铝佐剂是我国唯一临床批准使用的疫苗佐剂,但其自身难以引发有效的细胞免疫应答,无法对机体产生综合性的保护,难以满足日益增长的疫苗佐剂需求。因此,如何合理化改造铝佐剂,保证疫苗佐剂的安全及高效诱导免疫反应是亟待解决的问题。本工作通过对商品化铝佐剂制备乳液超声条件的优化,最终研究表明当颗粒浓度为2.0 mg/mL,水相缓冲液选择蒸馏水且pH为7.0时能制备得到稳定的颗粒化乳液(Alum Particulate Emulsion, APE),制备得到的乳液平均粒径为2723.7±435.3 nm,Zeta电位为+40.5±1.5 mV。离心发现此时体系中没有游离的铝佐剂,表明2.0 mg/mL是能稳定乳液的最小颗粒浓度。将乳液与抗原共混,测量抗原的吸附率,结果显示,抗原的吸附率接近100%,共聚焦的结果也验证了乳液对抗原的高吸附特性。当乳液与DC (Dendritic Cells)细胞共孵育,可以观察到乳液的内吞及溶酶体逃逸,而传统的铝佐剂无法实现。ELISpot结果显示,APE组脾细胞中分泌IFN-γ的T细胞数量比铝佐剂组增加300%左右。将铝佐剂通过颗粒化的策略制备得到APE以后,改变了佐剂增强抗原的免疫效果,显著提升了传统铝佐剂的细胞免疫效果。
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.