Hepatocellular carcinoma is the most common type of liver cancer and is responsible for approximately one million deaths each year. In the United States, persistent infection with hepatitis C virus (HCV) is among the leading causes of hepatocellular carcinoma. HCV vaccine efforts are hampered by genetic diversity of HCV envelope glycoproteins E1 and E2. Structural studies of broadly neutralizing antibodies (bNAbs) (e.g., HEPC3 and HEPC74) isolated from individuals who spontaneously cleared HCV infection will facilitate immunogen design to elicit antibodies against multiple HCV variants. However, challenges in expressing HCV glycoproteins previously limited bNAb-HCV structures to complexes with truncated E2 cores.New expression and purification techniques allowed us to produce bNAb complexes with full-length E2 ectodomains for structural studies. We solved crystal structures of HEPC3 and HEPC74 alone and complexed with E2 ectodomains. We measured the binding and neutralization potency of HEPC3/HEPC74-like germline precursors. Despite derivation from different individuals, HEPC3 and HEPC74 use the same germline heavy chain gene segments and possess a limited number of somatic mutations. We describe a shared CDRH3 disulfide motif that exhibits common interactions with a conserved epitope in the front layer of E2. The germline-encoded CDRH3 motif plays a critical role in initial recognition of HCV by naïve B cells. The structures of E2 ectodomain reveal regions (including a target of immunogen design) that were truncated or disordered in E2 core. We also identify candidate immunogens: E2 variants that bind to HEPC3/HEPC74-like germline precursors. These data reveal unusual structural features relevant to the fundamental understanding of antibody-antigen interactions. The identification of common genetic signatures of HCV bNAbs will facilitate lineage-targeted immunogen design to raise bNAbs against the conserved epitope in the E2 front layer.
Citation Format: Andrew I. Flyak, Stormy Ruiz, Michelle Colbert, Tiffany Luong, James E. Crowe, Jr., Justin R. Bailey, Pamela J. Bjorkman. Broadly neutralizing antibodies against HCV use a CDRH3 disulfide motif to recognize an E2 glycoprotein site that can be targeted for vaccine design [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B109.