The upregulation of programmed death 1 on peripheral blood T cells of glioma is correlated with disease progression

Glioma is the most common primary brain tumor. Programmed death 1 (PD-1) is a surface receptor expressed on activated and exhausted T cells, which mediate T cell inhibition upon binding with its ligand. In the current study, we investigated the expression of PD-1 on peripheral CD4+ and CD8+ T cells in glioma patients. Percentage of PD-1+ cells was measured by flow cytometry in 86 glioma cases and 62 healthy controls. Results showed that PD-1 expression was significantly increased in both peripheral CD4+ and CD8+ T cells in glioma ( p < 0.001 and p < 0.001, respectively). When comparing PD-1 level in glioma patients with different histological types, patients with astrocytomas revealed clearly higher proportion of PD-1 on CD4+ T cells than those with oligodendrogliomas ( p < 0.001), ependymomas ( p < 0.001), or pilocytic astrocytomas ( p < 0.001). Also, patients with the highest tumor grade (IV) demonstrated the most elevated expression of PD-1 on both CD4+ and CD8+ T cells. Interestingly, cases with tumor grade III and IV had downregulated PD-1 level on peripheral CD4+ T cells after surgery, whereas only grade IV patients showed decreased proportion of PD-1 on CD8+ T cells after treatment. In addition, no correlation between PD-1 expression and progression to secondary glioblastoma was observed. These data suggested PD-1 may act as a positive regulator in the pathogenesis and progression of glioma.