Immunological characterization and therapeutic activity of an altered-peptide ligand, NBI-6024, based on the immunodominant type 1 diabetes autoantigen insulin B-chain (9-23) peptide

Analysis of T cell receptor beta chains that combine with dominant conserved TRAV5D-4*04 anti-insulin B:9-23 alpha chains

OBJECTIVE

The objective of this study was to define the spectrum of TCR beta chains permissive for T cells with alpha chains containing the conserved TRAV5D-4*04 sequence to target the insulin B:9-23 peptide, a major epitope for initiation of diabetes in the NOD mouse.

MATERIALS AND METHODS

We produced T cell hybridomas from mice with single T cell receptors (BDC12-4.1 TCR alpha(+)beta(+) double transgenic mice and BDC12-4.4 TCR alpha(+)beta(+) double retrogenic mice) or from mice with only the corresponding alpha chains transgene or retrogene and multiple endogenous TCR beta chains.

RESULTS

Hybridomas with the complete BDC12-4.1 and BDC12-4.4 T cell receptors, despite having markedly different TCR beta chains, responded to similar B:9-23 peptides. Approximately 1% of the hybridomas from mice with the fixed TRAV5D-4*04 alpha chains and multiple endogenous beta chains responded to B:9-23 peptides while the majority of hybridomas with different beta chains did not respond. There was no apparent conservation of TCR beta chain sequences in the responding hybridomas.

CONCLUSIONS

Approximately 1% of hybridomas utilizing different TCR beta chains paired with the conserved TRAV5D-4*04 containing alpha chains respond to insulin peptide B:9-23. Therefore, TCR beta chain sequences make an important contribution to insulin B:9-23 peptide recognition but multiple beta chain sequences are permissive for recognition.

The good, the bad and the ugly: how altered peptide ligands modulate immunity

BACKGROUND

The basis of T cell immune responses is the specific recognition of an immunogenic peptide epitope by a T cell receptor. Peptide alterations of such T cell epitopes with single or few amino acid variations can have drastic effects on the outcome of this recognition. These altered peptide ligands can act as modulators of immune responses as they are capable of downregulating or upregulating responses.

OBJECTIVE/METHODS

We review how altered peptide ligands can have 'good' 'bad' and 'ugly' outcomes in treating diseases.

RESULTS/CONCLUSION

Altered peptide ligands have been used as immunotherapeutics in autoimmune (and allergic) diseases, infectious diseases and cancer. In the next five years we anticipate seeing a number of altered peptide ligands in clinical trials, progressing from contradictory classifications of good, bad or ugly, to the exciting outcome of 'useful'.

Mucosal administration of an altered CII263-272 peptide inhibits collagen-induced arthritis by suppression of Th1/Th17 cells and expansion of regulatory T cells

Rheumatoid arthritis (RA) is a systemic autoimmune disease mediated by T cells. Collagen type II (CII) is one of the autoantigens associated with RA. CII263-272 is a predominant CII antigenic peptide that can induce T-cell activation upon binding to MHC and interaction with the appropriate T-cell receptor (TCR). Altered CII263-272 peptides with substitution of specific amino acids could bind to RA-associated HLA-DR4/1 with no T cell stimulating effects and could inhibit T cell activation in RA. We performed this study to evaluate the effect of mucosal administration and to explore the mechanism of the inhibitory effect of altered CII263-272 peptide (267Q-->A, 270K-->A and 271G-->A) on collagen induced arthritis (CIA). CIA was induced in Lewis rats by immunization with bovine CII. Altered CII263-272 peptide was given intranasally beginning from arthritis onset. Wild CII263-272 peptide or PBS was administered as controls. Therapeutic effects were evaluated by arthritis scores, body weight change, and joint pathologic scores. The anti-CII antibody and its subtypes and the cytokines, IFN-gamma, IL-10, and IL-17 were measured with ELISA. Foxp3+CD4+CD25+ regulatory T cell induction was assessed by FACS analysis. Following treatment with the altered CII263-272 peptide, arthiritis scores were reduced and body weight was increased. The altered CII263-272 peptide could retard the histologic lesion of the joints. The titers of anti-CII antibodies IgG2a in altered CII263-272 peptide treated rats decreased markedly compared to PBS-treated rats. The serum levels of IFN-gamma in rats treated with altered peptide was lower than that of rats treated with wild CII263-272 peptide and PBS. No differences were observed in the levels of serum IL-10 among the three groups. The altered CII263-272 peptide could decrease serum level of IL-17 and increase peripheral Foxp3+CD4+CD25+ T cells at early stage of CIA. Mucosal administration of altered CII263-272 peptide could effectively inhibit the progression of CIA. Altered CII263-272 peptide could suppress Th17 cells and expand regulatory T cells in the early stage of the disease. The IgG2a subtype of anti-CII antibodies and IFN-gamma were reduced and in vivo Th1 responses were inhibited as a result of altered CII peptide treatment. Altered CII peptide is likely therapeutic in RA.

