 Clinical proof of concept for the use of JAK inhibitors for treatment of autoimmune and inflammatory disease has been demonstrated by Pfizer's tofacitinib, a JAK inhibitor recently approved in the US for the treatment of rheumatoid arthritis.Additionally, tofacitinib is currently being studied for the treatment of ankylosing spondylitis, psoriatic arthritis, psoriasis, atopic dermatitis, and inflammatory bowel disease.Furthermore, STAT1 and STAT2 are essential factors in the cellular antiviral and adaptive immune defenses.