Characterization of the neutralizing antibody response of COVID-19 recoverees

The coronavirus disease 19 (COVID-19) pandemic currently poses a challenge to the healthcare system and global public health. The upsurge of new SARS-CoV-2 variants, the uneven vaccine distribution worldwide, and the documented reinfections raise a concern about the protective immunity of COVID-19 recoverees. In this context, reliable methods for the detection of SARS-CoV-2 neutralizing antibodies are needed. Considering the methodological complexity and limitations of traditional virus neutralization tests, surrogate enzyme-linked immunosorbent assays (sELISA) constitute a promising alternative allowing high-throughput testing. However, there is still a need of assessing the specificity and sensibility of these assays so that they can be clinically applied. In this thesis, two goals were pursued; the detection of neutralizing antibodies in COVID-19 recoverees plasma samples using an in-house microneutralization assay and the comparison of these results with those obtained with two sELISA; SARS-CoV-NeutraLISA surrogate neutralization (Euroimmun) and cPass SARS-CoV-2 Neutralization Antibody Detection Kit (GenScript). The SARS-CoV-2 microneutralization assay was performed with VERO E6 cells and the Fin-1 strain of the SARS-CoV-2 virus. The plasma samples were provided by the Helsinki University Hospital and were previously screened with commercial IgG-ELISA targeting the anti-SARS-CoV-2 spike subunit 1 (Euroimmun) and nucleocapsid (Abbott) proteins. A total of 111 samples were tested, 74% of them presented a detectable NAb titer with at least two of the methods. The neutralizing antibody titer obtained with the microneutralization assays resulted in an overall proportion of positives lower than expected. Therefore, the in-house microneutralization assay needs further optimization or a different neutralization assay should be selected instead for future analysis. The combined data from the three tests was used to determine the sensitivity (99%, 83%, 81%) and specificity (72%, 100%, 100%) of cPass, Neutralisa and microneutralization assays respectively. This data suggests the use of cPass (GenScript) in primary screenings, in combination to Neutralisa (Euroimmun) to confirm secondary tests