Fig. 3

CAR-T-cell therapy and the four generations of improvements. The first-generation CARs were fused with a single-chain variable fragment (scFv) to a transmembrane domain and an intracellular signalling unit: the CD3 zeta chain. Then, the second-generation CARs improved the costimulatory molecule receptor-like CD28, which is the most commonly used. The second-generation CARs increased the production of cytokines and enhanced durability. The third-generation of CARs design in-corporated an additional costimulatory domain to enhance CAR function and included the scFv, the initial CD3ζ-chain, and the CD28 and 4-1BB or OX40 costimulatory domains [132]. At present, fourth-generation CAR-T therapy has been extended. In this type of CAR-T-cell therapy, cytokine genes have been added to the structure, which can stimulate high cytokines expression that enhances the activity of T-cells after CAR-T-cells are activated, thereby improving the antitumour activity of CAR-T-cells [133]