Bortezomib Enhances CD70 CAR-T Cell Therapy in Sunitinib Resistant Renal Cell Carcinoma by Inducing Mitochondrial DNA Mediated cGAS-STING Activation

Chimeric antigen receptor (CAR) T-cell therapy has shown remarkable efficacy in hematologic malignancies, yet its application to solid tumors remains limited by poor tumor infiltration, an immunosuppressive microenvironment, and insufficient antigen presentation. Here, we identify a mechanism by which the proteasome inhibitor bortezomib (BTZ) enhances CAR-T efficacy in renal cell carcinoma (RCC), particularly in sunitinib-resistant tumors characterized by immune exclusion and metabolic adaptation. Screening of an FDA-approved compound library revealed BTZ as a potent sensitizer that restores CAR-T cytotoxicity against resistant RCC cells. Mechanistically, BTZ induces mitochondrial and endoplasmic reticulum stress, leading to increased reactive oxygen species and voltage-dependent anion channel (VDAC)-dependent release of mitochondrial DNA (mtDNA) via extracellular vesicles. Tumor-derived mtDNA is internalized by dendritic cells, activating the cGAS-STING signaling axis, enhancing glycolytic metabolism, and promoting type I interferon responses and antigen presentation. This, in turn, augments CAR-T cell persistence, effector cytokine secretion, and tumor infiltration. Pharmacological inhibition of mtDNA release or glycolysis abrogates these effects, confirming the essential role of mtDNA-mediated innate immune activation. In multiple RCC models, including patient-derived xenografts and orthotopic tumors, BTZ synergized with CD70 CAR-T therapy to induce robust tumor regression, durable immune memory, and improved survival without overt toxicity. Collectively, these findings define a previously unrecognized immunometabolic mechanism by which proteasome inhibition transforms the tumor microenvironment and potentiate cellular immunotherapy, offering a clinically actionable strategy to overcome therapeutic resistance in solid tumors.