TCR from an allospecific HLA-A2-restricted, HCV:NS3:1406-1415-reactive CD8+ T cell clone and expressed this HCV TCR in Jurkat cells. Tetramer binding to HCV TCR-transduced Jurkat cells required CD8 expression, whereas antigen recognition did not. In conclusion, based on the reactivity of the TCR-transduced Jurkat cells, we have identified a TCR that transfers anti-HCV reactivity to alternate effectors. These data suggest this high affinity HCV-specific TCR might have potential new immunotherapic implications.

Prophylactic and therapeutic vaccination with dendritic cells against hepatitis C virus infection

Antigen uptake and presentation capacities enable DC to prime and activate T cells. Recently, several studies demonstrated a diminished DC function in hepatitis C virus (HCV) infected patients showing impaired abilities to stimulate allogenic T cells and to produce IFN-gamma in HCV infected patients. Moreover, DC of patients who have resolved HCV infection behave like DC from healthy donors responding to maturation stimuli, decrease antigen uptake, up-regulate expression of appropriate surface marker, and are potent stimulators of allogenic T cells. A number of studies have demonstrated in tumour models and models of infectious diseases strong induction of immune responses after DC vaccination. Because DC are essential for T-cell activation and since viral clearance in HCV infected patients is associated with a vigorous T-cell response, we propose a new type of HCV vaccine based on ex vivo stimulated and matured DC loaded with HCV specific antigens. This vaccine circumvents the impaired DC maturation and the down regulated DC function of HCV infected patients in vivo by giving the necessary maturation stimuli and the HCV antigens in a different setting and location ex vivo. Strong humoral and cellular immune responses were detected after HCV core DC vaccination. Furthermore, DC vaccination shows partial protection in a therapeutic and prophylactic model of HCV infection. In conclusion, mice immunized with HCV core pulsed DC generated a specific antiviral response in a mouse HCV challenge model. Our results indicate that HCV core pulsed DC may serve as a new modality for immunotherapy of HCV especially in chronically infected patients.

Differential contribution of hepatitis C virus NS5A and core proteins to the induction of oxidative and nitrosative stress in human hepatocyte-derived cells

BACKGROUND/AIMS

We aimed to explore the effects of hepatitis C virus (HCV) core and NS5A proteins on reactive oxygen (ROS) and nitrogen species (RNS) formation and on gene expression profile of iNOS in human hepatocyte-derived cells.

METHODS

Production of ROS and RNS and nitrotyrosine residues accumulation were determined by flow cytometry and fluorescent microscopy as well as by Western blot, respectively, in NS5A- and core-transfected cells. Northern blot, Western blot, real-time PCR, and luciferase assays were used to assess iNOS gene expression in both transfectants.

RESULTS

Cytokine-activated NS5A- and core-transfected cells induced ROS and RNS production but an earlier and more marked increase was observed in NS5A-expressing cells. Superoxide production was also augmented, showing a similar temporal pattern of appearance in both NS5A- and core-transfected cells. Although both NS5A and core HCV proteins were able to up-regulate iNOS gene expression, accompanied by a nitrotyrosine-containing proteins accumulation, an earlier iNOS overexpression was observed in NS5A-expressing cells, suggesting a different time course of iNOS activation pattern for core and NS5A HCV proteins.

CONCLUSIONS

Our results indicate a differential contribution of both HCV proteins to oxidative and nitrosative stress generation.

Cytotoxic capacity of hepatitis C virus (HCV)--specific lymphocytes after in vitro immunization with HCV-derived lipopeptides

BACKGROUND

Hepatitis C virus (HCV)-derived lipopeptides can induce epitope-specific immune responses in lymphocytes from HCV-naive individuals. We analyzed whether such T cells generated by in vitro immunization with HCV core-derived lipopeptides exert HCV-specific cytolytic activity.

METHODS

Using a sensitive flow cytometric cytotoxicity assay we characterized HCV-specific cytotoxicity in T cells generated in vitro with HCV core-derived 25-mer lipopeptides. In addition, we studied expressions of Fas ligand and perforin and interferon-gamma (IFN-gamma) secretion in HLA-A2-HCV(core_35-44) tetramer-positive T cells generated with lipopeptide amino acid 20-44 (LP20-44).

RESULTS

CD8+ T cells induced in vitro with HCV core-derived lipopeptides only infrequently exerted HCV-specific cytotoxicity, irrespective of whether antigen-coated T2 cells or autologous B lymphoblasts were used as targets. Detailed analysis of HLA-A2-HCV(core_35-44) tetramer-positive T cells generated with LP20-44 revealed that in vitro immunization resulted in T cells that secreted IFN-gamma after antigen-specific restimulation and that upregulated expression of Fas ligand but not of perforin.

CONCLUSIONS

Our data confirm at the functional level that HCV lipopeptides induce antigen-specific T lymphocytes that produce IFN-gamma but exert significant cytotoxicity in only a minority of experiments, probably because expression of cytolytic effector molecules is not enhanced in their granules.

