Long-Term Propagation of a Murine Leukemia Virus in an Established Cell Line

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Abstract
Cells derived from the spleens of suckling strain BALB/cAnN mice were established in long-term culture. The cells retained their susceptibility to infection by the Moloney leukemia virus. Cultures exposed to cell-free preparations of virus after 7.5 and 14 months of cultivation did not appear to be as sensitive to infection as were primary spleen cell cultures, since a comparatively longer period of incubation after exposure to virus was required before samples of culture fluids were leukemogenic for mice. The infected cells (MT-77) continuously released virus during 4 years of observation. No overt cytopathic changes were noted. The MT-77 line of cells, which could be propagated in suspension in 8-liter fermentors, provided large quantities of virus-containing fluids. When 8 × 105 cells were inoculated subcutaneously into baby mice, tumors developed at the site of implantation. No conclusions may be drawn concerning the role of the virus in the neoplastic change.