A Phase 2 Study of Interferon Beta-1a (Avonex®) in Ulcerative Colitis

Key Inclusion Criteria: * Established diagnosis of ulcerative colitis (UC) for ≥6 months * 20 cm active disease at Screening endoscopy * Must have active UC with a Mayo Score/Disease Activity Index (DAI) of 6 to 13 points and moderate to severe disease on endoscopy (Mayo endoscopic score of at least 2) despite prior or concomitant treatment * Colonoscopy within past 5 years for extent of disease and to exclude polyps * For subjects with UC for more than 10 years, colonoscopy with appropriate biopsies within 1 year prior to Screening to exclude dysplasia and neoplasia. * Must be willing and able to practice effective birth control during the study and for 1 month after the last dose of study treatment. Key Exclusion Criteria: * Diagnosis of indeterminate colitis or Crohn's disease * Need for imminent surgery * Diagnosis of primary sclerosing cholangitis or toxic megacolon * Hemoglobin ≤9 g/dL * White blood cell count \< 3500 cells/mm\^3 * Lymphocyte count \<1000 cells/µL * Platelet count \<100,000 cells/µL * Female subjects who are pregnant or who wish to become pregnant during the study, or who are lactating * Known symptomatic colonic stricture * Stool cultures positive for enteric infection * History of malignant disease * History of major abdominal surgery (e.g., gastrectomy) within past 5 years * History of small bowel or colonic obstruction or resection * History of drug or alcohol abuse (as defined by the Investigator) within 2 years prior to Screening * Use of anti-diarrheal agents during the screening period * Previous participation in this study * Previous treatment with interferon beta or other interferon products NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.