Harnessing proximal T cell signaling molecules for enhanced CAR T cell activity

Chimeric antigen receptor (CAR) T cells mediate durable complete responses in patients with certain hematologic malignancies, but antigen downregulation is a common mechanism of resistance. While the native TCR can respond to very low levels of peptide presented in MHC, engineered CARs are incapable of responding to antigen-low targets, likely due to a disorganized immune synapse and poor recruitment of proximal signaling molecules. We developed a platform that endows CARs with the ability to kill antigen-low cancer cells, consisting of a membrane tethered version of the signaling molecule SLP-76 (MT-SLP-76). MT-SLP-76 can be expressed alongside any CAR to lower its threshold for activation and overcomes antigen low escape in multiple xenograft models. While SLP-76 is natively in the cytosol, only the engineered membrane tethered version can adequately amplify CAR signaling, a process that is mediated through recruitment of ITK and PLC1. MT-SLP-76 was designed based on biologic principles to render CAR T cell therapies less susceptible to antigen downregulation and is poised for clinical development to overcome this common mechanism of resistance.