A Therapeutic System Regulating Iron Metabolism in CD63⁺ Macrophage Subsets Activates Anti-tumor Immunity for Bone Metastasis Therapy

Iron metabolism disorders are linked to tumor metastasis, with the iron imbalance in macrophages playing a pivotal role. However, due to the unclear identifiers for iron-metabolism-related macrophage subsets and corresponding key iron metabolic proteins promoting metastasis, precisely regulating macrophage iron metabolism in the tumor microenvironment remains challenging. Here, we have identified CD63+ macrophage subsets with activated iron metabolism in bone metastases and validated that the iron-storage-related protein FTH1 in macrophages facilitates bone metastasis using gene knockout mice. Herein, we report a gene therapy system (siFTH1@HEV-aCD63) that precisely regulates iron metabolism in CD63+ macrophages by encapsulating siFTH1 in fusion vesicles merging bacterial outer membranes with liposomes, coated with anti-CD63 antibodies. siFTH1@HEV-aCD63 achieves precise identification of iron-metabolizing activating macrophage subpopulations, effectively halting the progression of bone metastases by downregulating the FTH1 gene in CD63+ macrophages. Furthermore, by inhibiting the iron storage capacity of these macrophages, siFTH1@HEV-aCD63 notably reverses their immunosuppressive effects and robustly stimulates antitumor immune responses at the metastatic sites. Overall, this study introduces a therapeutic strategy targeting abnormal iron-metabolizing macrophages, providing a promising approach for the precise regulation of metabolically dysfunctional cells in antitumor immunotherapy.