GAD autoantibody epitope pattern after GAD-alum treatment in children and adolescents with type 1 diabetes

GAD65Abs Are Not Associated With Beta-Cell Dysfunction in Patients With T2D in the GRADE Study

Context

Autoantibodies directed against the 65-kilodalton isoform of glutamic acid decarboxylase (GAD65Abs) are markers of autoimmune type 1 diabetes (T1D) but are also present in patients with Latent Autoimmune Diabetes of Adults and autoimmune neuromuscular diseases, and also in healthy individuals. Phenotypic differences between these conditions are reflected in epitope-specific GAD65Abs and anti-idiotypic antibodies (anti-Id) against GAD65Abs. We previously reported that 7.8% of T2D patients in the GRADE study have GAD65Abs but found that GAD65Ab positivity was not correlated with beta-cell function, glycated hemoglobin (HbA1c), or fasting glucose levels.

Context

In this study, we aimed to better characterize islet autoantibodies in this T2D cohort. This is an ancillary study to NCT01794143.

Methods

We stringently defined GAD65Ab positivity with a competition assay, analyzed GAD65Ab-specific epitopes, and measured GAD65Ab-specific anti-Id in serum.

Results

Competition assays confirmed that 5.9% of the patients were GAD65Ab positive, but beta-cell function was not associated with GAD65Ab positivity, GAD65Ab epitope specificity or GAD65Ab-specific anti-Id. GAD65-related autoantibody responses in GRADE T2D patients resemble profiles in healthy individuals (low GAD65Ab titers, presence of a single autoantibody, lack of a distinct epitope pattern, and presence of anti-Id to diabetes-associated GAD65Ab). In this T2D cohort, GAD65Ab positivity is likely unrelated to the pathogenesis of beta-cell dysfunction.

Conclusion

Evidence for islet autoimmunity in the pathophysiology of T2D beta-cell dysfunction is growing, but T1D-associated autoantibodies may not accurately reflect the nature of their autoimmune process.

GAD-treatment of children and adolescents with recent-onset type 1 diabetes preserves residual insulin secretion after 30 months

BACKGROUND

This study aimed to analyse data from two different studies (phase II and phase III) regarding the safety and efficacy of treatment with alum formulated glutamic acid decarboxylase GAD65 (GAD-alum) at 30 months after administration to children and adolescents with type 1 diabetes.

METHODS

The phase II trial was a double-blind, randomised placebo-controlled study, including 70 children and adolescents who were followed for 30  months. Participants received a subcutaneous injection of either 20 µg of GAD-alum or placebo at baseline and 1 month later. During a subsequent larger European phase III trial including three treatment arms, participants received two or four subcutaneous injections of either 20 µg of GAD-alum and/or placebo at baseline, 1, 3 and 9  months. The phase III trial was prematurely interrupted at 15 months, but of the 148 Swedish patients, a majority completed the 21 months follow-up, and 45 patients completed the trial at 30 months. Both studies included GAD65 auto-antibodies-positive patients with fasting C-peptide ≥ 0.10 nmol/l. We have now combined the results of these two trials.

RESULTS

There were no treatment related adverse events. In patients treated with 2 GAD-alum doses, stimulated C-peptide area under the curve had decreased significantly less (9  m: p  <  0.037; 15 m: p  <  0.032; 21 m: p  <  0.003 and 30  m: p <  0.004), and a larger proportion of these patients were also able to achieve a peak stimulated C-peptide > 0.2  nmol/L (p  <  0.05), as compared with placebo.

CONCLUSION

Treatment with two doses of GAD-alum in children and adolescents with recent-onset type 1 diabetes shows no adverse events and preserves residual insulin secretion.

Characteristics of in-vitro phenotypes of glutamic acid decarboxylase 65 autoantibodies in high-titre individuals

Previous studies have indicated phenotypical differences in glutamic acid decarboxylase 65 autoantibodies (GADA) found in type 1 diabetes (T1D) patients, individuals at risk of developing T1D and stiff-person syndrome (SPS) patients. In a Phase II trial using aluminium-formulated GAD(65) (GAD-alum) as an immunomodulator in T1D, several patients responded with high GADA titres after treatment, raising concerns as to whether GAD-alum could induce GADA with SPS-associated phenotypes. This study aimed to analyse GADA levels, immunoglobulin (Ig)G1-4 subclass frequencies, b78- and b96·11-defined epitope distribution and GAD(65) enzyme activity in sera from four cohorts with very high GADA titres: T1D patients (n = 7), GAD-alum-treated T1D patients (n = 9), T1D high-risk individuals (n = 6) and SPS patients (n = 12). SPS patients showed significantly higher GADA levels and inhibited the in-vitro GAD(65) enzyme activity more strongly compared to the other groups. A higher binding frequency to the b78-defined epitope was found in the SPS group compared to T1D and GAD-alum individuals, whereas no differences were detected for the b96·11-defined epitope. GADA IgG1-4 subclass levels did not differ between the groups, but SPS patients had higher IgG2 and lower IgG4 distribution more frequently. In conclusion, the in-vitro GADA phenotypes from SPS patients differed from the T1D- and high-risk groups, and GAD-alum treatment did not induce SPS-associated phenotypes. However, occasional overlap between the groups exists, and caution is indicated when drawing conclusions to health or disease status.