The conserved bridging domain on HCV E1E2 glycoprotein complex is targeted by neutralizing antibodies from diverse lineages.

The bridging domain (BD) region on hepatitis C virus (HCV) E1E2 glycoprotein complex is a conserved, E1-dependent conformational site of vulnerability formed by E2 residues 646-704. Given its importance for rational vaccine design, here, we characterized the genetic, structural, functional, and epitope features of 25 BD-directed nAbs isolated from HCV-infected individuals or immunized macaques. These antibodies derive from diverse B cell lineages but frequently display recurrent CDRH3 motifs and recognize overlapping epitopes spanning antigenic regions AR4 and AR5, with variable engagement of the E2 back layer (BL) region. A crystal structure of the macaque nAb RM3-26 bound to E2 core domain reveals a BL-directed binding mode analogous to the human nAb hcab40. Importantly, BD-directed nAbs achieve broad neutralization with minimal somatic hypermutation at contact residues and act additively with neutralizing face-directed antibodies. Together, these findings underscore BD as a promising target for rational HCV vaccine design.