Effect of FN on the clonogenic capacity of human hematopoietic progenitor cells. (A) The human CD34⁺ cells were incubated with 100 μg/mL of BSA (○, □) or FN (•, ▪) in IMDM (□, ▪) or in IMDM containing 200 μg/mL transferrin and 10 μg/mL insulin (○, •) at 37°C for the indicated periods. The preincubated cells (5.0 × 10²) were subsequently cultured in methylcellulose media to assess their clonogenic growth. All of the results are shown as mean ± SD of triplicate cultures. (B) Human CD34⁺ cells were incubated with 100 μg/mL of BSA, human serum albumin, collagen type I, laminin, or FN in serum-free IMDM with no other proteins at 37°C for 1 hour and subsequently were cultured in methylcellulose media at 5.0 × 10²/mL to assess their clonogenic growth. The data represent mean ± SD of triplicate cultures. Statistically significant difference from a control (before incubation) value is indicated by two (P < .01) asterisks. Similar results were obtained in three independent experiments. (▨), BFU-E; (▪), CFU-GM.