Growth and Differentiation of Human Stem Cell Factor/Erythropoietin-Dependent Erythroid Progenitor Cells In Vitro

Stem cell factor (SCF) and erythropoietin (Epo) effectively supporterythroid cell development in vivo and in vitro. We have studied herean SCF/Epo-dependent erythroid progenitor cell from cord blood that canbe efficiently amplified in liquid culture to large cell numbers in thepresence of SCF, Epo, insulin-like growth factor-1(IGF-1), dexamethasone, and estrogen. Additionally, bychanging the culture conditions and by administration of Epo plusinsulin, such progenitor cells effectively undergo terminal differentiation in culture and thereby faithfully recapitulate erythroid cell differentiation in vitro. This SCF/Epo-dependent erythroid progenitor is also present in CD34⁺ peripheralblood stem cells and human bone marrow and can be isolated, amplified,and differentiated in vitro under the same conditions. Thus, highlyhomogenous populations of SCF/Epo-dependent erythroid progenitors canbe obtained in large cell numbers that are most suitable for furtherbiochemical and molecular studies. We demonstrate that such cellsexpress the recently identified adapter protein p62^dok thatis involved in signaling downstream of the c-kit/SCF receptor. Additionally, cells express the cyclin-dependent kinase (CDK) inhibitors p21^cip1 and p27^kip1 that are highlyinduced when cells differentiate. Thus, the in vitro system describedallows the study of molecules and signaling pathways involved inproliferation or differentiation of human erythroid cells.