Mucosal vaccine immunity induced by a new auxotrophic Pseudomonas aeruginosa strain is linked to Th17 and IgA responses

Pseudomonas aeruginosa ( P.a ) is a Gram-negative opportunistic pathogen that poses a major global health threat, particularly in immunocompromised individuals, patients with cystic fibrosis, and those with burn injuries or ventilator-associated pneumonia. Despite intense efforts, no licensed vaccine is currently available for human use. In this context, live attenuated vaccines (LAVs) represent a promising but underexplored approach, offering the potential to elicit robust, long-lasting, and multifaceted immune responses including that of inducing trained immunity. Here, we sub-cultured Δ LasB PAO1 (a P.a strain that we have shown previously shown to have reduced virulence) in artificial sputum medium (ASM), a culture medium mimicking CF sputum in which bacteria often show auxotrophy. We showed that such a strain (designed here ‘V’ for vaccine) was auxotrophic, less virulent, and had characteristics of ‘CF-like strains’. Crucially, V was able to induce both local (IgA) and systemic humoral responses as well as memory Th17 immune responses, and could, when administered intra-tracheally (but not intra-muscularly), fully protected mice against a lethal PAO1 infection. Overall, the present study demonstrates that our vaccine formulation, in addition to providing an advantageous auxotrophic phenotype adapted to the CF setting, was efficient, when given mucosally, in preferentially inducing secretory IgA and Th17 pathway at mucosal surfaces, a critical barrier that neutralizes pathogens before tissue invasion.