Multicomponent Pseudomonas aeruginosa vaccines eliciting Th17 cells and functional antibody responses confer enhanced protection against experimental acute pneumonia in mice

The Gram-negative pathogen Pseudomonas aeruginosa is a common cause of pneumonia in hospitalized patients. Its increasing antibiotic resistance and widespread occurrence present a pressing need for vaccines. We previously showed that a P. aeruginosa type III secretion system protein, PopB elicits a strong Th17 response in mice after intranasal (IN) immunization and confers antibody-independent protection against pneumonia in mice. In the current study, we evaluated the immunogenicity and protective efficacy in mice of the combination of PopB (purified with its chaperone protein PcrH) and OprF/I, an outer membrane hybrid fusion protein, compared to immunization with the proteins individually either by the intranasal (IN) or subcutaneous (SC) routes. Our results show that after vaccination, a Th17 recall response from splenocytes was detected only in mice vaccinated with PopB/PcrH, either alone or in combination with OprF/I. Mice that were immunized with the combination of PopB/PcrH and OprF/I had enhanced protection in an acute lethal P. aeruginosa pneumonia model, regardless of vaccine route, compared to the mice vaccinated the with either alone or adjuvant control. Immunization generated IgG titers against the vaccine proteins and whole P. aeruginosa cells. Interestingly, none of these antisera had opsonophagocytic killing activity, but antisera from mice immunized with vaccines containing OprF/I had the ability to block IFN-γ binding to OprF/I, a known virulence mechanism. Hence, vaccines combining PopB/PcrH with OprF/I that elicit functional antibodies lead to a broadly and potently protective vaccine against P. aeruginosa pulmonary infections.