Co-STARs: Combining the advantages of chimeric antigen and T cell receptors for cancer targeting

Two types of engineered T cells have been successfully used to treat cancer patients, one with an antigen recognition domain derived from antibodies (chimeric antigen receptors, CARs) and the other derived from T-cell receptors (TCRs). CARs employ high-affinity antigen binding domains and co-stimulatory domains to augment T-cell activation but can only react against target cells with relatively high amounts of antigen. TCRs have a much lower affinity for their antigens but can react against target cells displaying only a few antigen molecules. Here we describe a new type of receptor, called a Co-STAR (for Co-stimulatory Synthetic T-cell receptor and Antigen Receptor), that combines aspects of both CARs and TCRs. In Co-STARs, the antigen-recognizing components of TCRs are replaced by high-affinity antibody fragments and co-stimulation is provided by two modules that drive NFκB signaling (MyD88 and CD40). We demonstrate that Co-STARs produce robust T-cell expansion and induce long-term regressions of mouse tumors bearing very low densities of antigen.