mRNA booster vaccination protects aged mice against the SARS-CoV-2 Omicron variant

Figures

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  Fig. 1. Study design outlining longitudinal immunization of mRNA BNT162b2 across the lifespan. Schematic representation of the study design showing three mouse age groups (a) and treatments within each age group (b). Three- and 11-month-old BALB/c mice were included in the study at week 0 and received the following treatments: mock PBS injection (naive); primary mRNA vaccination series at weeks 32–34 (recent vax); primary vaccination series at weeks 0–2 (distant vax); and primary vaccination series at weeks 0–2 with booster dose at week 34 (booster vax). Additionally, 3-month-old BALB/c mice were enrolled in the study at week 32 and received the following treatments: mock PBS injection (naive); and primary vaccination series at weeks 32–34 (recent vax). N = 20 per group at enrollment. Serum samples were collected at week 36. Splenocytes were collected at week 36 from N = 4–7 mice per group. Mice were challenged with SARS-CoV-2 Omicron strain at week 38 (N = 5–9 per group). The graphics were created with BioRender.com.

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  Fig. 2. A booster dose of mRNA BNT162b2 restores waning humoral responses in aged mice and elicits potent neutralizing activity against SARS-CoV-2 Omicron. Sera were collected from immunized mice at week 36 to determine humoral responses as indicated in Fig. 1. Anti-WT spike IgG titers (a), hACE2-RBD (WT) inhibition rate (b, c), and neutralization titers against WT, Delta, and Omicron pseudoviruses (d, e) were determined. Results are presented as individual values with mean (a, d) or median (b, c). Dashed lines represent lower limit of detection. Data were analyzed by one-way ANOVA after log-transformation (a, d) or Kruskal–Wallis test (b, c) corrected for multiple comparisons. * indicates comparisons within the same age group and # indicates comparisons between different age groups. (a–c) N = 19–20 per group for 5 and 13 M aged mice, and N = 13–17 per group for 21 M aged mice. e Horizontal lines and numbers indicate geometric mean titers (GMTs). For GMT calculation, an arbitrary value of 10 was assigned to samples with values below the detection limit of 20. Dashed lines represent lower limit of detection. d, e N = 6–8 per group except for Naive mice (N = 3).*/#P < 0.05, **/##P < 0.01,…

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  Fig. 3. A booster dose of mRNA BNT162b2 elicits robust T cell responses that cross-recognize SARS-CoV-2 Omicron in aged mice. SARS-CoV-2 spike specific T cell responses were analyzed at week 36 as indicated in Fig. 1. Splenocytes were restimulated with overlapping spike peptides from Omicron (a–e) and wildtype (e) SARS-CoV-2, and expression of intracellular interferon-γ (IFNγ), IL-2, and TNF among CD4+ and CD8+ T cells were determined by flow cytometry. N = 6–7 per group, except for 21 M Distant vax and Booster groups (N = 4). a, b Frequencies of IFNγ and IL-2 positive T cells among CD4+ (a) and CD8+ (b) T cells are shown. c, d Frequency of mono-, double-, and triple- cytokine positive cells among CD4+ (c) and CD8+ (d) T cells are summarized. Lines represent mean ± SEM. Data were analyzed by one-way ANOVA corrected for multiple comparisons. # indicates for comparisons against naïve groups in the same age group. */#P < 0.05, **/##P < 0.01, ***/###P < 0.001, ****/####P < 0.0001. e Frequency of cytokine positive (expressing any of IFNγ, IL-2, and/or TNF) CD4+ and CD8+ T cells against wildtype or Omicron spike peptide pools were assessed. Each symbol represents one mouse. Omicron/wildtype…

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  Fig. 4. mRNA booster vaccination protects against lower respiratory infection by SARS-CoV-2 Omicron in aged mice. SARS-CoV-2 mRNA BNT162b2-immunized 5-, 13-, and 21-month-old mice were challenged intranasally with 105 plaque-forming units (PFU) of SARS-CoV-2 Omicron at week 38 as indicated in Fig. 1. Viral titers (a) and gene expression profiles of Rsad2 and Ifit2 shown as relative expression compared to Rlp13a (b) in lung homogenates at 2 days post challenge are shown. Bars represent geometric means. Pie charts show the proportion of mice within each group that had detectable virus in the lungs. Data were analyzed by Mann-Whitney test or Kruskal–Wallis test corrected for multiple comparisons. *P < 0.05, **P < 0.01, ***P < 0.001. N = 7–9 per group, except for 21 M Distant vax (N = 6) and 21 M Booster (N = 5) groups. c Correlations between lung PFU at 2 days post challenge and anti-spike IgG titer, hACE2-RBD inhibition rate, and pseudovirus neutralizing titers against SARS-CoV-2 WT and Omicron at week 36 are shown. Circles represent individual mice, and colors indicate the immunization regimens. Dotted lines indicate assay limits of detection. Black and gray lines respectively indicate…