Hepatitis C virus and the immune system: a concise review

Hepatitis C Virus (HCV) induces a chronic infection in 50%-80% of infected individuals, which can lead to cirrhosis and hepatocellular carcinoma. The inefficiency of the immune system in eliminating the virus is not well understood as humoral and cellular immune responses are induced. While a persistent infection is generally associated with a weak CD4+ and CD8+ T cell response during the acute phase, there is no good explanation as to why this response is strong enough in 20% of acutely infected people such that they spontaneously resolve the infection. However, the immune system partially controls the viral infection but due to a long-lasting inflammatory milieu, hepatic damage occurs. During the chronic phase of the infection, HCV does not seem to be cytopathic. This aspect is still controversial as the virus was linked to the development of cholestatic syndrome or acute lobular hepatitis after liver transplant in HCV infected patients. The development of new experimental systems such as HCV pseudoparticles, genomic replicon and transfected cell lines have improved our vision of the virus cycle as well as the understanding of the mechanism of persistence. However, a convincing explanation for the chronicity of the infection in the presence of a functional immune response is still missing and is an important area of research to understand HCV immune pathogenesis. Future research should dissect mechanisms that lead to quantitatively or qualitatively inadequate immune responses, the role of the high variability of the virus, the relevance of host's genetic factors and mechanisms of immunosuppression induced by the virus.

Treatment of chronic hepatitis C virus infection via antioxidants: results of a phase I clinical trial

BACKGROUND

The pathogenesis of chronic hepatitis C virus (HCV) infection is associated with a defective host antiviral immune response and intrahepatic oxidative stress. Oxidative stress and lipid peroxidation play major roles in the fatty liver accumulation (steatosis) that leads to necro-inflammation and necrosis of hepatic cells. Previous trials suggested that antioxidative therapy may have a beneficial effect on patients with chronic HCV infection.

AIMS

To determine the safety and efficacy of treatment of chronic HCV patients via a combination of antioxidants.

METHODS

Fifty chronic HCV patients were treated orally on a daily basis for 20 weeks with seven antioxidative oral preparations (glycyrrhizin, schisandra, silymarin, ascorbic acid, lipoic acid, L-glutathione, and alpha-tocopherol), along with four different intravenous preparations (glycyrrhizin, ascorbic acid, L-glutathione, B-complex) twice weekly for the first 10 weeks, and followed up for an additional 20 weeks. Patients were monitored for HCV-RNA levels, liver enzymes, and liver histology. Assessment of quality of life was performed using the SF-36 questionnaire.

RESULTS

In one of the tested parameters (eg, liver enzymes, HCV RNA levels, or liver biopsy score), a combination of antioxidants induced a favorable response in 48% of the patients (24). Normalization of liver enzymes occurred in 44% of patients who had elevated pretreatment ALT levels (15 of 34). ALT levels remained normal throughout follow-up period in 72.7% (8 of 11). A decrease in viral load (one log or more) was observed in 25% of the patients (12). Histologic improvement (2-point reduction in the HAI score) was noted in 36.1% of the patients. The SF-36 score improved in 26 of 45 patients throughout the course of the trial (58% of the patients). Treatment was well tolerated by all patients. No major adverse reactions were noted.

CONCLUSIONS

These data suggest that multi antioxidative treatment in chronic HCV patients is well tolerated and may have a beneficial effect on necro-inflammatory variables. A combination of antiviral and antioxidative therapies may enhance the overall response rate of these patients.

Rescue of in vivo FAS-induced apoptosis of hepatocytes by corticosteroids either associated with alcohol consumption by mice or provided exogenously

The pathogenic effects of many hepatic viral infections are mediated, at least in part, by the immune response to the infected hepatocyte. The immune response in the infected liver involves the interaction of cytotoxic T cells (CTL) with the hepatocytes through the interaction of FAS-ligand on the CTL and FAS on the hepatocyte. The initial hypothesis for this study was that alcohol consumption by mice would sensitize the liver to apoptosis induced by ligation of FAS. C57Bl/6 mice fed ethanol in a liquid diet did show an increased percentage of apoptotic cells 2 h after injection with anti-FAS as compared with the percentage in the control mice. However, 4 and 6 h after anti-FAS injection, control mice showed high percentages of apoptotic cells (20% to 41%) compared with 5% and 4% apoptotic cells in the ethanol-fed mice. The decreased apoptosis of ethanol-fed mice correlated closely with corticosterone levels in the sera. This was confirmed by the finding that adrenalectomized (ADX) mice provided a high level of corticosterone in drinking water were protected against FAS-induced hepatocyte apoptosis. Ethanol-fed mice showed a significant elevation of serum alanine aminotransferase (ALT) levels indicating the development of hepatitis in spite of the relatively low proportion of apoptotic cells in the liver. In conclusion, high levels of corticosterone protect hepatocytes from FAS-mediated apoptosis, but do not prevent the ultimate development of liver damage. In experiments where mice were provided ethanol chronically in drinking water, where stress is minimal, higher levels of ALT were noted in animals in the ethanol group as compared with animals in the control group. These data support the suggestion that ethanol increases hepatocyte sensitivity to FAS-mediated damage.

Peptide-loaded chimeric influenza virosomes for efficient in vivo induction of cytotoxic T cells

Virus-specific CD8(+) T cells are thought to play an important role in resolving acute hepatitis C virus (HCV) infection as viral clearance has been associated with a strong and sustained CD8(+) T cell response. During the chronic state of HCV infection virus-specific T cells have a low frequency and a reduced responsiveness. Based on this, a therapeutic vaccine increasing the frequency of specific T cells is a promising alternative for the treatment of chronic HCV infection. We improved an existing vaccine platform based on immunopotentiating reconstituted influenza virosomes (IRIVs) for efficient delivery of peptide epitopes to the MHC class I antigen presentation pathway. IRIVs are proteoliposomes composed of phospholipids and influenza surface glycoproteins. Due to their fusogenic activity, IRIVs are able to deliver encapsulated macromolecules, e.g. peptides to immunocompetent cells. We developed a novel method based on chimeric virosomes [chimeric immunopotentiating reconstituted influenza virosomes (CIRIVs)] combining the high peptide-encapsulation capacity of liposomes and the fusion activity of virosomes. This new approach resulted in a 30-fold increase of the amount of incorporated soluble peptide compared with current preparation methods. To study the immunogenicity of chimeric virosomes HLA-A2.1 transgenic mice were immunized with CIRIVs containing the HCV Core132 peptide. Core132-CIRIVs efficiently induced specific cytotoxic and IFNgamma-producing T cells already with low peptide doses. Vaccine formulations, which include combinations of different HCV-derived CTL epitopes could be used to induce not only a strong but also a multi-specific CTL response, making them potential candidates for therapeutic and maybe prophylactic T cell vaccines in humans.

