Baculovirus-mediated gene transfer is attenuated by sodium bicarbonate

Baculovirus transduction of cultured mammalian cells is typically performed by incubating the cells with virus using culture medium (e.g. Dulbecco's modified Eagle's medium (DMEM)) as the surrounding solution. However, we previously uncovered that DMEM hinders the baculovirus-mediated gene transfer.

In this study, we systematically explored the influences of promoter and medium constituents on the transduction efficiency by using different recombinant viruses and surrounding solutions for transduction, followed by flow cytometric analyses. Whether the key medium component impeded baculovirus binding to the cells and subsequent virus entry was investigated by immunofluorescence/confocal microscopy and quantitative real-time polymerase chain reaction (Q-PCR).

We demonstrated that the poorer transduction by using DMEM as the surrounding solution is independent of the promoter. Examination of the medium constituents group by group revealed that the balanced salt solution suppresses the baculovirus transduction. By omitting individual salt species in the balanced salt solution, we surprisingly uncovered that NaHCO(3), a common buffering agent, exerts the inhibitory effects in a concentration-dependent manner. Intriguingly, NaHCO(3) did not debilitate the baculovirus, nor did it inhibit virus binding to the cells. Instead, NaHCO(3) inhibited baculovirus transduction by reducing the intracellular virus number.

To our best knowledge, this is the first report unraveling the significance of NaHCO(3) in gene transfer. Our finding suggests that baculovirus-mediated gene transfer can be readily enhanced by omitting NaHCO(3) from the medium during the transduction period.