Generation of a non-transmissive Borna disease virus vector lacking both matrix and glycoprotein genes

Borna disease virus (BoDV), a prototype of mammalian bornavirus, is a non-segmented, negative strand RNA virus that often causes severe neurological disorders in infected animals, including horses and sheep. Unique among animal RNA viruses, BoDV transcribes and replicates non-cytopathically in the cell nucleus, leading to establishment of long-lasting persistent infection. This striking feature of BoDV indicates its potential as an RNA virus vector system. It has previously been demonstrated by our team that recombinant BoDV (rBoDV) lacking an envelope glycoprotein (G) gene develops persistent infections in transduced cells without loss of the viral genome. In this study, a novel non-transmissive rBoDV, rBoDV MG, which lacks both matrix (M) and G genes in the genome, is reported. rBoDV-MG expressing green fluorescence protein (GFP), rBoDV MG-GFP, was efficiently generated in Vero/MG cells stably expressing both BoDV M and G proteins. Infection with rBoDV MG-GFP was persistently maintained in the parent Vero cells without propagation within cell culture. The optimal ratio of M and G for efficient viral particle production by transient transfection of M and G expression plasmids into cells persistently infected with rBoDV MG-GFP was also demonstrated. These findings indicate that the rBoDV MG-based BoDV vector may provide an extremely safe virus vector system and could be a novel strategy for investigating the function of M and G proteins and the host range of bornaviruses.