Reduction of retrovirus-induced immunosuppression by in vivo modulation of T cells during acute infection

Chronic infection with Friend retrovirus is associated with suppressed antitumor immune responses. In the present study we investigated whether modulation of T-cell responses during acute infection would restore antitumor immunity in persistently infected mice. T-cell modulation was done by treatments with DTA-1 anti- glucocorticoid-induced tumor necrosis factor receptor monoclonal antibodies. The DTA-1 monoclonal antibody is nondepleting and delivers costimulatory signals that both enhance the activation of effector T cells and inhibit suppression by regulatory T cells. DTA-1 therapy produced faster Th1 immune responses, significant reductions in both acute virus loads and pathology and, most importantly, long-term improvement of CD8(+) T-cell-mediated antitumor responses.

Iron, the HFE gene, and hepatitis C

Intrahepatic iron overload is commonly seen in chronic hepatitis C infection. High levels of intrahepatic iron may lead to accelerated liver injury and development of fibrosis and cirrhosis. This is frequently seen in hereditary hemochromatosis, which in most of the cases is caused by homozygous mutations in the HFE gene. In patients suffering from chronic hepatitis C, the presence of heterozygous HFE mutations associates with higher hepatic iron scores and advanced stages of fibrosis. HFE mutations must therefore be considered as important comorbidity factors in chronic hepatitis C infection.

Prospects for dendritic cell vaccination in persistent infection with hepatitis C virus

Although hepatitis C virus (HCV) is classified in the Hepacivirus genus in the family Flaviviridae, it is unlike most of the other members of this family due to its propensity to cause persistent infections. This persistent infection eventually results in chronic liver disease, cirrhosis and hepatocellular carcinoma in a proportion of infected individuals. It has been difficult to examine correlates of clearance or persistence because most acute phase HCV infections are subclinical or result in symptoms which are non-specific; consequently, acute infections are not generally recognised and patients often present many years later with persistent infection and accompanying chronic liver disease. Nevertheless, seminal studies, performed during the acute phase, have identified a number of factors which are likely to influence the outcome of infection, although it is possible that the mechanism is multifactorial. One of these factors is impairment of dendritic cell function by a mechanism resulting from expression of an HCV protein(s) in these cells. This may be a major factor in the failure of the immune response to expand after HCV infection, leading to persistence. Nevertheless, it may be possible to overcome this defect by autologous transfusion of HCV antigen-loaded, mature dendritic cells and the purpose of this review is to highlight the need and general approaches for developing dendritic cell-based immunotherapy for HCV infection.

Different procarcinogenic potentials of lymphocyte subsets in a transgenic mouse model of chronic hepatitis B

The immune response to hepatitis viruses is believed to be involved in the development of chronic hepatitis; however, its pathogenetic potential has not been clearly defined. The current study, using a transgenic mouse model of chronic hepatitis B, was designed to determine the relative contributions of the immune cell subsets to the progression of liver disease that induces hepatocellular carcinogenesis. Hepatitis B virus transgenic mice were adoptively transferred with CD4+ and CD8+ T cell-enriched or -depleted and B cell-depleted splenocytes obtained from hepatitis B surface antigen-primed, syngeneic nontransgenic donors. The resultant liver disease, hepatocyte apoptosis, regeneration, and tumor development were assessed and compared with the manifestations in mice that had received unfractionated spleen cells. Transfer of CD8(+)-enriched splenocytes caused prolonged disease kinetics, and a marked increase in the extent of hepatocyte apoptosis and regeneration. In 12 of 14 mice the transfer resulted in multiple hepatocellular carcinomas (HCCs) comparable with the manifestations seen in the mice transferred with total splenocytes. In contrast, mice that had received CD4(+)-enriched cells demonstrated lower levels of liver disease and developed fewer incidences of HCC (4 of 17). The experiment also revealed that all of the groups of mice complicated with HCC developed comparable mean numbers and sizes of tumors. B-cell depletion had no effect on disease kinetics in this model. Taken together, these results demonstrate that the pathogenetic events induced by CD8+ T-cell subset are primarily responsible for the induction of chronic liver disease that increases tumor incidence, suggesting their potential in triggering the process of hepatocarcinogenesis.

Cytotoxic T lymphocytes derived from patients with chronic hepatitis C virus infection kill bystander cells via Fas-FasL interaction

The role of Fas-mediated lysis of hepatocytes in hepatitis C virus (HCV)-induced injury is frequently discussed. We therefore analyzed the effect of the number of HCV antigen-expressing cells, the mode of antigen presentation, and the number of cytotoxic T lymphocytes in a coculture system mimicking cellular components of the liver. Here, we show that endogenously processed HCV proteins are capable of inducing bystander killing. We further demonstrate that 0.8 to 1.5% of cells presenting HCV antigens suffice to induce lysis of 10 to 29% of bystander cells, suggesting that the mechanism may be operative at low fractions of infected versus uninfected hepatocytes in vivo. Our data underscore the role of the Fas pathway in HCV-related liver injury and support the exploration of Fas-based treatment strategies for patients with chronic hepatitis C virus infection.

