Fig. 3

The CAR-T cell therapy and its functional challenges. a Procedures of CAR-T cell-based immunotherapy and their trafficking to, and infiltration of, the tumor site. b Three generations of CAR structures and the synNotch receptor system. Upon the engagement of tumor surface antigens with extracellular scFv domains, CARs with the intracellular CD3ζ-costimulation (CD28 or 4-1BB) domain can induce native T-cell activation. c The synNotch receptor with Notch domain-mediated cleavage and release of specific transcription factors can initiate custom transcription programs upon engagement of surface antigens. d CAR-T cells recognize and kill the tumor cells. Different tumor-specific antigen-targeted CAR-T cells can combine to recognize and kill the tumor clones, resulting in enhanced potency and improved clinical outcome. Antigen A-targeted and antigen B-targeted CAR-T cells combine to kill the tumor cells bearing the antigen A and B. Additionally, CAR-T cells can differentiate into the exhausted state, promoting the emergence of therapeutic resistance. e Challenges in CAR-T cell-based immunotherapy involve CAR-T cell trafficking and infiltration, adequate CAR-T cell proliferation and persistence, targeted recognition and killing of tumor cells, remodeling of the immunosuppressive microenvironment and self-control regulation