Multiple vaccine candidates against SARS-CoV-2 based on viral spike protein are under development. However, there is limited information on the quality of antibody responses generated with these vaccine modalities. To better understand antibody responses induced by spike protein–based vaccines, we performed a qualitative study by immunizing rabbits with various SARS-CoV-2 spike protein antigens: S ectodomain (S1+S2; amino acids 16 to 1213), which lacks the cytoplasmic and transmembrane domains (CT-TM), the S1 domain (amino acids 16 to 685), the receptor binding domain (RBD) (amino acids 319 to 541), and the S2 domain (amino acids 686 to 1213, lacking the RBD, as control). Resulting antibody quality and function were analyzed by enzyme-linked immunosorbent assay (ELISA), RBD competition assay, surface plasmon resonance (SPR) against different spike proteins in native conformation, and neutralization assays. All three antigens (S1+S2 ectodomain, S1 domain, and RBD), but not S2, generated strong neutralizing antibodies against SARS-CoV-2. Vaccination-induced antibody repertoire was analyzed by SARS-CoV-2 spike genome fragment phage display libraries (SARS-CoV-2 GFPDL), which identified immunodominant epitopes in the S1, S1-RBD, and S2 domains. Furthermore, these analyses demonstrated that the RBD immunogen elicited a higher antibody titer with five-fold higher affinity antibodies to native spike antigens compared with other spike antigens, and antibody affinity correlated strongly with neutralization titers. These findings may help guide rational vaccine design and facilitate development and evaluation of effective therapeutics and vaccines against COVID-19 disease.

基于病毒刺突蛋白的针对SARS-CoV-2的多种候选疫苗正在开发中。但是，关于用这些疫苗形式产生的抗体反应质量的信息有限。为了更好地了解基于穗蛋白的疫苗诱导的抗体反应，我们通过用各种SARS-CoV-2穗蛋白抗原：Sectodomain（S1 + S2; 16至1213位氨基酸）免疫兔，进行了定性研究和跨膜结构域（CT-TM），S1结构域（氨基酸16至685），受体结合结构域（RBD）（氨基酸319至541）和S2结构域（氨基酸686至1213，缺少RBD），作为对照）。通过酶联免疫吸附测定（ELISA），RBD竞争测定，在天然构象和中和测定中针对不同刺突蛋白的表面等离振子共振（SPR）。所有这三种抗原（S1 + S2胞外域，S1域和RBD）而非S2均产生针对SARS-CoV-2的强中和抗体。通过SARS-CoV-2穗基因组片段噬菌体展示文库（SARS-CoV-2 GFPDL）分析了疫苗诱导的抗体库，该文库鉴定了S1，S1-RBD和S2域中的免疫优势表位。此外，这些分析表明，与其他刺突抗原相比，RBD免疫原引发的针对天然刺突抗原的抗体滴度更高，亲和力抗体高五倍，并且抗体亲和力与中和滴度密切相关。