Productive life span of donor-marked KTLS cells and KTLS subsets isolated from BM of HU-treated mice. Recipient mice were lethally irradiated and reconstituted with 10⁵ recipient-type BM cells and (a) 10 KTLS cells, (b) 10 G0/G1 Rh123^lo KTLS cells, or (c) 10 S/G2/M Rh123^mid KTLS cells isolated from HU-treated mice (100 mg/kg/d for 3 days). One group of mice received (d) 10 G0/G1 Rh123^lo KTLS cells from untreated mice as a control. The number of mice reconstituted with given populations is indicated. The percent of donor-derived myeloid cells in peripheral blood was assessed monthly for 6 months. Each line represents consecutive samples of peripheral blood taken from a single mouse. *Low but significant levels of donor-derived myeloid cells were detected in this chimera at week 16.