Inclusion Criteria:

1. Age ≥ 18 years.
2. Diagnosis of ulcerative colitis is established based on clinical manifestations, laboratory findings, colonoscopy, radiological imaging (CT or ultrasound), and histopathological examination.
3. Presence of moderate-to-severe disease activity, defined as a modified Mayo score (MMS) ≥ 5 points, accompanied by a rectal bleeding subscore (RBS) ≥ 1 and a Mayo endoscopic subscore (MES) ≥ 2.
4. Inadequate response or intolerance to at least one conventional therapy (5-aminosalicylates, corticosteroids, or immunosuppressants), as assessed by the investigator according to clinical practice.
5. Based on the research cohort requirements, the GUS real-world cohort may include patients who are biologic-naive, have failed first-line therapy, or have failed multiple lines of therapy.
6. Availability of baseline data for disease activity assessment, including symptom scores (partial Mayo score or PRO2), endoscopic evaluation (MES), biochemical markers (C-reactive protein or fecal calprotectin), or imaging parameters (CT or intestinal ultrasonography).
7. Patients enrolled in the prospective GUS cohort are required to provide written informed consent voluntarily.

Exclusion Criteria:

1. Diagnosed with other intestinal diseases, such as Crohn's disease, intestinal tuberculosis, infectious colitis, ischemic colitis or other chronic intestinal inflammatory diseases;
2. If there is an active intestinal infection, and the fecal culture or pathogen test shows positive within 8 weeks before the study (including Clostridium difficile, cytomegalovirus, etc.), and the re-examination turns negative without any signs of persistent infection, a re-evaluation can be conducted.
3. Combined with severe infections, malignant tumors, severe liver and kidney dysfunction, or accompanied by active autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, sarcoidosis, and Graves' disease that may interfere with disease assessment
4. Those who have undergone total colorectal resection or stoma surgery in the past and whose disease activity cannot be evaluated, or are expected to undergo major intestinal surgery during the study period;
5. Has had a severe allergic reaction to monoclonal antibodies;
6. During pregnancy or lactation (can be recorded as an independent cohort but not included in the primary analysis);
7. Severe absence of baseline and follow-up data makes it impossible to determine efficacy or safety.
8. Currently participating in other interventional clinical trials that may interfere with the results of this study.