关键词: 疫苗, Pickering 乳液, 铝佐剂, 细胞免疫, 溶酶体逃逸

Abstract: Combating against the emerging pandemics, exploring the immunogenicity of the approved formulations is regarded as the optimal strategy for rapid clinical translation. To date, aluminum hydroxide adjuvant (termed as "alum"), which was composed by AlO(OH) has been used as the sole licensed adjuvant approved in China. Unfortunately, they seldom induce effective T cells-mediated immune response to produce efficient protection to meet the increasing demand for vaccine adjuvant. Therefore, the rational design of alum-based adjuvant may offer a novel and clinical-translatable vaccine platform for the potent immune activations and safety profile. In this work, alum particulate emulsion (APE) droplets were prepared by alum, and alum was adsorbed on the interphase between the US food and drug administration (FDA)-approved squalene and water. In contrast to the surfactant-stabilized emulsion, alum tends to adsorb on the squalene/water interphase, conferring a low surface tension and enhanced stability. After a series of optimizations, APE was prepared, with an average size of 2723.7±435.3 nm and a Zeta potential of +40.5±1.5 mV. Centrifugation demonstrated that 2.0 mg/mL was the minimum particle concentration to stabilize the emulsion droplets, which possessed just enough alum to avoid both the coalescence of the emulsions and the formation of larger aggregates due to excess in the continuous phase. SEM images indicated that alum was closely wrapped on the oil/water interphase, demonstrating a raspberry-like morphology. Additionally, CLSM images illustrated that the antigens were adsorbed on the squalene/water interphase of emulsion droplets in high efficiency. When treated with dendritic cells (DC), the enlarged internalization and lysosomal escape of the antigens were observed, indicating the potential for higher immune responses. After intramuscular injection, ELISpot results showed that IFN-γ secreted T cells increased by about 300% compared with that of alum accepted group, suggesting that prepared emulsion droplets were efficiently stimulated the cellular immune response. Collectively, with the feasibility of alum adsorptions on the oil/water interphase, as well as the bedside mixing of antigens, APE may provide insights for the development of a safe, accessible, and efficient adjuvant strategy for potent cellular immune response, which may offer an efficient strategy for clinically approved vaccine formulations.

Key words: vaccine, Pickering emulsion, alum, cellular immunity, lysosomal escape