Injectable thermosensitive hydrogels loaded with irradiated tumor cell-derived microparticles and manganese activate anti-tumor immunity

Immunosuppressive tumor microenvironment and inadequate activation of the innate immune system are important reasons for the failure of systemic anti-tumor immunotherapy. Irradiated tumor cell-derived microparticles (RMPs) can induce immunogenic cell death (ICD) of tumor cells and inhibit the M2-like phenotype of tumor-associated macrophages (TAMs). The current study found that double-stranded DNA was enriched in RMPs, which combined with manganese ions (Mn²⁺), the natural activator of cGAS-STING signaling, and synergistically amplified cGAS-STING signaling cascade in antigen-presenting cells (APCs). On this basis, a polyamino acid thermosensitive hydrogel delivery system was designed to simultaneously load RMPs and Mn²⁺. The obtained RMPs@Mn²⁺ hydrogel exhibited thermosensitivity, biocompatibility and sustained release characteristics. The intratumoral injection of RMPs@Mn²⁺ slowly released RMPs and Mn²⁺, inducing ICD of tumor cells, continuously activating cGAS-STING signaling of APCs, reprograming TAMs to M1-like phenotype, and promoting the activation of dendritic cells in tumor draining lymph nodes. The full activation of innate immunity at the tumor site further promoted priming and tumor infiltration of T cells, leading to tumor regression. RMPs@Mn²⁺ combined with anti-PD-1 achieved strong anti-cancer efficacy in a refractory malignant ascites model, in which more than 50 % of mice with malignant ascites achieved complete regression and long-term immune memory.