CFTR and cystic fibrosis: CFTR modulator drugs have dramatically changed the trajectory of CF disease by significantly improving lung disease and nutrition, as well as reducing sweat chloride concentration as in vivo proof of restored CFTR function in people with CF (pwCF) (Ramsey et al., 2011; Wainwright et al., 2015; Keating et al., 2018; Heijerman et al., 2019).