Structural basis of a conserved, broad antigenic region surrounding the five-fold axis of foot-and-mouth disease virus revealed by swine neutralizing antibodies.

Foot-and-mouth disease virus (FMDV) exhibits extensive antigenic diversity and limited cross-protection among different serotypes, making the identification of broadly neutralizing antibodies (bnAbs) critical for the development of vaccines that confer broad and effective protection. Here, we isolated four porcine-derived bnAbs that broadly neutralized multiple representative strains from FMDV serotypes O and A. These bnAbs convergently target a conserved antigenic region, with residue 204 (K) towards the VP1 C-terminus serving as a key determinant. Notably, the bnAb pO18-10, which competes with antibodies recognizing the VP1 G-H loop, VP1 C-terminus, and VP3 epitopes, exhibits the broadest neutralization breadth, including cross-neutralization against serotype Asia1. Cryo-electron microscopy (cryo-EM) of pO18-10 in complex with FMDV serotype O (O/18074) revealed a novel cross-protomer antigenic region located around the icosahedral five-fold axis of the viral capsid, with an interaction footprint of up to 1452 Ų. pO18-10 engages this epitope through interactions with the VP1 C-terminus and VP3 G-H loop of one protomer, as well as the VP1 E-F loop of an adjacent protomer, demonstrating extensive antigenic coverage. Residues 204 (K) and 210 (K) on VP1 were identified as key determinants of this cross-serotype antigenic site. Furthermore, pO18-10 sterically blocks the integrin receptor αvβ6, effectively neutralizing FMDV by preventing viral attachment. In vivo, pO18-10 conferred robust prophylactic and therapeutic protection against FMDV-induced mortality and clinical disease in mice. Collectively, these findings provide a promising neutralizing antibody candidate for immunodiagnostic applications and define a cross-serotype antigenic structure for universal FMDV vaccine design.