In addition to its importance in various cancers, the JAK-STAT signaling pathway plays an important part in the human immune response and in particular with regards to adaptive immunity. 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.