Sericin-chitosan nanoassembly-based scalable and biocompatible manganese nanoadjuvant for high-performance...

Commercial adjuvants-formulated inactivated pseudorabies virus (PRV) vaccines have low protective performance due to the inadequate immune response and poor cellular immunity. This work developed a manganese (Mn²⁺)-loaded sericin-chitosan nanoparticle via ethylenediaminetetraacetic dianhydride (EDTAD)-assistant Mn²⁺ coordination (named as SS-CS-EDTAD-Mn), which was then utilized as a high-performance nanoadjuvant for an inactivated PRV vaccine. The SS-CS-EDTAD-Mn nanoparticles, served as a nanocarrier and nanoadjuvant, significantly prolonged antigen release at the injection sites and improved antigen uptake by antigen presenting cells. Flow cytometric analysis demonstrated that the nanoadjuvant efficiently promoted maturation of dendritic cells, stimulated the increase of CD4⁺/CD8⁺ T cell populations and their activation, and enhanced generation of memory CD4⁺/CD8⁺ T cells. The SS-CS-EDTAD-Mn-adjuvanted vaccine elicited strong immune responses characterized by elevated total serum IgG antibody levels, an enhanced IgG2a to IgG1 ratio, and increased Th1/Th2 cytokines production compared to commercial adjuvants aluminum hydroxide (Alum) and water-in-oil-in-water emulsion (ISA201). In murine challenge studies with wild-type PRV, the nanoadjuvant-formulated vaccine achieved a 100% protection rate (10/10), significantly outperforming Alum (40%, 4/10) and ISA201 (60%, 6/10). This work not only highlights the potential of SS-CS-EDTAD-Mn as a promising nanoadjuvant, but also elucidated its action mechanism.