A Study to Investigate How Well Ravagalimab (ABBV-323) Works and How Safe it is in Participants With Moderate to Severe Ulcerative Colitis Who Failed Prior Therapy

Inclusion Criteria:

• Participants must voluntarily sign and date an informed consent, approved by anindependent ethics committee (IEC)/institutional review board (IRB), prior to theinitiation of any screening or study-specific procedures.
• Diagnosis of UC for at least 3 months prior to Baseline. Appropriate documentation ofbiopsy results consistent with the diagnosis of UC in the assessment of theInvestigator, must be available.
• Participant meets the following disease activity criteria: Active UC with an AdaptedMayo score of 5 to 9 points and endoscopic subscore of 2 to 3 (confirmed by centralreview).
• History of inadequate response, loss of response, or intolerance to one or more of theapproved biologic therapies: infliximab, adalimumab, golimumab, vedolizumab, and/ortofacitinib (Note: If tofacitinib was received in a clinical trial, subject must havereceived open-label drug).

Exclusion Criteria:

• Participant having an active, chronic, or recurrent infection that based onInvestigator's clinical assessment makes the participant an unsuitable candidate forthe study.
• Participant having any malignancy except for successfully treated non-metastaticcutaneous squamous cell or basal cell carcinoma or localized carcinoma in situ of thecervix.
• Participant with history of dysplasia of the gastrointestinal tract or evidence ofdysplasia in any biopsy performed during the screening endoscopy other than completelyremoved low-grade dysplastic lesions.
• Laboratory values not meeting the following criteria : Serum aspartate transaminase (AST) and alanine transaminase (ALT) <= 2* upper limit of normal (ULN); Total whiteblood cell (WBC) count >= 3.0*10^9/L.