This clinical trial is examining the action and effects of several new drugs in the treatment of cystic fibrosis in children. In addition, several genetic factors are examined. The hope is that the ability to determine prior to treatment those individuals who will or will not respond to existing therapies will avoid needless risk of side effects and the high cost of a potentially ineffective treatment regimen. Understanding the way these drugs work in the body and the best way to study them is critical to expanding the use of these drugs to all patients with cystic fibrosis (CF).

Understanding variation in genetic response to pharmacological treatments and personalized CFTR modulator response is crucial to the optimization of the use of these novel compounds; expansion to all patients who might benefit from them; and development of predictive biomarkers. In addition, the ability to determine prior to treatment those individuals who will or will not respond to existing therapies will avoid needless risk of side effects and the high cost of a potentially ineffective treatment regimen. Understanding the way these drugs work in the body and the best way to study them and the downstream effects is critical to expanding the use of these drugs to all patients with cystic fibrosis (CF).

Inclusion Criteria:

• documentation of CF diagnosis per CFF diagnostic criteria and known CFTR genotype
• age 2 years and older
• ability to provide written informed consent and/or assent (by subject and/or legal guardian)
• on a stable dose of triple combination CFTR modulator therapy for at least two weeks prior to Visit 1
• clinically stable lung disease, defined as no documented acute decrease in FEV1 > 10%, OR use of additional antibiotics (intravenous [IV] or oral [PO]) within 4 weeks prior to screening

Exclusion Criteria:

• recent significant unintentional weight loss, as determined by the investigator, in the 4 weeks prior to screening
• pregnant or breastfeeding female
• history of alcohol or substance abuse in the 6 months prior to screening
• participation in a study involving an investigational intervention within 28 days (or 5 half-lives, whichever is longer) prior to screening
• in the opinion of the Investigator, medical or psychiatric illness, or other conditions that would interfere with participation