Mn2+-loaded carboxymethyl chitosan nanoparticle as a multifunctional adjuvant to efficiently enhance the performance of inactivated pseudorabies virus vaccines

Conventional adjuvants (such as Alhydrogel and oil-in-water emulsion) formulated vaccines normally induce an inadequate immune response and poor cellular immunity. In this work, a Mn 2+ -loaded carboxymethyl chitosan nanoparticle dispersed with sodium alginate (CMS adjuvant) has been designed and used as a novel nanoadjuvant in inactivated PRV vaccines to overcome above challenges. Comprehensive biocompatibility assessments confirmed the CMS adjuvant's favorable safety profile in both in vitro and in vivo models. CMS-adjuvated PRV vaccine successfully induced higher innate and adaptive immune response as compared with control adjuvants, including higher specific IgG antibody titres and IgG2a/IgG1 ratio, elevated Th1-/Th2-type cytokine secretion, and increased T cell activation and differentiation. The enhanced performance was attributed to three primary factors: (1) sustained antigen release at the injection site, (2) CMS-assisted highly efficient antigen uptake and presentation by dendric cells (DCs), and (3) Mn 2+ -induced activation of cyclic GMP-AMP synthase-stimulator of interferon gene (cGAS-STING) pathway, leading to increased type I interferons (IFNs) secretion and DCs maturation. In a mouse challenge experiment with a wild-type PRV, the CMS-adjuvanted vaccine demonstrated superior protective efficacy (90 % survival rate) to commercial Alum (40 %) and biphasic 201 (80 %) adjuvants. Thus, the CMS nanoparticles have a great potential to be a promising nanoadjuvant in various vaccines.