Extended Data Fig. 5: WT RBD binding and WT SARS-Cov-2 neutralization by monoclonal pentameric IgM antibodies.

a-b, Panels depict WT RBD binding and WT SARS-CoV-2 S pseudotype neutralizing activity of a representative panels of monoclonal antibodies derived from IgM-expressing RBD-specific memory B cells expressed either as human IgG1 (IgG, as in Fig. 3a–c) or pentameric IgM (IgM⁵). a, Panel shows WT RBD EC50s of 15 monoclonal antibodies isolated from vaccinated mAb recipients (also see Supplementary Table 4). Grey shaded area between horizontal dotted lines indicates antibodies with EC50s >10 µg ml⁻¹ (poor binding) and non-binding antibodies arbitrarily grouped at 10 and 20 µg ml⁻¹, respectively. b, Plots show IC50s of 2 IgM-derived control antibodies (covering a wide range of neutralizing activity) in blue and 15 IgM-derived monoclonal antibodies from mAb recipients (as in a) in green, expressed as human IgG1 (IgG) or pentameric IgM (IgM⁵). For both panels (a, b), ring plots summarize the fraction of antibodies in the indicated category among all tested (encircled number). Red horizontal bars and numbers indicate median values. For panel a, statistical significance was determined using the two-tailed Wilcoxon matched-pairs rank test to compare differences between the same monoclonal antibodies expressed as IgG or pentameric IgM, and the Chi-squared contingency statistic was used to compare categorical distributions from ring plots.