CD28 and neoplasm: CAR T cells have three components: 1) an extracellular single-chain variable fragment (scFv), which can specifically bind tumor-associated antigens (TAAs) through human leukocyte antigen (HLA)-independent recognition; 2) a hinge domain and transmembrane fragment from human CD8α; and 3) at least one intracellular costimulatory domain such as that from human CD28, CD137 or CD3ζ to promote cell proliferation and the release of cytokines and cytotoxic granules after activation by targeted tumor signals.