Potent cell permeable JAK3 inhibitor (IC50 = 1nM). Shows also JAK-1 inhibitory activity. Immunosuppressive and anti-inflammatory agent. Inhibits signaling through heterodimeric receptors associated with JAK3, JAK1, or both of them, with functional selectivity over JAK2-paired receptors. Blocks downstream STAT signaling, resulting in potent inhibition of several cytokines, including interleukins 2, 4, 7, 9, 15 and 21, which are integral to lymphocyte activation, function and proliferation. Investigated for several autoimmune disorders including, rheumatoid arthritis and psoriasis. Potent and selective inhibitor of HIV-1 replication and virus reactivation in vitro.