The Phase I clinical trial (NCT02564354) initiated in 2015 showed that repeated administration to the nasal epithelia (three times per week for 4 weeks) was well tolerated with a favourable safety profile and that CFTR activity was restored in the homozygous Phe508del CF patient cohort (n=7) after intranasal administration, as determined by improved total chloride transport measured by nasal potential difference (NPD). This evidence concerns the gene CFTR and cystic fibrosis.