PDCD1 and neoplasm: Tumor-associated Tregs highly express immunosuppressive molecules, including FOXP3, CTLA-4, PD-1, CD39, ICOS, CD38, and IL32, as well as several specific surface signaling molecules (PD-L1, PD-L2, interleukin-1 receptor 2, and chemokine CCR8) (16, 20).