Expression of programmed death 1 is correlated with progression of osteosarcoma.

Accumulating bodies of evidence indicate that immune dysregulation plays a key role in the development of osteosarcoma (OS). 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. Researches on PD-1 and OS remain extremely limited. Here, we investigated whether PD-1 could be involved in the development of OS. Expression of PD-1 was measured by flow cytometry on peripheral CD4+ and CD8+ T cells from 56 OS cases and 42 healthy controls. Data revealed that percentages of PD-1 were significantly upregulated on both peripheral CD4+ and CD8+ T cells from OS patients (p < 0.001 and p < 0.001, respectively). Patients with different tumor locations did not present obvious variations in PD-1 level. However, patients with metastasis showed significantly higher level of PD-1 on CD4+ T cells than those without metastasis (p < 0.001). Furthermore, PD-1 expression on CD4+ T cells started to increase in stage III, whereas PD-1 expression on CD8+ T cells started to increase in stage II. In addition, patients with pathological fracture were observed to have elevated PD-1 on both CD4+ and CD8+ T cells. These data suggest that PD-1 is involved in the pathogenesis of OS, especially in the progression of disease.