Effect of IFNα treatment on hematological parameters and malignant JAK2^V617F-positive cell proliferation. KI recipient animals (●) were transplanted with 30% CD45.2 KI and 70% CD45.1+2 WT BM cells from 1 (exp. 1, left) or 3 (exp. 2, right) month-old donor mice and treated for 11 (exp. 1) or 13 (exp. 2) weeks with IFNα (continuous line) or vehicle (dashed line) starting 7 weeks after transplantation. Control WT recipient animals (□) represent untreated mice grafted with 30% CD45.2 WT and 70% CD45.1+2 WT cells. (A) Variations in WBC (10⁶/mL), hematocrit (%), platelet (10⁹/mL), and the percentage of KI-derived myeloid blood cells (Gr-1/CD11b/CD45.2) analyzed during 11 or 13 weeks of treatment of primary recipient animals. Data are mean values ± SEM of 10 or 5 IFNα-treated, 10 or 5 vehicle-treated (exp.1 or 2, respectively) and 5 nontreated (WT) mice. (B) Variations after 11 weeks of treatment (from exp. 1) in the percentages of cells from KI origin in BM, spleen, and blood. Are represented the early cell pools in BM (Lin-, MEP, CMP, GMP, LK, LSK, and SLAM cells determined as supplemental figure 4) (upper left) and CD11b/Gr1, B220, CD3 in BM (upper right), blood (lower left) and spleen (lower right). Data are mean values ± SEM, n = 3. (C) Secondary transplantation from exp. 2: variations in the hematological parameters and the percentages of KI-derived cells, analyzed by allele-specific PCR, of animals transplanted with BM from donors treated during 13 weeks with IFNα (continuous line) and vehicle (dashed line). Data are mean values ± SEM of 2 groups of 5 mice, each transplanted with BM from 2 different donors. Results from the secondary transplantation of exp. 1 are figured in supplemental Figure 11.