Herrmann et al. developed a checkpoint inhibitory T cell-engaging (CiTE) antibody consisting of an αCD33 single-chain variable fragment (scFv), an αCD3ε scFv, and the extracellular domain of PD-1 (PD-1ex), which has a low affinity to PD-L1 compared with αPD-L1 scFv. The CiTE antibody selectively bound acute myeloid leukemia (AML) cells and T cells, efficiently activated T cells, and led to AML cell lysis in vitro and complete tumor eradication in a murine xenograft model. Locally restricted checkpoint blockade and the preferential targeting of CD33+PD-L1+ but not other PD-L1+ cells by CITE reduced on-target, off-leukemia side effects in mice.
The CD33-targeting bispecific T-cell engager (BiTE(R)) AMG 330 proved to be highly efficient in mediating cytolysis of acute myeloid leukemia (AML) cells in vitro and in mouse models. Yet, T-cell activation is correlated with upregulation of PD-L1 and other inhibitory checkpoints on AML cells that confer adaptive immune resistance. PD 1 and PD-L1 blocking agents may counteract T-cell dysfunction, however, at the expense of broadly distributed immune-related adverse events (irAEs). We developed a bifunctional checkpoint inhibitory T-cell-engaging (CiTE) antibody that combines T-cell redirection to CD33 on AML cells with locally restricted immune checkpoint blockade. This is accomplished by fusing the extracellular domain of PD-1 (PD-1ex), which naturally holds a low affinity to PD-L1, to an alphaCD3.alphaCD33 BiTE(R)-like scaffold. By a synergistic effect of checkpoint blockade and avidity-dependent binding, the PD-1ex attachment increases T-cell activation (3.3-fold elevation of IFN-gamma) and leads to efficient and highly selective cytotoxicity against CD33(+)PD-L1(+) cell lines (EC50 = 2.3 pM to 26.9 pM) as well as patient-derived AML cells (n=8). In a murine xenograft model, the CiTE induces complete AML eradication without initial signs of irAEs as measured by body weight loss. We conclude that our molecule preferentially targets AML cells, whereas high-affinity blockers, such as clinically approved anti-cancer agents, also address PD-L1(+) non-AML cells. By combining the high efficacy of T-cell engagers with immune checkpoint blockade in a single molecule, we expect to minimize irAEs associated with the systemic application of immune checkpoint inhibitors and suggest high therapeutic potential, particularly for patients with relapsed/ refractory AML.
Author Info: (1) Gene Center and Department of Biochemistry, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (2) Department of Medicine III, University Hospital, Ludwig-Maximilians-U
Author Info: (1) Gene Center and Department of Biochemistry, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (2) Department of Medicine III, University Hospital, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (3) Gene Center Munich, Laboratory of Translational Cancer Immunology, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (4) Department of Medicine III, University Hospital, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (5) Department of Medicine III, University Hospital, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (6) Department of Medicine III, University Hospital, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (7) Center for Integrated Protein Science Munich (CIPSM), Munich, Germany. (8) Institute of Molecular Immunology, Helmholtz Zentrum Muenchen, Munich, Germany. (9) Department of Medicine III, University Hospital, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (10) Clinical Cooperation Group Leukemia at the Helmholtz Institute Munich, Munich, Germany. (11) Division of Clinical Pharmacology, Department of Internal Medicine IV, Klinikum der Ludwig-Maximilians-Universitaet Muenchen, Member of the German Center for Lung Research, Munich, Germany. (12) Gene Center and Department of Biochemistry, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (13) Gene Center and Department of Biochemistry, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany. (14) Department of Medicine III, University Hospital, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany; marion.subklewe@med.uni-muenchen.de.