Ex vivo analysis of human memory CD4 T cells specific for hepatitis C virus using MHC class II tetramers

Containment of hepatitis C virus (HCV) and other chronic human viral infections is associated with persistence of virus-specific CD4 T cells, but ex vivo characterization of circulating CD4 T cells has not been achieved. To further define the phenotype and function of these cells, we developed a novel approach for the generation of tetrameric forms of MHC class II/peptide complexes that is based on the cellular peptide-exchange mechanism. HLA-DR molecules were expressed as precursors with a covalently linked CLIP peptide, which could be efficiently exchanged with viral peptides following linker cleavage. In subjects who spontaneously resolved HCV viremia, but not in those with chronic progressive infection, HCV tetramer-labeled cells could be isolated by magnetic bead capture despite very low frequencies (1:1,200 to 1:111,000) among circulating CD4 T cells. These T cells expressed a set of surface receptors (CCR7+CD45RA-CD27+) indicative of a surveillance function for secondary lymphoid structures and had undergone significant in vivo selection since they utilized a restricted Vbeta repertoire. These studies demonstrate a relationship between clinical outcome and the presence of circulating CD4 T cells directed against this virus. Moreover, they show that rare populations of memory CD4 T cells can be studied ex vivo in human diseases.

Managing occupational risks for hepatitis C transmission in the health care setting

Hepatitis C virus (HCV) infection is a significant contemporary health problem in the United States and elsewhere. Because it is primarily transmitted via blood, hepatitis C infection presents risks for both nosocomial transmission to patients and occupational spread to health care workers. Recent insights into the pathogenesis, immunopathogenesis, natural history, and treatment of infection caused by this unique flavivirus provide a rationale for the use of new strategies for managing occupational hepatitis C infections when they occur. This article reviews this developing information. Recently published data demonstrate success rates in the treatment of "acute hepatitis C syndrome" that approach 100\%, and although these studies are not directly applicable to all occupational infections, they may provide important clues to optimal management strategies. In addition, the article delineates approaches to the prevention of occupational exposures and also addresses the difficult issue of managing HCV-infected health care providers. The article summarizes currently available data about the nosocomial epidemiology of HCV infection and the magnitude of risk and discusses several alternatives for managing exposure and infection. No evidence supports the use of immediate postexposure prophylaxis with immunoglobulin, immunomodulators, or antiviral agents. Based on the very limited data available, the watchful waiting and preemptive therapy strategies described in detail in this article represent reasonable interim approaches to the complex problem of managing occupational HCV infections, at least until more definitive data are obtained.

Differential proteasomal processing of hydrophobic and hydrophilic protein regions: contribution to cytotoxic T lymphocyte epitope clustering in HIV-1-Nef

HIV proteins contain a multitude of naturally processed cytotoxic T lymphocyte (CTL) epitopes that concentrate in clusters. The molecular basis of epitope clustering is of interest for understanding HIV immunogenicity and for vaccine design. We show that the CTL epitope clusters of HIV proteins predominantly coincide with hydrophobic regions, whereas the noncluster regions are predominantly hydrophilic. Analysis of the proteasomal degradation products of full-length HIV-Nef revealed a differential sensitivity of cluster and noncluster regions to proteasomal processing. Compared with the epitope-scarce noncluster regions, cluster regions are digested by proteasomes more intensively and with greater preference for hydrophobic P1 residues, resulting in substantially greater numbers of fragments with the sizes and COOH termini typical of epitopes and their precursors. Indeed, many of these fragments correspond to endogenously processed Nef epitopes and/or their potential precursors. The results suggest that differential proteasomal processing contributes importantly to the clustering of CTL epitopes in hydrophobic regions.

Hepatitis C virus E2 and NS5A region variability during sequential treatment with two interferon-alpha preparations

To determine the pattern and significance of the HCV genetic heterogeneity before and during treatment with recombinant-2b or lymphoblastoid alpha-interferon, hypervariable region 1 (HVR-1) and NS5A quasispecies were characterised by cloning and sequencing in 12 HCV-1b-infected subjects. Patients were either responder-relapsers or non-responders to treatment. Extensive amino acid sequence analysis was applied to reveal the significance of HCV variation at key sites within HVR-1 and NS5A regions. Genetic complexity, genetic diversity, and the non-synonymous to synonymous substitution ratios of HVR-1 quasispecies decreased during treatment in responder-relapser patients only, and more markedly so following lymphoblastoid alpha-interferon. In non-responders, the HVR-1 quasispecies broadened. Amino acids G406 and Q409, which represent a major viral epitope, were highly conserved throughout treatment. Responder-relapser patients had a higher mutation frequency in NS5A than non-responders. Lymphoblastoid alpha-interferon promoted the selection of intermediate Interferon Sensitivity Determining Region (ISDR) sequences, whereas recombinant-2b alpha-interferon favoured maintenance or selection of conserved ISDR sequences. Variability upstream of the ISDR was associated with treatment response, but the amino acid substitutions conferring higher replicative ability to in vitro HCV replicons were absent in in vivo isolates. In conclusion, the pattern of HVR-1 quasispecies evolution correlates with the clinical response, and the conservation of specific amino acids may be useful for immune targeting in vivo. In responder-relapser patients, the initial HVR-1 evolution resembles that found in sustained responders. Variability within the entire NS5A, as opposed to a single region (ISDR), may have a role in influencing alpha-interferon treatment outcome. A differential effect of different alpha-interferon preparations on HCV quasispecies kinetics may exist.

