Antigen-Specific Therapy for Autoimmune Disease: Prospects for the Prevention of Insulin-Dependent Diabetes

No Association ofINS-VNTR Genotype and IAA Autoantibodies

Type 1 diabetes is associated with autoimmune responses against insulin, with insulin autoantibodies (IAA) being a hallmark of the disease. Genetic susceptibility to type 1 diabetes is polygenic and includes the INS VNTR-IDDM2 locus, which has been shown to regulate the expression of insulin in the pancreas and thymus. In order to determine whether insulin autoimmunity could be attributed to a genetic susceptibility conferred by the INS-VNTR (IDDM2) locus, we studied the frequency of INS-VNTR alleles and the presence of IAA in 90 patients with new-onset type 1 diabetes. IAA were detected in 49 of 67 class I/I individuals and 19 of 23 class III/X patients, indicating that there is no association between the INS VNTR-IDDM2-susceptible allele and humoral autoimmunity against insulin. This finding does not support the hypothesis of an allele-specific tolerance induction that could determine susceptibility toward autoimmunity against the insulin protein and subsequently the development of type 1 diabetes.

Autoimmune responses to the beta cell autoantigen, insulin, and the INS VNTR-IDDM2 locus

Type 1 diabetes is associated with autoimmunity to insulin. Genetic susceptibility to type 1 diabetes is polygenic and includes the INS VNTR-IDDM2 locus which may regulate the expression of insulin in pancreas and thymus. In order to determine whether insulin autoimmunity could be attributed to a genetic susceptibility conferred by the INS VNTR-IDDM2 locus, peripheral blood T cell proliferation to human insulin and insulin autoantibodies (IAA) was measured in patients with new onset type 1 diabetes and control subjects. IAA were detected in 21 of 53 patients and in none of 25 control subjects, while T cell responses were low (stimulation index range 0.4-7.2) and similar in both groups. Both antibody and T cell responses were higher in younger subjects and IAA were more prevalent in patients with the HLA-DR4 allele. No relationship was observed between humoral and cellular responses to insulin. No association was found between the INS VNTR-IDDM2-susceptible allele and insulin autoimmunity. Increased T cell responses and IAA were found in patients with either the diabetes-susceptible or the diabetes-protective INS VNTR-IDDM2 locus genotypes, and increased T cell responses were also found in control subjects with either susceptible or protective INS VNTR-IDDM2 locus genotypes. This study confirms that primary T cell proliferative responses to insulin are low and detectable also in control subjects. The detection of T cell proliferation and autoantibodies to insulin in subjects with and without the protective INS VNTR-IDDM2 locus genotypes does not support the hypothesis of an allele-specific capacity for tolerance induction which could determine a susceptibility to develop autoimmunity against the insulin protein and subsequently diabetes.

Induction of autoimmune diabetes by oral administration of autoantigen

An antigen administered orally can induce immunological tolerance to a subsequent challenge with the same antigen. Evidence has been provided for the efficacy of this approach in the treatment of human autoimmune diseases such as rheumatoid arthritis and multiple sclerosis. However, oral administration of autoantigen in mice was found to induce a cytotoxic T lymphocyte response that could lead to the onset of autoimmune diabetes. Thus, feeding autoantigen can cause autoimmunity, which suggests that caution should be used when applying this approach to the treatment of human autoimmune diseases.

Aerosol insulin induces regulatory CD8 gamma delta T cells that prevent murine insulin-dependent diabetes

Cellular immune hyporesponsiveness can be induced by the presentation of soluble protein antigens to mucosal surfaces. Most studies of mucosa-mediated tolerance have used the oral route of antigen delivery and few have examined autoantigens in natural models of autoimmune disease. Insulin is an autoantigen in humans and nonobese diabetic (NOD) mice with insulin-dependent diabetes mellitus (IDDM). When we administered insulin aerosol to NOD mice after the onset of subclinical disease, pancreatic islet pathology and diabetes incidence were both significantly reduced. Insulin-treated mice had increased circulating antibodies to insulin, absent splenocyte proliferation to the major epitope, insulin B chain amino acids 9-23, which was associated with increased IL-4 and particularly IL-10 secretion, and reduced proliferation to glutamic acid decarboxylase, another islet autoantigen. The ability of splenocytes from insulin-treated mice to suppress the adoptive transfer of diabetes to nondiabetic mice by T cells of diabetic mice was shown to be caused by small numbers of CD8 gamma delta T cells. These findings reveal a novel mechanism for suppressing cell-mediated autoimmune disease. Induction of regulatory CD8 gamma delta T cells by aerosol insulin is a therapeutic strategy with implications for the prevention of human IDDM.