Senecavirus A non-structural protein 2C and 3A-specific T cell-epitopes promote inactivated vaccine efficacy in pigs via synergistic cellular and humoral immunity.

Senecavirus A (SVA) infection causes vesicular disease in swine, which presents with clinical signs that are highly similar to those of foot-and-mouth disease, and thus leads to significant challenges for disease control. Although inactivated SVA vaccines effectively elicit humoral immunity, they induce sub-optimal cellular immune responses. To overcome this limitation, we systematically screened T-cell epitopes within the immunogenic non-structural proteins 2C and 3A of SVA to evaluate their potential as novel immune enhancers. Forty-four overlapping peptides spanning the full-length 2C/3A proteins were synthesized. Their capacity to stimulate IFN-γ+ T cell responses in peripheral blood mononuclear cells from SVA-infected pigs were assessed and six immunodominant T cell epitopes (2C-5/6/7/8/14, 3A-38) were identified. Notably, epitope 2C-5 activated both CD4+ and CD8+ T cells and promoted their proliferation. A recombinant protein incorporating these identified T cell epitopes was designed as an immuno-stimulant and co-administered with inactivated vaccine in pigs. Challenge experiments demonstrated complete absence of clinical symptoms and undetectable viremia in the inactivated vaccine alone and co-stimulation with the inactivated vaccine and the recombinant protein groups. Notably, the combination vaccine induced significantly higher epitope-specific IFN-γ+ T cell responses and neutralizing antibody titers at 28 days post-vaccination compared to the inactivated vaccine alone, implying that synergistic cellular and humoral immunity may contribute to enhanced protective efficacy. This study identified promising candidate components for developing efficacious SVA vaccines, while the identified conserved T cell epitopes provided a critical foundation for designing broad-spectrum multi-epitope vaccines.