Background: Jak3 is a member of the Janus family tyrosine kinases (Jaks), whose function is to transduce extracellular signals from cytokines and interferons. Jaks associate with cytokine receptors, upon ligand binding, Jaks phosphorylate the receptor. The phosphorylated receptors are bound by SH2-containing proteins, one class of which is the signal transducers and activators of transcription (STATs). Activated STATs translocate to the nucleus to mediate gene transcription (1, 2). Jak3 is activated after binding to the gamma chain of Interleukin receptors, specifically IL-2, IL-4, IL-7, IL-9, and IL-15 receptors. Jak3 has been implicated in mast cell-mediated immediate hypersensitivity reactions, autoimmune disorders, and acute lymphoblastic leukemia. Jak3 inhibitor has shown clinical potential as a new class of immunomodulatory agents with anti-leukemic and immunosuppressive properties (3).