CFTR and cystic fibrosis: In that context, cysteamine, approved for the treatment of cystinosis [207], was tested in CF mice, followed by a small open-label clinical trial in PwCF, where it was shown to reduce sweat chloride levels in F508del carrying PwCF, but not in a cohort which contained PwCF carrying two non-F508del mutations not responsive to current CFTR modulators [208,209].