GAD65 autoantibody epitopes in adult patients with latent autoimmune diabetes following GAD65 vaccination

Latent Autoimmune Diabetes in Adults (LADA): From Immunopathogenesis to Immunotherapy

Latent autoimmune diabetes in adults (LADA) is a type of diabetes characterized by slow autoimmune damage of pancreatic β cells without insulin treatment in the early clinical stage. There are differences between LADA and classical type 1 diabetes (T1D) and type 2 diabetes (T2D) in genetic background, autoimmune response, rate of islet function decline, clinical metabolic characteristics, and so on. The disease progression and drug response of patients with LADA are closely related to the level of islet autoimmunity, thus exploring the pathogenesis of LADA is of great significance for its prevention and treatment. Previous studies reported that adaptive immunity and innate immunity play a critical role in the etiology of LADA. Recent studies have shown that the intestinal microbiota which impacts host immunity hugely, participates in the pathogenesis of LADA. In addition, the progression of autoimmune pancreatic β cell destruction in LADA is slower than in classical T1D, providing a wider window of opportunities for intervention. Therefore, therapies including antidiabetic drugs with immune-regulation effects and immunomodulators could contribute to promising interventions for LADA. We also shed light on potential interventions targeting the gut microbiota and gut-associated immunity, which may be envisaged to halt or delay the process of autoimmunity in LADA.

GAD autoantibody affinity in adult patients with latent autoimmune diabetes, the study participants of a GAD65 vaccination trial

OBJECTIVE

Patients with latent autoimmune diabetes in adults (LADA) express autoantibodies against the 65-kDa isoform of GAD (GADA). Intervention with recombinant human GAD65 formulated with aluminium hydroxide (GAD-alum) given twice subcutaneously to LADA patients at intervals of 4 weeks was safe and did not compromise β-cell function in a Phase II clinical trial. GADA affinity has been shown to predict progression to type 1 diabetes. Here, we asked whether GADA affinity was affected by the GAD65 antigen-specific vaccination and/or associated with β-cell function in participants of this trial.

RESEARCH DESIGN AND METHODS

GADA affinity was measured in sera of 46 LADA patients obtained prior to the first week and 20 weeks after the second injection with GAD-alum or placebo using competitive binding experiments with [125I]-labeled and unlabeled human GAD65.

RESULTS

At baseline, GADA affinities ranged from 1.9 × 10(7) to 5.0 × 10(12) L/mol (median 2.8 × 10(10) L/mol) and were correlated with GADA titers (r = 0.47; P = 0.0009), fasting (r = -0.37; P = 0.01) and stimulated (r = -0.40; P = 0.006) C-peptide concentrations, and HbA1c (r = 0.39; P = 0.007). No significant changes in affinity were observed from baseline to week 24. Patients with GADA affinities in the lower first quartile (<4 × 10(9) L/mol) had better preserved fasting C-peptide concentrations at baseline than those with higher affinities (mean 1.02 vs. 0.66 nmol/L; P = 0.004) and retained higher concentrations over 30 months of follow-up (mean 1.26 vs. 0.62 nmol/L; P = 0.01).

CONCLUSIONS

Intervention with GAD-alum in LADA patients had no effect on GADA affinity. Our data suggest that patients with low GADA affinity have a prolonged preservation of residual β-cell function.

Immunotherapies in diabetes mellitus type 1

Type 1 diabetes is an autoimmune disease that gradually destructs insulin-producing beta cells. Over the years, clinicians' knowledge regarding the immunopathogenesis of this disease has greatly increased. Immunotherapies that can change the course of immune-mediated destruction and preserve and possibly regenerate the pancreatic beta cells seem to be promising in preclinical trials but so far have been unsuccessful in human studies. This article reviews the important immune interventions for type 1 diabetes that have been tried so far targeting the different stages of disease development and provides an insight into what the future might hold.

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

AIMS

We have previously shown that two injections of glutamic acid decarboxylase formulated in alum (GAD-alum) preserved residual insulin secretion in children and adolescents with recent onset type 1 diabetes (T1D), and was accompanied by increased GAD autoantibody (GADA) titers. The aim of this study was to investigate whether GAD-alum treatment affected the GADA epitope pattern.

METHODS

Serum samples from patients treated with GAD-alum (n = 33) or placebo (n = 27), at baseline, 1, 3, 9, and 15 months after the initial injection, were tested for their binding capacity to specific GADA epitopes in an epitope-specific radioligand binding assay with six recombinant Fab (rFab) (b96.11, DPA, DPD, MICA3, b78, and N-GAD(65) mAb).

RESULTS

No significant differences in variability of binding to any of the tested rFab were observed from baseline to 15 months. There was a sustained low binding of GADA to the b78- and N-GAD(65) mAb-defined epitopes, often recognized by GADA in patients with stiff person syndrome (SPS) and seldom in T1D patients. However, binding of GADA to the T1D-associated b96.11-defined epitope increased between baseline and 3 months in GAD-alum (-8.1%, min -72.4%, max 39.6%) compared to placebo patients (1.5%, min -28.3%, max 28.6%) (p = 0.02). Subsequently, the b96.11-defined epitope recognition returned to levels similar to that observed at baseline.

