GUselkumAb inteRvention and DIet evaluAtioN for Pouchitis

Inclusion Criteria: 1. Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any screening procedures 2. At least 18 years of age at the time of signing the Informed Consent Form (ICF) 3. Use of highly effective methods of birth control; defined as those that, alone or in combination, result in low failure rate (i.e., less than 1% per year) when used consistently and correctly; such as implants, injectables, combined oral contraceptives, some IUDs, true sexual abstinence (i.e. refraining from heterosexual intercourse during the entire period of risk associated with the Trial treatment(s)) or commitment to a vasectomised partner. 4. Participant with a proctocolectomy and IPAA for UC who heveloped chronic or relapsing pouchitis, defined as mPDAI score ≥5 and a minimum endoscopic subscore of 2 (outside the staple or suture line) with either: 1. ≥2 recurrent episodes within 1 year prior to the screening visit, each treated with ≥2 weeks of antibiotic or other prescription therapy, or 2. patients treated with maintenance antibiotic therapy taken continuously for four consecutive weeks before the screening visit and who are refractory to this antibiotic therapy, or 3. previously failure of another biologic therapy to treat chronic pouchitis. 5. The subject agrees to take ciprofloxacin (500 mg twice daily) on Day 1 and through Week 4, regardless of the previous treatment and to stop any previous antibiotic therapy on Day 1 of the study. For patients who did previously not tolerate quinolone therapy, an alternative antibiotic therapy between Day 1 and Week 4 with metronidazole (500 mg three times a day) will be allowed. (Additional courses of antibiotics will be allowed, as needed, for flares after Week 16.) All participants that are considered for Trial participation, per the above criteria will be documented via applicable log forms in Investigator Site File (including Screen Failures). Exclusion Criteria: 1. Crohn's disease (CD), CD-related complications of the pouch (pouch fistula, pouch strictures, ulcerations in the pre-pouch ileum without pouchitis), irritable pouch syndrome (IPS), isolated or predominant cuffitis, infectious pouchitis, diverting ostomy or mechanical complications of the pouch 2. Previous treatment with an anti-IL12/23 or an anti-IL23 antibody 3. Any investigational or approved biologic agent within 30 days of screening 4. Nonbiologic investigational therapy or JAK inhibitors within 30 days prior to screening 5. Active or untreated latent tuberculosis (TB). In case of a newly identified positive diagnostic TB test result (defined as a positive tuberculin skin test) , active TB has to be ruled out and appropriate treatment for latent TB has to be initiated for a minimum of 4 weeks prior to the first administration of study medication. 6. Chronic hepatitis B virus (HBV)\* infection, chronic hepatitis C virus (HCV)\*\* infection, a known history of human immunodeficiency virus (HIV) infection (or is found to be seropositive at screening) or subject is immunodeficient (e.g., due to organtransplantation, history of common variable immunodeficiency, etc). \* Subjects who are positive for hepatitis B virus surface antigen (HBsAg) will be excluded. For subjects who are negative for HBsAg but are positive for either surface antibodiesand/or core antibodies, HBV DNA polymerase chain reaction will be performed and if anytest result meets or exceeds detection sensitivity, the subject will be excluded.\*\* If subject is HCV antibody positive, then a viral load test will be performed. If the viralload test is positive then the subject will be excluded. 7. Active severe infection (eg sepsis, cytomegalovirus, listeriosis or C. difficile) 8. The subject has allergies to and/or contraindications for ciprofloxacin and metronidazole 9. Participant has a history of malignancy or current malignancy, except for the following: adequately treated non-metastatic basal cell skin cancer, squamous cell skin cancer and cervical carcinoma in situ. Subjects with a remote history of malignancy (e.g., \>10 years since completion of curative therapy without recurrence) will be considered based on the nature of the malignancy and the therapy. 10. Any disorder or laboratory abnormalities which in the Investigator's opinion might jeopardise the participant's safety or compliance with the protocol. 11. Any prior or concomitant treatment(s) that might jeopardise the participant's safety or that would compromise the integrity of the Trial (see list in 5.3). 12. Female who is pregnant, breast-feeding or intends to become pregnant before, during, or within 15 weeks after the last dose of study drug; or intending to donate ova during such time period or is of child-bearing potential and not using an adequate, highly effective contraceptive or males who want to make their partner pregnant or intends to donate sperm during the course of this study or for 18 weeks after the last dose of study drug 13. Participation in another interventional Trial with an investigational medicinal product (IMP) or device. Participants who meet one or more of the above exclusion criteria must not proceed to be enrolled/randomized in the Trial and will be identified via applicable log forms in Investigator Site File.