Effect of MS-5 cells on the number of week-5 CFC as a function of the size of the clone at day 10. Single CD34⁺CD38^neg cells were cultured in serum-free conditions, in low GF (A) or high GF (B) either in the presence (•) or the absence (○) of MS-5 cells. After 10 days, each clone was replated in standard LTC-IC assays and the number of LTC-IC–derived CFC assessed at week 5. Each point represents the number of CFC produced by an individual clone.