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

Hepatitis C virus hypervariable region 1 variants presented on hepatitis B virus capsid-like particles induce cross-neutralizing antibodies

Hepatitis C virus (HCV) infection is still a serious global health burden. Despite improved therapeutic options, a preventative vaccine would be desirable especially in undeveloped countries. Traditionally, highly conserved epitopes are targets for antibody-based prophylactic vaccines. In HCV-infected patients, however, neutralizing antibodies are primarily directed against hypervariable region I (HVRI) in the envelope protein E2. HVRI is the most variable region of HCV, and this heterogeneity contributes to viral persistence and has thus far prevented the development of an effective HVRI-based vaccine. The primary goal of an antibody-based HCV vaccine should therefore be the induction of cross-reactive HVRI antibodies. In this study we approached this problem by presenting selected cross-reactive HVRI variants in a highly symmetric repeated array on capsid-like particles (CLPs). SplitCore CLPs, a novel particulate antigen presentation system derived from the HBV core protein, were used to deliberately manipulate the orientation of HVRI and therefore enable the presentation of conserved parts of HVRI. These HVRI-CLPs induced high titers of cross-reactive antibodies, including neutralizing antibodies. The combination of only four HVRI CLPs was sufficient to induce antibodies cross-reactive with 81 of 326 (24.8%) naturally occurring HVRI peptides. Most importantly, HVRI CLPs with AS03 as an adjuvant induced antibodies with a 10-fold increase in neutralizing capability. These antibodies were able to neutralize infectious HCVcc isolates and 4 of 19 (21%) patient-derived HCVpp isolates. Taken together, these results demonstrate that the induction of at least partially cross-neutralizing antibodies is possible. This approach might be useful for the development of a prophylactic HCV vaccine and should also be adaptable to other highly variable viruses.

Combined adenovirus vector and hepatitis C virus envelope protein prime-boost regimen elicits T cell and neutralizing antibody immune responses

Despite the recent progress in the development of new antiviral agents, hepatitis C virus (HCV) infection remains a major global health problem, and there is a need for a preventive vaccine. We previously reported that adenoviral vectors expressing HCV nonstructural proteins elicit protective T cell responses in chimpanzees and were immunogenic in healthy volunteers. Furthermore, recombinant HCV E1E2 protein formulated with adjuvant MF59 induced protective antibody responses in chimpanzees and was immunogenic in humans. To develop an HCV vaccine capable of inducing both T cell and antibody responses, we constructed adenoviral vectors expressing full-length and truncated E1E2 envelope glycoproteins from HCV genotype 1b. Heterologous prime-boost immunization regimens with adenovirus and recombinant E1E2 glycoprotein (genotype 1a) plus MF59 were evaluated in mice and guinea pigs. Adenovirus prime and protein boost induced broad HCV-specific CD8+ and CD4+ T cell responses and functional Th1-type IgG responses. Immune sera neutralized luciferase reporter pseudoparticles expressing HCV envelope glycoproteins (HCVpp) and a diverse panel of recombinant cell culture-derived HCV (HCVcc) strains and limited cell-to-cell HCV transmission. This study demonstrated that combining adenovirus vector with protein antigen can induce strong antibody and T cell responses that surpass immune responses achieved by either vaccine alone.

IMPORTANCE

HCV infection is a major health problem. Despite the availability of new directly acting antiviral agents for treating chronic infection, an affordable preventive vaccine provides the best long-term goal for controlling the global epidemic. This report describes a new anti-HCV vaccine targeting the envelope viral proteins based on adenovirus vector and protein in adjuvant. Rodents primed with the adenovirus vaccine and boosted with the adjuvanted protein developed cross-neutralizing antibodies and potent T cell responses that surpassed immune responses achieved with either vaccine component alone. If combined with the adenovirus vaccine targeting the HCV NS antigens now under clinical testing, this new vaccine might lead to a stronger and broader immune response and to a more effective vaccine to prevent HCV infection. Importantly, the described approach represents a valuable strategy for other infectious diseases in which both T and B cell responses are essential for protection.

Immunogenic properties of chimeric potato virus X particles displaying the hepatitis C virus hypervariable region I peptide R9

The immunogenic properties of chimeric potato virus X (PVX) particles engineered to display the synthetic R9 peptide have been evaluated. The R9 peptide is a consensus sequence derived from diverse variants of the hypervariable region 1 from the hepatitis C virus (HCV) envelope protein E2. Two different constructs were designed, with the R9 peptide expressed either as an indirect fusion via the ribosomal skip 2A (PVX(R9-2A)CP) sequence or as a direct PVX coat protein fusion (PVX(R9)CP). Systemic infection of Nicotiana benthamiana plants was only achieved with PVX(R9-2A)CP constructs, and the presence of the R9 peptide was detected in extracts from these plants by ELISA, Western blot and electron microscopy using specific anti-R9 antibodies. The virus particles were recovered at yields of up to 125mg/kg from leaf material. BALB/c mice immunized with purified PVX(R9-2A)CP particles developed specific anti-R9 IgG titers of up to 1:50,000. Monoclonal anti-R9 antibodies were obtained from the spleen of a mouse immunized with PVX(R9-2A)CP particles and characterized by Western blot and electron microscopy. Sera from patients infected chronically with HCV were found to react specifically with PVX(R9-2A)CP particles in 35% of cases.

