SARS-CoV-2 Spike Pseudotype Neutralization Assay

SARS-CoV-2 spike-pseudotyped lentivirus-neutralization assays were performed as previously described^{30 (link)}, with the following slight modifications. Infections were carried out in poly-l-lysine- (P4707, Millipore Sigma, Burlington, MA, USA) coated black-walled, clear-bottom plates (655090, Greiner Bio-One, Kremsmünster, Austria), and luciferase activity was measured in these plates without transferring to opaque-bottom plates. Sera were diluted 3-fold 7 times starting at a 1:25 dilution, and luciferase activity was measured at 52 h post infection. Target cells were HEK-293T cells transduced to express hACE2^{30 (link)} (BEI Resources, NR-52511). Samples were run in duplicate, and each plate included two no-serum controls. Fraction infectivity was calculated by normalizing the luciferase reading for each sample by the average of the two no-serum control wells in the same row. Neutralization curves were plotted using the neutcurve Python package (https://jbloomlab.github.io/neutcurve/, 0.3.1). This package fits a three-parameter Hill curve, with the top baseline fixed to one and the bottom baseline fixed to zero. The neutralization curves are shown in Supplementary Fig. 1.