Lymphocyte trafficking out of secondary lymphoid organs is regulated by concentration gradient-dependent interactions between the membrane-derived lysophospholipid signaling molecule sphingosine 1-phosphate (S1P) and the G-protein-coupled receptor, S1P<sub>1</sub> Etrasimod is a novel, next-generation, small-molecule, oral S1P receptor modulator in clinical development for the treatment of immune-mediated inflammatory disorders, including ulcerative colitis.