CFTR and cystic fibrosis: Despite impressive rescue levels of F508del CFTR in patient-derived primary cultures of human bronchial epithelial cells, VX809, as well as newer derivatives (i.e., Tezacaftor, VX661), showed only modest efficacy in improving lung function of CF patients [23,24], probably because their action is limited to only one of the multiple defects of mutant F508del CFTR [25,26].