This study is an open-label extension (OLE) trial to evaluate the safety and tolerability of etrolizumab in participants with moderate to severe ulcerative colitis (UC) who were enrolled in the Phase II Study ABS4986g (NCT01336465) and meet the eligibility criteria for entry in the OLE study.

Inclusion Criteria:

• All participants (placebo or active) who were previously enrolled in the Phase II study (ABS4986g) and fulfill any of the following criteria:
• Participants who have not obtained a clinical response in the Phase II study (ABS4986g) by Week 10 (the end of the Phase II treatment phase) may enter this OLE trial at any time after Week 10 and up to and including Week 28
• Participants who have a clinical response in the Phase II study (ABS4986g) at Week 10 but have had a flare of UC between Week 10 and Week 28
• Males and females with reproductive potential must be willing to use a highly effective method of contraception, vaginal ring, intrauterine device, physical barrier, or vasectomized partner) from study start to a minimum of 4 months (approximately 5 half-lives)
• Concomitant immunosuppressive therapy must be tapered within 6 weeks after enrollment in this OLE study
• Participants must have tapered completely off oral corticosteroids within 24 weeks of enrollment to this OLE study

Exclusion Criteria:

• Participants who did not complete through Week 10 of the Phase II study (ABS4986g)
• Pregnancy or lactation
• Any new malignancy within the past 6 months
• Any new (since enrolling in the Phase II study [ABS4986g]), significant, uncontrolled, co- morbidity, such as neurological, cardiac, pulmonary, renal, hepatic, endocrine, or gastrointestinal (GI) disorders
• Any new clinically significant signs or symptoms of infection as judged by the investigator
• Any abnormal laboratory values recorded at the last visit completed in the Phase II study (ABS4986g)