Peptide immunogen mimicry of putative E1 glycoprotein-specific epitopes in hepatitis C virus

Hepatitis C virus E1 and modified E2 delivered from an mRNA vaccine induces protective immunity

Hepatitis C virus (HCV) is characterized by a high number of chronic cases due to an impairment of protective innate and adaptive immune responses. Here, we examined the contribution of the individual ectodomains of E1, E2, or a modified E2 with reduced CD81 binding and an inserted N-linked glycosylation site in combination as vaccine antigen mRNA-lipid nanoparticles (LNPs). The induction of a protective immune response to surrogate recombinant vaccinia virus (VV) expressing homologous HCV glycoprotein(s) challenge infection in a BALB/c mouse model was observed. Vaccination with a mRNA-LNP expressing soluble E1 (sE1) significantly reduced vv/HCV titer in the mouse ovary. However, the addition of sE2 mRNA-LNP for immunization impaired the efficacy of the sE1 construct. Further analysis showed that Th1 related cytokine responses to the sE1 mRNA-LNP were significantly altered in the presence of sE2 following co-immunization. Evaluation of immunogenicity revealed that the use of modified sE2F442NYT nucleoside mRNA-LNP vaccine results in an improved cellular immune response, IgG2a isotype switching, enhanced total IgG, and an increase in the neutralizing antibody response against HCV pseudotype virus. HCV cross genotype specific reactivity to peptides representing conserved E2 specific linear epitopes were enhanced in modified E2 vaccinated animal sera. In the absence of a suitable immunocompetent small animal model for HCV infection, protection from surrogate HCV vaccinia challenge infection model was observed in the immunized mice as compared to sE1 alone or an unmodified sE2 mRNA-LNP vaccine. Inclusion of sE1 with modified sE2F442NYT as mRNA-LNP vaccine candidate appeared to be beneficial for protection.

Modified E2 Glycoprotein of Hepatitis C Virus Enhances Proinflammatory Cytokines and Protective Immune Response

Hepatitis C virus (HCV) is characterized by a high number of chronic cases owing to an impairment of innate and adaptive immune responses. CD81 on the cell surface facilitates HCV entry by interacting with the E2 envelope glycoprotein. In addition, CD81/E2 binding on immunity-related cells may also influence host response outcome to HCV infection. Here, we performed site-specific amino acid substitution in the front layer of E2 sequence to reduce CD81 binding and evaluate the potential of the resulting immunogen as an HCV vaccine candidate. The modified sE2 protein (F442NYT), unlike unmodified sE2, exhibited a significant reduction in CD81 binding, induced higher levels of proinflammatory cytokines, repressed anti-inflammatory response in primary monocyte-derived macrophages as antigen-presenting cells, and stimulated CD4⁺ T cell proliferation. Immunization of BALB/c mice with an E1/sE2_F442NYT nucleoside-modified mRNA-lipid nanoparticle (mRNA-LNP) vaccine resulted in improved IgG1-to-IgG2a isotype switching, an increase in neutralizing antibodies against HCV pseudotype virus, a B and T cell proliferative response to antigens, and improved protection against infection with a surrogate recombinant vaccinia virus-expressing HCV E1-E2-NS2_aa134-966 challenge model compared to E1/unmodified sE2 mRNA-LNP vaccine. Further investigation of the modified E2 antigen may provide helpful information for HCV vaccine development. IMPORTANCE Hepatitis C virus (HCV) E2-CD81 binding dampens protective immune response. We have identified that an alteration of amino acids in the front layer of soluble E2 (sE2) disrupts CD81 interaction and alters the cytokine response. Immunization with modified sE2_F442NYT (includes an added potential N-linked glycosylation site and reduces CD81 binding activity)-mRNA-LNP candidate vaccine generates improved proinflammatory response and protective efficacy against a surrogate HCV vaccinia challenge model in mice. The results clearly suggested that HCV E2 exhibits immunoregulatory activity that inhibits induction of robust protective immune responses. Selection of engineered E2 antigen in an mRNA-LNP platform amenable to nucleic acid sequence alterations may open a novel approach for multigenotype HCV vaccine development.

Keyhole Limpet Hemocyanin-Conjugated Peptides from Hepatitis C Virus Glycoproteins Elicit Neutralizing Antibodies in BALB/c Mice

Currently, no vaccine to prevent hepatitis C virus (HCV) infection is available. A major challenge in developing an HCV vaccine is the high diversity of HCV sequences. The purpose of immunization with viral glycoproteins is to induce a potent and long-lasting cellular and humoral immune response. However, this strategy only achieves limited protection, and antigen selection plays a crucial role in vaccine design. In this study, we investigated the humoral immune responses induced by intraperitoneal injection of keyhole limpet hemocyanin conjugated with 4 highly conserved peptides, including amino acids [aa]317-325 from E1 and aa418-429, aa502-518, and aa685-693 from E2, or 3 peptides from hypervariable region 1 (HVR1) of E2, including the N terminus of HVR1 (N-HVR1, aa384-396), C terminus of HVR1 (C-HVR1, aa397-410), and HVR1 in BALB/c mice. The neutralizing activity against HCV genotypes 1-6 was assessed using the cell culture HCV (HCVcc) system. The results showed that the 4 conserved peptides efficiently induced antibodies with potent neutralizing activity against 3 or 4 genotypes. Antibodies induced by aa685-693 conferred potent protection (>50%) against genotypes 2, 4, and 5. Peptide N-HVR1 elicited antibodies with the most potent neutralization activities against 3 HCV genotypes: TNcc(1a), S52(3a), and ED43(4a). These findings suggested that peptides within HCV glycoproteins could serve as potent immunogens for vaccine design and development.