Vaccines for multiple sclerosis: progress to date

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS, characterized pathologically by a perivascular infiltrate consisting predominantly of T cells and macrophages. Although its aetiology remains unknown, several lines of evidence support the hypothesis that autoimmune mechanisms play a major role in the development of the disease. Several widely used disease-modifying agents are approved for the treatment of MS. However, these agents are only partially effective and their ability to attenuate the more progressive phases of the disease is not clear at this time. Therefore, there is a need to develop improved treatment options for MS. This article reviews the role of several novel, selective vaccine strategies that are currently under investigation, including: (i) T-cell vaccination (TCV); (ii) T-cell receptor (TCR) peptide vaccination; (iii) DNA vaccination; and (iv) altered peptide ligand (APL) vaccination. The administration of attenuated autoreactive T cells induces regulatory networks to specifically suppress pathogenic T cells in MS, a strategy named TCV. The concept of TCV was based on the experience of vaccination against aetiological agents of infectious diseases in which individuals are purposely exposed to an attenuated microbial pathogen, which then instructs the immune system to recognize and neutralize it in its virulent form. In regard to TCV, attenuated, pathogenic T cells are similarly used to instruct the immune system to recognize and neutralize disease-inducing T cells. In experimental allergic encephalomyelitis (EAE), an animal model for MS, pathogenic T cells use a strikingly limited number of variable-region elements (V region) to form TCR specific for defined autoantigens. Thus, vaccination with peptides directed against these TCR structures may induce immunoregulatory mechanisms, thereby preventing EAE. However, unlike EAE, myelin-reactive T cells derived from MS patients utilize a broad range of different V regions, challenging the clinical utility of this approach. Subsequently, the demonstration that injection of plasmid DNA encoding a reporter gene into skeletal muscle results in expression of the encoded proteins, as well as in the induction of immune responses in animal models of autoimmunity, was explored as another strategy to re-establish self-tolerance. This approach has promise for the treatment of MS and, therefore, warrants further investigation. APLs are molecules in which the native encephalitogenic peptides are modified by substitution(s) of one or a few amino acids critical for contact with the TCR. Depending on the substitution(s) at the TCR contact residues of the cognate peptide, an APL can induce immune responses that can protect against or reverse EAE. However, the heterogeneity of the immune response in MS patients requires further study to determine which patients are most likely to benefit from APL therapy. Other potential approaches for vaccines in MS include vaccination against axonal growth inhibitors associated with myelin, use of dendritic cells pulsed with specific antigens, and active vaccination against proinflammatory cytokines. Overall, vaccines for MS represent promising approaches for the treatment of this devastating disease, as well as other autoimmune diseases.

Combined insulin B:9-23 self-peptide and polyinosinic-polycytidylic acid accelerate insulitis but inhibit development of diabetes by increasing the proportion of CD4+Foxp3+ regulatory T cells in the islets in non-obese diabetic mice

Insulin peptide B:9-23 is a major autoantigen in type 1 diabetes. Combined treatment with B:9-23 peptide and polyinosinic-polycytidylic acid (poly I:C), but neither alone, induce insulitis in normal BALB/c mice. In contrast, the combined treatment accelerated insulitis, but prevented diabetes in NOD mice. Our immunofluorescence study with anti-CD4/anti-Foxp3 revealed that the proportion of Foxp3 positive CD4(+)CD25(+) regulatory T cells (Tregs) was elevated in the islets of NOD mice treated with B:9-23 peptide and poly I:C, as compared to non-treated mice. Depletion of Tregs by anti-CD25 antibody hastened spontaneous development of diabetes in non-treated NOD mice, and abolished the protective effect of the combined treatment and conversely accelerated the onset of diabetes in the treated mice. These results indicate that poly I:C combined with B:9-23 peptide promotes infiltration of both pathogenic T cells and predominantly Tregs into the islets, thereby inhibiting progression from insulitis to overt diabetes in NOD mice.

