Erythroblasts treated with SCF are able to expand after removal of chemotherapeutic drugs and have lower levels of drug-induced caspase activation. (A) Day-7 erythroblasts, untreated (control) or pretreated for 2 days with 100 ng/mL SCF (SCF days 5-9), were exposed to 3 μg/mL cisplatin (CDDP) for 48 hours, washed, and placed in fresh medium with or without SCF, which was maintained in the culture medium until day 9. (B) Day-7 erythroblasts, untreated (control), or pretreated for 2 days with SCF (SCF days 5-21) were exposed to cisplatin as in panel A. After 48 hours, 4 × 10⁴ cells were washed and replated in standard erythroid medium with or without 100 ng/mL SCF. In order to obtain equal numbers of erythroblasts after the cytotoxic treatment, a higher number of control cells were plated at the beginning of the experiment. The total number of cells obtained from the 4 × 10⁴ cells plated at day 9 is shown. (C) Western blot analysis of caspases in immature erythroblasts untreated (Con) or pretreated for 2 days with SCF and exposed for 8 hours to camptothecin (CPT), cisplatin (CDDP), and etoposide (VP-16), showing the proforms of caspase 3 (top panel), caspase 7 (middle), and caspase 8 (bottom). One representative experiment of 4 performed with cells from different donors is shown.