Targeting SPP1 (+)TAMs associated with liver metastasis reverses immunosuppression and synergizes with immunotherapy in colorectal cancer.

BACKGROUND: Tumor-associated macrophages (TAMs) are critically involved in colorectal cancer (CRC) progression, yet their spatial and metabolic heterogeneity across primary and metastatic microenvironments remains poorly defined, limiting therapeutic development. METHODS: Integrated single-cell RNA sequencing was performed on 998,204 cells from a multicenter cohort encompassing primary CRC, adjacent normal tissue, liver and lymph node metastases, and peripheral blood. Computational analyses included uniform manifold approximation and projection (UMAP) clustering, pseudotime inference, RNA velocity, and CellChat. Findings were validated using multiplex immunohistochemistry, spatial transcriptomics, and in vivo preclinical models. RESULTS: This study identified two distinct TAM populations: SPP1 (+) and SEPP1 (+) TAMs. SPP1 (+)TAMs, associated with angiogenesis, immune evasion, and liver metastasis, were linked to poorer prognosis. This population exhibited tissue-specific differentiation trajectories and comprised two metabolic subtypes: a glycolytic ATP5F1E (+) subtype enriched in primary tumors and lymph nodes, and an oxidative phosphorylation-dominant MT-CO1 (+)subtype specific to liver metastases. Spatially, MT-CO1 (+) SPP1 (+)TAMs localized to oxygen-rich invasive margins, while ATP5F1E (+) SPP1 (+)TAMs resided in hypoxic tumor cores. Functionally, SPP1 (+)TAMs drove CD8 (+) T-cell exhaustion and spatial exclusion. In preclinical models, combined regorafenib and anti-programmed cell death protein 1 therapy reduced SPP1 (+)TAM infiltration and suppressed tumor growth and metastasis. CONCLUSION: This study delineates the spatial, developmental, and metabolic heterogeneity of SPP1 (+)TAMs in CRC, identifying SPP1 (+)TAMs as key mediators of immunosuppression and metastasis. Targeting these populations with combination therapy effectively enhances antitumor immunity, presenting a novel translational strategy for CRC immunotherapy.