Peter van Mourik

171 Rationale of the HIT-CF Organoid study are present. It is important that the device opening has passed the anal sphincter to avoid pain. Collecting organoids using a rectal suction device has a very low risk of complications. Friedmacher et al. have recently published a systematic review, in which they found that the risk of any complication is 0.63%. Persistent rectal bleeding was the most common complication with an incidence of 0.5% 31 . The article states that in very young children (<1 year of age), the risk is relatively higher. We will perform this procedure in adult subjects, and subjects are instructed to call the hospital if bleeding is persistent or if they have any other complaints. To detect any prolonged bleeding and intervene as early as possible, patients will stay in the hospital for one hour after the procedure. Forceps biopsy Biopsies can be collected by forceps during rectoscopy. This device is used by trained gastro-enterologists to obtain material for a wide spectrum of diseases. The procedure is done endoscopically with a flexible endoscope. The endoscope is introduced rectally. The biopsies are obtained on sight, thereby avoiding any arteries or veins. In a recently published article, the safety of this procedure was evaluated by studying 353 forceps biopsies. No major complications were reported. Only one patient complained of abdominal pain following the procedure, but fully recovered after 4 hours observation 32 . Patients are observed after the procedure to quickly notice any possible complications. Generating organoids from rectal biopsies At the HUB organoids will be generated from the rectal biopsies using the protocol as previously published 22,33,34 . If organoids are received from study sites, these will be further cultured to ensure viability of material. From HUB, organoids will be transferred to the Cystic Fibrosis Research Laboratory of University Medical Center Utrecht, the Organ Systems Laboratory of KU Leuven and the Cystic Fibrosis Research Laboratory of the University of Lisbon. Samples will be transported by a specialist courier service. Organoid culturing and drug screening UMCU protocols for CFTR function measurements have been established under ISO-9001 conditions and HUB has ISO-270001 compliant protocols. The most updated protocols of UMC and HUB have been combined and shared with the laboratories in Leuven and Lisbon for preparation of organoid culture media, organoid growing, and CFTR function measurement by forskolin-induced swelling (FIS) 33 . From these, one standard lab manual has been generated for all the labs to make sure the procedures are standardised. Additionally, identical lot numbers 8