The core domain of hepatitis C virus glycoprotein E2 generates potent cross‐neutralizing antibodies in guinea pigs

Abstract

A vaccine that prevents hepatitis C virus (HCV) infection is urgently needed to support an emerging global elimination program. However, vaccine development has been confounded because of HCV's high degree of antigenic variability and the preferential induction of type‐specific immune responses with limited potency against heterologous viral strains and genotypes. We showed previously that deletion of the three variable regions from the E2 receptor‐binding domain (Δ123) increases the ability of human broadly neutralizing antibodies (bNAbs) to inhibit E2‐CD81 receptor interactions, suggesting improved bNAb epitope exposure. In this study, the immunogenicity of Δ123 was examined. We show that high‐molecular‐weight forms of Δ123 elicit distinct antibody specificities with potent and broad neutralizing activity against all seven HCV genotypes. Antibody competition studies revealed that immune sera raised to high‐molecular‐weight Δ123 was poly specific, given that it inhibited the binding of human bNAbs directed to three major neutralization epitopes on E2. By contrast, the immune sera raised to monomeric Δ123 predominantly blocked the binding of a non‐neutralizing antibody to Δ123, while having reduced ability to block bNAb binding to E2, and neutralization was largely toward the homologous genotype. This increased ability of oligomeric Δ123 to generate bNAbs correlates with occlusion of the non‐neutralizing face of E2 in this glycoprotein form. Conclusion: The results from this study reveal new information on the antigenic and immunogenic potential of E2‐based immunogens and provide a pathway for the development of a simple, recombinant protein‐based prophylactic vaccine for HCV with potential for universal protection. (Hepatology 2017;65:1117‐1131).

An Optimized Hepatitis C Virus E2 Glycoprotein Core Adopts a Functional Homodimer That Efficiently Blocks Virus Entry

“…The Δ123 protein may also limit the presentation of nonneutralizing domain A epitopes which are exposed at post-CD81 binding stages in virus entry and represents an antigenic cluster accounting for a substantial portion of isolate-specific antibody responses to E2 (13). We recently reported that higher-molecular-weight forms of Δ123 protein also generate more potent neutralizing antibodies in vivo due at least in part to the burial of nonneutralizing domain A epitopes at intermolecular interfaces (19). The Δ123 protein therefore represents a unique tool to further investigate how such immunogenic sites are presented within E2 and to evaluate the potential of recombinant E2 as a vaccine candidate.…”

“…Recombinant E2 and E1E2 have proven to be highly immunogenic; however, neutralizing antibody responses show limited breadth of neutralization (16)(17)(18)(19). E2 exhibits the highest degree of amino acid variability encoded in the HCV genome, which localizes to three discrete variable regions.…”

B cell immunodominance in primary hepatitis C virus infection

“…Neutralisation against cell culture-derived HCV (HCVcc) was performed as previously described with GT2a Jc1Flag2 (p7-nsGluc2A) and GT3a (S52) JFH-1 chimeras. 24 HCV E1E2 binding and competition ELISAs were performed as described previously. 4 Briefly, microtiter plates were pre-coated with Galanthus nivalis lectin (GNA), blocked with 5% non-fat dry milk before capturing GT1 (H77.20) or GT3 (UKN3A13.6) E1E2 for 1.5 h at saturating concentration.…”

“…The hypervariable region 1 (HVR1) within E2 forms an immunodominant epitope in HCV infection, however antibodies that target this region are highly strain specific. Furthermore, HVR1 is prone to high levels of mutation, driving immune escape, 13 making it unsuitable for vaccine design. Characterising the immunodominance hierarchy of epitopes with favourable neutralising potential is therefore required to understand what constitutes protective immunity to HCV.…”

Structure-based design of hepatitis C virus E2 glycoprotein improves serum binding and cross-neutralization

“…There have been a number of successful structure-based vaccine designs for variable viruses such as influenza (12,13), HIV (14,15), and RSV (16,17) where rationally designed immunogens optimize presentation of key conserved epitopes, mask sites using N-glycans, or stabilize conformations or assembly of the envelope glycoproteins. Recent studies have reported use of several of these strategies in the context of HCV glycoproteins, including removal or modification of N-glycans to improve epitope accessibility (18,19), removal of hypervariable regions (18,20,21), or presentation of key conserved epitopes on scaffolds (22,23). However, such studies have been relatively limited compared with other viruses, in terms of design strategies employed and number of designs tested, and immunogenicity studies have not shown convincing improvement of glycoprotein designs over native glycoproteins in terms of neutralization potency or breadth (18,21), with the possible exception of an HVR-deleted high molecular weight form of the E2 glycoprotein that was tested in guinea pigs (20).…”