<正> A malignant transformed mammary epithelial cell line （11A1） was transfected with liposome encapsulated eukaryotic expression plasmid pCMV-neo-RB

yielding 4 constant clones which have obvious pheno-typic reversion changes

and named 11A1-R1-R4 respectively. Further experiments showed that the 11A1-R1 behaved like normal epithelial cells in both morphological and biological characteristics

with decreased clonogenicity in solid argar medium as well as decreased tumorigenicity. Northern blot hybridization showed increased expression of RB gene and decreased expression of c-myc gene in 11A1-R1

11A1-R2 cells compared to 11A1 cells. This was an ideal phenotypic reversion model for epithelial transformed cell line and demonstrated that the RB gene can reexpress and suppress malignant phenotype in RB inactive cells.