Expanding the Antigen Targeting of CAR T Cells via a Universal Bispecific T cell Engager 2259699

Abstract

Although CAR T cell therapy has shown remarkable clinical effects in the treatment of hematological cancers, the application of CAR T cells to treat solid tumors remains ineffective. Bispecific T cell Engagers (BiTE) are chimeric proteins capable of retargeting T cell receptors (TCR) to specific tumor antigens. CAR T cells expressing BiTEs have demonstrated superior effects against solid tumors in mouse models and early human clinical trials. Here, we have engineered T cells to secrete a universal BiTE termed, “SNAP-BiTE”. Consisting of a fusion of the SNAPtag enzyme to an anti-CD3 scFv, this protein covalently assembles with co-administered antibody “adaptors” containing a benzylguanine (BG) motif, thus allowing for post-translational and user-defined antigen targeting. We engineered human T cells to secrete SNAP-BiTE and measured activity in vitro in tumor cell coincubation assays by flow cytometry. Primary human T cells were engineered via a retroviral vector to secrete SNAP-BiTE. Co-incubating these cells with tumor cells and various BG-conjugated antibody adaptors (trastuzumab, rituximab, cetuximab, and mirvetuximab) led to antigen specific T cell activation and target cell lysis. Activity was responsive to the dose of antibody adaptor. In addition, multiple adaptors could be used to simultaneously assemble BiTEs targeting multiple antigens and lyse multiple populations of target cells. Importantly, SNAP-BiTE expressed from engineered T cells also engaged and robustly activated BiTE(-) T cells, amplifying anti-tumor activity. Finally, SNAP-BiTE could be efficiently expressed by CAR T cells to amplify and broaden their antigen targeting. SNAP-BiTE is a powerful approach to program engineered and endogenous T cell activity against multiple user-specified tumor antigens for improved anti-tumor cell therapy function. In vivo testing of CAR T cells secreting SNAP-BiTE in human tumor xenograft mouse models is underway. NIH T32EB00102, NIH 1R01GM142007, NIH 1R01CA290866 Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)