A Study to Evaluate the Safety and Efficacy of Long Term Treatment With VX-661 in Combination With Ivacaftor in Participants With Cystic Fibrosis Who Have an F508del-CFTR Mutation

This is a Phase 3, multicenter, open-label, 3-part rollover study in subjects with CF who are homozygous or heterozygous for the F508del-CFTR mutation and who participated in studies VX13-661-103 (Study 103, NCT02070744), VX14-661-106 (Study 106, NCT02347657), VX14-661-107 (Study 107, NCT02516410), VX14-661-108 (Study 108, NCT02392234), VX14-661-109 (Study 109, NCT02412111), VX14-661-111 (Study 111, NCT02508207), VX15-661-112 (NCT02730208), and VX16-661-114 (NCT03150719). The study is designed to evaluate the safety and efficacy of long-term treatment of VX-661 in combination with ivacaftor.


Eligibility Criteria:
Inclusion Criteria:

Part A:

* Participants entering the Treatment Cohort must meet all of the following criteria:
* Elect to enroll in the Treatment Cohort
* Completed study drug Treatment Period in a parent study (NCT02070744, NCT02347657, NCT02516410, NCT02392234, NCT02412111) or study drug treatment and the Safety Follow up Visit for participants from NCT02508207.
* Willing to remain on a stable CF regimen through the Safety Follow-up Visit.
* Participants re-enrolling in the Part A Treatment Cohort must meet all of the following criteria:

  * Previously received at least 4 weeks of study drug before discontinuing in Part A of Study NCT02565914 to participate in another qualified Vertex study.
  * Completed the last required visit of another qualified Vertex study before or during the Returning Visit in Part A Study NCT02565914.
* Participants entering the Part A Observational Cohort must meet the following criteria:

  * \<18 years of age (age on the date of informed consent/assent in the parent study)
  * Completed study drug Treatment Period in a parent study or study drug treatment and the Safety Follow up Visit for subjects from NCT02508207, but do not elect to enroll in the NCT02565914 Treatment Cohort; or
  * Received at least 4 weeks of study drug treatment and completed visits up to the last scheduled visit of the Treatment Period of a parent study (and the Safety Follow up Visit for participants from NCT02508207), but do not meet eligibility criteria for enrollment into the Treatment Cohort

Part B:

Participants who meet all of the following inclusion criteria will be eligible for Part B.

* Did not withdraw consent from the parent study or Part A of Study NCT02565914.
* Completed study drug treatment during the Treatment Period in Part A of - Willing to remain on a stable CF medication (and supplement) regimen through the 96 week visit of Study NCT02565914.

Participants re enrolling in Part B must meet all of the following criteria:

* Previously received at least 4 weeks of study drug before discontinuing Study NCT02565914 to participate in another qualified Vertex study, which is defined as a Vertex study of investigational CFTR modulators that allows participation of participants in Study NCT02565914.
* Completed the last required visit of another qualified Vertex study before or during the Returning Visit in Part B.
* Willing to remain on a stable CF medication (and supplement) regimen through the 96 week visit in Part B.

Part C:

* Participants who meet all of the following inclusion criteria will be eligible for Part C.
* Did not withdraw consent from Part B of Study NCT02565914.
* Completed study drug treatment during Part B of NCT02565914.
* Willing to remain on a stable CF medication (and supplement) regimen through the 96 week visit of Part C.

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 to the subject.
* Pregnant and nursing females.
* Sexually active subjects of reproductive potential who are not willing to follow the contraception requirements.
* History of drug intolerance in the parent study that would pose an additional risk to the subject.
* Participation in an investigational drug trial (including studies investigating VX-661/ivacaftor or lumacaftor/ivacaftor) other than the parent studies of NCT02565914 or other eligible Vertex studies investigating VX-661 in combination with ivacaftor, or use of a commercially available CFTR modulator.

Other protocol defined Inclusion/Exclusion criteria may apply.