Extended Data Fig. 3: Flow-cytometry of human anti-RBD memory B cells.

a, Gating strategy for flow-cytometry phenotyping. Gating was on single lymphocytes that were CD19⁺ and CD20⁺, and CD3⁻ CD8⁻ CD16⁻ Ova⁻ without uptake of live-dead dye (L/D). Antigen-specific cells were those with dual binding to Wuhan-Hu1 RBD-PE and RBD-AF647. Anti-IgG, -IgM were used to phenotype dual RBD-labelled B cells. b,c, Representative flow-cytometry plots of Wuhan Hu-1 RBD-binding memory B cells from mAb recipients after one and two doses of vaccination (b) and pre-pandemic health donors (c) serving as negative controls. Numbers in RBD-gate denote percentage of RBD dual-labelled cells of parent gate (see a). Corresponding flow-cytometry plots and gating strategy for vaccinated controls can be found in¹¹. d-e, Number of IgG- (d) and IgM-expressing (e) WT RBD-specific memory B cells per 10 million CD20⁺ B cells. Each dot represents one individual from the mAb recipient (green, n = 18) and control group (blue, n = 10)^9,11. Horizontal red bars denote median values. f-i, Panels show the correlation of C135-LS (f, g) and C144-LS (h,i) serum levels at day 84 post-administration (around the times of vaccination as seen in Fig. 1b) with the percentage of WT RBD-specific memory B cells expressing either IgG (f, h) or IgM (g, i) after two vaccine doses as assessed by flow-cytometry. Green dots represent individual mAb recipients (n = 18). Statistical significance was determined using the two-tailed Mann-Whitney for d and e, and the Pearson r correlation statistic was used for f-i.