JAK1 and graft versus host disease: In 2019, the Food and Drug Administration has approved ruxolitinib, a JAK1/2 inhibitor, for treatment of Graft-versus-Host disease (GvHD) because ruxolitinib has shown in vitro and in vivo efficacy in modulating immune responses, especially those exerted by Natural Killer cells, DCs, Th1 and Th17 cells, and regulatory T lymphocytes, and in regulating release of several cytokines including TNFα.