Requirement for Cdk6 in MLL-AF9–driven murine AML. (A) Schematic of in vivo and ex vivo experiments. (B) Effects of Cdk6 suppression in methylcellulose cultures of sorted GFP^pos/mCherry^pos leukemic cells from mice with secondary MLL-AF9–induced AML. (C) Effects of Cdk6 suppression on myeloid differentiation of leukemic cells from mice with secondary MLL-AF9–induced AML. Original magnification of cytospin preparations, ×1000. (D) Flow cytometric quantification of GFP and mCherry expression after 4 weeks in the blood of tertiary recipient mice transplanted with Cdk6 knockdown cells or control cells. Shown are representative plots from 2 mice (left) and the percentage of GFP^pos/mCherry^pos cells from all mice (right; shCdk6, n = 13; shControl, n = 8). (E) Survival of tertiary recipient mice transplanted with Cdk6 knockdown cells or control cells (shCdk6, n = 9; shControl, n = 11). (F) Microscopic analysis of hematopoietic tissues from mice with tertiary MLL-AF9-induced AML. Shown are hematoxylin and eosin–stained tissue sections and May-Grünwald-Giemsa–stained cytospin preparations and blood smears from representative mice transplanted with Cdk6 knockdown cells or control cells. Original magnification, ×100 (spleen histology), ×200 (tibia histology), ×1000 (cytospin, blood).