Early Increase in Circulating PD-1⁺CD8⁺ T Cells Predicts Favorable Survival in Patients with Advanced Gastric Cancer Receiving Chemotherapy

The clinical significance of PD-1 expression in circulating CD8⁺ T cells in patients with gastric cancer (GC) receiving chemotherapy remains unelucidated. Therefore, we aimed to examine its prognostic significance in blood samples of 68 patients with advanced GC who received platinum-based chemotherapy. The correlation between peripheral blood mononuclear cells, measured using fluorescence-activated cell sorting, was evaluated. Patients were divided into two groups according to the changes in PD-1⁺CD8⁺ T-cell frequencies between day 0 and 7. They were categorized as increased or decreased PD-1⁺CD8⁺ T-cell groups. The increased PD-1⁺CD8⁺ T-cell group showed longer progression-free survival (PFS) and overall survival (OS) than the decreased PD-1⁺CD8⁺ T-cell group (PFS: 8.7 months vs. 6.1 months, p = 0.007; OS: 20.7 months vs. 10.8 months, p = 0.003). The mean duration of response was significantly different between the groups (5.7 months vs. 2.5 months, p = 0.041). Multivariate analysis revealed that an increase in PD-1⁺CD8⁺ T-cell frequency was an independent prognostic factor. We concluded that the early increase in PD-1⁺CD8⁺ T-cell frequency is a potential predictor of favorable prognoses and durable responses in patients with advanced GC receiving chemotherapy.