Data analysis software 10

RBD-mAb binding was assessed using an Octet^® RED96 system (ForteBio) with integrated data acquisition software 10.0. Streptavidin (SA) biosensors (Sartorius #18-5019) were saturated with biotinylated original RBD recombinant protein (Acrobiosystems #SPD-C82E9) in 1X Kinetics Buffer (Sartorius #18-1105). The RBD loaded SA biosensors were then dipped in 3-fold serially diluted mAbs with the initial concentration of 15 μg/ml in 1X Kinetics Buffer for up to 300 s for association, followed by immersion in 1X Kinetics Buffer alone for another 300–600 s for dissociation. In epitope binning experiments, the RBD loaded SA biosensors were dipped in 17B10 mAb (50 μg/ml in 1X Kinetics Buffer) for 600 s. After briefly washing in 1X Kinetics buffer for 60 s, the loaded biosensors were dipped in competing mAbs (50 μg/ml in 1X Kinetics Buffer) for another 600 s. Any binding shift indicates competing mAb targets a different epitope from 17B10. A spike-specific rabbit polyclonal Ab^{29 (link)} was used as the positive control. All steps were conducted at 26°C with constant shaking at 1,000 RPM. Collected data were analyzed using a built-in 1:2 global curve-fitting model and the Kd values were calculated using ForteBio Data Analysis software 10.0.