CFTR and cystic fibrosis: In vitro models, often described as the Air-Liquid Interface (ALI) culture method, use primary human bronchial epithelial cells (HBECs) derived from bronchial brushing or transplanted CF lungs, and are considered the gold standard to measure CFTR function from CFTR variants and to validate the efficacy of CFTR therapeutics preclinically (Awatade et al., 2018).