TIM-3 Expression and M2 Polarization of Macrophages in the TGF-Activated Tumor Microenvironment in Colorectal Cancer

TGF beta signaling in the tumor microenvironment (TME) drives immune evasion and is a negative predictor of immune checkpoint inhibitor (ICI) efficacy in colorectal cancer (CRC). TIM-3, an inhibitory receptor implicated in anti-tumor immune responses and ICI resistance, has emerged as an immunotherapeutic target. This study investigated TIM-3, M2 macrophages and the TGF beta-activated TME, in association with microsatellite instability (MSI) status and consensus molecular subtypes (CMSs). Transcriptomic cohorts of CRC tissues, organoids and xenografts were examined (n = 2240). TIM-3 and a TGF beta-inducible stromal protein, VCAN, were evaluated in CRC specimens using immunohistochemistry (n = 45). TIM-3 expression on monocytes and generated M2 macrophages was examined by flow cytometry. We found that the expression of HAVCR2 (TIM-3) significantly correlated with the transcriptional signatures of TGF beta, TGF beta-dependent stromal activation and M2 macrophage, each of which were co-upregulated in CMS4, CMS1 and MSI CRCs across all datasets. Tumor-infiltrating TIM-3(+) immune cells accumulated in TGF beta-responsive cancer stroma. TIM-3 was increased on M2-polarized macrophages, and on monocytes in response to TGF beta treatment. In conclusion, we identified a close association between TIM-3 and M2-like polarization of macrophages in the TGF beta-rich TME. Our findings provide new insights into personalized immunotherapeutic strategies based on the TME for CRCs.