S1PR1 and multiple sclerosis: Phospho-fingolimod (FTY720-P), the active form of the orally administered pro-drug fingolimod23, is a S1PR1 agonist that acts as immunosuppressant by inducing a deep lymphopenia24 and retention in lymph nodes of myelin-autoreactive T cell clones that is beneficial for people with multiple sclerosis (MS).