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This trial assessed alum-formulated glutamic acid decarboxylase, the 65-kD isoform (GAD65), a major autoantigen in type 1 diabetes. In patients with recent-onset disease; the compound did not significantly alter the loss of C peptide or improve clinical outcomes. The clinical onset of type 1 diabetes is manifested by the effects of inadequate insulin secretion due to the immunologic destruction of pancreatic-islet beta cells. 1 Despite replacement therapy with exogenous insulin, type 1 diabetes is associated with substantial morbidity and mortality. 2 , 3 Even modest preservation of insulin secretion appears to reduce short- and long-term complications of type 1 diabetes. 4 – 9 Initial attempts at immunosuppression to treat type 1 diabetes had a positive effect but one that was outweighed by treatment-related adverse events. 10 – 12 More recently, selective immunosuppression has been attempted. Phase 2 trials showed promising efficacy, but phase 3 studies . . .

This study aimed to test whether injections of alum-formulated glutamic acid decarboxylase 65 (GAD), a major autoantigen in type 1 diabetes mellitus, would reverse recent-onset disease. C-peptide levels declined in both the treatment group and the control group, without significant between-group differences at month 15 (the primary end point), but they had declined significantly more slowly with treatment by month 30. The authors conclude that alum-formulated GAD may help preserve residual insulin secretion in patients with recent-onset type 1 diabetes. Study patients received injections of alum-formulated glutamic acid decarboxylase 65 (GAD). C-peptide levels declined in both the treatment group and the control group, but they had declined significantly more slowly with treatment by month 30. Type 1 diabetes mellitus is an autoimmune disease 1 that causes substantial morbidity and mortality. 2 , 3 Even modest residual insulin secretion, with stimulated C-peptide levels above 0.2 nmol per liter (0.6 ng per milliliter), has been reported to provide clinically meaningful benefits in terms of reducing long-term complications. 4 However, most attempts to preserve residual beta-cell function have achieved minimal benefits or have been associated with adverse effects. 5 – 14 Treatment with anti-CD3 monoclonal antibodies appears promising, although many patients in whom this approach has been used have had therapy-related adverse events. 15 , 16 As an alternative to immunosuppression, autoantigens may be used to . . .

The enzyme glutamate decarboxylase (GAD) produces the neurotransmitter GABA, using pyridoxal-5’-phosphate (PLP). GAD exists as two isoforms, GAD65 and GAD67. Only GAD65 acts as a major autoantigen, frequently implicated in type 1 diabetes and other autoimmune diseases. Here we characterize the structure and dynamics of GAD65 and its interaction with the autoimmune polyendocrine syndrome type 2-associated autoantibody b96.11. Using hydrogen-deuterium exchange mass spectrometry (HDX), X-ray crystallography, cryo-electron microscopy, and computational approaches, we examine the conformational dynamics of apo- and holoGAD65 and the GAD65-autoantibody complex. HDX reveals local dynamics accompanying autoinactivation, with the catalytic loop promoting collective motions at the CTD-PLP domain interface. In the GAD65-b96.11 complex, heavy chain CDRs dominate the interaction, with a long CDRH3 bridging the GAD65 dimer via electrostatic interactions with the 260 PEVKEK 265 motif. This bridging links structural elements controlling GAD65’s conformational flexibility to its autoantigenicity. Thus, intrinsic dynamics, rather than sequence differences within epitopes, appear to be responsible for the contrasting autoantigenicities of GAD65 and GAD67. Our findings elucidate the structural and dynamic factors that govern the varying autoantibody reactivities of GAD65 and GAD67, offering a revised rationale for the autoimmune response to GAD65. Using HDX-MS, X-ray crystallography, cryo-EM, and MD simulations, the authors examined the conformational dynamics of GAD65 in its apo- and holo- states and its interaction with the autoimmune polyendocrine syndrome type 2-associated autoantibody b96.11.

