This research aims to better understand how the new substances of Galapagos work on the defective CFTR, using mini-intestines (organoids) and cells from the nasal mucosa (nasal epithelial cells). Depending on the CFTR defect 1, 2 or a combination of 3 substances are required to show a clear effect. A better understanding of these reactions in the mini-arms and the nasal mucosa will help to better understand the variation in later use by the patient and provide the opportunity to give ‘person-directed medication’.