EPCAM+CD68+ Macrophages Originate from Tumor Macrophage Cell Fusion as a Common Subtype in Cold Tumors

The analysis of tumor samples through single-cell transcriptome sequencing (scRNA-seq) frequently reveals unique cell subsets that exhibit antithetical immune and malignant characteristics, although these findings are often overlooked. Clarifying the origin of these distinct cells and assessing their roles within the tumor immune microenvironment (TIME) is crucial. In this study, our findings suggest that the EPCAM+CD68+ macrophage subset originates from cell fusion events between tumor cells and macrophages, differentiating it from tumor-endocytic macrophages. This cell population is present in both primary tumors and metastases across various cold tumor types. It exhibits traits of both parental cells, including the entrapment of T cells within the collagenous matrix, suppression of T cell activity, and facilitation of M2 polarization of macrophages via signaling involving NECTIN2, SPP1, and LGALS9. Consequently, this cell population promotes tumor proliferation, immune evasion, and metastasis, as confirmed by in vivo experiments. The presence of this cell population correlates with poor survival outcomes in both mouse models and clinical cohorts. Overall, these findings underscore the importance of carefully identifying unique cells with contradictory markers, which may have the potential to predict prognosis and improve therapeutic responses in patients.