Production of primitive HPCs.

Production of primitive hematopoietic cells from cobblestone-forming cells beneath the primary stromal cell layer (■) or hTERT-stromal cell layer (▪) over 7 weeks. Expanded hematopoietic cells were harvested each week and analyzed. The x-axis indicates the period of cell expansion, and the y-axis indicates the number of cells. (A) Total number of cells. (B) Number of CD34⁺ cells. The number of CD34⁺ cells was calculated from the percentage of CD34⁺ cells, which was determined by flow cytometric analysis. (C) Total number of clonogenic cells (CFU-Cs). (D) Number of CFU-Mix cells. *P < .05 versus primary stromal cells (Student t test).