Bispecific antibodies enable synthetic agonistic receptor-transduced T cells for tumor immunotherapy.

Background: Genetically engineered T cells are powerful anti-cancer treatments but are limited by safety and specificity issues. We herein describe a MHC-unrestricted modular platform combining autologous T cells, transduced with a targetable synthetic agonistic receptor (SAR), with bispecific antibodies (BiAb) that specifically recruit and activate T cells for tumor killing. Methods: BiAbs of different formats were generated by recombinant expression. T cells were retrovirally transduced with synthetic agonistic receptors. T cell activation, proliferation, differentiation and T cell induced-lysis were characterized in three murine and human tumor models in vitro and in vivo . Results: Murine T cells transduced with SAR composed of an extracellular domain EGFRvIII fused to CD28 and CD3z signaling domains could be specifically recruited towards murine tumor cells expressing EpCAM by anti-EGFRvIII x anti-EpCAM BiAb. BiAb induced selective antigen-dependent activation, proliferation of SAR-T cells and redirected tumor cell lysis. Selectivity was dependent on the monovalency of the antibody for EGFRvIII. We identified FAS ligand as a major mediator of killing utilized by the T cells. Similarly, human SAR-T cells could be specifically redirected towards mesothelin-expressing human pancreatic cancer cells. In vivo , treatment with SAR-T cells and BiAb mediated anti-tumoral activity in three human pancreatic cancer cell xenograft models. Importantly, SAR-activity unlike CAR-activity was reversible in vitro and in vivo . Conclusions: We describe a novel ACT platform with anti-tumor activity in murine and human tumor models with a distinct mode of action that combines adoptive T cell therapy with bispecific antibodies.