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