PDCD1 and neoplasm: Moreover, immunosuppressive factors within the tumor microenvironment i.e., the presence of an innate anti-PD-1 resistance signature (IPRES) transcriptional signature (27), the absence of an interferon signature, increase in Tregs number, upregulation of PD-L1 molecule and the induction of indoleamine 2,3-dioxygenase (IDO) [209,210] also play an important role.