Choi et al. (93) showed that baricitinib (JAK1/JAK2 inhibitor) completely prevented GVHD in murine models without hampering GVL by multiple mechanisms including expansion of Tregs by preserving JAK3-STAT5 signaling; downregulation of CXCR3 and helper T cells 1 and 2. Here, JAK3 is linked to graft versus host disease.