Fig. 2

CAR-NK cell design. a Schematic overview of the building blocks for CAR-NK cells. From left to right: the extracellular single-chain variable fragment (scFv) consists linker-bound heavy and light chain and it determines the specificity of the CAR. The hinge region connects the tumor antigen-binding domain to the transmembrane region, ensures CAR stability and provides the flexibility for easy access to the target protein. The transmembrane region joins the extracellular and intracellular CAR domains, docks the CAR to the cell membrane and transduces activation signals to the intracellular activation signals. The number of intracellular activation domains determines the CAR generation. Various combinations of activating domains are used to mount a strong anti-tumor response. One example of a “fourth-generation” CAR is shown, co-expressing stimulating cytokines. Other examples of next-generation CAR constructs are discussed in Table 3. b and c Analysis of the most frequently used hinge (b) and transmembrane (c) regions for CAR-NK construction. Only studies reporting on the hinge region were included for this analysis. d Quantification of experimental studies with the indicated CAR-NK generations for cell line-derived (black) and primary NK cell-derived (pink) CAR-NK cells. e Pie charts showing the activation signals used for cell line-derived and primary cell CAR-NK cells, separated by CAR generation. Only the most frequently used combinations are shown