Polyethyleneimine modified Pickering emulsion as a novel adjuvant to induce strong and long-lasting immune responses

Poly (lactic-co-glycolic acid) (PLGA) nanoparticles are widely-investigated vaccine adjuvants owing to their safety, antigen slow-release ability, and good adjuvants activity. This study involved the preparation of the polyethyleneimine-modified immunopotentiator Alhagi honey polysaccharide encapsulated PLGA nanoparticles (PEI-AHPP) and the assembly of the Pickering emulsion with PEI-AHPP as shell and squalene as core (PEI-PPAS). Furthermore, PEI-AHPP and PEI-PPAS were characterized. To assess the strength and type of immune responses induced by different adjuvants, the chickens were immunized with H9N2-absorbed nanoparticle formulations. Our results showed that since the PEI-PPAS possess rough strawberry-like surfaces, a large number of antigens can be absorbed on their surfaces through simple mixing. Compared to PEI-AHPP, PEI-PPAS was found to exhibit better stability and antigen-loading efficiency. The adjuvant activity of the nanoparticles showed PEI-PPAS/H9N2 to induce long-lasting and high Hemagglutination inhibition (HI) titers, high thymus, spleen, and organ index of the bursa of Fabricius. Moreover, the chickens immunized with PEI-PPAS/H9N2 showed a mixture of high CD4⁺ and CD8a⁺ T-cells in the spleen and strong Th1 and Th2-type cytokines secretion. Thus, these findings demonstrated PEI-PPAS to be a vaccine adjuvant inducing a mixed cellular and humoral immune response, which can potentially serve as an effective vaccine delivery adjuvant system for the H9N2 antigen.