Vaccination with citrullinated GRP78 peptide induces regulatory T-cell-driven tolerance in NOD mice

Background. Type 1 diabetes (T1D) is an autoimmune disease in which the immune system destroys insulin-producing pancreatic beta-cells. Although pro-insulin is probably the primary autoantigen, other non-beta-cell specific proteins behave as autoantigens. Data indicate that such proteins can become beta-cell specific target antigens when posttranslationally modified, as this could explain their escape from thymic tolerization. We have previously demonstrated that GRP78 is citrullinated upon inflammatory stress and is recognized as an autoantigen in non-obese diabetic (NOD) mice. Moreover, first evidence of autoreactivity against citrullinated GRP78 epitope 292-305 (292-305X) was shown in CD4+ T-cell outgrowth from an islet of a T1D patient. The aim of this project was to investigate whether this GRP78 peptide 292-305X can induce tolerance in NOD mice.

Methods. 3-week old pre-diabetic female NOD mice (n=17) were injected s.c. with 50µg of 292-305X (emulsified 1:1 in IFA) and followed-up for 26 weeks. As controls, mice were injected with the native peptide (292-305R in IFA, n=12) or IFA alone (n=17).

Results. Diabetes incidence was decreased in the group injected with 292-305X (18%) when compared with the IFA group (53%, p p<0.05) and the group vaccinated with the native peptide (67%, p<0.01). At 26 weeks of age, mice vaccinated with 292-305X showed a trend of reduced insulitis as compared to controls. The percentages of CD4+ and CD8+ effector memory cells (CD62L- CD44+) in the spleen, pancreatic lymph nodes and pancreas did not significantly differ between the groups. However, a significant increase in percentage of regulatory T cells (CD4+ CD25+ Foxp3+) was observed in pancreatic lymph nodes of protected mice vaccinated with 292-305X (p<0.05), as compared to the IFA group. These results indicate that peptide 292-305X can induce tolerance in pre-diabetic NOD mice by increasing regulatory T-cell frequencies. These findings may open new pathways for the development of therapeutic approaches for T1D.