CFTR and cystic fibrosis: While additional experiments are required to determine why these studies reach different conclusions regarding the effect of VX-770 on VX-809 stimulated F508del-CFTR Cl secretion, our data show that P. aeruginosa inhibits both the VX-809 and the VX-809 + VX-770 stimulated increase in F508del-CFTR Cl secretion in primary cultures of CF-HBE cells.