Iron diminishes immunosuppressive macrophages and enhances anti-PD-1 immunotherapy in breast cancer models

Breast cancer remains a leading cause of cancer-related mortality among women globally, necessitating the development of innovative therapeutic strategies. The efficacy of immune checkpoint inhibitor-based immunotherapy in triple-negative breast cancer has provided a rationale for exploring its expansion to other breast cancer subtypes. Immunosuppressive tumor-associated macrophages (TAMs) within the tumor microenvironment have been demonstrated as a formidable barrier to the efficacy of approved immunotherapy. We aimed to identify and therapeutically modulate pathways that regulate the immunosuppressive properties of TAMs for more effective breast cancer immunotherapies. We integrated analyses of publicly available human breast cancer single-cell RNA sequencing (scRNA-seq) datasets with scRNA-seq profiling of murine mammary tumors to identify the signaling pathways associated with immunosuppression. The therapeutic implications of our findings were subsequently assessed through both in vitro and in vivo models. Single-cell transcriptional profiling was further performed to characterize the tumor immune microenvironment and understand the mechanisms of therapeutic activity. We revealed a strong positive correlation between iron metabolic gene signature and immunosuppressive features in TAMs of breast cancers. We showed that iron treatment on primary macrophages enhanced the proliferation of activated T cells, which was accompanied by downregulation of immunosuppressive mediators in macrophages. Importantly, we demonstrated that iron supplementation augmented the antitumor effect of PD-1 based immunotherapy in two preclinical models, with increased infiltration and cytotoxic activity of CD8 + T cells. Furthermore, iron treatment functionally reprogramed TAMs toward a less immunosuppressive state, potentially due to the downregulation of NF-κB inflammatory pathways and a shift in cellular metabolism. These findings advance the pivotal roles of iron in modulating the functional phenotypes of TAMs and anti-tumor immunity, and suggest that iron supplementation may represent a valuable clinical strategy for optimizing anti-PD-1 immunotherapy in breast cancer.