Neutralizing antibody response during acute and chronic hepatitis C virus infection

Immunity and hepatitis C: a review

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and hepatocellular carcinoma worldwide. Due to shared transmission routes, the prevalence of HCV is especially high among individuals infected with HIV. HIV uninfected individuals spontaneously clear HCV approximately 30 % of the time, while the rate of control in HIV infected individuals who subsequently acquire HCV is substantially lower. In addition, complications of HCV are more frequent in those with HIV infection, making liver disease the leading cause of non-AIDS-related death in HIV infected individuals. This review summarizes recent advances in understanding the role of the innate and adaptive immune responses to HCV in those with and without HIV. Further defining the interaction between hepatitis C and the host immune system will potentially reveal insights into HCV pathogenesis and the host's ability to prevent persistent infection, as well as direct the development of vaccines.

Prospects for prophylactic hepatitis C vaccines based on virus-like particles

Given the global prevalence and long-term complications of chronic hepatitis C virus (HCV) infection, HCV constitutes one of the greatest challenges to human health of this decade. Considerable efforts have focused on the development of new effective treatments, but about three to four million individuals become infected each year, adding to the world reservoir of HCV infection. The development of a prophylactic vaccine against hepatitis C virus has thus become an important medical priority. Only a few vaccine candidates have progressed to the clinical phase, and published data on both the efficacy and safety of these vaccines are limited, due to many scientific, logistic and bioethic challenges. Fortunately, new innovative vaccine formulations, modes of vaccination and delivery technologies have been developed in recent years. Several preclinical trials of virus-like particle (VLP)-based vaccination strategies are currently underway and have already generated very promising results. In this commentary, we consider the current state of prophylactic HCV vaccines, the hurdles to be overcome in the future and the various VLP-based vaccination approaches currently being developed.

Isolation of human monoclonal antibodies to the envelope e2 protein of hepatitis C virus and their characterization

We isolated and characterized two human monoclonal antibodies to the envelope E2 protein of hepatitis C virus (HCV). Lymphoblastoid cell lines stably producing antibodies were obtained by immortalizing peripheral blood mononuclear cells of a patient with chronic hepatitis C using Epstein-Barr virus. Screening for antibody-positive clones was carried out by immunofluorescence with Huh7 cells expressing the E2 protein of HCV strain H (genotype 1a) isolated from the same patient. Isotype of resulting antibodies, #37 and #55, was IgG1/kappa and IgG1/lambda, respectively. Epitope mapping revealed that #37 and #55 recognize conformational epitopes spanning amino acids 429 to 652 and 508 to 607, respectively. By immunofluorescence using virus-infected Huh7.5 cells as targets both antibodies were reactive with all of the nine different HCV genotypes/subtypes tested. The antibodies showed a different pattern of immuno-staining; while #37 gave granular reactions mostly located in the periphery of the nucleus, #55 gave diffuse staining throughout the cytoplasm. Both antibodies were shown by immuno-gold electron microscopy to bind to intact viral particles. In a neutralization assay (focus-forming unit reduction using chimeric infectious HCV containing structural proteins derived from genotypes 1a, 1b, 2a, 2b, 3a, 4a, 5a, 6a, and 7a), #55 inhibited the infection of all HCV genotypes tested but genotype 7a to a lesser extent. #37 did not neutralize any of these viruses. As a broadly cross-neutralizing human antibody, #55 may be useful for passive immunotherapy of HCV infection.

Adaptive immune responses in hepatitis C virus infection

The adaptive immune response plays a central role in the outcome of hepatitis C virus (HCV) infection. Indeed, spontaneous viral clearance is associated with an early neutralizing antibody response as well as vigorous and sustained HCV-specific CD4+ and CD8+ T cell responses. In persistent HCV infection, however, all three components of the antiviral adaptive immune response fail due to different viral evasion strategies. In this chapter, we will describe the components of a successful immune response against HCV and summarize the mechanisms of immune failure. We will also highlight characteristics of protective CD8+ T cell responses which is the key factor to the design of an efficacious vaccine.

Primary, post-primary and non-specific immunoglobulin M responses in HCV infection

Delayed and variable antibody responses to HCV make it difficult to diagnose acute HCV infection reliably. Immunoglobulin (Ig)M and IgG anti-HCV may be observed simultaneously as disease persists. IgM plays a key role in mixed cryoglobulinemia (MC), an immune complex disease strongly associated with persistent HCV infection. In MC, clonal or oligoclonal IgM rheumatoid factors facilitate the deposition of immune complexes in small blood vessels and tissue, leading to inflammation, complement activation and tissue damage. Clonally expanded IgM(+)κ(+) B-cells expressing rheumatoid factor-like IgM are abundant in many HCV patients with MC. The observation that identical or similar IgM antibodies are expressed in different patients' clonally expanded B-cells supports the hypothesis that MC is driven by antigen-specific B-cell activation, rather than polyclonal B-cell activation or HCV replication in B-cells. More study is required to identify the antigens that drive the development of MC.

Insertion and recombination events at hypervariable region 1 over 9.6 years of hepatitis C virus chronic infection

Hepatitis C virus (HCV) exists as a quasispecies within an infected individual. We have previously reported an in-frame 3 bp insertion event at the N-terminal region of the E2 glycoprotein from a genotype 4a HCV isolate giving rise to an atypical 28 aa hypervariable region (HVR) 1. To further explore quasispecies evolution at the HVR1, serum samples collected over 9.6 years from the same chronically infected, treatment naïve individual were subjected to retrospective clonal analysis. Uniquely, we observed that isolates containing this atypical HVR1 not only persisted for 7.6 years, but dominated the quasispecies swarm. Just as striking was the collapse of this population of variants towards the end of the sampling period in synchrony with variants containing a classical HVR1 from the same lineage. The replication space was subsequently occupied by a second minor lineage, which itself was only intermittently detectable at earlier sampling points. In conjunction with the observed genetic shift, the coexistence of two distinct HVR1 populations facilitated the detection of putative intra-subtype recombinants, which included the identification of the likely ancestral parental donors. Juxtaposed to the considerable plasticity of the HVR1, we also document a degree of mutational inflexibility as each of the HVR1 subpopulations within our dataset exhibited overall genetic conservation and convergence. Finally, we raise the issue of genetic analysis in the context of mixed lineage infections.

Neutralizing antibodies and pathogenesis of hepatitis C virus infection

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease worldwide. The interplay between the virus and host innate and adaptive immune responses determines the outcome of infection. There is increasing evidence that host neutralizing responses play a relevant role in the resulting pathogenesis. Furthermore, viral evasion from host neutralizing antibodies has been revealed to be an important contributor in leading both to viral persistence in acute liver graft infection following liver transplantation, and to chronic viral infection. The development of novel model systems to study HCV entry and neutralization has allowed a detailed understanding of the molecular mechanisms of virus-host interactions during antibody-mediated neutralization. The understanding of these mechanisms will ultimately contribute to the development of novel antiviral preventive strategies for liver graft infection and an urgently needed vaccine. This review summarizes recent concepts of the role of neutralizing antibodies in viral clearance and protection, and highlights consequences of viral escape from neutralizing antibodies in the pathogenesis of HCV infection.

