Importantly, a myriad of cytokines, including IFN-γ, TNF-α, type 1 interferons, GM-CSF, IL-2, IL-7 and IL-15, are actively involved in enhancing the expression of PD-1 on T cells and its ligands on antigen-presenting cells and tumour cells at sites of disease [93]. This evidence concerns the gene IFNG and neoplasm.