Inclusion Criteria:

1. Subject has provided written informed consent
2. Diagnosis of UC (newly diagnosed or established patients) as determined by medical history, endoscopic and histological confirmation with the proximal disease extent limited to the left colon (distal to the splenic flexure), and accessible by flexible sigmoidoscopy. Patients with left-sided disease and the presence of a periappendiceal red patch (limited cecal inflammation) will be eligible as long as there is no intervening evidence of colitis between the cecal base and the upper boundary of inflammation in the left colon.
3. Mayo score ≥ 4, as scored at Screen 2
4. If taking the following medications at Screen 1, subjects must meet the following criteria:
   1. Oral Corticosteroids: stable treatment for at least 4 weeks prior to Day 0 with a maximum dose equivalent to ≤ 15 mg/day of prednisone
   2. Immunosuppressants (azathioprine (AZA) or 6-mercaptopurine (6-MP)): treatment for at least 12 weeks with a stable dose, not exceeding 2.5 mg/kg/day of AZA or 1.5 mg/kg/day of 6-MP, during the 4 weeks prior to Day 0
   3. Aminosalicylates: stable oral doses up to 4.8 g/day for at least 4 weeks prior to Day 0

Exclusion Criteria:

1. Subjects whose UC is anticipated to require surgical, endoscopic, or radiologic intervention during study participation
2. Uncontrolled GI bleeding
3. Subjects who have disease limited to the rectum (maximum disease extent of less than 15 cm)
4. Women who are pregnant, breast-feeding, or planning to become pregnant during the study. All women of childbearing potential must have a negative serum pregnancy test at Screen 2 prior to randomization of treatment.
5. Women of childbearing potential not using adequate birth control measures (e.g., total abstinence, oral contraceptives, intrauterine device, barrier method with spermicide, surgical sterilization, Depo-Provera, or hormonal implants)
6. Current or recent serious systemic disorder including clinically significant impairment in cardiac, pulmonary, liver, renal, endocrine, hematologic, or neurologic function, based on investigator discretion
7. Subjects currently receiving the following concomitant medications:
   1. Prednisone or its equivalent at unstable doses or at doses exceeding 15 mg/day within 4 weeks prior to Day 0
   2. Local steroids such as budesonide, Colifoam, or Predsol enemas within 2 weeks prior to Screen 2
   3. Topical therapies, either mesalamine or steroids, taken within 2 weeks of Screen 2.
   4. Non-steroidal anti-inflammatory drugs (NSAIDs), Cyclooxygenase (COX)-2 inhibitors, or aspirin >100 mg/day within 2 weeks prior to Screen 2
   5. TNF-alpha inhibitors including but not limited to infliximab (Remicade) or adalimumab (Humira) within 12 weeks of Day 0
   6. Any biological agent within 12 weeks of Day 0
   7. Metronidazole within 4 weeks of Day 0
   8. Receipt of any investigational agent within the 12 weeks prior to Day 0
   9. Antibacterial or oral antifungal agents within 4 weeks of Screen 2
   10. IFN therapy
   11. Anticoagulants
   12. Methotrexate
8. Blood transfusion within the 12 weeks prior to Day 0
9. Presence of any of the following abnormal laboratory parameters at Screen 1:
   1. Hemoglobin < 10.0 g/dL
   2. White Blood Count (WBC) < 4,000 or > 20,000/L (equivalent to WBC < 4 or > 20 x109/L)
   3. Platelets < 100,000 or > 800,000/L (equivalent to platelets < 100 or > 800 x109/L)
   4. Total bilirubin > 1.5 × Upper limit of normal (ULN)
   5. Alanine transaminase (ALT) > 2 × ULN
   6. Aspartate transaminase (AST) > 2 × ULN
   7. Alkaline phosphatase (ALK) > 1.5 × ULN
   8. Gamma-glutamyl transferase (GGT) > 1.5 × ULN
   9. Creatinine > 1.5 × ULN
10. History of drug or alcohol abuse within one year prior to Day 0
11. Inability to understand the nature and requirements of the study, or to comply with the study procedures or planned schedule of study visits
12. Evidence of infection with human immunodeficiency virus (HIV), hepatitis B, or hepatitis C
13. Active infection with C. difficile, bacterial enteric pathogens, or pathogenic ova/parasites
14. History of malignancy within the last 5 years, except for resected basal or squamous cell carcinoma, treated cervical dysplasia, or treated in situ cervical cancer Grade I
15. History of colonic dysplasia
16. Any social or medical condition that, in the opinion of the investigator, would preclude provision of informed consent, make participation in the study unsafe, complicate interpretation of study outcome data, or otherwise interfere with achieving the study objectives.