Submicron-sized ultrasound contrast agents as therapeutic peptide delivery vehicles in type 1 diabetes.

Background: Type 1 diabetes (T1D) is an autoimmune disease where autoreactive T cells infiltrate pancreatic islets, resulting in beta-cell destruction. Antigen-specific immunotherapy with tolerogenic peptides to induce peripheral tolerance has shown promise in preclinical studies but has not shown clinical efficacy. Methods: Here, we develop peptide-nanobubbles (NBs) as an image-guided platform for induction of peripheral immune tolerance in mouse models of T1D. Sub-micron sized NB ultrasound contrast agents can passively accumulate in pancreatic islets of non-obese diabetic (NOD) mice during the development of diabetes as a result of increased microvascular permeability. We incorporated an insulin B:9-23 peptide mimotope into NBs to target peptides to pancreatic islets for expansion of islet-resident regulatory T cells. Results: NBs retained normal size distribution and acoustic properties following peptide incorporation. Peptide-NBs accumulated in islets of NOD mice and this accumulation could be visualized in real time using contrast enhanced ultrasound. This resulted in an increased proportion of islet insulin-reactive regulatory T cells. Further, peptide-NBs prepared with a hybrid insulin peptide (HIP) expanded islet HIP-reactive regulatory T cells and substantially delayed diabetes onset in an adoptive transfer mouse model of autoimmune diabetes. Conclusions: Peptide-NBs offer a promising 'theranostic' approach for induction of peripheral tolerance in T1D while monitoring delivery and action via ultrasound contrast.