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Objective: Due to the tumor immune microenvironment (TIME) complexity and cancer heterogeneity, the clinical outcomes of hepatocellular carcinoma (HCC) are barely elicited from the conventional treatment options, even from the promising anti-cancer immunotherapy. As a suppressive TIME-related marker, the role played by cyclooxygenase-2 (COX-2) in HCC TIME, and its potential effects on anti-cancer T cell immune response remains unknown. In our study, to investigate the COX-2-dependent immune regulation pathway, we verified that the macrophages phenotypes were correlated to COX-2/PGE2 expressions among HCC patients. A multi-cellular co-culture platform containing HCC cells, macrophages, and T cells were established to mimic HCC TIME in vitro and in animal model. M2 macrophage polarization and activated CD8 + T cells exhaustion were observed under high COX-2 levels in HCC cells, with further evaluation using CRISPR/Cas9-based PTGS2 knocking out and COX-2 blockade (celecoxib) treatment controls. PGE2, TGF-β, Granzyme B, and IFN-γ levels were testified by flow cytometry and ELISA to fully understand the mechanism of COX-2 suppressive effects on T cell-based anti-HCC responses. The activation of the TGF-β pathway evaluated by auto-western blot in T cells was confirmed which increased the level of phosphorylated Smad3, phosphorylated Samd2, and FoxP1, leading to T cell de-lymphotoxin. In conclusion, high COX-2-expressing HCC cell lines can induce anti-tumor abilities exhaustion in activated CD8 + T cell through M2 TAMs polarization and TGF beta pathway. COX-2 inhibitors may reduce the inhibitory effect on CD8 + T cells through regulating TAMs in TIME, thus enhance the T cell-based cytotoxicity and improve the prognosis of HCC patients., Competing Interests: None., (AJTR Copyright © 2021.)