Abstract
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.
Highlights
The ongoing pandemic of SARS-CoV-2 has resulted in more than 4.3 million human cases and 290,000 deaths as of 12th May 2020 [1]
A better understanding of the humoral immune response generated by different vaccine antigens, including antibody epitope repertoire, antibody binding affinity, and functional activity, could greatly benefit the development and evaluation of vaccines against COVID-19
We performed an in-depth evaluation of the stm.sciencemag.org (Page numbers not final at time of first release) 3 antibody response generated by various SARS-CoV-2 spike antigens that are similar to the vaccine antigens being used in clinical development [6, 17, 18]
Summary
The ongoing pandemic of SARS-CoV-2 has resulted in more than 4.3 million human cases and 290,000 deaths as of 12th May 2020 [1]. The spike glycoprotein has been identified as the key target for protective antibodies against both SARS-CoV-1 and SARSCoV-2 [2,3,4,5]. Multiple versions of the SARSCoV-2 spike proteins are currently under evaluation as vaccine candidates using different modalities and delivery systems [6]. It is important to perform a comprehensive evaluation of post-vaccination antibody response to elucidate the quality of the immune responses elicited by spike-based vaccine candidates. This could determine immune markers that may predict clinical benefit which would facilitate evaluation of vaccine candidates
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