Successful vaccination induces multifunctional memory T-cell precursors associated with early control of hepatitis C virus

BACKGROUND & AIMS

T cells are an important component for development of a vaccine against hepatitis C virus (HCV), but little is known about the features of successful vaccine-induced T cells.

METHODS

We compared the phenotype, function, and kinetics of vaccine-induced and infection-induced T cells in chimpanzees with HCV infection using multicolor flow cytometry and real-time polymerase chain reaction.

RESULTS

In chimpanzees successfully vaccinated with recombinant adenovirus and DNA against HCV NS3-5, HCV-specific T cells appeared earlier, maintained better functionality, and persisted at higher frequencies for a longer time after HCV challenge, than those of mock-vaccinated chimpanzees. Vaccine-induced T cells displayed higher levels of CD127, a marker of memory precursors, and lower levels of programmed death-1 (PD-1) than infection-induced T cells. Vaccine-induced, but not infection-induced, T cells were multifunctional; their ability to secrete interferon gamma and tumor necrosis factor α correlated with early expression of CD127 but not PD-1. Based on a comparison of vaccine-induced and infection-induced T cells from the same chimpanzee, the CD127(+) memory precursor phenotype was induced by the vaccine itself rather than by low viremia. In contrast, induction of PD-1 correlated with viremia, and levels of intrahepatic PD-1, PD-L1, and 2,5-OAS-1 messenger RNAs correlated with peak titers of HCV.

CONCLUSIONS

Compared with infection, vaccination-induced HCV-specific CD127(+) T cells with high functionality that persisted at higher levels for a longer time. Control of viremia prevented up-regulation of PD-1 on T cells and induction of PD-1, PD-L1, and 2,5-OAS-1 in the liver. Early development of a memory T-cell phenotype and, via control of viremia, attenuation of the inhibitory PD1-PD-L1 pathway might be necessary components of successful vaccine-induced protection against HCV.

Complete definition of immunological correlates of protection and clearance of hepatitis C virus infection: a relevant pending task for vaccine development

Hepatitis C virus (HCV) infects approximately 3% of global population. This pathogen is one of the main causes of chronic viral hepatitis, cirrhosis, and liver cancer, as well as the principal reason for liver transplant in Western countries. Therapy against HCV infection is effective in only half of treated patients. There is no vaccine available against HCV. Some vaccine candidates have reached the clinical trials but several factors, including the incomplete definition of immunological correlates of protection and treatment-related clearance have slowed down vaccine development. Precisely, the present review discusses the state of the art in the establishment of parameters related with immunity against HCV. Validity and limitations of the information accumulated from chimpanzees and other animal models, analysis of studies in humans infected with HCV, and relevance of aspects like type, strength, duration, and specificity of immune response related to successful outcome are evaluated in detail. Moreover, the immune responses induced in some clinical trials with vaccine candidates resemble the theoretical immunological correlates, raising questions about the validity of those correlates. When all facts are taken together, complete definition of immunological correlates for protection or treatment-related clearance is an urgent priority. A limited or wrong criterion with respect to this relevant matter might cause incorrect vaccine design and selection of immunization strategies or erroneous clinical evaluation.

Amino acid residue-specific neutralization and nonneutralization of hepatitis C virus by monoclonal antibodies to the E2 protein

Antibodies to epitopes in the E2 protein of hepatitis C virus (HCV) reduce the viral infectivity in vivo and in vitro. However, the virus can persist in patients in the presence of neutralizing antibodies. In this study, we generated a panel of monoclonal antibodies that bound specifically to the region between residues 427 and 446 of the E2 protein of HCV genotype 1a, and we examined their capacity to neutralize HCV in a cell culture system. Of the four monoclonal antibodies described here, two were able to neutralize the virus in a genotype 1a-specific manner. The other two failed to neutralize the virus. Moreover, one of the nonneutralizing antibodies could interfere with the neutralizing activity of a chimpanzee polyclonal antibody at E2 residues 412 to 426, as it did with an HCV-specific immune globulin preparation, which was derived from the pooled plasma of chronic hepatitis C patients. Mapping the epitope-paratope contact interfaces revealed that these functionally distinct antibodies shared binding specificity for key amino acid residues, including W(437), L(438), L(441), and F(442), within the same epitope of the E2 protein. These data suggest that the effectiveness of antibody-mediated neutralization of HCV could be deduced from the interplay between an antibody and a specific set of amino acid residues. Further understanding of the molecular mechanisms of antibody-mediated neutralization and nonneutralization should provide insights for designing a vaccine to control HCV infection in vivo.

Constraints on viral evolution during chronic hepatitis C virus infection arising from a common-source exposure

Extraordinary viral sequence diversity and rapid viral genetic evolution are hallmarks of hepatitis C virus (HCV) infection. Viral sequence evolution has previously been shown to mediate escape from cytotoxic T-lymphocyte (CTL) and neutralizing antibody responses in acute HCV infection. HCV evolution continues during chronic infection, but the pressures driving these changes are poorly defined. We analyzed plasma virus sequence evolution in 5.2-kb hemigenomes from multiple longitudinal time points isolated from individuals in the Irish anti-D cohort, who were infected with HCV from a common source in 1977 to 1978. We found phylogenetically distinct quasispecies populations at different plasma time points isolated late in chronic infection, suggesting ongoing viral evolution and quasispecies replacement over time. We saw evidence of early pressure driving net evolution away from a computationally reconstructed common ancestor, known as Bole1b, in predicted CTL epitopes and E1E2, with balanced evolution toward and away from the Bole1b amino acid sequence in the remainder of the genome. Late in chronic infection, the rate of evolution toward the Bole1b sequence increased, resulting in net neutral evolution relative to Bole1b across the entire 5.2-kb hemigenome. Surprisingly, even late in chronic infection, net amino acid evolution away from the infecting inoculum sequence still could be observed. These data suggest that, late in chronic infection, ongoing HCV evolution is not random genetic drift but rather the product of strong pressure toward a common ancestor and concurrent net ongoing evolution away from the inoculum virus sequence, likely balancing replicative fitness and ongoing immune escape.

Efficient replication of primary or culture hepatitis C virus isolates in human liver slices: a relevant ex vivo model of liver infection

The development of human cultured hepatitis C virus (HCV) replication-permissive hepatocarcinoma cell lines has provided important new virological tools to study the mechanisms of HCV infection; however, this experimental model remains distantly related to physiological and pathological conditions. Here, we report the development of a new ex vivo model using human adult liver slices culture, demonstrating, for the first time, the ability of primary isolates to undergo de novo viral replication with the production of high-titer infectious virus as well as Japanese fulminant hepatitis type 1, H77/C3, and Con1/C3. This experimental model was employed to demonstrate HCV neutralization or HCV inhibition, in a dose-dependent manner, either by cluster of differentiation 81 or envelope protein 2-specific antibodies or convalescent serum from a recovered HCV patient or by antiviral drugs.

CONCLUSION

This new ex vivo model represents a powerful tool for studying the viral life cycle and dynamics of virus spread in native tissue and also allows one to evaluate the efficacy of new antiviral drugs.

