Structure-based design of stable recombinant hepatitis C virus E1E2 heterodimers

Hepatitis C virus (HCV) affects 47 million people and causes 239,000 deaths annually, yet no vaccine is on the horizon. Generating a stable native-like mimic of the envelope complex E1E2, the only target for known neutralizing antibodies, is an important aim for HCV vaccine development. Starting from a recombinant E1E2 design that utilizes a leucine zipper for proper folding, we used an iterative structure-based design approach to engineer antigens with at least 100-fold stronger binding to conformational antibodies and increased thermal stability. These new E1E2 designs facilitate production of native-like E1E2 antigens based on strains from different HCV genotypes and enable the generation of a recombinant E1E2 antigen design that lacks the immunogenic leucine zipper. A cryo-EM structure of one of the stabilized E1E2 antigens in complex with neutralizing antibody AT1211 provides atomic-level insights into an atypical epitope on the E2 subunit. Finally, immunogenicity studies in rabbits with adjuvanted E1E2 proteins show that immunogen stabilization alone does do not enhance serum neutralization breadth, but that removing the leucine zipper does increase homologous serum neutralization.