FIG. 2.

Limiting dilution cell transplantation analysis. Tumor cells were introduced into recipient animals at various doses. In this hypothetical example, the tumor is comprised of two subpopulations of cells (R+ vs. R−). The number of animals that engraft disease from unfractionated tumor cells (total) compared with fractionated cells (R+ or R−) are shown (top, A). Data are converted into percentage of animals that fail to engraft disease (bottom, A) and plotted graphically (B). Specifically, percent negative is plotted as a log scale and cell number is on the X-axis. Linear regression was completed and an equation was fit to the data; R² values denote the accuracy of the data. A line at 37% negative denotes the number of cells in which one self-renewing cell resides. For the total cell population, this line crosses at 1.1 × 10⁴, indicating that 1 in 1.1 × 10⁴ cells is capable of self-renewal. Tumor-initiating cell number (TIC #) for this illustrative example is also shown (extreme bottom, A).