Figure 3. Cancer‐cell‐intrinsic type I IFNs are required for efficient 5‐FU‐induced reduction of tumor burden.

• A
  Control (Ctrl) or STING‐KO MC38 cells were treated in vitro with STING agonist cGAMP (left) for 6 h or 5‐FU (right) or relevant vehicle controls for 24 h. The expression of indicated genes was determined by qRT–PCR. N = 3.
• B
  Ctrl or STING‐KO CT26 cells were treated with 5‐FU or vehicle control for 24 h. The RNA expression levels of indicated genes were determined by qRT–PCR. N = 3.
• C
  Ctrl or STING‐KO YUMM1.7 cells were treated with (left panel) vehicle control (DMSO) or DTIC, or (right panel) PBS or 5‐FU for 24 h. The expression of indicated genes was determined by qRT–PCR. N = 3.
• D
  Western blot analysis was performed with Ifnα and GAPDH antibodies, for control (Ctrl) and Ifna1‐Ifnb1‐double KO (Ifn‐DKO) MC38 cells. Two independent KO clones are shown.
• E
  MC38 Ctrl or Ifn‐DKO cells were treated with (left panel) control or the STING agonist DMXAA for 4 h, or (right panel) control or 5‐FU for 16 h. Ifnβ levels were determined in harvested culture media by ELISA. N = 2.
• F–H
  Mice were injected with Ctrl MC38 cells or Ifn‐DKO cells and treated with 5‐FU or PBS. (F) Pictures of tumors and spleens from a representative experiment. Image panels were cropped from the same picture. (G) Tumor volumes were quantified at the indicated days after cancer cell injection. N = 5. (H) Tumor and spleen weights at the endpoint for (G), with each dot representing a mouse.

Data information: For all panels, error bars stand for SD, and center values represent mean. Two‐tailed unpaired Student’s t‐test was used. **P < 0.01; ***P < 0.001; ****P < 0.0001; ns: not significant. Data are representative of two or more independent experiments.