PDCD1 and neoplasm: Tumour cells, immune-suppressive T regulatory cells (FOXP3+ CD4+), tumour-associated macrophages (TAMs) are responsible of the inhibition of the activity of immune effectors cells within the tumour microenvironment, including CD4+ T cells, CD8+ T cells, and NK cells, through the concerted action of a plethora of mediators comprising cytokines (such as IL-10, TGF-β, PGE2) and membrane-bound ligands including B7-H1 and programmed cells death protein 1 (PD-1)9.