PDCD1 and neoplasm: Moreover, the quantities of Th17 and Treg cells in peripheral blood are closely related to clinical stage, tumor burden, chemotherapy sensitivity, and prognosis (39, 40).An increase in Treg cell numbers or their enhanced function can lead to upregulation of immune checkpoints such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), glucocorticoid-induced tumor necrosis factor receptor (GITR), and programmed cell death protein 1 (PD-1).