Bortezomib impairs myeloproliferative syndrome in TPO^high mice. Blood and spleen parameters are shown and include (A) leukocyte number, (B) platelet number, (C) hematocrit level, (D) blood-circulating CFCs, (E) spleen CFCs, and (F) spleen weight. Bortezomib decreases leukocyte, platelet, and blood-circulating CFC numbers as well as spleen weight in a dose-dependent manner, with the respective P_(DE) values ≤ .001, .002, .022, and ≤ .001. Results of leukocyte number, platelet number, and hematocrit level are presented as the mean ± SEM of 12 animals per experimental group (except for the “1 mg/kg” group that included only 6 surviving mice at week 8). Results of blood-circulating CFCs, spleen CFCs, and spleen weight are presented as the mean ± SEM of 3 animals per experimental group (similar results were obtained in 3 other animals per experimental group at week 16 after engraftment, except for the “1 mg/kg” group). Results of statistical analysis with the Wilcoxon test are as follows: treated (bortezomib 0.25 mg/kg, 0.5 mg/kg, and 1 mg/kg) versus untreated (vehicle) mice; *P < .05; **P < .001. Bzb indicates bortezomib.