SUMMARY

Explants of 15 polyoma-induced mouse tumor lines of known degree of sensi-tivity to polyoma challenge were in-fected with vaccinia virus, and the appearance of cytopathic changes and hemadsorption by the infected cells was scored. A correlation was found between the degree of polyoma and vacclDla sensitivity of the different lines. The findings are interpreted as probably reflecting differences in inter-feron production or virus adsorption between the tumor lines studied, which will be further investigated.-J Nat Cancer Inst 31: 1525-1532,1963. MOST mouse polyoma tumors studied have shown some resistance to the cytopathogenic effect (OPE) of polyoma virus infection, as compared to embryonic cells, even though some lines were equally as susceptible as embryonic cells (1, 2), The resistance varied in degree for different polyoma tumors and also for different sublines established from single cells isolated from the same tumor (2, 3). No consistent differences in virus sensitivity have been detected between polyoma tumors and neo-plasms of other etiology (2, 3). As one step in analyzing the mechanism of resistance to the OPE of polyoma virus, we were interested in whether increased resistance to polyoma was correlated with increased resistance to other viruses. This paper describes studies on the vaccinia virus sensitivity of a number of polyoma tumor lines that differ in their susceptibility to superinfection with polyoma virus. MATERIALS AND METHODS All tests were made on explanted cells grown in roller tubes containing 1.5 ml medium which, at the time of virus infection, consisted of Parker'