In vitro growth and differentiation of erythroid progenitors from CD34⁺ peripheral blood stem cells. (A) Erythroid progenitors from CD34⁺ peripheral blood stem cells (starting cell population, day 0) were grown in liquid culture in the presence of SCF, Epo, IGF-1, dexamethasone, and estrogen. At days 4, 9, and 14 of culture, cells were subjected to cytocentrifugation and staining with neutral benzidine plus histological dyes. (B) Cultures of erythroid progenitors from CD34⁺ peripheral blood stem cells shown in (A) were analyzed for proportion of proerythroblasts (proerbl), polychromatic and orthochromatic erythroblasts (pchrom and ochrom erbl, respectively), erythrocytes (ery), granulocytes (gran), macrophages (mac), and lymphocytes (lymph). The starting cell population (day 0) consisted mainly of small progenitor cells (striped box) and some granulocytes and macrophages as indicated. At day 0, only nucleated cells are evaluated. (C) Erythroid progenitor cells were induced to differentiate in the presence of Epo and insulin (see Materials and Methods). After 2, 3, 4, and 5 days of differentiation, cells were subjected to cytocentrifugation and staining with neutral benzidine and histological dyes and evaluated for the proportion of proerythroblasts, polychromatic and orthochromatic erythroblasts, and erythrocytes as in (B).