Schematic diagram of the recombinant toxins used. GM-CSF–PE38KDEL, encoded by pRKGM9K, contains the 127 amino acids of human GM-CSF followed by amino acids 253 through 364 and 381 through 608 of PE and then the sequence KDEL. DT388–GM-CSF, encoded by pRKDTGM, contains the first 388 amino acids of DT followed by human GM-CSF. Anti-TFR(Fv)–PE38KDEL and DT388–anti-TFR(Fv), encoded by pRKHB9K and pJBDT1–anti-TFR(Fv), respectively, contain the same toxin domains as the respective GM-CSF toxins, but the ligand is the single-chain Fv of an antitransferrin receptor antibody.