CBFβ-SMMHC/FLT3-ITD blasts are malignant in nonirradiated secondary hosts. (A) A primary CBFβ-SMMHC/FLT3-ITD animal was killed at 3 months after transplantation, and 1 million bone marrow cells were transplanted into each of 6 secondary recipient mice that received different doses of irradiation. Representative FACS analysis of bone marrow cells from the primary donor animal and a moribund secondary recipient. Numbers on plots are percentages of total cells. (B) Kaplan-Meier survival curve for one representative experiment that was repeated using bone marrow from an independent, moribund primary CBFβ-SMMHC/FLT3-ITD animal. (C) Southern blot analysis using DNA isolated from splenocytes obtained from one of multiple secondary recipient mice transplanted at limiting dilution with bone marrow cells isolated from 5 independent, moribund primary CBFβ-SMMHC/FLT3-ITD mice. Lanes 1-5 represent one secondary recipient animal that was analyzed from each of 5 primary animals that were killed, with lane numbers representing the same DNA sample used for both blots. Blots were hybridized with radiolabeled sequences complementary to FLT3 or CBFβ sequences to detect unique proviral integrants. Arrows indicate the endogenous murine Flt3 and Cbfβ bands that were highly homologous to the radiolabeled probe derived from the human FLT3-ITD and CBFβ-SMMHC cDNA sequences. Wild-type C57BL/6 splenocytes served as control samples for each blot.