Analysis of the erythroblastosis in mice expressing Mpl from the PGK promoter. (A) Kaplan-Meier survival curves of mice transplanted with lin⁻Mpl^−/− BM cells transduced with SIN lentiviral vectors expressing Mpl from indicated promoters, or GFP from the PGK promoter. Untransduced C57Bl/6 lin⁻ BM was transplanted as positive control (wt). Ticks indicate mice removed from the experiment either because of final analysis at 25 or 31 weeks or because of death of unrelated cause (n = 2). (B) Spleen weight of Mpl^−/− mice transplanted with lin⁻Mpl^−/− BM expressing Mpl from the PGK promoter (n = 4) when killed or found dead after 5 days. Spleen weight of untransplanted reference C57Bl/6 mice for comparison (n = 7). P < .0001 (Student t test, 2-tailed, unpaired). (C) Flow cytometric analysis of spleen cells from Mpl^−/− mice transplanted with lin⁻Mpl^−/− BM expressing Mpl from the PGK promoter. Cells were identified as early or late erythroid progenitors based on expression of CD71 alone or together with Ter119, respectively. Only minor amounts of granulocytic/monocytic cells (CD11b/Gr1) or lymphoid cells (CD3/CD19) were detectable. Spleen cells expressed high levels of Mpl as detected with anti-HA antibody. Percentages for each quadrant or gate are given in the lower right of each flow cytometry plot. (D) Spleen histopathology from Mpl^−/− mice transplanted with lin⁻Mpl^−/− BM expressing Mpl from the PGK promoter. (i) Black arrows indicate bleedings resulting from splenic rupture; and white arrow, necrotic area (hematoxylin and eosin staining, original magnification ×200). (ii) Close-up of a necrotic area with erythroid blasts (hematoxylin and eosin staining, original magnification ×400).