Malignant cells from MSCV-Myc and MSCV-Myc+Bcl-2 mice are readily transplantable into secondary recipients. Kaplan-Meier survival analysis of secondary recipients of (A) MSCV-Myc and (B) MSCV-Myc+Bcl2 cells. Viable mononuclear cells isolated from the spleens of moribund primary animals were counted, serially diluted, and injected into sublethally irradiated syngeneic mice. Number of mononuclear cells injected per mouse is shown. Comparison of panels A and B shows a higher frequency of leukemia-initiating cells in MSCV-Myc+Bcl2 mice.