Growth factor independence combines with Hhex overexpression to elicit lethal promyelocytic leukemia in vivo. (A) Survival of irradiated congenic (Ly5.1) recipient mice transplanted with factor-dependent or factor-independent (V449E-expressing) MH8 and MH9 cell lines. (B) Peripheral blood (PB) profiles of leukemic mice injected with factor-independent lines (+V449E) vs control mice injected with factor-dependent lines (control) at time of sacrifice. (C) Spleen weight, splenocyte counts, and percentage of GFP⁺ splenocytes and BM cells in leukemic and control mice as in panel B. (D) Histological sections stained with hematoxylin and eosin showing myeloid infiltration in spleen, liver, and lung of mice transplanted with factor-independent cell lines (MH8-V449E, MH9-V449E) but not factor-dependent control (MH8). Images are at ×4 (spleen) and ×10 magnification (liver, lung). Insets are images of the same tissues at ×100 magnification.