Occurrence of antibodies reactive with more than one variant of the putative envelope glycoprotein (gp70) hypervariable region 1 in viremic hepatitis C virus-infected patients

Hypervariable Region 1 in Envelope Protein 2 of Hepatitis C Virus: A Linchpin in Neutralizing Antibody Evasion and Viral Entry

Chronic hepatitis C virus (HCV) infection is the cause of about 400,000 annual liver disease-related deaths. The global spread of this important human pathogen can potentially be prevented through the development of a vaccine, but this challenge has proven difficult, and much remains unknown about the multitude of mechanisms by which this heterogeneous RNA virus evades inactivation by neutralizing antibodies (NAbs). The N-terminal motif of envelope protein 2 (E2), termed hypervariable region 1 (HVR1), changes rapidly in immunoglobulin-competent patients due to antibody-driven antigenic drift. HVR1 contains NAb epitopes and is directly involved in protecting diverse antibody-specific epitopes on E1, E2, and E1/E2 through incompletely understood mechanisms. The ability of HVR1 to protect HCV from NAbs appears linked with modulation of HCV entry co-receptor interactions. Thus, removal of HVR1 increases interaction with CD81, while altering interaction with scavenger receptor class B, type I (SR-BI) in a complex fashion, and decreasing interaction with low-density lipoprotein receptor. Despite intensive efforts this modulation of receptor interactions by HVR1 remains incompletely understood. SR-BI has received the most attention and it appears that HVR1 is involved in a multimodal HCV/SR-BI interaction involving high-density-lipoprotein associated ApoCI, which may prime the virus for later entry events by exposing conserved NAb epitopes, like those in the CD81 binding site. To fully elucidate the multifunctional role of HVR1 in HCV entry and NAb evasion, improved E1/E2 models and comparative studies with other NAb evasion strategies are needed. Derived knowledge may be instrumental in the development of a prophylactic HCV vaccine.

Virus-Specific Cellular Response in Hepatitis C Virus Infection

Studies performed on chimpanzees and humans have revealed that strong, multispecific and sustained CD4(+) and CD8(+) T cell immune responses is a major determinant of hepatitis C virus (HCV) clearance. However, spontaneous elimination of the virus occurs in minority of infected individuals and cellular response directed against HCV antigens is not persistent in individuals with chronic infection. This review presents characteristics of the HCV-specific T cell response in patients with different clinical course of infection, including acute and chronic infection, persons who spontaneously eliminated HCV and non-infected subjects exposed to HCV. Detection of HCV-specific response, especially in non-infected subjects exposed to HCV, may be indicative of HCV prevalence in population and rate of spontaneous viral clearance. Understanding the mechanisms and role of HCV-specific cellular immune response would contribute to better understanding of HCV epidemiology, immunopathogenesis and may help to design an effective vaccine.

Antigenic cooperation among intrahost HCV variants organized into a complex network of cross-immunoreactivity

Hepatitis C virus (HCV) has the propensity to cause chronic infection. Continuous immune escape has been proposed as a mechanism of intrahost viral evolution contributing to HCV persistence. Although the pronounced genetic diversity of intrahost HCV populations supports this hypothesis, recent observations of long-term persistence of individual HCV variants, negative selection increase, and complex dynamics of viral subpopulations during infection as well as broad cross-immunoreactivity (CR) among variants are inconsistent with the immune-escape hypothesis. Here, we present a mathematical model of intrahost viral population dynamics under the condition of a complex CR network (CRN) of viral variants and examine the contribution of CR to establishing persistent HCV infection. The model suggests a mechanism of viral adaptation by antigenic cooperation (AC), with immune responses against one variant protecting other variants. AC reduces the capacity of the host's immune system to neutralize certain viral variants. CRN structure determines specific roles for each viral variant in host adaptation, with variants eliciting broad-CR antibodies facilitating persistence of other variants immunoreacting with these antibodies. The proposed mechanism is supported by empirical observations of intrahost HCV evolution. Interference with AC is a potential strategy for interruption and prevention of chronic HCV infection.

Three different functional microdomains in the hepatitis C virus hypervariable region 1 (HVR1) mediate entry and immune evasion

High genetic heterogeneity is an important characteristic of hepatitis C virus (HCV) that contributes to its ability to establish persistent infection. The hypervariable region 1 (HVR1) that includes the first 27 amino acid residues of the E2 envelope glycoprotein is the most variable region within the HCV polyprotein. HVR1 plays a major role in both HCV cell entry and immune evasion, but the respective contribution of specific amino acid residues is still unclear. Our mutagenesis analyses of HCV pseudoparticles and cell culture-derived HCV using the H77 isolate indicate that five residues at positions 14, 15, and 25-27 mediate binding of the E2 protein to the scavenger receptor class B, type I receptor, and any residue herein is indispensable for HCV cell entry. The region spanning positions 16-24 contains the sole neutralizing epitope and is dispensable for HCV entry, but it is involved in heparan binding. More importantly, this region is necessary for the enhancement of HCV entry by high density lipoprotein and interferes with virus neutralization by E2-neutralizing antibodies. Residues at positions 1-13 are also dispensable for HCV entry, but they can affect HCV infectivity by modulating binding of the envelope protein to scavenger receptor class B, type I. Mutations occurring at this site may confer resistance to HVR1 antibodies. These findings further our understanding about the mechanisms of HCV cell entry and the significance of HVR1 variation in HCV immune evasion. They have major implications for the development of HCV entry inhibitors and prophylactic vaccines.

Vaccination with dendritic cells pulsed with hepatitis C pseudo particles induces specific immune responses in mice

AIM

To explore dendritic cells (DCs) multiple functions in immune modulation.

METHODS

We used bone-marrow derived dendritic cells from BALB/c mice pulsed with pseudo particles from the hepatitis C virus to vaccinate naive BALB/c mice. Hepatitis C virus (HCV) pseudo particles consist of the genotype 1b derived envelope proteins E1 and E2, covering a non-HCV core structure. Thus, not a single epitope, but the whole "viral surface" induces immunogenicity. For vaccination, mature and activated DC were injected subcutaneously twice.

RESULTS

Humoral and cellular immune responses measured by enzyme-linked immunosorbent assay and interferon-gamma enzyme-linked immunosorbent spot test showed antibody production as well as T-cells directed against HCV. Furthermore, T-cell responses confirmed two highly immunogenic regions in E1 and E2 outside the hypervariable region 1.

CONCLUSION

Our results indicate dendritic cells as a promising vaccination model for HCV infection that should be evaluated further.

Hepatitis C virus antigenic convergence

Vaccine development against hepatitis C virus (HCV) is hindered by poor understanding of factors defining cross-immunoreactivity among heterogeneous epitopes. Using synthetic peptides and mouse immunization as a model, we conducted a quantitative analysis of cross-immunoreactivity among variants of the HCV hypervariable region 1 (HVR1). Analysis of 26,883 immunological reactions among pairs of peptides showed that the distribution of cross-immunoreactivity among HVR1 variants was skewed, with antibodies against a few variants reacting with all tested peptides. The HVR1 cross-immunoreactivity was accurately modeled based on amino acid sequence alone. The tested peptides were mapped in the HVR1 sequence space, which was visualized as a network of 11,319 sequences. The HVR1 variants with a greater network centrality showed a broader cross-immunoreactivity. The entire sequence space is explored by each HCV genotype and subtype. These findings indicate that HVR1 antigenic diversity is extensively convergent and effectively limited, suggesting significant implications for vaccine development.

