Figure 4

Intradermal administration of GP∆-delta DNA vaccine protects mice from SARS-CoV-2 delta variant infection. (a) Animal protocol for intradermal administration of the GP∆-delta DNA vaccine in female SP-C KI mice. The GP∆-delta DNA vaccine was intradermally injected through PJI two times at 2-week intervals. Six weeks after the first dose, the SARS-CoV-2 delta strain was challenged to mice via intranasal inoculation. Two days-post infection, the lungs were extracted to determine virus infection using a TCID assay. (b) Antibody titer specific for the delta variant spike, as determined through ELISA. *p < 0.05 vs. control pVAX ID group (Student’s t-test). (c) The viral load, which was determined through a plaque assay in the lungs at 2 dpi. *p < 0.01 vs. control pVAX ID group (Student’s t-test). (d–h) The inflammatory chemokines (d) CCL2, (e) CXCL10, (f) CXCL11 and cytokines (g) TNFα, (h) IL6 expression in the lungs after SARS-CoV-2 challenge was evaluated using real-time qPCR. The value was normalized through GAPDH expression. *p < 0.05 vs. control pVAX ID group (Student’s t-test). (i, j) H&E staining of the lung sections at 2 dpi following SARS-CoV-2 infection. Bar = 200 μm. (i) control mice, (j) vaccinated mice. (k, l) Immunohistochemical staining with SARS-CoV-2 nucleocapsid antibody, (k) control mice, (l) vaccinated mice. Bar = 200 μm. Data are shown as mean ± SEM. See also Supplementary Figs. 5–8.