Fig. 2: AMP-CpG immunization generates long-lived memory T cell responses that rapidly expand upon antigen re-exposure in mice.

C57Bl/6 J mice (n = 5) were immunized twice with 10 µg WH-01 RBD protein and 1 nmol soluble or AMP-CpG. a, b 17 weeks post dose 2, blood was collected for a pre-recall time point, followed by subcutaneous challenge with 10 µg WH-01 RBD protein on the next day, and a second blood collection 7 days later. a Pre-challenge peripheral blood leukocytes were stained for CD44 and CD62L. Shown are percentages of tetramer⁺ CD44⁺ CD62L⁺ cells among CD8⁺ T cells. b Peripheral blood CD8⁺ T cells collected before and after challenge were stained with tetramer specific for Spike RBD and analyzed by flow cytometry. c–g 30 weeks post dose 2, mice were challenged subcutaneously with 10 µg WH-01 RBD protein and assayed 7 days later. CD8⁺ T cells collected from blood (c) and perfused lung (e), and CD4⁺ T cells collected from blood (d) and perfused lung (f) were stimulated with WH-01 RBD OLPs and assayed for intracellular cytokines by flow cytometry. g Splenocytes were restimulated with WH-01 RBD OLPs and assayed for IFNγ production by ELISpot. Mock vaccines contained AMP-CpG without the addition of antigen. Values depicted are means±standard deviation. ^*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 tetramer⁺ or cytokine⁺ T cell frequencies, or SFC numbers (a–g).