Development of a competitive ELISA kit for evaluation of SARS-CoV-2 neutralizing antibody capacity in vaccinated individuals

ABSTRACT

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has been devastating human lives since 2019.While each country carries out their vaccination program, many of them also continue to work on vaccine development. Determination of SARS-CoV-2 neutralizing antibodies offers important information for evaluating immune responses to the virus. Neutralization capacity can contribute to the understanding of subjects such as the immune status of individuals, the need for revaccination, relapse and recovery from the disease, as well as evaluation of vaccine efficacy. Neutralizing antibodies block the virus by preventing the interaction of the virus's S protein receptor binding domain (RBD) with human angiotensin converting enzyme-2(ACE-2). The most commonly used methods for the detection of neutralizing antibody titer are cell culture experiments with the virus such as the plaque neutralization assay. While these tests require biosafety level 3 conditions, ELISA tests can be performed in general laboratory without any sterile environment. Furthermore, while traditional methods take 2-3 days, ELISA stands out with its ease of application and can give results in just 90 minutes. In this study, we developed a prototype ELISA kit which is based on the principle of blocking the protein-protein interaction between RBD-HRP and ACE-2 with a possible neutralizing antibody in serum. For this purpose, the RBD protein was first labeled with horseradish peroxidase (HRP). Optimum use concentrations of RBD-HRP protein and human serum in the selected dilution buffer and the amount of ACE-2 protein to be coated on the ELISA plate were determined. As a result of repeated studies with a large scale of serum, the coefficients of variation(CV) for intra/inter-assay were calculated as 10% and 12%, respectively. Preliminary results of accelerated shelf-life studies showed that the ELISA kit maintained its shelf life up to 1 year at +4°C.