CAR T Cell Structure: CAR T cells are composed of 3 parts: (1) single-chain variable domain of an antibody (scFv), (2) a transmembrane domain, and (3) a signal transduction domain of the T-cell receptor (TCR). First-generation CAR T cells used a CD3ζ as the signal transduction domain of the TCR. Second-generation CAR T cells contained a co-stimulatory domain, either CD28 or 4-1BB. Third-generation CAR T cells were designed with two co-stimulatory domains. The first domain was either CD28 or 4-1BB, and the second domain was CD28, 4-1BB, or OXO40. This figure was created with images adapted from Servier Medical Art by Servier. Original images are licensed under a Creative Commons Attribution 3.0 Unported License.