Mitochondrial DNA released by senescent cells triggers immunosuppression in cancer

DNA is a potent damage-associated molecular pattern signaling that, once in the extracellular space, triggers the activation of the innate immune system. Here we find that senescent cells release mtDNA to both the cytosol and the extracellular space. In cells undergoing cellular senescence, the release of mtDNA precedes that of nuclear DNA resulting in the activation of the cGAS/STING pathway and establishment of cellular senescence. Intriguingly, by exploiting co-culture and in vivo cross-species experiments, we show that extracellular mtDNA released by senescent tumors cells is specifically captured by polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in the tumor microenvironment (TME). Mechanistically we find that PMN-MDSCs uptake mtDNA to enhance their immunosuppressive ability. Pharmacological inhibition of mtDNA released from senescent tumor cells blocks the PMN-MDSCs immunosuppressive activity, improving the efficacy of therapy-induced senescence (TIS) in cancer. These results reveal the crucial role of mtDNA in initiating cellular senescence and immunosuppression independently of the SASP. Thus, targeting mtDNA release-mediated pathway may hold promise to reprogram the immune suppressive microenvironment in patients treated with chemotherapy.