The biotechnology of chimeric antigen receptors for cytotoxic T cell-based cancer immunotherapy. A. Map of pELPS 19-BB-3ζ, a lentiviral vector that was approved for clinical trials . The open reading frame encoding the chimeric fusion protein CD19-BBζ contains portions coding for an anti-CD19 single-chain variable region fragment (scFv), the hinge and transmembrane (TM) domain of CD8, and a pair of signaling endodomains (one from CD137, the other from CD3ζ). This fusion protein gene is embedded within a disabled HIV-derived backbone containing truncated gag, pol and env sequences and the 5' and 3' long terminal repeats (LTR). In addition, the construct contains elongation factor 1α (EF-1α) coding sequences, the woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) and the bovine growth hormone polyadenylation (GH poly A) tail, as well as the ampicillin resistance gene and a bacterial replication origin. The total size of the construct is 11,556 base pairs. B. Diagram of the chimeric receptor protein in the T cell plasma membrane. The extracellular antibody recognition domain is linked via the CD8 TM domain to the cytoplasmic signaling domains of CD137 and CD3ζ. These endodomains accomplish the activation of transduced T cells and they stimulate T cell survival and proliferation in vivo.