Pseudomonas aeruginosa (P.a) infections are a major public health issue in ventilator-associated pneumoniae, cystic fibrosis and chronic obstructive pulmonary disease (COPD) exacerbations. This bacterium is multidrug resistant and there is an urgent need to develop new therapeutic approaches. Our group has recently shown that P.a-derived Elastase B (LasB) degrades the cytokine interleukin (IL)-6 and the antimicrobial molecule Elafin, and down regulates a lung epithelial-IL-6-antimicrobial-repair pathway [1Saint-Criq V., et al. Thorax 2018 ;  73 : 49-61 [cross-ref]

Cliquez ici pour aller à la section Références], which Results in a stronger inflammatory response and a higher mortality rate in P.a-infected mice.

To counteract P.a activity, we reasoned that over-expressing IL-6 and elafin may be beneficial, and that the alveolar macrophage (AM), also targeted by P.a LasB [2Bastaert F., et al. Front Immunol 2018 ; 9

Cliquez ici pour aller à la section Références] may be an ideal vessel for the transfer of this protective activity. We therefore used an Adenovirus strategy to over-express these genes in AMs and transferred these modified cells in the lungs of recipient WT C57/Bl6 mice, 48hrs prior to P.a infection.

(1) Mechanistically, we demonstrate that prior to transfer, the ‘elafin-IL-6′ AMs had on their own an ‘IL-6/IL-10/IL-4R/IL-22/antimicrobial’ molecular signature. (2) Furthermore, when these AMs were transferred in vivo in the lungs of WT C57/Bl6 recipient mice, they conferred a further ‘regulatory’ phenotype to the alveolar unit (as assessed by FACS, RT-qPCR and ELISA: decrease in iNOS, increase in Arg-1, Yim+, IL-10). In keeping with this, BALF recovered after infection had higher IL-10 levels, and was able to suppress splenocyte proliferation in vitro.

Our study demonstrates that AMs genetically modified ex-vivo with IL-6 and the anti-inflammatory molecule elafin provide protection when administered in lungs of mice infected with P.a, by conferring local a regulatory/anti-inflammatory phenotype. This study strenghthens the idea that gene/cell transfer therapy aiming at reinforcing an anti-inflammatory/repairing phenotype could benefit acutely infected respiratory patients (VAP, ARDS.).