Furthermore, primary nasal epithelial cells harvested from an individual with CF harboring E831X (in trans with F508del) exhibited residual CFTR function (Fig 4D, black tracing) that was increased by ivacaftor and further augmented by correctors (lumacaftor and tezacaftor) (Fig 4D, green and red tracings). This evidence concerns the gene CFTR and cystic fibrosis.