Preproinsulin-specific regulatory T cell-derived exosomes loaded with immune-checkpoint ligands can suppress autoimmune responses in type 1 diabetes.

Background: Type 1 diabetes (T1D) involves selective destruction of pancreatic beta (β) cells, mainly by infiltrating CD8+ T cells. These CD8+ T cells also express immune-checkpoint molecules (ICMs) that can be targeted by immune-checkpoint ligands (ICLs) or β cell-specific Tregs. Here, we combined both approaches to suppress autoimmune responses in T1D.

Methods: We first performed profiling of various ICMs on peripheral CD8+ T cells in 40 recent-onset T1D and 20 age-matched healthy subjects by flow cytometry. Tregs were isolated from the same subjects and stimulated with preproinsulin (PPI) in vitro. Exosomes were isolated from PPI-specific Tregs and characterized by western blotting, transmission electron microscopy, zeta potential, and particle size analysis. Based on ICM profile, ICLs corresponding to the 3 most abundant ICMs (PD-1, TIGIT, BTLA) expressed on the peripheral CD8+ T cells were used for loading exosomes. The efficacy of ICL-loaded exosomes (PPI-T-EXO) was further assessed by various in vitro and in vivo approaches.

Results: The PPI-T-EXO inhibited the proliferation of autologous CD8+ and CD4+ Teff cells. The PPI-T-EXO and PPI-Tregs infused with PPI-T-EXO significantly downregulated the activation and cytotoxic potential of autologous PPI-pulsed CD8+ T cells. These Tregs also reduced CD8+ T cell-mediated apoptosis of human 1.1B4 β-cell line. In STZ-induced diabetic C57BL/6 mice, the mice-specific ICL-loaded exosomes delayed the onset of hyperglycemia, particularly when administered before the onset of diabetes and prolonged their survival by inhibiting perivascular lymphocytic intra-islet infiltration.

Conclusions: ICL-loaded PPI-Treg-derived exosomes can suppress β cell-specific T cell responses, offering a promising therapeutic intervention in T1D.