Cellular immune responses persist and humoral responses decrease two decades after recovery from a single-source outbreak of hepatitis C

Safety and immunogenicity of HCV E1E2 vaccine adjuvanted with MF59 administered to healthy adults

BACKGROUND

Hepatitis C virus (HCV) causes chronic liver disease that often leads to cirrhosis and hepatocellular carcinoma. In animal studies, chimpanzees were protected against chronic infection following experimental challenge with either homologous or heterologous HCV genotype 1a strains which predominate in the USA and Canada. We describe the first in humans clinical trial of this prophylactic HCV vaccine.

METHODS

HCV E1E2 adjuvanted with MF59C.1 (an oil-in-water emulsion) was given at 3 different dosages on day 0 and weeks 4, 24 and 48 in a phase 1, placebo-controlled, dose escalation trial to healthy HCV-negative adults.

RESULTS

There was no significant difference in the proportion of subjects reporting adverse events across the groups. Following vaccination subjects developed antibodies detectable by ELISA, CD81 neutralization and VSV/HCV pseudotype neutralization. There were no significant differences between vaccine groups in the number of responders and geometric mean titers for each of the three assays. All subjects developed lymphocyte proliferation responses to E1E2 and an inverse response to increasing amounts of antigen was noted.

CONCLUSIONS

The vaccine was safe and generally well-tolerated at each of the 3 dosage levels and induced antibody and lymphoproliferative responses. A larger study to further evaluate safety and immunogenicity is warranted.

Hepatitis C virus evasion of adaptive immune responses: a model for viral persistence

Hepatitis C virus (HCV) infects over 170 million people worldwide and is a leading cause of cirrhosis and hepatocellular carcinoma. Approximately 20% [corrected] of those acutely infected clear the infection, whereas the remaining 80% [corrected] progress to chronic infection. Hepatitis C thus provides a model in which successful and unsuccessful responses can be compared to better understand the human response to viral infection. Our laboratory studies the strategies by which HCV evades the adaptive immune response. This review describes the impact of viral mutation on T cell recognition, the role of cell surface inhibitory receptors in recognition of HCV, and the development of antibodies that neutralize HCV infection. Understanding what constitutes an effective immune response in the control of HCV may enable the development of prophylactic and therapeutic vaccines for HCV and other chronic viral infections.

The seroprevalence of hepatitis C virus (HCV) among 559,890 first-time volunteer blood donors in China reflects regional heterogeneity in HCV prevalence and changes in blood donor recruitment models

BACKGROUND

A decrease in the prevalence of hepatitis C virus antibody (anti-HCV) has been reported among voluntary blood donors in some regions of China. However, the prevalence of HCV among volunteer blood donors in other regions of China has not been reported. The aim of this study was to investigate the seroprevalence of HCV among 559,890 first-time volunteer blood donors recruited during 2004 through 2007 at the Guangzhou Blood Center, China.

STUDY DESIGN AND METHODS

Anti-HCV was detected using two different third-generation enzyme immunoassay kits. HCV RNA was detected using reverse transcription-polymerase chain reaction (RT-PCR) targeting the 5'-untranslated region of HCV.

RESULTS

Among 559,890 donors, 1877 (0.335%) were positive for anti-HCV. The anti-HCV+ rate was significantly higher in males than females (0.37% vs. 0.28%; p < 0.001) and significantly lower among donors living in Guangdong Province than donors who had migrated from other locations (0.30% vs. 0.40%; p < 0.001). Among the 1877 anti-HCV+ donors, 450 were randomly selected for HCV nucleic acid amplification by RT-PCR. Of these, 270 (60%) were HCV RNA+ and 180 (40%) were HCV RNA-.

CONCLUSIONS

Many donors from outside Guangdong Province were migrant laborers from other areas in China, suggesting that there is regional heterogenicity in HCV prevalence within China. The overall anti-HCV+ rate reported here is among the lowest reported among blood donors in China reflecting the effect of the current recruitment of exclusively volunteer donors.

An overview about hepatitis C: a devastating virus

Hepatitis C (HCV) is the disease that has affected around 200 million people globally. HCV is a life threatening human pathogen, not only because of its high prevalence and worldwide burden but also because of the potentially serious complications of persistent HCV infection. Chronicity of the disease leads to cirrhosis, hepatocellular carcinoma and end-stage liver disease. HCV positive hepatocytes vary between less than 5% and up to 100%, indicating the high rate of replication of viral RNA. HCV has a very high mutational rate that enables it to escape the immune system. Viral diversity has two levels; the genotypes and Quasiaspecies. Major HCV genotypes constitute genotype 1, 2, 3, 4, 5 and 6 while more than 50 subtypes are known. All HCV genotypes have their particular patterns of geographical distribution and a slight drift in viral population has been observed in some parts of the globe.

Prospective follow-up of patients with acute hepatitis C virus infection in Brazil

BACKGROUND

The natural outcome of infection with hepatitis C virus (HCV) varies substantially among individuals. However, little is known about host and viral factors associated with a self-limiting or chronic evolution of HCV infection.

METHODS

From 1 January 2001 through 31 December 2008, a consecutive series of 65 patients from Rio de Janeiro, Brazil, with a well-documented diagnosis of acute HCV infection, acquired via various routes, were enrolled in this study. Patients were prospectively followed up for a median of 40 months after the estimated date of HCV infection with serial measurements of serum alanine aminotransferase, HCV RNA, and anti-HCV antibodies. Spontaneous viral clearance (SVC) was defined as undetectable levels of HCV RNA in serum, in the absence of treatment, for 3 consecutive HCV polymerase chain reaction tests within the first 6 months of follow-up. Cox proportional hazards regression was used to identify host and viral predictors of SVC.

RESULTS

The cumulative rate of SVC was 44.6% (95% confidence interval, 32.3%-57.5%). Compared with chronic HCV evolution, patients with self-limiting disease had significantly lower peak levels of anti-HCV antibodies (median, 109.0 vs 86.7 optical density-to-cutoff ratio [od/co]; P<.02), experienced disease symptoms more frequently (69.4% vs 100%; P<.001), and had lower viral load at first clinical presentation (median, 4.3 vs 0.0 log copies; P=.01). In multivariate analyses, low peak anti-HCV level (<93.5 od/co) was the only independent predictor for SVC; the hazard ratio compared with high anti-HCV levels (> or =93.5 od/co) was 2.62 (95% confidence interval, 1.11-6.19; P=.03).

CONCLUSION

Our data suggest that low levels of anti-HCV antibodies during the acute phase of HCV infection are independently related to spontaneous viral clearance.

