Stability of EGFP expression in leukemia cells in culture. Stability of EGFP expression in leukemia cells in culture after transfection with the expression plasmid (▴) VR-EGFP and transduction by the retroviral vector (▪) L-EGFP-SN and the lentiviral vector (•) pHR′-CMV-EGFP. The transfected cells and the lentiviral-transduced cells were not FACS sorted before culture, but the retroviral-transduced cells were. Day 0 is 48 hours after transfection or transduction. (A) Nalm-6 cells; (B) Reh cells.