Induction of antigen-specific tolerance is perceived as the Holy Grail for the treatment of T1D, either early after onset or following islet transplantatio. Although the list of auto-antigens in T1D is far from being complete, and it is still unknown which one (if any) is the most """"""""important"""""""" one, accumulating evidence suggests that insulin is a key target of pathogenic T cells in type 1 diabetes in both NOD mice and humans, and that it may even be the long-sought-after 'initiating antigen'in this disease. Given the important role of dendritic cells (DCs) in the establishment of peripheral T cell tolerance, DC-based strategies are being explored as an important route to promote tolerance. In fact, advancements in the understanding of fetal-maternal and of tumor-induced tolerance highlight the key role that tolerogenic DC expressing Indoleamine-2,3 Dioxygenase (IDO) play in this process. Moreover, in vitro transfection of DC shows that IDO is sufficient to induce a tolerogenic phenotype. Current DC-based protocols aimed at the induction of tolerance require the in vitro preparation and transfection of autologous DC before reinfusion into patients. As such, the cost and technical challenges of the procedure appear overwhelming and require highly specialized centers. To overcome this limit, we propose the use of a novel nanostructure gene-based vaccine delivery that efficiently and specifically targets antigen-presenting cells (APC). Our strategy is therefore based on the selective targeting of DCs to co-deliver, as DNA, a disease-relevant autoantigen together with IDO in vivo using our nano-platform. We expect that, following targeted DNA transfection, the simultaneous expression of insulin and IDO by DC will induce a tolerogenic response that will mitigate/halt autoimmune destruction of islets. This platform is based on polyamidoamine (PAMAM) dendrimer (as a DNA loading surface) covalently conjugated to an MHC class II binding peptide that acts as a ligand to target APC, in particular DCs. The platform will be tested in NOD mice by evaluating: 1) its capacity to induce tolerance in adoptively transferred insulin-specific T cells and 2) its therapeutic efficacy in prevention of or at diabetes onset. The proposed peptide-dendrimer platform for in vivo targeted gene delivery should result in the same (or even a higher) tolerogenic efficacy seen with traditional methods for APC preparation, with sizable advantages including: i) low cost (one dose of peptide-dendrimer is estimated to cost 1$), and ii) simplicity in preparation and administration reducing the need for specialized center. Moreover, by using the INS B9-B29 targeting peptide that binds with high affinity not only the IAg7 MHC class II molecule, but also the human HLA DQ8 molecule, this platform opens the realistic possibility of an easy translation of positive findings towards the clinic.
Type-1 diabetes is caused by the destruction of pancreatic insulin-producing cells by the immune system. The immune system is a complex machinery in which different players interact to determine the outcome of any given response. Within the immune system, there is a well defined hierarchy, where cells called APCs (Antigen Presenting Cells) act somehow as orchestrators of the highly complex responses, with immune cells (lymphocytes) attacking and destroying a target (e.g. islets) or protecting it depending by the instruction received by the APCs. By conjugating the better understanding on the biology of the APC, with the advancement in the nanotechnology field, here we propose to modify in vivo the APC to express an enzyme called IDO (Indoleamine 2,3-dioxygenase) able to force the APCs and the lymphocytes to preserve rather than destroy the insulin producing tissue in the pancreas, thus preventing and possibly curing type 1 diabetes.
