Peter van Mourik

169 Rationale of the HIT-CF Organoid study alleles. Subsequently the study aims to identify the predicted best clinical responders (based on amount of organoid swelling) to new CFTR-modulators from different pharmaceutical companies. The study design is an international multi-center study. Rectal biopsies are collected from 500 subjects in different clinical sites across Europe, all members of the clinical trial network of the European Cystic Fibrosis Society (ECFS-CTN). Investigational study drugs will be tested on each organoid in one of three academic laboratories (University Medical Centre Utrecht (UMCU), Katholieke Universiteit Leuven (KUL) and the University of Lisboa (LIS)). A subset of responsive organoids in the academic laboratories will be further screened at HUB and ranked according to level of response to one of the lead drug combinations from each pharmaceutical partner. The subjects with the highest organoid responses will then be asked to participate in subsequent clinical trials. For more details see ‘organoid culturing and drug screening’ below. Patient population The target population is male and female adult (older than 16 or 18 years depending on country-specific ethical regulations)subjects diagnosed with Cystic Fibrosis with a sweat chloride concentration >60 mmol/L, without a mutation for whom CFTR- modulating drugs are currently available (homozygous or heterozygous F508del mutations or gating mutations), and without combinations of frequently occurring class I mutations (1717-1G>A, 621+1G>T, 3120+1G>A, 1898+1G->A, CFTRdele2,3 and 2183AA->G). Patients that have a comorbidity that (to the opinion of the investigator) might pose a risk while participating in a clinical trial will be excluded from study participation. Moreover, patients that have had a lung transplantation are also ineligible. Sample size The study goal is to identify responders that are eligible for subsequent HIT-CF clinical trials. Our preliminary power calculations for the clinical trial with lung function (FEV1) as the primary endpoint, indicate a power of >80% if 16 subjects are included. Therefore the study aims at recruiting 20 patients to mitigate drop-out during the study. This sample size is comparable to a previously published trial in a similar patient population and intervention 30 . As we expect that some patients will not be eligible for a clinical trial, we aim to identify 27 patients per trial eligible for recruitment. This will allow us to contact a new subject if a subject is not eligible to participate. The inclusion rate for the clinical trial needed to include 20 out of 27 patients is thus 74%. To include 16 evaluable subjects the minimum needed inclusion rate is 55%. In experiments performed so far on ultra-rare organoids, we have observed that ~16% of them react to the CFTR-modulating drugs ivacaftor 8