An Extension Study for Treatment of Moderately to Severely Active Ulcerative Colitis

The purpose of this open-label extension (OLE) study is to evaluate the safety and efficacy of etrasimod in participants with moderately to severely active ulcerative colitis (UC) who previously received double-blind treatment (either etrasimod 2 mg per day or placebo) during participation in one of the qualified Phase 3 or Phase 2 double-blind, placebo-controlled parent studies including but not limited to: (APD334-301 \[NCT03945188\] or APD334-302 \[NCT03996369\] or APD334-210 \[NCT04607837\]).

Inclusion Criteria: * Must have met the eligibility criteria and have been enrolled in the qualified Phase 2 or 3 parent studies listed below or other qualified region-specific studies and meet the following additional criteria: 1. Participants previously enrolled in Study APD334-301 (NCT03945188) or APD334-210 (NCT04607837) must have completed the Week 12 visit and have been assessed to have active UC that has not improved or has worsened from baseline or completed the Week 52 visit 2. Participants previously enrolled in APD334-302 (NCT03996369) must have completed the Week 12 visit Exclusion Criteria: * If Investigator considers the participant to be unsuitable for any reason to participate in the Open-Label Extension study * Experienced an adverse event that led to discontinuation from parent study