VirG-specific antibodies mediate antimicrobial functions and confer cross-protection against Shigella

Shigella species are a major cause of diarrheal diseases and child mortality worldwide. There is no licensed vaccine to prevent shigellosis, and most candidates target the bacterial O-polysaccharide, which limits their coverage to the vaccine serotype. Conserved Shigella proteins capable of eliciting broadly protective immunity are compelling alternatives for overcoming serotype-restricted responses. We previously reported that VirG is a broadly protective Shigella antigen. Here, we demonstrate the antimicrobial function and cross-protective efficacy of VirG-specific antibodies. Immunization with VirG-derived constructs induced high and durable antigen-specific IgG responses in rabbits, and passive transfer of VirG-specific rabbit antisera conferred significant protection (57.1-75.0%) in mice against lethal S. flexneri 2a and S. sonnei challenge. VirG-specific antibodies recognized native VirG expressed unipolarly by live bacteria and exhibited a range of antimicrobial activities, including bactericidal and opsonophagocytic killing, and inhibition of bacterial adherence and invasion of human colonoids. We demonstrate, for the first time, that Shigella protein-specific antibodies can mediate Shigella killing. In summary, VirG-directed antibodies exhibited robust antimicrobial activity and mediated cross-serotype protection. These findings support VirG as a promising component of next-generation protein-based Shigella vaccines.