Let-7b-5p loaded Mesenchymal Stromal Cell Extracellular Vesicles reduce Pseudomonas - biofilm formation and inflammation in CF Bronchial Epithelial Cells

Cystic Fibrosis (CF) is a multiorgan disease caused by mutations in the CFTR gene, leading to chronic pulmonary infections and hyperinflammation. Among pathogens colonizing the CF lung, Pseudomonas aeruginosa is predominant, infecting over 50% of adults with CF, and becoming antibiotic-resistant over time. Current therapies for CF, while providing tremendous benefits, fail to eliminate persistent bacterial infections, chronic inflammation, and irreversible lung damage, necessitating novel therapeutic strategies. Our group engineered mesenchymal stromal cell derived extracellular vesicles (MSC EVs) to carry the microRNA let-7b-5p as a dual anti-infective and anti-inflammatory treatment. MSC EVs are low-immunogenicity platforms with innate antimicrobial and immunomodulatory properties, while let-7b-5p reduces biofilm formation and inflammation. In a preclinical CF mice model, we reported that let-7b-5p-loaded MSC EVs reduced P. aeruginosa burden, immune cells, and proinflammatory cytokines in the lungs. We hypothesize four complementary mechanisms for the observed in-vivo effects of the let-7b-5p loaded MSC EVs: antimicrobial activity, anti-inflammatory properties, inhibition of antibiotic-resistant P. aeruginosa biofilm formation in CF airways, and stimulation of anti-inflammatory macrophage behaviors. This study focused on the second and third mechanisms and demonstrates that MSC EVs engineered to contain let-7b-5p effectively blocked the formation of antibiotic-resistant P. aeruginosa biofilms on primary human bronchial epithelial cells (pHBECs) while also reducing P. aeruginosa -induced inflammation. This approach holds promise for improving outcomes for people with CF. Future work will focus on optimizing delivery strategies and expanding the clinical applicability of MSC EVs to target other CF-associated pathogens.