FIG 3.

Specific antibody responses in mice after immunization with DNA vaccines. (A) Mouse immunization and sample collection schedule. Six- to eight-week-old female BALB/c mice (n = 9) were intramuscularly immunized with three doses of 100 µg of asd-pVAX1-S1, asd-pVAX1-S1-fliCΔD2D3, empty vector, or PBS administered at 2-week intervals. Serum samples were collected at the indicated time points after immunization. (B) S1-specific IgG in the mouse sera on day 40, as determined by ELISA. (C) NAb against the SARS-CoV-2 pseudovirus as evaluated by a neutralization assay. SARS-CoV-2 pseudovirus-specific NAb titers were determined for sera samples collected on day 40 from mice immunized with the indicated vaccine candidate or control. S1-specific IgG1 titer (D) and IgG2a titer (E) on day 40, as evaluated by ELISA. *P < 0.05, **P < 0.01, and ***P < 0.001 were considered significant.