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 Authors:Walker et al. 

Journal/ Pre-Print:BioRxiv 

Tags: Immunology/Immunity, Clinical/ Diagnostics, Vaccines, Virology 

Research Highlights

  1. Developed a competitive ELISA to test for antibodies which inhibit SARS-CoV-2 spike protein RBD interaction with ACE2, which has the potential to test for vaccine efficacy. 

  1. In mice, antibodies had greater ACE2 inhibition for S1+S2 compared to only S1 for SARS-CoV-2 spike protein.  


The authors tested a competitive ELISA assay with bound SARS-CoV-2 spike protein, with competition between ACE2 and purified IgG or sera from vaccinated animal models (mice, rabbits, guinea pigs, rhesus macaques) and Covid-19 patients. The animals were vaccinated with the INO-4800 vaccine, and naive animals (mock saline vaccination) and Day 0 sera were used as negative controls. Healthy human pre-pandemic samples were used as a negative control. There was no blinding used in the study. 

Impact for SARS-CoV2/COVID19 research efforts  

Develop diagnostic tools for SARS-CoV2/COVID19 

Others: Also suggests tool could be used to test efficacy of the vaccines 

Study Type  

  • In vitro study 

  • In vivo study (e.g. mouse, NHP) 

Strengths and limitations of the paper 

Novelty:New tool to detect antibodies from sera which inhibit RBD-ACE2 interaction of SARS-CoV-2 

Standing in the field:Another antibody assay, ELISA-based 

Appropriate statistics:Some statistics, but lacking and poorly explained 

Viral model used:SARS-CoV-2 spike protein (S1+S2) and S1, SARS-CoV-2 pseudovirus 

Translatability:Might be useful as an antibody test, including for vaccine efficacy investigation 

Main limitations: 

  • No blinding of samples before experiments, and previous vaccine study in animal models which was referenced also had no blinding. 

  • No descriptions of repeats, or mention of duplicates or triplicates for ELISAs 

  • Low numbers of animals for each test 

  • Barely anything done with SPR assay - did not use purified IgG or sera to validate assay 

  • No rationale for the steps taken in the study and unclear descriptions and figures 

  • No comparison between their competitive ELISA and a sandwich ELISA to show sera/purified IgG/ACE2 binding to SARS-CoV-2 RBD, matrix effects, and quantification.