TNFRSF9 and neoplasm: CARs are anti-tumor targeted antibodies that have been fused genetically to a stalk or linker, a transmembrane domain, and intracellular T cell activation domains that have been borrowed from activation checkpoint receptors such as CD28, TNFRSF9 (CD137), and/or TNFRSF4 (OX40) (Fig. 1M; Figueroa et al., 2015; van der Stegen et al., 2015; Ruella and Gill, 2015; Smith et al., 2016; Ruella and June, 2016; Lim and June, 2017).