Clearance of extracellular DNA prevents senescence-associated antitumor immunity

Background Tumor tissues are characterized by high tumor cell turnover, driven by oncogenic proliferation and counteracted by tumor-suppressive mechanisms such as apoptosis and senescence. Dying cancer cells go through apoptosis and release apoptotic particles containing fragmented DNA—which are chromatin- or nucleosome-bound—into the tumor microenvironment. Given the immunogenicity of extracellular DNA, its efficient clearance is crucial for cancer cells to evade immune defense. However, the consequences of failed clearance of these DNA fragments on cancer cells remain poorly defined. Methods To uncover the outcome of impaired extracellular DNA clearance in tumors, we disrupted this machinery in MMTV-PyMT spontaneous breast tumor mice by deleting both Dnase1l3 and Ighm (the immunoglobulin heavy chain), thereby eliminating the DNase and its compensatory autoantibodies, and monitored tumor progression and performed histopathological, molecular, and transcriptomic profiling on harvested tumors. To determine whether cGAS or TLR9 mediates this phenotype, we intercrossed these double-deficient mice with Sting1 -/- or Tlr9 -/- mice and assessed antitumor immunity when extracellular DNA clearance was abrogated. Results Combined deficiency of Dnase1l3 and anti-DNA autoantibody led to profound suppression of tumor growth in the MMTV-PyMT model. This antitumor effect was associated with senescence induction in cancer cells triggered by accumulation of uncleared extracellular chromatin DNA. Mechanistically, the senescence-associated antitumor immune response was driven by the cancer cell-intrinsic TLR9, but not cGAS. Conclusions Our findings establish that combined deficiency of Dnase1l3 and anti-DNA autoantibodies disrupts extracellular DNA clearance and elicits a TLR9-dependent senescence-associated antitumor immune response. This pathway may represent a tissue-level immunotherapeutic strategy for cancer.