STEPS IN THE NEOPLASTIC TRANSFORMATION OF HAMSTER EMBRYO CELLS BY POLYOMA VIRUS

Cultures of hamster embryo cells infected with polyoma virus undergo a characteristic transformation within several weeks after infection. The transformed cultures are constituted by highly atypical cells which have an abnormal morphology, grow rapidly in vitro, and give rise to progressively growing tumors when inoculated subcutaneously into the adult hamster. In the previous experiments, the transformed cells arose in mass cultures and their properties were only studied many cell generations after the original viruscell interaction had taken place. The experiments to be reported in this communication were undertaken to get some information on the properties of transformed cells at earlier stages after infection with polyoma virus. The experiments show that the atypical cells are produced in two main steps; moreover, they reveal some new characteristics of the transformed cells which may contribute to a clarification of the mechanism of transformation.