Virus-specific CD4+ T cell responses in chronic HCV infection in blood and liver identified by antigen-specific upregulation of CD154

BACKGROUND & AIMS

Virus-specific CD4+ T cells play a major role in hepatitis C virus (HCV) infection. Viral clearance is associated with vigorous and multispecific CD4+ T cell responses, while chronic infection has been shown to be associated with weak or absent T cell responses. Most of these studies, however, have used functional assays to analyse virus-specific CD4+ T cell responses. Therefore, the important question, of whether virus-specific CD4+ T cells are completely absent or primarily impaired in specific effector functions during chronic infection, has yet to be analysed in detail.

METHODS

To address this issue, a novel assay, where CD4+ T cell frequencies can be determined by de novo CD154 (CD40 ligand) expression in response to HCV antigens, was used in a cohort of chronically infected HCV patients and patients who spontaneously resolved HCV infection. These responses were compared to functional assays, such as the IFN-gamma ELISpot and flow cytometry-based proliferative assays.

RESULTS

Our results reveal that using the CD154 assay, virus-specific CD4+ T cells are readily detectable during chronic HCV infection albeit at a lower frequency when compared to patients who spontaneously resolved the infection. Importantly, no CD4+ T cell responses were detectable from these patients when using functional assays. Finally, these cell populations were enriched in the intrahepatic compartment.

CONCLUSIONS

Our findings suggest that HCV-specific CD4+ T cell responses are readily detectable in chronic HCV infection and enriched in the infected liver.

Virus-host interactions in hepatitis C virus infection: implications for molecular pathogenesis and antiviral strategies

With a global burden of 170 million chronically infected patients and a major cause of liver cirrhosis and hepatocellular carcinoma, hepatitis C virus (HCV) is a major public health challenge. Recent discoveries of viral and cellular factors mediating virus-host interactions have allowed scientists to uncover the key molecular mechanisms of viral infection and escape from innate and adaptive immune responses. These include the discovery of tight junction proteins as entry factors and microRNA-122, cyclophilins and lipoproteins as host factors for virus translation, replication and production. Furthermore, global genetic analyses have identified IL-28B as a genetic factor associated with the outcome of HCV infection. These discoveries markedly advance the understanding of the molecular pathogenesis of HCV infection and uncover novel targets for urgently needed antiviral strategies.

Natural epitope variants of the hepatitis C virus impair cytotoxic T lymphocyte activity

AIM: To understand how interactions between hepatitis C virus (HCV) and the host’s immune system might lead to viral persistence or effective elimination of HCV.

METHODS: Nucleotides 3519-3935 of the non-structural 3 (NS3) region were amplified by using reverse transcription polymerase chain reaction (PCR). PCR products of the HCV NS3 regions were integrated into a PCR^® T7TOPO^® TA vector and then sequenced in both directions using an automated DNA sequencer. Relative major histocompatibility complex binding levels of wild-type and variant peptides were performed by fluorescence polarization-based peptide competition assays. Peptides with wild type and variant sequences of NS3 were synthesized locally using F-moc chemistry and purified by high-performance liquid chromatography. Specific cytotoxic T lymphocytes (CTLs) clones toward HCV NS3 wild-type peptides were generated through limiting dilution cloning. The CTL clones specifically recognizing HCV NS3 wild-type peptides were tested by tetramer staining and flow cytometry. Cytolytic activity of CTL clones was measured using target cells labeled with the fluorescence enhancing ligand, DELFIA EuTDA.

RESULTS: The pattern of natural variants within three human leukocyte antigen (HLA)-A2-restricted NS3 epitopes has been examined in one patient with chronic HCV infection at 12, 28 and 63 mo post-infection. Results obtained may provide convincing evidence of immune selection pressure for all epitopes investigated. Statistical analysis of the extensive sequence variation found within these NS3 epitopes favors a Darwinian selection model of variant viruses. Mutations within the epitopes coincided with the decline of CTL responses, and peptide-binding studies suggested a significant impact of the mutation on T cell recognition rather than peptide presentation by HLA molecules. While most variants were either not recognized or elicited low responses, such could antagonize CTL responses to target cells pulsed with wild-type peptides.

CONCLUSION: Cross-recognition of CTL epitopes from wild-type and naturally-occurring HCV variants may lead to impaired immune responses and ultimately contribute to viral persistence.

Core-specific adaptive regulatory T-cells in different outcomes of hepatitis C

CD4+ Treg-cells (regulatory T-cells) probably contribute to the impaired virus-specific T-cell responses in chronic HCV (hepatitis C virus) infection; however, their antigen-specificity has remained elusive. In the present study, we analysed peripheral blood CD4+ Treg-cells in patients with chronic hepatitis C and subjects with self-limited HCV infection and characterized individual Treg-cell clones obtained from both groups at the phenotypic and functional level. Foxp3 (forkhead box p3)+CD25+CD4+ Treg-cells were detected more frequently in patients with chronic hepatitis C than self-limited HCV infection, which responded to HCV core stimulation and inhibited proliferation of reporter cells. Cloning under limiting dilution conditions resulted in 14 and six hypoproliferative Foxp3+CD25+CD127-CD4+ T-cell clones from patients with chronic hepatitis C and subjects with self-limited HCV infection respectively. All clones expressed Treg-cell markers and produced IL (interleukin)-10 upon mitogen stimulation. However, exclusively Treg-cell clones from chronic hepatitis C produced IL-10 in response to HCV core and inhibited proliferation of reporter T-cells. These core-specific Treg-cell clones recognized epitopes in two regions of HCV core (amino acids 1-44 and 79-113). Co-culture inhibition assays demonstrated Treg-cells to inhibit reporter T-cells via secretion of IL-10 and IL-35 rather than cell-contact-dependent mechanisms. Finally, the HCV-specific Treg-cell clones lost their functional capacity, along with Foxp3 expression, if kept in culture without HCV core exposure. In conclusion, we identified functionally active HCV core-specific Treg-cells in patients with chronic hepatitis C, which share their epitopes with conventional T-cells and require the continued presence of antigen to maintain their functional differentiation. Thus HCV core-specific Treg-cells may contribute to the immunoregulatory balance in chronic hepatitis C.

Abundant numbers of regulatory T cells localize to the liver of chronic hepatitis C infected patients and limit the extent of fibrosis

BACKGROUND & AIMS

Weak hepatitis C virus (HCV) specific immunity in peripheral blood has been shown to be partially controlled by regulatory T cells (Treg). However, little is known about Treg present in livers of HCV-infected patients, their association with clinical parameters, and immunopathology resulting in disease progression.

