JAK1 and graft versus host disease: For GVHD after failure of at least one line of systemic therapy, 3 therapies have been approved by the US Food and Drug Administration (FDA) since 2017: ibrutinib and belumosudil are approved for treatment of cGVHD only, and the selective Janus kinase 1/2 (JAK1/JAK2) inhibitor ruxolitinib is approved for treatment of both aGVHD and cGVHD [15].