Fusion expression and immunogenicity of the antigen epitope/VP1 protein against swine O-type foot-and-mouth disease virus

Objective  To obtain Chinese hamster ovary cell line (CHO-K1) which can stably express antigen epitope fusing VP1 protein of swine O-type foot-and-mouth disease virus (FMDV), and prepare subunit vaccine.

Method  A recombinant gene RP1 containing FMDV antigen epitope and its VP1 gene sequence was designed, synthesized and cloned into expression vector pCDH-CMV-MCS-EF1-Puro. The constructed recombinant plasmid was co-transfected into HEK-293T cells with helper plasmids PLP1, PLP2 and PLP3 to obtain recombinant lenti virus HIV-RP1. CHO-K1 cells were infected by the harvested virus solution, and the monoclonal cell lines were obtained by screening. The expressing RP1 positive cell line named CHO-K1-RP1 was obtained by indirect immunofluorescence assay (IFA) and Western blot identification. The CHO-K1-RP1 was passed on continuously for 30 generations, and the same number of cell samples were collected every five generations for Western blot identification.

Result  IFA results showed that the cells expressing RP1 emitted green fluorescence, while the blank control had no green fluorescence. Western blot results showed that a clear band was observed at about 55 kU. The above results indicated that the fusion protein was successfully obtained. Female BALB/c mice were immunized with subunit vaccine prepared by mixing equal volumes of fusion protein and adjuvant. The antibody titer identification results showed that after the second immunization, foot-and-mouth disease (FMD) subunit vaccine group and FMD commercial inactivated vaccine group had no significant difference at antibody levels, but both were significantly higher than those of control (P<0.05).

Conclusion  The subunit vaccine constructed in this study can effectively stimulate the immune response in mice, which provides a reference for the development of a new vaccine against FMD in pigs.