Preclinical development of desmoglein chimeric autoantibody receptor (CAAR) T cells for pemphigus therapy

Pemphigus vulgaris (PV) is a potentially fatal autoimmune blistering disease caused by autoantibodies to desmoglein (Dsg) 3 in the mucosal-dominant subtype and both Dsg3 and Dsg1 in mucocutaneous PV. Previously, we demonstrated preclinical proof-of-concept that a Dsg3 chimeric autoantibody receptor (CAAR) can redirect T cell cytotoxicity specifically toward anti-Dsg3 B cells, potentially leading to complete and durable remission of PV while avoiding toxicity from generalized B cell depletion. To move CAAR-T technology forward to clinical trials, we have now developed a combined Dsg3+Dsg1 CAAR-T product for the treatment of mucocutaneous PV, the most common and also the most severe pemphigus subtype. Dsg1 CAAR-Ts specifically kill anti-Dsg1 but not anti-Dsg3 B cells in vitro. Among Dsg1 CAAR-Ts engineered to include various Dsg1 extracellular cadherin (EC) domains, Dsg1 EC1-4 CAAR-Ts show optimal potency and breadth of cytotoxicity. Dsg CAAR-Ts maintain effective cytotoxicity even when CAAR expression is titrated down to 7%-23% cell surface positivity to minimize the number of lentiviral integration sites per cell, as measured by qPCR. A 1:1 mixture of Dsg3 and Dsg1 (D31) CAAR-Ts kills both anti-Dsg1 and anti-Dsg3 B cells, without apparent synergistic or antagonistic effect. Dsg3 CAAR-Ts alone, Dsg1 CAAR-Ts alone, and D31 CAAR-Ts show no toxicity against human skin xenografts in vivo in comparison to anti-CD19 chimeric antigen receptor (CAR)-Ts, which are known from human clinical trials not to cause direct skin toxicity. In an active immune PV mouse model, Dsg3 CAAR-Ts eliminate serum autoantibody titers compared to control-treated mice. These data establish the foundation for the design of the first-in-human phase 1 clinical trial of Dsg CAAR-Ts in PV patients in order to evaluate the safety and curative potential of CAAR-T technology for autoantibody-mediated diseases.