Junctional and somatic hypermutation-induced CX4C motif is critical for the recognition of a highly conserved epitope on HCV E2 by a human broadly neutralizing antibody

• Published in: Cellular & molecular immunology 2021-03, Vol.18 (3), p.675-685
• Main Authors: Yi, Chunyan, Xia, Jing, He, Lan, Ling, Zhiyang, Wang, Xuesong, Yan, Yu, Wang, Jiangjun, Zhao, Xinhao, Fan, Weiguo, Sun, Xiaoyu, Zhang, Ronghua, Ye, Sheng, Zhang, Rongguang, Xu, Yongfen, Ma, Liyan, Zhang, Yaguang, Zhou, Honglin, Huang, Zhong, Niu, Junqi, Long, Gang, Lu, Junxia, Zhong, Jin, Sun, Bing
• Format: Article
• Language: English
• Subjects: 631/250/2152; 631/250/254; Antibodies; Biomedical and Life Sciences; Biomedicine; CD81 antigen; Cell culture; Disulfide bonds; E2 protein; Epitope mapping; Gene mapping; Genotypes; Glycoproteins; Hepatitis; Hepatitis C; Immunology; Medical Microbiology; Microbiology; Monoclonal antibodies; Somatic hypermutation; V(D)J recombination; Vaccine; Vaccines; Virions
• ISSN: 1672-7681; 2042-0226
• DOI: 10.1038/s41423-020-0403-1

Induction of broadly neutralizing monoclonal antibodies (bNAbs) that bind to the viral envelope glycoproteins is a major goal of hepatitis C virus (HCV) vaccine research. The study of bNAbs arising in natural infection is essential in this endeavor. We generated a human antibody, 8D6, recognizing the E2 protein of HCV isolated from a chronic hepatitis C patient. This antibody shows broadly neutralizing activity, which covers a pan-genotypic panel of cell culture-derived HCV virions (HCVcc). Functional and epitope analyses demonstrated that 8D6 can block the interaction between E2 and CD81 by targeting a highly conserved epitope on E2. We describe how the 8D6 lineage evolved via somatic hypermutation to achieve broad neutralization. We found that the V(D)J recombination-generated junctional and somatic hypermutation-induced disulfide bridge (C-C) motif in the CDRH3 is critical for the broad neutralization and binding activity of 8D6. This motif is conserved among a series of broadly neutralizing HCV antibodies, indicating a common binding model. Next, the 8D6 inferred germline (iGL) was reconstructed and tested for its binding affinity and neutralization activity. Interestingly, 8D6 iGL-mediated relatively strong inhibition of the 1b genotype PR79L9 strain, suggesting that PR79L9 may serve as a potential natural viral strain that provides E2 sequences that induce bNAbs. Overall, our detailed epitope mapping and genetic studies of the HCV E2-specific mAb 8D6 have allowed for further refinement of antigenic sites on E2 and reveal a new mechanism to generate a functional CDRH3, while its iGL can serve as a probe to identify potential HCV vaccine strains.