Efficacy and Safety of BBT-401-1S in Ulcerative Colitis

Inclusion Criteria: * Provision of signed and dated informed consent form (ICF) * Stated willingness to comply with all study procedures and availability for the duration of the study * Male or female, aged \>=18 years * Diagnosed with active UC for at least 3 months prior to screening * Total Mayo score \>=5 and Endoscopic sub-score \>=1 * Stable dosing regimens of oral drugs (if currently administered) as follows: 5-ASA or sulfasalazine at a stable dose for at least 4 weeks, purine analogues (azathioprine, mercaptopurine, thiopurines) or methotrexate at a stable dose for at least 12 weeks, and low-dose oral corticosteroid (up to 20 mg prednisone/day or equivalent) for at least 4 weeks prior to the first dose of study treatment. Doses of oral drugs must remain stable until the end of study treatment (with possible exception for tapering steroid dose after 8 weeks) * For females of reproductive potential: use of highly effective contraception for at least 1 month prior to screening and agreement to use such a method during study participation and for an additional 3 months after the last dose * For males of reproductive potential: use of condoms or other methods to ensure effective contraception with partner during study participation and for an additional 3 months after the last dose Exclusion Criteria: * Use of anti-TNF-a biologics or any other biologics for treatment of UC within 60 days prior to randomization. * Any rectal therapy for treatment of UC or intravenous corticosteroids within 2 weeks prior to randomization. * Presence of Crohn's disease, indeterminate colitis, ischemic colitis, fulminant colitis, ulcerative proctitis, or toxic mega-colon * Previous extensive colonic resection (subtotal or total colectomy) * Ileostomy, colostomy, or known fixed symptomatic stenosis of the intestine * Evidence of or treatment for Clostridium difficile infection or other pathogenic bowel infection within 60 days or for another intestinal pathogen within 30 days prior to randomization * Active infection with the HIV or Hepatitis B or C viruses * Clinically significant active extra-intestinal infection (e.g., pneumonia, pyelonephritis) * Clinically significant abnormal vital signs, physical examination or 12-lead electrocardiogram (ECG) at screening or baseline * Clinically significant abnormal results of liver function tests (ALT/AST, bilirubin and alkaline phosphatase) \> 2X the upper limit of normal (ULN) at screening * Other clinically significant abnormal laboratory results at screening in the investigator's opinion * History of any clinically significant medical condition that, in the investigator's opinion, would preclude participation in the study * Pregnancy or lactation * Treatment with another investigational drug or other intervention within 30 days prior to screening