We conducted two phase 3 , randomized , double-blind , placebo-controlled studies that were designed to assess the effects of lumacaftor ( VX-809 ) , a CFTR corrector , in combination with ivacaftor ( VX-770 ) , a CFTR potentiator , in patients 12 years of age or older who had cystic fibrosis and were homozygous for the Phe508del CFTR mutation .