Hepatitis C virus-mediated modulation of cellular immunity

The hepatitis C virus (HCV) is a major cause of chronic liver disease globally. A chronic infection can result in liver fibrosis, liver cirrhosis, hepatocellular carcinoma and liver failure in a significant ratio of the patients. About 170 million people are currently infected with HCV. Since 80 % of the infected patients develop a chronic infection, HCV has evolved sophisticated escape strategies to evade both the innate and the adaptive immune system. Thus, chronic hepatitis C is characterized by perturbations in the number, subset composition and/or functionality of natural killer cells, natural killer T cells, dendritic cells, macrophages and T cells. The balance between HCV-induced immune evasion and the antiviral immune response results in chronic liver inflammation and consequent immune-mediated liver injury. This review summarizes our current understanding of the HCV-mediated interference with cellular immunity and of the factors resulting in HCV persistence. A profound knowledge about the intrinsic properties of HCV and its effects on intrahepatic immunity is essential to be able to design effective immunotherapies against HCV such as therapeutic HCV vaccines.

Therapeutic vaccination against chronic hepatitis C virus infection

Approximately 170 million people worldwide are chronic carriers of Hepatitis C virus (HCV). To date, there is no prophylactic vaccine available against HCV. The standard-of-care therapy for HCV infection involves a combination of pegylated interferon-α and ribavirin. This therapy, which is commonly associated with side effects, has a curative rate varying from 43% (HCV genotype 1) to 80% (HCV genotype 2). In 2011, two direct-acting antiviral agents, telaprevir and boceprevir, were approved by the US Food and drug Administration and are now being used in combination with standard-of-care therapy in selected patients infected with HCV genotype 1. Although both drugs are promising, resulting in a shortening of therapy, these drugs also induce additional side effects and have reduced efficacy in patients who did not respond to standard-of-care previously. An alternative approach would be to treat HCV by stimulating the immune system with a therapeutic vaccine ideally aimed at (i) the eradication of HCV-infected cells and (ii) neutralization of infectious HCV particles. The challenge is to develop therapeutic vaccination strategies that are either at least as effective as antiviral drugs but with lower side effects, or vaccines that, when combined with antiviral drugs, can circumvent long-term use of these drugs thereby reducing their side effects. In this review, we summarize and discuss recent preclinical developments in the area of therapeutic vaccination against chronic HCV infection. Although neutralizing antibodies have been described to exert protective immunity, clinical studies on the induction of neutralizing antibodies in therapeutic settings are limited. Therefore, we will primarily discuss therapeutic vaccines which aim to induce effective cellular immune response against HCV.

Hepatitis C virus clearance, reinfection, and persistence, with insights from studies of injecting drug users: towards a vaccine

Hepatitis C virus (HCV) was discovered more than two decades ago, but progress towards a vaccine has been slow. HCV infection will spontaneously clear in about 25% of people. Studies of spontaneous HCV clearance in chimpanzees and human beings have identified host and viral factors that could be important in the control of HCV infection and the design of HCV vaccines. Although data from studies of chimpanzees suggest that protection against reinfection is possible after spontaneous clearance, HCV is a human disease. Results from studies of reinfection risk after spontaneous clearance in injecting drug users are conflicting, but some people seem to have protection against HCV persistence. To guide future vaccine development, we assess data from studies of HCV reinfection after spontaneous clearance, discuss flaws in the methods of previous human studies, and suggest essential components for future investigations of control of HCV infection.

A point mutation at Asn-534 that disrupts a conserved N-glycosylation motif of the E2 glycoprotein of hepatitis C virus markedly enhances the sensitivity to antibody neutralization

The molecular basis of antibody neutralization against hepatitis C virus (HCV) is poorly understood. The E2 glycoprotein of HCV is critically involved in viral infectivity through specific binding to the principal virus receptor component CD81, and is targeted by anti-HCV neutralizing antibodies. A previous study showed that a mutation at position 534 (N534H) within the sixth N-glycosylation motif of E2 of the J6/JFH1 strain of HCV genotype 2a (HCV-2a) was responsible for more efficient access of E2 to CD81 so that the mutant virus could infect the target cells more efficiently. The purpose of this study was to analyze the sensitivity of the parental J6/JFH1, its cell culture-adapted variant P-47 possessing 10 amino acid mutations and recombinant viruses with the adaptive mutations to neutralization by anti-HCV antibodies in sera of HCV-infected patients. The J6/JFH1 virus was neutralized by antibodies in sera of patients infected with HCV-2a and -1b, with mean 50% neutralization titers being 1:670 and 1:200, respectively (P < 0.00001). On the other hand, the P-47 variant showed 50- to 200-times higher sensitivity to antibody neutralization than the parental J6/JFH1 without genotype specificity. The N534H mutation, and another one at position 416 (T416A) near the first N-glycosylation motif to a lesser extent, were shown to be responsible for the enhanced sensitivity to antibody neutralization. The present results suggest that the residues 534, and 416 to a lesser extent, of the E2 glycoprotein are critically involved in the HCV infectivity and antibody neutralization.

Evaluation of the immunogenicity of liposome encapsulated HVR1 and NS3 regions of genotype 3 HCV, either singly or in combination

Background

Hepatitis C virus displays a high rate of mutation and exists as a quasispecies in infected patients. In the absence of an effective universal vaccine, genotype-specific vaccine development represents an alternative. We have attempted to develop a genotype 3 based, liposome encapsulated HCV vaccine with hypervariable region-1 (HVR1) and non-structural region-3 (NS3) components.

Results

HCV RNA extracted from serum samples of 49 chronically infected patients was PCR amplified to obtain HVR1 region. These amplified products were cloned to obtain 20 clones per sample in order to identify the quasispecies pattern. The HVR1 consensus sequence, along with three variants was reverse transcribed to obtain peptides. The peptides were checked for immunoreactivity individually, as a pool or as a single peptide tetramer interspersed with four glycine residues. Anti-HCV positivity varied from 42.6% (tetramer) to 92.2% (variant-4) when 115 anti-HCV positive sera representing genotypes 1, 3, 4 and 6 were screened. All the 95 anti-HCV negatives were scored negative by all antigens. Mice were immunized with different liposome encapsulated or Al(OH)₃ adjuvanted formulations of HVR1 variants and recombinant NS3 protein, and monitored for anti-HVR1 and anti-NS3 antibody titres, IgG isotypes and antigen specific cytokine levels. A balanced Th1/Th2 isotyping response with high antibody titres was observed in most of the liposome encapsulated antigen groups. The effect of liposomes and aluminium hydroxide on the expression of immune response genes was studied using Taqman Low Density Array. Both Th1 (IFN-gamma, Il18) and Th2 (Il4) genes were up regulated in the liposome encapsulated HVR1 variant pool-NS3 combination group. In-vitro binding of the virus to anti-HVR1 antibodies was demonstrated.

Conclusion

The optimum immunogen was identified to be combination of peptides of HVR1 consensus sequence and its variants along with pNS3 encapsulated in liposomes, which could generate both cellular and humoral immune responses in mice deserving further evaluation in a suitable cell culture system/non-human primate model.

