Unfractionated UCB engrafts to levels similar to those achieved with CD34⁺ cells. (A) Fifteen-week hCD45⁺ engraftment in BM, SPL, and PB from mice that received either UCB WBCs or UCB CD34⁺ cells from the same UCB unit. Flow cytometry was performed prior to engraftment to ensure that each mouse received either 10 000 or 50 000 total CD34⁺ cells for each approach. (B) Mice received various numbers of OKT3-pretreated UCB WBCs. The 12-week BM graft is plotted against original cell dose. (C) Limiting dilution analysis was performed to estimate the SRC frequency as measured by unfractionated UCB engraftment at 10 weeks in the BM. SRC frequency and 95% confidence intervals are shown on the plots. Plots and calculations were drawn and determined by extreme limiting dilution analysis.¹⁸