Tumor Induction by Genetically Homogeneous Lines of Polyoma Virus2

Polyoma virus, reisolated from mouse parotid, kidney, and mammary-tumor cells in culture, has been purified by 3 successive single plaque isolations. Inoculation of the third-passage single plaque isolates into hamsters, mice, and rats can result in the development of multiple tumors. Homogeneous lines of polyoma virus are therefore capable of inducing more than one tumor type. Plaque-purified virus of kidney and mammary-tumor origin induced parotid tumors in mice to the same degree as virus initially isolated from the parotid-tumor cells. However, virus of kidney-tumor origin appeared to have a greater ability for producing multiple tumors in AKR mice than virus of parotid-tumor origin. Data have been obtained which suggest that the dosage, in addition to its effect on the proportion of animals developing tumors, also appears to determine how many of these will develop multiple tumors after inoculation with plaque-purified virus. The results have also provided further evidence that there is a difference in susceptibility of different strains of mice. With the use of the same plaque-purified virus at the same dosage level, AKR mice had a much higher susceptibility than SWR mice, but C57BL/6 mice in these experiments were completely resistant to tumor induction. Thus, despite the fact that the same plaque-purified virus can produce tumors in different rodents, there still appears to be some strain specificity in mice.