TNFRSF9 and cancer: The rationale for agonizing 4-1BB in cancer is strong, given the ability of 4-1BB to drive CD8 T cell and NK cytotoxic activity (3–5, 10, 12), and was spearheaded by the first-generation agonist antibodies, urelumab (BMS-663513) and utomilumab (PF-05082566) that were evaluated both as monotherapies and combined with other therapies (28, 37, 55–62).