Tumorigenicity of human bk papovavirus plaque isolates, wild‐type and plaque morphology mutant, in hamsters

The polyoncogenic prototype human papovavirus BKV (Gardner's strain) produced clear, small and large plaques. Two small-plaque isolates (wt-500 and wt-502), as well as a large-plaque-forming isolate (wt-501), induced frequent brain tumors and occasional osteosarcomas (but no insulinomas) in hamsters. The large-plaque former (wt 501) was more tumorigenic than the two small-plaque mutant (pm-525), which had been rescued from hamster tumor cell lines and have small deletion near the origin of DNA replication, induced frequent brain tumors and insulinomas. Mutant 522 was about five times more tumorigenic than wt-501. These results support the hypothesis that the polyoncogenicity of prototype BKV is accounted for by the presence of BKV mutants.