METHODS

The frequency and phenotype of CD4+FoxP3+ Treg, conventional CD4+ T cells, and the distribution of lymphocytes and leukocytes were studied by multi-color flowcytometry in liver and peripheral blood of 43 chronic HCV patients at different phases of liver disease. Comparisons between healthy blood and liver and correlations with disease parameters were made.

RESULTS

An extensive lymphocyte infiltration containing abundant numbers of CD4+FoxP3+ Treg was present in HCV-infected livers, while absent from healthy liver. Moreover, in all patients, intrahepatic CD4+FoxP3+ Treg showed a fully differentiated and highly activated phenotype on the basis of the surface markers CD45RO, CCR7, CTLA-4 and HLA-DR. These Treg were more numerous in those HCV-infected livers showing only limited fibrosis. However, HCV RNA loads or alanine transaminase levels did not correlate with CD4+FoxP3+ Treg frequencies.

CONCLUSIONS

Our data demonstrate that large numbers of highly activated and differentiated CD4+FoxP3+ Treg localize to the infiltrated chronic HCV-infected liver and may result in limiting the extent of fibrosis. This suggests that CD4+FoxP3+ Treg play a pivotal role in limiting collateral damage by suppressing excessive HCV-induced immune activation.

Characterization of the cellular immune response in hepatitis C virus infection

Hepatitis C virus (HCV), a hepatotropic RNA virus, is a major causative agent of chronic hepatitis, liver cirrhosis, and hepatocellular carcinomas. The host immune responses, especially cellular immune responses, play an important role in viral clearance, liver injury, and persistent HCV infection. A thorough characterization of the HCV cellular immune responses is important for understanding the interplays between host immune system and viral components, as well as for developing effective therapeutic and prophylactic HCV vaccines. Recent advances that provide better understanding the cell immune responses in HCV infection are summarized in this article.

HCV-core and NS3 antigens play disparate role in inducing regulatory or effector T cells in vivo: Implications for viral persistence or clearance

A distinguishing feature of HCV is its ability to persist in majority of the infected people. We investigated the role of HCV-core and NS3 in inducing effector T cells to mediate antiviral immunity. Our studies revealed that immunization with recombinant adenoviral vector containing HCV-core or NS3 leads to differential development of regulatory vs. effector T cells in mice, resulting in distinct outcomes of virus infection. For the first time, our studies directly demonstrate that HCV-core enhances both CD4(+) and CD8(+) T(regs) which possibly contribute to persistent infection, whereas HCV NS3 induces both CD4(+) and CD8(+) effector T cells to allow viral clearance.

Preservation of immune function and anti-hepatitis C virus (HCV) immune responses after liver transplantation in HIV-HCV coinfected patients (ANRS-HC08 "THEVIC" trial)

BACKGROUND/AIMS

Liver transplantation (LT) in immune-suppressed human immunodeficiency virus (HIV) and hepatitis C virus (HCV) coinfected patients is feasible but raises questions regarding the severity of HCV recurrence on the liver graft and preservation of immune function. We investigated whether LT is deleterious to the immune system.

METHODS

Fourteen HIV-HCV coinfected patients (HIV viral load [VL] <50 copies/ml; median CD4 count of 276/mm(3) pretransplantation) were grafted for HCV-cirrhosis and followed over 2 years. Nine patients received anti-HCV therapy post-transplantation. HCV and HIV VLs and degree of acute and chronic hepatitis were monitored. Peripheral blood T-cell phenotypes and interferon-gamma (IFN-gamma) immune responses against opportunistic pathogens, HCV, and HIV-1 p24 were evaluated.

RESULTS

Median HCV VLs, CD4 counts, T-cell subsets, and IFN-gamma-producing T-cell frequencies against opportunistic pathogens and HIV-1 p24 did not change over time. HCV-specific T cells were observed ex vivo in two patients pretransplantation and in two others post-transplantation. HCV-specific in vitro amplification enabled the detection of HCV-specific IFN-gamma-producing responses in three further patients post-transplantation. Anti-HCV responses were observed independently of anti-HCV therapy and were undetectable in patients with severe hepatitis or liver fibrosis.

CONCLUSIONS

These results demonstrate that LT in HIV-HCV coinfected patients is not deleterious to the immune system and does not alter immune responses directed against HCV, HIV, or opportunistic pathogens.

Liver is able to activate naïve CD8+ T cells with dysfunctional anti-viral activity in the murine system

The liver possesses distinct tolerogenic properties because of continuous exposure to bacterial constituents and nonpathogenic food antigen. The central immune mediators required for the generation of effective immune responses in the liver environment have not been fully elucidated. In this report, we demonstrate that the liver can indeed support effector CD8⁺ T cells during adenovirus infection when the T cells are primed in secondary lymphoid tissues. In contrast, when viral antigen is delivered predominantly to the liver via intravenous (IV) adenovirus infection, intrahepatic CD8⁺ T cells are significantly impaired in their ability to produce inflammatory cytokines and lyse target cells. Additionally, intrahepatic CD8⁺ T cells generated during IV adenovirus infection express elevated levels of PD-1. Notably, lower doses of adenovirus infection do not rescue the impaired effector function of intrahepatic CD8⁺ T cell responses. Instead, intrahepatic antigen recognition limits the generation of potent anti-viral responses at both priming and effector stages of the CD8⁺ T cell response and accounts for the dysfunctional CD8⁺ T cell response observed during IV adenovirus infection. These results also implicate that manipulation of antigen delivery will facilitate the design of improved vaccination strategies to persistent viral infection.

Coinfection with HIV-1 and HCV--a one-two punch

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, cirrhosis, and death; it is estimated that 180 million persons are infected with HCV worldwide. The consequences of HCV are worse in those who are coinfected with human immunodeficiency virus 1 (HIV-1), which is unfortunately a common scenario because of shared risk factors of the viruses. More studies into effects of HCV/HIV-1 coinfection are needed, but efforts have been hampered by limitations in our understanding of the combined pathogenesis of the 2 viruses. Gaining insight into the mechanisms that underlie the immunopathogenesis of these persistent viral infections could lead to new therapeutic strategies for patients with HCV/HIV-1 coinfection.

Prophylactic and Therapeutic Vaccination against Hepatitis C Virus (HCV): Developments and Future Perspectives

Studies in patients and chimpanzees that spontaneously clear Hepatitis C Virus (HCV) have demonstrated that natural immunity to the virus is induced during primary infections and that this immunity can be cross protective. These discoveries led to optimism regarding prophylactic HCV vaccines and a number of studies in the chimpanzee model have been performed, all of which resulted in modified infections after challenge but did not always prevent persistence of the virus. Therapeutic vaccine strategies have also been pursued in an effort to reduce the costs and side effects associated with anti-viral drug treatment. This review summarizes the studies performed thus far in both patients and chimpanzees for prophylactic and therapeutic vaccination, assesses the progress made and future perspectives.

