Ruxolitinib is an orally bioavailable JAK1/2 inhibitor that functions by inhibiting STAT3 phosphorylation and is approved by the U.S. Food and Drug Administration (FDA) for treating steroid refractory graft-versus-host-disease [128,129], myelofibrosis [130], and polycythemia vera [130]. The gene discussed is JAK1; the disease is graft versus host disease.