STAT5 is activated in macrophages by breast cancer cell-derived factors and regulates macrophage function in the tumor microenvironment.

BACKGROUND: In breast cancer, complex interactions between tumor cells and cells within the surrounding stroma, such as macrophages, are critical for tumor growth, progression, and therapeutic response. Recent studies have highlighted the complex nature and heterogeneous populations of macrophages associated with both tumor-promoting and tumor-inhibiting phenotypes. Defining the pathways that drive macrophage function is important for understanding their complex phenotypes within the tumor microenvironment. Signal transducer and activator of transcription (STAT) transcription factors, such as STAT5, are key regulators of immune cell function. The studies described here investigate the functional contributions of STAT5 to tumor-associated macrophage function in breast cancer. METHODS: Initial studies were performed using a panel of human breast cancer and mouse mammary tumor cell lines to determine the ability of tumor cell-derived factors to induce STAT5 activation in macrophages. Further studies used these models to identify soluble factors that activate STAT5 in macrophages. To delineate STAT5-specific contributions to macrophage function, a conditional model of myeloid STAT5 deletion was used for in vitro, RNA-sequencing, and in vivo studies. The effects of STAT5 deletion in macrophages on tumor cell migration and metastasis were evaluated using in vitro co-culture migration assays and an in vivo tumor cell-macrophage co-injection model. RESULTS: We demonstrate here that STAT5 is robustly activated in macrophages by tumor cell-derived factors and that GM-CSF is a key cytokine stimulating this pathway. The analysis of RNA-seq studies reveals that STAT5 promotes expression of immune stimulatory genes in macrophages and that loss of STAT5 in macrophages results in increased expression of tissue remodeling factors. Finally, we demonstrate that loss of STAT5 in macrophages promotes tumor cell migration in vitro and mammary tumor metastasis in vivo. CONCLUSIONS: Breast cancer cells produce soluble factors, such as GM-CSF, that activate the STAT5 pathway in macrophages and drive expression of inflammatory factors. STAT5 deletion in myeloid cells enhances metastasis, suggesting that STAT5 activation in tumor-associated macrophages protects against tumor progression. Understanding mechanisms that drive macrophage function in the tumor microenvironment will ultimately lead to new approaches that suppress tumor-promoting functions while enhancing their anti-tumor functions.

Characterization of high-density mapping in catheter ablation for persistent atrial fibrillation: results from the Advisor™ HD Grid Mapping Catheter Observational study.

BACKGROUND: We quantified and characterized the outcomes of ablation in persistent atrial fibrillation (PersAF) subjects, and the utility of electroanatomical mapping with a market-released high-density (HD) mapping catheter. METHODS: PersAF subjects received electroanatomical mapping with the Advisor™ HD Grid mapping catheter, Sensor Enabled™ (HD Grid) and radiofrequency (RF) ablation to gather data regarding ablation strategies, mapping efficiency, quality, and outcomes. Subjects were enrolled from January 2019 to April 2020 across 25 international sites and followed for 12 months after the procedure. RESULTS: Three hundred thirty-four PersAF subjects (average age 64.2 years; 76% male; 25.4% previous AF ablation) were enrolled. Multiple map types were generated in a variety of rhythms using HD Grid. Significant differences in low voltage areas were identified in maps generated with the HD Wave Solution™ electrode configuration when compared to the standard configuration, which in some cases, influenced physicians' ablation strategies. PV-only ablation strategy was used in 59.0% of subjects and 34.1% of subjects received PV ablation and additional lesions. Of the subjects, 82.0% were free from recurrent atrial arrhythmias at 12 months and new or increased dose of class I/III antiarrhythmic drugs. About 6.0% of subjects experienced a serious adverse event or serious adverse device effect through 12 months including 1 event deemed related to HD Grid and the index procedure by the investigator and 1 death unrelated to study devices. CONCLUSIONS: The results of this study (NCT03733392) support the safety and utility of electroanatomical mapping with HD Grid in subjects with complex arrhythmias, such as PersAF in the real-world setting.