Efficacy of anti–Erb-B2 IT to eliminate tumor cells during ex vivo expansion of CD34⁺ cells. MDA-MB-453 and MCF-7 cells were mixed with CD34⁺ cells at a ratio of tumor cells to CD34⁺ cells of 1:10 as indicated, cultured in medium containing SCF, IL-1β, IL-3, IL-6, Epo, and 10% FCS, and treated with the anti–Erb-B2 IT at several concentrations and for various time periods as indicated. Numbers of cytokeratin-positive cells (•) and cytokeratin-negative cells (□) were determined after immunocytochemical analysis as described in the Methods. Data shown are a representative experiment of 3 independent experiments and show mean values of duplicate cultures. *No cytokeratin-positive cells were detected in at least 3 × 10⁴ total cells evaluated.