Evaluation of cross-reactive antibody response to HVR1 in chronic hepatitis C

AIM: To evaluate the presence and cross-reactive antibodies against hypervariable region 1 (HVR1) in hepatitis C virus (HCV) infected patients and its relationship with the progression of the disease.

METHODS: Sixteen representative HVR1 proteins selected from a unique set of 1600 natural sequences were used to semiquantitate the cross-reactivity of HVR1 antibodies in the sera of HCV patients. Fifty-five chronic HCV patients including 23 with asymptomatic mild hepatitis, 18 with chronic hepatitis and 16 with liver cirrhosis patients were studied.

RESULTS: The degree of the cross-reactivity of anti-HVR1 antibodies in 23 patients with mild asymptomatic hepatitis was 3.09 ± 2.68, which was significantly lower than in those with chronic hepatitis (5.44 ± 3.93, P < 0.05) and liver cirrhosis (7.44 ± 3.90, P < 0.01). No correlation was observed between the broadness of the cross-reactivity anti-HVR1 antibodies and patient’s age, infection time, serum alanine aminotransferase activity, or serum HCV-RNA concentration. It was the breath of cross-reactivity rather than the presence of anti-HVR1 antibody in HCV sera that was associated with the progression of liver disease.

CONCLUSION: The broadly cross-reactive HVR1 antibodies generated in natural HCV patients can not neutralize the virus, which results in persistent infection in patients with chronic hepatitis.

Hepatitis C virus quasispecies in HIV-infected women: role of injecting drug use and highly active antiretroviral therapy (HAART)

Despite the high frequency of HCV and HIV coinfection, little is known about HCV quasispecies in HIV-positive patients. The current analysis included 236 HIV+/anti-HCV+ women enrolled in the Women's Interagency HIV Study (WIHS). Hypervariable region 1 of the second envelope gene was analyzed by single-strand conformation polymorphism (SSCP). The relationship between the HCV quasispecies and clinical and demographic features were analyzed in multivariate models. Age over 40 years and high HCV RNA load were the only factors significantly associated with quasispecies complexity, assessed as the number of SSCP bands. High HIV and HCV plasma loads were associated with quasispecies stability over time, as reflected by stable SSCP band patterns. However, women who were actively injecting drugs were 3 times more likely to experience quasispecies changes than their noninjecting counterparts. No affect on HCV quasispecies dynamics was noted in relation to CD4 count or highly active antiretroviral therapy (HAART).

CONCLUSION

among HIV/HCV coinfected patients, HCV quasispecies complexity and dynamics correlate more closely with HIV and HCV plasma loads than with CD4+ cell counts. Active drug use is associated with quasispecies changes probably due to repeated superinfections with new HCV strains. This needs to be considered when planning treatment and prevention strategies for HCV in coinfected individuals.

A self-adjuvanting multiepitope immunogen that induces a broadly cross-reactive antibody to hepatitis C virus

We describe a peptide-based strategy for HCV vaccine design that addresses the problem of variability in hypervariable region 1 (HVR1). Peptides representing antibody epitopes of HVR1 from genotype 1a were synthesized and incorporated into multideterminant immunogens that also included lipid moieties and helper T (T(h)) cell epitopes. Mice inoculated with these polyepitopes generated strong antibody responses. Antibody titers were highest in mice inoculated with polyepitope immunogens which contained the lipid moiety dipalmitoyl-S-glyceryl cysteine (Pam2Cys). Antisera were tested for their potential to neutralize HCV by 3 currently available assays. Antibodies elicited in mice by the polyepitope-based vaccine candidates were able to (1) bind to E2 expressed on the surface of E1/E2-transfected human embryonic kidney (HEK) 293T cells, (2) capture HCV of different genotypes (1, 2, and 3) from the serum of chronically infected humans in an immune capture RT-PCR assay and (3) inhibit HCVpp entry into Huh7 cells. Antibody present in the sera of patients chronically infected with HCV genotypes 1, 2, 3, and 4 also bound to the HVR1-based polyepitope.

CONCLUSION

These results demonstrate the potential of self-adjuvanting epitope-based constructs in the development and delivery of cross-reactive immunogens that incorporate potential neutralizing epitopes present within the viral envelope of HCV.

Induction of neutralizing antibody responses to hepatitis C virus with synthetic peptide constructs incorporating both antibody and T‐helper epitopes

We describe a peptide-based strategy for hepatitis C virus (HCV) vaccine design that exploits synthetic peptides representing antibody epitopes of the hypervariable region 1 (HVR1) of the E2 glycoprotein and also less variable regions immediately downstream of HVR1. These epitopes were linked to a T-helper (T(h)) epitope (KLIPNASLIENCTKAEL) derived from the Morbillivirus canine distemper virus. Antibody titres induced by the two vaccine candidates T(h)-A (E2 amino acid 384-414) and T(h)-B (E2 amino acid 390-414) were significantly higher than those produced against vaccines lacking the T(h) epitope (P<0.05). Mice inoculated with the vaccine candidates T(h)-C (E2 amino acids 412-423) and T(h)-F (E2 amino acids 436-447) emulsified in complete Freund's adjuvant each elicited antibody titres that were significantly higher than those elicited by T(h)-E (E2 amino acids 396-407) and T(h)-D (E2 amino acids 432-443) (P<0.01). Antisera obtained from mice inoculated with the epitope vaccines T(h)-A, T(h)-B, T(h)-D and T(h)-E bound to E2 expressed at the surface of 293T cells that had been transfected with E1E2. Furthermore, IgG from the sera of mice inoculated with four of the vaccine candidates, T(h)-A, T(h)-C, T(h)-D and T(h)-E, inhibited the entry of HCV/human immunodeficiency virus pseudoparticles (HCVpps) into Huh-7 cells. These results demonstrate the potential of synthetic peptide-based constructs in the delivery of potential neutralizing epitopes that are present within the viral envelope of HCV.

Protective immunity against hepatitis C virus infection

There is increasing evidence that a small percentage of individuals exposed to the hepatitis C virus have the capacity to generate a strong cellular immune response against the virus and avoid persistent infection, and perhaps do so repeatedly after re-exposure. This article reviews the evidence that the responses identified in this unique group of individuals represent the protective immunity that will need to be elicited by hepatitis C virus vaccines.

Analysis of hepatitis C virus quasispecies transmission and evolution in patients infected through blood transfusion

BACKGROUND & AIMS

Studies on hepatitis C virus (HCV) quasispecies dynamics in the natural course of infection are rare owing to difficulties in obtaining samples from the early phase of infection.

METHODS

We studied 15 patients from the Transfusion-Transmitted Viruses Study who seroconverted to anti-HCV after receiving infected blood. Follow-up serum samples were collected every 2-3 weeks for 6 months, at 10 months, and at 11-16 years. Viral quasispecies in the second envelope hypervariable region 1 (E2/HVR1) and 5' untranslated region (5'UTR) were analyzed with single-strand conformation polymorphism (SSCP) and heteroduplex mobility assay (HMA).