Computational reconstruction of Bole1a, a representative synthetic hepatitis C virus subtype 1a genome

Hepatitis C virus (HCV) research is hampered by the use of arbitrary representative isolates in cell culture and immunology. The most replicative isolate in vitro is a subtype 2a virus (JFH-1); however, genotype 1 is more prevalent worldwide and represents about 70% of infections in the United States, and genotypes differ from one another by 31% to 33% at the nucleotide level. For phylogenetic and immunologic analyses, viruses H77 and HCV-1 (both subtype 1a) are commonly used based on their historic importance. In an effort to rationally design a representative subtype 1a virus (Bole1a), we used Bayesian phylogenetics, ancestral sequence reconstruction, and covariance analysis on a curated set of 390 full-length human HCV 1a sequences from GenBank. By design, Bole1a contains variations present in widely circulating strains and matches more epitope-sized peptides in a full-genome comparison to subtype 1a isolates than any other sequence studied. Parallel analyses confirm that selected epitopes from the Bole1a genome were able to elicit a robust T cell response. In a proof of concept for infectivity, the envelope genes (E1 and E2) of Bole1a were expressed in an HIV pseudoparticle system containing HCV envelope genes and HIV nonenvelope genes with luciferase expression. The resulting Bole1a pseudoparticle robustly infected Hep3B cells. In this study, we demonstrate that a rationally designed, fully synthetic HCV genome contains representative epitopes and envelope genes that assemble properly and mediate entry into target cells.

Spontaneous clearance of chronic hepatitis C virus infection is associated with appearance of neutralizing antibodies and reversal of T-cell exhaustion

BACKGROUND

Hepatitis C virus (HCV) readily establishes chronic infection with exhaustion of HCV-specific T cells and escape from neutralizing antibodies. Spontaneous recovery from chronic infection is rare and has never to our knowledge been studied immunologically.

METHODS

We prospectively studied, from prior to infection through >2 years of follow-up, cytokines, HCV-specific T cells, and antibodies, as well as viral sequence evolution in a white male who spontaneously cleared HCV genotype 1a after 65 weeks.

RESULTS

Significant alanine aminotransferase and plasma cytokine elevation and broad HCV-specific T-cell responses did not result in HCV clearance in the acute phase. Frequency and effector function of HCV-specific T cells decreased thereafter, and HCV titers stabilized as is typical for the chronic phase. HCV clearance after 65 weeks followed the appearance of neutralizing antibodies at week 48 and was associated with reversal of HCV-specific T-cell exhaustion, as evidenced by reduced programmed death-1 (PD-1) expression and improved T-cell function. Clearance occurred without inflammation or superinfection with hepatitis B virus, human cytomegalovirus virus, influenza, and Epstein-Barr virus.

CONCLUSIONS

T-cell exhaustion is reversible at least in the first 2 years of chronic HCV infection, and this reversion in conjunction with neutralizing antibodies may clear HCV. These findings are relevant for immunotherapy of chronic infections.

The role of humoral innate immunity in hepatitis C virus infection

Infection with Hepatitis C Virus (HCV) causes chronic disease in approximately 80% of cases, resulting in chronic inflammation and cirrhosis. Current treatments are not completely effective, and a vaccine has yet to be developed. Spontaneous resolution of infection is associated with effective host adaptive immunity to HCV, including production of both HCV-specific T cells and neutralizing antibodies. However, the supporting role of soluble innate factors in protection against HCV is less well understood. The innate immune system provides an immediate line of defense against infections, triggering inflammation and playing a critical role in activating adaptive immunity. Innate immunity comprises both cellular and humoral components, the humoral arm consisting of pattern recognition molecules such as complement C1q, collectins and ficolins. These molecules activate the complement cascade, neutralize pathogens, and recruit antigen presenting cells. Here we review the current understanding of anti-viral components of the humoral innate immune system that play a similar role to antibodies, describing their role in immunity to HCV and their potential contribution to HCV pathogenesis.

Naturally occurring antibodies that recognize linear epitopes in the amino terminus of the hepatitis C virus E2 protein confer noninterfering, additive neutralization

Chronic hepatitis C virus (HCV) infection can persist even in the presence of a broadly neutralizing antibody response. Various mechanisms that underpin viral persistence have been proposed, and one of the most recently proposed mechanisms is the presence of interfering antibodies that negate neutralizing responses. Specifically, it has been proposed that antibodies targeting broadly neutralizing epitopes located within a region of E2 encompassing residues 412 to 423 can be inhibited by nonneutralizing antibodies binding to a less conserved region encompassing residues 434 to 446. To investigate this phenomenon, we characterized the neutralizing and inhibitory effects of human-derived affinity-purified immunoglobulin fractions and murine monoclonal antibodies and show that antibodies to both regions neutralize HCV pseudoparticle (HCVpp) and cell culture-infectious virus (HCVcc) infection albeit with different breadths and potencies. Epitope mapping revealed the presence of overlapping but distinct epitopes in both regions, which may explain the observed differences in neutralizing phenotypes. Crucially, we failed to demonstrate any inhibition between these two groups of antibodies, suggesting that interference by nonneutralizing antibodies, at least for the region encompassing residues 434 to 446, does not provide a mechanism for HCV persistence in chronically infected individuals.

A prime-boost strategy using virus-like particles pseudotyped for HCV proteins triggers broadly neutralizing antibodies in macaques

Chronic hepatitis C virus (HCV) infection, with its cohort of life-threatening complications, affects more than 200 million persons worldwide and has a prevalence of more than 10% in certain countries. Preventive and therapeutic vaccines against HCV are thus much needed. Neutralizing antibodies (NAbs) are the foundation for successful disease prevention for most established vaccines. However, for viruses that cause chronic infection such as HIV or HCV, induction of broad NAbs from recombinant vaccines has remained elusive. We developed a vaccine platform specifically aimed at inducing NAbs based on pseudotyped virus-like particles (VLPs) made with retroviral Gag. We report that VLPs pseudotyped with E2 and/or E1 HCV envelope glycoproteins induced high-titer anti-E2 and/or anti-E1 antibodies, as well as NAbs, in both mouse and macaque. The NAbs, which were raised against HCV 1a, cross-neutralized the five other genotypes tested (1b, 2a, 2b, 4, and 5). Thus, the described VLP platform, which can be pseudotyped with a vast array of virus envelope glycoproteins, represents a new approach to viral vaccine development.

Hepatitis C virus epitope exposure and neutralization by antibodies is affected by time and temperature

A recent study with flaviviruses suggested that structural dynamics of the virion impact antibody neutralization via exposure of ostensibly cryptic epitopes. To determine whether this holds true for the distantly related hepatitis C virus (HCV), whose neutralizing epitopes may be obscured by a glycan shield, apolipoprotein interactions, and the hypervariable region on the E2 envelope protein, we assessed how time and temperature of pre-incubation altered monoclonal antibody (MAb) neutralization of HCV. Notably, several MAbs showed increased inhibitory activity when pre-binding was performed at 37°C or after longer pre-incubation periods, and a corresponding loss-of-neutralization was observed when pre-binding was performed at 4°C. A similar profile of changes was observed with acute and chronic phase sera from HCV-infected patients. Our data suggest that time and temperature of incubation modulate epitope exposure on the conformational ensembles of HCV virions and thus, alter the potency of antibody neutralization.

