JAK1 and graft versus host disease: In other studies (126), baricitinib, a best-in-class Jak1/2 inhibitor, blunted IFNγR and IL6R signaling, resulting in complete protection from GVHD lethality as well as the reversal of active GVHD prevents GVHD with 100% survival, and reverses ongoing GVHD with dramatically increased Tregs along with decreased Th1 and Th2 differentiation, MHC class II and B7 ligand expression on APCs (126).