Human and primate poxviruses: I. Growth characteristics of cytolytic and tumor variants

The dual potential of poxviruses to be cytolytic and tumorgenic has been extended. Yaba monkey tumor virus formed foci on monkey and human embryonic cells. Cytolytic or plaque-forming virus was isolated from Yaba tumor homogenates by selective sucrose centrifugation and passage through monkey or human embryonic cells. Monkey pox virus (MPV) was cytolytic for monkey cells or human embryonic cells, but upon passage onto young monolayers of human carcinoma cells, HeLa, produced a restricted cytopathic effect on first transfer, foci on second transfer and cytolysis after the fourth transfer. If HeLa monolayers were compact, the rapid growth precluded overt expression of cytolytic MPV. Electron micrographs of cytolytic Yaba indicated that Yaba development was similar to vaccinia and MPV but not totally organized. Growth curves of vaccinia, MPV and cytolytic Yaba were essentially identical in monkey and human embryonic cell lines.