Function of the HCV E1 envelope glycoprotein in viral entry and assembly

HCV envelope glycoproteins, E1 and E2, are multifunctional proteins. Until recently, E2 glycoprotein was thought to be the fusion protein and was the focus of investigations. However, the recently obtained partial structures of E2 and E1 rather support a role for E1 alone or in association with E2 in HCV fusion. Moreover, they suggest that HCV harbors a new fusion mechanism, distinct from that of other members of the Flaviviridae family. In this context, E1 aroused a renewed interest. Recent functional characterizations of E1 revealed a more important role than previously thought in entry and assembly. Thus, E1 is involved in the viral genome encapsidation step and influences the association of the virus with lipoprotein components. Moreover, E1 modulates HCV–receptor interaction and participates in a late entry step potentially fusion. In this review, we outline our current knowledge on E1 functions in HCV assembly and entry.

Development and characterization of a human monoclonal antibody targeting the N-terminal region of hepatitis C virus envelope glycoprotein E1

Monoclonal antibodies (mAbs) targeting the hepatitis C virus (HCV) envelope have been raised mainly against envelope protein 2 (E2), while the antigenic epitopes of envelope protein 1 (E1) are not fully identified. Here we describe the detailed characterization of a human mAb, designated A6, generated from an HCV genotype 1b infected patient. ELISA results showed reactivity of mAb A6 to full-length HCV E1E2 of genotypes 1a, 1b and 2a. Epitope mapping identified a region spanning amino acids 230-239 within the N-terminal region of E1 as critical for binding. Antibody binding to this epitope was not conformation dependent. Neutralization assays showed that mAb A6 lacks neutralizing capacity and does not interfere with the activity of known neutralizing antibodies. In summary, mAb A6 is an important tool to study the structure and function of E1 within the viral envelope, a crucial step in the development of an effective prophylactic HCV vaccine.

Fine mapping of murine antibody responses to immunization with a novel soluble form of hepatitis C virus envelope glycoprotein complex

The hepatitis C virus (HCV) envelope glycoprotein E1E2 complex is a candidate vaccine antigen. Previous immunization studies of E1E2 have yielded various results on its ability to induce virus-neutralizing antibodies in animal models and humans. The murine model has become a vital tool for HCV research owing to the development of humanized mice susceptible to HCV infection. In this study, we investigated the antibody responses of mice immunized with E1E2 and a novel soluble form of E1E2 (sE1E2) by a DNA prime and protein boost strategy. The results showed that sE1E2 elicited higher antibody titers and a greater breadth of reactivity than the wild-type cell-associated E1E2. However, immune sera elicited by either immunogen were only weakly neutralizing. In order to understand the contrasting results of binding and serum neutralizing activities, epitopes targeted by the polyclonal antibody responses were mapped and monoclonal antibodies (MAbs) were generated. The results showed that the majority of serum antibodies were directed to the E1 region 211 to 250 and the E2 regions 421 to 469, 512 to 539, 568 to 609, and 638 to 651, instead of the well-known immunodominant E2 hypervariable region 1 (HVR1). Unexpectedly, in MAb analysis, ∼ 12% of MAbs isolated were specific to the conserved E2 antigenic site 412 to 423, and 85% of them cross-neutralized multiple HCV isolates. The epitopes recognized by these MAbs are similar but distinct from the previously reported HCV1 and AP33 broadly neutralizing epitopes. In conclusion, E1E2 can prime B cells specific to conserved neutralizing epitopes, but the levels of serum neutralizing antibodies elicited are insufficient for effective virus neutralization. The sE1E2 constructs described in this study can be a useful template for rational antigen engineering.

IMPORTANCE

Hepatitis C virus infects 2 to 3% of the world's population and is a leading cause of liver failures and the need for liver transplantation. The virus envelope glycoprotein complex E1E2 produced by detergent extraction of cells overexpressing the protein was evaluated in a phase I clinical trial but failed to induce neutralizing antibodies in most subjects. In this study, we designed a novel form of E1E2 which is secreted from cells and is soluble and compared it to wild-type E1E2 by DNA immunization of mice. The results showed that this new E1E2 is more immunogenic than wild-type E1E2. Detailed mapping of the antibody responses revealed that antibodies to the conserved E2 antigenic site 412 to 423 were elicited but the serum concentrations were too low to neutralize the virus effectively. This soluble E1E2 provides a new reagent for studying HCV and for rational vaccine design.

