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Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating viral disease of pigs. Safer and more effective vaccines are urgently needed. In this study, a synthetic ORF5 gene of porcine reproductive and respiratory syndrome virus (PRRSV) was adsorbed onto poly(D, L-lactide-co-glycolide)/polyethylenimine (PLGA/PEI) nanoparticles. We prepared a PLGA-nanoparticle-adsorbed PRRSV DNA vaccine and a PEI-DNA complex. The results showed that these model vaccines could significantly enhance humoral and cellular immune responses when compared with the responses induced by pcDNA3.1-SynORF5, a plasmid construct for expression of PRRSV ORF5. PLGA-branched PEI nanoparticles induced the most efficient immune response. The delivery system and adjuvant provide new models for the development of vaccines against PRRSV.

Porcine reproductive and respiratory syndrome virus (PRRSV) induces reproductive failure in sows and respiratory problems in pigs of all ages. Live attenuated and inactivated vaccines are used on swine farms to control PRRSV. However, their protective efficacy against field strains of PRRSV remains questionable. New vaccines have been developed to improve the efficacy of these traditional vaccines. In this study, virus-like particles (VLPs) composed of the GP5 and M proteins of PRRSV were developed, and the capacity of the VLPs to elicit antigen-specific immunity was evaluated. Serum antibody titers and production of cytokines were measured in BALB/C mice immunized intramuscularly three times with different doses (0.5, 1.0, 2.0, and 4.0 μg) of the VLP vaccine. A commercial vaccine consisting of inactivated PRRSV and phosphate-buffered saline (PBS) were used as positive and negative controls, respectively. IgG titers to GP5 were significantly higher in all groups of mice vaccinated with the VLPs than in control mice. Neutralizing antibodies were only detected in mice vaccinated with 2.0 and 4.0 μg of the VLPs. Cytokine levels were determined in cell culture supernatants after in vitro stimulation of splenocytes with the VLPs for 3 days. Mice immunized with 4.0 μg of the VLPs produced a significantly higher amount of interferon-gamma (IFN-γ) than mice immunized with the commercial inactivated PRRSV vaccine and PBS. In contrast, immunization with the commercial vaccine induced higher production of IL-4 and IL-10 in mice than mice vaccinated with VLPs. These data together demonstrate the capacity of VLPs to induce both neutralizing antibodies and IFN-γ in immunized mice. The VLP vaccine developed in this study could serve as a platform for the generation of improved VLP vaccines to control PRRSV.