TNF and neoplasm: On the other hand, tumor cells often express ligands for ICs that can be induced with oncogenic pathways and extrinsic factors in the TME such as the cytokines IFN-γ, IL-6, and TNF-α [229,230] that contribute to the upregulation of PD-1 ligands 1 and L2 (PD-L1 and PD-L2) on tumor cells.