Figure 3. Mosaic-8b immunizations in mice previously immunized with an mRNA-LNP vaccine elicit cross-reactive Ab responses, related to ^{Figure S3}.

For experiments shown schematically in panels A and D, binding responses at day 0 (immediately prior to nanoparticle or other vaccine immunizations) showed significant differences across cohorts in titers elicited by the pre-vaccinations. We therefore applied baseline corrections to account for different mean responses at day 0 prior to immunizations in each of the four groups for data in panel B and each of the three groups for data in panel E (see Methods). Non-baseline corrected binding data for panel E are shown in Figure S3G.

Geometric means of fold change in ED₅₀ or geometric means of ID₅₀ values for all animals in each cohort are indicated by symbols connected by thick colored lines. Mean titers against indicated viral antigens or pseudoviruses were compared pairwise across immunization cohorts by Tukey’s multiple comparison test with the Geisser-Greenhouse correction (as calculated by GraphPad Prism). Significant differences between cohorts linked by vertical lines are indicated by asterisks: p<0.05 = *, p<0.01 = **, p<0.001 = ***, p<0.0001 = ****.

(A) Left: Schematic of vaccination/immunization regimen for panels B and C. Mice were vaccinated at the indicated days prior to RBD-nanoparticle prime and boost immunizations at days 0 and 28 or mRNA-LNP prime immunization at day 0. Right: Phylogenetic tree of selected sarbecoviruses calculated using a Jukes-Cantor generic distance model using Geneious Prime^® 2023.1.2 based on amino acid sequences of RBDs aligned using Clustal Omega.⁹⁷ RBDs included in mosaic-8b are highlighted in gray rectangles.

(B) Geometric mean fold change ELISA binding titers at the indicated days after immunization with mosaic-8b, admix-8b, homotypic SARS-2, or WA1 mRNA-LNP against indicated viral antigens.

(C) Geometric mean neutralization titers at the indicated weeks after immunization with mosaic-8b, admix-8b, homotypic SARS-2, or WA1 mRNA-LNP against indicated sarbecovirus pseudoviruses.

(D) Schematic of vaccination/immunization regimen for panels E and F. Mice were vaccinated at the indicated days prior to RBD-nanoparticle prime and boost immunizations at days 0 and 28 or mRNA-LNP prime immunization at day 0.

(E) Geometric mean fold change ELISA binding titers at the indicated days after immunization with mosaic-8b, mosaic-7, or WA1/BA.5 mRNA-LNP against indicated viral antigens. Compare with Figure S3G (non-baseline corrected geometric mean ELISA binding titers).

(F) Geometric mean neutralization titers at the indicated weeks after immunization with mosaic-8b, mosaic-7, or WA1/BA.5 mRNA-LNP against indicated sarbecovirus pseudoviruses.