Effect of MS-5 cells on the proportion of CD34⁺CD38^low or CD38^neg clones that contain LTC-IC at day 10. Single CD34⁺CD38^low (A) cells and CD34⁺ CD38^neg (B,C) cells were seeded in the presence (▪) or absence () of MS-5 either in 10% serum (A,B) or in serum-free condition (C) with low and high GF. At day 10, each proliferating well (containing >1 cell) was transferred in standard LTC-IC conditions in wells precoated with MS-5. After 5 weeks, each well was assessed for its content in CFC and a well was scored as LTC-IC positive if it contained at least one CFC. Each histogram represents the proportion of LTC-IC–positive wells at day 10 among proliferating clones. In brackets is indicated the number of experiments. * paired t-test was statistically significant. Paired t-test calculated for pooled A + B data was also significant.