ABX464 in Subjects With Moderate to Severe Active Ulcerative Colitis

Inclusion Criteria:

• Diagnosis of moderate to severe active UC confirmed by endoscopy and histology atleast 12 weeks prior to screening visit. Moderate to severe active UC defined byMayo Clinic Score (MCS) of 6 to 12 inclusive (on a scale of 0-12). Moderate tosevere active UC should be confirmed at screening visit with a centrally read MCSendoscopy score of at least 2 (on a scale of 0-3);

• Subjects receiving oral corticosteroids must have been on a stable dose ofprednisone or prednisone equivalent ≤20 mg/day) or on beclomethasone diproprionate (≤5mg/day) or on budesonide MMX (≤9mg/day), for ≥2 weeks before first dosing (i.e.baseline);

• Topical corticosteroids and topical 5-aminosalicylic acid preparations must havebeen withdrawn ≥2 weeks before first dosing (i.e. baseline);

• Subjects who are on oral 5-aminosalicylic acid must have been on a stable dose ≥4weeks before first dosing (i.e. baseline);

• Subjects who are receiving immunosuppressants in the form of azathioprine, 6-mercaptopurine, or methotrexate needed to be on a stable dose for 4 weeks beforefirst dosing (i.e. baseline). Subjects taking methotrexate also are advised to takefolic acid 1 mg/day (or equivalent) supplementation if there is no contraindication;

• Subjects on probiotics (e.g., Culturelle® [Lactobacillus GG, i-Health, Inc.],Saccharomyces boulardii) must be on stable doses for 2 weeks before first dosing (i.e. baseline);

• Subjects on antidiarrheals (e.g., loperamide, diphenoxylate with atropine) must beon stable doses for 2 weeks before first dosing (i.e. baseline);

• Subjects who have previously received anti-tumor necrosis factor (TNF) therapy orvedolizumab must have discontinued therapy ≥8 weeks before first dosing (i.e.baseline);

• Subjects previously treated with cyclosporine or tacrolimus must have discontinuedtherapy ≥4 weeks before first dosing (i.e. baseline);

• Subjects previously treated with tube feeding, defined formula diets, or parenteralalimentation/nutrition must have discontinued treatment 3 weeks before first dosing (i.e. baseline).

Exclusion Criteria:

• Subject with Crohn's Disease (CD), indeterminate colitis (IC) or presence or historyof fistula with CD;

• History of toxic megacolon, abdominal abscess, symptomatic colonic stricture orstoma; history or is at imminent risk of colectomy;

• History or current evidence of colonic dysplasia or adenomatous colonic polyps.Subject with severe gastrointestinal complications; e.g., short bowel syndromes,obstructing strictures, recent or planned bowel surgery, Ileostomy and/or colostomy,recent bowel perforation;

• Subject with significant and known active infections at screening such as Infectedabscess, positive for Clostridium difficile (stool antigen and toxin), CMV, TB andrecent infectious hospitalization;