Conditional deletion of Cdc42 blocks AML initiation. (A) Cre⁺;Cdc42FL-MA9 cells treated with TAM to delete Cdc42 had reduced CFU cell (CFU-C) in primary plating in methylcellulose compared with heterozygous Cdc42 FL/WT and Cre null (–) controls (CON). Data are representative of 3 to 5 experiments using 2 distinct cell lines per genotype. (B) Colony size, as determined by cell count per colony, was also decreased. (C) CFU-C numbers were still reduced on replating in secondary methylcellulose cultures. (D) TAM-induced deletion of Cdc42 from Cre⁺;Cdc42FL-MA9 cells suppressed leukemia initiation vs Cre null (–) and corn oil (CO) injected controls (P < .001).