Intratumoral PD-1+CD8+ T cells associate poor clinical outcomes and adjuvant chemotherapeutic benefit in gastric cancer

Background Although PD-1 has been reported to be a marker of T-cell exhaustion in several malignancies, the biological role of PD-1⁺CD8⁺ T cells in gastric cancer (GC) remains unclear. Herein, we aimed to investigate the role of PD-1⁺CD8⁺ T cells in the tumour microenvironment and its clinical significance in GC.Designs This study included 441 tumour microarray specimens and 60 Flow cytometry specimens of GC patients from Zhongshan Hospital, and 250 GC patients from the Asian Cancer Research Group.Results Here, we demonstrated that PD-1⁺CD8⁺ T cells functioned as an independent adverse prognosticator in GC. In addition, an abundance of intratumoral PD-1⁺CD8⁺ T cells indicated worse chemotherapeutic responsiveness to fluorouracil in Stage III GC patients. Mechanistically, PD-1⁺CD8⁺ T cell high infiltration indicated an exhausted phenotype of global CD8⁺ T cells in GC tissues, which was characterised by elevated immune checkpoint expression including CTLA-4 and TIM-3, whereas decreased expression of perforin. Furthermore, PD-1⁺CD8⁺ T cell high-infiltration patients with Stage III GC held elevated activity of several therapeutic signal pathways.Conclusions Our study highlighted that PD-1⁺CD8⁺ T cell abundance predicts inferior prognosis in GC, and may serve as a novel predictive biomarker to guide therapeutic option.Subject terms: Gastric cancer, Cancer microenvironment, Tumour immunology