The deletion of the pif gene improves the biosafety of the baculovirus-based technologies

Our goal was to improve the biosafety of baculovirus-based technologies by deleting the pif (per os infectivity factor) gene from baculovirus expression vectors. Such a deletion would block transmission in nature without disturbing protein production. A pif deletion mutant of Autographa californica multiplecapsid nucleopolyhedrovirus (AcMNPV) was constructed and its infectivity to two host species was tested by oral or intrahemocoelic inoculation. Virus replication after oral inoculation was monitored using PCR. Oral inoculations with a mixture of the wild type and the pif deletion viruses were carried out. The pif deletion blocked oral infection but it did not hamper infectivity in cell culture. The blockage took place early after inoculation and could not be overcome by mixed inoculations with the wild type. The cat gene was inserted under the control of the polyhedrin promoter in the deletion mutant and the wild type CAT yield was measured in Spodoptera frugiperda insect cells (Sf9) infected with either recombinant. The pif deletion did not hamper CAT production. This deletion significantly improved CAT yields early in the infection. Hence, expression vectors lacking pif may produce higher quality protein. The pif deletion is a simple measure that dramatically reduces the chances of virus spread or gene transfer in nature.