A "plug-and-display" nanoparticle based on attenuated outer membrane vesicles enhances the immunogenicity of protein antigens

As natural nanoparticle, the bacterial outer membrane vesicles (OMV) hold great potential in protein vaccines because of its self-adjuvant properties and good biocompatibility. However, the inherent immunotoxicity seriously hampers the application of OMV as protein antigens delivery carrier. Here, an attenuated OMV was constructed by elimination of the flagella protein from its surface and removal of the phosphate group of LPS at position one via gene-editing strategy. The gene-edited outer membrane vesicles (EMV) effectively reduced the levels of pro-inflammatory factors TNF-α and IL-6 in mouse blood by at least 10-fold and 15-fold respectively, compared to wild type OMV (WT-OMV). Importantly, protein antigens are conveniently displayed on EMV by employing a plug-and-display procedure, whereby the exterior of biotinylated EMV can be readily decorated with a synthetic protein comprised of target antigen fused to a biotin-binding protein. EMV greatly increased the uptake of antigen by dendritic cells (DCs) and promoted their maturation. EMV-antigen complex induces a robust antigen-specific antibody responses and cellular immune responses. We propose that EMV have great potential as protein antigens delivery vehicle for preventing different infectious diseases.