Kinetics of CB CD34⁺ cells during SFSD culture. Representative flow cytometric profiles of CFSE-labeled CB CD34⁺ cells. CB CD34⁺ cells were stained with CFSE and cultured in the SFSD system. The fluorescence intensity was analyzed at 2 days (gray histogram), 4 days (top, black histogram), and 5 days (bottom, black histogram) after culture. The number above each peak represents the number of divisions according to the fluorescence intensity. The relative frequencies of undivided cells were 51.24% ± 3.12% % at day 2, 0.09% ± 0.04% at day 4, and 0.04% ± 0.03% at day 5 (n = 3). The fluorescence intensity of the cells incubated with colcemid confirms the position of the cells that have not divided (dotted line).