Cytokine-induced cell cycling up-regulates cell surface Fas expression on NOD-SCID repopulating cells. CD34⁺CB cells were cultured in SF medium supplemented with SFT3 for 5 days and sorted into Lin^-Fas^- and Lin^-Fas⁺ cells as shown in Figure 5. Irradiated NOD-SCID mice received transplants of 450 000 Lin^-Fas^- (A) or 450 000 Lin^-Fas⁺ cells (B), representing the EE of 30 000 freshly isolated CD34⁺ cells. At 6 weeks following transplantation, NOD-SCID BM was analyzed for human multilineage reconstitution (“Materials and methods”). Results are from representative mice that received transplants of Lin^-Fas^- and Lin^-Fas⁺ cells.