Inhibition of JAK-STAT signaling with INCB16562 treatment of primary cells from hMPLW515L mice. (A) Western blotting of JAK-STAT signaling intermediates in hMPLW515L splenocytes after 12 days of INCB16562 treatment reveals abrogation of phosphorylation of STAT3, STAT5, and MAPK with INCB16562 treatment compared with vehicle. (B) Phosphoprotein-specific flow cytometry of CD11b⁺ and CD61⁺ myeloid cells in hMPLW1515L bone marrow cells treated ex vivo with INCB16562 at 1μM or with vehicle for 2 hours. Treatment with INCB16562 greatly decreased phosphorylation of STAT3 and STAT5 in response to 10-minute ex vivo stimulation with rhGCSF (375 ng/mL) and rhTPO (1250 ng/mL). (C) Immunohistochemical staining (×40) of pSTAT3Y705 in mouse spleen after 12 days of treatment with vehicle or INCB16552 at 60 mg/kg or 120 mg/kg reveals a decrease in pSTAT3 in treated versus control mice tissue.