CircRNAs also participate in immune regulation under hypoxic conditions, facilitating tumor cells to evade the cytotoxic effects of immune cells by inducing M2 polarization of macrophages, suppressing T cell infiltration, and enhancing the expression of tumor PD-L1, for instance, in esophageal squamous cell carcinoma, hsa-circ-0048117 is significantly upregulated and enriched in exosomes secreted by tumor cells after hypoxia preconditioning, hsa-circ-0048117 acts as a sponge for miR-140, promoting macrophage polarization towards the M2 phenotype by competing with TLR4 [82]. Here, TLR4 is linked to esophageal squamous cell carcinoma.