Polyoma Virus Mutant with a Reduction in Tumour Formation

Abstract

INFECTION with polyoma virus in vivo can, result in a cytopathic effect, hyperplasia, and the formation of benign or of malignant tumours¹. The use of single plaque isolations has indicated that these different types of response can be produced by the same virus². During the course of investigations on the induction of different responses to virus infection in vitro, a plaque-type mutant of polyoma, with a smaller-sized plaque than the wild type, was found in the virus produced by a line of mouse cells with a stable cell-virus association³. This line of cells was established by the culture of survivors after cytopathic effect in primary mouse embryo monolayers that had been infected with wild type polyoma. The cell line has now been releasing virus in culture for more than 1 year, and the plaques made by the virus are still of the mutant type. The mutant has been designated as Sp (= small plaque). Cross-neutralization of plaques has so far shown no antigenic difference between sp and the wild type.