Chronic hepatitis C and persistent occult hepatitis C virus infection are characterized by distinct immune cell cytokine expression profiles

Hepatitis C virus (HCV) replicates in immune cells in both chronic hepatitis C (CHC) and occult HCV infection, but the extent of virus replication in this compartment in these opposing infection forms varies greatly. It was unknown whether this could be linked to HCV genotype or to differences in host gene expression shaping the immune response, and whether HCV replication in immune cells is sensitive to endogenous antiviral cytokines. In this study, we uncovered that significantly greater HCV load in peripheral blood mononuclear cells (PBMC), but not in plasma, coincided with HCV genotypes 2 and 3 in CHC, but with genotype 1 in residual occult infection after clinical resolution of hepatitis C. Moreover, PBMC from individuals with occult infection transcribed significantly greater levels of IFN-alpha, IFN-gamma and TNF-alpha, but less interleukin (IL)-10 than those from CHC. In CHC, PBMC with low HCV load expressed significantly more IFN-gamma but less IL-12 than did cells with high virus content. In occult infection, HCV RNA detection in PBMC was associated with much lower IFN-alpha and IL-12 expression. Further, HCV replication in T lymphocytes could be completely eliminated by activation of endogenous IFN-gamma in CHC, but of IFN-alpha in occult infection. In conclusion, CHC and persistent occult HCV infection are characterized by clearly different profiles of antiviral cytokine response in circulating immune cells which are also different from those of healthy individuals. Higher expression of IL-10, combined with lower transcription of IFN-alpha, IFN-gamma and TNF-alpha, is associated with a more robust HCV replication in immune cells.

Significance of changes in serum IL-18 and IL-1β levels in patients with chronic hepatitis C

AIM: To investigate the roles of serum IL-18 and IL-1β in the progression of chronic hepatitis C and explore the correlation between serum IL-18 and IL-1β levels and the efficacy of interferon (IFN) therapy.

METHODS: The levels of IL-18 and IL-1β in the serum of 30 chronic hepatitis C patients were determined before and after they received IFN therapy to observe changes in the serum levels of the two cytokines in different periods after HCV infection. Moreover, the correlations of serum IL-18 and IL-1β levels with ALT level, HCV genotype, IL-2 and IL-6 levels were analyzed. The differences in the serum levels of the two cytokines were also compared between patients with response and nonresponse to interferon treatment. The levels of serum cytokines were determined by ELISA. HCV genotypes were classified by direct sequencing. HCV RNA loads were determined by fluorescence quantitative PCR.

RESULTS: The level of IL-18 in the serum of chronic hepatitis C patients was higher than that of healthy controls (1077.44 ± 657.58 ng/L vs 259.92 ± 328.47 ng/L, P < 0.001). No significant difference in the level of serum IL-1β was noted between chronic hepatitis C patients and healthy controls though it had an upward trend over time (in contrast to a downward trend for IL-18). Severe patients had higher serum IL-1β level than mild ones (4.99 ± 1.44 ng/L vs 3.68 ± 0.76 ng/L, P < 0.05). The levels of the two cytokines were not significantly different among patients with different genotypes or subtypes of HCV. The level of IL-18 was positively correlated with that of IL-2 (r = 0.434, P < 0.05) rather than IL-6. The level of IL-1β was not correlated with those of IL-2 and IL-6. No significant differences were noted in the serum levels of IL-18 and IL-1β between patients with response and nonresponse to IFN therapy.

CONCLUSION: Serum IL-18 and IL-1β levels may be correlated with the chronicity and severity of hepatitis C but can not be used for prediction of the efficacy of IFN therapy.

Hepatitis C virus versus innate and adaptive immune responses: a tale of coevolution and coexistence

Since the identification of the hepatitis C virus (HCV) 20 years ago, much progress has been made in our understanding of its life cycle and interaction with the host immune system. Much has been learned from HCV itself, which, via decades of coevolution, gained an intricate knowledge of host innate and adaptive immune responses and developed sophisticated ways to preempt, subvert, and antagonize them. This review discusses the clinical, virological, and immunological features of acute and chronic hepatitis C and the role of the immune response in spontaneous and treatment-induced HCV clearance.

Measurements of HCV neutralizing antibodies and of HCV-specific CD4+ and CD8+ cells using hepatitis C virus pseudo-particles (HCVpp)

BACKGROUND

For the medical management, it would be of great relevance to get a diagnostic marker predicting the outcome of infection.

OBJECTIVES

For this purpose, the envelope antigens of the individual HCV strain in a patient was tested for their capacity to induce neutralizing antibodies and cytotoxic T lymphocytes.

STUDY DESIGN

A system for the measurement of neutralizing antibodies as well as for the stimulation of a HCV-specific T-cell response using pseudo-typed HCV particles (HCVpp) was established. A report on results of a pilot study conducted with blood specimens of 19 chronically infected patients is also presented.

RESULTS

Neutralization of HCVpp could be measured in nearly all HCV sero-positive patient samples. Nevertheless, in more than half of the patient samples (11/19), no HCV-specific CD4+ response was detectable. In addition, HCV-specific CD8+ response was measurable in most of the patients when HCVpp were used for T-cell stimulation. Although the same antigens (HCVpp) were used, there was no relevant correlation between neutralization titers and T-cell response.

CONCLUSION

Our study shows that HCVpp are appropriate antigens for specific stimulation of lymphocytes as well as for the investigation of antibody neutralization activity.

Hepatitis C virus virology and new treatment targets

Hepatitis C virus (HCV) infection is the leading cause of chronic liver disease. An estimated 130 million people worldwide are persistently infected with HCV. Almost half of patients who have chronic HCV infection cannot be cured with the standard treatment consisting of pegylated IFN-alpha and ribavirin. For those patients who do not respond to this standard antiviral therapy, there is currently no approved treatment option available. Recent progress in structure determination of HCV proteins and development of a subgenomic replicon system enables the development of a specifically targeted antiviral therapy for hepatitis C. Many HCV-specific compounds are now under investigation in preclinical and clinical trials.

