The hMAbs used in this study were generated and purified as described (22 (link)). CB6, REGN10987, and REGN10933 hMAbs were included as controls (25 (link), 26 (link)). To test the neutralizing activity of hMAbs, confluent monolayers of Vero E6 cells (4 × 104 cells/well, 96-plate well format, quadruplicates) were infected (MOI of 0.01 or 0.1) with the indicated rSARS-CoV-2 for 1 h at 37°C. After viral absorption, postinfection media containing 3-fold dilutions of the indicated hMAbs (starting concentration of 500 ng/well) were added to the cells and incubated at 37°C for 48 h. Cells were then fixed in 10% neutral buffered formalin overnight and washed with PBS before fluorescence signal was measured and quantified using a Synergy LX microplate reader and Gen5 data analysis software (Bio-Tek). The mean and SD of viral infections were calculated from individual wells of three independent experiments conducted in quadruplicates with Microsoft Excel software. Nonlinear regression curves and NT50 values were determined using GraphPad Prism Software (San Diego, CA, USA; version 8.2.1). Representative images were captured with an EVOS M5000 imaging system (Thermo Fisher) at ×10 magnification.