In summary, this study shows for the first time to our knowledge that ivacaftor is an essential component of ETI required to induce constitutive activity of F508del-CFTR chloride channels in the absence of exogenous cAMP-dependent stimulation and that this constitutive CFTR-mediated chloride secretion is essential to improve viscoelastic properties of the mucus and restore MCT on nasal epithelial cultures from patients with CF. This evidence concerns the gene CFTR and cystic fibrosis.