a, Schematic of LIBRA-seq with ligand blocking applied to cross-reactive antibody discovery. b, For identification of cross-reactive coronavirus antibodies with ligand-blocking capabilities, all IgGs recovered from the LIBRA-seq experiment (n = 2,569) are shown, with LIBRA-seq scores for SARS-CoV (x axis) and SARS-CoV-2 (y axis). Each dot represents a cell, and the color of the dots shows the ACE2 LIBRA-seq score, with a color heat map shown on the right. c, Cells selected for expression and validation are shown in blue (ACE2 score < –1) or gray (ACE2 score ≥ –1). Of these selected cells, eight had high LIBRA-seq scores (>1) for SARS-CoV-2 and SARS-CoV and low scores (<–1) for ACE2. Additional candidates with a variety of scores for SARS-CoV-2, SARS-CoV and ACE2 were also selected for expression and validation as controls. d, The eight IgGs with high LIBRA-seq scores for SARS-CoV-2 and SARS-CoV and low scores for ACE2 are shown above the dotted line. Control antibodies with other LIBRA-seq score patterns are shown below the dotted line. For each antibody, complementarity-determining region (CDR) sequences and lengths are shown at the amino acid level, and V-gene and J-gene identities are shown at the nucleotide level. LIBRA-seq scores for antigens included in the screening library (SARS-CoV-2 S, SARS-CoV S, ACE2, HIV ZM197 envelope and influenza hemagglutinin H1 NC99) are shown as a heat map; the heat map is colorized from negative (tan) to zero (white) to positive (purple). Scores outside of this range are shown as the minimum and maximum values. e,f, ELISA AUC values from binding to coronavirus S proteins, influenza hemagglutinin H1 NC99 (negative control) (e) and recombinant antigen domains (f) are shown as heat maps from minimum (white) to maximum (purple) binding. g, Percent reduction in ACE2 binding by ELISA is shown for SARS-CoV-2 and SARS-CoV S proteins and displayed as a heat map from 0% (white) to 100% (blue). h, For the eight IgGs with high LIBRA-seq scores for SARS-CoV-2 and SARS-CoV and low scores for ACE2, the percent reduction in ACE2 binding due to antibody blocking by ELISA is shown for SARS-CoV (x axis) and SARS-CoV-2 (y axis).