PDCD1 and esophageal squamous cell carcinoma: The CD8+ TEXs expressed a high level of GZMK rather than typical exhaustion markers like PDCD1 or CTLA4, suggesting that CD8+ TEXs in intramucosal ESCC were mainly in an intermediate state before total exhaustion, and could become terminal TEX through the ‘Tn to IL7R+Tm to GZMK+TEM/EX’ pathway.40