Stem cell factor amplifies newborn and sickle erythropoiesis in liquid cultures

A two-phase liquid-culture system was used to substantially amplify and differentiate erythroblasts, starting with mononuclear cells from the blood of normal adults, newborn infants, and patients with sickle cell anemia. After the first 7 days (phase 1), in medium plus fetal bovine serum (FBS) alone, or in combination with stem cell factor (SCF) or conditioned medium (CM), the cell number was unchanged, and the cells all looked like lymphocytes. These cells were then diluted into medium with erythropoietin (Ep) alone, with Ep and either SCF or CM, or in methylcellulose with the same factors (phase 2). After 14 days in liquid phase 2 with SCF and Ep, the cell numbers increased an average of 30-fold in the sickle, 24-fold in the newborn, and 4-fold in the normal adult cultures; almost all the cells were erythroblasts and erythrocytes. SCF in phase 1 increased the number of late progenitors (CFU-E) assayed in methylcellulose, with the largest number in sickle, followed by newborn cultures and then adult cultures. We conclude that erythroid progenitor cells survive for at least 7 days without Ep (but with FBS). Progenitor cells are amplified, particularly with SCF. Later in culture, SCF with Ep increases the final number of differentiated erythroid cells. Both the early and the late effects of SCF are most effective in sickle, followed by newborn cultures and then adult cultures.