Fig. 5. Immunization with CMS:O/W-adjuvanted RBD nanoparticle completely protects aged mice from SARS-CoV-2 challenge.

Aged (14-month-old) BALB/c mice were immunized on Day 0 (prime) and 14 (boost) with PBS, 0.3 µg of RBD nanoparticle (RBD-NP) alone or formulated with AddaVax, AddaS03, CMS:O/W, or AS01B, or 10 µg of monomeric RBD formulated with CMS:O/W. Seven weeks after the final immunization, mice were infected with 10³ plaque-forming units (PFU) of mouse-adapted SARS-CoV-2 and monitored for up to 4 days for weight loss. Daily weights (a) and weight loss at 4 days post infection (b) of infected mice are shown. c–e On Day 4, mice were euthanized, and lungs were collected to assess viral titers (c), hematoxylin and eosin-stained lung images (d), and gene expression profiles shown as relative expression compared to Rlp13a (e). N = 8–10 per group except for AS01B group (N = 4). a Results represent mean ± SEM. Data were compared to the PBS group by Kruskal–Wallis test corrected for multiple comparisons. b, c, e Data were analyzed by one-way ANOVAs corrected for multiple comparisons. Asterisks indicate comparisons to groups indicated by the color code. d Representative lung images are shown. Scale bar, 500 µm. Box-and-whisker plots represent the minimum, first quartile, median, third quartile, and maximum value. Each symbol represents an individual sample. *, **, ***, and **** respectively indicate p < 0.05, 0.01, 0.001, and 0.0001. Source data are provided as Supplementary Data.