Regulation of the CD8⁺ T cell and PDL1/PD1 axis in gastric cancer: Unraveling the molecular landscape.

Gastric cancer (GC) remains a significant global health burden, mainly due to immune evasion mechanisms within its complex tumor microenvironment (TME). The interaction between CD8⁺ T cells and the PD1/PDL1 axis is central to these mechanisms. CD8⁺ T cells, key players in antitumor immunity, often exhibit impaired functionality in the GC TME, primarily due to PD1-mediated inhibitory signaling induced by PDL1 expressed on tumor and immune cells. Recent findings have elucidated intricate molecular interactions governing PD1 expression on CD8⁺ T cells and the modulation of PDL1 on tumor cells and immune cells by diverse signals such as cytokines, metabolic factors, and noncoding RNAs. While high PD1 expression typically indicates CD8⁺ T cell exhaustion and poor clinical outcomes, recent studies highlight scenarios where elevated PD1 levels correlate with preserved or enhanced T cell cytotoxic activity, suggesting nuanced regulatory pathways. Therapeutic strategies that disrupt PD1/PDL1 interactions, through checkpoint inhibitors or pharmacological modulation, have demonstrated potential in reactivating antitumor responses. However, resistance mechanisms, including altered antigen presentation, metabolic reprogramming, and immunosuppressive cell infiltration, continue to limit efficacy. Emerging combination therapies, biomarker-driven patient stratification, and novel targets like noncoding RNAs and exosomal PDL1 represent promising avenues to enhance treatment effectiveness. This review synthesizes current insights into the molecular regulation of CD8⁺ T cell functionality and the PD1/PDL1 axis, highlighting potential therapeutic strategies to restore antitumor immunity and improve patient outcomes in gastric cancer.