A GP5 Mosaic T-cell vaccine for porcine reproductive and respiratory syndrome virus is immunogenic and confers partial protection to pigs

The great genetic and antigenic diversity of PRRSV, an RNA virus that causes PRRS, makes the control of this disease very difficult. To achieve broad protection to infection with this divergent virus, two T-cell mosaic sequences were designed based on 748 glycoprotein 5 (GP5) sequences using the Mosaic T-Cell Vaccine Tool Suite from the Los Alamos National Laboratory. Two DNA vaccines were constructed using the mosaic sequences thus designed. The amino acid sequences of the GP5-Mosaic vaccines were closer to strains that differ from VR2332 by at least 10%. Expression of the GP5-Mosaic vaccines was verified in E. coli BL21 (DE3) by western blot. The immunogenicity of the GP5-Mosaic vaccines was tested by vaccinating young pigs with either a gene gun (Trial 1) or by electroporation (Trial 2) followed by challenge with VR2332. Lymphocyte proliferative responses detected in virus-stimulated peripheral blood mononuclear cells (PBMC) of GP5-Mosaic-vaccinated pigs were higher than those of control pigs in both trials. In Trial 2, significantly higher levels of IFN-γ mRNA expression and lower levels of IL-10 mRNA were detected in virus-stimulated PBMC of GP5-Mosaic-vaccinated pigs as compared to control pigs. In ELISA, higher virus-specific antibodies were detected in sera from GP5-Mosaic-vaccinated animals than those detected in control animals. These antibodies were proven to be neutralizing. The viral copy numbers in serum 5 days after challenge with VR2332 decreased over 260-fold within 2 days in GP5-Mosaic-vaccinated pigs, while the viral copy numbers increased by 1.2 to 5-fold in control animals in the same period. Additionally, the viral loads in inguinal lymph nodes and spleen, and lung lesions scores of GP5-Mosaic-vaccinated animals were lower compared to those of control animals. Together the data led us to conclude that the GP5-Mosaic vaccine was immunogenic and induced partial protection in vaccinated pigs.