Pevonedistat and ruxolitinib combination treatment is efficacious in the Jak2 V617F mouse model of polycythemia vera. (A-D) Cellular measurements of Jak2 transplanted mice (n = 5 for each group) after 4-week treatment with pevonedistat (60 mg/kg), ruxolitinib (90 mg/kg), or combination. White blood cells (A); hematocrit (B); platelets (C); and BM CD45.2⁺ cells (D). *P < .05; **P < .01; ***P < .001 by 1-way analysis of variance (ANOVA) with Dunnett’s multiple comparisons test. (E) Normalized spleen weights of mice at endpoint. (F) Representative H&E staining of tibia sections from treated mice at endpoint. Scale bar: 1 mm (top), 0.25 mm (middle), and 80 µm (bottom).