SARS-CoV-2 Neutralizing Antibody Assay

Detection of plasma antibodies that can neutralize a pseudotyped VSV virus expressing the SARS-CoV-2 S protein was performed as previously described (8 (link)). Briefly, various dilutions of heat-inactivated plasma were incubated with 10⁴ PFU of VSV-SARS-CoV-2-S_△21 virus for 1 hour at 37°C. Antibody-virus complexes were added to Vero E6 cells and incubated for 7.5 h at 37°C. Cells were then fixed and stained with Hoechst 33342 nuclear stain (Invitrogen). Images were acquired with the InCell 2000 Analyzer (GE Healthcare) automated microscope to visualize nuclei and infected cells (eGFP-positive cells). Images were analyzed in InCell Analyzer 1000 Workstation Software (GE Healthcare) and data were processed using Prism version 8 (GraphPad Software, Inc).