JAK2 and graft versus host disease: JAK2 mediates intracellular signaling of multiple pro-inflammatory cytokines implicated in GVHD pathogenesis, including interferon-γ (IFN-γ), interleukin-6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF), and interleukin-12 (IL-12) [2,3].