S1PR1 and relapsing-remitting multiple sclerosis: The synthetic compound FTY720 is a structural analogue of the natural molecule sphingosine that modulates the Sphingosine 1-phosphate receptor (S1PR) in immune and brain cells [17,18,19,35,36,37,38], and is FDA approved as an oral therapeutic for relapsing-remitting MS (RRMS).