Fig. 8. SpiN-induced protective immunity to the Delta and Omicron variants of SARS-CoV-2.

K18-hACE2 mice were vaccinated with SpiN associated to Poly ICLC and challenged 30 days after the second dose with 5 × 10⁴ PFU of Delta (a, b) or 2.5 × 10⁴ PFU of Omicron (c, d) variants. Body weight (a, c) and survival (b) were measured for 11 days. d Viral load was measured by RT-PCR at 6 dpi with Omicron, data are presented as mean + /- SEM. a–e 6 mice/group. e Photomicrographs of lung tissue from mice infected with SARS-CoV-2 Omicron strain. Furthermore, in control mice that received Poly ICLC only, the lungs showed a diffuse interstitial pneumonia characterized by a mixed inflammatory infiltration (mononuclear and polymorphonuclear cells), accompanied by intense congestion (black arrows), intra-alveolar exudate (white arrows with black outline), hemorrhagic foci (white star) and areas of alveolar collapse (asterisks) (e, top panels). In the immunized group it is noted the preservation of the pulmonary architecture, with the presence of predominantly mononuclear inflammatory infiltrate (e, bottom panels). a–e Data are representative of two independent experiments. Statistical analysis of viral load (d) was performed with Two-way ANOVA followed by Sidak’s multiple comparisons test. **** P < 0.0001.