CCL5 and esophageal squamous cell carcinoma: In esophageal squamous cell carcinoma (ESCC), gram-negative bacterial enrichment drives LPS accumulation, which activates the CCL3/CCL5–CCR1–MAPK axis to upregulate tumor PD-L1 while suppressing T cell proliferation/cytotoxicity, elevating PD-1/LAG-3, and reducing CD107a/IFN-γ (244).