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

Chronic Pseudomas aeruginosa infection in the lung is a common in people with cystic fibrosis (CF). Current therapies for CF fail to eliminate persistent bacterial infections, chronic inflammation, or irreversible lung damage. Our group engineered mesenchymal stromal cell (MSC)-derived extracellular vesicles (EVs) to carry the microRNA let-7b-5p as a dual anti-infective and anti-inflammatory treatment. In a preclinical CF mice model, we found that let-7b-5p-loaded MSC EVs reduced P. aeruginosa burden, immune cells and proinflammatory cytokines in the lungs. This research hypothesized two mechanisms of the observed effects in the mouse model: anti-inflammatory properties of the let-7b-5p-loaded MSC EVs and inhibition of antibiotic-resistant P. aeruginosa biofilm formation in CF airways. Primary human broncial epithelial cells (pHBECs) were exposed to P. aeruginosa and treated with differet MSC EV conditions. The results demonstrated that MSC EVs engineered to contain let-7b-5p effectively blocked the formation of P. aeruginosa biofilms on pHBECs while also reducing P. aeruginosa-induced inflammation by CF-pHBECs. pHBECs from 3 different CF donors (22F, 32G, 29H) were cultured in a monolayer. P. aeruginosa was exposed to the apical side for 1 hour, after which the culture was given 1 of 4 different conditions for 5 hours: process control (PC), negative control (NC) MSC Evs, let-7b-5p-loaded MSC EVs, or no EVs. Additionally, one sample from each donor was not exposed to P. aeruginosa or EVs (untreated, UT).