TNFRSF9 and acute lymphoblastic leukemia: The second generation CAR-T cells were generated by adding a costimulatory domain, such as CD28, 4-1BB (CD137L) or OX40 (CD134) to the CD3ζ domain, thus amplifying signals and inducing a CR in patients with relapsing acute lymphoblastic leukemia (ALL) and in relapsed/refractory (R/R) mature B-cell malignancies [23,24,25,26,27].