RESULTS

Seven patients cleared infection within 7-24 weeks (mean, 14.0 wk) and 3 patients eventually became anti-HCV negative. In 6 patients with resolving hepatitis the SSCP band pattern remained stable, whereas in one patient minor changes appeared before clearance. In contrast, in all 8 patients progressing to chronicity, major changes in the E2/HVR1 quasispecies developed at 8-22 weeks (mean, 13.1 wk). Shannon entropy and medium mobility shift values derived from HMA gels remained stable in patients with resolving hepatitis but changed in those who developed chronic infection. Only 2 patients showed minor changes in 5'UTR. A decrease in E2/HVR1 complexity at the time of transmission (bottleneck) was found in 5 patients altogether.

CONCLUSIONS

Changes in E2/HVR1 quasispecies 8-22 weeks after infection, likely caused by mounting immune pressure, were predictive of ensuing chronic infection, whereas stability was associated with resolution. Our study also showed that composition of HCV quasispecies may be preserved during transmission from host to host.

Anti-envelope 1 and 2 immune response in chronic hepatitis C patients: Effects of hepatitis B virus co-infection and interferon treatment

Antibodies against envelope glycoprotein 1 and 2 (anti-E1/E2) have been suggested to influence HCV replication levels. Hepatitis B virus (HBV) may interfere with hepatitis C virus (HCV) replication. At present there are no data on anti-E1/E2 antibody responses or on the effect of interferon (IFN) treatment in HBV-HCV co-infection. Accordingly, we evaluated serum anti-E1/E2 antibodies in 50 patients (median age, 26.5; males, 30) with chronic hepatitis, 38 with HCV and 12 with HBV-HCV co-infection, who had undergone alpha-IFN treatment. Before starting IFN, the HCV group showed higher HCV-RNA levels (bDNA assay) than the HBV-HCV group (median 3.75 vs. 0.64 x 10(6) Eq/ml, respectively; P < 0.05). Similarly, the anti-E2 levels (EIA assay) were higher in the HCV group than in the HBV-HCV (mean +/- SD, 53.8 +/- 54.58 vs. 24.5 +/- 41.50 U/ml, respectively; P < 0.02), and the prevalence of anti-E2 was also higher in the HCV group (94 vs. 58%, respectively; P < 0.007). No correlation was found between anti-E1/E2 antibodies and the HCV-RNA levels. The prevalence of E1/E2 antibodies was similar in the different HCV genotypes. Higher baseline levels of anti-E2 antibodies and a decrease or disappearance of anti-E2 antibodies during IFN were associated with IFN sustained response in both groups, whereas no reduction in the anti-E1/E2 levels was observed in non-responders. The data show that HBV co-infection influences both HCV replication and the anti-E1/E2 antibody production. High pre-treatment levels of anti-E2 antibodies and their decrease or disappearance during interferon treatment are often associated with HCV clearance in sustained responders, irrespective of the HCV genotype.

Cross-reactivity of hypervariable region 1 chimera of hepatitis C virus

AIM: To analyze the amino acid sequences of hypervariable region 1 (HVR1) of HCV isolates in China and to construct a combinatorial chimeric HVR1 protein having a very broad high cross-reactivity.

METHODS: All of the published HVR1 sequences from China were collected and processed with a computer program. Several representative HVR1's sequences were formulated based on a consensus profile and homology within certain subdivision. A few reported HVR1 mimotope sequences were also included for a broader representation. All of them were cloned and expressed in E.coli. The cross-reactivity of the purified recombinant HVR1 antigens was tested by ELISA with a panel of sera from HCV infected patients in China. Some of them were further ligated together to form a combinatorial HVR1 chimera.

RESULTS: Altogether 12 HVR1_s were selected and expressed in E.coli and purified to homogeneity. All of these purified antigens showed some cross-reactivity with sera in a 27 HCV positive panel. Recombinant HVR1s of No. 1, 2, 4, and 8# showing broad cross-reactivities and complementarity with each other, were selected for the ligation elements. The chimera containing these 4 HVR1s was highly expressed in E.coli. The purified chimeric antigen could react not only with all the HCV antibody positive sera in the panel but also with 90/91 sera of HCV -infected patients.

CONCLUSION: The chimeric antigen was shown to have a broad cross-reactivity. It may be helpful for solving the problem caused by high variability of HCV, and in the efforts for a novel vaccine against the virus.

Expression of hepatitis C virus hypervariable region 1 and its clinical significance

AIM: To explore the properties of hypervariable region 1 (HVR1) in the envelope 2 gene of hepatitis C virus by analyzing the reactivity of HVR1 fusion proteins from different Chinese HCV strains with sera of patients with chronic hepatitis C and by comparing their reactivity between interferon therapy responders and non-responders.

METHODS: Gene fragments of HVR1 of four HCV strains (three genotype 1b and one genotype 2a) were amplified from pGEMT-E2 plasmids and sub-cloned into pQE40 vectors respectively to construct recombinant expression plasmids which expressed HVR1 fused downstream to DHFR in Escherichia coli strain TG1. The purified DHFR-HVR1 proteins were then used to detect the anti-HVR1 antibodies in 70 serum samples of patients with chronic hepatitis C.

RESULTS: Four DHFR-HVR1 fusion proteins were successfully expressed in E. coli (320-800 ug fusion proteins per 100 ml culture). Each fusion protein (SH1b, BJ1b, SD1b and SD2a) reacted with 72.8% (51/70), 60% (42/70), 48.6% (34/70), and 58.6% (41/70) of the anti-HCV positive patients’ sera respectively by ELISA. 57.1% (4/7) of non responders reacted with all four HVR1 fusion proteins, while only 15.3% (2/13) of responders reacted with all of them. The O.D. values of sera from IFN therapy responders were significantly higher than those of non responders (P < 0.05).

CONCLUSION: The selected HVR1 fusion proteins expressed in E. coli can broadly react with HCV-infected patients’ sera. The intensity and/or quality of the immune response against HCV may be a critical factor determining the response to interferon treatment. With the evolution of virus strains, anti-HVR1 antibodies can not neutralize all the quasispecies. A polyvalent and high immunogenic vaccine comprising a mixture of several HVR1 sequences that cover the reactivity of most HCV isolates may be useful.

Variability or conservation of hepatitis C virus hypervariable region 1? Implications for immune responses

The hypervariable region 1 (HVR1) of the E2 protein of hepatitis C virus (HCV) is highly heterogeneous in its primary sequence and is responsible for significant inter- and intra-individual variation of the infecting virus, which may represent an important pathogenetic mechanism leading to immune escape and persistent infection. A binding site for neutralizing antibodies (Ab) has also been allegedly identified in this region. Prospective studies of serological responses to synthetic oligopeptides derived from naturally-occurring HVR1 sequences showed promiscuous recognition of HVR1 variants in most patients via binding to C-terminal amino acid residues with conserved physicochemical properties. Monoclonal antibodies generated by immunization of mice with peptides derived from natural HVR1 sequences were shown to recognize several HVR1 variants in line with evidence gathered from studies using human sera. In addition, selected mAbs were able to bind HVR1 in the context of a complete soluble form of the E2 glycoprotein, indicating recognition of correctly folded sequences, and were shown to specifically capture circulating and recombinant HCV particles, suggesting that HVR1 is expressed on intact virus particles and therefore potentially able to interact with cellular receptor(s). These findings suggest that it is possible to induce a broadly reactive clonal immune response to multiple HCV variants and that this mechanism could be used in principle to induce protective immunity for a large repertoire of HCV variants.

