The Part 1 primary objective is to compare the efficacy of ABX464 versus placebo on the proportion of subjects in clinical remission \[SFS = 0 or 1, RBS = 0 and endoscopy sub-score = 0 or 1\] at Week 44.

The Part 2 primary objective is safety

The Part 2 primary objective is safety

The Part 2 primary objective is safety

To compare the efficacy of ABX464 versus placebo on clinical remission

To evaluate the long-term safety of ABX464 given at 25 mg once daily in subjects with Moderate to Severe Active Ulcerative Colitis.

Clinical remission (based on the Mayo scoring system) is defined as: a rectal bleeding sub-score = 0, and an endoscopy sub-score ≤1 (excluding friability), and at least 1-point decrease in stool frequency sub-score from baseline to achieve a stool frequency sub-score ≤1

Reduction from baseline in Modified Mayo Score (MMS) MMS is a composite score of UC disease activity based on the following 3 subscores: 1. Stool frequency subscore (SFS), scored from 0 (normal number of stools) to 3 (5 or more stools more than normal). 2. Rectal bleeding subscore (RBS), scored from 0 (no blood seen) to 3 (blood alone passed). 3. Endoscopic subscore, scored from 0 (normal or inactive disease) to 3 (severe disease, spontaneous bleeding, ulceration). The overall MMS ranges from 0 to 9 where higher scores represent more severe disease.

Number of treatment-emergent adverse events in ABX464 treated subjects

Number of treatment-emergent adverse events in the ABX464 treated subjects compared to placebo