Mouse monoclonal antibody towards e1 specific epitope blocks viral entry and intracellular viral replication in vitro

We characterized viral neutralization by a murine monoclonal antibody (mAb315) developed against conserved E1 specific epitope aa 315-323 at pre- and post-binding steps of infection into Huh7 cells. Detection of native virus in infected Huh7 cells by mAb315 were demonstrated by immunostaining. Inhibitions of viral entry by three different concentrations of mAb315 were measured by intracellular amplification of HCV RNA post infection. HCV RNA positive sera from 24 patients were used to infect Huh7 cell line in absence or presence of mouse monoclonal antibody produced in Balb/c mice or culture supernatant of mouse hybrid cells. Monoclonal Ab mAb315 could detect synthetic peptide p315 adsorbed on peripheral human lymphocytes by flow cytometry and showed high immuno reactivity to E1 viral antigen in infected Huh7 cells by immunostaining. Antibody-mediated neutralization assays demonstrated the ability of mAb315 to block HCV binding/entry to target cells at 0.73 mg/mL ascitic fluid or 250 µg/mL culture supernatant of mouse hybrid cells. Sixteen of 24 infected sera could infect Huh7 cells (67%). Binding/entry of HCV was completely blocked by mAb315 in 11/16 cases (69%). These findings suggest that mAb315 can induce HCV neutralization in vitro, which makes it a candidate for developing HCV therapeutic antibodies.

Progress toward development of a hepatitis C vaccine with broad shoulders

Hepatitis C virus (HCV) infection in humans can cause progressive and end-stage liver disease. As such, preventive measures against HCV, including vaccine development, are a priority among researchers in the field. The report from Garrone et al. describes the development of a vaccine platform to generate HCV-neutralizing antibodies that are based on retrovirus-derived virus-like particles (VLPs) pseudotyped with heterologous viral envelope proteins. Immunization with these VLPs induced neutralizing antibodies in mouse and macaque models. These results, when considered in the context of an earlier clinical trial that used recombinant HCV E1/E2 purified protein as a subunit vaccine and additional findings from the VLP strategy, may lead to a new HCV vaccine that induces a neutralizing antibody response.

Hepatitis C virus E1 envelope glycoprotein interacts with apolipoproteins in facilitating entry into hepatocytes

Our previous studies demonstrated that hepatitis C virus (HCV) envelope glycoproteins 1 and 2 (E1 and E2) display distinct reactivity to different cell-surface molecules. In this study, we characterized the interaction of E1 and E2 with apolipoproteins in facilitating virus entry. The results suggested a higher neutralization of vesicular stomatitis virus (VSV)/HCV E1-G pseudotype infectivity by antibodies to apolipoprotein E (ApoE) than apolipoprotein B (ApoB), with VSV/HCV E2-G pseudotype infectivity remaining largely unaffected. Neutralization of cell-culture-grown HCV infectivity by antiserum to ApoE and, to a lesser extent, by ApoB further verified their involvement in virus entry. HCV E1, but not E2, displayed binding with ApoE and ApoB by enzyme-linked immunosorbent assay. Binding of E1 with apolipoproteins were further supported by coimmunoprecipitation from human hepatocytes expressing E1. Rabbit antiserum to a selected E1 ectodomain-derived peptide displayed ∼ 50% neutralization of E1-G pseudotype infectivity. Furthermore, E1 ectodomain-derived synthetic peptides significantly inhibited the interaction of E1 with both the apolipoproteins. Investigation on the role of low-density lipoprotein receptor (LDL-R) as a hepatocyte surface receptor for virus entry suggested a significant reduction in E1-G pseudotype plaque numbers (∼ 70%) by inhibiting LDL-R ligand-binding activity using human proprotein convertase subtilisin/kexin type 9 and platelet factor-4, whereas they had a minimal inhibitory effect on the E2-G pseudotype.

CONCLUSION

Together, the results suggested an association between HCV E1 and apolipoproteins, which may facilitate virus entry through LDL-R into mammalian cells.

Big changes are coming in hepatitis C

The story of hepatitis C virus (HCV) therapy is about to add one of its biggest chapters. From the serendipitous beginnings in the 1980s when investigators noted that interferon improves liver enzymes in non-A, non-B hepatitis, to the discovery and naming of the hepatitis virus, to the addition of ribavirin, to the pegylation of interferon, and now to the first direct-acting antivirals (DAA), the history of HCV is an intriguing one that continues to unfold. Along with the first DAAs, other important findings have helped explain long-observed differences between various ethnic groups, as well as new predictive information that can be gleaned from some of the observed adverse events.

Characterization of antibodies induced by vaccination with hepatitis C virus envelope glycoproteins

Hepatitis C virus (HCV) envelope glycoproteins E1 and E2 were used with MF59 adjuvant as a candidate vaccine for a phase 1 safety and immunogenicity trial. Ten of 41 vaccinee serum samples displayed a neutralization titer of ⩾1:20 against vesicular stomatitis virus (VSV)-HCV pseudotype, 15 of 36 serum samples tested had a neutralization titer of ⩾1:400 against human immunodeficiency virus (HIV)-HCV pseudotype, and 10 of 36 serum samples tested had a neutralization titer of ⩾1:20 against cell culture-grown HCV genotype 1a. Neutralizing serum samples had increased affinity levels and displayed >2-fold higher specific activity levels to well-characterized epitopes on E1/E2, especially to the hypervariable region 1 of E2.

