FTY720 is an immunomodulator with demonstrated efficacy in a phase II trial of relapsing multiple sclerosis. FTY720-phosphate, the active metabolite generated upon phosphorylation in vivo, acts as a potent agonist on four of the five known sphingosine-1-phosphate (S1P₁) receptors. AUY954, an aminocarboxylate analog of FTY720, is a low nanomolar, monoselective agonist of the S1P₁ receptor. Due to its selectivity and pharmacokinetic profile, AUY954 is an excellent pharmacological probe of S1P₁-dependent phenomena. Oral administration of AUY954 induces a profound and reversible reduction of circulating lymphocytes and, in combination with RAD001 (Certican/Everolimus, an mTOR inhibitor), is capable of prolonging the survival of cardiac allografts in a stringent rat transplantation model. This demonstrates that a selective agonist of the S1P₁ receptor is sufficient to achieve efficacy in an animal model of transplantation.