Baculovirus as a highly efficient gene delivery vector for the expression of hepatitis delta virus antigens in mammalian cells.

Baculovirus has been employed for a wide variety of applications. In this study, we further expanded the application to the high-level expression of hepatitis delta virus (HDV) antigens and the formation of virus-like particles (VLP) in transduced mammalian cells. To this end, two recombinant baculoviruses were constructed to express large hepatitis delta antigen (L-HDAg) and hepatitis B surface antigen (HBsAg) under mammalian promoters. With a simplified transduction protocol using unconcentrated virus, high transduction efficiencies were achieved in hepatoma cells, in which L-HDAg and HBsAg were expressed abundantly, allowing for easy colorimetric detection in Western blots. L-HDAg alone was nucleus-bound and HBsAg alone was secreted; formation and secretion of HDV-like particles were readily detected upon coexpression, indicating that the baculovirus-expressed proteins were processed correctly as the authentic proteins. Quantitative real-time PCR (Q-PCR) analyses quantitatively revealed that baculovirus transduction was more efficient than plasmid transfection with respect to DNA uptake and DNA transport to the nucleus. Furthermore, superinfection introduced more baculovirus DNA into cells in the long-term culture as revealed by Q-PCR, thereby enhancing and prolonging the expression. In summary, baculovirus transduction can be an attractive method as an alternative to the plasmid transfection commonly employed for HDV research thanks to the significantly higher gene delivery efficiencies as well as the abundant expression and proper processing. Baculovirus can also be envisaged as a useful tool for investigating protein-cell interactions and virus assembly.