The novel antigen, lipopolysaccharide export protein LptH, protects mice against Pseudomonas aeruginosa acute pneumonia in monovalent and multivalent vaccines

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that is a leading cause of morbidity and mortality worldwide in susceptible patients, particularly in those with respiratory disorders. The rising prevalence of multidrug-resistant strains and the failure of previous P. aeruginosa vaccine candidates in clinical trials highlight the urgent need to investigate novel vaccine antigens. In this study, we evaluated the protective potential of two antigen candidates, LptH and OprM, previously identified based on their involvement in host-cell attachment in a murine acute pneumonia model. Recombinant Escherichia coli BL21 clones overexpressing these proteins showed 8.8- and 3.5-fold increased attachment to 16HBE14o^- cells in vitro, confirming their role in host-cell attachment. Immunisation with rLptH significantly reduced bacterial burden in the lungs by 1.12 log₁₀ CFU and improved animal welfare scores compared to adjuvant-only controls. Serological and immunophenotyping analyses revealed that the monovalent rLptH vaccine stimulated antigen-specific IgG1 and IgG2c isotype production, and enhanced IFN-γ and IL-17 recall responses in the spleen. Moreover, a trivalent vaccine comprising rLptH and two other P. aeruginosa antigens, rFtsZ, and rOpmH, achieved a 2.33 log₁₀ CFU reduction in lung bacterial burden, and 1.85 log₁₀ CFU reduction in dissemination. These encouraging findings support the potential of LptH as a promising antigen for the development of a protective multivalent vaccine against P. aeruginosa infections.