<i>In situ</i> programming of CAR-macrophages <i>via</i> a polyplex nanomaterial and STING activation for triple-negative breast cancer immunotherapy

Triple-negative breast cancer (TNBC) is an aggressive type of breast cancer characterized by the absence of an estrogen receptor, a progesterone receptor, and HER2. Current treatment modalities, including surgery, chemotherapy, and radiotherapy, are used in combination, but offer minimal clinical benefit, resulting in relapse and poor prognosis. Recently, therapy using chimeric antigen receptor (CAR) T-cells has proved to be successful for treating hematological malignancies, but is known to have limited therapeutic efficacy in solid tumors due to their inability to infiltrate and inactivation by the tumor microenvironment. Macrophages can infiltrate solid tumors, and when modified to express CAR, known as CAR-macrophages (CAR-M), have demonstrated promising outcomes in pre-clinical models. Given the challenges in scaling the complex <i>ex vivo</i> modification of cells, we have designed a polyplex-based system for <i>in situ</i> programming of macrophages to express CAR specific to programmed death ligand-1 (PD-L1) on TNBC. Intraperitoneal polyplex injection reprogrammed macrophages into CAR-M, enabling tumor infiltration and PD-L1⁺ cell phagocytosis, while intratumoral STING agonist injection enhanced CD8⁺ T-cell infiltration, collectively reducing the tumor burden. Thus, our approach offers a cost-effective and scalable solution for TNBC treatment, providing specificity over macrophage modification and eliciting a robust anti-tumor response.