Extended Data Fig. 1: Isolation and characterization of antibodies.
a, Demographics of study subjects. PBMCs were collected from 6 confirmed COVID-19 patients in hospital at a mean duration of 14 (±7) days after symptom onset. b, Construction and screening of phage antibody display libraries. A total of 6 convalescent patients’ PBMCs were collected. The 6 scFv phage libraries displaying the variable regions of antibody heavy chain (VH) and light chain (VL) were established from the individual convalescent patient’s PBMC. The phage libraries screening used the SARS-CoV-2 RBD recombinant protein as a bait. Based on monoclonal phage ELISA, positive binding clones of single phage were sequenced and the pairs of VH/VL were reconstructed into human IgG1 antibodies for expression. Finally, the purified antibodies were functionally verified. c, Polyclonal phage ELISA binding activities (mean ± SD) of the unpanned, 1st panned and 2nd panned phage libraries using SARS-CoV-2 RBD. Control used an unrelated antigen. Data are shown from a single experiment with 2 replicates. d, The 6 strongest binding single phages were colored among the 497 reactive clones from the 2nd panning. e, RBD binding activities (mean ± SD) of the 6 isolated monoclonal antibodies (mAbs) by ELISA. f, Neutralization activities (mean ± SEM) of the 6 mAbs against SARS-CoV-2 pseudovirus. Data are shown from a single experiment with 3 replicates (e, f). g, Binding kinetics of six candidate antibodies to the SARS-CoV-2 RBD were measured by biolayer interferometry (BLI) with antibody immobilized on the biosensor and RBD in solution. The black lines represent the experimentally recorded sensorgram traces, the colored lines represent fittings to the sensorgram traces. A 2-fold RBD dilution series (200 nM to 3.125 nM) were used in the BLI assays, detailed binding kinetics parameters were summarized in Supplementary Table 5. h, Competitive binding between R1-32 and ACE2 to the SARS-CoV-2 RBD as assessed by BLI. Biosensors immobilized with SARS-CoV-2 RBD were first saturated with R1-32 (upper panel) or ACE2 (lower panel) as indicated by the dashed lines, and then dipped into R1-32 (red) or ACE2 (blue) solutions of the same concentration. An ACE2 competing antibody B38 (orange) or buffer (green) were used as controls. Controls without binding of the first ligand were also included (purple). i, Characteristics of isolated antibodies. EC50 and KD of antibody binding to SARS-CoV-2 RBD measured by ELISA (data shown in e) and BLI (data shown in g) respectively were summarized. Sequence analysis of antibodies was performed by IMGT.
