Fig. 3. B_MEM cells of individuals double- and triple-vaccinated with BNT162b2 broadly recognize VOCs and are further boosted by Omicron BA.1 breakthrough infection.

PBMC samples from double-vaccinated individuals (BNT162b2²) at 22 days after the second dose (green, open squares) and 5 months after the second dose (green, open circles), from triple-vaccinated individuals (BNT162b2³) at 84 days after the third dose (green, closed circles), from double-vaccinated individuals with Omicron breakthrough infection (BNT162b2² + Omi) at 46 days post-infection (purple, open triangles), and from triple-vaccinated individuals with Omicron breakthrough infection (BNT162b2³ + Omi) at 44 days post-infection (purple, closed triangles) were analyzed via flow cytometry for SARS-CoV-2-specific B_MEM cell (B_MEM – CD3^-CD19⁺CD20⁺IgD^-CD38^int/low) frequencies via B cell bait staining. (a) Schematic of one-dimensional staining of B_MEM cells with fluorochrome-labeled SARS-CoV-2 S glycoprotein tetramer bait allowing discrimination of variant recognition. Frequencies of Wuhan or VOC full-length S glycoprotein- (b) and RBD- (c) specific B_MEM cells for the four groups of individuals were analyzed. Variant-specific B_MEM cell frequencies were normalized to Wuhan frequencies for S glycoprotein (d) and RBD (e) binding. (f) The frequency ratios of RBD protein-specific B_MEM cells over full-length S glycoprotein-specific B_MEM cells are depicted. Mean values and standard error of the mean (SEM) are shown in (b)-(f). Statistical comparisons between individuals of each group presented in (b) and (c) were performed using the nonparametric Friedman test with Dunn’s multiple comparisons correction presented in fig S4 (a-j). n = number of individuals per group. Schematic in (a) was created with BioRender.com.