The human scavenger receptor class B type I is a novel candidate receptor for the hepatitis C virus

We discovered that the hepatitis C virus (HCV) envelope glycoprotein E2 binds to human hepatoma cell lines independently of the previously proposed HCV receptor CD81. Comparative binding studies using recombinant E2 from the most prevalent 1a and 1b genotypes revealed that E2 recognition by hepatoma cells is independent from the viral isolate, while E2-CD81 interaction is isolate specific. Binding of soluble E2 to human hepatoma cells was impaired by deletion of the hypervariable region 1 (HVR1), but the wild-type phenotype was recovered by introducing a compensatory mutation reported previously to rescue infectivity of an HVR1-deleted HCV infectious clone. We have identified the receptor responsible for E2 binding to human hepatic cells as the human scavenger receptor class B type I (SR-BI). E2-SR-BI interaction is very selective since neither mouse SR-BI nor the closely related human scavenger receptor CD36, were able to bind E2. Finally, E2 recognition by SR-BI was competed out in an isolate-specific manner both on the hepatoma cell line and on the human SR-BI-transfected cell line by an anti-HVR1 monoclonal antibody.

DNA immunization with fusion genes encoding different regions of hepatitis C virus E2 fused to the gene for hepatitis B surface antigen elicits immune responses to both HCV and HBV

AIM: Both Hepatitis B virus (HBV) and Hepatitis C virus (HCV) are major causative agents of transfusion-associated and community-acquired hepatitis worldwide. Development of a HCV vaccine as well as more effective HBV vaccines is an urgent task. DNA immunization provides a promising approach to elicit protective humoral and cellular immune responses against viral infection. The aim of this study is to achieve immune responses against both HCV and HBV by DNA immunization with fusion constructs comprising various HCV E2 gene fragments fused to HBsAg gene of HBV.

METHODS: C57BL/6 mice were immunized with plasmid DNA expressing five fragments of HCV E2 fused to the gene for HBsAg respectively. After one primary and one boosting immunizations, antibodies against HCV E2 and HBsAg were tested and subtyped in ELISA. Splenic cytokine expression of IFN-γ and IL-10 was analyzed using an RT-PCR assay. Post-immune mouse antisera also were tested for their ability to capture HCV viruses in the serum of a hepatitis C patient in vitro.

RESULTS: After immunization, antibodies against both HBsAg and HCV E2 were detected in mouse sera, with IgG2a being the dominant immunoglobulin sub-class. High-level expression of INF-γ was detected in cultured splenic cells. Mouse antisera against three of the five fusion constructs were able to capture HCV viruses in an in vitro assay.

CONCLUSION: The results indicate that these fusion constructs could efficiently elicit humoral and Th1 dominant cellular immune responses against both HBV S and HCV E2 antigens in DNA-immunized mice. They thus could serve as candidates for a bivalent vaccine against HBV and HCV infection. In addition, the capacity of mouse antisera against three of the five fusion constructs to capture HCV viruses in vitro suggested that neutralizing epitopes may be present in other regions of E2 besides the hypervariable region 1.

Induction of cross-reactive humoral immune response by immunization with mimotopes of the hypervariable region 1 of the hepatitis C virus

Hepatitis C Virus (HCV) is a major cause of chronic hepatitis, liver cirrhosis and hepatocellular carcinoma, worldwide, and the development of an effective vaccine represents a high priority goal. The Hyper Variable Region 1 (HVR1) of the second Envelope protein (E2) of HCV contains a principal neutralizing determinant, but it is highly variable among different isolates and it is involved in the escape from host immune response. Thus, to be effective, a vaccine should elicit a cross-reacting humoral response against the majority of viral variants. We show that it is possible to achieve a broadly cross-reactive immune response in rabbits by immunization with mimotopes of the HVR1. selected from a specialized phage library using HCV patients' sera. At least some of the cross-reacting anti-mimotope antibodies, elicited in rabbits, recognize discontinuous epitopes in a manner similar to those induced by the virus in infected patients.

Antibody responses against B-cell epitopes of the hypervariable region 1 of hepatitis C virus in self-limiting and chronic human hepatitis C followed-up using consensus peptides

A rare collection of serum samples from patients with hepatitis C virus (HCV) infection followed up from the onset of clinical symptoms was acquired. RNA corresponding to the hypervariable region 1 (HVR1) of E2 protein of HCV isolated from nine patients was reverse-transcribed, amplified, sequenced, and HVR1 amino acid sequences were deduced. These sequences and a selection of HVR1 amino acid sequences of matching HCV genotypes from protein and translated DNA sequence databanks were used to create the HVR1 amino acid consensus. The degenerated peptides mimicking N- and C-termini of the consensus were synthesized. Most (76%) of 17 patients followed up for the period from 1 week to a minimum of 7 months from the onset of acute symptoms developed antibodies reacting with peptides representing N- and/or C- termini of HVR1. Antibody recognition of the consensus HVR1 peptides indicates that the variability of HVR1 sequence on the protein level is limited with certain conserved structure(s) being untouched. A tendency was observed for a slower development of anti-HVR1 antibody response in patients developing chronic HCV, as compared to those with self-limiting HCV infection.

[Role of neutralizing antibodies and cellular immunity in hepatitis C virus infection]

Hepatitis C virus (HCV) is responsible for the development of a chronic carrier state that can lead to the induction of cirrhosis and liver cancer. These clinical manifestations are believed to be the direct consequence of the viral persistence and the incapacity of the host to develop vigorous and sustained immune responses. Still contradictory data suggest the existence of neutralizing antibodies specifically directed at the second glycoprotein (E2). These antibodies may nonetheless play only a minor role in the control of infection. In contrast, it is now generally recognized that cellular-mediated immune responses, CD4+ and CD8+ mediated, if in place early enough, of a vigorous and polyclonal nature as well as long-lasting, appear by themselves competent enough to control an infection. One of the mechanisms possibly responsible for the establishment and persistence of a chronic infection could be the alteration of the ability of antigen-presenting cells (dendritic cells) to stimulate a T cell response. Such alteration could be the result of a direct infection of these cells by HCV.

Mimotopes of the hyper variable region 1 of the hepatitis C virus induce cross-reactive antibodies directed against discontinuous epitopes

Hepatitis C virus (HCV) is a major cause worldwide of chronic hepatitis, liver cirrhosis and hepatocellular carcinoma, and the development of an effective vaccine represents a high priority goal. The hyper variable region 1 (HVR1) of the second envelope protein (E2) of HCV contains a principal neutralizing determinant, but it is highly variable among different isolates and it is involved in the escape from host immune response. To be effective, a vaccine should elicit a cross-reacting humoral response against the majority of viral variants. We show that it is possible to achieve a broadly cross-reactive immune response in rabbits by immunization with mimotopes of the HVR1, selected from a specialized phage library using HCV patients' sera. Some of the cross-reacting anti-mimotope antibodies elicited in rabbits, recognize discontinuous epitopes in a manner similar to those induced by the virus in infected patients.

Hypervariable region 1 of hepatitis C virus: immunological decoy or biologically relevant domain?