The role of neutralizing antibodies in hepatitis C virus infection

Hepatitis C virus (HCV) is a blood-borne virus estimated to infect around 170 million people worldwide and is, therefore, a major disease burden. In some individuals the virus is spontaneously cleared during the acute phase of infection, whilst in others a persistent infection ensues. Of those persistently infected, severe liver diseases such as cirrhosis and primary liver cancer may develop, although many individuals remain asymptomatic. A range of factors shape the course of HCV infection, not least host genetic polymorphisms and host immunity. A number of studies have shown that neutralizing antibodies (nAb) arise during HCV infection, but that these antibodies differ in their breadth and mechanism of neutralization. Recent studies, using both mAbs and polyclonal sera, have provided an insight into neutralizing determinants and the likely protective role of antibodies during infection. This understanding has helped to shape our knowledge of the overall structure of the HCV envelope glycoproteins--the natural target for nAb. Most nAb identified to date target receptor-binding sites within the envelope glycoprotein E2. However, there is some evidence that other viral epitopes may be targets for antibody neutralization, suggesting the need to broaden the search for neutralization epitopes beyond E2. This review provides a comprehensive overview of our current understanding of the role played by nAb in HCV infection and disease outcome and explores the limitations in the study systems currently used. In addition, we briefly discuss the potential therapeutic benefits of nAb and efforts to develop nAb-based therapies.

New neutralizing antibody epitopes in hepatitis C virus envelope glycoproteins are revealed by dissecting peptide recognition profiles

One of the greatest challenges to HCV vaccine development is the induction of effective immune responses using recombinant proteins or vectors. In order to better understand which vaccine-induced antibodies contribute to neutralization of HCV the quality of polyclonal anti-E1E2 antibody responses in immunized mice and chimpanzees was assessed at the level of epitope recognition using peptide scanning and neutralization of chimeric 1a/2a, 1b/2a and 2a HCVcc after blocking or affinity elution of specific antibodies. Mice and chimpanzees were immunized with genotype 1a (H77) HCV gpE1E2; all samples contained cross-neutralizing antibody against HCVcc. By functionally dissecting the polyclonal immune responses we identified three new regions important for neutralization within E1 (aa264-318) and E2 (aa448-483 and aa496-515) of the HCV glycoproteins, the third of which (aa496-515) is highly conserved (85-95%) amongst genotypes. Antibodies to aa496-515 were isolated by affinity binding and elution from the serum of a vaccinated chimpanzee and found to specifically neutralize chimeric 1a/2a, 1b/2a and 2a HCVcc. IC50 titres (IgG ng/mL) for the aa496-515 eluate were calculated as 142.1, 239.37 and 487.62 against 1a/2a, 1b/2a and 2a HCVcc, respectively. Further analysis demonstrated that although antibody to this new, conserved neutralization epitope is efficiently induced with recombinant proteins in mice and chimpanzees; it is poorly induced during natural infection in patients and chimpanzees (7 out of 68 samples positive) suggesting the epitope is poorly presented to the immune system in the context of the viral particle. These findings have important implications for the development of HCV vaccines and strategies designed to protect against heterologous viruses. The data also suggest that recombinant or synthetic antigens may be more efficient at inducing neutralizing antibodies to certain epitopes and that screening virally infected patients may not be the best approach for finding new cross-reactive epitopes.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Neutralizing antibodies to hepatitis C virus in perinatally infected children followed up prospectively

Little is known about the presence and role of neutralizing antibodies (NtAbs) in perinatal hepatitis C virus (HCV) infection. Using HCV pseudoparticles, NtAbs were studied longitudinally in 12 HCV-infected children with or without evidence of acute hepatitis during the first year of life. Broadly reactive NtAbs of maternal origin did not prevent vertical HCV transmission or progression to chronicity. NtAbs against homologous genotype or subtype appeared during the chronic phase and were more abundant and sustained in children with acute hepatitis. Cross-reactive NtAbs were present in both groups of children, but their appearance did not correlate with better control of viremia or HCV clearance.

Divergent quasispecies evolution in de novo hepatitis C virus infection associated with bone marrow transplantation

Quasispecies is a remarkable characteristic of hepatitis C virus (HCV) and has profound roles in HCV biology and clinical practice. The understanding of HCV quasispecies behavior, in particular in acute HCV infection, is valuable for vaccine development and therapeutic interference. However, acute HCV infection is seldom encountered in clinic practice due to its silent onset. In the present study, we reported a unique case of de novo HCV infection associated with the transplantation of bone marrow from a HCV-positive donor. HCV quasispecies diversity was determined in both the donor and the recipient over a 4-year follow-up, accompanied with simultaneous measurement of HCV neutralizing antibody. Detailed genetic and phylogenetic analyses revealed a divergent quasispecies evolution, which was not related to dynamic changes of HCV neutralizing antibody. Instead, our data suggested an essential role of the fitness adaptation of founder viral population in driving such an evolutionary pattern.

The hepatitis C virus glycan shield and evasion of the humoral immune response

Despite the induction of effective immune responses, 80% of hepatitis C virus (HCV)-infected individuals progress from acute to chronic hepatitis. In contrast to the cellular immune response, the role of the humoral immune response in HCV clearance is still subject to debate. Indeed, HCV escapes neutralizing antibodies in chronically infected patients and reinfection has been described in human and chimpanzee. Studies of antibody-mediated HCV neutralization have long been hampered by the lack of cell-culture-derived virus and the absence of a small animal model. However, the development of surrogate models and recent progress in HCV propagation in vitro now enable robust neutralization assays to be performed. These advances are beginning to shed some light on the mechanisms of HCV neutralization. This review summarizes the current state of knowledge of the viral targets of anti-HCV-neutralizing antibodies and the mechanisms that enable HCV to evade the humoral immune response. The recent description of the HCV glycan shield that reduces the immunogenicity of envelope proteins and masks conserved neutralizing epitopes at their surface constitutes the major focus of this review.

Antibody V(h) repertoire differences between resolving and chronically evolving hepatitis C virus infections

Despite the production of neutralizing antibodies to hepatitis C virus (HCV), many patients fail to clear the virus and instead develop chronic infection and long-term complications. To understand how HCV infection perturbs the antibody repertoire and to identify molecular features of antibody genes associated with either viral clearance or chronic infection, we sequenced the V(D)J region of naïve and memory B cells of 6 persons who spontaneously resolved an HCV infection (SR), 9 patients with a newly diagnosed chronically evolving infection (CE), and 7 healthy donors. In both naïve and memory B cells, the frequency of use of particular antibody gene subfamilies and segments varied among the three clinical groups, especially between SR and CE. Compared to CE, SR antibody genes used fewer VH, D and JH gene segments in naïve B cells and fewer VH segments in memory B cells. SR and CE groups significantly differed in the frequency of use of 7 gene segments in naïve B cell clones and 3 gene segments in memory clones. The nucleotide mutation rates were similar among groups, but the pattern of replacement and silent mutations in memory B cell clones indicated greater antigen selection in SR than CE. Greater clonal evolution of SR than CE memory B cells was revealed by analysis of phylogenetic trees and CDR3 lengths. Pauciclonality of the peripheral memory B cell population is a distinguishing feature of persons who spontaneously resolved an HCV infection. This finding, previously considered characteristic only of patients with HCV-associated lymphoproliferative disorders, suggests that the B cell clones potentially involved in clearance of the virus may also be those susceptible to abnormal expansion.