Immunogenic epitopes on the surface of the hepatitis A virus capsid: Impact of secondary structure and/or isoelectric point on chimeric virus assembly

Hepatitis A virus (HAV) protein 2A has the capacity to harbor and expose a short foreign epitope. The chimeric virus, HAV-gp41, bearing seven amino acids of the 2F5 epitope of the HIV glycoprotein gp41, was shown to replicate in cell culture and laboratory animals and to induce a humoral immune response. As an extension of this work, we now investigated the possibility to insert longer epitopes, their impact on genetic stability, and the production of chimeric HAV. Twenty-seven amino acid residues of either HIV gp41, comprising the 2F5 epitope, or of a mimotope (F78) of the hypervariable region 1 of the hepatitis C virus (HCV) envelope protein E2 were inserted near the C-terminus of HAV 2A and viral capsid formation and replication were studied. The genome of the chimeric virus (HAV-F78) had reduced replication ability, yet the sedimentation profile of the chimeric particles was unchanged and the HCV sequence was maintained over serial viral passages. In contrast, no capsids were formed when an extended HIV epitope of 27 residues was inserted, precluding the rescue of infectious chimeric virus. Based on structural analyses, the data suggest that the isoelectric point (pI) and/or the secondary structure of the chimeric proteins are essential determinants that affect HAV particle formation for which protein 2A serves as an assembly signal.

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.

The hypervariable region 1 of the E2 glycoprotein of hepatitis C virus binds to glycosaminoglycans, but this binding does not lead to infection in a pseudotype system

The hypervariable region 1 (HVR1) of hepatitis C virus (HCV) E2 envelope glycoprotein is a 27-amino-acid sequence located at its N terminus. In this study, we investigated the functional role of HVR1 for interaction with the mammalian cell surface. The C-terminal truncated E2 glycoprotein was appended to a transmembrane domain and cytoplasmic tail of vesicular stomatitis virus (VSV) G protein for generation of the chimeric E2-G gene construct. A deletion of the HVR1 sequence from E2 was created for the construction of E2DeltaHVR1-G. Pseudotype virus, generated separately by infection of a stable cell line expressing E2-G or E2DeltaHVR1-G with a temperature-sensitive mutant of VSV (VSVts045), displayed unique functional properties compared to VSVts045 as a negative control. Virus generated from E2DeltaHVR1-G had a reduced plaquing efficiency ( approximately 50%) in HepG2 cells compared to that for the E2-G virus. Cells prior treated with pronase (0.5 U/ml) displayed a complete inhibition of infectivity of the E2DeltaHVR1-G or E2-G pseudotypes, whereas heparinase I treatment (8 U/ml) of cells reduced 40% E2-G pseudotype virus titer only. E2DeltaHVR1-G pseudotypes were not sensitive to heparin (6 to 50 micro g/ml) as an inhibitor of plaque formation compared to the E2-G pseudotype virus. Although the HVR1 sequence itself does not match with the known heparin-binding domain, a synthetic peptide representing 27 amino acids of the E2 HVR1 displayed a strong affinity for heparin in an enzyme-linked immunosorbent assay. This binding was competitively inhibited by a peptide from the V3 loop of a human immunodeficiency virus glycoprotein subunit (gp120) known to bind with cell surface heparin. Taken together, our results suggest that the HVR1 of E2 glycoprotein binds to the cell surface proteoglycans and may facilitate virus-host interaction for replication cycle of HCV.

Broadly cross-reactive mimotope of hypervariable region 1 of hepatitis C virus derived from DNA shuffling and screened by phage display library

The hypervariable region 1 (HVR1) is the target of neutralizing antibodies but with isolate specificity. The aim of this study was to obtain immunogenic mimotopes of HVR1, which can react broadly with different HVR1 antibodies and could be one of the candidate immunogens in an effective vaccine against HCV. Thirty-one HVR1 cDNA fragments were digested by DNase I into a pool of random fragments and reassembled by repeated cycles of annealing in the presence of DNA polymerase to their original size. The shuffled HVR1 was then inserted into the gene III phagemid vector pCANTAB-5E and displayed on the surface of the phage. Eight individual phages were selected after four rounds of biopanning against anti-HVR1. ELISA was carried out on immobilized purified phages, respectively, to detect their reactivity with a panel of sera. DNA sequences of the inserts were analyzed and compared with the consensus sequences defined by Puntoriero et al. [(1998) EMBO J 17:3521-3533]. The reactivity of the eight selected clones to the 30 sera were from 53.3 to 80%. Among these, phage 13 (ETYVSGGSAARNAYGLTSLFTVGPAQK, aa 384-410) reacted most broadly. None of the selected sequences encoded for peptides corresponded to known HVR1 from original viral isolates. The two high reactive phages had the similar amino acid sequences with the consensus, which might play a particular role in determining the frequency of reactivity. In conclusion, this study has used effectively DNA shuffling combined with phage display technology to identify broadly cross-reactive mimotopes recognized by human polyclonal antibodies. Mimotope 13 and 23 appeared to be most reactive immunologically and could be candidate immunogens. Efforts are now underway to identify their neutralizing antibodies by immunization of animals.

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.