In vitro safety and in vivo proof of concept of bacterial lysate-loaded inhalable locust bean gum microparticles aimed at respiratory infection prevention

Bacterial lysates (BL) are used as immunomodulators to prevent respiratory infections, though clinical evidence on efficacy remains inconsistent. Conventional oral administration may not provide optimal lung protection. This study explores inhalable microparticles containing BL associated to a locust bean gum (LBG) matrix as a strategy for pulmonary immunization against respiratory infections. LBG is a galactomannan showing mucoadhesive properties and potential to target antigen-presenting cells through mannose receptor interactions. BL-loaded LBG microparticles (LBG:BL = 10:0.2, w/w) were assessed regarding safety profile in respiratory cells (A549, Calu-3 and differentiated THP-1 cells) and in an airway 3D tissue model (MucilAir®). Assays demonstrated absence of toxicity (cell viability >70%) at physiological concentrations (38–76 μg/cm 2 or 125–250 μg/mL). Minimal generation of reactive oxygen species (ROS) was detected, and no significant alterations were observed on transepithelial electrical resistance (TEER), indicating satisfactory safety profile. In vivo pulmonary delivery of BL-loaded LBG microparticles more effectively induced mucosal IgA responses than controls. These findings support repurposing BL as immunomodulators for preventing respiratory infections through inhalable BL-loaded LBG microparticles, enhancing immune responses through antigen delivery to lung-resident immune cells and antigen presentation in bronchus-associated lymphoid tissue.