Episomal simian virus 40 genomes in human brain tumors

Eight out of 35 human intracranial tumors were shown by restriction enzyme analysis to contain unintegrated simian virus 40 (SV40) DNA molecules. The relative amount of viral DNA was estimated to be the equivalent of one viral genome within every 10th to 20th cell. No infectious virus was detected in tissue cultures established from the tumors. From only one tumor was it possible to rescue, by cell fusion, infectious SV40 displaying wild-type properties. In those cases that permitted a more detailed analysis, the restriction enzyme cleavage patterns appeared to correspond to the wild-type patterns with one exception, in which the SV40 episomes displayed a deletion of approximately 70 base pairs close to the origin of DNA replication. From one tumor, the SV40 genomes were transferred into permissive CV-1 monkey cells by transfection with the total tumor DNA. Despite their persistence as episomes no infectious virus was produced. Furthermore, no viral antigens were detectable, although the SV40 messengers for the small and the large tumor antigens were present. These cells had, however, acquired the ability to form colonies in low concentrations of serum. Thus this report provides, by restriction enzyme analysis, direct evidence for the presence of SV40 DNA in human tumors.