Comparison of the LTC-IC activity of cells that have completed 4 divisions in 4, 5, 6, or 7 days.

Results are from 1 experiment. CD34⁺CD38^low/negcells were cultured with cytokines in the presence (closed circles) or absence (open circles) of MS5 cells. On day 4, 4-division cells were sorted, and their LTC-IC activity was assessed (50 cells/well). Cells that undertook 0 to 3 divisions during the same time were also sorted and kept in culture 1 more day. The next day (day 5), 4-division cells were sorted and assessed in LTC and 0- to 3-division cells were recultured for 1 more day. This procedure was repeated on days 6 and 7. Each point represents the number of CFCs produced after 5 weeks by 50 cells that had accomplished 4 divisions by the day indicated. Horizontal bars indicate the geometric mean of the number of CFCs produced. There were no statistically significant differences in the mean number of CFCs generated by 4-division cells grown on MS5 (closed symbols) on day 4, 5, or 6, or by 4-division cells grown without MS5 (open symbols) on day 4, 5, or 6 (P > .5). However, each day, the mean number of CFCs generated in the presence of MS5 cells was significantly higher than that produced by cells grown without MS5 cells (P < .01).