Fig. 6: Protective immunity in mice immunized with the SpiN chimeric protein and challenged SARS-CoV-2.

Mice were challenged with the Wuhan strain of SARS-CoV-2. Body weight (a), survival (b) and viral load in lungs (c) and brain (d) were evaluated in K18-hACE-2 mice immunized with SpiN plus Poly ICLC and controls that received Poly ICLC alone. e Titers of nAbs in the sera from control and immunized mice at 5 dpi. Convalescent patients were used as positive control. c–e Data are presented as mean ± SEM. f Histopathological analysis at 2,5x, 5x, and 20x magnification of the lungs from Poly ICLC or SpiN + Poly ICLC groups, at 5 dpi. Black arrows: congestion; white arrows: intra-alveolar exudate; white star: hemorrhagic foci; asterisks: alveolar collapse; red arrows: inflammatory infiltrate. g, h mRNA expression of cytokines (g) and chemokines (h) quantified by qRT-PCR in mice lungs at 5 dpi. i–o, Frequency of myeloid (i) and lymphoid (j) as well as total numbers of neutrophils (k), monocytes (l), monocyte derived dendritic cells (m), resident CD8⁺ T cells (n) and conventional dendritic cells (o) in the lungs of control, vaccinated, challenged (infected) or not (NI) with SARS-CoV2 at 5 dpi. g–o Data are presented as mean ± SEM. a, b Individual values of pooled data from two independent experiments, Poly ICLC n = 4 and SpiN + Poly ICLC n = 7. c–o Data are representative of two independent experiments, n = 3 mice/group (c–h). i–o, n = 4 PBS N.I. and infected, n = 3 SpiN + Poly ICLC N.I., n = 6 SpiN + Poly ICLC infected. Statistical analysis of weight measurements (a) was performed using Two-way ANOVA. Survival analysis (b) was performed with Log–rank test. Data of viral quantification (c, d) was analyzed using Two-way ANOVA followed by Sidak’s multiple comparisons test. qRT-PCR data (g, h) was analyzed with unpaired two-tailed t tests. Flow cytometry of the lungs (i–o) was analyzed by Kruskal–Wallis followed by Dunn’s multiple comparisons test. * P < 0.05, ** P < 0.01, *** P < 0.001 and **** P < 0.0001.