PD-1 expression on peripheral blood T-cell subsets correlates with prognosis in non-small cell lung cancer

PD-1 expression in peripheral blood T-cells has been reported in several kinds of cancers, including lung cancer. However, the relationship between PD-1 expression in peripheral blood T-cells and prognosis after treatment with a cancer vaccine has not been reported. To elucidate this relationship, we analyzed PD-1 expression in the peripheral blood T-cells of patients with non-small cell lung cancer. The blood samples used in this study were obtained from patients enrolled in phase II clinical trials of a personalized peptide vaccine. Seventy-eight samples obtained before and after a single vaccination cycle (consisting of six or eight doses) were subjected to the analysis. PD-1 was expressed on lymphocytes in the majority of samples. The relative contents of PD1(+)CD4(+) T-cells against total lymphocytes before and after the vaccination cycle correlated with overall survival (OS) with a high degree of statistical significance (P<0.0001 and P=0.0014). A decrease in PD-1(+)CD8(+) T-cells after one cycle of vaccination also correlated with longer OS (P=0.032). The IgG response to the non-vaccinated peptides suggested that the epitope spreading seemed to occur more frequently in high-PD-1(+)CD4(+) T-cell groups. Enrichment of CD45RA(-)CCR7(-) effector-memory phenotype cells in PD-1(+) T-cells in PBMCs was also shown. These results suggest that PD-1 expression on the peripheral blood T-cell subsets can become a new prognostic marker in non-small cell lung cancer patients treated with personalized peptide vaccination.