Calculation of the frequency of lineage-specific malignancy-initiating cells. Limiting dilution analysis of the frequency of T-cell malignancy-initiating cells (A) and JMML-initiating cells (B). Lethally irradiated CD45.1 recipient mice received transplants of various numbers of total bone marrow cells expressing oncogenic Kras together with competitor cells in a 1:1 ratio. At each data point, at least 10 recipient mice were used. Plotted is the percentage of recipient mice free of T-cell malignancy (A) or JMML (B) 6 to 8 months after transplantation. The frequency of malignancy-initiating cells was calculated as described in “Methods.”