Construction and characterization of novel CD33/CD3 tandem diabodies (TandAbs) for the treatment of acute myeloid leukemia (AML).

7067 Background: CD33 had been validated as an AML target in randomized studies of the antibody-drug conjugate, gemtuzumab ozogamicin (GO) in a subset of patients, but currently explored CD33-targeted therapeutics are ineffective in many patients. Here, we explored the potential therapeutic activity in AML of a series of novel CD33/CD3-directed tandem diabodies (TandAbs). These tetravalent bispecific antibodies comprised of single chain antibody variable fragments (scFv) have avidity due to two binding sites for each antigen and attractive pharmacokinetics due to a molecular size that is larger than the renal clearance threshold. Methods: CD33/CD3 TandAbs were generated from humananti-CD33 and anti-CD3 scFv domains and expressed in CHO cells. Binding affinities of purified TandAbs were determined via flow cytometry. T-cell activation was assessed via quantitation of CD25 and CD69 on T-cells. Cytotoxic properties of TandAbs against CD33+ AML cell lines and primary specimens from adults with AML, selected a...