Gene-gun biolistic immunization encoding glutamic acid decarboxylase: a model for studying Langerhans cell abnormalities and mimicry in the nonobese diabetic mouse

Gene gun-mediated DNA vaccination enhances antigen-specific immunotherapy at a late preclinical stage of type 1 diabetes in nonobese diabetic mice

Type 1 diabetes (T1D) is characterized by the T cell mediated destruction of the insulin-producing beta cells. Antigen-specific immunotherapies are used to selectively tolerize beta cell-specific pathogenic T cells either directly, or indirectly through the induction of immunoregulatory T cells. A key concern of antigen-specific immunotherapy is exacerbating autoimmunity. We compared the T cell reactivity and efficacy induced by plasmid DNA (pDNA) encoding glutamic acid decarboxylase 65 (GAD65) administered via intramuscular versus gene gun vaccination in NOD mice at a late preclinical stage of T1D. Whereas intramuscular injection of pGAD65 promoted a predominant type 1 CD4(+) T cell response and failed to suppress ongoing beta cell autoimmunity, gene gun vaccination preferentially induced IL-4 secreting CD4(+) T cells and significantly delayed the onset of diabetes. These findings demonstrate that gene gun delivery of autoantigen-encoding pDNA preferentially elicits immunoregulatory T cells and offers a safe, effective mode of pDNA vaccination for the treatment of T1D and other autoimmune diseases.

HLA class I epitope discovery in type 1 diabetes

Type 1 diabetes mellitus (T1DM) results from the destruction of beta cells by autoantigen-specific T cells. In the non-obese diabetic (NOD) mouse model, CD8+ T cells play an essential role in both the initial triggering of insulitis and its destructive phase, and proinsulin (PI) is one of the dominant target antigens (Ags). However, little is known about the beta cell epitopes presented by HLA class I molecules and recognized by human CD8+ T cells. We and other groups recently applied reverse immunology approaches to identify HLA class I-restricted PI epitopes. To establish an inventory of potential naturally processed epitopes, whole human PI or the transitional region between the B-chain and C-peptide were digested with purified proteasome complexes. By combining proteasome digestion data with epitope prediction algorithms, candidate epitopes restricted by HLA-A2.1 and other HLA class I molecules were identified. We validated immunogenicity and natural processing of the identified PI epitopes in HLA-A2.1-transgenic mice, while others demonstrated recognition of multiple PI epitopes by CD8+ T cells from T1DM and healthy subjects in the context of different HLA class I molecules. These results demonstrate the power of reverse immunology strategies for epitope discovery. DNA vaccination of HLA-transgenic mice may be another rapid and efficient reverse immunology approach to map additional epitopes derived from other T1DM Ags, such as IA-2 and glutamic acid decarboxylase 65 (GAD 65). Transfer of this information to Elispot- and MHC tetramer-based assay formats should allow to reliably detect and characterize autoreactive CD8+ T cell responses in T1DM, and may open new avenues for early T1DM diagnosis and immune intervention.