Decline in Helicoverpa armigera nucleopolyhedrovirus occlusion body yields with increasing infection cell density in vitro is strongly correlated with viral DNA levels

Abstract

The phenomenon of the reduction in the cell-specific yield with increasing infection cell density (ICD), the cell density effect, is one of the main hurdles for improving virus yields in vitro. In the current study, the reduction in cell-specific yields (viral DNA [vDNA], polyhedrin mRNA and occlusion body [OB]) with increasing ICD for Helicoverpa armigera nucleopolyhedrovirus (HearNPV)-infected HzAM1 (Helicoverpa zea) insect cells has been investigated. HzAM1 cells were propagated in Sf900™ III serum-free medium and synchronously infected with wild-type HearNPV at various ICDs of 0.5-5 × 10(6) cells/mL at an MOI of 5 PFU/cell. Infection was conducted either in the original medium or in fresh medium. As found previously for Sf9 and High Five cells, there were negative correlations between the three key virus infection indicators (vDNA, mRNA and OB) and the peak cell density (PCD). Generally, the yield decline with increasing PCD was most pronounced for OB, followed by mRNA, and was more moderate for vDNA. The decline was significantly reduced, but not totally arrested, when fresh medium was used. There were also strong correlations between OB and mRNA, mRNA and vDNA, and OB and vDNA levels. These results suggest that the reduction in baculovirus yield (OB) at high PCDs is associated with limitations during the upstream processes of replication and transcription together with limitations during protein translation. Furthermore, the peak protein productivity per unit of cell volume in the HzAM1/HearNPV system was shown to be higher than that of the Sf9/rAcMNPV system, but lower than that of the High Five/rAcMNPV system.

Characterization of a Chrysodeixis includens nucleopolyhedrovirus Isolate from Brazilian Cerrado and Assessment of its Co-Infection with Anticarsia gemmatalis multiple nucleopolyhedrovirus

“…In vitro production could potentially overcome the difficulties of large-scale production of baculovirus biopesticides 6 . Therefore, insect cell cultures are interesting systems that support viral replication 7,8,9 . However, due to several technical limitations and prohibitive costs of production, baculovirus in vitro production is still unpractical on the commercial scale 9 .…”

In vitro infectivity of Spodoptera frugiperda multiple nucleopolyhedrovirus to different insect cell lines

“…Cell cultures of insects are an interesting means to select systems that support viral replication (Castro et al, 2006;Almeida et al, 2010;Huynh et al, 2015). These cell systems are useful in studies of virus-host interactions, but the present technical limitations should be solved for their need in large-scale production of biopesticides, such as the accumulation of "few polyhedra mutants" or "defective interfering particles" in the cell culture (Moscardi et al, 2011;Reid et al, 2014).…”