Figure 1. Single chain variable fragment-based targeting of CD123. (A) The CD123-specific single chain variable fragments (scFvs) 26292 and 32716 were originally incorporated as recombinant immunotoxins targeting CD123⁺ acute myeloid leukemia (AML). (B) Schematic representation of our CD123 chimeric antigen receptor (CAR) T cell binding to CD123 on the surface of an AML cell. The CARs we developed include intracellular CD28 derived costimulatory and CD3ζ signaling domains. The extracellular portion of our CD123 CARs consists of a modified hinge-CH2-CH3 spacer derived from the Fc domain of IgG4 and either of 2 scFvs targeting CD123 (26292 or 32716).