Th33 - Developing Islet Antigen-Specific Regulatory T Cell For Therapy in Type 1 Diabetes

Early-phase clinical trials of ex vivo expanded polyclonal CD4⁺ T regulatory cells (Tregs) in Type 1 Diabetes (T1D) have shown persistence of the infused Tregs and promising safety profile. However, efficacy in stopping islet destruction has not yet been demonstrated, likely due to the very low frequency of islet antigen-specific Tregs among the polyclonal Treg preparations. Chimeric antigen receptor (CAR) is one potential strategy to redirect polyclonal Tregs to islet antigens. We thus constructed islet-specific CARs using previously validated nanobodies for human DPP6, a protein preferentially expressed by human islet endocrine cells. Nanobodies derived from camelidae antibodies have the advantages of being smaller, having a more stable structure, lower immunogenicity, and better access to target antigens than single chain variable fragments of antibodies that are commonly used in CAR construction. DPP6-CARs with IgG4 hinge, CD28 transmembrane, and CD28 and CD3 zeta signaling domains are expressed at the cell surface of primary human T conventional cells (Tconvs) and Tregs. When co-cultured with human islets, DPP6-CAR expressing T cells are strongly and specifically activated. In addition, DPP6-CAR Tregs suppress in vitro Tconv proliferation more efficiently than polyclonal Tregs. Since mouse islets do not express DPP6, we have developed a humanized T1D mouse model in which transplanted human islets or pluripotent stem cells-derived beta-like cells (BLC) are rejected by islet antigen-specific human Tconvs. Ongoing experiments are evaluating the in vivo suppressive capacity of DPP6-CAR Tregs. Results from this study will inform future efforts in translating this strategy to the clinic.