The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of SION-719 when given to people with CF who are already taking Trikafta.

Inclusion Criteria:

• Diagnosis of CF with F508del homozygous genotype based on documented CFTR genotype laboratory report.
• Adherent to physician-prescribed Trikafta, as assessed by the Investigator, for at least 3 months prior to the Screening visit, taken at the recommended dose without modifications and on the regimen described in the current prescribing information.
• Stable CF disease without pulmonary exacerbation within 28 days before Baseline or acute non-CF-related illness within 14 days before Baseline.

Exclusion Criteria:

• Participant has clinically significant current or recurrent illness, other than CF
• Participant has a history of malignancy, except for basal cell or squamous epithelial carcinomas of the skin that have been resected with no evidence of recurrence for at least 1 year.