Deletion of Stat5 inhibits the development of MPN in Jak2V617F knockin mice. (A) Immunoblot analysis for total Stat5 protein show efficient deletion of Stat5 in the BM of MxCre;Jak2V617F/+;Stat5fl/fl mice after induction with pI:pC. Peripheral blood HCT (B), Hb (C), RBC (D), MCV (E), WBC (F), NE (G), and PLT (H) counts were assessed at 4, 8, and 12 weeks after pI:pC induction in control, MxCre;Jak2V617F/+, and MxCre;Jak2V617F/+;Stat5fl/fl mice (n = 15 for control; n = 17 for MxCre;Jak2V617F/+; n = 28 for MxCre;Jak2V617F/+;Stat5fl/fl mice at all time points). All the peripheral blood parameters in MxCre;Jak2V617F/+;Stat5fl/fl mice were within normal range and comparable with those in controls. Spleen weight/size (I) was significantly reduced in MxCre;Jak2V617F/+;Stat5fl/fl mice compared with MxCre; Jak2V617F/+ mice, and was identical to those of controls (12 weeks after induction with pI:pC; n = 15). Asterisks indicate significant differences by 1-way ANOVA (*P < .05; **P < .005). Data are shown as mean ± SEM