['cystic fibrosis']
['tezacaftor/ivacaftor', 'ivacaftor', 'placebo', 'placebo']

        Inclusion Criteria:

          -  Homozygous for the F508del CFTR mutation

          -  Confirmed diagnosis of CF

          -  Percent predicted forced expiratory volume (ppFEV1) ≥70% of predicted normal for age,
             sex, and height during screening.

          -  Stable CF disease as judged by the investigator

        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.

          -  An acute upper or lower respiratory infection, pulmonary exacerbation, or changes in
             therapy (including antibiotics) for pulmonary disease within 28 days before Day 1
             (first dose of study drug)

          -  Pregnant or nursing females.

          -  Sexually active subjects of reproductive potential who are not willing to follow the
             contraception requirements.

          -  Any contraindication to undergoing chest imaging, as per the site's institutional
             guidelines
      