Effect of MS5 cells on the LTC-IC potential of CD34⁺CD38^low/neg exposed 4 days to cytokines with or without MS5 cells.

CFSE-labeled CD34⁺CD38^low/neg were cultured with 6 growth factors (see “Materials and methods”) in the presence (closed circles) or absence (open circles) of stromal cells. On day 4, cells that had completed fewer than 2 divisions or 2, 3, or 4 divisions were sorted. One thousand cells from each were then assayed for LTC-IC activity. Each point represents the number of CFCs produced by 1000 cells derived from primary cultures containing MS5 cells (closed symbols) or not (open symbols). Each point is from a different experiment. The horizontal bar represents the geometric mean of the number of CFCs. Differences in the number of CFCs between cultures with and without MS5 cells were significant (*P < .01) for experiments performed with 3- and 4-division cells, but not for those with 2-division cells (NS). (Inset) Each point corresponds to the mean of the increments, calculated in each experiment, in the number of week 5 CFCs obtained from cells originally cultured for 4 days with or without MS5 cells.