A Study of VX-121 Combination Therapy in Participants With Cystic Fibrosis (CF) Who Are Homozygous for F508del, Heterozygous for F508del and a Gating (F/G) or Residual Function (F/RF) Mutation, or Have At Least 1 Other Triple Combination Responsive (TCR) CFTR Mutation and No F508del Mutation

Key Inclusion Criteria:

• Participant has one of the following genotypes:

• Homozygous for F508del;

• Heterozygous for F508del and a gating (F/G) mutation;

• Heterozygous for F508del and a residual function (F/RF) mutation;

• At least 1 other TCR CFTR gene mutation identified as responsive to ELX/TEZ/IVAand no F508del mutation

• Forced expiratory volume in 1 second (FEV1) value >=40% and <=90% of predicted meanfor age, sex, and height for participants currently receiving CFTR protein modulatortherapy; FEV1 >=40% and <=80% for participants not currently receiving CFTR proteinmodulator therapy

Key Exclusion Criteria:

• History of solid organ or hematological transplantation

• Hepatic cirrhosis with portal hypertension, moderate hepatic impairment (Child PughScore 7 to 9), or severe hepatic impairment (Child Pugh Score 10 to 15)

• Lung infection with organisms associated with a more rapid decline in pulmonarystatus

• Pregnant or breast-feeding females

Other protocol defined Inclusion/Exclusion criteria may apply.