Sequence uniqueness and sequence variability as modulating factors of human anti-HCV humoral immune response

We recently compared the HCV polyprotein to the human proteome in order to test whether amino acid sequences unique to the virus could represent immunodominant epitopic determinants of the human humoral immune response against HCV. We identified a relatively limited number of HCV fragments with no/low similarity to the human host that represented exclusive HCV motifs. In this study, the peptides corresponding to low/zero similarity sequences were synthesized and assayed with HCV-infected sera. With different patterns, the synthetic HCV peptides corresponding to low/zero similarity sequences were found to be immunoreactive. In particular, the HCV E1 (315-323) HRMAWDMMM, HCV E2/NS1 (547-555) NWFGCTWMN, and HCV NS5 (2638-2646) YDTRCFDST sequences were immunodominant in the HCV-infected cohort under study. These three peptides correspond to sequences that are endowed with low-similarity to the human proteome, are highly conserved among various HCV strains, and have, potentially, a scarce susceptibility to proteolytic attacks. These data may be of help in defining the multiple factors which concur in the modulation of the human immune response against HCV, eventually providing information for the design of effective anti-HCV vaccines.

Isolation and characterization of broadly neutralizing human monoclonal antibodies to the e1 glycoprotein of hepatitis C virus

The relative importance of humoral and cellular immunity in the prevention or clearance of hepatitis C virus (HCV) infection is poorly understood. However, there is considerable evidence that neutralizing antibodies are involved in disease control. Here we describe the detailed analysis of human monoclonal antibodies (MAbs) directed against HCV glycoprotein E1, which may have the potential to control HCV infection. We have identified two MAbs that can strongly neutralize HCV-pseudotyped particles (HCVpp) bearing the envelope glycoproteins of genotypes 1a, 1b, 4a, 5a, and 6a and less strongly neutralize HCVpp bearing the envelope glycoproteins of genotype 2a. Genotype 3a was not neutralized. The epitopes for both MAbs were mapped to the region encompassing amino acids 313 to 327. In addition, robust neutralization was also observed against cell culture-adapted viruses of genotypes 1a and 2a. Results from this study suggest that these MAbs may have the potential to prevent HCV infection.

Expression and immunoreactivity of an epitope of HCV in a foreign epitope presenting system

AIM: To construct and highly express an epitope of hepatitis C virus (HCV) in a foreign epitope presenting vector based on an insect virus, and to study the antigenicity of the epitope.

METHODS: The HCV epitope sequence (amino acid residues 315 to 328: EGHRMAWDMMMNWS) of the E1 region was constructed at different positions of a foreign epitope presenting vector based on an insect virus, flock house virus (FHV) capsid protein encoding gene as a vector, and expressed in E. coli cells. Western blotting and ELISA were used to detect the immunoreactivity of these recombinant proteins.

RESULTS: The gene encoding of the concerned B-cell epitope of HCV E1 envelope protein was expressed on FHV capsid carrier protein at positions I1 (aa 106), I2 (aa 153) and I3 (aa 305), respectively, on the surface of FHV capsid protein. The recombinant proteins in this system could be highly expressed in more than 40% of total cell protein of E. coli BL21. All the expressed recombinant proteins were in inclusion body form, and showed obvious immunoreactivity by Western blotting. Further purified recombinant proteins were detected by indirect ELISA as coating antigen respectively. All recombinant proteins could still show immunoreactivity.

CONCLUSION: The epitope of HCV E1 envelope protein can be highly expressed in FHV carrier system as a chimeric protein with high immunoreactivity. This system has multiple entry sites conferring many possible conformations closer to the native one for a given sequence.

Uses of biosensor technology in the development of probes for viral diagnosis

BACKGROUND

Since 1990, a new biosensor technology based on surface plasmon resonance makes it possible to visualize molecular recognition as a function of time, in terms of change in mass concentration occurring on a sensor chip surface. One of the reactants is immobilized on a dextran matrix while the other is introduced in a flow passing over the surface. The binding is followed in real time by the increase in refractive index caused by the mass of bound species.

OBJECTIVES

In the present review, the applications of this new technology for developing probes intended for viral diagnosis will be described.

STUDY DESIGN

In contrast with other immunoassay systems, the biosensor technique preserves the conformational integrity of the reactants since no labelling is required. It also makes it possible to follow every step of a multiple-layer assay and allows interaction measurements in real time. Suitable antigen and antibody probes can be selected on the basis of the conditions of the diagnostic assay that is being developed, especially in terms of affinity and specificity.

RESULTS

Our results suggest that when the cyclic peptide 209-222 of the E1 protein of hepatitis C virus (HCV) is immobilized on the sensor chip via a biotin moiety, it retains a constrained conformation which is better recognized by HCV antibodies than the linear form. Data are presented which indicate that the biosensor technique facilitates the screening and selection of anti HIV-1 antibodies that are likely to possess the most potent neutralizing potential.

CONCLUSION

Since there is a good correlation between BIAcore and ELISA data, it seems likely that the biosensor technology will be increasingly used for developing reagents intended for viral diagnosis.

