Study of GS-1427 in Participants With Moderately to Severely Active Ulcerative Colitis
The goal of this study is to learn if GS-1427 is effective and safe in treating participants with moderate to severe ulcerative colitis. The study will compare participants in different treatment groups treated with GS-1427 with participants treated with placebo (Part 1), and participants treated with GS-1427 or ustekinumab alone with participants treated with GS-1427 in combination with ustekinumab (Part 2).

The primary objectives of this study are:

Part 1: To assess the efficacy of GS-1427, compared with placebo control, in achieving clinical response at Week 12

Part 2: To assess the efficacy of combination therapy with GS-1427 and ustekinumab, compared with GS-1427 and ustekinumab monotherapies, in achieving clinical response at Week 12
- EligibilityCriteria: Key Inclusion Criteria:  Individuals have Ulcerative Colitis (UC) of at least 90-days duration before randomization confirmed by endoscopy and histology at any time in the past. Documentation of endoscopy and histology consistent with the diagnosis of UC must be available in the source documents. Individuals have UC with minimum disease extent of 15 cm from the anal verge. Individuals have moderately to severely active UC as determined by endoscopy occurring during screening with a total modified Mayo Clinic Score (mMCS) of 5 to 9 points, including a centrally read endoscopic subscore of at least 2. Individuals have an inadequate response or loss of response or is intolerant to at least 1 of the following conventional UC treatments  Individuals have an inadequate response or loss of response or are intolerant to:  At least one of these conventional UC treatments: Corticosteroids, azathioprine or 6-mercaptopurine (6-MP)  OR  No more than two advanced therapies: Tumor necrosis factor-alpha inhibitors, interleukin (IL)-12/23 inhibitors (Part 1 only; no prior use in Part 2), sphingosine 1-phosphate receptor modulators, and Janus kinase inhibitors  Key Exclusion Criteria:  Have a current diagnosis of Crohn's Disease (CD) or clinical findings suggestive of CD, diagnosis of indeterminate colitis due to etiologies such as an enteric pathogen, or lymphocytic or collagenous colitis. Have a current diagnosis of toxic megacolon, symptomatic colonic stricture, acute severe colitis, fulminant colitis, or abdominal abscess at screening or randomization. Part 1 and 2; have any history of exposure to vedolizumab Part 2 only: have any history of exposure to interleukin - 12/23 or 23 inhibitor (eg ustekinumab) Requirement for ongoing therapy with or use of any prohibited medication as specified in the protocol  Note: Other protocol defined Inclusion/Exclusion criteria may apply - HealthyVolunteers: No - Gender: All - MinimumAge: 18 Years - MaximumAge: 75 Years - StdAgeList: Adult, Older Adult