JAK3 and rheumatoid arthritis: One JAK3 inhibitor, tofacitinib, (Xeljanz®, Pfizer), has received approval from the Food and Drug Administration (FDA) for the treatment of rheumatoid arthritis, psoriatic arthritis, and ulcerative colitis, and other JAK inhibitors are being investigated in a variety of immune-mediated inflammatory diseases in people [8, 9].