Population kinetics during simultaneous infection of insect cells with two different recombinant baculoviruses for the production of rotavirus-like particles

Background: The simultaneous production of various recombinant proteins in every cell of a culture is often needed for the production of virus-like particles (VLP) or vectors for gene therapy. A common approach for such a purpose is the coinfection of insect cell cultures with different recombinant baculoviruses, each containing one or more recombinant genes. However, scarce information exists regarding kinetics during multiple infections, and to our knowledge, no studies are available on the behavior of the different populations that arise during coinfections. Such information is useful for designing infection strategies that maximize VLP or vector yield. In this work, kinetics of cell populations expressing rotavirus GFPVP2 ( infected with bacGFPVP2), VP6 ( infected with bacVP6), or both proteins simultaneously ( coinfected with both baculoviruses) were followed by flow cytometry. Results: In single infections, the population infected with any of the recombinant baculoviruses followed the Poisson distribution, as the population expressing a recombinant protein exhibited a hyperbolic-type function with respect to the multiplicity of infection ( MOI) up to 5 pfu/cell. In coinfections, the population fraction expressing each recombinant protein could not be anticipated from results of single infections, as in some cases interference and synergistic effects were found. Only cultures with a total MOI below 5 pfu/cell followed the Poisson distribution. For cultures with a MOI of bacGFPVP2 above that of bacVP6 ( overall MOI above 5 pfu/cell), the total population expressing one or both recombinant proteins was as low as 50% below that predicted by Poisson. In contrast, the population fraction expressing VP6 increased in coinfections, compared to that in single infections. The largest population fraction simultaneously expressing both recombinant proteins was 58%, and corresponded to cultures infected at a MOI of 5 and 1 pfu/cell of bacGFPVP2 and bacVP6, respectively. Conclusion: The infection conditions that maximize the cell population simultaneously expressing two recombinant proteins were determined. Such conditions could not have been anticipated from population kinetics in individual infections. This information should be taken into account for improved simultaneous production of various recombinant proteins in any work dealing with coinfections.