Cell tracking in vitro of cultured bone marrow G₀CD34⁺ cells using the membrane dye PKH2. G₀CD34⁺ cells were isolated, stained with PKH2, and cultured in IMDM containing 10% FCS in the presence of SCF, IL-3, and IL-6 for 7 days. A sample fixed in 1% paraformaldehyde on day 0 (A) was used to identify the fluorescence intensity corresponding to freshly stained cells. On day 7, cells were harvested and stained with either a PE-conjugated isotype control monoclonal antibody (B) or PE-conjugated CD34 (C). Samples were analyzed for PKH2 (X axis) and PE (Y axis) fluorescence to estimate the fraction of CD34⁺ cells remaining as CNR cells. As can be seen in C, 83% of cultured cells remained CD34⁺, and 16% could be identified as CNR cells.