TNFRSF9 and neoplasm: Regarding the lack of change in the percentage of CD137+ Tregs after Wt-mAb treatment, there is evidence that tumor-resident Tregs exhibit tumor neoantigen reactivity, which leads to their activation and clonal expansion in the tumor microenvironment, perhaps indicating that CD137 signaling may be essential for controlling the population of Tregs and their transient expansion.