MSI-H tumors hijack TREX1 to suppress the activation of tumor-intrinsic cGAS–STING pathway. (A) MC38 cells (n = 3/group) were collected for Ifnb1 mRNA detection by RT-qPCR. (B) The culture supernatants of MC38 cells (n = 3/group) were collected to detect IFNβ by ELISA. (C) The culture supernatants of 4T1, 4T1-Trex1^−/−, 4T1-Mlh1^−/− (day 115), 4T1-Mlh1^−/−Trex1^−/− (day 115), 4T1-Mlh1^−/−Sting^−/− (day 105), 4T1- Sting^−/−Trex1^−/−, and 4T1-Mlh1^−/−Sting^−/−Trex1^−/− (day 105) cells (n = 3/group) were collected to detect IFNβ by ELISA. (D) C57BL/6 mice (n = 5) were transplanted s.c. with 2 × 10⁶ MC38, MC38-Sting^−/−, MC38-Tbk1^−/−, MC38-Trex1^−/−, MC38-Trex1^−/−Sting^−/−, and MC38-Trex1^−/−Tbk1^−/− cells. (E–G) C57BL/6 mice (n = 4) were transplanted s.c. with 1 × 10⁷ MC38, MC38-Trex1^−/−, MC38 Cgas^−/−, and MC38-Trex1^−/−Cgas^−/− cells. 12 days later, tumor tissues were collected and analyzed by flow cytometry. The percentage of CD8⁺ T cell (E) and CD69⁺CD8⁺ T cell (F) in CD45⁺CD3⁺ cells and PD1⁺TIM3⁺ CD8⁺ T cell (G) in CD8⁺ T cells is shown. (H) Dot plot shows the significantly enriched hallmark pathways for highly expressed genes in MC38-Trex1^−/− vs. MC38 WT; the point color indicates the adjusted P value, and the point size indicates the upregulated gene count in each signal pathway. (I) Heatmap showing the expression of IFN response, immune cell activation, and chemotaxis-related genes in total CD8⁺ T cells from four different group mice. Data indicate mean ± SEM and are representative of two (A–G) independent experiments. The statistical analysis was performed by unpaired Student’s two-tailed t test in A–C and E–G and two-way ANOVA in D. NS, not significant, *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001.