Diabetes protection induced by liposome mediated antigen-specific immunotherapy is dependent on islet-specific T cell reprogramming

Background. In type 1 diabetes (T1D), insulin-producing pancreatic β cells are destroyed by CD4⁺ and CD8⁺ autoreactive T cells. Antigen-specific tolerance is desirable for T1D immunotherapy to avoid generalised immunosuppression. Our vaccine strategy uses liposome nanocarriers encapsulating disease-specific peptide and an immunomodulatory drug, both of which have excellent clinical safety records. This protocol is designed to generate tolerogenic DC that will inhibit antigen-specific effector immune cells but favour regulatory immune cells, and protect from disease.

Methods. We encapsulated the islet autoantigen Chromogranin A (ChgA) mimetope peptide and the NF-kB inhibitor calcitriol (active form of vitamin D3) into liposomes. Female NOD mice were injected subcutaneously with our liposomes or PBS, at day 0 and day 7 to target APCs. T cell responses were studied at day 4 and 11 in pancreatic draining LNs (pLN), spleens and pancreata by FACS using specific tetramer. Disease protection was compared by treating NOD mice at the onset of hyperglycemia and using NOD-SCID disease transfer models. 

Results. At day 4 the proportion of ChgA-reactive endogenous T cells expanded in pLN and spleen in response to liposomes delivering ChgA mimotope with or without calcitriol. By day 11, the T cells recognising ChgA were enriched in ChgA-specific Foxp3⁺ Tregs and Foxp3^-PD1⁺CD73⁺ICOS⁺ pTreg producing more IL-10 and less IFNg compared to control PBS treatment. Multiple ChgA/calcitriol treatments of NOD mice at onset of hyperglycaemia significantly delayed diabetes progression. The induction of a regulatory cell population was confirmed by co-transfer of splenocytes from liposome treated mice with diabetic splenocytes, which delayed disease transfer into NOD-SCID hosts.

Conclusions. These data indicate that endogenous ChgA-specific T cells can be reprogrammed to functional regulatory T cells after administration of liposomes. This protocol is a proof-of-concept for a translation towards a T1D clinical trial.