Abstract
Refractory acute myeloid leukemia (AML) remains an incurable malignancy despite the clinical use of novel targeted therapies, new antibody-based therapies, and cellular therapeutics. Here, we describe the preclinical development of a novel cell therapy that targets the antigen CLEC12A with a biparatopic bridging protein. Bridging proteins are designed as "CAR-T cell engagers," with a CAR-targeted protein fused to antigen binding domains derived from antibodies. Here, we created a CD19-anti-CLEC12A bridging protein that binds to CAR19 T cells and to the antigen CLEC12A. Biparatopic targeting increases the potency of bridging protein-mediated cytotoxicity by CAR19 T cells. Using CAR19 T cells that secrete the bridging protein we demonstrate potent activity against aggressive leukemic cell lines in vivo This CAR-engager platform is facile and modular, as illustrated by activity of a dual-antigen bridging protein targeting CLEC12A and CD33, designed to counter tumor heterogeneity and antigen escape, and created without the need for extensive CAR T-cell genetic engineering. CAR19 T cells provide an optimal cell therapy platform with well-understood inherent persistence and fitness characteristics.