Robust immunoreaction induced by a subunit vaccine of PEDV spike protein based on GEM surface-display system

The global porcine epidemic diarrhea (PED) pandemic underscores the urgent need for safe, effective, and readily deployable subunit vaccines against porcine epidemic diarrhea virus (PEDV). In this study, we developed a subunit vaccine by displaying the PEDV spike (S) protein on Gram-positive enhancer matrix (GEM) particles via a protein anchor (PA), resulting in stable particulate antigen complexes designated GEM-S. The immunogenicity of GEM-S was evaluated in mice. Immune responses in lymph nodes (LNs), spleen, and serum were assessed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), flow cytometry, enzyme-linked immunosorbent assay (ELISA), and virus neutralization assays. Compared to soluble S protein, both GEM-S and the oil-adjuvanted control 206-S significantly upregulated cytokine/chemokine expression, increased antigen-presenting cell (APC) numbers in LNs, enhanced co-stimulatory molecule expression on dendritic cells (DCs), and elevated systemic antibody titers. Notably, GEM-S induced a higher IgG2a/IgG1 ratio, stronger intestinal mucosal IgA production, and a more sustained antibody response than 206-S, despite generating lower total IgG levels. These findings indicate that the particulate GEM-S formulation can effectively elicit robust PEDV-specific humoral and mucosal immune responses in mice, supporting its further investigation as a promising subunit vaccine candidate against PEDV.