Bacterial outer membrane vesicles in immune modulation: from mechanisms to applications

Outer membrane vesicles (OMVs), naturally secreted by Gram-negative bacteria, have emerged as versatile tools for immune modulation due to their intrinsic immunogenicity and engineerable properties. This review explores how OMVs activate and regulate both innate and adaptive immunity. They stimulate innate defenses by engaging immune receptors like Toll-like receptors (TLRs), triggering inflammatory pathways, while also shaping adaptive responses through antigen delivery to dendritic cells, promoting T-cell activation and antibody production. We further discuss engineered applications: OMVs serve as customizable vaccine platforms, efficiently delivering antigens and adjuvants, and as targeted drug carriers modified to reduce toxicity. By integrating recent findings on their roles in breaking tumor immunosuppression and enhancing vaccine efficacy, this work underscores OMVs' dual utility as natural immunostimulants and engineered therapeutics. Our synthesis aims to clarify OMV-driven immune mechanisms and accelerate their translation into clinical strategies for cancer treatment and infection prevention, bridging foundational research with practical innovations in immune engineering.