Figure 2: Effect of Ido1 expression on tumor growth and spontaneous metastasis formation. (a) BALB/c mice were inoculated s.c. with 1 × 105 cells/mouse of 4T1/vector or 4T1/Ido1− tumor cells, and tumor growth was monitored. (b) Percentage of surviving mice bearing 4T1/vector and 4T1/Ido1− tumors. (c) Cytotoxic activity of spleen cells from mice bearing 4T1 or 4T1/Ido1− tumors against 4T1 and 4T1/Ido1− tumor cells. Spleen cells from mice bearing 4T1/vector or 4T1/Ido1− tumors were cultured with irradiated 4T1/vector tumor cells and 300 IU/mL of IL-2 for 5–8 days. The cytotoxic activity of the spleen cells was tested against 51Cr-labeled 4T1 or 4T1/Ido1− cells at the E : T ratio 100 : 1. (d) Growth of 4T1 and 4T1/Ido1− tumors in immunocompetent BALB/c and immunodeficient SCID-beige mice.