Figure 1

Formation of tumors by a challenge with CT26/HER2 tumor cells in HER2 DNA vaccine-immunized mice (A), and the tumor-forming (B,C) and immune cell stimulating (D) activity of CT26/HER2, CT26/HER2-A1 and CT26/HER2-A2 cells. (A) Mice (n = 5/group) were immunized at 0 and 1 weeks by IM-EP with 50 μg of HER2 DNA vaccines. At 2 weeks, the mice were challenged with 1 × 10⁶ CT26/HER2 cells per mouse. The tumor sizes were measured over time. The values and bars indicate mean tumor sizes and the SD, respectively. The values in (/) represent the number of mice displaying tumors at 28 days post-challenge/the number of mice tested. *p < 0.05 compared to pVAX1. (B,C) Each of the naïve (B, n = 4/group) and HER2 DNA vaccine-immunized mice (C, n = 4/group) was challenged s.c. with 3 × 10⁵ CT26/HER2 (upper left flank), CT26/HER2-A1 (lower left flank) and CT26/HER2-A2 (upper right flank) cells per mouse. HER2 DNA vaccine-immunized mice indicate the mice that were injected at 0 and 1 weeks by IM-EP with 50 μg of HER2 DNA vaccines and then re-immunized by IM-EP with HER2 DNA vaccines one week prior to a challenge with 3 different tumor cell types. The tumor sizes were measured over time. The values and bars indicate mean tumor sizes and the SD, respectively. *p < 0.05 compared to CT26/HER2. (D) Each of UV-exposed tumor cells (5 × 10⁵), CT26/HER2, CT26/HER2-A1 and CT26/HER2-A2 was incubated for 1 and 2 days with 6 × 10⁶ immune cells from naïve and HER2 DNA vaccine-immunized mice. HER2 DNA vaccine-immunized mice were obtained by injecting the mice with 50 μg of HER2 DNA vaccines by IM-EP, followed by a booster injection at 1 week following the first injection. One week after the final immunization, the mice were sacrificed to obtain immune cells. The cell supernatants were collected after 1 and 2 days of cell culture for an IFN-γ assay. The values and bars indicate mean IFN-γ amounts and the SD, respectively. *p < 0.05 compared to CT26. **p < 0.05 compared to control mice.