The hypervariable region 1 (HVR1) of the E2 protein of hepatitis C virus (HCV) is highly heterogeneous and is responsible for significant inter- and intra-individual variation of the infecting virus, which may represent an important pathogenetic mechanism leading to escape and persistent infection. Moreover, a binding site for neutralizing antibodies (Ab) has been allegedly identified in this region. Prospective studies of serological responses to synthetic oligopeptides derived from HVR1 sequences of patients with acute and chronic HCV infection showed extensive serological cross-reactivity for unrelated HVR1 peptides in the majority of the patients. A significant correlation was found between HVR1 sequence variation, and intensity, and cross-reactivity of humoral immune responses providing strong evidence in support of the contention that HCV variant selection is driven by the host immune pressure. Monoclonal Ab (mAb) generated following immunization of mice with peptides derived from natural HVR1 sequences also showed cross-reactivity for several HVR1 sequences attesting to the existence of conserved amino acid motifs among different variants. These findings suggest that it is possible to induce a broadly cross-reactive immune response to HVR1 and that this mechanism can be used to generate protective immunity for a large repertoire of HCV variants.

Hepatitis C virus. The importance of viral heterogeneity

Although recent evidence indicates that the quasispecies nature of HCV constitutes a critical strategy for the virus to survive in the host, the mechanisms of viral persistence remain unknown. Similarly, the correlates of immune protection in a limited proportion of individuals who succeed in clearing HCV are still largely undefined. Understanding the mechanisms of sterilizing immunity is essential for devising preventive measures against HCV and unraveling how the virus eludes such immunity. As in other viral infections, the complex interactions between the virus and the host early in the course of HCV infection probably determine the outcome of the disease (i.e., resolution or persistence). The evidence now accumulated on HCV and other models of viral infection is compatible with the hypothesis that both cellular and humoral components are needed for definitive viral clearance. Nevertheless, detailed studies of the specific cellular and humoral immune responses during the incubation period and the acute phase of hepatitis C, in relation to the viral quasispecies evolution and the clinical outcome, are still lacking both in humans and in the chimpanzee model. Until such studies are performed, most ideas of viral clearance mechanisms remain hypothetical, and the immunologic basis of HCV clearance will continue to be inferred from associations rather than from causal relationships.

The dynamics of hepatitis C virus binding to platelets and 2 mononuclear cell lines

Hepatitis C virus (HCV) binds to platelets in chronically infected patients where free HCV constitutes only about 5% of total circulating virus. Free HCV preferentially binds to human mononuclear cell lines but free and complexed virus binds equally to platelets. The extent of free HCV binding to human Molt-4 T cells (which express CD81) and to human promonocytic U937 cells or to platelets (which do not express CD81) was similar. The binding of free HCV to the cell lines was saturated at a virus dose of 1 IU HCV RNA per cell but binding to platelets was not saturable. Human anti-HCV IgG, but not anti-CD81, markedly inhibited HCV binding to target cells in a dose-dependent manner. Human antibodies to HCV hypervariable region 1 of E2 glycoprotein partially inhibited viral binding to target cells. Recombinant E2 also inhibited viral binding to target cells in a dose-dependent manner, with the efficacy of this decreasing in the rank order of Molt-4 cells more than U937 cells more than platelets. In contrast to HCV, recombinant E2 bound to Molt-4 cells to an extent markedly greater than that apparent with U937 cells or platelets. These results suggest that the binding of HCV to blood cells is mediated by multiple cell surface receptors and that recombinant E2 binding may not be representative of the interaction of the intact virus with target cells.

The dynamics of hepatitis C virus binding to platelets and 2 mononuclear cell lines

Hepatitis C virus (HCV) binds to platelets in chronically infected patients where free HCV constitutes only about 5% of total circulating virus. Free HCV preferentially binds to human mononuclear cell lines but free and complexed virus binds equally to platelets. The extent of free HCV binding to human Molt-4 T cells (which express CD81) and to human promonocytic U937 cells or to platelets (which do not express CD81) was similar. The binding of free HCV to the cell lines was saturated at a virus dose of 1 IU HCV RNA per cell but binding to platelets was not saturable. Human anti-HCV IgG, but not anti-CD81, markedly inhibited HCV binding to target cells in a dose-dependent manner. Human antibodies to HCV hypervariable region 1 of E2 glycoprotein partially inhibited viral binding to target cells. Recombinant E2 also inhibited viral binding to target cells in a dose-dependent manner, with the efficacy of this decreasing in the rank order of Molt-4 cells more than U937 cells more than platelets. In contrast to HCV, recombinant E2 bound to Molt-4 cells to an extent markedly greater than that apparent with U937 cells or platelets. These results suggest that the binding of HCV to blood cells is mediated by multiple cell surface receptors and that recombinant E2 binding may not be representative of the interaction of the intact virus with target cells.

Monoclonal antibodies with broad specificity for hepatitis C virus hypervariable region 1 variants can recognize viral particles

The hypervariable region 1 (HVR1) of the E2 protein of hepatitis C virus (HCV) is a highly heterogeneous sequence that is promiscuously recognized by human sera via binding to amino acid residues with conserved physicochemical properties. We generated a panel of mAbs from mice immunized with HVR1 surrogate peptides (mimotopes) affinity-selected with sera from HCV-infected patients from a phage display library. A high number of specific clones was obtained after immunization with a pool of nine mimotopes, and the resulting mAbs were shown to recognize several 16- and 27-mer peptides derived from natural HVR1 sequences isolated from patients with acute and chronic HCV infection, suggesting that HVR1 mimotopes were efficient antigenic and immunogenic mimics of naturally occurring HCV variants. Moreover, most mAbs were shown to bind HVR1 in the context of a complete soluble form of the E2 glycoprotein, indicating recognition of correctly folded HVR1. In addition, a highly promiscuous mAb was able to specifically capture bona fide viral particles (circulating HCV RNA) as well as rHCV-like particles assembled in insect cells expressing structural viral polypeptides derived from an HCV 1a isolate. These findings demonstrate that it is possible to induce a broadly cross-reactive clonal Ab response to multiple HCV variants. In consideration of the potentially important role of HVR1 in virus binding to cellular receptor(s), such a mechanism could be exploited for induction of neutralizing Abs specific for a large repertoire of viral variants.

A possible role of hypervariable region 1 quasispecies in escape of hepatitis C virus particles from neutralization

We examined serial changes in the hypervariable region 1(HVR1) quasispecies both in immune and nonimmune complexed hepatitis C virus (HCV) particles from 12 patients with chronic hepatitis C to elucidate the mechanism by which genetic diversification of HCV during the course of infection allows escape of virus from the humoural immune response. Immune and nonimmune complexes were separated by differential flotation centrifugation and immunoprecipitation, and their HVR1 quasispecies were determined by subcloning and sequencing. The presence of a specific antibody against a specific viral clone in serum was examined in two patients by Western blotting of the corresponding recombinant HVR1 protein. The distribution of HVR1 quasispecies in both immune and nonimmune complexes conspicuously changed over time in most of the patients studied. In seven patients, various HCV clones serially shifted from nonimmune complexes to immune complexes. In four of them, a group of clones with similar HVR1 sequences to each other remained predominant in nonimmune complexes, whereas minor clones with sequences considerably divergent from the predominant clones shifted from nonimmune complexes to immune complexes. These results suggest a mechanism for persistent infection of HCV, in which major HCV clones escape from neutralization by anti-HVR1 antibodies by generating considerably divergent minor 'decoy' clones which may be preferentially neutralized.

