多孔PLGA微球作为新型冠状病毒疫苗佐剂的研究

Porous PLGA microsphere as a vaccine adjuvant against COVID-19

聚乳酸-羟基乙酸共聚物(PLGA)制备的纳/微颗粒已被证明具有良好的疫苗佐剂效果。现有研究中,对于PLGA疫苗递送微球的研究主要集中在抗原装载/吸附效率的提升或多佐剂共递送以增强免疫效果上。然而,对于微球结构本身的多样性在免疫效果提升方面的探索仍较为匮乏。通过对微球结构进行合理化设计,制备出多孔微球将抗原“后装载”到微球内部的方法或可实现抗原的无损装载与延长递送,从而开发出高效的新型冠状病毒疫苗递送佐剂。本工作以乳液法制备了PLGA多孔微球与实心微球,二者除了多孔微球具有内部空腔和表面小孔的独特结构外,在微球粒径、表面电势上均无显著区别。由于PLGA多孔微球内孔大、外孔小的特征,抗原投入浓度5.71 mg/mL时,包埋率达到10.81%。在延长抗原体内滞留时间上,相对于游离抗原3天的滞留终点和实心微球混合抗原5天的滞留终点,装载于多孔微球中的抗原的体内滞留时间延长至15天。在体液免疫效果的提升上,与新冠抗原混合实心微球疫苗组相比,装载新冠抗原的多孔微球疫苗组的IgG滴度上升速度最大值V_(max)是其1.73倍,响应水平更高;达到V_(max)的时间t比其提前了2.8天,起效时间更早;疫苗接种后6~16周期间,IgG抗体滴度均高于实心微球组,具有更优维持抗体滴度的潜力。

Poly(lactic-co-glycolic acid)(PLGA)nano-/microspheres have been proven to be effective as vaccine adjuvants.In current studies,the investigations on PLGA vaccine delivery microspheres have mainly focused on improving antigen loading/adsorption efficiency or codelivery of multiple adjuvants to enhance the immunization effect.However,there is still a lack of discussion on the impact of the structural diversity of microspheres in promoting the vaccination effects.By rationalizing the design of the microsphere structure,we describe that the development of an effective SARS-CoV-2 vaccine adjuvant was achieved by the post-loading of SARS-CoV-2 antigen into porous PLGA microspheres,which provided nondestructive loading and prolonged release of antigen.In this work,PLGA porous microspheres and solid microspheres were prepared with the emulsification method,and there was no significant difference in microsphere particle size and surface potential between the two,except for the porous microspheres having cavities internally and tiny pores on the surface.Such characteristics of"large inner pores and tiny outer pores"enabled the antigen encapsulation efficiency to reach 10.81%at the antigen input concentration of 5.71 mg/mL.In terms of prolonging the in vivo retention of the antigen,the release endpoint in the antigen-loaded porous microspheres was prolonged to 15 days compared with that of the free antigen at 3 days and that of the solid microsphere-mixed antigen at 5 days.Concerning the enhancement of humoral immunization,compared with the solid microsphere vaccine group mixed with SARS-CoV-2 antigen,the porous microsphere vaccine group loaded with SARS-CoV-2 antigen had a higher onset of effect as the maximum value of the IgG titer rising rate,V_(max)was 1.73 times higher;and the onset of effect was much earlier,as the time to reach the V_(max) was 2.8 days earlier;also,the IgG antibody titer of which was higher during 6~16 weeks post-immunization,presenting a better antibody maintenance effect.