Fig. 4. Correlates of SARS-CoV-2 antibody titers 28 days after second dose of vaccine.

a,b, Linear model effect size estimates indicate strength of association between spike-specific (RBD⁺S1⁺) cell frequency in the cell clusters (rows) with antibody endpoints (IgA and IgG titers for S-2P and RBD) relative to pre-vaccination baseline level (v1D0) at four timepoints between v1 and v2 (a), and relative to v2 baseline (v2D0) at four timepoints after v2 (b). Only clusters with at least one significant (unadjusted p ≤ 0.05) association at any timepoint are shown. At each timepoint, clusters that had fewer than five samples with any RBD⁺S1⁺ cells were excluded from analysis (missing boxes). c-e, Scatter plots illustrating correlations between endpoint (v2D28) RBD IgG titers and RBD⁺S1⁺ cell frequencies in C9 on v2D7, C6 on v2D0, and C2 on v2D14, respectively. Effect sizes and p values were estimated by the linear models above. FDR estimate of the statistical significance was calculated within each antibody endpoint and timepoint combination. f, Effect size estimates of association between first principal component (PC1) of endpoint SARS-CoV-2 antibody titers and frequencies of each cell cluster as a fraction of total CD19⁺ cells. PC1 was derived from IgA and IgG titers against S-2P and RBD proteins at v2D28. Only cell clusters with at least one significant (unadjusted p ≤ 0.05) association at any timepoint are shown. D, day; FDR, false discovery rate; RBD, receptor binding domain; rho, Spearman’s rank correlation; S1, spike subunit 1; S-2P, stabilized spike trimer; v, vaccine dose.