JAK1 and acquired polycythemia vera: The JAK inhibitors that are currently approved by the Food and Drug Administration(FDA) and the European Medicines Agency (EMA) are Ruxolitinib (Jakavi®), which aims to inhibit JAK1 and JAK2 in patients with myelofibrosis and polycythemia vera; Tofacitinib (Xeljanz, Jakvinus, CP-690550), which inhibits JAK1 and JAK3 in rheumatoid and psoriatic arthritis; and finally, Baricitinib, targeting JAK1 and JAK2, for the treatment of rheumatoid arthritis [39].