A Cellular Assay for Spike/ACE2 Fusion: Quantification of Fusion-Inhibitory Antibodies after COVID-19 and Vaccination
Fabien Abdul,
Pascale Ribaux,
Aurélie Caillon,
Astrid Malézieux-Picard,
Virginie Prendki,
Nathalie Vernaz,
Nikolay Zhukovsky,
Flavien Delhaes,
Karl-Heinz Krause,
Olivier Preynat-Seauve
Affiliations
Fabien Abdul
Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, 1 Rue Michel Servet, 1211 Geneva, Switzerland
Pascale Ribaux
Department of Pathology and Immunology, Faculty of Medicine, University of Geneva, 1 Rue Michel Servet, 1211 Geneva, Switzerland
Aurélie Caillon
Department of Pathology and Immunology, Faculty of Medicine, University of Geneva, 1 Rue Michel Servet, 1211 Geneva, Switzerland
Astrid Malézieux-Picard
Division of Internal Medicine for the Aged, Department of Rehabilitation and Geriatrics, Geneva University Hospitals, Chemin du Pont Bochet 3, 1226 Thônex, Switzerland
Virginie Prendki
Division of Internal Medicine for the Aged, Department of Rehabilitation and Geriatrics, Geneva University Hospitals, Chemin du Pont Bochet 3, 1226 Thônex, Switzerland
Nathalie Vernaz
Division of Clinical Pharmacology and Toxicology, Geneva University Hospitals, Rue Gabrielle-Perret-Gentil 4, 1205 Geneva, Switzerland
Nikolay Zhukovsky
Neurix SA, 64 Avenue de la Roseraie, 1205 Geneva, Switzerland
Flavien Delhaes
Department of Pathology and Immunology, Faculty of Medicine, University of Geneva, 1 Rue Michel Servet, 1211 Geneva, Switzerland
Karl-Heinz Krause
Department of Pathology and Immunology, Faculty of Medicine, University of Geneva, 1 Rue Michel Servet, 1211 Geneva, Switzerland
Olivier Preynat-Seauve
Department of Medicine, Faculty of Medicine, University of Geneva, 1 Rue Michel Servet, 1211 Geneva, Switzerland
Not all antibodies against SARS-CoV-2 inhibit viral entry, and hence, infection. Neutralizing antibodies are more likely to reflect real immunity; however, certain tests investigate protein/protein interaction rather than the fusion event. Viral and pseudoviral entry assays detect functionally active antibodies but are limited by biosafety and standardization issues. We have developed a Spike/ACE2-dependent fusion assay, based on a split luciferase. Hela cells stably transduced with Spike and a large fragment of luciferase were co-cultured with Hela cells transduced with ACE2 and the complementary small fragment of luciferase. Cell fusion occurred rapidly allowing the measurement of luminescence. Light emission was abolished in the absence of Spike and reduced in the presence of proteases. Sera from COVID-19-negative, non-vaccinated individuals or from patients at the moment of first symptoms did not lead to a significant reduction of fusion. Sera from COVID-19-positive patients as well as from vaccinated individuals reduced the fusion. This assay was more correlated to pseudotyped-based entry assay rather than serology or competitive ELISA. In conclusion, we report a new method measuring fusion-inhibitory antibodies in serum, combining the advantage of a complete Spike/ACE2 interaction active on entry with a high degree of standardization, easily allowing automation in a standard bio-safety environment.
