Figure 6.

High-titer SARS-CoV-2 neutralizing antibody responses generated by capsid display of RBD

(A) BALB/c mice (six per group) were immunized intramuscularly in homologous prime-boost regimens as described. The RBD protein dose in groups 2 and 3 was calculated to be < 0.2 μg per mouse. (B) Serum IgG antibody responses to RBD at D20 measured by endpoint ELISA. (C) Serum IgG antibody responses to RBD at D35 measured by endpoint ELISA. (D) Fold increase in anti-RBD IgG titer post boost (D35 titer in C divided by D20 titer in B). (E) SARS-CoV-2 neutralization titers (pVNT assay) in D35 serum against Wuhan strain (WT) and variants of concern alpha (B.1.1.7), delta (B.1.617.2), and beta (B.1.351). Data on beta variant collected separately. (F) IFNγ-ELISpot response in spleen at D35 against peptide pool spanning SARS-CoV-2 S-RBD. (G) IFNγ-ELISpot response in spleen at D35 against peptides spanning full-length SARS-CoV-2 S protein (summed responses from two peptide pools spanning residues 1–643 and 633–1,273 are shown, responses from individual pools shown in Figure S8). Dashed lines represent limit of detection. Median responses shown by a horizontal line. Statistical analyses performed by Kruskal-Wallis with Dunn’s test for multiple comparisons, ∗p < 0.05; ∗∗p < 0.01; ∗∗∗p < 0.001; ns, not significant.