Experimental tumour induction by SV40 transformed cells

Although SV40 transforms cells from many species, transformed cells from species other than the Syrian hamster are rarely tumorigenic in immunocompetent animals. However, secondary manipulations of SV40-transformed cells can result in increased tumorigenicity. Some early observations on tumour induction by SV40 and transformed cells will be followed by a selected review of evidence suggesting that tumorigenicity of SV40-transformed cells involves serial mutations. An SV40-transformed rat cell model will be described to illustrate the changes in tumorigenic phenotype that can occur during tumour progression. This information will be used to propose that SV40 immortalization of cells (other than hamster cells) is only the first in a series of steps in the pathway toward tumorigenicity and that a complete understanding of the oncogenicity of SV40 will require definition of the secondary genetic events which complement SV40 immortalization to create the fully tumorigenic phenotype.