CD28 and neoplasm: Generally, CARs comprise three domains: an extracellular single-chain antibody fragment (scFv), which serves as a target moiety that redirects T-cells to tumor cells by specifically binding to tumor-associated antigens (TAAs); a transmembrane domain and an endodomain, which is often the signal transduction domain comprising a CD3ζ chain and costimulatory factors such as CD28 and 4-1BB (CD137) (5, 6).