S100A9-Dependent CXCR2 hi Neutrophils Mediate Systemic Immune Suppression and Checkpoint Resistance in Metastatic TNBC
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Most high-dimensional studies of tumor-immune interactions focus on metastatic models, limiting insight into how immune remodeling in primary tumors shapes metastatic competence. Here, integrating single-cell RNA sequencing, CyTOF, and functional studies across metastatic (4T1) and non-invasive (EMT6) triple-negative breast cancer (TNBC) murine models, we define tumor state-specific immune programs that distinguish metastatic competence. Tumors with metastatic capacity uniquely drive early bone marrow expansion of CXCR2⁺ neutrophils, which infiltrate primary tumors acquiring a CXCL2-producing phenotype that promotes EMT-associated cancer stem cell (CSC) plasticity. This program depends on TGF-β/CEBPD-mediated induction of S100A9. Elevated CXCL2, together with G-CSF, establishes a feed-forward circuit that drives systemic neutrophil mobilization and recruitment to distant organs, where neutrophil-derived S100A8/A9 (calprotectin) promotes MET-driven CSC outgrowth and metastatic colonization. Clinically, gene signatures associated with CXCR2⁺ neutrophils predict poor survival in TNBC patients, whereas monocyte/macrophage (CX3CR1⁺) and T cell activation signatures correlate with improved outcomes. S100A9 ablation disrupts this cascade and enhances immunotherapy responsiveness, defining a TGF-β/S100A9/CXCR2 axis linking immune remodeling, CSC plasticity and metastasis.
Highlights
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Metastatic TNBC engages a TGF-β/C/EBPδ/S100A9 axis that expands CXCR2⁺ neutrophils
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Non-invasive EMT6 tumors retain a CX3CR1⁺ monocyte/macrophage and T-cell landscape
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CXCR2 + neutrophils in pre-metastatic niches suppress T cell response while promoting tumor cell proliferation
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S100A9 loss redirects myelopoiesis and potentiates anti-PD-L1 in TNBC models
In Brief
Alkan et al. dissect how tumor state programs the myeloid compartment in TNBC. Metastatic 4T1 tumors uniquely engage a TGF-β/C/EBPδ/S100A9 axis driving CXCR2⁺ neutrophil expansion and CXCL2/G-CSF-dependent systemic mobilization, coupling immune remodeling to EMT/MET cancer-stem-cell plasticity, while S100A9 loss restores CX3CR1⁺ myeloid identity and unlocks checkpoint-inhibitor responsiveness.
