Inactivation of Bombyx mori macula-like virus under physical conditions

A novel rhabdovirus persistently infects lepidopteran cell lines

A novel rhabdovirus was identified in BmN-4 (BmN) cells derived from Bombyx mori and Sf9 cells derived from Spodoptera frugiperda. Genome sequence homology revealed that this novel virus is distinct from the previously reported Spodoptera frugiperda rhabdovirus (SfRV). Given the high similarity of the large protein sequence of this virus to that of the Taarstrup virus, we named it Bombyx mori taarstrup virus (BmTV). When BmTV-negative B. mori-derived cultured cells were inoculated with BmTV, an increase in virus RNA was observed, but no impact on host cell proliferation occurred, suggesting that BmTV exhibits latent infection in insect cells. On the other hand, oral and hemocoel inoculation in B. mori larvae did not cause significant increase in BmTV replication. After subcutaneous inoculation, no difference in adult metamorphosis was observed between BmTV- and mock-inoculated larvae. No virus RNA was detected in eggs laid by adults that had been inoculated with BmTV at larval stage. These findings demonstrate that BmTV is a novel rhabdovirus that persistently infects several lepidopteran cultured cells.

Infectious Virions of Bombyx Mori Latent Virus Are Incorporated into Bombyx Mori Nucleopolyhedrovirus Occlusion Bodies

The Bombyx mori latent virus (BmLV) belongs to the unassigned plant virus family Tymoviridae and contains a positive-sense, single-stranded RNA genome. BmLV has infected almost all B. mori-derived cultured cell lines through unknown routes. The source of BmLV infection and the BmLV life cycle are still unknown. Here, we examined the interaction between BmLV and the insect DNA virus Bombyx mori nucleopolyhedrovirus (BmNPV). Persistent infection with BmLV caused a slight delay in BmNPV propagation, and BmLV propagation was enhanced in B. mori larvae via co-infection with BmNPV. We also showed that BmLV infectious virions were co-occluded with BmNPV virions into BmNPV occlusion bodies. We propose a new relationship between BmLV and BmNPV.

Adventitious viruses in insect cell lines used for recombinant protein expression

Insect cells are widely used for recombinant protein expression, typically as hosts for recombinant baculovirus vectors, but also for plasmid-mediated transient transfection or stable genetic transformation. Insect cells are used to express proteins for research, as well as to manufacture biologicals for human and veterinary medicine. Recently, several insect cell lines used for recombinant protein expression were found to be persistently infected with adventitious viruses. This has raised questions about how these infections might affect research performed using those cell lines. Furthermore, these findings raised serious concerns about the safety of biologicals produced using those cell lines. In response, new insect cell lines lacking adventitious viruses have been isolated for use as improved research tools and safer biological manufacturing platforms. Here, we review the scientific and patent literature on adventitious viruses found in insect cell lines, affected cell lines, and new virus-free cell lines.