In vitro-induced antibody production in chronic hepatitis C virus infection

The objectives of the present study were to assess the in vitro-induced anti-hepatitis C virus (HCV) antibody production (IVIAP) in relation to the clinical, biochemical, virologic and histologic variables of patients with HCV infection. The study included 57 patients (60% males) with HCV infection (anti-HCV and HCV-RNA positive). Alanine aminotransferase (ALT) was elevated in 89% of the patients. Mean viral load was 542,241 copies/ml and histology of the liver showed chronic hepatitis in 27/52 (52%) and cirrhosis in 11/52 (21%) patients. IVIAP levels were determined by immunoenzymatic assay at median absorbance of 0.781 at 450 nm. IVIAP was negative in 14% of the patients. When groups with IVIAP levels above and below the median were compared, high IVIAP levels were associated with the male sex, elevated ALT levels and more advanced disease stage. After logistic regression analysis, advanced histologic damage to the liver remained as the only independent variable associated with elevated IVIAP levels. Using a receiver operator characteristic curve, the best cut-off level for IVIAP was established (= 1.540), with 71% sensitivity and 94% specificity for the detection of more advanced disease stages (grades 3 and 4). These findings are consistent with the participation of immunological mechanisms in the genesis of the hepatic lesions induced by HCV and indicate that the IVIAP test may be useful as a noninvasive marker of liver damage either alone or in combination with other markers.

Generation of CTL responses using Kunjin replicon RNA

The Kunjin replicon was used to express a polytope that consisted of seven hepatitis C virus cytotoxic T lymphocyte epitopes and one influenza cytotoxic T lymphocyte epitope for vaccination studies. The self-replicating nature of, and expression from, the ribonucleic acid was confirmed in vitro. Initial vaccinations with one dose of Kun-Poly ribonucleic acid showed that an influenza-specific cytotoxic T lymphocyte response was elicited more efficiently by intradermal inoculation compared with intramuscular delivery. Two micrograms of ribonucleic acid delivered in the ear pinnae of mice was sufficient to elicit a detectable cytotoxic T lymphocyte response 10 days post-vaccination. Further vaccination studies showed that four of the seven hepatitis C virus cytotoxic T lymphocyte epitopes were able to elicit weak cytotoxic T lymphocyte responses whereas the influenza epitope was able to elicit strong, specific cytotoxic T lymphocyte responses following three doses of Kun-Poly ribonucleic acid. These studies vindicate the use of the Kunjin replicon as a vector to deliver encoded proteins for the development of cell-mediated immune responses.

Tissue culture and animal models for hepatitis C virus

In recent years, significant advances have been achieved both in the development of animal- and tissue-culture models for HCV. Among all the new systems, the small animal model based on transgenic mice with chimeric mouse-human livers and the replicon system will presumably have the most profound impact on future HCV research. Yet, in spite of this progress, much more work will be required to optimizse both systems. In case of the mouse model, breeding homozygous Alb-uPa animals is difficult because of the toxicity of the transgene, and the transplantation of primary human hepatocytes into mice a few days after birth is technically challenging. These are immunodeficient, and, therefore, it will be desirable to furnish them with components of the human immune system in order to expand the applicability of this in vivo model to questions related to pathogenesis. Advances in cryopreservation techniques are urgently needed, moreover, as this would improve the availability of primary hepatocytes and in turn also the accessibility of this small animal model. As regards the replicon system, a number of open questions remain that will hopefully be answered by future research. Why, for instance, has replication in cell culture so far been achieved only with genotype 1b isolates, whereas an isolate with proven infectivity derived from genotype 1a failed to replicate in Huh-7 cells? And why can replicons so far be propagated only in this particular cell line? Is this attributable to the lack of certain inhibitory factors, or the presence of specific activators? What are the mechanisms underlying cell-culture adaptation. and what determines whether a certain Huh-7 cell replicates HCV RNA more efficiently? Finally, the replicon system may also lead the way to the development of systems for efficient virus production in cell culture, and ultimately also a permissive cell line. These developments would at last allow us to model the complete viral life cycle, something researchers have been struggling with ever since the first identification of HCV.

Immunopathogenesis of hepatitis C virus infection

HCV infection becomes persistent in many patients who are otherwise immune competent. There is increasing support for potential contribution of innate immune response and viral interference with its components to the subsequent outcome. As for the adaptive immune response, humoral immunity may be largely ineffective despite evidence for neutralizing antibody response directed to the E2 HVR region, perhaps due to rapid selection of antibody escape variants. Cellular immune response does seem to play a role in the virologic outcome during acute infection based on strong association of a sustained vigorous and multispecific antiviral CD4 and CD8 T cell response with HCV clearance during acute infection. Following clearance, vigorous CD4 T cell response to HCV is maintained for many years, whereas the memory CD8 T cell response may be maintained with variable efficiency. If unable to clear the virus quickly, the T cell response (particularly if focused) may also select for T cell escape variants that are poorly recognized by the circulating T cells or even actively inactivate them through T cell antagonism. In established chronic infection. HCV-specific T cell response is quantitatively weak, providing only minimal selection pressure for further escape mutation. Although earlier studies using conventional in vitro techniques suggest that this low-frequency T cell response may help control the virus and liver disease progression, the role and nature of these apparently defective T cells in the outcome of chronic HCV infection remains to be fully determined. In summary, much progress has been made in the field of HCV immune pathogenesis since the initial identification of HCV. Although more work is needed to define the mechanism of HCV persistence and liver cell injury, there is considerable hope as well as challenge for potential development of vaccine and immunotherapy for HCV infection (see article by Drs. Inchaupsé and Feinstone). A better understanding of the relevant host and viral factors for clinical and virologic outcome, and the mechanism of selective immune defect against HCV, will be invaluable in our ability to treat the many patients infected with HCV.

