This proposed functional antagonism of fingolimod at S1P1 is in line with the observation that mutant mice that express an internalization-defective S1P1 have delayed lymphopenia kinetics in response to fingolimod (Thangada et al., 2010) and that a lymphocytic knock-down of S1P1 also inhibits their egress from thymus (Allende et al., 2004). This evidence concerns the gene S1PR1 and lymphopenia.