Figure 2. SARS-CoV-2 mRNA vaccines generate durable and functional memory B cell responses.

A) Experimental design and B) gating strategy for quantifying the frequency and phenotype of SARS-CoV-2-specific memory B cells by flow cytometry. Antigen specificity was determined based on binding to fluorophore-labeled Spike, RBD, and influenza HA tetramers. C) Frequencies of SARS-CoV-2 Spike+, Spike+ RBD+, and influenza HA+ memory B cells over time in PBMC samples from vaccinated individuals. Data are represented as a percentage of total B cells and fractions above plots indicate the number of individuals above their individual baseline at memory timepoints. Decay rates were calculated using a piecewise linear mixed effects model with censoring. D) Frequency of isotype-specific Spike+ and E) Spike+ RBD+ memory B cells over time. F) Percent CD71+ of total Spike+ memory B cells over time. G) Experimental design for differentiation of memory B cells into antibody secreting cells. H) anti-Spike IgG levels in culture supernatants over time from PBMCs stimulated with PBS control or R848 + IL-2 (n=4). I) anti-Spike IgG levels in culture supernatants after 10 days of stimulation J) Correlation of Spike+ memory B cell frequencies by flow cytometry with anti-Spike IgG levels from in vitro stimulation. K) Correlation of anti-Spike IgG levels from in vitro stimulation with RBD-binding inhibition. For J and K, correlations were calculated using non-parametric Spearman rank correlation. Statistics were calculated using unpaired non-parametric Wilcoxon test with Holm correction for multiple comparisons. Blue and red values indicate comparisons within naïve or recovered groups.