Autographa Californica Nuclear Polyhedrosis Virus (AcNPV) DNA Does Not Persist in Mass Cultures of Mammalian Cells

Autographa californica nuclear polyhedrosis virus (AcNPV) is one of the most extensively studied baculoviruses. We have investigated whether AcNPV or its DNA can replicate and/or persist in cultures of mammalian cells. Human HeLa cells or primary human embryonic kidney cells, simian CV1 cells, hamster BHK21 (B3) cells or Muntiacus muntjak cells growing in monolayer cultures were used in these studies. Cells were inoculated with AcNPV at multiplicities ranging from 0.1 to 100 PFU/cell. Subsequently, the inoculated cells were investigated for virus production and for the replication and the persistence of viral DNA. Extracts of inoculated cells were also screened for the occurrence of AcNPV-specific RNA. AcNPV does not multiply in any of the cell lines studied. Viral DNA replication or transcription could not be detected by blotting and nucleic acid hybridization experiments using nick-translated, cloned viral probes. Furthermore, there was no evidence for the persistence of viral DNA or of fragments of viral DNA in mass cultures of mammalian cells. A puzzling homology between pBR322 plasmid DNA and human, simian, and hamster DNAs was detected. Since mammalian cells can take up and integrate any foreign DNA at very low frequency, it cannot be ruled out by the approach chosen that a very small number of cells might have incorporated and fixed viral DNA in their genomes. As this caveat is always pertinent for any population of cells exposed to foreign DNA, this reservation does not appear to be of particular significance in safety considerations when working with baculoviruses or any virus for that matter.