Vorinostat treatment normalizes peripheral blood counts and improves extramedullary hematopoiesis in Jak2V617F knock-in mice. Treatment with vorinostat at 200 mg/kg for 2 weeks resulted in significant improvement in RBC (A), Hb (B), HCT (C), and WBC (D) counts in Jak2V617F knock-in mice (n = 10) compared with placebo (vehicle)–treated mice (n = 10). (E) Platelet counts in the peripheral blood of placebo- and vorinostat-treated animals (n = 10). (F) Spleen weight was significantly reduced in Jak2V617F knock-in mice after 2 weeks of vorinostat treatment (n = 7).