A Recombinant OMV-Based Vaccine Elicits Potent Protective Immunity Against Pseudomonas aeruginosa

This study aimed to construct a recombinant Pseudomonas aeruginosa outer membrane vesicle (OMV) vector vaccine delivering pcrV and compare the immunological impacts of OMVs as carriers versus as adjuvants.

The recombinant plasmid pBBRMCS5-pcrV was constructed and transformed into P. aeruginosa. Recombinant OMVs (OMV_PcrV) were prepared via ultracentrifugation and characterized in terms of their morphology and particle size by means of transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). After a biosafety evaluation, mice were intramuscularly immunized with PcrV or OMV_PcrV, followed by a booster immunization on day 21. On day 42, the mice were challenged subcutaneously and intranasally with PAO1. Bacterial loads in tissues and blood, pulmonary T-cell subsets, and serum antibody levels were assessed.

The recombinant plasmid was successfully constructed, and Western blotting confirmed the delivery of PcrV into OMVs. TEM revealed typical spherical nanostructures, and NTA showed a median particle size of 127.4 ± 5.3 nm. Upon subcutaneous challenge, the OMV, OMV_PcrV, and OMV + PcrV groups all achieved 100% protection. Both the OMV_PcrV and OMV + PcrV groups exhibited increased CD4⁺ and CD8⁺ T-cell counts and higher induction levels of specific IgM, IgG1, and IgG2a antibodies. The OMV_PcrV group showed superior clearance of respiratory bacterial colonization and reduced inflammatory injury compared with the PBS control group.

The constructed vector successfully delivered the PcrV antigen, and the OMVPcrV vaccine induced effective immune responses. Compared with wild-type outer membrane vesicles (OMVs) and the strategy of directly mixing free PcrV antigen with OMVs (OMV + PcrV), the recombinant OMV_PcrV vaccine exhibited superior immunoprotective efficacy in terms of bacterial clearance and tissue protection, providing experimental evidence for the development of a Pseudomonas aeruginosa vaccine.