Induction of a carcinogenic oncornavirus in C57BL/6 mouse embryo cells by 5-iododeoxyuridine

THE presence in mouse cells of oncornavirus-related genetic material has been documented^1-3 and the activation and release of latent oncornaviruses from virus-negative mouse cells by halogenated pyrimidines has been demonstrated^4-6. The relationship, if any, between the endogenous viral genes, the activated oncornaviruses and the oncogenic process is not known, although one chemically activated mouse oncornavirus was shown to induce lymphatic leukaemia⁷. Here we describe a system in which the induction of an oncornavirus is followed by the transformation of an epithelioid line of mouse embryo cells to carcinoma cells. This system is particularly interesting because the normal cells are derived from a mouse strain with a very low incidence of spontaneous cancers⁸, and also because the majority of tumours in man arise from epithelial tissues^9,10.