Regulatory Networks Shaping Human Tumor-Associated Macrophages In Vivo Identify MAFB as a Key Transcriptional Driver

Tumor-associated macrophages (TAMs) are central drivers of resistance to conventional and immune-based therapies. Recent single-cell studies have uncovered an unexpected heterogeneity of macrophage states in human cancers, moving beyond the simplistic “M1–M2” paradigm. However, progress in understanding human TAM biology has been hampered by the lack of physiologically relevant in vivo models. Here, we leverage next-generation humanized mouse models implanted with cell line xenografts (CDX) to dissect the transcriptional and epigenetic programs that shape monocyte-to-macrophage differentiation within the tumor microenvironment. We show that these immuno-CDX models faithfully reproduce the phenotypic and molecular hallmarks of TAMs observed in patient tumors. By integrating single-cell transcriptomic and chromatin accessibility profiling with high-dimensional co-expression and enhancer-driven regulatory network analyses, we reconstruct a comprehensive framework of human TAM states. Furthermore, CRISPR-mediated gene editing of hematopoietic stem cells prior to humanization identifies MAFB as a key regulator of TAM plasticity. Our findings establish humanized models as a powerful platform to study TAM biology in vivo, uncover fundamental regulators of macrophage plasticity, and highlight new therapeutic targets for next-generation cancer immunotherapies.