SCF does not promote the growth of nonerythroid cells in erythroid unilineage culture. (A) Clonogenetic assay of CD34⁺ cells (day 0) or cells grown in liquid culture and subsequently plated in semisolid medium at day 5 or day 7 of erythroid differentiation. Control cells (day 5 and day 7 Epo) were cultivated in standard erythroid medium before the colony assay, whereas SCF-treated cells (day 7 Epo + SCF) received 100 ng/mL SCF from day 5 to day 7 of liquid culture. The results are expressed as number of granulomonocytic (▦) or erythroid (▪) colonies per 100 plated cells. Mixed colonies were rare in day 0 cultures and not present thereafter. (B) Cytofluorimetric analysis of glycophorin A-positive cells in erythroid unilineage culture. Cells were analyzed after 5 (day 5) or 7 days (day 7) of erythroid differentiation in standard erythroid medium (Epo) or in the same medium supplemented with 100 ng/mL SCF starting from day 5 (Epo + SCF). At day 7, cells were treated with cisplatin (CDDP days 7-9), and SCF-treated cells that survived the treatment were analyzed at day 20 of culture in standard erythroid medium supplemented with SCF. (C) May-Grünwald-Giemsa staining of day-7 erythroid cells treated with cisplatin for 48 hours in standard erythroid medium alone (-SCF) or with 100 ng/mL SCF (+ SCF), which was supplied 2 days before and during the cytotoxic treatment. Original magnification, × 400.