Proliferation of CD34⁺ CD38⁻cells in allogeneic stromal and PMVEC coculture. Immunomagnetically selected CD34⁺ baboon marrow cells were labeled with the lipophilic dye PKH-26, which stably integrates into the cell membrane and is distributed equally to daughter cells at division, and placed onto preestablished allogeneic baboon marrow stromal cell (light bars) or PMVEC monolayers (dark bars) in the presence of exogenous human SCF, IL-3, IL-6, and GM-CSF. After 7 and 10 days of culture, CD34 and CD38 expression of the expanded cells was determined using the MoAbs K6.1 and OKT-10, respectively. Proliferative status of the cells was determined by PKH fluorescence as described. The total numbers of CD34⁺ cells (A), CD34⁺ cells, which have undergone division in vitro (B), CD34⁺CD38⁻ cells (C), and CD34⁺CD38⁻ cells, which have undergone division (D) in the cultures are shown. The data represent the mean ± standard deviation (SD) of experiments performed on three separate animals. ND, not detectable above 0.005% of events. *P < .05 (Student’st-test); †P < .02; and ‡P < .001.