The article focuses on the use of immune-engineered extracellular vesicles (EVs) to modulate T cell activation in the context of type 1 diabetes. Topics include the generation of designer EVs expressing HLA-A2 and costimulatory CD80, the immunoregulatory response produced by adding coinhibitory PD-L1 to these EVs, and the importance of both peptide-HLA complex and costimulation for EV-mediated immune modulation.