Membrane proximal epitope facilitates efficient T cell synapse formation by CD3-bispecific antibodies and is a requirement for myeloma cell killing by anti-FcRH5/CD3
J. Li1, N. Stagg1, J. Johnston1, M. J. Harris2, S. A. Menzies2, D. DiCara1, V. Clark1, R. Cook1, D. Slaga1, R. Nakamura1, L. MacCarty1, S. Sukumaran1, E. Luis1, Z. Ye1, T. Sumiyoshi1, D. Danilenko1, G. Lee1, K. Totpal1, D. Ellerman1, I. Hotzel1, J. R. James2, T. T. Junttila1*
1Genentech, Inc. 1 DNA Way, South San Francisco, CA 94080;
2Department of Medicine, University of Cambridge, MRC-LMB, Cambridge, CB2 0QH
*Corresponding author: Teemu T. Junttila, Genentech Inc. 1 DNA Way, South San Francisco, CA 94080
Bispecific antibodies that retarget cytotoxic T cell activity to kill cancer cells are currently under clinical evaluation. However, the molecular mechanism for how CD3-bispecific antibodies ‘trigger’ intracellular T cell signaling is not known. We demonstrate that bispecific antibodies invoke an equivalent biophysical mechanism of TCR triggering as that observed for the TCR/pMHC interaction, including target clustering and exclusion of CD45 phosphatase from the synapse. The dimensions of the target molecule play a key role in the efficiency of the synapse formation. However, we demonstrate that rational epitope selection can overcome the spatial inhibition caused by target molecules with a large extracellular domain and result in efficient synapse formation and highly potent T cell triggering. With this insight, we developed a novel T-cell dependent bispecific (TDB) antibody, anti-FcRH5/CD3 TDB, targeting the B cell lineage marker FcRH5 for multiple myeloma. Anti-FcRH5/CD3 TDB demonstrated cytotoxicity against human plasma cells and patient derived myeloma tumor cells at picomolar doses. Very low target expression level is sufficient to induce anti-FcRH5/CD3 TDB mediated killing, indicating broad activity in multiple myeloma where the prevalence of FcRH5 expression is 100%. In primates, anti-FcRH5/CD3 treatment resulted in complete depletion of tissue B cells and bone marrow plasma cells. Anti-FcRH5/CD3 TDB induces immunosuppressive feedback signaling, including PD1 up-regulation, which can be overcome by PD-L1 antibodies. These data demonstrate the potential for the anti-FcRH5/CD3 TDB, alone or in combination with inhibition of PD1/PDL1 signaling in the treatment of multiple myeloma and other B-cell malignancies.