CONCLUSIONS

GAD-alum injections did not affect binding of GADA to SPS-related epitopes, further supporting the safety of the treatment. There were no changes in GADA epitope specificity to the T1D-related epitopes, except for a temporarily increased binding to one of the tested epitopes.

Interventions for latent autoimmune diabetes (LADA) in adults

BACKGROUND

Latent autoimmune diabetes in adults (LADA) is a slowly developing type 1 diabetes.

OBJECTIVES

To compare interventions used for LADA.

SEARCH STRATEGY

Studies were obtained from searches of electronic databases, supplemented by handsearches, conference proceedings and consultation with experts. Date of last search was December 2010.

SELECTION CRITERIA

Randomised controlled trials (RCT) and controlled clinical trials (CCT) evaluating interventions for LADA or type 2 diabetes with antibodies were included.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data and assessed risk of bias. Studies were summarised using meta-analysis or descriptive methods.

MAIN RESULTS

Searches identified 13,306 citations. Fifteen publications (ten studies) were included, involving 1019 participants who were followed between three months to 10 years (1060 randomised). All studies had a high risk of bias. Sulphonylurea (SU) with insulin did not improve metabolic control significantly more than insulin alone at three months (one study, n = 15) and at 12 months (one study, n = 14) of treatment and follow-up. SU (with or without metformin) gave poorer metabolic control compared to insulin alone (mean difference in glycosylated haemoglobin A1c (HbA1c) from baseline to end of study, for insulin compared to oral therapy: -1.3% (95% confidence interval (CI) -2.4 to -0.1; P = 0.03, 160 participants, four studies, follow-up/duration of therapy: 12, 30, 36 and 60 months; however, heterogeneity was considerable). In addition, there was evidence that SU caused earlier insulin dependence (proportion requiring insulin at two years was 30% in the SU group compared to 5% in conventional care group (P < 0.001); patients classified as insulin dependent was 64% (SU group) and 12.5% (insulin group, P = 0.007). No intervention influenced fasting C-peptide, but insulin maintained stimulated C-peptide better than SU (one study, mean difference 7.7 ng/ml (95% CI 2.9 to 12.5)). In a five year follow-up of GAD65 (glutamic acid decarboxylase formulated with aluminium hydroxide), improvements in fasting and stimulated C-peptide levels (20 μg group) were maintained after five years. Short term (three months) follow-up in one study (n = 74) using Chinese remedies did not demonstrate a significant difference in improving fasting C-peptide levels compared to insulin alone (0.07 µg/L (95% CI -0.05 to 0.19). One study using vitamin D with insulin showed steady fasting C-peptide levels in the vitamin D group but declining fasting C-peptide levels (368 to 179 pmol/L, P = 0.006) in the insulin alone group at 12 months follow-up. Comparing studies was difficult as there was a great deal of heterogeneity in the studies and in their selection criteria. There was no information regarding health-related quality of life, complications of diabetes, cost or health service utilisation, mortality and limited evidence on adverse events (studies on oral agents or insulin reported no adverse events in terms of severe hypoglycaemic episodes).

AUTHORS' CONCLUSIONS

Two studies show SU leading to earlier insulin dependence and a meta-analysis of four studies with considerable heterogeneity showed poorer metabolic control if SU is prescribed for patients with LADA compared to insulin. One study showed that vitamin D with insulin may protect pancreatic beta cells in LADA. Novel treatments such as GAD65 in certain doses (20 μg) have been suggested to maintain fasting and stimulated C-peptide levels. However, there is no significant evidence for or against other lines of treatment of LADA.

Vaccination against type 1 diabetes

The clinical onset of type 1 diabetes or autoimmune diabetes occurs after a prodrome of islet autoimmunity. The warning signals for the ensuing loss of pancreatic islet beta cells are autoantibodies against insulin, GAD65, IA-2 and ZnT8, alone or in combinations. Autoantibodies against, for example, insulin alone have only a minor risk of type 1 diabetes. However, progression to clinical onset is increased by the induction of multiple islet autoantibodies. At the time of clinical onset, insulitis may be manifest, which seems to reduce the efficacy of immunosuppression. Autoantigen-specific immunotherapy with alum-formulated GAD65 (Diamyd(®)) shows promise to reduce the loss of beta-cell function after the clinical onset of type 1 diabetes. The mechanisms are unclear but may involve the induction of T regulatory cells, which may suppress islet autoantigen reactivity. Past and ongoing clinical trials have been safe. Future clinical trials, perhaps as combination autoantigen-specific immunotherapy, may increase the efficacy in preventing the clinical onset in subjects with islet autoantibodies or preserve residual beta-cell function in patients newly diagnosed with type 1 diabetes.

