ABTECT - Maintenance

Inclusion Criteria in maintenance phase: * Subjects must have completed the induction treatment study (ABX464-105 or ABX464-106), and patients' clinical response status must be available. * Subjects with a valid endoscopy performed at the end of the induction study and results from central reader available at Day 1. * Subjects must understand, sign and date the written voluntary informed consent form at the visit prior to any protocol-specific procedures. For under-aged subjects, national requirements regarding consent should also be met. * Women of childbearing potential (WOCBP) subjects and male subjects with WOCBP partner must agree to comply with contraception requirements as described in Section 4.4. (Contraception) of the protocol. * Subjects must be able and willing to comply with study visits and procedures as per protocol. * Subjects should be affiliated to a health insurance policy whenever required by a participating country or state Inclusion criteria in LTE phase: * Subject must have completed the maintenance phase * Investigator and subject must assess and agree that the subject has received, and will continue to receive benefit from being in the study Exclusion Criteria in maintenance phase: * Subjects who permanently discontinued the study treatment during the induction study (either ABX464-105 or ABX464-106). * Subjects who have developed any major illness/condition (eg. primary sclerosis cholangitis, Crohn's disease, colectomy, diverting ileostomy, colon cancer or colonic adenomas \[low or high grade dysplasia\]). * Subjects with evidence of an unstable clinical condition (eg. toxic megacolon, fulminant colitis, bowel perforation, uncontrolled ischemic disease, congestive heart failure with NYHA class 3 or 4 symptoms) during the induction study that, in the investigator's judgment, will substantially increase the risk to the subject if he or she participates in the study. * Subjects who plan to participate in other investigational studies during the maintenance study. * Male or female planning a pregnancy, or pregnant female subjects * Introduction during induction study of prohibited medications, dosages, surgical or non-medicinal procedures indicated for UC (except antidiarrheals and motility agents for acute diarrhea). * Any changes in the laboratory values during the induction period that could jeopardize subject's safety in the opinion of the investigator. If any doubts, the investigator should contact the sponsor study medical monitor. * Subject who is planning to receive live vaccine during the study. * Subjects committed to an institution by virtue of an order issued either by the judicial or the administrative authorities. Exclusion criteria for LTE phase: * Subject continues to satisfy exclusion criteria listed above for the maintenance phase * Introduction during maintenance phase of prohibited medications, dosages, surgical or non-medicinal procedures indicated for UC (except antidiarrheals and motility agents for acute diarrhea).