Fig. 1: AMP-CpG immunization elicits potent, long-lived immunity to SARS-CoV-2 in mice.

a Schema showing animal dosing and experimental schedule. C57Bl/6 J mice were immunized twice with 10 µg WH-01 Spike RBD protein and 1 nmol soluble or AMP-CpG. b Splenocytes were restimulated with Spike RBD OLPs 7 days post booster dose and assayed for IFNγ production by ELISpot. Shown is the frequency of IFNγ SFCs per 1 × 10⁶ splenocytes. Flow cytometric analysis of cytokine production by CD8⁺ (c, e, g) and CD4⁺ T cells (d, f, h). Shown are percentages of cytokine⁺ cells among CD8⁺ or CD4⁺ T cells: peak responses 7 days post booster dose in peripheral blood (c, d), and perfused lung tissue (e, f), and longitudinal analysis over 32 weeks in peripheral blood (g, h). Serum anti-RBD IgG titers were determined against WH-01 RBD (i) and Delta RBD (j) protein. Mock vaccines contained AMP-CpG without the addition of antigen. Values depicted are means±standard deviations. ^*p < 0.05, ^**p < 0.01, ^***p < 0.001, ^****p < 0.0001 by one-way ANOVA followed by Tukey’s post-hoc analysis applied to cytokine⁺ T cell frequencies or antibody titers (b–j).