Many cancers have an unusual dependence on glutamine. However, most previous studies have focused on the contribution of glutamine to metabolic building blocks and the energy supply. Here, we report that cancer cells with aberrant expression of glutamate decarboxylase 1 (GAD1) rewire glutamine metabolism for the synthesis of γ-aminobutyric acid (GABA)—a prominent neurotransmitter—in non-nervous tissues. An analysis of clinical samples reveals that increased GABA levels predict poor prognosis. Mechanistically, we identify a cancer-intrinsic pathway through which GABA activates the GABA B receptor to inhibit GSK-3β activity, leading to enhanced β-catenin signalling. This GABA-mediated β-catenin activation both stimulates tumour cell proliferation and suppresses CD8 + T cell intratumoural infiltration, such that targeting GAD1 or GABA B R in mouse models overcomes resistance to anti-PD-1 immune checkpoint blockade therapy. Our findings uncover a signalling role for tumour-derived GABA beyond its classic function as a neurotransmitter that can be targeted pharmacologically to reverse immunosuppression. Huang et al. report upregulation of GABA synthesis and activation of β-catenin after rewiring of glutamine metabolism, which suppresses T-cell infiltration, enhances tumour growth and can be targeted to overcome resistance to immune checkpoint blockade.

Glutamic acid decarboxylase (GAD) is a major target of the autoimmune response that occurs in type 1 diabetes mellitus. In animal models of autoimmunity, treatment with a target antigen can modulate aggressive autoimmunity. We aimed to assess whether immunisation with GAD formulated with aluminum hydroxide (GAD-alum) would preserve insulin production in recent-onset type 1 diabetes. Patients aged 3–45 years who had been diagnosed with type 1 diabetes for less than 100 days were enrolled from 15 sites in the USA and Canada, and randomly assigned to receive one of three treatments: three injections of 20 μg GAD-alum, two injections of 20 μg GAD-alum and one of alum, or 3 injections of alum. Injections were given subcutaneously at baseline, 4 weeks later, and 8 weeks after the second injection. The randomisation sequence was computer generated at the TrialNet coordinating centre. Patients and study personnel were masked to treatment assignment. The primary outcome was the baseline-adjusted geometric mean area under the curve (AUC) of serum C-peptide during the first 2 h of a 4-h mixed meal tolerance test at 1 year. Secondary outcomes included changes in glycated haemoglobin A 1c (HbA 1c) and insulin dose, and safety. Analysis included all randomised patients with known measurements. This trial is registered with ClinicalTrials.gov, number NCT00529399. 145 patients were enrolled and treated with GAD-alum (n=48), GAD-alum plus alum (n=49), or alum (n=48). At 1 year, the 2-h AUC of C-peptide, adjusted for age, sex, and baseline C-peptide value, was 0·412 nmol/L (95% CI 0·349–0·478) in the GAD-alum group, 0·382 nmol/L (0·322–0·446) in the GAD-alum plus alum group, and 0·413 nmol/L (0·351–0·477) in the alum group. The ratio of the population mean of the adjusted geometric mean 2-h AUC of C-peptide was 0·998 (95% CI 0·779–1·22; p=0·98) for GAD-alum versus alum, and 0·926 (0·720–1·13; p=0·50) for GAD-alum plus alum versus alum. HbA 1c, insulin use, and the occurrence and severity of adverse events did not differ between groups. Antigen-based immunotherapy therapy with two or three doses of subcutaneous GAD-alum across 4–12 weeks does not alter the course of loss of insulin secretion during 1 year in patients with recently diagnosed type 1 diabetes. Although antigen-based therapy is a highly desirable treatment and is effective in animal models, translation to human autoimmune disease remains a challenge. US National Institutes of Health.

