The investigational F508del corrector VX-809 (Lumacaftor), which is endowed with rescuing efficacy in vitro and in primary cultures of lung cells from F508del-CFTR homozygous CF patients [9], showed only the modest efficacy in a phase II clinical trial in CF patients homozygous for the F508del-CFTR mutant [10]. This evidence concerns the gene CFTR and cystic fibrosis.