A Study of LY3471851 in Adult Participants With Moderately to Severely Active Ulcerative Colitis (UC)

Inclusion Criteria: * Have moderately to severely active ulcerative colitis (UC) as defined by a modified Mayo score (MMS) of 4 to 9 with an endoscopic subscore (ES) ≥2, with endoscopy performed within 14 days before baseline. * Have evidence of UC extending proximal to the rectum (with ≥15 centimeters (cm) of involved colon). * Have up-to-date colorectal cancer surveillance performed according to local standard. * Participants are either one of the following: * Have failed conventional treatments including inability to tolerate oral or intravenous corticosteroids or immunomodulators (6-mercaptopurine or azathioprine or methotrexate), or history of corticosteroid dependence (an inability to successfully taper corticosteroids without return of UC) and neither failed or demonstrated intolerance to advanced therapy (eg, tumor necrosis factor (TNF) antagonists, anti-integrin therapies, anti-IL12/23p40 therapies, Janus kinase (JAK) inhibitor) OR, * Have failed advanced therapies such as treatment with 1 or more advance therapies (eg, tumor necrosis factor \[TNF\] antagonists, anti-integrin therapies, anti-IL12/23p40 therapies, Janus kinase \[JAK\] inhibitor) at doses approved for the treatment of UC with documented history of failure to respond to or tolerate such treatment. * Have had an established diagnosis of UC of ≥3 months in duration before baseline which includes endoscopic evidence of UC and a histopathology report that supports a diagnosis of UC. Supportive endoscopy an…