Effective Induction of Cellular Immunity in Piglets Using a Single-Dose Bivalent Vaccine Against CSFV and PCV2

Porcine circovirus type 2 (PCV2) compromises the immune system in pigs, increasing their susceptibility to co-infections of other pathogens. Classical swine fever virus (CSFV) is one of those diseases and is listed as a highly contagious disease by the World Organization for Animal Health (WOAH). Effective vaccination is one of multipleeffective strategies to prevent diseases and requires the stimulation of T helper cell-mediated immune responses to enhance the effectiveness of vaccines. We developed a bivalent subunit vaccine containing PCV2 ORF2 and CSFV E2 antigens, formulated with a porcine-specific CpG adjuvant. Those specific pathogen-free piglets were immunized with only a single dose and challenged with virulent strains of PCV2 or CSFV four weeks post-vaccination. Vaccinated piglets had significantly higher neutralizing and ELISA antibody titers against both viruses. Improved cellular immunity is demonstrated by increasing percentages of CD3⁺CD4⁺CD8⁺ T cells and significantly upregulated mRNA expression of IL-2, IFN-α, and IFN-γ in peripheral blood mononuclear cells in vaccinated pigs after a challenge. No clinical signs or lesions were observed in vaccinated pigs, and viral loads in serum and tissues were markedly reduced or undetectable. In conclusion, a single dose of the PCV2/CSFV bivalent subunit vaccine induces both robust humoral and cellular immune responses, offering strong protection against infection. These findings highlight its potential as a practical and effective strategy for swine disease control.