Extended Data Fig. 4. Antibodies isolated from yeast sorts are cross-reactive.

(A) SDS-page analysis of of IgG proteins made from clones identified in the SARS-CoV-1 FACS sorts. MW ladders are in the left-most lanes of the two gels. (B) ELISA binding of IgG proteins made from scFv clones identified by FACS sorting for SARS-CoV-1 binding. Biotinylated hCoV antigens were plated and dilutions of IgGs were tested for binding. Normalized A₄₅₀ calculated by adjusting for pathlength. Except for COV2-2490, CV21, COVA2-18 all IgGs bind to SARS-CoV-2 and SARS-CoV-1. (C) BLI binding for the 7 identified SARS-CoV-1 cross-reactive clones against MERS (left) or OC43 (middle) spike proteins. Only COV2-2449 shows any binding affinity for MERS or weakly to OC43 spike proteins. No Fabs tested bind to the SARS-CoV-2 NTD, consistent with its low sequence conservation between SARS-CoV-2 and SARS-CoV-1.