Porcine parvovirus (PPV) virus-like particles (VLPs) are a potential
vaccine candidate for the prevention of parvovirus-induced reproductive failure in pregnant sows. Currently, the Escherichia coli (E. coli) expression system is the most cost-efficient to express
recombinant proteins. To overcome the limitations of
protein misfolding and to prepare soluble highly bioactive
antigen and high yields of
protein, we optimized the PPV-VP2 gene, subcloned it into pET24a, pET26b, pET28a, and pET30a, and transformed it into E. coli BL21(DE3)-Tf16 competent cells. The pET28a plasmid was selected for further manipulations because it expressed high levels of the bioactive PPV-VP2
protein. Under optimal high-density fermenting conditions in a 70-L fermenter, the total yield of wet weight E. coli cells was 124.86 g/L, and PPV-VP2
protein was 2.5 g/L. After large-scale purification with
Triton X-114 two-phase extraction as well as activated
carbon powder adsorption, hemagglutination (HA) titers in the purified PPV-VP2
protein reached 219 and
endotoxin was reduced to 2500 EU/mL. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) results indicated that the purified PPV-VP2
protein self-assembled into VLPs. Immunogenicity assays in guinea pigs and pigs indicated that the ISA-201 VG adjuvanted PPV-VP2 VLP
vaccine elicited hemagglutination inhibition (HI) and virus neutralization (VN) antibody titers comparable with PPV commercial
inactivated vaccines, whereas viral loads in the spleen and liver of challenged guinea pigs were significantly reduced. In conclusion, our study provides a method for producing the PPV-VLP
vaccine against PPV
infection in E. coli and may offer a novel strategy for the soluble expression of other
vaccine antigens.