Ruxolitinib (Jakafi®) is an oral, potent, highly bioavailable JAK1/2 inhibitor that is approved by the Food and Drug Administration (FDA) for use in patients with myeloproliferative neoplasms and steroid refractory graft-vs.-host-disease (GVHD), where it has shown to induce responses, even in those with the most advanced disease (32–34). This evidence concerns the gene JAK1 and graft versus host disease.