This is a multicenter, long-term extension (LTE) study in participants with ulcerative colitis (UC) from Study SPY123-201 (The SKYLINE-UC study).

This is a multicenter, long-term extension (LTE) study in participants with ulcerative colitis (UC) from Study SPY123-201 (The SKYLINE-UC study) who have completed Part A and are deemed to be receiving clinical benefit, completed Part B, or met escape criteria in Part B. The primary aim of this LTE study is to characterize the long-term safety of various investigational drugs, to offer participants the option to extend treatment if they are clinically benefiting, or if they have not achieved sufficient clinical benefit (particularly placebo insufficient responders), to offer the opportunity to receive investigational drug.

Inclusion Criteria:

Participants must meet 1 of the following criteria from Study SPY123-201:

1. Completed Part A and deemed to be receiving clinical benefit by the judgement of the Investigator
2. Completed Part B
3. Participated in Part B and met escape criteria per the SPY123-201 protocol (ie, did not achieve sufficient improvement after the induction treatment period [ITP] or experienced disease worsening during the maintenance treatment period [MTP]).

Exclusion Criteria:

1. Met any treatment discontinuation criteria from Study SPY123-201.

2. Is on any of the following prohibited medications:

   1. Immunosuppressants (eg, azathioprine, 6-mercaptopurine [6-MP], or methotrexate)
   2. Systemic tacrolimus, systemic cyclosporine, oral mycophenolate mofetil (MMF), immunoadsorption columns (such as Prosorba columns), penicillamine, leflunomide, thalidomide, or any other medications that may have immunosuppressive effects
   3. Any marketed advanced therapy (ie, biologic or small molecule)
   4. Any investigational therapy other than SPY123-201 study drug
   5. Total parenteral nutrition

3. Development of any new, unstable, or uncontrolled metabolic, dermatological, hepatic, renal, hematological, pulmonary, cardiovascular, gastrointestinal, neurological (including current and past neurological symptoms suggestive of demyelinating disease), respiratory, endocrine, or psychiatric disorder, acute or chronic infectious diseases, suspected or confirmed immunodeficiency, and suspected or confirmed malignancies, as determined by the Investigator that is likely to unfavorably alter the risk of study participation, confound study results, or interfere with the study conduct or compliance.

4. Ongoing infection requiring oral or intravenous antimicrobial therapy on Day 1.