Structure-Based Design of Hepatitis C Virus E2 Glycoprotein Improves Serum Binding and Cross-Neutralization.

Brian G Pierce,Melissa C Kerzic,Thomas R Fuerst,Roy A Mariuzza,Richard A Urbanowicz,Steven K H Foung,Khadija Elkholy,Kyle Garagusi,Ruixue Wang,Alexander K Andrianov,Pragati Agnihotri,Zhen-Yong Keck,Johnathan D Guest,Eric A Toth,Patrick Lau,Alexander Marin,Jonathan K Ball

doi:10.1128/jvi.00704-20

Abstract

An effective vaccine for hepatitis C virus (HCV) is a major unmet need, and it requires an antigen that elicits immune responses to key conserved epitopes. Based on structures of antibodies targeting HCV envelope glycoprotein E2, we designed immunogens to modulate the structure and dynamics of E2 and favor induction of broadly neutralizing antibodies (bNAbs) in the context of a vaccine. These designs include a point mutation in a key conserved antigenic site to stabilize its conformation, as well as redesigns of an immunogenic region to add a new N-glycosylation site and mask it from antibody binding. Designs were experimentally characterized for binding to a panel of human monoclonal antibodies (HMAbs) and the coreceptor CD81 to confirm preservation of epitope structure and preferred antigenicity profile. Selected E2 designs were tested for immunogenicity in mice, with and without hypervariable region 1, which is an immunogenic region associated with viral escape. One of these designs showed improvement in polyclonal immune serum binding to HCV pseudoparticles and neutralization of isolates associated with antibody resistance. These results indicate that antigen optimization through structure-based design of the envelope glycoproteins is a promising route to an effective vaccine for HCV.IMPORTANCE Hepatitis C virus infects approximately 1% of the world's population, and no vaccine is currently available. Due to the high variability of HCV and its ability to actively escape the immune response, a goal of HCV vaccine design is to induce neutralizing antibodies that target conserved epitopes. Here, we performed structure-based design of several epitopes of the HCV E2 envelope glycoprotein to engineer its antigenic properties. Designs were tested in vitro and in vivo, demonstrating alteration of the E2 antigenic profile in several cases, and one design led to improvement of cross-neutralization of heterologous viruses. This represents a proof of concept that rational engineering of HCV envelope glycoproteins can be used to modulate E2 antigenicity and optimize a vaccine for this challenging viral target.

Highlights

We used the previously reported structure of the affinity-matured broadly neutralizing antibodies (bNAbs) HC84.26.5D bound to its epitope from E2 antigenic domain D [31] (PDB code 4Z0X), which shows the same epitope conformation observed in the context of other domain D human monoclonal antibodies (HMAbs) targeting this site [32]
The molecular basis for the differential serum reactivity when HCV pseudoparticles (HCVpp) were used instead of purified recombinant E1E2 in enzyme-linked immunosorbent assays (ELISA) is unclear, given that soluble E2 (sE2) was used as an immunogen, yet these results collectively provide evidence that H445P may improve targeting of conserved glycoprotein epitopes on the intact hepatitis C virus (HCV) virion
We tested the E2 ΔHVR1 mutant in which residues 384 to have been removed and residues to 661 of E2 are retained; this is a more conservative truncation than that of previously tested ΔHVR1 mutants in order to retain residue 408 which is a binding determinant for the HC33.4 HMAb and other HMAbs [28, 34]. We found that this mutant was not advantageous from an immunogenicity standpoint, which is in agreement with findings of most other previous immunogenicity studies testing ΔHVR1 mutants [18, 21, 23]

Summary

Introduction

Selected E2 designs were tested for immunogenicity in mice, with and without hypervariable region 1, which is an immunogenic region associated with viral escape One of these designs showed improvement in polyclonal immune serum binding to HCV pseudoparticles and neutralization of isolates associated with antibody resistance. These results indicate that antigen optimization through structure-based design of the envelope glycoproteins is a promising route to an effective vaccine for HCV. Designs were tested in vitro and in vivo, demonstrating alteration of the E2 antigenic profile in several cases, and one design led to improvement of cross-neutralization of heterologous viruses This represents a proof of concept that rational engineering of HCV envelope glycoproteins can be used to modulate E2 antigenicity and optimize a vaccine for this challenging viral target. Development of an effective preventative vaccine for HCV is necessary to reduce the burden of infection and transmission and to achieve global elimination of HCV [3]

Methods

Results

Conclusion