A Study to Learn How the Study Medicine Called Etrasimod is Taken up Into Blood and Breastmilk of Healthy Breastfeeding Women

Inclusion 1. Healthy (as determined by medical evaluation including medical history, physical examination, laboratory tests, vital signs and 12-lead ECGs) lactating women who are actively breastfeeding or expressing breast milk, who are at least 12 weeks post partum and not currently pregnant (must have a negative pregnancy test), and must be 18 to 55 years of age, inclusive, at the time of signing the informed consent document (ICD). 2. Body mass index (BMI) of 16-35 kg/m2; and a total body weight \>45 kg (99 lb). 3. Participants must be willing to temporarily discontinue breastfeeding their infants for a total of 21 days, ie, from the evening of the day before Day 1 through to 14 days after the last dose (approximately 8 AM the morning of Day 21). Participants must be willing to regularly pump breasts throughout the study and express breast milk according to a schedule designed to maintain lactation until the completion of breast milk collection Exclusion 1. Evidence or history of clinically significant hematological, renal, endocrine, pulmonary (such as moderate or severe chronic pulmonary disorders like asthma or chronic obstructive pulmonary disease \[COPD\]), gastrointestinal, cardiovascular, hepatic, neurological/psychiatric, anaphylactic, ophthalmologic disorders (such as macular edema, uveitis, retinopathy), or allergic disease (including drug allergies, but excluding untreated, asymptomatic, seasonal allergies at the time of dosing). 2. Participants with history or presence of second-degree or third-degree atrioventricular (AV) block, sick sinus syndrome, or sinoatrial block. 3. Resting HR \<50 bpm at Screening or pre-randomization on Day 1. Measurement can be repeated up to 3 times to confirm the finding. Mean values will be used if repeated. 4. Recurrent symptomatic bradycardia or recurrent cardiogenic syncope 5. Any condition possibly affecting drug absorption (eg, gastrectomy, cholecystectomy). 6. Known immunodeficiency disorder, including positive serology for human immunodeficiency virus (HIV), or a first degree relative with a hereditary immunodeficiency, and history of organ transplant (except corneal transplant). 7. History or evidence of hepatitis B or hepatitis C viruses. Hepatitis B vaccination is allowed.89. 8. Participants with any of the acute or chronic infections or infection history