TNFRSF9 and neoplasm: Firstly, some phenotypes are activated and expressed by T cells undergoing tumor antigen recognition, such as PD-1, CD39, CD103 and CD137, which have been demonstrated to be markers associated with TSTs; secondly, considering tumor reactivity and tumor responsiveness (secretion of antitumor cytokines, release of cytotoxic granules and upregulation of activation markers), some reports suggested that the combination of intracellular CD137-specific activation marker and cytokines, including IFN-γ and TNF-α, could identify tumor-specific responsive T cells more accurately (80).