Structural basis for cross-alphaherpesvirus neutralization by an antibody targeting a conserved hotspot on glycoprotein B.

Alphaherpesviruses, including herpes simplex viruses (HSV-1/2) and pseudorabies virus (PRV), pose significant threats to human and animal health, yet broad-spectrum interventions remain elusive. Here, we characterize C12A6, a neutralizing antibody (nAb) targeting glycoprotein B (gB) that cross-neutralizes HSV-1, HSV-2, and PRV and confers substantial, although incomplete, therapeutic protection against lethal HSV-1 or PRV infection. Cryo-electron microscopy structures of C12A6 in complex with PRV gB and HSV-2 gB reveal that the antibody engages a conserved conformational epitope on Domain I (DI). A conserved interaction framework, anchored by invariant polar contacts and a hydrophobic core, supports recognition across divergent alphaherpesvirus gBs. Comparison with the broader alphaherpesvirus antibody 16F9 shows that C12A6 additionally engages less-conserved peripheral residues, providing a structural basis for its more restricted recognition breadth. These findings define the structural basis for C12A6-mediated cross-neutralization and illuminate the functional architecture of gB DI as a target for broad-spectrum antiviral development.