A Study to Assess the Efficacy and Safety of Afimkibart (Also Known as RO7790121) for Induction and Maintenance Therapy in Participants With Moderately to Severely Active Ulcerative Colitis

Prior treatment

• Has received protocol-specified prohibited medicines, including known exposure to any type of anti-TL1A therapy

Other illness

• Current diagnosis of Crohn's disease (CD) or indeterminate colitis, microscopic colitis, ischemic colitis, infectious colitis, radiation colitis
• History of malignancy within 5 years, with the exception of malignancies adequately treated with resection for non-metastatic basal cell or squamous cell cancer or in situ cervical cancer
• Evidence of infection with Clostridioides difficile (C. difficile; formerly known as Clostridium difficile), cytomegalovirus (CMV), human immunodeficiency virus (HIV), Hepatitis B (HBV), Hepatitis C (HCV)
• Has evidence of active tuberculosis (TB), latent TB not successfully treated (per local guidance) or inadequately treated TB

Other

• Currently known complications of UC (e.g. fulminant colitis, toxic megacolon)
• Presence of an ostomy or ileoanal pouch
• Current diagnosis or suspicion of primary sclerosing cholangitis
• Pregnancy or breastfeeding, or intention of becoming pregnant during the study
• Past or current evidence of definite low-grade or high-grade colonic dysplasia or adenomas or neoplasia not completely removed

• Confirmed diagnosis of UC
• Moderately to severely active UC assessed by mMS
• Bodyweight \>= 40 kilogram (kg)
• Up to date with colorectal cancer (CRC) screening performed according to local standards
• Demonstrated inadequate response, loss of response and/or intolerance to at least one protocol-specified conventional or advanced UC therapy
• Males and females of childbearing potential must meet protocol criteria for contraception requirements