A Study of the Efficacy and Safety of Etrolizumab Treatment in Maintenance of Disease Remission in Ulcerative Colitis (UC) Participants Who Are Naive to Tumor Necrosis Factor (TNF) Inhibitors

Inclusion Criteria:

• Diagnosis of ulcerative colitis (UC) established at least 3 months prior to Day 1 byclinical and endoscopic evidence
• Moderately to severely active UC as determined by an MCS of 6-12 with an endoscopicsubscore greater than or equal to (≥)2 as determined by the central reading procedure (endoscopy to be performed 4-16 days prior to Day 1), a rectal bleeding subscore ≥1,and a stool frequency subscore ≥1 during the screening period (prior to Day 1)
• Evidence of UC extending a minimum of 20 centimeters (cm) from the anal verge asdetermined by baseline endoscopy (flexible sigmoidoscopy or colonoscopy) performedduring screening, 4-16 days prior to Day 1
• Naive to treatment with any anti-TNF therapy
• Participants must have had an inadequate response, loss of response, or intolerance toprior corticosteroid and/or immunosuppressant treatment
• Background regimen for UC may include oral 5-aminosalicylate (5-ASA), oralcorticosteroids, budesonide, probiotics, azathioprine (AZA), 6-mercaptopurine (6-MP),or methotrexate (MTX) if doses have been stable during the screening period
• Use of highly effective contraception
• Must have received a colonoscopy within the past year or be willing to undergo acolonoscopy in lieu of a flexible sigmoidoscopy at screening

Exclusion Criteria:

• A history of or current conditions and diseases affecting the digestive tract, such asindeterminate colitis, suspicion of ischemic colitis, radiation colitis, ormicroscopic colitis, Crohn's disease, fistulas or abdominal abscesses, colonic mucosaldysplasia, intestinal obstruction, toxic megacolon, or unremoved adenomatous colonicpolyps
• Prior or planned surgery for UC
• Past or present ileostomy or colostomy
• Any prior treatment with etrolizumab or other anti-integrin agents (includingnatalizumab, vedolizumab, and efalizumab) as stated in the protocol
• Any prior treatment with anti-adhesion molecules (such as mucosal addressin celladhesion molecule [MAdCAM-1])
• Any prior treatment with rituximab
• Any treatment with tofacitinib during screening
• Cogenital or acquired immune deficiency, chronic hepatitis B or C infection, humanimmunodeficiency virus (HIV) positive, or history of tuberculosis (active or latent)
• Evidence of or treatment for Clostridium difficile within 60 days prior to Day 1 orother intestinal pathogens within 30 days prior to Day 1
• History of recurrent opportunistic infections and/or severe disseminated viralinfections
• History of organ transplant
• Any major episode of infection requiring treatment with intravenous (IV) antibioticswithin 8 weeks prior to screening or oral antibiotics within 4 weeks prior toscreening
• Received a live attenuated vaccine within 4 weeks prior to Day 1