Development of a vaccine vector based on a subgenomic replicon of porcine reproductive and respiratory syndrome virus

In this study, a DNA-launched subgenomic replicon of porcine reproductive and respiratory syndrome virus (PRRSV) was developed for use as a vaccine vector. This replicon plasmid contained a PRRSV subgenome without structural genes ORF2–ORF6, and was under the transcriptional control of the immediate-early promoter of cytomegalovirus (CMV). Using enhanced green fluorescent protein (EGFP) as a reporter gene, the DNA-launched subgenomic replicon of PRRSV, named pOK-Clone20-rep, could express heterologous genes in vitro. After direct inoculation of pOK-Clone20-rep, mice developed antibody responses that were specific for both the EGFP and the N gene in a dose-dependent manner. Furthermore, mice immunized with pOK-Clone20-rep at a dose of 100 μg showed significantly enhanced levels of IFN-γ compared with those inoculated with 100 μg of pcD-EGFP, a conventional DNA vaccine that encodes EGFP. In summary, the results show that the DNA-launched subgenomic replicon of PRRSV could not only mediate foreign gene expression in vitro but also induced an immune response in vivo. Similarly, expression and immunogenicity of the N gene also strengthened the potential of the replicon to serve as a vaccine vector expressing multiple genes. It therefore provides a useful tool for vaccine development and the study of the transcription and replication of PRRSV.