Fig. 2

Optimized CAR designs. a The anti-tag uCAR is designed to express an antigen recognition domain specific for a tag (often FITC) molecule attached to a monoclonal antibody specific to the TAA on the surface of tumor cells. b SUPRA CAR is composed of two parts: the zipFv component consists of a scFv specific for the TAA to be targeted and a leucine zipper (AZip). The second component is zipCAR-T cell expressing a CAR with an extracellular leucine zipper (BZip). The zipFv binds to the TAA via the scFv domain and to the zipCAR via binding of the AZip and BZip leucine zipper domains, leading to CAR T cell activation. c, d Bi-specific or trivalent CAR T cells are designed to co-express two or three CARs within the same cell that are directed to two or three different brain TAAs, respectively. Alternatively, two or three different CAR T cell populations could be pooled together to simultaneously target multiple TAAs on the tumor cell surface. e Tandem CAR is composed of two or more scFvs in tandem followed by hinge, transmembrane and signaling domains. Binding of either one or more TAAs may fully activate T cell signaling and function. f Split CAR is designed to co-express two different CARs for targeting two different TAAs. One CAR contains the CD3ζ signal and the other contains the co-stimulation signal. Binding to both TAAs is required for CAR T cell activation. g The activation of a synNotch CAR T cell requires two TAAs be present on the cancer cell surface and occurs in two steps: (1) the synNotch receptor recognizes and binds to the first antigen, leading to release of a transcription activator for the CAR transcription; and (2) the CAR recognizes and binds to the second antigen, leading to full CAR T cell activation. Only when both antigens are present will the T cells be activated and kill the target tumor cells