Macrophages are the most abundant tumor infiltrating immune cells and perform diverse immune functions including phagocytosis and incitation of T cells to mount an immune attack against tumors. However, the macrophage plasticity can lead to different outcomes of tumor progression and the amino acid, arginine, plays a central role in macrophage dichotomy. The exact role of arginine on the management of macrophage polarization is not completely understood. We have discovered that a methylated arginine metabolite, asymmetric dimethylarginine (ADMA), serves as an important regulator of macrophage functions. Upon stimulation by ADMA, macrophages have reduced survival and show a delayed tumor-phagocytic capacity. Additionally, ADMA blocks the Nitric Oxide Synthase (NOS) but not the Arginase activity in macrophages leading to a tendency of M2-like phenotype polarization. ADMA has minor effect on tumor cell proliferation but significantly drives the epithelial to mesenchymal transition. Tumor cells, particularly the tumor stem cells, are the major sources of ADMA. Production and secretion of ADMA by tumor (stem) cells profoundly increase when co-cultured with activated T cells or treated with T cell associated inflammatory cytokine, interferon-gamma (IFN-r). IFN-r initiates autophagy of tumor (stem) cells and inhibition of autophagy reduces the output of ADMA by tumor (stem) cells. Similarly, IFN-r enhances the proteasomal degradation and inhibition of the proteasomal pathway also reduces the ADMA production induced by IFN-r. In summary, our work shows that tumor (stem) cells may escape from immune surveillance (such as their exposure to activated T lymphocytes or to cytotoxic cytokine, IFN-r) through the secretion of ADMA generated via both autophagic and proteasomal pathways. Citation Format: Yiling Chen, AKaychia T. Lowery, Andres Becerril, Zaida T. Laventure, Shareda Ferguson, Kuan-Hui Ethan Chen. Tumor stem cell derived asymmetric dimethylarginine drives immune evasion via functional modulation of macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3847.