The main purpose of this study is to determine the safety and efficacy of eltrekibart and mirikizumab in adult participants with moderately to severely active ulcerative colitis (UC).

The study will last approximately 4-5 years. Screening is required within 35 days prior to enrollment. For each participant, the total duration of the clinical trial will be about 69 weeks including screening.

Inclusion Criteria:

• Have had an established diagnosis of UC of ≥3 months in duration before baseline.
• Have moderately to severely active UC as assessed by the UC disease activity score.
• Have an inadequate response to, loss of response to, or intolerance to at least one conventional medication (including corticosteroids) or one advanced therapy (including biologics, Janus Kinase (JAK) inhibitors, or sphingosine-1-phosphate (S1P) immunomodulators).
• Are on a stable dose of certain oral UC medications (including corticosteroids).
• Must meet contraception requirements.

Exclusion Criteria:

• Have received anti-interleukin (IL)-23p19 or anti-IL-12p40 antibodies in the past.
• Have experienced a thrombotic event within 24 weeks before baseline.
• Have a current diagnosis of Crohn's Disease or certain other inflammatory gastrointestinal diseases.
• Have had certain abdominal surgeries within the past 3 months or are likely to require surgery for UC during the study.
• Have a history of certain adenomas, dysplasia's, or malignancies.

Anonymized individual patient level data will be provided in a secure access environment upon approval of a research proposal and a signed data sharing agreement.

Data are available 6 months after the primary publication and approval of the indication studied in the US and European Union (EU), whichever is later. Data will be indefinitely available for requesting.

A research proposal must be approved by an independent review panel and researchers must sign a data sharing agreement.

Double-blind