Key Inclusion Criteria:  male and female subjects aged 18 to 75 years (inclusive) with a diagnosis of UC ≥ 90 days before screening; active UC defined as a total Mayo Score of 4 to 10 (inclusive), at baseline, with a Mayo endoscopic subscore (MES) ≥ 2 confirmed by a central reader; baseline fecal calprotectin ≥ 250 μg/g; biologic-naïve or having stopped biologic therapy ≥ 8 weeks before the start of the study; 5-aminosalicylates must be stable for ≥ 1 month prior to randomization.  Key Exclusion Criteria:  Crohn's disease (CD), indeterminate colitis, or presence or history of fistula with CD; a history of toxic megacolon, abdominal abscess, symptomatic colonic stricture, or stoma; history of or at imminent risk of colectomy; history of or current colonic dysplasia ; recent history (within 2 years prior to randomization) or current adenomatous colonic polyps; treatment with an immunosuppressant within 3 months of randomization; bacterial or parasitic pathogenic enteric infection; live virus vaccination within 1 month prior to screening.