Figure 1. CAR-T-cell design.
All chimeric antigen receptor (CAR) designs contain an antigen-recognition domain and a signalling domain that provides ‘signal 1’ to activate T cells. Only this signalling domain is present in first-generation CARs. By contrast, a co-stimulatory signalling domain that provides ‘signal 2’ is added in second-generation CARs, and in third-generation CARs two co-stimulatory signalling domains are added.