T-Switch: A specificity-based engineering platform for developing safe and effective T cell therapeutics.

Many promising targets for adoptive T cell therapy (ACT) are self-antigens, but self-reactive T cells are generally eliminated during thymic selection or diverted to regulatory phenotypes. To bypass T cell tolerance and obtain potent and safe T cell therapeutics, we developed T-Switch, an in vitro T cell receptor (TCR) engineering platform for the creation, modification, and comprehensive profiling of TCRs that can target self-antigens. T-Switch first expands T cells that recognize a "foreign" peptide closely related to a self-antigen. The fine specificity of the TCR is then modified by directed evolution of the peptide binding region to switch its specificity to the self-antigen of interest. We applied T-Switch to engineer synthetic TCRs reactive to a tumor-associated self-antigen, validated the safety and efficacy of this approach, and detected no off-target recognition as measured against the human proteome. Thus, T-Switch represents a resource for the creation of collections of highly sensitive synthetic TCRs for T cell-based immunotherapies.