Multiple viral/self immunological cross-reactivity in liver kidney microsomal antibody positive hepatitis C virus infected patients is associated with the possession of HLA B51

Liver Kidney Microsomal autoantibody type 1(LKM1) directed to cytochrome P4502D6 (CYP2D6) characterises autoimmune hepatitis type-2 (AIH-2), but is also found in a proportion of chronic hepatitis C virus (HCV) infected patients, CYP2D6252-271 being a major B- cell autoepitope. Molecular mimicry and immunological cross-reactivity between CYP2D6252-271, HCV polyprotein and the infected cell protein 4 (ICP4) of herpes simplex virus type 1 (HSV-1) have been suggested as triggers for the induction of LKM1, but reactivity and cross-reactivity to the relevant sequences have not been investigated experimentally. CYP2D6252-271 and its viral homologues were constructed and tested by ELISA in the sera of 46 chronically infected HCV patients, 23 of whom were LKM1 positive. Reactivity to the E1 HCV and ICP4 HSV1 mimics was frequently found in HCV infected patients irrespectively of their LKM1 status; viral/self cross-reactivity (as indicated by inhibition studies), however, was present in the only 2 of the 23 LKM1 seropositive HCV patients, who possessed the HLA allotype B51. Our results indicate that in HCV infected patients virus/self cross-reactivity is dependent on a specific immunogenetic background, a finding awaiting confirmation by studies in larger series of patients.

Influence of N-linked glycans on intracellular transport of hepatitis C virus E1 chimeric glycoprotein and its role in pseudotype virus infectivity

We have previously reported a functional role associated with hepatitis C virus (HCV) E1 glycoprotein using vesicular stomatitis virus (VSV)/HCV pseudotype. In this study, we have investigated the role of glycosylation upon intracellular transport of chimeric E1-G, and in infectivity of the pseudotyped virus. Interestingly, surface expressed E1-G exhibited sensitivity to Endoglycosidase H (Endo H) treatment, which was similar to full-length E1, suggesting that additional complex oligosaccharides were not added while E1-G was in transit from the endoplasmic reticulum (ER) to the mammalian cell surface. As a next step, each of the four potential N-linked glycosylation sites located at amino acid position 196, 209, 234, or 305 of the E1 ectodomain were mutated separately (asparagine --> glutamine), or in some combination. FACS analysis suggested that mutation(s) of the glycosylation sites affect the translocation of E1-G to the cell surface to different extents, with no single site being particularly essential. VSV pseudotype virus generated from glycosylation mutants exhibited a decrease in titer with an increasing number of mutations at the glycosylation sites on chimeric E1-G. In a separate experiment, N-glycosidase F treatment of pseudotype generated from the already synthesized E1-G or its mutants decreased virus titer by approximately 35%, and the neutralization activity of patient sera was not significantly altered with N-glycosidase F-treated pseudotype virus. Taken together, our results suggested that E1-G does not add complex sugar moieties during transport to the cell surface and retain the glycosylation profile of its parental E1 sequence. Additionally, the removal of glycans from the E1-G reduced, but does not completely impair, virus infectivity.

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

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

Mapping and characterization of B cell linear epitopes in the conservative regions of hepatitis C virus envelope glycoproteins

Forty-eight overlapping octapeptides covering highly conservative regions of E1 and E2 hepatitis C virus (HCV) envelope proteins were synthesized and tested by ELISA against different groups of sera obtained from HCV-infected patients. All sera from patients with acute infection, except a single case of serum reactivity with the region HINRTALN, were nonreactive with any peptide. Sera obtained from chronic patients reacted with 12 peptides from five selected regions. Two immunodominant B epitopes were found, one being the precisely mapped antigenic site RMAWDM positioned inside the earlier shown immunodominant epitope from E1, and the second site, PALSTGLIH from E2, detected for the first time. New minor antigenic site was determined as PTDCFRKH from E2. We found only minor seroreactivity for one of the putative sites involved in CD81 binding, PYCWHYAP.

The immunopathogenesis of hepatitis C virus infection

The outcome of HCV infection is determined by the interaction between the virus and the host immune system. The persistence of infection in most HCV-infected individuals, despite the presence of HCV-directed antibodies, suggests that such antibodies fail to induce viral clearance. Patients with self-limited hepatitis C have evidence of a polyclonal, multispecific CD8+ T-cell response along with a coordinated CD4+ T-cell response that is associated with eradication of HCV infection. Cytokines are produced both locally within the liver and systemically and may play an important role in controlling viral replication and contributing to hepatocellular damage through amplification of a nonspecific immune response. In most patients, the humoral, cellular immune, and cytokine response seem insufficient to eradicate infection. In its attempt to clear the virus from the liver, the immune system contributes to the hepatocellular injury seem in most chronically infected patients. A better understanding of the host's immune response may provide further insight on the pathogenetic mechanisms involved in development of chronic hepatitis and aid the development of better therapeutic strategies.

[Characteristics of the hepatitis C virus and viral predictors of therapeutic response]

NATURAL HISTORY OF HEPATITIS C-INFECTION AND VIRAL CHARACTERISTICS: Hepatitis C-virus (HCV) infection is a major cause of non-A, non-B-hepatitis and, additionally, is associated with liver cirrhosis and hepato-cellular carcinoma. The high degree of chronificity of HCV-infection is reasonable due to antigenic variability of neutralizing epitopes leading to incomplete immunoresponse with subsequent virus persistence. Besides genetic variants of HCV within a virus population (quasispecies nature of HCV), different genotypes are classified being genetically and phenotypically distinct, and geographically restricted in part. Genotyping of HCV is not only important for phylogenetic and epidemiological studies, but also a predictive marker for pathogenesis and therapy. VIRAL PREDICTORS OF HCV THERAPY: In a meta-analysis of 18 therapeutical studies of chronical HCV infections, genotype 1 and high levels of viremia determined markedly the response to interferon therapy. In this context, clinical trials have proven the effect of a combined therapy with interferon and ribavirin. Especially patients with HCV genotype 1 or high levels of viremia had a real benefit from combined antiviral therapy in comparison to monotherapy with interferon. CONCLUSION AND FUTURE CONCEPTS: Besides recent concepts improving the therapeutical response to HCV infection, further effort is necessary to develop more successful strategies for eradication of hepatitis C virus. In this context, variations of interferon therapy should be evaluated (e.g. higher and daily doses, longer duration of interferon therapy, "retarded" interferon (PEG-IFN). In addition, new therapeutical concepts should be performed including a combination of interferon with other known antiviral agents (amantadine), a combination with immunomodulators (GM-CSF, thymosin alpha 1), the development of new antiviral agents (inhibitors of viral proteases, helicases and polymerases) and the exploration of anti-viral, molecular strategies (specific ribozymes, antisense oligonucleotides and DNA-vaccination). Nevertheless, the development of an effective vaccination should be the most important challenge for the future.