Sequence evolution and cross-reactive antibody responses to hypervariable region 1 in acute hepatitis C virus infection

Hepatitis C virus (HCV) infection may result in acute resolving or chronic infection. Patients that clear the infection have a more vigorous cellular immune response and an early humoral response to the hypervariable region 1 (HVR1) of the E2 envelope protein. To analyse further the properties of the early anti-HVR1 response, cross-reactivity of anti-HVR1 responses was assessed in five patients with acute HCV infection, who were infected by the same virus strain during a nosocomial outbreak. The sequence evolution of HVR1 was examined in sequential serum samples up to 37 months post infection. Peptides were synthesised corresponding to the obtained HVR1 sequences and unrelated HVR1 sequences, and antibody reactivity to the peptides in sequential sera was investigated by ELISA. The results suggest an association between specific gaps in humoral immunity and the HVR1 sequence evolution during early infection. Possible interpretations of this phenomenon include immune escape mechanisms or suppression of specific anti-HVR1 antibodies.

Antigenicity and immunogenicity of novel chimeric hepatitis B surface antigen particles with exposed hepatitis C virus epitopes

The small envelope protein of hepatitis B virus (HBsAg-S) can self-assemble into highly organized virus like particles (VLPs) and induce an effective immune response. In this study, a restriction enzyme site was engineered into the cDNA of HBsAg-S at a position corresponding to the exposed site within the hydrophilic a determinant region (amino acid [aa] 127-128) to create a novel HBsAg vaccine vector allowing surface orientation of the inserted sequence. We inserted sequences of various lengths from hypervariable region 1 (HVR1) of the hepatitis C virus (HCV) E2 protein containing immunodominant epitopes and demonstrated secretion of the recombinant HBsAg VLPs from transfected mammalian cells. A number of different recombinant proteins were synthesized, and HBsAg VLPs containing inserts up to 36 aa were secreted with an efficiency similar to that of wild-type HBsAg. The HVR1 region exposed on the particles retained an antigenic structure similar to that recognized immunologically during natural infection. VLPs containing epitopes from either HCV-1a or -1b strains were produced that induced strain-specific antibody responses in immunized mice. Injection of a combination of these VLPs induced antibodies against both HVR1 epitopes that resulted in higher titers than were achieved by vaccination with the individual VLPs, suggesting a synergistic effect. This may lead to the development of recombinant particles which are able to induce a broad anti-HCV immune response against the HCV quasispecies or other quasispecies-like infectious agents.

Recombinant human monoclonal antibodies against different conformational epitopes of the E2 envelope glycoprotein of hepatitis C virus that inhibit its interaction with CD81

The antibody response to the envelope proteins of hepatitis C virus (HCV) may play an important role in controlling the infection. To allow molecular analyses of protective antibodies, we isolated human monoclonal antibodies to the E2 envelope glycoprotein of HCV from a combinatorial Fab library established from bone marrow of a chronically HCV-infected patient. Anti-E2 reactive clones were selected using recombinant E2 protein. The bone marrow donor carried HCV genotype 2b, and E2 used for selection was of genotype 1a. The antibody clones were expressed as Fab fragments in E. coli, and as Fab fragments and IgG1 in CHO cells. Seven different antibody clones were characterized, and shown to have high affinity for E2, genotype 1a. Three clones also had high affinity for E2 of genotype 1b. They all bind to conformation-dependent epitopes. Five clones compete for the same or overlapping binding sites, while two bind to one or two other epitopes of E2. Four clones corresponding to the different epitopes were tested as purified IgG1 for blocking the CD81-E2 interaction in vitro; all four were positive at 0.3-0.5 microg/ml. Thus, the present results suggest the existence of at least two conserved epitopes in E2 that mediate inhibition of the E2-CD81 interaction, of which one appeared immunodominant in this donor.

High prevalence of hypervariable region 1-specific and -cross-reactive CD4(+) T cells in HCV-infected individuals responsive to IFN-alpha treatment

The hypervariable region 1 (HVR1) of the putative envelope 2 protein of the hepatitis C virus (HCV) is the most variable part of the whole HCV polyprotein. Anti-HVR1 antibodies have been shown to protect against HCV infection, indicating that this region contains an important neutralization determinant. Recently we and others have demonstrated that HVR1 is also a T cell determinant able to activate helper T cell responses during HCV infection. In order to investigate the role of the immune response against HVR1 during HCV infection we have evaluated the humoral and lymphoproliferative responses to a panel of HVR1 peptides in HCV-infected patients with different outcomes of the disease following interferon-alpha (IFN-alpha) treatment. We observed that the frequency of anti-HVR1 T cell responses was significantly higher in patients who recovered after IFN-alpha therapy than in those who did not, while no differences in the anti-HVR1 antibody reactivities were detected. In addition, by generating HVR1-specific T cell lines and clones we identified human leukocyte-associated antigens DR4 restricted T cell epitopes in the carboxy-terminus of HVR1 and we demonstrated that broadly cross-reactive HVR1 T cells are elicited by HVR1.

Enhancement of immunoglobulin G2a and cytotoxic T-lymphocyte responses by a booster immunization with recombinant hepatitis C virus E2 protein in E2 DNA-primed mice

The induction of strong cytotoxic T-lymphocyte (CTL) and humoral responses appear to be essential for the elimination of persistently infecting viruses, such as hepatitis C virus (HCV). Here, we tested several vaccine regimens and demonstrate that a combined vaccine regimen, consisting of HCV E2 DNA priming and boosting with recombinant E2 protein, induces the strongest immune responses to HCV E2 protein. This combined vaccine regimen augments E2-specific immunoglobulin G2a (IgG2a) and CD8(+) CTL responses to a greater extent than immunizations with recombinant E2 protein and E2 DNA alone, respectively. In addition, the data showed that a protein boost following one DNA priming was also effective, but much less so than those following two DNA primings. These data indicate that sufficient DNA priming is essential for the enhancement of DNA encoded antigen-specific immunity by a booster immunization with recombinant E2 protein. Furthermore, the enhanced CD8(+) CTL and IgG2a responses induced by our combined vaccine regimens are closely associated with the protection of BALB/c mice from challenge with modified CT26 tumor cells expressing HCV E2 protein. Together, our results provide important implications for vaccine development for many pathogens, including HCV, which require strong antibody and CTL responses.

Evolutionary rate and genetic drift of hepatitis C virus are not correlated with the host immune response: studies of infected donor-recipient clusters

Six donor-recipient clusters of hepatitis C virus (HCV)-infected individuals were studied. For five clusters the period of infection of the donor could be estimated, and for all six clusters the time of infection of the recipients from the donor via blood transfusion was also precisely known. Detailed phylogenetic analyses were carried out to investigate the genomic evolution of the viral quasispecies within infected individuals in each cluster. The molecular clock analysis showed that HCV quasispecies within a patient are evolving at the same rate and that donors that have been infected for longer time tend to have a lower evolutionary rate. Phylogenetic analysis based on the split decomposition method revealed different evolutionary patterns in different donor-recipient clusters. Reactivity of antibody against the first hypervariable region (HVR1) of HCV in donor and recipient sera was evaluated and correlated to the calculated evolutionary rate. Results indicate that anti-HVR1 reactivity was related more to the overall level of humoral immune response of the host than to the HVR1 sequence itself, suggesting that the particular sequence of the HVR1 peptides is not the determinant of reactivity. Moreover, no correlation was found between the evolutionary rate or the heterogeneity of the viral quasispecies in the patients and the strength of the immune response to HVR1 epitopes. Rather, the results seem to imply that genetic drift is less dependent on immune pressure than on the rate of evolution and that the genetic drift of HCV is independent of the host immune pressure.