Opposing roles of STAT1 and STAT3 in T cell-mediated hepatitis: regulation by SOCS

T cell-mediated fulminant hepatitis is a life-threatening event for which the underlying mechanism is not fully understood. Injection of concanavalin A (Con A) into mice recapitulates the histological and pathological sequelae of T cell-mediated hepatitis. In this model, both signal transducer and activator of transcription factor 1 (STAT1) and STAT3 are activated in the liver. Disruption of the STAT1 gene by way of genetic knockout attenuates liver injury, suppresses CD4(+) and NK T cell activation, and downregulates expression of proapoptotic interferon regulatory factor-1 protein and suppressor of cytokine signaling-1 (SOCS1), but enhances STAT3 activation and STAT3-controlled antiapoptotic signals. Studies from IFN-gamma-deficient mice indicate that IFN-gamma not only is the major cytokine responsible for STAT1 activation but also partially accounts for STAT3 activation. Moreover, downregulation of STAT3 activation in IL-6-deficient mice is associated with decreased STAT3-controlled antiapoptotic signals and expression of SOCS3, but upregulation of STAT1 activation and STAT1-induced proapoptotic signals and exacerbation of liver injury. Taken together, these findings suggest that STAT1 plays a harmful role in Con A-mediated hepatitis by activation of CD4(+) and NK T cells and directly inducing hepatocyte death, whereas STAT3 protects against liver injury by suppression of IFN-gamma signaling and induction of antiapoptotic protein Bcl-X(L). STAT1 and STAT3 in hepatocytes also negatively regulate one another through the induction of SOCS.

Comparative vaccine studies in HLA-A2.1-transgenic mice reveal a clustered organization of epitopes presented in hepatitis C virus natural infection

A polyepitopic CD8(+)-T-cell response is thought to be critical for control of hepatitis C virus (HCV) infection. Using transgenic mice, we analyzed the immunogenicity and dominance of most known HLA-A2.1 epitopes presented during infection by using vaccines that carry the potential to enter clinical trials: peptides, DNA, and recombinant adenoviruses. The vaccines capacity to induce specific cytotoxic T lymphocytes and interferon gamma-producing cells revealed that immunogenic epitopes are clustered in specific antigens. For two key antigens, flanking regions were shown to greatly enhance the scope of epitope recognition, whereas a DNA-adenovirus prime-boost vaccination strategy augmented epitope immunogenicity, even that of subdominant ones. The present study reveals a clustered organization of HCV immunogenic HLA.A2.1 epitopes and strategies to modulate their dominance.

Opposing roles of STAT1 and STAT3 in T cell-mediated hepatitis: regulation by SOCS

T cell-mediated fulminant hepatitis is a life-threatening event for which the underlying mechanism is not fully understood. Injection of concanavalin A (Con A) into mice recapitulates the histological and pathological sequelae of T cell-mediated hepatitis. In this model, both signal transducer and activator of transcription factor 1 (STAT1) and STAT3 are activated in the liver. Disruption of the STAT1 gene by way of genetic knockout attenuates liver injury, suppresses CD4(+) and NK T cell activation, and downregulates expression of proapoptotic interferon regulatory factor-1 protein and suppressor of cytokine signaling-1 (SOCS1), but enhances STAT3 activation and STAT3-controlled antiapoptotic signals. Studies from IFN-gamma-deficient mice indicate that IFN-gamma not only is the major cytokine responsible for STAT1 activation but also partially accounts for STAT3 activation. Moreover, downregulation of STAT3 activation in IL-6-deficient mice is associated with decreased STAT3-controlled antiapoptotic signals and expression of SOCS3, but upregulation of STAT1 activation and STAT1-induced proapoptotic signals and exacerbation of liver injury. Taken together, these findings suggest that STAT1 plays a harmful role in Con A-mediated hepatitis by activation of CD4(+) and NK T cells and directly inducing hepatocyte death, whereas STAT3 protects against liver injury by suppression of IFN-gamma signaling and induction of antiapoptotic protein Bcl-X(L). STAT1 and STAT3 in hepatocytes also negatively regulate one another through the induction of SOCS.

Features of the CD4+ T-cell response in liver and peripheral blood of hepatitis C virus-infected patients with persistently normal and abnormal alanine aminotransferase levels

BACKGROUND/AIMS

The liver is the primary site of hepatitis C virus (HCV) replication; intrahepatic T-cell responses may influence liver disease severity.

METHODS

HCV-specific CD4(+) T-cell reactivity was investigated ex vivo in paired liver tissue and peripheral blood from 42 chronic HCV patients.

RESULTS

The frequencies with which HCV-specific HLA class-II-restricted CD4(+) T-cell proliferation were observed were 29% in liver and 36% in peripheral blood. Among responses, non-structural-3 protein (NS3)-specific T-cell proliferation was dominant but non-exclusive and did rarely occur concurrently in liver infiltrate and peripheral blood suggesting liver compartmentalization of a CD4(+) T-cells population. Compared with 24 patients with abnormal ALT levels, 18 HCV carriers with persistently normal ALT levels had similar serum and liver viral loads but showed: (i) a low-activity grade and stage chronic hepatitis (P<0.001); (ii) less intrahepatic CD4(+) T-lymphocytes (P<0.01); (iii) less frequent intrahepatic (17 vs. 33%) and peripheral (17 vs. 38%) NS3-specific CD4(+) T-cell proliferation; (iv) less often in vitro T-helper (Th)1 (interferon-gamma) cytokine production (2 vs. 18%; P<0.001).

