RP-001 is a picomolar short-acting S1P1 (EDG1) selective agonist, with an EC₅₀ of 9 pM. RP-00 induces internalization and polyubiquitination of S1P1. RP-001 has little activity on S1P2-S1P4 and only moderate affinity for S1P5^[1]. In Vitro: RP-001 elicits dose-dependent lymphopenia of CD4⁺ T cells. RP-001 induces acute lymphopenia with rapid recovery to untreated levels^[1]. In Vivo: RP-001 causes dose-dependent rapid lymphopenia with an EC₅₀ of 0.03 mg/kg^[1].