Biomimetic model of human small airways reveals functional impacts of the cystic fibrosis microenvironment on monocytes and macrophages

Several muco-obstructive lung diseases in humans, including cystic fibrosis (CF), feature the chronic recruitment of blood leukocytes and their reprogramming within the lumen of small airways to drive pathological adaptations such as altered immune mediator secretion and defective killing of bacteria. To investigate these mechanisms, we engineered a biomimetic model in which primary human blood monocytes migrate through a human small airway epithelium, andepithelium and differentiate into macrophages upon 4-day exposure to macrophage colony-stimulating factor. We observed that airway-recruited monocytes (ArMos) obtained with the control chemoattractant C-C motif ligand 2 (CCL2) altered their transcriptome and secretome upon transmigration, and further upon differentiation into airway-recruited macrophages (ArMas), as compared to circulating monocytes. We observed specific additional alterations in transcriptomic and secretomic properties of ArMos and ArMas when they were conditioned in CF airway supernatant (derived from cell- and bacteria-free sputum) [CFASN], compared CCL2 conditions. Critically, CF ArMas (but not CF ArMos), showed a much reduced ability to kill P. aeruginosa, a common CF pathogen. These findings extend prior studies on small airway-recruited neutrophils, and identify immune tolerance by macrophages as one underlying cause of bacterial colonization in CF. This biomimetic model support further mechanistic and preclinical investigations of small airway-recruited monocytes and macrophages in CF and other diseases featuring chronic inflammation and infection, like non-CF bronchiectasis, and chronic obstructive pulmonary disease.