CONCLUSIONS

Our data show a low frequency of intrahepatic HCV-specific HLA class-II-restricted CD4(+) Th1 responses in patients with chronic HCV. However, these Th1 responses are detected more often in those patients with overt clinical and histological disease.

Transfection of single-stranded hepatitis A virus RNA activates MHC class I pathway

Although infection of single-stranded RNA viruses can enhance expression of major histocompatibility complex (MHC) class I genes, the mechanism underlying this process remains unclear. Recent studies have indicated that exposure of non-immune cells to double-stranded deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) of viral origin can directly increase the expression of MHC class I and related molecules without immune cell interaction. In this report, we show that transfection of single-stranded hepatitis A virus RNA into cultured hepatocytes results in the induction of genes for MHC class I, LMP2 and transporter for antigen processing (TAP1), in addition to the generation of viral proteins. We suggest that this stimulatory effect is due to the double-stranded RNA formed during replication of single-stranded viral RNA, and involves both double-stranded, RNA-dependent protein kinase PKR and the secretion of IFNbeta.

Quantitative and functional differences in CD8+ lymphocyte responses in resolved acute and chronic hepatitis C virus infection

CD8+ T lymphocyte responses are important in the clearance of viral infections. In chronic infections they may contribute to pathogenesis. To investigate the role of CD8+ T lymphocyte responses in viral clearance and chronic hepatitis C we have compared hepatitis C virus (HCV) specific cytotoxicity and interferon-gamma (IFN-gamma) production in patients with resolved-acute, and chronic HCV infection. CD8+ T cell responses to a panel of 13 HCV T cell peptide epitopes were studied using Elispot assays of IFN-gamma production and chromium release cytotoxicity assays. Responses of seven patients with resolved acute HCV infection were compared with those of 14 chronically infected patients. HCV-specific cytotoxicity differentiated the two populations of patients. The majority (71%) of patients with resolved acute infection tested positive to 42% of relevant peptides compared with the minority (28%) of patients with chronic hepatitis C (P=0.03) who responded to only 8% of relevant peptides (P=0.0009). In contrast, HCV-specific IFN-gamma production was detected in 86% of patients with either resolved or chronic infection in response to 42% and 35%, respectively, of relevant peptides tested (not significant). In patients with chronic infection the magnitude of the HCV-specific IFN-gamma production was inversely correlated to viral load (R2=0.52; P=0.042). Failure to clear HCV infection may be attributable to the presence of noncytolytic IFN-gamma producing CD8+ T lymphocytes in chronically infected patients. However these CD8+ T cells may play a beneficial role in contributing to the control of viral load in chronic hepatitis C.

Immunopathogenesis of hepatitis C virus infection

Hepatitis C virus, a recently identified member of the family Flaviviridae, is an important cause of chronic viral hepatitis and cirrhosis. There are similarities in the nature of the immune response to this pathogen with immunity in other flavivirus and hepatotropic virus infections, such as hepatitis B. However, the high rate of viral persistence after primary hepatitis C infection, and the observation that neutralizing antibodies are not protective, would suggest that there are a number of important differences between hepatitis C, other flaviviruses, and hepatitis B. The phenomenon of quasispecies evolution and other viral factors have been proposed to contribute to immune evasion by hepatitis C virus. In the face of established persistent infection, virus-specific cytotoxic T lymphocytes may exert some control over viral replication. However, these same effectors may also be responsible for the progressive liver damage characteristic of chronic hepatitis C infection. The nature of protective immunity, including the role of innate immune responses early after hepatitis C exposure, remains to be defined.

Determinants of viral clearance and persistence during acute hepatitis C virus infection

The virological and immunological features of hepatitis C virus (HCV) infection were studied weekly for 6 months after accidental needlestick exposure in five health care workers, four of whom developed acute hepatitis that progressed to chronicity while one subject cleared the virus. In all subjects, viremia was first detectable within 1-2 weeks of inoculation, 1 month or more before the appearance of virus-specific T cells. The subject who cleared the virus experienced a prolonged episode of acute hepatitis that coincided with a CD38+ IFN-gamma- CD8+ T cell response to HCV and a small reduction in viremia. Subsequently, a strong CD4+ T cell response emerged and the CD8+ T cells became CD38- and started producing IFN-gamma in response to HCV, coinciding with a rapid 100,000-fold decrease in viremia that occurred without a corresponding surge of disease activity. Chronic infection developed in two subjects who failed to produce a significant T cell response and in two other subjects who initially mounted strong CD4+ T cell responses that ultimately waned. In all subjects, viremia was higher at the peak of acute hepatitis than it was when the disease began, and the disease improved during the viremia. These results provide the first insight into the host-virus relationship in humans during the incubation phase of acute HCV infection, and they provide the only insight to date into the virological and immunological characteristics of clinically asymptomatic acute HCV infection, the commonest manifestation of this disease. In addition, the results suggest that the vigor and quality of the antiviral T cell response determines the outcome of acute HCV infection, that the ability of HCV to outpace the T cell response may contribute to its tendency to persist; that the onset of hepatitis coincides with the onset of the CD8+ T cell response, that disease pathogenesis and viral clearance are mediated by different CD8+ T cell populations that control HCV by both cytolytic and noncytolytic mechanisms, and that there are different pathways to viral persistence in asymptomatic and symptomatic acute HCV infection.

