TNFRSF9 and neoplasm: On day 7, the 4 tumor-infiltrating populations had higher surface CD137 expression in the Delta-24-ACT–treated tumors than in the controls (Figure 5D) (CD8+, P = 0.1889; CD4+, P = 0.0101; Tregs, P = 0.0137; NK cells, P < 0.0001), indicating that they could directly interact with the cells expressing 4-1BBL in a Delta-24-ACT–dependent manner.