TNFRSF9 and B-cell chronic lymphocytic leukemia: Several studies reported that 35% (23/65) of patients with acute myelocytic leukemia (AML) [53] and 32% (28/89) of patients with B cell chronic lymphocytic leukemia (B-CLL) [54] expressed a high level of 4-1BB ligand, and at the same time, almost all NK cells in these patients expressed 4-1BB.