Antibodies to glutamic acid decarboxylase (GAD) have been associated with several neurological syndromes, including stiff-person syndrome, cerebellar ataxia and epilepsy. These antibodies were first described in 1988, but several controversies about GAD autoimmunity still remain. No criteria exist to establish when a neurological syndrome is pathogenically linked to GAD antibodies, often leading to the assumption that any syndrome in which these antibodies are present is immune mediated, sometimes resulting in misdiagnosis and unnecessary treatment. In this Review, we provide recommendations for assessing the association between a neurological syndrome and the presence of GAD antibodies, and we critically review the evidence on the pathogenicity of GAD antibodies. Given that stiff-person syndrome is usually autoimmune, the presence of GAD antibodies in the cerebrospinal fluid is sufficient to confirm a pathogenic link with GAD autoimmunity. However, for cerebellar ataxia, epilepsy and other syndromes with different aetiologies, we propose that confirmation of a pathogenic link with GAD autoimmunity requires demonstration of intrathecal GAD antibody synthesis. Nevertheless, the evidence that GAD antibodies are directly pathogenic is not yet convincing. Studies in animal models are needed to demonstrate whether neurological syndromes are directly caused by specific disruption of GAD function by GAD antibodies.Antibodies to glutamic acid decarboxylase (GAD) are associated with several neurological syndromes but their importance and role are controversial. In this Review, Graus et al. propose criteria for assessing the association between GAD antibodies and neurological syndromes and discuss the pathogenicity of GAD antibodies.

The γ-aminobutyric acid (GABA)ergic system is the primary inhibitory neurotransmission system in the mammalian brain. Its dysregulation has been shown in multiple brain conditions, but in Alzheimer’s disease (AD) studies have provided contradictory results. Here, we conducted a systematic review with meta-analysis to investigate whether the GABAergic system is altered in AD patients compared to healthy controls (HC), following the PRISMA 2020 Statement. We searched PubMed and Web of Science from database inception to March 18 th , 2023 for studies reporting GABA, glutamate decarboxylase (GAD) 65/67, GABA A , GABA B, and GABA C receptors, GABA transporters (GAT) 1–3 and vesicular GAT in the brain, and GABA levels in the cerebrospinal fluid (CSF) and blood. Heterogeneity was estimated using the I 2 index, and the risk of bias was assessed with an adapted questionnaire from the Joanna Briggs Institute Critical Appraisal Tools. The search identified 3631 articles, and 48 met the final inclusion criteria (518 HC, mean age 72.2, and 603 AD patients, mean age 75.6). Random-effects meta-analysis [standardized mean difference (SMD)] revealed that AD patients presented lower GABA levels in the brain (SMD = −0.48 [95% CI = −0.7, −0.27], adjusted p value (adj. p)  <  0.001 ) and in the CSF (−0.41 [−0.72, −0.09], adj. p  =  0.042 ), but not in the blood (−0.63 [−1.35, 0.1], adj. p  =  0.176 ). In addition, GAD65/67 (−0.67 [−1.15, −0.2], adj. p  =  0.006 ), GABA A receptor (−0.51 [−0.7, −0.33], adj. p  <  0.001 ), and GABA transporters (−0.51 [−0.92, −0.09], adj. p  =  0.016 ) were lower in the AD brain. Here, we showed a global reduction of GABAergic system components in the brain and lower GABA levels in the CSF of AD patients. Our findings suggest the GABAergic system is vulnerable to AD pathology and should be considered a potential target for developing pharmacological strategies and novel AD biomarkers.

OBJECTIVE: To assess long-term metabolic and immunological follow-up of microencapsulated human islet allografts in nonimmunosuppressed patients with type 1 diabetes (T1DM). RESEARCH DESIGN AND METHODS: Four nonimmunosuppressed patients, with long-standing T1DM, received intraperitoneal transplant (TX) of microencapsulated human islets. Anti-major histocompatibility complex (MHC) class I–II, GAD65, and islet cell antibodies were measured before and long term after TX. RESULTS: All patients turned positive for serum C-peptide response, both in basal and after stimulation, throughout 3 years of posttransplant follow-up. Daily mean blood glucose, as well as HbA1c levels, significantly improved after TX, with daily exogenous insulin consumption declining in all cases and being discontinued, just transiently, only in patient 4. Anti-MHC class I–II and GAD65 antibodies all tested negative at 3 years after TX. CONCLUSIONS: The grafts did not elicit any immune response, even in the cases where more than one preparation was transplanted, as a unique finding, compatible with encapsulation-driven \"bioinvisibility\" of the grafted islets. This result had never been achieved with the recipient’s general immunosuppression.

