This is a Phase 2, randomized, double-blind, placebo- and active-controlled, parallel group, multicenter study to evaluate the safety, tolerability, and efficacy of VX-440 in dual and triple combination with tezacaftor (TEZ; VX-661) and ivacaftor (IVA; VX-770) in subjects with cystic fibrosis (CF) who are homozygous for the F508del mutation of the CF transmembrane conductance regulator (CFTR) gene (F508del/F508del), or who are heterozygous for the F508del mutation and a minimal function (MF) CFTR mutation not likely to respond to TEZ and/or IVA therapy (F508del/MF).

Inclusion Criteria:

• Willing and able to comply with scheduled visits, treatment plan, study restrictions, laboratory tests, contraceptive guidelines, and other study procedures.

• To prevent pregnancy, female participants of childbearing potential and their male partners will be required to use pre-specified, highly effective methods of non-hormonal contraception. Male participants with female partners of childbearing potential will be required to use a condom.

• Body weight ≥35 kg.

• Sweat chloride value ≥60 mmol/L from test results obtained during screening.

• Subjects must have an eligible CFTR genotype:

  • Heterozygous for F508del and a minimal function (MF) mutation known or predicted not to be responsive to TEZ and/or IVA.
  • Homozygous for F508del

• Subjects must have an FEV1 ≥40% and ≤90% of predicted normal for age, sex, and height at the Screening Visit

• Stable CF disease as judged by the investigator.

• Willing to remain on a stable CF medication regimen through the planned end of treatment or, if applicable, the Safety Follow up Visit.

Exclusion Criteria:

• History of any comorbidity that, in the opinion of the investigator, might confound the results of the study or pose an additional risk in administering study drug to the subject.
• History of cirrhosis with portal hypertension.
• Risk factors for Torsade de Pointes
• History of hemolysis.
• Glucose-6-phosphate dehydrogenase (G6PD) deficiency assessed at Screening.
• Clinically significant abnormal laboratory values at screening
• An acute upper or lower respiratory infection, pulmonary exacerbation, or changes in therapy for pulmonary disease within 28 days before the first dose of study drug.
• Lung infection with organisms associated with a more rapid decline in pulmonary status
• An acute illness not related to CF within 14 days before the first dose of study drug
• A standard digital ECG demonstrating QTc >450 msec at screening.
• History of solid organ or hematological transplantation.
• History or evidence of cataract or lens opacity determined to be clinically significant by the ophthalmologist or optometrist based on the ophthalmologic examination during the Screening Period.
• History of alcohol or drug abuse in the past year, including but not limited to, cannabis, cocaine, and opiates, as deemed by the investigator.
• Ongoing or prior participation in an investigational drug study, with certain exceptions. (e.g., ongoing participation in NCT02565914)
• Use of commercially available CFTR modulator (e.g., Kalydeco, Orkambi) within 14 days before screening (applies only to the Heterozygous F508del/MF cohorts; does not apply to the Homozygous F508del/F508del Cohort).
• Pregnant or nursing females: Females of childbearing potential must have a negative pregnancy test at screening and Day 1.