Epitope-Based Multimeric Subunit Vaccine (ATOMSSUISpenta) Confers Cross-Protection Against Streptococcus suis Infection

Abstract Streptococcus suis (S. suis) is a zoonotic pathogen that causes significant losses in the swine industry and serious invasive infections in humans. The high serotype variability and genomic diversity of S. suis have substantially limited the development of cross-reactive vaccines. Although recent advances in in silico prediction and database-driven antigen discovery have accelerated the development of protein-based vaccines, several studies have reported inconsistencies between predicted immunogenic profiles and the protective efficacy observed in animal models, emphasizing the importance of integrating computational design with experimental validation. In this study, we selected key antigens of S. suis based on previous experimental reports (HP0197, Fnbp, Sao, ScpB, and SLY) and analyzed their predicted T- and B-cell epitopes. For each antigen, we identified surface-exposed epitope regions (approximately 109–210 amino acids) through structural modeling or available PDB data. These regions were then assembled into a multimeric conjugated vaccine construct (ATOMSSUISpenta) by optimizing based on predicted immunogenicity, solubility, and allergenicity profiles. As predicted by the in silico design, ATOMSSUISpenta elicited strong humoral immune responses against each of the five component antigens in the mouse model. Notably, the vaccine also induced robust Th1- and Th17-type cellular immune responses, which are known to be essential for effective opsonic and mucosal defense against S. suis infection. In the protection studies, ATOMSSUISpenta conferred significant protection against S. suis serotypes 2, 4, and 9, as demonstrated by improved survival rates and reduced bacterial burdens. These findings highlight the potential of ATOMSSUISpenta as a broadly protective subunit vaccine against S. suis and demonstrate the value of epitope-based multimeric design for targeting antigenically diverse Gram-positive pathogens.