SignificanceAutoimmune type 1 diabetes is characterized by the formation of self-reactive antibodies. A prevalent human autoantigen is glutamate decarboxylase (GAD)65, a highly predictive marker that can precede the emergence of disease by up to several years. Intriguingly, the closely related isoform GAD67 is not immunogenic. What are the determinants of the unique self-reactivity of GAD65 vs. GAD67? We show that, unlike GAD67, GAD65 is highly flexible and exists in multiple structural forms. We show that self-antibodies bind differentially to these GAD65 forms. These properties may be an undesirable consequence of conformational flexibility necessary for enzyme function. Our findings, thus, provide insights into how structural flexibility governs protein immunogenicity in autoimmune diabetes and have implications for therapeutic antibody and vaccine design. The human neuroendocrine enzyme glutamate decarboxylase (GAD) catalyses the synthesis of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) using pyridoxal 5′-phosphate as a cofactor. GAD exists as two isoforms named according to their respective molecular weights: GAD65 and GAD67. Although cytosolic GAD67 is typically saturated with the cofactor (holoGAD67) and constitutively active to produce basal levels of GABA, the membrane-associated GAD65 exists mainly as the inactive apo form. GAD65, but not GAD67, is a prevalent autoantigen, with autoantibodies to GAD65 being detected at high frequency in patients with autoimmune (type 1) diabetes and certain other autoimmune disorders. The significance of GAD65 autoinactivation into the apo form for regulation of neurotransmitter levels and autoantibody reactivity is not understood. We have used computational and experimental approaches to decipher the nature of the holo → apo conversion in GAD65 and thus, its mechanism of autoinactivation. Molecular dynamics simulations of GAD65 reveal coupling between the C-terminal domain, catalytic loop, and pyridoxal 5′-phosphate–binding domain that drives structural rearrangement, dimer opening, and autoinactivation, consistent with limited proteolysis fragmentation patterns. Together with small-angle X-ray scattering and fluorescence spectroscopy data, our findings are consistent with apoGAD65 existing as an ensemble of conformations. Antibody-binding kinetics suggest a mechanism of mutually induced conformational changes, implicating the flexibility of apoGAD65 in its autoantigenicity. Although conformational diversity may provide a mechanism for cofactor-controlled regulation of neurotransmitter biosynthesis, it may also come at a cost of insufficient development of immune self-tolerance that favors the production of GAD65 autoantibodies.

Gene transfer of glutamic acid decarboxylase ( GAD) and other methods that modulate production of GABA in the subthalamic nucleus improve basal ganglia function in parkinsonism in animal models. We aimed to assess the effect of bilateral delivery of AAV2- GAD in the subthalamic nucleus compared with sham surgery in patients with advanced Parkinson's disease. Patients aged 30–75 years who had progressive levodopa-responsive Parkinson's disease and an overnight off-medication unified Parkinson's disease rating scale (UPDRS) motor score of 25 or more were enrolled into this double-blind, phase 2, randomised controlled trial, which took place at seven centres in the USA between Nov 17, 2008, and May 11, 2010. Infusion failure or catheter tip location beyond a predefined target zone led to exclusion of patients before unmasking for the efficacy analysis. The primary outcome measure was the 6-month change from baseline in double-blind assessment of off-medication UPDRS motor scores. This trial is registered with ClinicalTrials.gov, NCT00643890. Of 66 patients assessed for eligibility, 23 were randomly assigned to sham surgery and 22 to AAV2- GAD infusions; of those, 21 and 16, respectively, were analysed. At the 6-month endpoint, UPDRS score for the AAV2- GAD group decreased by 8·1 points (SD 1·7, 23·1%; p<0·0001) and by 4·7 points in the sham group (1·5, 12·7%; p=0·003). The AAV2- GAD group showed a significantly greater improvement from baseline in UPDRS scores compared with the sham group over the 6-month course of the study (RMANOVA, p=0·04). One serious adverse event occurred within 6 months of surgery; this case of bowel obstruction occurred in the AAV2- GAD group, was not attributed to treatment or the surgical procedure, and fully resolved. Other adverse events were mild or moderate, likely related to surgery and resolved; the most common were headache (seven patients in the AAV2- GAD group vs two in the sham group) and nausea (six vs two). The efficacy and safety of bilateral infusion of AAV2- GAD in the subthalamic nucleus supports its further development for Parkinson's disease and shows the promise for gene therapy for neurological disorders. Neurologix.