Structural and Biophysical Characterization of the HCV E1E2 Heterodimer for Vaccine Development

A panel of hepatitis C virus glycoproteins for the characterization of antibody responses using antibodies with diverse recognition and neutralization patterns

A vaccine against Hepatitis C virus (HCV) is urgently needed to limit the spread of HCV. The large antigenic diversity of the HCV glycoprotein E1E2 makes it difficult to design a vaccine but also to fully understand the antibody response after infection or vaccination. Here we designed a panel of HCV pseudoparticles (HCVpps) that cover a wide range of genetically and antigenically diverse E1E2s. We validate our panel using neutralization and a binding antibody multiplex assay (BAMA). The panel of HCVpps includes E1E2 glycoproteins from acute and chronically infected cases in the Netherlands, as well as E1E2 glycoproteins from previously reported HCVs. Using eight monoclonal antibodies targeting multiple antigenic regions on E1E2, we could categorize four groups of neutralization sensitive viruses with viruses showing neutralization titers over a 100-fold range. One HCVpp (AMS0230) was extremely neutralization resistant and only neutralized by AR4-targeting antibodies. In addition, using binding antibody multiplex competition assay, we delineated mAb epitopes and their interactions. The binding and neutralization sensitivity of the HCVpps were confirmed using patient sera. At the end, eleven HCVpps with unique antibody binding and neutralization profiles were selected as the final panel for standardized HCV antibody assessments. In conclusion, this HCVpp panel can be used to evaluate antibody binding and neutralization breadth and potency as well as delineate the epitopes targeted in sera from patients or candidate vaccine trials. The HCVpp panel in combination with the established antibody competition assay present highly valuable tools for HCV vaccine development and evaluation.

Influence of glycosylation on the immunogenicity and antigenicity of viral immunogens

A key aspect of successful viral vaccine design is the elicitation of neutralizing antibodies targeting viral attachment and fusion glycoproteins that embellish viral particles. This observation has catalyzed the development of numerous viral glycoprotein mimetics as vaccines. Glycans can dominate the surface of viral glycoproteins and as such, the viral glycome can influence the antigenicity and immunogenicity of a candidate vaccine. In one extreme, glycans can form an integral part of epitopes targeted by neutralizing antibodies and are therefore considered to be an important feature of key immunogens within an immunization regimen. In the other extreme, the existence of peptide and bacterially expressed protein vaccines shows that viral glycosylation can be dispensable in some cases. However, native-like glycosylation can indicate native-like protein folding and the presence of conformational epitopes. Furthermore, going beyond native glycan mimicry, in either occupancy of glycosylation sites or the glycan processing state, may offer opportunities for enhancing the immunogenicity and associated protection elicited by an immunogen. Here, we review key determinants of viral glycosylation and how recombinant immunogens can recapitulate these signatures across a range of enveloped viruses, including HIV-1, Ebola virus, SARS-CoV-2, Influenza and Lassa virus. The emerging understanding of immunogen glycosylation and its control will help guide the development of future vaccines in both recombinant protein- and nucleic acid-based vaccine technologies.

Genomics-based strategies toward the identification of a Z-ISO carotenoid biosynthetic enzyme suitable for structural studies

Over the past 20years, structural genomics efforts have proven enormously successful for the determination of integral membrane protein structures, particularly for those of prokaryotic origin. However, traditional genomic expansion screens have included up to hundreds of targets, necessitating the use of robotics and other automation not available to most laboratories. Moreover, such large-scale screens of eukaryotic targets are not easily performed at such a scale. To have broader appeal, traditional structural genomic approaches need to be modified and improved such that they are feasible for most laboratories and especially so for proteins from eukaryotic organisms. One such refinement, termed "microgenomic expansion," has been recently described. This approach improves the process of target selection by making target screening a two-step process, with a minimal number of targets tested at each step. Microgenomic expansion methods are applied here theoretically to a project that has the objective of acquiring a structure for the plant 15-cis-ζ-carotene isomerase, Z-ISO.

Where to Next? Research Directions after the First Hepatitis C Vaccine Efficacy Trial

Thirty years after its discovery, the hepatitis C virus (HCV) remains a leading cause of liver disease worldwide. Given that many countries continue to experience high rates of transmission despite the availability of potent antiviral therapies, an effective vaccine is seen as critical for the elimination of HCV. The recent failure of the first vaccine efficacy trial for the prevention of chronic HCV confirmed suspicions that this virus will be a challenging vaccine target. Here, we examine the published data from this first efficacy trial along with the earlier clinical and pre-clinical studies of the vaccine candidate and then discuss three key research directions expected to be important in ongoing and future HCV vaccine development. These include the following: 1. design of novel immunogens that generate immune responses to genetically diverse HCV genotypes and subtypes, 2. strategies to elicit broadly neutralizing antibodies against envelope glycoproteins in addition to cytotoxic and helper T cell responses, and 3. consideration of the unique immunological status of individuals most at risk for HCV infection, including those who inject drugs, in vaccine platform development and early immunogenicity trials.