Early IL-10 predominant responses are associated with progression to chronic hepatitis C virus infection in injecting drug users

The critical events in clearance or persistence of hepatitis C virus (HCV) infection are unknown but likely to be determined early in acute infection. Type 1 and type 2 cytokine production was assessed by HCV peptide ELISpot and multiplex in vitro cytokine production assays in longitudinally collected samples from 20 untreated participants enrolled in the Australian Trial in Acute Hepatitis C (ATAHC); a prospective cohort of acute HCV infection (77% injecting drug users, IDU). Significantly higher interleukin-10 (IL-10) production (P = 0.048), in the relative absence of interferon-gamma (IFN-γ) and IL-2 production, was present early in HCV infection in those who progressed to chronic infection. In contrast, viral clearance was associated with a greater magnitude and broader specificity of IFN-γ (magnitude P < 0.001, breadth P = 0.004) and IL-2 responses, in the relative absence of IL-10. Early IL-10 production was correlated with higher HCV RNA level at baseline (P = 0.046) and week 12 (P = 0.018), while IFN-γ and IL-2 production was inversely correlated with HCV RNA level at baseline (IFN-γ P = 0.020, IL-2 P = 0.050) and week 48 (IFN-γ P = 0.045, IL-2 P = 0.026). Intracellular staining (ICS) indicated the HCV-specific IFN-γ response was primarily from CD8(+) T cells and NK cells, whereas IL-10 production was predominantly from monocytes, with a subset of IL-10 producing CD8(+) T cells present only in those who progressed to chronic infection. IL-10, an immunoregulatory cytokine, appears to play a key role in progression to chronic HCV infection.

Prospects for prophylactic and therapeutic vaccines against the hepatitis C viruses

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

Hepatitis C patient-derived glycoproteins exhibit marked differences in susceptibility to serum neutralizing antibodies: genetic subtype defines antigenic but not neutralization serotype

Neutralizing antibodies have a role in controlling hepatitis C virus (HCV) infection. A successful vaccine will need to elicit potently neutralizing antibodies that are capable of preventing the infection of genetically diverse viral isolates. However, the specificity of the neutralizing antibody response in natural HCV infection still is poorly understood. To address this, we examined the reactivity of polyclonal antibodies isolated from chronic HCV infection to the diverse patient-isolated HCV envelope glycoproteins E1 and E2 (E1E2), and we also examined the potential to neutralize the entry of pseudoparticles bearing these diverse E1E2 proteins. The genetic type of the infection was found to determine the pattern of the antibody recognition of these E1E2 proteins, with the greatest reactivity to homologous E1E2 proteins. This relationship was strongest when the component of the antibody response directed only to linear epitopes was analyzed. In contrast, the neutralization serotype did not correlate with genotype. Instead, serum-derived antibodies displayed a range of neutralization breadth and potency, while different E1E2 glycoproteins displayed different sensitivities to neutralization, such that these could be divided broadly into neutralization-sensitive and -resistant phenotypes. An important additional observation was that entry mediated by some E1E2 proteins was enhanced in the presence of some of the polyclonal antibody fractions isolated during chronic infection. These data highlight the need to use diverse E1E2 isolates, which represent extremes of neutralization sensitivity, when screening antibodies for therapeutic potential and for testing antibodies generated following immunization as part of vaccine development.

Hepatitis C virus protects human B lymphocytes from Fas-mediated apoptosis via E2-CD81 engagement

HCV infection is often associated with B-cell regulatory control disturbance and delayed appearance of neutralizing antibodies. CD81 is a cellular receptor for HCV and can bind to HCV envelope protein 2 (E2). CD81 also participates to form a B cell costimulatory complex. To investigate whether HCV influences B cell activation and immune function through E2 -CD81 engagement, here, human Burkitt's lymphoma cell line Raji cells and primary human B lymphocytes (PHB) were treated with HCV E2 protein and cell culture produced HCV particles (HCVcc), and then the related cell phenotypes were assayed. The results showed that both E2 and HCVcc triggered phosphorylation of IκBα, enhanced the expression of anti-apoptosis Bcl-2 family proteins, and protected Raji cells and PHB cells from Fas-mediated death. In addition, both E2 protein and HCVcc increased the expression of costimulatory molecules CD80, CD86 and CD81 itself, and decreased the expression of complement receptor CD21. The effects were dependent on E2-CD81 interaction on the cell surface, since CD81-silenced Raji cells did not respond to both treatments; and an E2 mutant that lose the CD81 binding activity, could not trigger the responses of both Raji cells and PHB cells. The effects were not associated with HCV replication in cells, for HCV pseudoparticle (HCVpp) and HCVcc failed to infect Raji cells. Hence, E2-CD81 engagement may contribute to HCV-associated B cell lymphoproliferative disorders and insufficient neutralizing antibody production.

Characterization of the cross-neutralizing antibody response against hepatitis C virus in the liver transplantation setting

Neutralizing antibody (nAb) activity during the course of natural infection is believed to be crucial to combating virus propagation. The aim of this study was to measure the impact of nAb response on HCV early kinetics and genetic evolution in the liver transplantation (LT) setting. A cohort of 28 patients undergoing LT for HCV-related cirrhosis was included in the study. Viral load, nAb titers and hypervariable region 1 (HVR1) sequences were determined in serum samples obtained before and at different time points after LT. Serum nAb titers were assessed using HCV pseudoparticles (HCVpp). HVR1 sequences were obtained by direct sequencing. Patients were classified according to viral kinetic patterns (plateau or increasing), during the first week after LT. All patients demonstrated high titers of nAbs before LT, although this was not associated with early kinetic patterns or HVR1 evolution during the first week after LT. We found that in patients with plateau HCV early kinetics, the virus required adaptive mutations, while in those with increasing viral loads, the HVR1 region remained largely conserved (p = 0.015). These data suggest that HCV adaptation via selection of the best-fitted variants may account for early viral kinetics following LT.

In vivo evaluation of the cross-genotype neutralizing activity of polyclonal antibodies against hepatitis C virus

Control of hepatitis C virus (HCV) infection remains a huge challenge of global medical importance. Using a variety of in vitro approaches, neutralizing antibodies (nAbs) have been identified in patients with acute and chronic hepatitis C. The exact role these nAbs play in the resolution of acute HCV infection still remains elusive. We have previously shown that purified polyclonal antibodies isolated from plasma obtained in 2003 from a chronic HCV patient (Patient H) can protect human liver chimeric mice from a subsequent challenge with the autologous HCV strain isolated from Patient H in 1977 (H77). In this study we investigated whether polyclonal antibodies isolated from Patient H in 2006 (H06), which display high cross-genotype neutralizing activity in both the HCV pseudoparticle (HCVpp) and HCV cell culture (HCVcc) systems, were also able to prevent HCV infection of different genotypes (gt) in vivo. Following passive immunization with H06-antibodies, chimeric mice were challenged with the consensus strains H77C (gt1a), ED43 (gt4a), or HK6a (gt6a). In accordance with previous results, H06-antibodies prevented infection of chimeric mice with the autologous virus. However, the outcome of a homologous challenge is highly influenced by the amount of challenge virus injected. Depending on the viral genotype used, H06-antibodies were able to protect up to 50% of chimeric mice from a heterologous challenge. Animals in which the antibody pretreatment failed displayed a clear delay in the kinetics of viral infection. Sequence analysis of the recovered viruses did not suggest antibody-induced viral escape.

