Poria cocos polysaccharide-loaded Alum Pickering emulsion as vaccine adjuvant to enhance immune responses

Traditional Alum adjuvants mainly elicit a Th2 humoral immune response, but fail to generate a robust Th1 cellular immune response. However, the cellular immune response is essential for vaccination against cancer and a number of chronic infectious diseases, including human immunodeficiency virus infection and tuberculosis. In our previous study, we demonstrated that the polysaccharide from Poria cocos (PCP) has the potential to serve as an immunologic stimulant, enhancing both humoral and cellular immune responses. However, this effect was only observed at high concentrations. In this study, to enhance the immune-stimulation effect of PCP and modify the type of immune response elicited by Alum adjuvant, we successfully developed a Pickering emulsion delivery system (PCP-Al-Pickering) using PCP-loaded Alhydrogel particles as the stabilizer. After optimization, the Pickering emulsion exhibited excellent storage capacity and effectively adsorbed the PCP and antigen. As an adjuvant delivery system, the PCP-Al-Pickering emulsion facilitated the antigen uptake by macrophages, increased the recruitment of cells at injection sites, improved the activation of dendritic cells in draining lymph nodes, elicited a potent and durable antibody response, and promoted the activation of CD4+ and CD8+ T cells. Importantly, the PCP-Al-Pickering emulsion adjuvant elicited a balanced Th1 and Th2 immune response, in comparison to Alum adjuvant. The PCP-Al-Pickering emulsion may serve as a safe and promising adjuvant delivery system to enhance immune responses.