E experiments, we chose, therefore, MCF-7 cells, because they do not express MAGE-A1 mRNA (Table 1). Based on the usually low transfection efficiency we sorted the transfected MCF-7 cells from untransfected cells by FACS and observed a transfection efficiency of about 10 . Subsequently, sodium bisulfite mapping showed a demethylation of the MAGE-A1 promoter of approximately 56 (range from 44 to 6