FORMATION OF VARIANTS WITH A REVERSION OF PROPERTIES OF TRANFORMED CELLS .1. VARIANTS FROM POLYOMA-TRANSFORMED CELLS GROWN IN VIVO

It has been shown that cloned polyoma virus (PV)-transformed cells with fibroblast cell morphology inoculated into animals can produce tumors consisting of variant cells that are epithelioid in vitro. When compared with the parental transformed cells, these variants showed a decrease in cloning efficiency in fluid medium and soft agar, and in saturation density, and a gain of the ability to form colonies on glutaraldehyde-fixed normal cells. In contrast to the lack of contact inhibition of cell replication between the parental transformed cells, the cells of the variants behaved like normal cells in that they contact inhibited one another, and inhibited the parental transformed cells from which they were derived. The variants also resembled normal cells in that they had lost the ability to multiply at 41 °, but unlike normal cells they showed a high degree of tumorogenicity in vivo. The tumors produced by the transformed cells with fibroblastic morphology and by the epithelioid variants were fibrosarcomas. Both the parental and variant cells contained the PV specific nuclear tumor (T) antigen. The results indicate that variants with a reversion of in vitro properties of transformed cells can be obtained from cloned PV-transformed cells grown in animals, and that these variants showed a dissociation between tumorogenicity and properties characteristic of transformed cells in vitro. The results suggest that the variants have a different cell surface. © 1969.