<i>In Situ</i> Bioconjugation of Synthetic Peptides onto Universal Chimeric Antigen Receptor T Cells for Targeted Cancer Immunotherapies

The recent development of modular universal chimeric antigen receptor (CAR) T-cell platforms that use bifunctional adaptor intermediates to redirect engineered T-cell effector function has greatly expanded the capabilities of adoptive T-cell therapy, enabling safer and more comprehensive cancer treatment. However, universal CAR receptor systems rely on unstable transient recognition of tag-coupled intermediates for T-cell activation, and the array of targeting intermediates has been limited to antibodies and small molecules. Addressing these shortcomings, we engineered universal CAR T-cell receptors that can be covalently modified with synthetic biomaterials <i>in vivo</i> by accelerated SpyCatcher003-SpyTag003 chemistry for cancer-cell targeting. SpyCatcher003-modified CARs, nicknamed DB5 CARs, displayed fast, low-nanomolar reaction kinetics with a synthetic αvβ6-binding peptide that incorporates a SpyTag003 peptide via branched peptide synthesis to comprise a bifunctional intermediate. Prearming DB5 CAR T cells or prelabeling target cells with the bifunctional peptide produced selective CD4⁺ and CD8⁺ CAR T-cell responses against αvβ6⁺ cancer cells <i>in vitro</i>. Furthermore, the synthetic targeting intermediate showed robust DB5 CAR T-cell arming <i>in vivo</i> and selectively reduced αvβ6⁺ tumor progression in a dual flank xenograft model. We demonstrate the versatility and therapeutic potential of "Cyborg" CAR T-cell therapies that utilize synthetic biomaterials to direct CAR T-cell activity via highly selective bioconjugation that occurs <i>in vivo</i>.