We generated designer EVs to modulate T cells in the context of type 1 diabetes, a T cell–mediated autoimmune disease, by engineering a lymphoblast cell line, K562, to express HLA-A*02 (HLA-A2) alongside costimulatory CD80 and/or coinhibitory programmed death ligand 1 (PD-L1). The gene discussed is CD274; the disease is type 1 diabetes mellitus.