Stable high-level expression of heterologous genes in vitro and in vivo by noncytopathic DNA-based Kunjin virus replicon vectors

primary features of the flavivirus Kunjin (KUN) subgenomic replicons include continuous noncytopathic replication in host cell cytoplasm and the ability to be encapsidated into secreted virus-like particles (VLPs). Previously we reported preparation of RNA-based KUN replicon vectors and expression of heterologous genes (HG) in cell culture after RNA transfection or after infection with recombinant KUN VLPs (A. N. Varnavski and A. A. Khromykh, Virology 255:366-375, 1999). In this study we describe the development of the next generation of KUN replicon vectors, which allow synthesis of replicon RNA in vivo from corresponding plasmid DNAs. These DNA-based vectors were able to direct stable expression of beta-galactosidase (beta-Gal) in several mammalian cell lines, and expression remained high (similar to 150 pg per cell) throughout cell passaging. The applicability of these vectors in vivo was demonstrated by beta-Gal expression in the mouse lung epithelium for at least 8 weeks after intranasal inoculation and induction of anti-beta Gal antibody response after intramuscular inoculation of the beta-Gal-encoding KUN replicon DNA. The noncytopathic nature of DNA based KUN replicon vectors combined with high-level and stability of HG expression in a broad range of host cells should prove them to be useful in a variety of applications in vitro and in vivo.