Quantitative SRC analysis in sublethally irradiated NOD/SCID mice injected with CD34⁺ cells cultured with UTP or control medium. (A) The gate used to exclude platelets, dead cells, and debris. (B) The negative control. (C) A representative evaluation of the presence of human lymphoid (CD45⁺CD19⁺) and myeloid (CD45⁺CD19^-) cells in mice given transplants. (D) A representative evaluation of the presence of human endothelial (CD45^-CD31⁺) cells in mice receiving transplants. Panels E and F show the percentage of human CD45⁺ cells in the marrow of mice given injections with increasing numbers of purified CD34⁺ cells (ranging from 1000 to 20 000) cultured as described in “Materials and methods” with UTP (E) or control medium (F; n = 6/study group). Each symbol represents the data from an individual mouse evaluated 60 to 90 days after transplantation. A limiting dilution analysis using the single-hit Poisson model and the maximum likelihood estimator³⁸  was used to calculate SRC frequency in mice given transplants with CD34⁺ cells cultured with UTP or control medium. The Poisson statistic was further validated by χ² analysis.