Fig. 4: Generation of human anti-SARS-CoV-2 S1 antibodies that do not bind the RBD.
a, Human anti-S1 antibody discovery. B cells were negatively selected from PBMCs 7 days after the second BNT162b2 vaccine dose and then used in the workflow. RBD/S1-specific ASCs were sorted with fluorescently labeled RBD- and S1-streptavidin tetramers. b, Index sorting of S1-specific human ASCs. Layout for sorting of IgG- or IgA-secreting ASCs isolated on day 7 post vaccination with fluorescently labeled S1- and RBD-streptavidin tetramers. Based on index sorting, the ratio of the S1/RBD fluorescence signal was calculated for all sequenced cells, and four sequences that corresponded to events with the highest S1/RBD fluorescence signal ratio were selected for expression (highlighted as red squares). The plot shows 719 events at a 5% contour level, and the percentage of events in each window is indicated. c, Characteristics of human anti-S1 antibodies—variable domain genes (V and J), third complementarity-determining region amino acid sequences (CDR3), equilibrium dissociation constants (KD) and IC50 against WT SARS-CoV-2. En dashes (–) denote that binding or inhibition was not quantifiable at the tested concentrations. d, Anti-S1 and anti-RBD ELISA of anti-S1 antibodies. An RBD-binding positive control (human IgG1κ, clone AM001414; BioLegend) is shown in black, and an isotype control (human IgG1κ, clone QA16A12; BioLegend) is shown in gray. The table shows the EC50 with an antibody concentration range of 0.0002–400 nM. The plots show mean values ± s.d. of two independent experiments performed in duplicate.
