Development of in vitro plaque-based assay for assessment of antibody-dependent enhancement in SARS-CoV-2 infection

Abstract

Antibody-dependent enhancement (ADE) of infection is a concerning phenomenon in SARS-CoV-2 infection, since it may develop disease severity. Although ADE has been demonstrated in animal models, the pathogenic mechanism has not been fully elucidated. The present study aimed to develop a simple assay system for detecting SARS-CoV-2 ADE activity in any antibody specimen. Vero E6/TMPRSS2/FcγRIIA, a Vero E6 cell strain expressing TMPRSS2 and FcγRIIA, was established. Seventeen plasma samples from convalescent patients and seven commercial antibodies were used as antibody specimens. Vero E6/TMPRSS2/FcγRIIA cells, infected with SARS-CoV-2 in the presence of antibody, were shown to exhibit ADE activity, with the plaque number increasing dramatically compared with the control in the absence of antibody specimens. Most plasmas displayed both ADE and neutralizing activities. Furthermore, 6 commercial antibodies recognizing structural proteins (membrane, nucleocapsid, envelope, and spike [transmembrane and cytoplasmic domains] proteins and non-structural protein ORF7) showed no potential ADE activity, while a commercial antibody recognizing spike RBD displayed ADE activity. These results indicate that antibodies possessing neutralizing and/or enhancing activity might be generated by either viral infection or vaccination. The present ADE assay may help to evaluate the risk of disease severity for individuals upon future reinfection, vaccination and/or immunotherapy.