Serum BLyS/BAFF predicts the outcome of acute hepatitis C virus infection

B-lymphocyte stimulator/B activating factor (BLyS/BAFF) is a tumour necrosis factor-family cytokine that plays a key role in generating and maintaining the mature B-cell pool. BLyS/BAFF expression by macrophages is stimulated by interferon-gamma and interleukin-10, and its serum levels are increased in chronic hepatitis C (CHC). The aim of this study was to assess serum levels of BLyS/BAFF in patients with acute hepatitis C (AHC) and correlate them with disease outcome. We studied 28 patients with AHC (14 males, mean age 59.3 +/- 15 years), followed for at least 7 months since onset, comparing them with 86 CHC patients and 25 healthy blood donors (HBD). BLyS/BAFF levels were assessed at baseline (within 4 weeks of onset) and during follow-up. BLyS/BAFF median levels were significantly higher in AHC (1485 pg/mL) than in CHC (1058 pg/mL) and in HBD (980 pg/mL) (P < 0.001). BLyS/BAFF levels were higher in AHC patients evolving to chronicity (1980 pg/mL) than in those with a self-limited course (1200 pg/mL), (P = 0.02). By logistic regression analysis, higher BLyS/BAFF levels were independently associated with persistence of HCV infection (OR 29.7; 95% CI: 1.73-508.20). High serum levels of BLyS/BAFF at onset of AHC can predict its evolution to chronic infection.

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.

Hepatitis C virus and alcohol

This review will focus on the prevalence of hepatitis c virus (HCV) infection in alcoholics with and without liver disease. Evidence will be presented to demonstrate that ethanol and chronic HCV infection synergistically accelerate liver injury. Some of the major postulated mechanisms responsible for disease progression include high rates of apoptosis, lipid peroxidation, and generation of free radicals and reactive oxygen species with reduced antioxidant capacity of the liver. Acquisition and persistence of HCV infection may be due to the adverse effects of ethanol on humoral and cellular immune responses to HCV. Dendritic cells (DC) appear to be one of the major targets for ethanol's action and DC dysfunction impairs the ability of the host to generate viral specific cluster of differentiation 4 (CD4+) and cluster of differentiation 8 (CD8+) immune responses. There is a relationship between increased alcohol intake and decreased response to interferon (IFN) therapy, which may be reversed by abstinence. Clinical studies are needed to optimize treatment responses in alcoholic patients with chronic HCV infection.

Acute infection with a single hepatitis C virus strain in dialysis patients: Analysis of adaptive immune response and viral variability

BACKGROUND/AIMS

While the adaptive immune response is crucial for spontaneous resolution of acute hepatitis C virus (HCV) infection, it also constitutes the driving force for viral escape. For acutely HCV-infected dialysis patients, little is known about the host response and its impact on viral evolution.

METHODS

Four haemodialysis patients accidentally infected with the same HCV strain were prospectively investigated with respect to the clinical course, CD4+ and CD8+ T-cell responses, neutralizing antibodies, viral kinetics and sequence variability.

RESULTS

In one patient, a robust CD4+ T-cell response was associated with transient control of infection, while in the other patients, weak responses correlated with persistently high viremia. Despite the presence of CD8+ T-cell effectors in the first patient, no sequence differences were detected in targeted regions of the viral genome in any of the patients when viral persistence was established. Genetic stability in the envelope genes, including the hypervariable regions, correlated with low-level or absent neutralizing antibodies in all of the patients.

CONCLUSIONS

The establishment of viral persistence in the special patient group of dialysis patients is due to a failure of the adaptive immune system, as shown by the absence of significant T-cell and antibody responses, as well as viral variability.

Sustained virological response is associated with clearance of hepatitis C virus RNA and a decrease in hepatitis C virus antibody

BACKGROUND/AIM

Viral eradication in chronic hepatitis C patients with sustained virological response (SVR) after interferon (IFN) therapy remains controversial.

METHODS

During a long-term follow-up study, 157 patients with SVR to IFN-alpha-2b-based therapy were investigated with a transcription-mediated amplification (TMA) assay in serum. The hepatitis C virus (HCV) antibody was assessed by measuring the optical density (OD) (Axsym HCV v3.0) and the semiquantitative titres (RIBA HCV v3.0) of the HCV antibodies directed against the core, NS3, NS4 and NS5 proteins. A control group included 23 untreated patients with persistently normal serum alanine aminotransferase and detectable serum HCV-RNA.

RESULTS

The median duration of follow-up was 4.0 (0-10) years. Serum HCV-RNA remained undetectable in all patients. The mean HCV antibody OD were 93 +/- 19 and 45 +/- 21 before therapy and in the last available serum sample respectively (P=0.001). There was a marked decrease in the HCV antibodies directed against the NS3, NS4 and NS5 proteins (P=0.001), while the core protein titre remained strongly positive. The 23 control patients were followed for a median of 5 (2-14) years. The mean HCV antibody OD were 65 +/- 14 and 64 +/- 19 in the first and the last measurements, respectively (NS), and HCV antibody titres for structural and non-structural proteins remained unchanged.

CONCLUSION

This long-term study evaluating 157 patients demonstrated that SVR assessed by TMA is durable, and HCV antibodies were markedly decreased (mainly those directed against the non-structural proteins), emphasizing an absence of ongoing infection. These results strongly suggest that HCV infection cured in patients who achieve an SVR.

New insights into the immunopathogenesis of chronic hepatitis C

Despite the high propensity of hepatitis C virus to establish chronic viral persistence, immune-mediated viral clearance occurs in some patients, fostering hopes that therapeutic induction of specific antiviral immune responses might be able to contribute to viral clearance in chronically infected patients. Indeed, recent clinical trials of therapeutic vaccination have provided clear proof of concept that specific immunotherapy can reduce the viral load in some patients. Further improvement of these strategies will depend on a detailed analysis of the immunopathogenesis of chronic hepatitis C. Recent advances in our understanding of the mechanisms of down-regulation of virus-specific immune responses during chronic infection, including the role of regulatory T cells and inhibitory molecules such as programmed death receptor 1, may open up new avenues for second-generation immunotherapeutic interventions.

Cellular immune response to Hantaan virus nucleocapsid protein in the acute phase of hemorrhagic fever with renal syndrome: correlation with disease severity

BACKGROUND

The cellular immune response to Hantaan virus (HTNV) is incompletely understood, especially in humans.

METHODS

To investigate the cellular immunity during acute HTNV infection, the magnitude of the CD4(+) and CD8(+) T cell responses to HTNV nucleocapsid protein was quantitated by direct ex vivo interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot analysis, using an array of overlapping peptides.

RESULTS

We found that the combined frequencies of HTNV-specific T cells at the earliest available time point (5-8 days after fever onset) were significantly higher in patients who had mild or moderate hemorrhagic fever with renal syndrome (HFRS) than in those who had severe or critical HFRS (P= .006). Moreover, these frequencies were higher in patients with subsequent mild renal failure (maximum serum creatinine level, <or=707 micromol/L) than in those with subsequent severe renal failure (maximum serum creatinine level, >707 micromol/L) (P= .006). Kinetic analysis showed that a decrease in the serum creatinine level during the acute phase of illness was often accompanied by an increase in the magnitude of IFN-gamma-producing T cells.

