Confirmatory Clinical Study in Active Ulcerative Colitis

Inclusion Criteria: * Documented diagnosis (histologic diagnosis and either endoscopic or radiographic diagnosis) of ulcerative colitis (UC) at least 3 months prior to Screening. * Diagnosis of active mild-to-moderate UC at Screening as defined by an mMS of 4 to 7, including a MES ≥2 (confirmed by central reading), a Mayo Rectal Bleeding score of 1 or 2, and a Mayo Stool Frequency score ≥1. * UC lesions extending ≥10 cm from the anal verge. * Participant must either receive a stable dose of orally administered 5-aminosalicylic acid (5-ASA); have failed, due to insufficient efficacy, oral 5-ASA; have a documented intolerance or poor tolerance to an aminosalicylic acid treatment, including 5-ASA, or be contra-indicated to receive 5-ASA treatment per local labeling. * Participant must provide written informed consent or assent (parent or legal guardian must provide consent for a participant \<18 years of age who has assented to participate in the study, or as required per local regulations). * In countries not allowing females of childbearing potential (FOCBP) to participate without an acceptable contraceptive method, the FOCBP must agree to abide to local requirements and eg, use at least an acceptable method of contraception until the end of treatment. Exclusion Criteria: * Diagnosis of Crohn's disease, undetermined colitis, ischemic colitis, fulminant colitis, or toxic megacolon. * Evidence of a clinically significant, active infection of the gastrointestinal tract. * Seve…