Long-term follow-up of chimpanzees inoculated with the first infectious clone for hepatitis C virus

Two chimpanzees (Ch1535 and Ch1536) became infected with hepatitis C virus (HCV) following intrahepatic inoculation with RNA transcribed from a full-length cDNA clone of the virus. Both animals were persistently infected and have been followed for 60 weeks. They showed similar responses to infection, with transient liver enzyme elevations and liver inflammatory responses, which peaked at weeks 17 (Ch1535) and 12 (Ch1536) postinoculation (p.i.). Antibody responses to structural and nonstructural proteins were first detected at weeks 13 (Ch1535) and 10 (Ch1536) p.i. Serum RNA titers increased steadily during the first 10 to 13 weeks but decreased sharply in both animals following antibody and inflammatory responses. Despite direct evidence of humoral immune responses to multiple viral antigens, including hypervariable region 1 (HVR1), both animals remained chronically infected. Detailed sequence analysis of serum HCV RNA revealed no change in the majority HVR1 sequence in Ch1535 and a single-amino-acid mutation in Ch1536, with very little clonal variation in either animal. Full-length genome analysis at week 60 revealed several amino acid substitutions localized to antigens E1, E2, p7, NS3, and NS5. Of these, 55.6 and 40% were present as the majority sequence in serum RNA isolated at week 26 p.i. (Ch1535) and week 22 p.i. (Ch1536), respectively, and could represent immune escape mutations. Mutations accumulated at a rate of 1.57 x 10(-3) and 1.48 x 10(-3) nucleotide substitutions/site/year for Ch1535 and Ch1536, respectively. Taken together, these data indicate that establishment of a persistent HCV infection in these chimpanzees is not due to changes in HVR1; however, the possibility remains that mutations arising in other parts of the genome contributed to this persistence.

Immunodominant B-cell domains of hepatitis C virus envelope proteins E1 and E2 identified during early and late time points of infection

BACKGROUND/AIMS

We characterized immunoreactive B-cell domains of hepatitis C virus (HCV) envelope proteins E1 and E2 by a peptide ELISA using sera of patients who were infected by the same isolate of HCV (HCV-AD78).

METHODS

Fifty-four overlapping peptides which corresponded to the sequence of E1 and E2 of isolate HCV-AD78 were used to detect specific antibodies. Three groups of HCV-AD78 related sera were analyzed. Two groups were from sera obtained at early time points of infection (months 4-15) from patients who later resolved infection (group A), or who later developed chronic disease (group B). Group C sera were from later time points of chronic disease. As a control, sera of chronic HCV patients who did not have HCV-AD78 infection were also analyzed (group D).

RESULTS

In group A, 25 of the 54 peptides produced OD405 above the cut-off, whereas 17 peptides produced such values in group B. Only 10 and 3 peptides yielded such values in groups C and D, respectively. The overall prevalence of antibodies against peptides was high in the early phase of infection (means of 28.7+/-14.8% and 25.9+/-14.5% in groups A and B, respectively). At later time points of chronic infection (group C), the overall prevalence was lower (mean 18.6+/-15.4%). Group D sera produced the lowest overall prevalence (mean 13.2+/-14.1%). Three peptides, covering aa271-290, aa481-500 and aa551-570, were recognized significantly more frequently (p<0.05) by group A sera than group B sera.

CONCLUSIONS

We conclude that more linear epitopes of the HCV envelope are recognized with a high prevalence of antibodies, as was suggested previously. However, most B-cell domains of the HCV envelope induce a similarly high antibody response in patients who resolve infection or develop chronic disease.

Functional role of hepatitis C virus chimeric glycoproteins in the infectivity of pseudotyped virus

