Liquid culture in the presence of SCF, FL, IL-3, and MGDF of PBPCs enriched by immunoaffinity removal of lineage-positive cells and further exposed to mafosfamide and taxol or cultured for 7 days in the presence of 5-FU, SCF, and IL-3 (n = 5). At the indicated time interval the total number of CD34⁺ cells (open square) and the total number of nucleated cells (solid square) was calculated from the cell counts and the percentage of viable cells measured by 7AAD staining and flow cytometry. (A and C) Cells cultured in the presence of cytokines but without stroma supernatant did not proliferate. Conversely, a 1.5- 2-fold expansion of the total number of CD34⁺ cells was observed when drug-exposed PBPCs were cultured in the presence of the same cytokine combination supplemented by 30% supernatant from the human L87/4 stromal line (B and D).