Porcine IL-12 plasmid as an adjuvant improves the cellular and humoral immune responses of DNA vaccine targeting transmissible gastroenteritis virus spike gene in a mouse model

Transmissible gastroenteritis (TGE), caused by transmissible gastroenteritis virus (TGEV), is a highly infectious disease in pigs. Vaccination is an effective approach to prevent TGEV infection. Here, we evaluated the potential of TGEV S1 as a DNA vaccine and porcine interleukin (pIL)-12 as an adjuvant in a mouse model. A DNA vaccine was constructed with the TGEV S1 gene to induce immune response in an experimental mouse model; pIL-12 was chosen as the immunological adjuvant within this DNA vaccine. The pVAX1-(TGEV-S1) and pVAX1-(pIL-12) vectors were transfected into BHK-21 cells and expressed in vitro. Experimental mice were separately immunized with each of the recombinant plasmids and controls through the intramuscular route. The lymphocytes isolated from the blood and spleen were analyzed for proliferation, cytotoxic activities, and populations of CD4(+) and CD8(+) cells. The titers of TGEV S1 in an enzyme-linked immunosorbent assay (ELISA) and TGEV neutralizing antibodies and the concentrations of interferon (IFN)-γ and IL-4 were also analyzed in the serum. The plasmids pVAX1-(TGEV-S1) and pVAX1-(pIL-12) could be expressed in BHK-21 cells, and the combination of pVAX1-(TGEV-S1) and pVAX1-(pIL-12) could induce a significant increase in all markers. pIL-12 could act as an immunological adjuvant in the DNA vaccine for TGEV-S1. Furthermore, the DNA vaccine prepared using TGEV-S1 and porcine IL-12 could induce excellent humoral and cellular immune responses.