Poria cocos polysaccharide-honeycomb manganese oxide nanoparticles as a vaccine adjuvant to induce potent immune responses.

As indispensable components of vaccines, adjuvants play a critical role in inducing potent immune responses. In our previous study, we isolated and purified a water-soluble polysaccharide from Poria cocos (PCP), and found that the PCP had the potential to act as an immunostimulant to induce a balanced Th1/Th2 immune response. However, the PCP showed effective immunomodulatory activity only at high concentrations. Herein, we prepared a novel and biodegradable adjuvant system (PCP-hMnO), in which the PCP was loaded onto the honeycomb manganese oxide nanoparticles (hMnO). The developed PCP-hMnO adjuvant system not only acted as an immunostimulant, but also as a delivery system to enhance antigen uptake by antigen-presenting cells (APCs), stimulate the activation of APCs and facilitate the formation of germinal center in draining lymph nodes. Furthermore, the PCP-hMnO adjuvant system facilitated the antibody production, the activation of CD4 and CD8 T cells, and the generation of IFN-γ, thus inducing a robust and durable immune response with a balanced Th1/Th2 response in comparison to commercial alum adjuvant. Our results demonstrated that the PCP-hMnO adjuvant system improved the immunomodulatory activity of the PCP, and had the potential to provide a simple, safe, and efficient nanoparticles-based strategy to induce potent immune responses.