Development of a DNA vaccine against foot-and-mouth disease in swine

Foot-and-mouth disease (FMD) is a widely spread contagious disease of cloven hoofed animals. The causative reagent of FMD is the foot-and-mouth disease virus (FMDV), which belongs to the Picornaviridae family. VP1 is a capsid protein of FMDV and contains two of the viral epitopes (amino acid 141-160 and 200-213). DNA immunization is a new vaccination method. DNA vaccines are DNA constructs encoding specific immunogens. In this study, a FMD DNA vaccine candidate was constructed by linking the two VP1 epitopes with the constant region of a host-derived immunoglobulin G and inserting them into a mammalian expression vector pCDNA3.1. Animal testing was carried out on mice and swine with plasmid pCEIM or pCEIS, which contained mouse IgG and swine IgG, respectively. pCEIM was administered into mice twice at the abdomen using a genegun and both FMDV-specific T cell proliferation and neutralizing antibody were detected. pCEIS was administered into swine either twice at the ear or thigh with a genegun device. Immune responses in swine were detected only after the secondary administration. To investigate the different mechanisms between protein- and DNA-based vaccines, another group of swine was immunized with a protein, F1-sIgG, which is encoded by the plasmid pCEIS, and the B and T cells responses were compared. The results showed that immunization with pCEIS elicited a higher T cell response but lower B cell response than immunization with Fl-sIgG protein. The results suggest that DNA- and protein-based vaccine elicited different immune responses: DNA vaccine through MHC-I and protein vaccine through MHC-II pathway. The immune response elicited by immunization with pCEIS provided protection against 10LD50 FMDV challenge in swine and indicated this plasmid has the potential to be a novel vaccine against FMD. In order to enhance the immunogenicity of the DNA vaccine candidate, swine interleukine-2 (IL-2) was cloned into pCDNA3.1 and administrated to swine together with pCEIS. The results showed that co-inoculation with IL2 enhanced the T cell proliferation, but not the neutralizing antibody response