Cancer-cell-derived cGAMP limits the activity of tumor-associated CD8 ⁺ T cells

Using a mouse tumor model with inducible cancer-cell-intrinsic cGAS expression, we show that cancer-cell-derived cGAMP is essential and sufficient to trigger a sustained type I interferon response within the tumor microenvironment. This led to improved CD8 ⁺ T cell-dependent tumor restriction. However, cGAMP limits the proliferation, survival, and function of STING-expressing but not of STING-deficient CD8 ⁺ T cells. In vivo , STING deficiency in CD8 ⁺ T cells enhanced tumor restriction. Consequently, cancer-cell-derived cGAMP both drives and limits the anti-tumor potential of CD8 ⁺ T cells. Mechanistically, T cell-intrinsic STING is associated with pro-apoptotic and antiproliferative gene signatures. Our findings suggest that STING signaling acts as a checkpoint in CD8 ⁺ T cells that balances tumor immunity.