FACS analysis of EGFP expression in relation to ER-MP12 and ER-MP20 antigen expression in normal murine BM cells directly after transduction. The cells were stained sequentially with unlabeled ER-MP20 followed by GaR-Cy5 for detection of ER-MP20 antigen expression in the FL4 channel (ER-MP20), and with biotinylated ER-MP12 followed by SA-Tricolor for detection of ER-MP12 antigen expression in the FL3 channel (ER-MP12) of the FACSCalibur. The dot-plot profiles of ER-MP12 versus ER-MP20 (A) and of ER-MP12 and ER-MP20 versus green fluorescence (B and C, respectively) are shown. The lines used to discriminate between negative and positive cell populations are indicated and defined on the basis of appropriate control samples. In (B) and (C) the percentages of cells occurring in each quadrant are indicated.