CONCLUSION

Taken together with published data on the similar associations with neutralizing antibody, these data suggest that IFN-gamma-producing T cells may help reduce the risk of progression to acute renal failure caused by HTNV infection.

Comparisons of CD8+ T cells specific for human immunodeficiency virus, hepatitis C virus, and cytomegalovirus reveal differences in frequency, immunodominance, phenotype, and interleukin-2 responsiveness

To better understand the components of an effective immune response to human immunodeficiency virus (HIV), the CD8(+) T-cell responses to HIV, hepatitis C virus (HCV), and cytomegalovirus (CMV) were compared with regard to frequency, immunodominance, phenotype, and interleukin-2 (IL-2) responsiveness. Responses were examined in rare patients exhibiting durable immune-mediated control over HIV, termed long-term nonprogressors (LTNP) or elite controllers, and patients with progressive HIV infection (progressors). The magnitude of the virus-specific CD8(+) T-cell response targeting HIV, CMV, and HCV was not significantly different between LTNP and progressors, even though their capacity to proliferate to HIV antigens was preserved only in LTNP. In contrast to HIV-specific CD8(+) T-cell responses of LTNP, HLA B5701-restricted responses within CMV pp65 were rare and did not dominate the total CMV-specific response. Virus-specific CD8(+) T cells were predominantly CD27(+)45RO(+) for HIV and CD27(-)45RA(+) for CMV; however, these phenotypes were highly variable and heavily influenced by the degree of viremia. Although IL-2 induced significant expansions of CMV-specific CD8(+) T cells in LTNP and progressors by increasing both the numbers of cells entering the proliferating pool and the number of divisions, the proliferative capacity of a significant proportion of HIV-specific CD8(+) T cells was not restored with exogenous IL-2. These results suggest that immunodominance by HLA B5701-restricted cells is specific to HIV infection in LTNP and is not a feature of responses to other chronic viral infections. They also suggest that poor responsiveness to IL-2 is a property of HIV-specific CD8(+) T cells of progressors that is not shared with responses to other viruses over which immunologic control is maintained.

Cellular immune response to hepatitis C virus (HCV) in nonviremic blood donors with indeterminate anti-HCV reactivity

BACKGROUND

Blood donors with indeterminate hepatitis C virus antibody (anti-HCV) reactivity are rejected from blood donation. As they are mostly nonviremic, the source of these reactions remains unclear. Reasons for such findings can be resolved HCV infections as well as unspecific antibody reactions. The aim of this study was to investigate HCV-specific T-cell response in blood donors to determine the reason for the weak antibody detection.

STUDY DESIGN AND METHODS

Anti-HCV reactivity was tested in 72 blood donors initially diagnosed with an indeterminate HCV result by enzyme-linked immunosorbent assay and immunoblot. Cellular immune response was measured by proliferation assay and enzyme-linked immunosorbent spot analysis after stimulation with viral proteins core, NS3, and NS4.

RESULTS

In 56% of donors anti-HCV reactivity was detectable in the screening assay whereas 72% had a reaction in the confirmation immunoblot. Forty-six percent of donors had a cellular immune response against HCV proteins. The response was most frequent to NS3 protein.

CONCLUSION

In almost half of donors the indeterminate result in serologic testings could be explained by a previous resolved HCV infection as the pattern of T-cell response was similar to these patients. These findings indicate that HCV-specific antibodies disappear more rapidly after resolved infection than HCV-specific T cells. These results are important for counseling blood donors and patients with indeterminate serologic results.

T-cell vaccines that elicit effective immune responses against HCV in chimpanzees may create greater immune pressure for viral mutation

A prime/boost vaccine strategy that transfects antigen-presenting cells using ligand-modified immunoliposomes to efficiently deliver plasmid DNA, followed by boosting with non-replicating recombinant adenovirus was used in chimpanzees to generate HCV-specific memory T-cells. Three chimpanzees (two vaccines, one control) were immunized with immunoliposomes complexed with DNA expressing NS3-NS5B or complexed with empty vector. Animals were boosted with adenovirus expressing NS3-NS5B, or non-recombinant adenovirus (control). Using liposome delivery we were able to obtain specific HCV responses following DNA priming in the chimpanzees. This data and mouse immunization studies confirm this as a more efficient delivery system than direct intramuscular inoculations with naked DNA. Subsequent to the adenovirus boost significant increases in peripheral HCV-specific T-cell responses and intrahepatic IFN-gamma and CD3varepsilon mRNA were also observed in the two vaccinated animals. Following challenge (100 CID(50)) both vaccinated animals showed immediate and significant control of viral replication (peak titers 3.7x10(4) and 9x10(3)IU/mL at weeks 1 and 2), which coincided with increases in HCV-specific T-cell responses. Viral kinetics in the control animal were comparable to historical controls with exponential increases in titer during the first several weeks. One vaccinated animal developed a low-level persistent infection (2x10(3)IU/mL) which correlated with a decrease in HCV-specific T-cell responses. Circulating virus isolated from both vaccinated animals showed approximately 2-fold greater nonsynonymous mutation rates compared to controls and the nonsynonymous/synonymous mutation rate ratio was indicative of positive selection. These data suggest that although T-cell vaccines can induce immune responses capable of controlling HCV, they also induce high levels of immune pressure for the potential selection of escape mutants.

Identification of serologically silent occult hepatitis C virus infection by detecting immunoglobulin G antibody to a dominant HCV core peptide epitope

BACKGROUND/AIMS

Occult HCV infection has been described among anti-HCV-HCV RNA-negative individuals with abnormal transaminase values in whom HCV RNA is detected in liver.

METHODS

IgG antibody to an HCVcore-derived peptide (anti-HCVcore) was investigated in 145 patients with serologically silent occult HCV infection.

RESULTS

At the time of the diagnostic biopsy 45/145 (31%) occult HCV-infected patients tested IgG anti-HCVcore-positive but none of the 140 patients with HCV-unrelated liver disease (P<0.001). Among 23 IgG anti-HCVcore-positive patients at baseline, 22 remained antibody-reactive (one became antibody-negative). Similarly, 17/31 baseline anti-HCVcore-negative patients remained non-reactive whereas 14 seroconverted to IgG anti-HCVcore (although transiently in 10 patients). Thus, a total of 59/145 (40.7%) patients with occult HCV infection showed IgG anti-HCVcore reactivity at any time point analyzed, including 14 initially non-reactive patients. By supplemental immunoblot assay 16 sera reacted weakly with an HCVcore-peptide band (indeterminate result) of which 10 (62.5%) reacted in the IgG anti-HCVcore assay. Occult HCV-infected patients who tested anti-HCVcore-positive showed more frequently signs of necro-inflammation (P=0.035) and greater percentages of HCV RNA-positive hepatocytes (P=0.004) compared with those anti-HCVcore-negative.

