A study led by researchers from the McGill University Health Centre and McGill University, who are also scientific advisors to the CITF, evaluated multiple assays that detect antibodies capable of neutralizing the SARS-CoV-2 virus. The study published in pre-print, was done in collaboration with the National Microbiology Laboratory, Héma-Québec, and Centre de Recherche du Centre hospitalier de l’Université de Montréal and was partially supported by the COVID-19 Immunity Task Force and the Canadian Institutes of Health Research.
The spike protein of SARS-CoV-2 mediates the virus’ entry into human cells. The region of the spike that binds to the cellular receptor to trigger entry is known as the Receptor Binding Domain (or RBD for short). Among the antibodies that individuals make in response to SARS-CoV-2 infection, or in response to vaccination, some have more impact than others. An important kind of antibody, called neutralizing antibodies, can bind to the spike RBD region, preventing it from binding to the human receptor, therefore blocking new infections. The presence of these antibodies in high levels is an indirect measure of protection and therefore developing assays that can detect them fast and reliably is imperative.
Classic neutralization assays have a few drawbacks: they require live virus, are time consuming, and few samples can be done at once. Alternative assays have been developed to overcome these limitations. They rely on the binding between the RBD of spike and the cellular receptor. These surrogate neutralization assays measure the loss of binding between these two proteins when in contact with sera containing neutralizing antibodies. This research team evaluated the cPass SARS-CoV-2 Neutralization Antibody Detection Kit from Genscript (cPass for short). Many reports suggest that the levels of neutralizing antibodies correlate to the levels of antibodies directed to the RBD region itself (as many of these are indeed neutralizing), and therefore, non-blocking ELISA assays detecting antibodies against RBD were included in the comparison as well.
When compared side-by-side, cPass performed similarly to a non-blocking anti-RBD ELISA. Both techniques yield very similar results when compared to classic neutralization assays, especially when high levels of neutralizing antibodies were present in the samples. The authors concluded that the added value of cPass compared to the cheaper anti-RBD ELISA assay that measures IgG was modest. Finally, the amounts of these antibodies needed to confer protection remains to be determined.
Read their pre-print here: https://www.medrxiv.org/content/10.1101/2021.01.23.21250325v2.full.pdf