Hepatitis C virus E1 protein-specific linear B-cell epitopes, pan-genotype reactivity, and functional relevance

Hepatitis C virus (HCV) infection poses a major global risk for chronic liver disease, underscoring the critical need for prevention. Our previous studies demonstrated that HCV-modified soluble E1/E2_F442NYT envelope glycoproteins delivered from an mRNA-lipid nanoparticle (LNP) vaccine platform induce immune responses in vitro in human cells and in vivo in immunized mice. These findings prompted us to analyze the sE1-derived induction of broadly cross-genotype HCV protective antibody response.

Analyses for the evaluation of linear B-cell epitopes, specifically antibody elicitation by genotype 1a E1 mRNA-LNP immunization, were performed using a panel of E1 overlapping peptides. HCV pseudotype neutralization, interruption by antibody binding to epitope regions, and association between E1/E2 were biochemically analyzed for the impairment of known E2 receptor-binding functions, including surrogate virus neutralization.

Binding inhibition-based ELISA identified peptides having a distinct reactivity pattern of immune mouse sera, revealing four linear regions (Groups A-D). One of the peptides (Group A, P1) corresponded to an antigenic region previously characterized as a key linear B-cell epitope. HCV pseudotype neutralization assay using rabbit anti-P1 peptide serum demonstrated multi-HCV genotype neutralization. The relatively conserved linear B-cell epitope was found to localize in the α1 helix region, closer to the N-terminal ectodomain of E1/E2 major receptor-binding area. However, a much-conserved P2 epitope (Group D), with residues reported to interplay with the tight junction protein claudin-1 and scavenger receptor B type I, induced a detectable HCV pseudotype neutralization. Interruption by antibody binding to the P1 and P2 regions may impair intimate association between E1/E2, leading to the impairment of known E2 receptor-binding functions, including virus neutralization activity. Surface plasmon resonance suggested similar antibody binding affinity of the two rabbit antibodies (~10^-8 M) to the unmodified E1/E2. The Group B peptide awaits further characterization for HCV functional inhibitory roles, while the Group C peptide is characterized as a putative fusion peptide and involved in cross-talk with E2.

Collectively, the findings identified novel B-cell epitopes of E1 glycoprotein cross-reactive among HCV genotypes and may serve as a promising candidate to include for a rational design of a pan-genotypic HCV vaccine.