The putative envelope glycoproteins of hepatitis C virus (HCV) likely play an important role in the initiation of viral infection. Available information suggests that the genomic regions encoding the putative envelope glycoproteins, when expressed as recombinant proteins in mammalian cells, largely accumulate in the endoplasmic reticulum. In this study, genomic regions which include the putative ectodomain of the E1 (amino acids 174 to 359) and E2 (amino acids 371 to 742) glycoproteins were appended to the transmembrane domain and cytoplasmic tail of vesicular stomatitis virus (VSV) G protein. This provided a membrane anchor signal and the VSV incorporation signal at the carboxy termini of the E1 and E2 glycoproteins. The chimeric gene constructs exhibited expression of the recombinant proteins on the cell surface in a transient expression assay. When infected with a temperature-sensitive VSV mutant (ts045) and grown at the nonpermissive temperature (40.5 degrees C), cells transiently expressing the E1 or E2 chimeric glycoprotein generated VSV/HCV pseudotyped virus. The resulting pseudotyped virus generated from E1 or E2 surprisingly exhibited the ability to infect mammalian cells and sera derived from chimpanzees immunized with the homologous HCV envelope glycoproteins neutralized pseudotyped virus infectivity. Results from this study suggested a potential functional role for both the E1 and E2 glycoproteins in the infectivity of VSV/HCV pseudotyped virus in mammalian cells. These observations further suggest the importance of using both viral glycoproteins in a candidate subunit vaccine and the potential for using a VSV/HCV pseudotyped virus to determine HCV neutralizing antibodies.

Antibodies directed to envelope proteins of hepatitis C virus outside of hypervariable region 1

The relatively high variability of the hepatitis C virus (HCV) envelope proteins E1 and E2 suggests that parts of these proteins other than the hypervariable region 1 (HVR1) might be involved in the induction of virus neutralizing antibodies. To test this hypothesis, two HCV proteins, pE1 and pE2 delta, were generated by in vitro translation. They represent amino acids 174-337 of E1 and 411-688 of E2, respectively, of isolate HCV-AD78; the protein pE2 delta contained no HVR1. As a control, protein pG.HVR1, which represents amino acids 384-410 of HVR1 of isolate HCV-AD78, was expressed separately. These three proteins were used in an immunoprecipitation assay to detect the presence of antiviral antibodies in sera of patients infected with the same isolate of HCV (HCV-AD78). Sera were obtained 4-8 months postinfection from patients who later resolved an acute infection or developed chronic liver disease. A high prevalence of antibodies (up to 85.7%) against pE1 and pE2 delta could be detected in both groups of patients, suggesting that these forms of the HCV envelope proteins contain B-cell epitopes. The antibody responses against proteins pE1 and pE2 delta did not differ significantly between patients with resolving or chronic infection, whereas antibodies against protein pG.HVR1 were associated with resolution of infection. Rabbit antisera raised against pE1 and pE2 delta were tested for their ability to neutralize the binding of HCV to susceptible cells in tissue cultures. The results suggested that although a few B-cell epitopes outside of HVR1 can induce virus neutralizing antibodies, these antibodies are probably not associated with the resolution of infection.

Pathogenesis of hepatocellular damage in chronic hepatitis C virus infection

Multiple factors may influence the host-virus interaction in patients infected with hepatitis C virus (HCV), and these may result in diverse disease presentations. In immune competent hosts, there is little evidence that direct cytopathicity plays a significant role in liver cell injury. However, when host conditions are altered to allow for unusually high levels of viral replication and viral protein expression (i.e., immunosuppression), HCV may induce direct hepatocellular damage. In most patients infected with HCV, a wide array of humoral and cell-mediated immune responses are triggered in response to HCV polypeptides; however, despite this host immune response, HCV infections usually persist. Furthermore, the host immune response, in its attempt to clear the virus from the liver, contributes to the hepatocellular damage (chronic hepatitis) seen in the majority of chronically infected patients.

Evaluation of hepatitis C virus envelope proteins expressed in E. coli and insect cells for use as tools for antibody screening

BACKGROUND/METHODS

The two envelope proteins of hepatitis C virus, E1 and E2, were expressed in E. coli and, as secretory proteins, in Sf9 insect cells using recombinant baculoviruses. Co-infection of insect cells with E1 and E2-recombinant baculoviruses was performed, which has been shown to result in formation of E1-E2 dimers. All envelope proteins were purified by Ni2+-NTA chromatography and used for screening of serum samples in a HCV EIA assay. Serum samples of normal blood donors, chronically HCV-infected patients, a mixed titer panel and several seroconversion panels were screened and compared to test results with Cobas Core Anti-HCV EIA.

RESULTS

Screening of the sera of chronically HCV-infected patients (100% positive in Cobas Core Anti-HCV EIA) revealed 10-40% anti-E1 positive sera using different Sf9-expressed, glycosylated proteins and 93% using E. coli-expressed, non-glycosylated E1 protein. When the same sera were tested with different E2 proteins expressed in Sf9 cells and in E. coli, about 70-73% showed anti-E2 reactivity. When the proteins from Sf9 cells co-infected with E1- and E2-recombinant baculoviruses were tested, 70-80% of the same sera showed anti-envelope reactivity.

CONCLUSIONS

Testing of these patient antisera, and those from the well-characterized mixed titer panel BBI-PHV203, showed that recombinant E1 expressed in E. coli and co-expressed E1 and E2 proteins from Sf9 cells could be used as additional tools for anti-HCV antibody screening.

Hepatitis C virus core protein cooperates with ras and transforms primary rat embryo fibroblasts to tumorigenic phenotype

We have previously demonstrated that hepatitis C virus (HCV) core protein regulates cellular protooncogenes at the transcriptional level; this observation implicates core protein in the alteration of normal hepatocyte growth. In the present study, the transforming potential of the HCV core gene was investigated by using primary rat embryo fibroblast (REF) cells which were transfected with or without cooperative oncogenes. Integration of the HCV core gene resulted in expression of the viral protein in REF stable transformants. REF cells cotransfected with HCV core and H-ras genes became transformed and exhibited rapid proliferation, anchor-independent growth, and tumor formation in athymic nude mice. Results from these studies suggest that the core protein plays an important role in the regulation of HCV-infected cell growth and in the transformation to tumorigenic phenotype. These observations suggest a possible mechanism for this viral protein in the pathogenesis of hepatocellular carcinoma in HCV-infected humans.

