Enhanced Solid Tumor Recognition and T cell Stemness with SynNotch CAR Circuits

The lack of highly tumor-specific antigens limits the development of engineered T cell therapeutics because of life-threatening “on-target/off-tumor” toxicities. Here we identify ALPPL2 as a tumor-specific antigen expressed in a spectrum of solid tumors, including mesothelioma. ALPPL2 can act as a sole target for chimeric antigen receptor (CAR) therapy or be combined with tumor-associated antigens such as MCAM or mesothelin in synthetic Notch (synNotch) CAR combinatorial antigen circuits. SynNotch CAR T cells display superior tumor control when compared to CAR T cells to the same antigens by prevention of CAR-mediated tonic signaling allowing T cells to maintain a long-lived memory and non-exhausted phenotype. Collectively, we establish ALPPL2 as a clinically viable target for multiple solid tumors and demonstrate the multi-faceted therapeutic benefits of synNotch CAR T cells. ONE SENTENCE SUMMARY SynNotch CAR circuits targeting novel solid tumor antigens enhance specificity and improve therapeutic efficacy by regulating T cell exhaustion. ### Competing Interest Statement K.T.R. is a cofounder of Arsenal Biosciences. K.T.R. is an inventor on patents for synthetic Notch receptors (WO2016138034A1, PRV/2016/62/333,106) and receives licensing fees and royalties. The patents were licensed by Cell Design Labs and are now part of Gilead. He was a founding scientist/consultant and stockholder in Cell Design Labs, now a Gilead Company. K.T.R. holds stock in Gilead. The remaining authors declare no competing financial interests.