CC-4047 inhibits development of erythroid progenitor cells. (A) Schematic representation of the cell culture systems used in the study. CD34⁺ cells cultured with SCF plus Epo develop into SCF/Epo-dependent erythroid progenitors (SCF/Epo cells) that can be induced to further differentiate into fully mature red cells by Epo plus insulin. Alternatively, CD34⁺ cells are induced to develop first into Epo-independent progenitors with SCF plus IL-3 plus hyper–IL-6 (SI2 cells) and then induced to yield SCF/Epo cells by SCF plus Epo plus Dex. SI2 cells and SCF/Epo cells represent progenitors at the early and late stage of erythroid cell development, respectively. (B) A total of 4 × 10⁵ CD34⁺ cells were cultured with SCF plus Epo to generate SCF/Epo cells in the presence of thalidomide (10 μM), CC-4047 (10 μM), or 0.1% DMSO (control). At day 10 in culture, cells were analyzed for surface antigen expression by flow cytometry (filled area). The open area indicates staining with isotype control antibody. Horizontal lines represent the percent of positive cells for each staining. (C) The growth kinetics of cells from panel B are shown as cumulative cell numbers. ○ indicates thalidomide; •, CC-4047; and × with dotted line, control. Data represent means ± standard deviation from 3 independent experiments. ^*Significant change (P = .05) from control on each day.