Outer membrane vesicle-coated nanoparticle vaccine protects against Acinetobacter baumannii pneumonia and sepsis

Summary

This vaccine study uses Acinetobacter baumannii outer membrane vesicles as the antigenic shell on standardized gold nanoparticle cores. The pathogen is highly drug resistant, and its naturally shed vesicles contain membrane lipids and virulence-associated antigens but vary in size and contents. Coating a defined core was intended to combine this immunogenic complexity with more reproducible particle construction. In rabbits, vaccination generated strong IgG responses. Those antibodies increased killing of A. baumannii by human neutrophils through opsonophagocytosis and, when transferred passively, protected mice from lethal sepsis. Active vaccination of mice protected against both sepsis and pneumonia. Immune correlates included B-cell recruitment to draining lymph nodes, activation of dendritic-cell markers, improved splenic neutrophil responses, and reduced proinflammatory cytokine storm. The principal finding is that an OMV-coated particle can produce functional antibodies and protect across two severe infection models, linking a standardized core with a broad bacterial membrane antigen source. This supports the platform for resistant Gram-negative pathogens. The abstract does not define strain breadth, duration, toxicology, manufacturing reproducibility, or comparative advantage over uncoated OMVs and other vaccines.