SUN-563 Safety And Efficacy Of Antigen Specific Car Tregs For Type 1 Diabetes Reversal. A Six Month Preclinical Trial.

Abstract Disclosure: S. Imam: AdopTracell. S. Rafiqi: None. J.C. Jaume: AdopTracell. The onset of human autoimmune Type 1 Diabetes (T1D) requires two key factors: genetic susceptibility and the presence of target autoantigen. Once activated, the immune system deploys autoantigen-specific cytotoxic T cells that destroy insulin-producing beta cells. Regulatory T cell (Treg) responses are often insufficient to suppress immune activity at inflammation sites.While Treg therapy shows promise for autoimmune diseases, its clinical application remains limited due to the low availability of antigen-specific Tregs. The ability to engineer Tregs with specificity to known autoantigens could enable targeted immune suppression and provide effective treatments. One strategy to impart antigen specificity involves using chimeric antigen receptors (CARs), which endow T cells with antibody-like antigen recognition. Adoptive cell transfer (ACT) therapies using CAR-engineered cytotoxic T cells have achieved notable success in treating hematologic cancers. This same technology can potentially redirect Tregs to autoimmune sites, offering therapeutic benefit across a range of autoimmune and alloimmune disorders.To this end, we developed a novel CAR-Treg approach targeting Glutamic Acid Decarboxylase 65 (GAD65) for the prevention and treatment of T1D. GAD65 is an enzyme critical for gamma-aminobutyric acid (GABA) synthesis in beta cells and neurons. Within beta cells, GAD65 resides in a vesicular compartment distinct from insulin granules. It is mainly anchored to Golgi membranes and trafficked via small cytoplasmic synaptic-like microvesicles (SLMVs) that carry GABA to the extracellular space. To support paracrine GABA signaling, SLMVs containing membrane-bound GAD65 are secreted from beta cells into the intra-islet interstitial space. As a well-established autoantigen in T1D-and with autoantibodies to GAD65 often detectable years before clinical symptoms—we have selected it as the target for our CAR-Treg therapy.We developed GAD65-CAR-Tregs and tested their therapeutic potential in a 6-month preclinical study in T1D mice. Treatment resulted in significant improvements in fasting blood glucose, insulin concentrations, and glucose tolerance. Histological analysis showed retrieval of infiltration of effector T cells and signs of Treg-mediated immune modulation, leading to the preservation and regeneration of pancreatic islet architecture. Notably, GAD65-CAR-Tregs did not cross the blood-brain barrier, and no neurological symptoms or cytokine release syndrome (CRS) were observed—supporting a favorable safety profile.Collectively, our findings demonstrate that GAD65-CAR-Tregs can home to pancreatic islets, suppress diabetogenic T cells, and reverse T1D in a clinically relevant mouse model. These results suggest that GAD65-CAR-Treg therapy holds strong potential for restoring immune tolerance and promoting beta-cell recovery in T1D patients. Presentation: Sunday, July 13, 2025