Escherichia coli J5-derived OMVs with hypoendotoxic LPS: Potential boosters of T-cell immunity and IL-17 production for enhanced vaccine efficacy.

Lipopolysaccharide (LPS) is the core epitope of Escherichia coli (E. coli) J5 (O111:B4), a vaccine strain for bovine mastitis. It provides a significant protective effect in host suffering from Gram-negative bacteremia. However, LPS remains the main toxin in bacterial outer membrane vesicles (OMVs), which are non-replicative nanoparticles capable of robust immune modulation. Here, we focused on the immunomodulatory effect of hypoendotoxic LPS containing penta-acylated monophosphoryl lipid A on OMVs derived from E. coli J5. OMVs containing penta-acylated monophosphoryl LPS (referred to as mOMVs) induced a moderate inflammatory response. mOMVs still remained nanoparticle diameters of approximately 30 nm and 100 nm, facilitating antigen drainage to lymph nodes and presentation to dendritic cells (DCs). OMVs could stimulate cell aggregation at injection sites, conducive to DCs activation, with mOMVs enhancing CD3+T cell proliferation and differentiation of CD4+ and CD8+T cell. Notably, CD4+T cells activated by DCs primed with mOMVs produced higher levels of IL-17, suggesting potential enhanced mucosal immunity. Additionally, mOMVs elicited protective antibody responses against clinically isolated E. coli strain. These findings suggest that detoxified LPS endows OMVs with increased efficacy and safety, thereby further promoting the optimization of these vesicles for inducing cross-protection.