CFTR and cystic fibrosis: Chronic treatment with IVA has been shown to reduce ENaC and CaCC activity in primary CF human bronchial epithelial (HBE) cells (F508del/G551D), with a similar effect also reported for IVA in combination with lumacaftor (LUM) in normal and F508del/F508del CF HBE, suggestive of an off-target effect of CFTR modulators [9].