Quantitation of SARS-CoV-2 neutralizing antibodies with a virus-free, authentic test (preprint)

ABSTRACT

Neutralizing antibodies (NAbs), and their concentration in sera of convalescents and vaccinees are a solid correlate of protection from COVID-19. The antibody concentrations in clinical samples that neutralize SARS-CoV-2 are difficult and very cumbersome to assess with conventional virus neutralization tests (cVNTs), which require work with the infectious virus and biosafety level 3 containment precautions. Alternative virus neutralization tests currently in use are mostly surrogate tests based on direct or competitive ELISA formats or use viral vectors with the spike protein as the single structural component of SARS-CoV-2. To overcome these obstacles, we developed a virus-free, safe and very fast (4.5 h) in vitro diagnostic test based on engineered yet authentic SARS-CoV-2 virus-like-particles (VLPs). They share all features of the original SARS-CoV-2 but lack the viral RNA genome and thus are non-infectious. NAbs induced by infection or vaccination, but also potentially neutralizing monoclonal antibodies can be reliably quantified and assessed with ease and within hours with our test, because they interfere and block the ACE2-mediated uptake of VLPs by recipient cells. Results from the VLP neutralization test (VLPNT) show excellent correlation to a cVNT with fully infectious SARS-CoV-2 and allow to estimate the reduced neutralization capacity of COVID-19 vaccinee sera with variants of concern of SARS-CoV-2.