In vivo–isolated stress erythroid progenitors are similar to in vitro–expanded stress erythroid progenitors. (A) CD34⁺CD133⁺KS, CD34CD133⁺KS, and CD34⁻CD133⁻KS cells were sorted from the spleen on days 6, 8, and 12, respectively, by flow cytometry. mRNA expression of the indicated genes was determined by qRT-PCR and expressed relative to the housekeeping gene Gapdh (2^ΔΔCt). (B) CD34⁺CD133⁺KS cells were sorted from the spleen on days 6 and 8 and combined and cultured in SEEM + Epo for 3 (top) or 7 days (bottom). Representative flow cytometry analysis of resulting cells is shown.