Among various tyrosine kinases, a family of Janus kinases (JAK) has been elucidated as key players in signal transduction from vital cytokine receptors, such as interleukins and interferons. Indeed, recent rapid progress in JAK inhibitors in addition to biological agents provided therapeutic options for various diseases, including immune-mediated inflammatory diseases and hematological disorders. Efforts have culminated in the approval of nine JAK inhibitors in Japan in the recent decade. The safety profiles of JAK inhibitors seem to largely depend on patient populations and drug dosing, rather than on JAK selectivity. Thus, the comparison of various disease indications is pivotal for the understanding and proper use of JAK inhibitors.
Keywords: Cytokine; Janus kinase; Tyk2; selectivity.