CONCLUSIONS

This work documents that IgG anti-HCVcore testing identifies occult HCV infection among seronegative, non-viremic patients using screening tests and may be useful in tracking anti-HCV-negative infections.

Hepatitis C virus (HCV)--specific T cell responses in injection drug users with apparent resistance to HCV infection

BACKGROUND

Injection drug users (IDUs) are at risk of acquiring hepatitis C virus (HCV) infection. We have identified a cohort of long-term IDUs who remain uninfected by HCV despite high-risk behavior. We have categorized these subjects as "exposed uninfected" and have sought immunological correlates with this apparent resistance.

METHODS

We studied 40 exposed uninfected subjects testing negative for both HCV antibody and HCV RNA. Details of injection behavior were ascertained by questionnaire. In vitro interferon (IFN)-gamma production by T cells in response to HCV proteins (core, E1, NS3, NS4, and NS5) was quantified by enzyme-linked immunospot assay, and findings were compared with those in 21 healthy control subjects.

RESULTS

All exposed uninfected subjects reported sharing needles or other injection paraphernalia on multiple occasions. The mean duration of injecting was 9.3 years (range, 0.5-26 years), with a median estimated number of injection episodes of 8760. IFN-gamma production in response to HCV proteins was found in 23 (58%) of 40 exposed uninfected subjects versus 4 (19%) of 21 control subjects (P = .004), with 14 exposed uninfected subjects responding to multiple antigens, compared with none of the control subjects (P = .001).

CONCLUSIONS

The majority of long-term IDUs who remain uninfected by HCV despite their high-risk behavior have HCV-specific T cell responses. These responses were frequently found for multiple HCV proteins, making cross-reactivity to other homologous antigens unlikely. These responses may represent an immunological footprint of HCV exposure that has not resulted in viremia or HCV antibody seroconversion. The potential role played by these responses in protection from HCV infection is of clinical importance.

Natural killer cell function is intact after direct exposure to infectious hepatitis C virions

Although hepatitis C virus (HCV) has been shown to readily escape from virus-specific T and B cell responses, its effects on natural killer (NK) cells are less clear. Based on two previous reports that recombinant, truncated HCV E2 protein inhibits NK cell functions via crosslinking of CD81, it is now widely believed that HCV impairs NK cells as a means to establish persistence. However, the relevance of these findings has not been verified with HCV E2 expressed as part of intact virions. Here we employed a new cell culture system generating infectious HCV particles with genotype 1a and 2a structural proteins, and analyzed direct and indirect effects of HCV on human NK cells. Antibody-mediated crosslinking of CD16 stimulated and antibody-mediated crosslinking of CD81 inhibited NK cell activation and interferon gamma (IFN-gamma) production. However, infectious HCV itself had no effect even at titers that far exceeded HCV RNA and protein concentrations in the blood of infected patients. Consistent with these results, anti-CD81 but not HCV inhibited NK cell cytotoxicity. These results were independent of the presence or absence of HCV-binding antibodies and independent of the presence or absence of other peripheral blood mononuclear cell populations.

CONCLUSION

HCV 1a or 2a envelope proteins do not modulate NK cell function when expressed as a part of infectious HCV particles. Without direct inhibition by HCV, NK cells may become activated by cytokines in acute HCV infection and contribute to infection outcome and disease pathogenesis.

Hepatitis C virus-specific T-cell immune responses in seronegative injection drug users

T-cell responses to hepatitis C virus (HCV) antigens have been reported in high-risk HCV seronegative persons, suggesting that an effective cellular immune response might be able to clear infection without the development of antibodies. Such findings, however, could be explained by waning antibody or cross-reactivity to other antigens. To address these issues, we evaluated HCV-specific T-cell responses in 26 young (age 18-33 years) aviremic, seronegative injection drug users (IDUs) (median duration of injection, 6 years) by interferon-gamma enzyme-linked immunospot (ELISpot) assay using 429 overlapping HCV peptides pooled in 21 mixes. Seventeen aviremic, seropositive IDUs (spontaneous resolvers) and 15 healthy people were used as positive and negative controls, respectively. The percentage of patients with HCV-specific cellular immune responses was similar in seronegative and seropositive aviremic IDUs (46%vs 59%, P = 0.4), while these responses were not detected in any of the negative controls. Among the seronegative IDUs, six (23%) had intermediate to very strong responses to 10-20 peptide mixes and another six (23%) had moderately strong responses for two to six mixes. The 12 seronegative IDUs with HCV-specific T-cell responses had higher demographical and behavioural risk profiles than the 14 IDUs without T-cell responses (estimated risk of HCV infection, 0.47 vs 0.26, P < 0.01). In conclusion, HCV-specific T-cell responses are common among high-risk, seronegative IDUs. The responses are broad and are associated with risk factors for HCV exposure, suggesting that they reflect true exposure to HCV in seronegative persons.

Generation of immune responses against hepatitis C virus by dendritic cells containing NS5 protein-coated microparticles

Dendritic cells (DCs) internalize and process antigens as well as activate cellular immune responses. The aim of this study was to determine the capacity of DCs that contain antigen-coated magnetic beads to induce immunity against the nonstructural hepatitis C virus (HCV) antigen 5 (NS5). Splenocytes derived from Fms-like tyrosine kinase receptor 3 (Flt3) ligand-pretreated BALB/c mice were incubated with magnetic beads coated with HCV NS5, lipopolysaccharide (LPS), and/or anti-CD40; purified; and used for immunization. Cellular immunity was measured using cytotoxic T-lymphocyte (CTL) and T-cell proliferation assays, intracellular cytokine staining, and a syngeneic tumor challenge using NS5-expressing SP2/0 myeloma cells in vivo. Splenocytes isolated from animals vaccinated with DCs containing beads coated with NS5, LPS, and anti-CD40 secreted elevated levels of interleukin-2 (IL-2) and gamma interferon in the presence of NS5. The numbers of CD4(+), IL-2-producing cells were increased >5-fold in the group immunized with DCs containing beads coated with NS5, LPS, and anti-CD40, paralleled by an enhanced splenocyte proliferative response. Immunization promoted antigen-specific CTL activity threefold compared to the level for control mice and significantly reduced the growth of NS5-expressing tumor cells in vivo. Thus, strategies that employ NS5-coated beads induce cellular immune responses in mice, which correlate well with the natural immune responses that occur in individuals who resolve HCV.

