Therapeutic potential of tyrosine kinase 2 in autoimmunity.

Tyrosine kinase 2 (Tyk2) is a Janus kinase family member that is crucial for signaling transduction in response to a wide variety of cytokines, including type I IFNs, IL-6, IL-10, IL-12 and IL-23. An appropriate expression of Tyk2-mediated signaling might be essential for maintaining normal immune responses. This review summarizes that Tyk2 is essential for the differentiation and function of a wide variety of immune cells, including natural killer cells, B cells, as well as T helper cells. In addition, Tyk2-mediated signaling promoted the production of autoimmune-associated components, which is implicated in the pathogenesis of autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis. Aberrant expression of Tyk2 was observed in many autoimmune conditions. Until recently, no patent filings had claimed selective inhibitors of Tyk2. Both CP-690,500 and CMP6 failed to be used in clinical treatment due to the difficulties of finding suitable selective leads or due to detrimental toxicities. Although the result of Cmpd1 is promising, it remains to be seen how specific the Tyk2 inhibitor is and how they are working. Currently, structure-based drug design (SBDD) technology has provided us with a quite useful window for SBDD of Tyk2 inhibitors.