A combination dual-sized microparticle system modulates dendritic cells and prevents type 1 diabetes in prediabetic NOD mice

•Microparticles encapsulating multiple factors are fabricated in two size classes.•Microparticles encapsulate vitamin D3, insulin B peptide, TGF-β1 or GM-CSF.•Microparticle formulations maintain dendritic cell immature state.•Microparticle treated dendritic cells inhibit allogeneic T cell proliferation.•Microparticles prevent T1D in NOD mice when administered at 4 and 5 weeks of age.

We developed a novel poly(lactic-co-glycolic acid)-based, microparticle (MP) system providing concurrent delivery of multiple encapsulated immuno-suppressive factors and antigen, for in vivo conditioning of dendritic cells (DCs) toward a tolerance promoting pathway. Subcutaneous administration prevents onset of type 1 diabetes (T1D) in NOD mice. Two MP sizes were made: phagocytosable MPs were fabricated encapsulating vitamin D3 or insulin B(9–23) peptide, while unphagocytosable MPs were fabricated encapsulating TGF-β1 or GM-CSF. The combination of Vit D3/TGF-β1 MPs confers an immature and LPS activation-resistant phenotype to DCs, and MP-delivered antigen is efficiently and functionally presented. Notably, two subcutaneous injections into 4 week old NOD mice using the combination of MPs encapsulating Vit D3, Ins B, TGF-β1 and GM-CSF protected 40% of mice from T1D development, significant in comparison to the control. This work represents one of the first applications of a biomaterial-based, MP vaccine system to successfully prevent autoimmune diabetes.