Development, expansion, and characterization of erythroblasts derived from differentiated ES cells. (A) Flow cytometry analysis of CD34, Sca-1, and Ter119 expression during embryoid body differentiation. The gold section marks EB from which erythroid outgrowth could be observed. (B) To determine which stage of EB differentiation sustains expansion of erythroid progenitors, cells from EBs differentiated for 0 to 9 days were dissociated, cultivated under erythroid conditions, and cumulative cell numbers were determined for 20 days. (C) Morphology of ES-EPs and FL-EPs cultivated for 12 days. Cytospin preparations were stained with benzidine and hematologic dyes. Original magnification, × 63.