A Bispecific Anti-Fluorescein × Anti-CD3 T-cell Engager in Combination with Fluoresceinated Adaptors Enables Lysis of AML Cells.

Tumor-targeting antibodies, antibody-drug conjugates, and radionuclide antibody conjugates are established therapeutic tools in clinical use. Furthermore, bispecific T cell-engaging antibodies (TCEs) and chimeric antigen receptor (CAR) T cells are becoming the clinical standard of care in hemato-oncology and in some solid tissue neoplasms. To allow for on-off switching and targeting of multiple antigens, CAR T cells designed to recognize tumor-bound adaptor molecules (adaptor-CAR T cells) are now being investigated in clinical trials. We hypothesized that like adaptor-CAR T cells, a bispecific TCE recognizing CD3ε on T cells and fluorescein on tumor-bound adaptors would be able to direct T cells against target cells, potentially enabling multiplexing. We here show that a newly generated single-chain Fv-based anti-CD3 × anti-FITC construct (AdFITC-TCE) activates T cells toward acute myeloid leukemia (AML). Recognition of multiple targets through binding to fluoresceinated antibody constructs against CD33 and CD117 enables efficient tumor cell lysis in vitro. Moreover, we demonstrate that AdFITC-TCE plus fluoresceinated adaptors and T cells inhibit AML cell growth in NOD.Cg-Prkdcscid Il2rgtm1WjI/SzJ mice in vivo with similar efficacy as AdFITC-CAR T cells. Together, these data suggest that AdFITC-TCE, in combination with any given fluoresceinated binder, might be a versatile tool to activate T cells, leading to respective target cell lysis.