Identification of SARS-CoV-2 Neutralizing Potency of Human Convalescent Plasma Using Pseudovirus Neutralization Assay

Convalescent plasma samples that can be collected from individuals after the resolution of infection and vaccination are an invaluable source of neutralization antibodies against the virus. Although plaque reduction assay with replicative virus is the gold standard of analyzing neutralization potency of convalescent plasma, it is a technically demanding procedure requiring high biosafety level (BSL-3/4) laboratory and equipment. The abundance of neutralizing antibodies varies among individuals, therefore fast and reliable methods to identify neutralization potency of plasma samples are needed. In this paper, G-protein deficient vesicular stomatitis virus (VSV-ΔG) carrying a C-terminal 21 amino acid truncated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike protein was generated for pseudovirus neutralization assay. We analyzed SARS-CoV-2 neutralizing potency of vaccinated human convalescent plasma samples (n=13) and plasma samples of healthy people (n=2). Human convalescent plasma samples were examined against the ancestral Wuhan strain and two SARS-CoV-2 variants (B.1.1.7, and B.1.351) using a VSV-ΔG-Sdel21 pseudovirus and Vero E6 cell line. Neutralization values against pseudotyped virus were compared to those of plaque reduction assay against authentic virus. The serum neutralizing titer of convalescent plasma measured by pseudovirus assay has a good correlation with that measured by plaque reduction assay (R = 0.7). The pseudovirus assay is safer and timesaving than the replicative virus-based plaque reduction assay, and has several advantages in evaluating a new vaccine, newly emergent variants, and approved vaccine efficacy against variants of concern as well as in viral fusion-focused treatment analysis that can be performed under BSL-2 conditions.