HUBEC noncontact cultures and HUBECs + TSF support the differential maintenance of CD34⁺CD38^– cells. BM CD34⁺CD38^– cells were placed in 7-day cultures to determine phenotype changes over time (N = 3 each). (A) Following 7-day noncontact culture with HUBECs + GM36SF, a high percentage of CD34⁺CD38^– cells persisted over time. (B) Following 7-day culture with GM36SF alone, significant losses of CD34⁺CD38^– cells were observed. (C) Following 7-day culture with HUBECs + TSF, the majority of cells remained CD34⁺CD38^– after culture. (D) Conversely, at day 7 of culture with TSF alone, the majority of the input CD34⁺CD38^– population was lost. Numbers indicate the percentage of cells in each quadrant.