CONCLUSION

Polyclonal anti-HCV antibodies isolated from a chronic HCV patient can protect against an in vivo challenge with different HCV genotypes. However, the in vivo protective efficacy of cross-genotype neutralizing antibodies was less than predicted by cell culture experiments.

Immunotherapeutic potential of neutralizing antibodies targeting conserved regions of the HCV envelope glycoprotein E2

HCV is a major cause of chronic liver disease worldwide. There is no vaccine available and the current antiviral therapies fail to cure approximately half of treated patients. Liver disease caused by HCV infection is the most common indication for orthotopic liver transplantation. Unfortunately, reinfection of the new liver is universal and often results in an aggressive form of the disease leading to graft loss and the need for retransplantation. Immunotherapies using antibodies that potently inhibit HCV infection have the potential to control or even prevent graft reinfection. The virion envelope glycoproteins E1 and E2, which are involved in HCV entry into host cells, are the targets of neutralizing antibodies. To date, a number of monoclonal antibodies targeting conserved regions of E2 have been described that display outstanding neutralizing capabilities against HCV infection in both in vitro and in vivo systems. This article will summarize the current literature on these neutralizing anti-E2 antibodies and discuss their potential immunotherapeutic efficacy.

Hepatitis C virus soluble E2 in combination with QuilA and CpG ODN induces neutralizing antibodies in mice

Several studies have emphasized the importance of an early, highly neutralizing antibody response in the clearance of Hepatitis C virus (HCV) infection. The envelope glycoprotein E2 is a major target for HCV neutralizing antibodies. Here, we compared antibody responses in mice immunized with native soluble E2 (sE2) from the H77 1a isolate coupled with different adjuvants or combinations of adjuvants. Adjuvanting sE2 with Freund's, monophosphoryl lipid A (MPL), cytosine phosphorothioate guanine oligodeoxynucleotide (CpG ODN), or alpha-galactosylceramide (αGalCer) derivatives elicited only moderate antibody responses. In contrast, immunizations with sE2 and QuilA elicited exceptionally high anti-E2 antibody titers. Sera from these mice effectively neutralized HCV pseudoparticles (HCVpp) 1a entry. Moreover, the combination of QuilA and CpG ODN further enhanced neutralizing antibody titers wherein cross-neutralization of HCVpp 4 was observed. We conclude that the combination of QuilA and CpG ODN is a promising adjuvant combination that should be further explored for the development of an HCV subunit vaccine. Our work also emphasizes that the ideal combination of adjuvant and immunogen has to be determined empirically.

Sporadic reappearance of minute amounts of hepatitis C virus RNA after successful therapy stimulates cellular immune responses

BACKGROUND & AIMS

Several studies have reported hepatitis C virus (HCV) RNA sequences in the circulation after treatment-induced or spontaneous recovery. We investigated whether the HCV RNA represents persistence of HCV infection or reinfection.

METHODS

We studied 117 patients who recovered from HCV infection (98 following therapy and 19 spontaneously). A reverse-transcription polymerase chain reaction assay was used to detect the 5'-untranslated region of HCV. T-cell responses were studied by enzyme-linked immunospot for interferon-γ.

RESULTS

Plasma samples from 15% of treatment-recovered patients and no spontaneously recovered patient tested positive for HCV RNA. Lymphocytes from 3 patients who responded to therapy and 1 who recovered spontaneously tested positive. The frequency of HCV RNA detection in plasma correlated inversely with the time after the end of treatment. Post-treatment HCV 5'-untranslated region sequences matched pretreatment sequences in 85% of cases. T-cell responses were significantly greater at time points with detectable trace amounts of HCV RNA than at time points without detectable HCV RNA (P = .035) and were primarily against nonstructural HCV antigens. The immune hierarchy was preserved over 5 years in patients whose post-treatment HCV RNA sequences matched pretreatment sequences, indicating HCV RNA persistence. An altered immune hierarchy with dominant immune responses, shifting from nonstructural to structural antigens, was observed in a single patient whose post-treatment HCV genotype differed from that of the pretreatment genotype, indicating HCV reinfection.

CONCLUSIONS

Trace amounts of HCV RNA of pretreatment sequence persisted and reappeared sporadically in the circulation within 8 years after recovery from hepatitis C but not thereafter, indicating that patients are cured of HCV infection. Reappearance of HCV RNA induced HCV-specific T-cell responses.

Extracellular hepatitis C virus core protein activates STAT3 in human monocytes/macrophages/dendritic cells via an IL-6 autocrine pathway

Hepatitis C virus (HCV) infection is highly efficient in the establishment of persistent infection, which leads to the development of chronic liver disease and hepatocellular carcinoma. Impaired T cell responses with reduced IFN-γ production have been reported to be associated with persistent HCV infection. Extracellular HCV core is a viral factor known to cause HCV-induced T cell impairment via its suppressive effect on the activation and induction of pro-inflammatory responses by antigen-presenting cells (APCs). The activation of STAT proteins has been reported to regulate the inflammatory responses and differentiation of APCs. To further characterize the molecular basis for the regulation of APC function by extracellular HCV core, we examined the ability of extracellular HCV core to activate STAT family members (STAT1, -2, -3, -5, and -6). In this study, we report the activation of STAT3 on human monocytes, macrophages, and dendritic cells following treatment with extracellular HCV core as well as treatment with a gC1qR agonistic monoclonal antibody. Importantly, HCV core-induced STAT3 activation is dependent on the activation of the PI3K/Akt pathway. In addition, the production of multifunctional cytokine IL-6 is essential for HCV core-induced STAT3 activation. These results suggest that HCV core-induced STAT3 activation plays a critical role in the alteration of inflammatory responses by APCs, leading to impaired anti-viral T cell responses during HCV infection.

Adaptive immunity to the hepatitis C virus

The hepatitis C virus (HCV) is a global public health problem affecting approximately 2% of the human population. The majority of HCV infections (more than 70%) result in life-long persistence of the virus that substantially increases the risk of serious liver diseases, including cirrhosis and hepatocellular carcinoma. The remainder (less than 30%) resolves spontaneously, often resulting in long-lived protection from persistence upon reexposure to the virus. To persist, the virus must replicate and this requires effective evasion of adaptive immune responses. In this review, the role of humoral and cellular immunity in preventing HCV persistence, and the mechanisms used by the virus to subvert protective host responses, are considered.

Antibody dynamics and spontaneous viral clearance in patients with acute hepatitis C infection in Rio de Janeiro, Brazil

Background

The anti-HCV antibody response has not been well characterized during the early phase of HCV infection and little is known about its relationship to the clinical course during this period.

