TNF and cancer: By identifying the various upregulated ligands in cancer cells (e.g., MHC class I-related chains A/B and UL16-binding proteins), Vγ9Vδ2 T cells can either kill tumor cells indirectly by releasing abundant cytokines (e.g., IFN-γ and TNF-α), thereby displaying a Th1 cell-like property, or do so directly via death receptor signal (e.g., Fas-FasL and TNF-TNFR), secreting cytotoxic molecules such as granzymes (71, 72).