Differences in Response of Hamster Tumor Cells Induced by Polyoma Virus to Interfering Virus and Interferon2

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Abstract
Two cell lines, derived from tumors induced by inoculation of hamsters at birth with polyoma virus, were compared with respect to their responses to interfering virus and interferon preparations. Both lines, H-1 and H-2, were free from, and resistant to, polyoma virus. They were similar in morphology, cultural growth pattern, capacity to produce tumors in weanling hamsters, and susceptibility to Newcastle disease virus (NDV) and vesicular stomatitis virus (VSV). They differed slightly in acid production and strikingly in the degrees of resistance to NDV and VSV, which could be induced in them by ultraviolet-inactivated NDV (NDVuv) or interferon, and in their capacities to synthesize interferon. With reduction in cytopathic effects, immunofluorescence, and viral yields as criteria, H-1 cells and their various sublines showed moderate or no protection after exposure to NDVuv when challenged with NDV and VSV, respectively; they could not be rendered resistant by any interferon tested and produced irregularly an interferon ineffective in homologous and H-2 cultures but active in hamster embryo and Earle's strain L cell population. In contrast, H-2 cells were readily protected by NDVuv and interferon preparations, whether derived from homologous, hamster embryo, or L cell cultures; they yielded a potent interferon which, in turn, made hamster embryo and L cells resistant. Protection was more pronounced in the homologous than in heterologous systems. A third tumor line (H-3) reacted, as far as ascertained, like the H-2 cells. Apparently, lack of response to interfering virus and interferon is not a reliable criterion for the malignant state of cells.