Methods

We analyzed serial anti-HCV antibodies longitudinally obtained from a prospective cohort of 65 patients with acute HCV infection by using a microparticle enzyme immunoassay AxSYM HCV 3.0 (Abbott Diagnostics) during the first 12 months from HCV acquisition in Rio de Janeiro, Brazil. Spontaneous viral clearance (SVC) was defined as undetectable HCV RNA in serum, in the absence of treatment, for three consecutive HCV PCR tests within 12-months of follow-up.

Results

Baseline antibody values were similar among patient groups with self-limiting HCV evolution (n = 34) and persistent viremia (n = 31) [median (interquartile range) signal/cut-off ratio (s/co) 78.7 (60.7-93.8) vs. 93.9 (67.8-111.9), p = 0.26]. During 12-months follow-up, patients with acute spontaneous resolving HCV infection showed significantly lower serial antibody response in comparison to individuals progressing to chronic infection [median (interquartile range) s/co 62.7 (35.2-85.0) vs. 98.4 (70.4-127.4), p < 0.0001]. In addition, patients with self-limiting HCV evolution exhibited an expeditious, sharp decline of serial antibody values after SVC in comparison to those measured before SVC [median (interquartile range) s/co 56.0 (25.4-79.3) vs. 79.4 (66.3-103.0), p < 0.0001].

Conclusion

Our findings indicate a rapid short-term decline of antibody values in patients with acute spontaneous resolving HCV infection.

Experimental models to study the immunobiology of hepatitis C virus

Effective host immune responses are essential for the control of hepatitis C virus (HCV) infection and persistence of HCV has indeed been attributed to their failure. In recent years, several in vitro and in vivo experimental models have allowed studies of host immune responses against HCV. Numerous observations derived from these models have improved our understanding of the mechanisms responsible for the host's ability to clear the virus as well as of the mechanisms responsible for the host's failure to control HCV replication. Importantly, several findings obtained with these model systems have been confirmed in studies of acutely or chronically HCV-infected individuals. Collectively, several mechanisms are used by HCV to escape host immune responses, such as poor induction of the innate immune response and escaping/impairing adaptive immunity. In this review, we summarize current findings from experimental models available for studies of the immune response targeting HCV and discuss the relevance of these findings for the in vivo situation in HCV-infected humans.

An Assessment of the Use of Chimpanzees in Hepatitis C Research Past, Present and Future: 2. Alternative Replacement Methods

The use of chimpanzees in hepatitis C virus (HCV) research was examined in the report associated with this paper ( 1: Validity of the Chimpanzee Model), in which it was concluded that claims of past necessity of chimpanzee use were exaggerated, and that claims of current and future indispensability were unjustifiable. Furthermore, given the serious scientific and ethical issues surrounding chimpanzee experimentation, it was proposed that it must now be considered redundant — particularly in light of the demonstrable contribution of alternative methods to past and current scientific progress, and the future promise that these methods hold. This paper builds on this evidence, by examining the development of alternative approaches to the investigation of HCV, and by reviewing examples of how these methods have contributed, and are continuing to contribute substantially, to progress in this field. It augments the argument against chimpanzee use by demonstrating the comprehensive nature of these methods and the valuable data they deliver. The entire life-cycle of HCV can now be investigated in a human (and much more relevant) context, without recourse to chimpanzee use. This also includes the testing of new therapies and vaccines. Consequently, there is no sound argument against the changes in public policy that propose a move away from chimpanzee use in US laboratories.

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.

A new insight into hepatitis C vaccine development

Chronic hepatitis C virus (HCV) infection remains a serious burden to public health worldwide. Currently, HCV-infected patients could undergo antiviral therapy by giving pegylated IFN-α with ribavirin. However, this therapy is only effective in around 50% of patients with HCV genotype 1, which accounts for more than 70% of all HCV infection, and it is not well tolerated for most patients. Moreover, there is no vaccine available. The efforts on identifying protective immunity against HCV have progressed recently. Neutralizing antibodies and robust T cell responses including both CD4⁺ and CD8⁺ have been shown to be related to the clearance of HCV, which have shed lights on the potential success of HCV vaccines. There are many vaccines developed and tested before entering clinical trials. Here, we would first discuss strategies of viral immune evasion and correlates of protective host immunity and finally review some prospective vaccine approaches against chronic HCV infection.

Challenge pools of hepatitis C virus genotypes 1-6 prototype strains: replication fitness and pathogenicity in chimpanzees and human liver-chimeric mouse models

Chimpanzees represent the only animal model for studies of the natural history of hepatitis C virus (HCV). To generate virus stocks of important HCV variants, we infected chimpanzees with HCV strains of genotypes 1-6 and determined the infectivity titer of acute-phase plasma pools in additional animals. The courses of first- and second-passage infections were similar, with early appearance of viremia, HCV RNA titers of >10(4.7) IU/mL, and development of acute hepatitis; the chronicity rate was 56%. The challenge pools had titers of 10(3)-10(5) chimpanzee infectious doses/mL. Human liver-chimeric mice developed high-titer infections after inoculation with the challenge viruses of genotypes 1-6. Inoculation studies with different doses of the genotype 1b pool suggested that a relatively high virus dose is required to consistently infect chimeric mice. The challenge pools represent a unique resource for studies of HCV molecular virology and for studies of pathogenesis, protective immunity, and vaccine efficacy in vivo.

Novel infectious cDNA clones of hepatitis C virus genotype 3a (strain S52) and 4a (strain ED43): genetic analyses and in vivo pathogenesis studies

Previously, RNA transcripts of cDNA clones of hepatitis C virus (HCV) genotypes 1a (strains H77, HCV-1, and HC-TN), 1b (HC-J4, Con1, and HCV-N), and 2a (HC-J6 and JFH1) were found to be infectious in chimpanzees. However, only JFH1 was infectious in human hepatoma Huh7 cells. We performed genetic analysis of HCV genotype 3a (strain S52) and 4a (strain ED43) prototype strains and generated full-length consensus cDNA clones (pS52 and pED43). Transfection of Huh7.5 cells with RNA transcripts of these clones did not yield cells expressing HCV Core. However, intrahepatic transfection of chimpanzees resulted in robust infection with peak HCV RNA titers of approximately 5.5 log(10) international units (IU)/ml. Genomic consensus sequences recovered from serum at the times of peak viral titers were identical to the sequences of the parental plasmids. Both chimpanzees developed acute hepatitis with elevated liver enzymes and significant necroinflammatory liver changes coinciding with detection of gamma interferon-secreting, intrahepatic T cells. However, the onset and broadness of intrahepatic T-cell responses varied greatly in the two animals, with an early (week 4) multispecific response in the ED43-infected animal (3 weeks before the first evidence of viral control) and a late (week 11) response with limited breadth in the S52-infected animal (without evidence of viral control). Autologous serum neutralizing antibodies were not detected during the acute infection in either animal. Both animals became persistently infected. In conclusion, we generated fully functional infectious cDNA clones of HCV genotypes 3a and 4a. Proof of functionality of all genes might further the development of recombinant cell culture systems for these important genotypes.