Proliferation and survival of HCD57 and HCD57-SREI cells. (A) The cells were cultured in the indicated factor, 1 U EPO/mL, 100 ng SCF/mL, a combination of 100 ng SCF and 1 U EPO/mL, or no added factors in medium containing 25% fetal calf serum. At the indicated day after culture, viable cells were counted in the presence of trypan blue. Error bars indicate the standard deviation from triplicate measurements. (B) HCD57-SREI cells have escaped apoptosis in the absence of EPO. HCD57 cells and HCD57-SREI cells were cultured in the presence of 1 U EPO/mL (+) absence of EPO (−) for 72 hours. The genomic DNA was isolated and analyzed for fragmentation of DNA characteristic of apoptosis as described previously.5