Novel Liposomal Adjuvants Enhance the Immune Response to Recombinant Staphylococcus aureus Antigens in Dairy Heifers

The development of effective adjuvant systems remains a critical challenge in veterinary vaccine design, particularly for infectious diseases causing significant economic losses in dairy cattle. This study evaluated the immunological profile induced by a mixture of recombinant antigens, formulated with cationic liposomes containing different combinations of gemini lipopeptide AG2-C16, bovine-specific CpG oligodeoxynucleotide, and S. cerevisiae mannans, in dairy heifers. Thirty-five dairy heifers aged 8-10 months were randomly assigned to seven groups and immunized with recombinant Staphylococcus aureus antigens (α-toxin, β-toxin, clumping factor A, and fibronectin-binding protein A) formulated with different adjuvant combinations. Animals received two primary doses 21 days apart, followed by a booster dose 8 months later. Humoral immune responses were assessed through ELISA measuring specific immunoglobulin G (IgG), IgG1, and IgG2 levels, while cytokine production was evaluated via whole-blood assays. Results demonstrate that liposomal formulations combining AG2-C16, CpG-ODN, and mannans induce a significant immune response, in heifers, with IFN-γ production. These findings provide valuable insights for the development of new vaccine strategies in cattle.