EVIDENCE OF CONTINUOUS TRANSMISSION OF NONINFECTIOUS SV 40 VIRAL GENOME IN MOST OR ALL SV 40 HAMSTER TUMOR CELLS

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Abstract
Very small amounts of SV 40 virus were recovered irregularly and only from occasional SV 40 virus-induced tumors during the course of 31 serial transplant passages in adult hamsters. Tumors without virus could give rise to tumors with virus and vice versa. The hamsters bearing the transplanted tumors had no neutralizing antibody, and the tumor extracts contained no inhibitors for small amounts of SV 40 virus. In primary cultures, large numbers of tumor cells either failed to release virus or did so in single bursts of minute amounts on rare occasions. Viral antigen was not detected by the fluorescent antibody technique in the nuclei of tumor cells in primary cultures. Prolonged propagation and serial passage of the tumor cells in tissue culture induced the release of larger, though still small, amounts of virus in cultures that were previously virus-free for a month or more. There was no production of infectious virus when large amounts of SV 40 virus were added to in vitro cultures of the tumor cells. Nine of 12 tumors produced by transplantation of approximately two cells in adult hamsters yielded minute amounts of virus, indicating that most, and perhaps all, of the tumor cells carried the SV 40 viral genome in a noninfectious state and that maturation of the virus occurred only rarely in an occasional cell. The similarity between these findings and bacterial lysogeny requires further comparative study.