B-tropic oncornavirus production by BALB/c methylcholanthrene-induced sarcoma cells

Six oncogenic cell lines were established from primary sarcomas that had been induced in thymectomized, aged, BALB/cSt mice by the injection of 3-methylcholanthrene. Of these lines, three produced B-tropic murine leukemia virus (MuLV), i.e. MuLV that would patently infect fibroblasts of BALB/c origin but not those from NIH Swiss mice. One of these lines, M-138, produced large quantities of virus, permitting the isolation of milligram quantities of B-tropic MuLV. Neonatal BALB/c mice injected with the M-138 MuLV developed high plasma levels of the species-specific virion antigen p30, but during 9 months of observation failed to manifest clinical signs of leukemia. Plasma p30 levels of NIH Swiss mice (non-permissive host) that were inoculated also as neonates with the same virus preparation, remained undetectable by radioimmunoassay. Xenotropic MuLV, i.e. that which infects cells of species other than the species of origin, was released by one of the three remaining cell lines. Two of the six original lines have remained free of detectable oncornavirus production. Our results suggest that cell lines that are stable sources of large quantities of B-tropic MuLV may be easily obtainable by the described manipulations. Equally important, however, is the fact that these data re-emphasize the danger that is inherent in assuming that a cell line is virus-free simply because it was isolated from a chemical carcinogen-induced neoplasm