Abstract：
Selecting appropriate adjuvants is crucial for developing an effective vaccine. However, studies on the immune responses triggered by different adjuvants in COVID-19 inactivated vaccines are scarce. Herein, we evaluated the efficacy of Alum, CpG HP021, Alum combined with CpG HP021 (Alum/CpG), or MF-59 adjuvants with COVID-19 inactivated vaccines in K18-hACE2 mice, and compared the different immune responses between K18-hACE2 and BALB/c mice. In K18-hACE2 mice, the Alum/CpG group produced a 6.5-fold increase in anti-receptor-binding domain (RBD) IgG antibody titers compared to the Alum group, and generated a comparable level of antibodies even when the antigen amount was reduced by two-thirds, possibly due to the significant activation of germinal center (GC) structures in the central region of the spleen. Different adjuvants induced a variety of binding antibody isotypes. CpG HP021 and Alum/CpG were biased towards Th1/IgG2c, while Alum and MF-59 were biased toward Th2/IgG1. Cytokines IFN-γ, IL-2, and TNF-α were significantly increased in the culture supernatants of splenocytes specifically stimulated in the Alum/CpG group. The antibody responses in BALB/c mice were similar to those in K18-hACE2 mice, but with lower levels of neutralizing antibodies (NAbs). Notably, the Alum/CpG-adjuvanted inactivated vaccine induced a higher number of T cells secreting IFN-γ and IL-2, increased the percentage of effector memory T (TEM) cells among CD8+ T cells, and effectively protected K18-hACE2 mice from Delta variant challenge. Our results showed that Alum/CpG complex adjuvant significantly enhanced the immune response to inactivated COVID-19 antigens and could induce a long-lasting immune response.
摘要：
选择合适的佐剂对于开发有效的疫苗至关重要。然而,关于COVID-19灭活疫苗中不同佐剂引发的免疫反应的研究很少。在这里，我们评估了明矾的疗效，CpGHP021，明矾与CpGHP021（明矾/CpG）结合，或MF-59佐剂与COVID-19灭活疫苗在K18-hACE2小鼠中，并比较了K18-hACE2和BALB/c小鼠的不同免疫反应。在K18-hACE2小鼠中，与明矾组相比，明矾/CpG组抗受体结合域（RBD）IgG抗体滴度增加7.5倍，即使抗原量减少了三分之二，也产生了相当水平的抗体，可能是由于脾中央区域生发中心（GC）结构的显着激活。不同的佐剂诱导多种结合抗体同种型。CpGHP021和明矾/CpG偏向Th1/IgG2a，明矾和MF-59偏向于Th2/IgG1。细胞因子IFN-γ，在明矾/CpG组中特异性刺激的脾细胞的培养上清液中，IL-2和TNF-α显着增加。BALB/c小鼠的抗体反应与K18-hACE2小鼠相似，但中和抗体（NAb）水平较低。值得注意的是,Alum/CpG佐剂灭活疫苗诱导更多的T细胞分泌IFN-γ和IL-2，增加CD8+T细胞中效应记忆T（TEM）细胞的百分比，并有效保护K18-hACE2小鼠免受Delta变体攻击。我们的结果表明，明矾/CpG复合佐剂显着增强了对灭活的COVID-19抗原的免疫反应，并可以诱导持久的免疫反应。