GAD-alum immunotherapy in Type 1 diabetes mellitus

Glutamic acid decarboxylase (GAD)-alum (Diamyd®, Diamyd Medical, Stockholm, Sweden) is an adjuvant-formulated vaccine incorporating recombinant human GAD65, the specific isoform of GAD expressed in human pancreatic β-cells and a major antigen targeted by autoreactive T lymphocytes in Type 1 diabetes mellitus. Intermittent vaccination with this protein is theorized to induce immune tolerance to GAD65, thereby potentially interrupting further β-cell destruction. Hence, clinical trials are ongoing to examine the efficacy and safety of GAD-alum immunotherapy in patients with autoimmune-mediated forms of diabetes, including Type 1 diabetes and latent autoimmune diabetes in adults.

Changes in GAD65Ab-specific antiidiotypic antibody levels correlate with changes in C-peptide levels and progression to islet cell autoimmunity

CONTEXT

The previously reported absence of 65-kDa glutamate decarboxylase antibody (GAD65Ab)-specific antiidiotypic antibodies (anti-Id) in type 1 diabetes (T1D) patients at clinical onset could be due to an inability to mount an antibody response to GAD65Ab or a longitudinal decline in anti-Id levels.

OBJECTIVE AND DESIGN

We investigated anti-Id levels in longitudinal samples obtained from T1D patients (n = 41) (clinical diagnosis - 12 months), and latent autoimmune diabetes in adults (LADA) patients (n = 32) who received alum-formulated human recombinant GAD65 (baseline - 12 months). We also determined anti-Id levels in a small cohort of Type 2 diabetes patients during their development of autoimmune T cell responses.

RESULTS

At clinical onset T1D patients presented no or low anti-Id levels. However, 22/41 T1D patients showed ≥50% increase in GAD65Ab-specific anti-Id levels during follow-up; peaking at 3 (n = 1), 6 (n = 10), 9 (n = 10), or 12 (n = 1) months. Increasing anti-Id levels marked patients who experienced a temporary increase in C-peptide levels. Anti-Id levels correlated significantly with glycated hemoglobin and C-peptide levels at 6 and 9 months (P values ranged from <0.001 to <0.05). In LADA patients receiving placebo, anti-Id levels declined in seven of nine patients, whereas four of five patients receiving 20 μg alum-formulated human recombinant GAD65 showed increasing anti-Id levels. Changes in anti-Id and C-peptide levels closely correlated (P < 0.0001). The significant decline in anti-Id levels (P = 0.03) in T2D patients developing T cell autoimmune responses supports our hypothesis that declining anti-Id levels are associated with developing islet autoimmunity.

CONCLUSIONS

The close association between GAD65Ab-specific anti-Id levels and β-cell function may provide a novel marker for the progression of autoimmune diabetes.

Genetic-induced variations in the GAD65 T-cell repertoire governs efficacy of anti-CD3/GAD65 combination therapy in new-onset type 1 diabetes

To enhance efficacy of forthcoming type 1 diabetes (T1D) clinical trials, combination therapies (CTs) are envisaged. In this study, we showed that efficacy of a CT, using anti-CD3 antibody and glutamic acid decarboxylase of 65 kd (GAD65)-expressing plasmid, to reverse new-onset T1D was dependent upon the genetic background. Synergism between both treatments was only observed in the RIP-LCMV-GP but not in the nonobese diabetic (NOD) or RIP-LCMV-NOD models. Efficacy was associated with an expansion of bystander suppressor regulatory T cells (Tregs) recognizing the C-terminal region of GAD65 and secreting interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta), and interferon-gamma (IFN-gamma). In addition, we found that frequency and epitope specificity of GAD65-reactive CD4(+) T cells during antigen priming at diabetes onset and Tregs detected after CT correlated. Consequently, NOD mice harbored significantly lower levels of GAD65-reactive CD4(+) T cells than RIP-LCMV-GP before and after treatment. Our results demonstrate that antigen-specific T cells available at treatment may differ between various major histocompatibility complex (MHC) and genetic backgrounds. These cells play a major role in shaping T-cell responses following antigen-specific immune intervention and determine whether a beneficial Tregs response is generated. Our findings hold important implications to understand and predict the success of antigen-based clinical trials, where responsiveness to immunotherapy might vary from patient to patient.

Type 1 diabetes mellitus: primary, secondary, and tertiary prevention

We have entered the era of clinical trials to prevent type 1 diabetes mellitus (T1DM). Before 1922, when insulin was first given to a patient with diabetes, a diagnosis of T1DM was considered a death sentence. Advances in treatment for subjects with diabetes are not yet sufficient to prevent the deleterious impact of diabetes on both day-to-day activities and the early morbidity and mortality still associated with the disease. We now understand a great deal about blood glucose regulation and potential health complications associated with long-term T1DM, but the mystery of why, or the pathogenesis of this devastating disease, remains elusive. Great strides toward unraveling this mystery have been made over the past several decades. Even without definitive answers, we are moving from the period of discovery and animal research to the era of clinical trials. In this review, we wish to convey the palpable excitement in the field. It is time to determine if we can safely change the course of T1DM.