Ruxolitinib targets JAK1/JAK2 (with moderate inhibition of TYK2) [393] and is approved for true erythrocytosis and intermediate- to high-risk primary myelofibrosis [394, 395] and showed potential to improve ACR response and HAQ-DI in a phase IIa trial in RA [396]; baricitinib, a selective JAK1/JAK2 inhibitor, is effective in ulcerative colitis (UC) by blocking prokinetic factors such as IL-6, IL-12, IL-23 and IFN-γ. Here, JAK1 is linked to myelofibrosis.