Murine humoral immune response against recombinant structural proteins of hepatitis C virus distinct from those of patients

We examined the humoral immune response to recombinant structural proteins of hepatitis C virus (HCV) such as C, E1 and E2 in immunized mice. Mice showed high induction of antibodies against these three structural proteins. Conformational and/or linear epitopes of these regions showed high responses in mice. Comparison with patients revealed higher anti-E1 and anti-E2 responses in mice and 15 immunoreactive peptides which are unique to mice, especially 11 peptides from the E2 region. The hydrophilic regions of these proteins were found to be the most immunogenic. Therefore, the murine immune system against recombinant E1 and E2 glycoproteins was distinct from those of patients in natural infection, and may be a target to find protective activity against HCV infection.

Immune responses to plasmid DNA encoding the hepatitis C virus core protein

Hepatitis C virus (HCV) is a major causative agent of parenterally transmitted non-A, non-B hepatitis. The genomic region encoding the virion-associated core protein is relatively conserved among HCV strains. To generate a DNA vaccine capable of expressing the HCV core protein, the genomic region encoding amino acid residues 1 to 191 of the HCV-1 strain was amplified and cloned into an eukaryotic expression vector. Intramuscular inoculation of recombinant plasmid DNA into BALB/c mice (H-2d) generated core-specific antibody responses, lymphoproliferative responses, and cytotoxic T-lymphocyte activity. Our results suggest that the HCV core polynucleotide warrants further investigation as a potential vaccine against HCV infection.

Human monoclonal antibodies for the immunological characterization of a highly conserved protein domain of the hepatitis C virus glycoprotein E1

Although both envelope glycoproteins of the hepatitis C virus, E1 and E2/NS1, show a high degree of sequence variation, the E1 protein includes a well conserved domain, which may be functionally important. We have analysed the human B cell response to a peptide fragment from amino acid residues 314-330 (EP3) covering the central conserved sequence of this domain. Anti-hepatitis C virus-positive blood donors were screened for anti-EP3 antibodies with an ELISA based on immobilized peptide. Thirty out of 92 (32%) RIBA-confirmed donors displayed a significant antibody response to EP3. From three of these blood donors we established four anti-EP3-producing heterohybridoma cell lines: Ul/F30 and Ul/F31 produced IgM-kappa, whereas Ul/F32 and Ul/F33 secreted the isotypes IgG1-lambda and IgG1-kappa, respectively. Epitope analysis with overlapping nonapeptides suggests the existence of different antigenic determinants within the EP3 fragment. Although both IgG antibodies Ul/F32 and Ul/F33 have dissociation constants to the peptide of approximately 10(-9) M, binding to recombinant E1 protein expressed in COS-7 cells was different. Only Ul/F33 detected envelope protein of approximately 24-35 kD in Western blot. This human MoAb will be useful for further investigations on the hepatitis C virus glycoprotein E1.

Transcriptional regulation of cellular and viral promoters by the hepatitis C virus core protein

The genomic region encoding the hepatitis C virus (HCV) core protein was cloned into a mammalian expression vector to study its role on the transcriptional regulation of cellular proto-oncogene and viral promoters. Using a transient transfection assay in human hepatocellular carcinoma (HepG2) cells, we demonstrate that the HCV core protein activates the human c-myc, Rous sarcoma virus long terminal repeat (LTR), and simian virus 40 (SV40) early promoters; and suppresses the c-fos promoter and human immunodeficiency virus type 1 (HIV-1) LTR activity. The transcriptional regulation of cellular proto-oncogenes by the HCV core protein suggests possible involvement of the core protein in the deregulation of normal hepatocyte growth and hepatocarcinogenesis.

Hepatitis C: progress and problems

The hepatitis C virus (HCV), a single-stranded RNA virus, is the major cause of posttransfusion hepatitis. HCV isolates differ in nucleotide and amino acid sequences. Nucleotide changes are concentrated in hypervariable regions and may be related to immune selection. In most immunocompetent persons, HCV infection is diagnosed serologically, using antigens from conserved regions. Amplification of RNA may be necessary to detect infection in immunosuppressed patients. Transmission by known parenteral routes is frequent; other means of spread are less common and may represent inapparent, percutaneous dissemination. Infection can lead to classical acute hepatitis, but most infected persons have no history of acute disease. Once infected, most individuals apparently remain carriers of the virus, with varying degrees of hepatocyte damage and fibrosis ensuing. Chronic hepatitis may lead to cirrhosis and hepatocellular carcinoma. However, disease progression varies widely, from less than 2 years to cirrhosis in some patients to more than 30 years with only chronic hepatitis in others. Determinants important in deciding outcome are unknown. Alpha interferon, which results in sustained remission in selected patients, is the only available therapy. Long-term benefits from such therapy have not been demonstrated. Prevention of HCV infection by vaccination is likely to be challenging if ongoing viral mutation results in escape from neutralization and clearance.