This is a phase 2/3, multi-center, randomized, double-blind, study for patients with moderate to severe Crohn's disease. Subjects with refractory CD or who are intolerant to at least one current therapy will be considered. The study consists of four substudies. They are designed to investigate efficacy, safety, tolerability of etrasimod as therapy for CD.

The study consists of a screening period, a 14-week induction period, a 6-week extended induction period (if applicable), and a follow-up period. •The subject will have to go to the study center for the visits and follow the instructions the study doctor and the study team give them, and take the study medication, as directed.They are required to bring all unused study medication and packaging to each study visit. The subject should complete their eDiary every day and bring it with you to all visits. They also must remember to return your Holter monitor to the study clinic.Other tests that the subject is required to complete will include ECG, drug test, TB test at screening. Also urine and blood tests at all induction visits except day 1 extension, vital signs and physical at every visit, eye and pulmonary function tests will be done at screening.

$600