Neutrophil-Driven Trogocytosis in PDAC Liver Metastases Restrains Immunosuppressive Macrophage Polarization and Limits Metastatic Progression

BACKGROUND & AIMS: Pancreatic Ductal Adenocarcinoma (PDAC) metastasizes early and frequently to the liver, limiting therapeutic options and resulting in poor prognosis. Neutrophils are key immune players in cancer progression, yet their role in PDAC liver metastases remains unclear. This study investigates how neutrophils influence hepatic macrophages and modulate the immune landscape in the metastatic microenvironment using intravital calcium imaging and single-cell RNA sequencing (scRNA-seq). METHODS: Intravital microscopy was used to monitor neutrophil behavior and interactions within the metastatic niche. We employed intravital calcium imaging in LysMcre-PCG5-tdt mice to visualize real-time immune cell interactions and their functional impact in a PDAC metastasis model. To dissect the effect of neutrophils on the immune landscape, we performed single-cell RNA sequencing of liver-infiltrating leukocytes in tumor-bearing mice. RESULTS: Intravital calcium imaging revealed that neutrophils are recruited to hepatic metastases by CCL2/CCL5, where they take up tumor cell fragments via trogocytosis and subsequently present these tumor fragments to hepatic macrophages. This neutrophil-driven immunomodulation was abolished upon neutrophil depletion, resulting in a permissive tumor-promoting macrophage phenotype. Single-cell RNA sequencing identified distinct macrophage subpopulations, demonstrating that neutrophils suppress the development of immunosuppressive macrophages by C3-dependent signaling and enhance anti-tumor signaling pathways. CONCLUSIONS: This study provides in vivo evidence of neutrophil-macrophage crosstalk in PDAC liver metastases and highlights the functional consequences of neutrophil depletion. By integrating intravital calcium imaging with single-cell RNA sequencing, we uncover a previously unrecognized mechanism of neutrophil-driven immunomodulation, emphasizing the potential for therapeutic strategies targeting neutrophil-macrophage interactions in metastatic PDAC.