The hypervariable region 1 protein of hepatitis C virus broadly reactive with sera of patients with chronic hepatitis C has a similar amino acid sequence with the consensus sequence

Hypervariable region 1 (HVR1) proteins of hepatitis C virus (HCV) have been reported to react broadly with sera of patients with HCV infection. However, the variability of the broad reactivity of individual HVR1 proteins has not been elucidated. We assessed the reactivity of 25 different HVR1 proteins (genotype 1b) with sera of 81 patients with HCV infection (genotype 1b) by Western blot. HVR1 proteins reacted with 2-60 sera. The number of sera reactive with each HVR1 protein significantly correlated with the number of amino acid residues identical to the consensus sequence defined by Puntoriero et al. (G. Puntoriero, A. Lahm, S. Zucchelli, B. B. Ercole, R. Tafi, M. Penzzanera, M. U. Mondelli, R. Cortese, A. Tramontano, G. Galfre', and A. Nicosia. 1998. EMBO J. 17, 3521-3533. ) (r = 0.561, P < 0.005). The most widely reactive HVR1 protein, 12-22, had a sequence similar to the consensus sequence. The peptide with C-terminal 13-amino-acids sequence of HVR1 protein 12-22 (NH2-CSFTSLFTPGPSQK) was injected into rabbits as an immunogen. The rabbit immune sera reacted with 9 of 25 HVR1 proteins of genotype 1b including HVR1 protein 12-22 and with 3 of 12 proteins of genotype 2a. These results indicate that the HVR1 protein broadly reactive with patients' sera has a sequence similar to the consensus sequence, can induce broadly reactive sera, and could be one of the candidate immunogens in a prophylactic vaccine against HCV.

Expression of noncovalent hepatitis C virus envelope E1-E2 complexes is not required for the induction of antibodies with neutralizing properties following DNA immunization

Interactive glycoproteins present on the surface of viral particles represent the main target of neutralizing antibodies. The ability of DNA vaccination to induce antibodies directed at such structures was investigated by using eight different expression plasmids engineered either to favor or to prevent interaction between the hepatitis C virus (HCV) envelope glycoproteins E1 and E2. Independently of the injection route (intramuscular or intraepidermal), plasmids expressing antigens capable of forming heterodimers presumed to be the prebudding form of the HCV envelope protein complex failed to induce any significant, stable antibodies following injection in mice. In sharp contrast, high titers of antibodies directed at both conformational and linear determinants were induced by using plasmids expressing severely truncated antigens that have lost the ability to form native complexes. In addition, only a truncated form of E2 induced antibodies reacting against the hypervariable region 1 of E2 (specifically with the C-terminal part of it) known to contain a neutralization site. When injected intraepidermally into small primates, the truncated E2-encoding plasmid induced antibodies able to neutralize in vitro the binding of a purified E2 protein onto susceptible cells. Because such antibodies have been associated with viral clearance in both humans and chimpanzees, these findings may have important implications for the development of protective immunity against HCV.

Antibody responses to hepatitis C virus hypervariable region 1: evidence for cross-reactivity and immune-mediated sequence variation

Sequence heterogeneity of hepatitis C virus (HCV) is unevenly distributed along the genome, and maximal variation is confined to a short sequence of the HCV second envelope glycoprotein (E2), designated hypervariable region 1 (HVR1), whose biological function is still undefined. We prospectively studied serological responses to synthetic oligopeptides derived from HVR1 sequences of patients with acute and chronic HCV infection obtained at baseline and after a defined follow-up period. Extensive serological cross-reactivity for unrelated HVR1 peptides was observed in the majority of the patients. Antibody response was restricted to the IgG1 isotype and was focused on the carboxyterminal end of the HVR1 region. Cross-reactive antibodies could be readily elicited following immunization of mice with multiple antigenic peptides carrying HVR1 sequences derived from our patients. The vigor and heterogeneity of cross-reactive antibody responses were significantly higher in patients with chronic hepatitis compared with those with acute hepatitis and in patients infected with HCV type 2 compared with patients infected with other viral genotypes (predominantly type 1), which suggest that higher time-related HVR1 sequence diversification previously described for type 2 may result from immune selection. The finding of a statistically significant correlation between HVR1 sequence variation, and intensity, and cross-reactivity of humoral immune responses provided stronger evidence in support of the contention that HCV variant selection is driven by the host's immune pressure.

Evolution of the hypervariable region of hepatitis C virus

Despite being the most intensively studied part of the hepatitis C virus genome, our understanding of the function of the hypervariable region (HVR) at the NH2-terminus of the E2 protein remains very limited. During chronic infection the HVR usually changes over time, with changes usually mirrored by those of HVR-specific antibodies. Evidence is presented suggesting that the HVR is subject to constraint in its length, amino acid composition, and in the amino acid replacements that are tolerated at different positions. These constraints, and the pattern of HVR variation during chronic infection, suggest that it has an important role in virus infection. A causal relationship between HVR variation and persistence of HCV remains to be demonstrated.

Multiple sequence-reactive antibodies induced by a single peptide immunization with hypervariable region 1 of hepatitis C virus

Hypervariable region 1 (HVR1) of hepatitis C virus (HCV) is known to contain neutralizing epitopes. We previously found that murine antibodies against HVR1-#6 captured a different isolate, HCV-#7, and cross-reacted with the HVR1 peptide of HCV-#7. We investigated the inducibility and generality of cross-reaction of animal anti-HVR1 antibody responses in this study. Anti-HVR1-#7 antibodies, which were induced in mice and a chimpanzee by immunization, were found to be cross-reactive to HVR1-#6 peptide. Antibody responses against HVR1-#6-1 and HVR1-#7 peptides were detected in 11/165 (6.7%) and 26/165 (15.8%) HCV-infected individuals, respectively. Nine HVR1 sequences from six individuals, who were strongly positive for anti-HVR1-#7 antibodies, were only 50-64.5% identical to that of HVR1-#7. All nine of these HVR1 peptides were reactive to sera from the six patients and/or to antisera against HVR1-#6 and HVR1-#7 produced in mice and chimpanzees. Cross-inhibition tests of chimpanzee antisera indicated that a given species of anti-HVR1 antibodies was reactive to multiple HVR1 sequences. Fine epitope mapping of polyclonal and monoclonal anti-HVR1 antibodies showed that conserved subregions in HVR1 sequences determined the observed immunological cross-reactivity. Our data demonstrate that cross-reacting anti-HVR1 antibodies are inducible by a single peptide immunization.

