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.

Chunyan Yi,Xuesong Wang,Jin Zhong,Zhiyang Ling,Sheng Ye,Honglin Zhou,Bing Sun,Xiaoyu Sun,Jiangjun Wang,Yu Yan,Gang Long,Yaguang Zhang,Liyan Ma,Zhong Huang,Yongfen Xu,Rongguang Zhang,Junqi Niu,Jing Xia,Wendy Fan ,Long He ,Junxia Lü ,Xinhao Zhao ,Ronghua Zhang

doi:10.1038/s41423-020-0403-1

Abstract

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.

Highlights

Hepatitis C virus (HCV) infection is a global health problem
The fully human mAb 8D6 was isolated from an HCV-infected patient and showed broad neutralizing activity against different isolates of HCV Using single-cell PCR to generate fully human monoclonal antibodies specific for a viral antigen,[9] we isolated HCV E2 antigen-specific memory B cells (CD19+ IgG+ E2+) from the peripheral blood of an HCV 2a chronically infected patient
8D6 was able to bind to the E2 protein of HCV, covering a panel of 12 different HCV strains from 6 distinct genotypes (Fig. 1a)

Summary

Introduction

Hepatitis C virus (HCV) infection is a global health problem. More than 71 million people worldwide have been infected.[1] In addition, 50–80% of infected individuals develop a chronic infection that increases the risk of serious liver diseases, such as liver cirrhosis and hepatocellular carcinoma.[2,3]. HCV remains the sole human hepatitis virus for which a vaccine is not yet commercially available.[4] Highly effective directacting antivirals (DAAs) for the treatment of chronic hepatitis C have been developed recently; resistance-associated variants have been identified during DAA therapy and can lead to therapy failure.[5] In addition, some HCV-infected populations, especially in developing countries, do not have access to DAAs owing to their high cost. An effective prophylactic vaccine is essential for combating the global HCV epidemic

Methods

Results

Conclusion