FTY720 is a derivative of ISP-1 (myriocin), a fungal metabolite of the Chinese herbIscaria sinclari as well as a structural analog of sphingosine. It is a novel immune modulator that prolongs allograft transplant survival in numerous models by inhibiting lymphocyte emigration from lymphoid organs. FTY720 is phosphorylated by sphingosine kinase, which then acts as a potent agonist at four of the sphingosine-1-phosphate (S1p) receptors. Down-regulation of S1P receptors on T and B lymphocytes by FTY720 results in defective egress of these cells from spleen, lymph nodes, and Peyer's patch. FTY720 also enhances the activity of the sphingosine transporter Abcb1 and the leukotriene C transporter Abcc1 and inhibits cystolic phospholipase A activity.