Cells from Plt6 mice are resistant to transformation by AML oncogenes in vitro. (A) Fetal liver cells from WT mice but not Plt6 mice serially form colonies in replating assays following transduction with AML oncogene–encoding retroviruses. Error bars represent SD of three biological replicates; *P < .05 (Mann-Whitney U test). (B) These exhibit a more differentiated morphology with increased numbers of monocytes.