CFTR and cystic fibrosis: This is at odds with clinical trials with VX-809 + VX-770 that demonstrated significant improvement in FEV1 and several other improvements in clinical outcomes in CF patients homozygous for the F508del-CFTR mutation [11], as well as the studies in this report in which the combination of VX-809 + VX770 (48 hours) significantly increased F508del-CFTR Cl secretion in CFBE cells and in CF-HBE cells (Figs 1–3 and 5, S1–S3 and S5 Tables).