Human recombinant single-chain antibody fragments, specific for the hypervariable region 1 of hepatitis C virus, from immune phage-display libraries

The hypervariable region 1 (HVR1) of hepatitis C virus (HCV) may contain a potential neutralization site and the generation of human single-chain antibody fragments (scFv) to HVR1 may therefore provide a useful tool for the study of HCV. In this report, we have isolated and characterized three anti-HVR1 scFv clones from two patient-derived phage-displayed libraries and HCV HVR1 peptides. scFv S52/20 and S53/6 were selected with serologically cross-reactive HVR1 peptides. scFv p3f10 was obtained by screening the library from patient MH with an autologous HVR1 peptide. Nucleotide sequencing showed that the VH chains and Vkappa chains of all three scFv antibodies were derived from VH3 and Vkappa1 family germline V-genes, respectively. The specificity and affinity of the recombinant scFv antibodies were examined by enzyme-linked immunosorbent assay (ELISA) and an affinity biosensor, using HVR1 peptides. S52/20 scFv binding to S52 HVR1 peptide was blocked by preincubation with soluble peptide S52 and was partially competed by one of three HCV-infected patient sera. In addition, scFv S52/20 blocked the binding of HCV-susceptible Molt-4 cells to immobilized S52 peptide. This study demonstrates that recombinant human scFv antibodies to HCV HVR1 can be produced in vitro and directly confirms that HVR1 of HCV elicits highly specific antibodies. The very high specificity of these antibodies to HVR1 may limit their potential use in passive immunization therapy against HCV, and further engineering of the scFvs needs to be performed to generate broad-spectrum blocking scFvs.

Limited humoral immunity in hepatitis C virus infection

BACKGROUND & AIMS

The extremely high rate of chronicity to hepatitis C virus (HVC) infection suggests an inefficient immune response. The humoral immune response to HCV was evaluated in 60 patients with chronic HCV infection and in 12 patients acutely infected with HCV.

METHODS

A number of recombinant HCV antigens including the core, envelope 2 (E2), nonstructural (NS) 3, NS4, and NS5 proteins, and NS4a and E2-HVR-1 peptides were used in enzyme-linked immunoassays.

RESULTS

Immunoglobulin (Ig) G antibody responses to these viral antigens, except for the HCV core, were highly restricted to the IgG1 isotype. The prevalence of antibodies of the IgG1 isotype specific for the HCV core, E2, E2-HVR1, NS3 (helicase domain), NS4, and NS5 antigens was 97%, 98%, 28%, 88%, 33%, and 68%, respectively. Antibodies of the IgG3 isotype specific for E2, E2-HVR-1, NS3, NS4, and NS5 were detected in a minority of serum samples. The IgG2 and IgG4 isotypes were rarely if ever detected. Furthermore, antibody responses to HCV viral antigens were of relatively low titer and, with the exception of anti-HCV core, were delayed in appearance until the chronic phase of infection.

CONCLUSIONS

The IgG1 restriction, low titer, and delayed appearance of antibody responses elicited during HCV infection suggest that the immunogenicity of HCV proteins is limited in the context of natural infection. Inasmuch as recombinant HCV viral antigens perform as relatively normal immunogens in small animals, we suggest that the defective humoral immune responses during HCV infection may be attributable to an "immune avoidance" strategy.

Identification of a domain containing B-cell epitopes in hepatitis C virus E2 glycoprotein by using mouse monoclonal antibodies

Evidence from clinical and experimental studies of human and chimpanzees suggests that hepatitis C virus (HCV) envelope glycoprotein E2 is a key antigen for developing a vaccine against HCV infection. To identify B-cell epitopes in HCV E2, six murine monoclonal antibodies (MAbs), CET-1 to -6, specific for HCV E2 protein were generated by using recombinant proteins containing E2t (a C-terminally truncated domain of HCV E2 [amino acids 386 to 693] fused to human growth hormone and glycoprotein D). We tested whether HCV-infected sera were able to inhibit the binding of CET MAbs to the former fusion protein. Inhibitory activity was observed in most sera tested, which indicated that CET-1 to -6 were similar to anti-E2 antibodies in human sera with respect to the epitope specificity. The spacial relationship of epitopes on E2 recognized by CET MAbs was determined by surface plasmon resonance analysis and competitive enzyme-linked immunosorbent assay. The data indicated that three overlapping epitopes were recognized by CET-1 to -6. For mapping the epitopes recognized by CET MAbs, we analyzed the reactivities of CET MAbs to six truncated forms and two chimeric forms of recombinant E2 proteins. The data suggest that the epitopes recognized by CET-1 to -6 are located in a small domain of E2 spanning amino acid residues 528 to 546.

Murine antibodies against E2 and hypervariable region 1 cross-reactively capture hepatitis C virus

The absence of readily available animal and cell culture models for hepatitis C virus (HCV) replication has bottlenecked research on protective immunity to HCV infection. Antibodies reactive with HCV virions in vitro are assumed to be candidates for neutralizing or inhibitory antibodies against HCV. To find potentially neutralizing or inhibitory antibody candidates, anti-C, anti-E1, anti-E2, and anti-HVR1 antisera acquired from mice immunized with corresponding recombinant proteins or synthetic peptides were used to capture HCV viral particles in vitro based on antibody-virus interaction assays. Both anti-E2 and anti-HVR1 antibodies effectively captured HCV in vitro. Furthermore, it was found that anti-E2 and anti-HVR1 antibodies could immunoprecipitate an isolate of HCV unrelated to the original antigenic HCV isolate. ELISA confirmed that anti-HVR1 antibodies cross-reactively bind to these unrelated HVR1 peptides. These findings suggest that anti-E2 and anti-HVR1 antibodies induced in mice have the ability to bind with HCV particles in an isolate cross-reactive manner and highlight the possible application of combining several sequences of HVR1 to generate broadly reactive anti-HVR1 antibodies.

Optimal induction of hepatitis C virus envelope-specific immunity by bicistronic plasmid DNA inoculation with the granulocyte-macrophage colony-stimulating factor gene

In this study, we have constructed various DNA vaccine vectors that carried hepatitis C virus (HCV) envelope genes without and with the granulocyte-macrophage colony-stimulating factor (GM-CSF) gene in several different ways. In Buffalo rats that received plasmids carrying the HCV envelope genes, which encode envelope proteins E1 and E2, both antibody and lymphoproliferative responses against these proteins were induced. These responses were greatly enhanced by the codelivery of the GM-CSF gene. In particular, inoculation with a bicistronic plasmid that independently expressed the GM-CSF gene and the envelope genes in the same construct generated the highest antibody titers and significantly increased lymphoproliferative responses against these proteins. Moreover, strong antibody responses to homologous and heterologous hypervariable region 1 peptides were elicited in the immunized rats.

Towards a solution for hepatitis C virus hypervariability: mimotopes of the hypervariable region 1 can induce antibodies cross-reacting with a large number of viral variants

The hypervariable region 1 (HVR1) of the putative envelope protein E2 of hepatitis C virus (HCV) is the most variable antigenic fragment in the whole viral genome and is mainly responsible for the large inter-and intra-individual heterogeneity of the infecting virus. It contains a principal neutralization epitope and has been proposed as the major player in the mechanism of escape from host immune response. Since anti-HVR1 antibodies are the only species shown to possess protective activity up to date, developing an effective prevention therapy is a very difficult task. We have approached the problem of HVR1 variability by deriving a consensus profile from >200 HVR1 sequences from different viral isolates and used it as a template to generate a vast repertoire of synthetic HVR1 surrogates displayed on M13 bacteriophage. This library was affinity selected using many different sera from infected patients. Phages were identified which react very frequently with patients' sera and bind serum antibodies that cross-react with a large panel of HVR1 peptides derived from natural HCV variants. When injected into experimental animals, the 'mimotopes' with the highest cross-reactivity induced antibodies which recognized the same panel of natural HVR1 variants. In these mimotopes we identified a sequence pattern responsible for the observed cross-reactivity. These data may hold the key for future development of a prophylactic vaccine against HCV.