Chinese Yam Polysaccharide-Loaded Aluminum Hydroxide Nanoparticle-Stabilized Pickering Emulsion as an Adjuvant to Enhance Immune Responses for the H9N2 Vaccine

Adjuvants, as vital components of vaccines, possess the capacity to augment the intensity, breadth, and persistence of immune responses. Traditional alum adjuvants are incapable of inducing Th1 cellular immunity. To enhance the efficacy and alter the type of immune responses triggered by alum adjuvants, we constructed a Pickering emulsion platform stabilized by Chinese yam polysaccharide-loaded aluminum hydroxide nanoparticles (C-AlPE). The Chinese yam polysaccharide (CYP) was utilized as the immunopotentiator, and the aluminum hydroxide nanoparticles (Al NPs) loaded with CYP were employed as solid nanoparticle stabilizers. The C-AlPE as an adjuvant for the H9N2 vaccine elicited a robust humoral immune response. Compared to commercial Algel adjuvant and ISA206 adjuvant, the C-AlPE adjuvant obviously promoted the generation of CD4⁺ and CD8⁺ T cells and increased the production of Th1- and Th2-type cytokines, thereby stimulating a balanced Th1/Th2 immune response. In addition, the C-AlPE adjuvant exhibited great biosafety <i>in vivo</i> against the H9N2 vaccine. RNA-seq analysis of the spleen indicated that the C-AlPE adjuvant modulated complex signaling pathways, thereby activating innate immune responses and subsequently adaptive immune responses. Our findings highlighted the considerable potential of C-AlPE as a safe and effective vaccine adjuvant, providing valuable insights for the development of novel polysaccharide- and alum-based adjuvants in a Pickering emulsion formulation, with potential applications in veterinary vaccines.