While both BARI and RUX show well-balanced inhibitory activity against JAK1/JAK2 to effectively block IFNGR and IL-6R signaling, we found that BARI is superior to RUX in preventing GvHD by increasing regulatory T cells (Tregs) through sparing JAK3 signaling in our preclinical mouse models of allo-HCT [13,15]. Here, JAK1 is linked to graft versus host disease.