Spontaneous viral clearance, viral load, and genotype distribution of hepatitis C virus (HCV) in HIV-infected patients with anti-HCV antibodies in Europe

BACKGROUND

Variables influencing serum hepatitis C virus (HCV) RNA levels and genotype distribution in individuals with human immunodeficiency virus (HIV) infection are not well known, nor are factors determining spontaneous clearance after exposure to HCV in this population.

METHODS

All HCV antibody (Ab)-positive patients with HIV infection in the EuroSIDA cohort who had stored samples were tested for serum HCV RNA, and HCV genotyping was done for subjects with viremia. Logistic regression was used to identify variables associated with spontaneous HCV clearance and HCV genotype 1.

RESULTS

Of 1940 HCV Ab-positive patients, 1496 (77%) were serum HCV RNA positive. Injection drug users (IDUs) were less likely to have spontaneously cleared HCV than were homosexual men (20% vs. 39%; adjusted odds ratio [aOR], 0.36 [95% confidence interval {CI}, 0.24-0.53]), whereas patients positive for hepatitis B surface antigen (HBsAg) were more likely to have spontaneously cleared HCV than were those negative for HBsAg (43% vs. 21%; aOR, 2.91 [95% CI, 1.94-4.38]). Of patients with HCV viremia, 786 (53%) carried HCV genotype 1, and 53 (4%), 440 (29%), and 217 (15%) carried HCV genotype 2, 3, and 4, respectively. A greater HCV RNA level was associated with a greater chance of being infected with HCV genotype 1 (aOR, 1.60 per 1 log higher [95% CI, 1.36-1.88]).

CONCLUSIONS

More than three-quarters of the HIV- and HCV Ab-positive patients in EuroSIDA showed active HCV replication. Viremia was more frequent in IDUs and, conversely, was less common in HBsAg-positive patients. Of the patients with HCV viremia analyzed, 53% were found to carry HCV genotype 1, and this genotype was associated with greater serum HCV RNA levels.

Immunology of hepatitis B and hepatitis C virus infections

Hepatitis B (HBV) and hepatitis C (HCV) viruses are the two major causes of chronic liver inflammation worldwide. Despite distinct virologic features, both viruses are preferentially hepatotropic, not directly cytopathic, and elicit liver diseases that share several aspects of their natural history. HBV and HCV infections also share some important features of the adaptive antiviral immune response. We describe the innate immune response in the early phase following infection, and how these early events may influence the development of the adaptive immune response in these two important viral infections. The mechanisms by which high levels of viral antigens, liver immunological features, the presence of regulatory T cells and impaired dendritic cell functions may maintain the HBV- and HCV-specific immunological failure, characteristic of chronic hepatitis B and C patients, are also evaluated.

Adaptive immune responses to hepatitis C virus: from viral immunobiology to a vaccine

Hepatitis C virus (HCV) causes chronic infection in approximately two-thirds of cases, leading to chronic hepatitis, liver cirrhosis, liver disease, liver failure, and hepatocellular carcinoma in a substantial proportion of the 170 million HCV-infected individuals worldwide. It is generally accepted that the cellular immune response plays the most important role in determining the outcome of HCV infection. First, vigorous, multispecific and sustained CD4+ and CD8+ T-cell responses are associated with viral clearance. Second, depletion studies in chimpanzees, the only other host of HCV besides humans, have shown that both CD4+ and CD8+ T-cells are required for virus elimination. Third, the host's human leukocyte antigen alleles, which restrict the repertoire of CD4+ and CD8+ T-cell responses, influence the outcome of infection. Of note, protective immunity has been demonstrated in population-based studies, as well as in experimentally infected chimpanzees. Thus, a detailed understanding of the mechanisms contributing to the failure of the antiviral immune response should allow successful development of prophylactic and therapeutic vaccination strategies.

Hepatic transcriptome analysis of hepatitis C virus infection in chimpanzees defines unique gene expression patterns associated with viral clearance

Hepatitis C virus infection leads to a high rate of chronicity. Mechanisms of viral clearance and persistence are still poorly understood. In this study, hepatic gene expression analysis was performed to identify any molecular signature associated with the outcome of hepatitis C virus (HCV) infection in chimpanzees. Acutely HCV-infected chimpanzees with self-limited infection or progression to chronicity were studied. Interferon stimulated genes were induced irrespective of the outcome of infection. Early induction of a set of genes associated with cell proliferation and immune activation was associated with subsequent viral clearance. Specifically, two of the genes: interleukin binding factor 3 (ILF3) and cytotoxic granule-associated RNA binding protein (TIA1), associated with robust T-cell response, were highly induced early in chimpanzees with self-limited infection. Up-regulation of genes associated with CD8+ T cell response was evident only during the clearance phase of the acute self-limited infection. The induction of these genes may represent an initial response of cellular injury and proliferation that successfully translates to a “danger signal” leading to induction of adaptive immunity to control viral infection. This primary difference in hepatic gene expression between self-limited and chronic infections supports the concept that successful activation of HCV-specific T-cell response is critical in clearance of acute HCV infection.

Induction of multispecific Th-1 type immune response against HCV in mice by protein immunization using CpG and Montanide ISA 720 as adjuvants

Recent studies demonstrate that Th1-type immune responses against a broad spectrum of hepatitis C virus (HCV) gene products are crucial to the resolution of acute HCV infection. We investigated new vaccine approaches to augment the strength of HCV-specific Th1-type immune responses. ELISPOT assay revealed that single or multiple protein immunization using both CpG ODN and Montanide ISA 720 as adjuvants induced much stronger IFN-gamma-producing Th1 responses against core, NS3 and NS5b targets than did the formulation without these adjuvants. Protein vaccination using CpG ODN and Montanide ISA 720 as adjuvants also greatly enhanced humoral responses to HCV core, E1/E2 and NS3. When specific IgG isotypes were assayed, protein immunization using CpG ODN and Montanide ISA 720 as adjuvants produced higher titers of IgG2a dominant antibodies than did protein immunization alone, indicating a more Th1-biased pathway. This increase in IgG2a is consistent with the induction of Th1 cells secreting IFN-gamma demonstrated by ELISPOT assay. In conclusion, protein immunization using CpG ODN and Montanide ISA 720 as adjuvants greatly enhanced cellular (Th1 type) as well as humoral immune responses against HCV in Balb/c mice. The use of adjuvants appears critical to the induction of Th1 immune responses during HCV vaccination with recombinant proteins.