Natural cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC) is not impaired in patients suffering from chronic hepatitis C

BACKGROUND/AIMS

Recent observations suggest that natural killer (NK) cell activity might be impaired in chronic hepatitis C. However, to date antibody-dependent cellular cytotoxicity (ADCC) has not been studied in chronic hepatitis C in detail.

METHODS

Therefore, we investigated spontaneous and cytokine-induced (interleukin-2 and interferon-gamma) natural cytotoxicity and ADCC in 29 patients suffering from chronic hepatitis C and 19 healthy controls. Cytotoxicity was determined with a flow-cytometric assay, which can also assess monocyte cytotoxicity. As target cells we used the colorectal tumor cell line HT29 and the lymphoma cell line Raji.

RESULTS

We found no significant differences with respect to spontaneous cytotoxicity (HCV versus healthy controls (32 vs. 46%) and 17-1A specific ADCC (59 vs. 48%), even if isolated monocytes or NK cells were studied. Preincubation and stimulation of effector cells with cytokines increased both natural cytotoxicity and ADCC by 20-30%. However, natural cytotoxicity and ADCC after stimulation did not differ between the two groups.

CONCLUSIONS

Our data obtained with a long-term cytotoxicity assay do not reveal impaired cytolytic capacity of the innate immune system in chronic hepatitis C, even when isolated monocytes and NK cells were studied as effector cells.

Different levels of T-cell receptor triggering induce distinct functions in hepatitis B and hepatitis C virus-specific human CD4(+) T-cell clones

CD4(+) T cells play a major role in the host defense against viruses and intracellular microbes. During the natural course of such an infection, specific CD4(+) T cells are exposed to a wide range of antigen concentrations depending on the body compartment and the stage of disease. While epitope variants trigger only subsets of T-cell effector functions, the response of virus-specific CD4(+) T cells to various concentrations of the wild-type antigen has not been systematically studied. We stimulated hepatitis B virus core- and hepatitis C virus NS3-specific CD4(+) T-cell clones which had been isolated from patients with acute hepatitis during viral clearance with a wide range of specific antigen concentrations and determined the phenotypic changes and the induction of T-cell effector functions in relation to T-cell receptor internalization. A low antigen concentration induced the expression of T-cell activation markers and adhesion molecules in CD4(+) T-cell clones in the absence of cytokine secretion and proliferation. The expression of CD25, HLA-DR, CD69, and intercellular cell adhesion molecule 1 increased as soon as T-cell receptor internalization became detectable. A 30- to 100-fold-higher antigen concentration, corresponding to the internalization of 20 to 30% of T-cell receptor molecules, however, was required for the induction of proliferation as well as for gamma interferon and interleukin-4 secretion. These data indicate that virus-specific CD4(+) T cells can respond to specific antigen in a graded manner depending on the antigen concentration, which may have implications for a coordinate regulation of specific CD4(+) T-cell responses.

The chimpanzee model of hepatitis C virus infections

The chimpanzee (Pan troglodytes) is the only experimental animal susceptible to infection with hepatitis C virus (HCV). The chimpanzee model of HCV infection was instrumental in the initial studies on non-A, non-B hepatitis, including observations on the clinical course of infection, determination of the physical properties of the virus, and eventual cloning of the HCV nucleic acid. This review focuses on more recent aspects of the use of the chimpanzee in HCV research. The chimpanzee model has been critical for the analysis of early events in HCV infection because it represents a population for which samples are available from the time of exposure and all exposed animals are examined. For this reason, the chimpanzee represents a truly nonselected population. In contrast, human cohorts are often selected for disease status or antibody reactivity and typically include individuals that have been infected for decades. The chimpanzee model is essential to an improved understanding of the factors involved in viral clearance, analysis of the immune response to infection, and the development of vaccines. The development of infectious cDNA clones of HCV was dependent on the use of chimpanzees, and they will continue to be needed in the use of reverse genetics to evaluate critical sequences for viral replication. In addition, chimpanzees have been used in conjunction with DNA microarray technology to probe the entire spectrum of changes in liver gene expression during the course of HCV infection. The chimpanzee will continue to provide a critical aspect to the understanding of HCV disease and the development of therapeutic modalities.

Lipidation of T helper sequences from hepatitis C virus core significantly enhances T-cell activity in vitro

Successful elimination of the hepatitis C virus (HCV) during acute infection has been linked to strong HCV-specific in vitro T-cell proliferation, whereas T cells from patients with chronic hepatitis C respond only weakly to HCV antigens. Lipid-coupled peptides are immunostimulants, which might provide a basis for novel therapeutic strategies against HCV. Therefore, in 20 patients with chronic hepatitis C, we studied whether tri-palmitoyl-S-cysteine-coupled peptides could modify in vitro T-cell proliferation (by [3H]thymidine uptake) in response to virus core and NS4. The lipopeptides corresponded to five immunodominant T helper epitopes of HCV core. Contrary to unmodified peptides, the lipopeptides specifically enhanced [3H]thymidine uptake in response to HCV antigens but not to a non-HCV related control antigen. They increased the frequency of responders (stimulation index, SI > or = 4) to core (13/20 versus 2/20; p = 0.0008) and NS4 (20/20 versus 7/20; p < 0.0001) among our patients with chronic hepatitis C. This immunostimulatory effect was dose-dependent, and was observed specifically with lipopeptides corresponding to the HCV epitopes. Our data demonstrate that the poor in vitro T-cell proliferation of patients with chronic hepatitis C can be improved when T cells are co-stimulated with HCV core-derived T helper lipopeptides, while the same peptides in unlipidated form had no effects. Thus, lipopeptides corresponding to HCV T-cell epitopes may offer novel immunomodulatory strategies against HCV.