Immunotherapeutic potential of the immunodominant T-cell epitope of lipocalin allergen Bos d 2 and its analogues

Lipocalin allergens, which contain most of the important animal-derived respiratory sensitizers, induce T helper type 2 (Th2) deviation, but the reasons for this are not clear. To explore the prospects for peptide-based allergen immunotherapy and to elucidate the characteristics of the immunodominant epitope of Bos d 2, BALB/c mice were immunized with a peptide containing the epitope, peptides containing its analogues, peptides from the corresponding regions of other lipocalin proteins, and peptides with a homologous sequence. We observed that murine spleen cells recognized the immunodominant epitope of Bos d 2, p127-142, in almost the same way as human Bos d 2-specific T cells did. Enzyme-linked immunosorbent spot-forming cell assay (ELISPOT) analyses showed that p127-142 and a corresponding peptide from horse Equ c 1 induced a Th2-deviated cellular response, whereas a homologous bacterial peptide from Spiroplasma citri induced a Th0-type response. Interestingly, the spleen cell response to the bacterial peptide and p127-142 was cross-reactive, that is, able to induce reciprocally the proliferation and cytokine production of primed spleen cells in vitro. More importantly, the peptides were able to skew the phenotype of T cells primed with the other peptide. Our results suggest that modified peptides can be useful in allergen immunotherapy.

Deleting islet autoimmunity

Even though there are numerous autoantigens for type 1 diabetes, current evidence suggests that a single autoantigen, namely insulin, is responsible for the key initiating event in autoimmunity. If a single autoantigen is necessary for triggering the autoimmune process, then antigen-specific therapy to block or delete the immune response against that autoantigen before epitope spreading occurs, may become a larger focus of future immunotherapeutic strategies. In this article, we review current literature regarding insulin as an autoantigen and potential approaches to deleting insulin-reactive T cells through the use of peptide vaccines and targeted T cell receptor immunizations.

Altered B:9–23 Insulin, When Administered Intranasally with Cholera Toxin Adjuvant, Suppresses the Expression of Insulin Autoantibodies and Prevents Diabetes

Insulin peptide B:9-23 is a major autoantigen in type 1 diabetes that contains two distinct CD4 epitopes (B:9-16 and B:13-23). One of the two epitopes, B:13-23, overlaps with a CTL epitope (B:15-23). In this study, we report that the elimination of the CTL epitope from the B:9-23 peptide by amino acid substitution (with alanine) at positions B:16 and 19 (A16,19 altered peptide ligand) or truncation of the C-terminal amino acids from the peptide (B:9-21), neither of which stimulated the proliferation of insulin B:15-23 reactive CD8 T cells, provided significant intranasally induced suppression of diabetes when coadministered with a potent mucosal adjuvant cholera toxin (CT). Intranasal treatment with A16,19 resulted in the elimination of spontaneous insulin autoantibodies, significant inhibition of insulitis and remission from hyperglycemia, and prevented the progression to diabetes. Intranasal administration of native B:9-23/CT or B:11-23/CT resulted in a significant enhancement of insulin autoantibody expression and severity of insulitis and failed to prevent diabetes. Our present study indicates that elimination of the CTL epitope from the B:9-23 peptide was critically important for mucosally induced diabetes prevention. The A16,19 altered peptide ligand, but not other native insulin peptides, suppresses insulin autoantibodies associated with protection from and remission of diabetes.

The insulin-specific T cells of nonobese diabetic mice recognize a weak MHC-binding segment in more than one form

Several naturally occurring anti-insulin CD4 T cells were isolated from islet infiltrates of NOD mice. In accordance with the results of others, these T cells recognized the segment of the beta-chain from residues 9-23. Peptides encompassing the B:(9-23) sequence bound weakly to I-Ag7 in two main contiguous registers in which two residues at the carboxyl end, P20Gly and P21Glu, influenced binding and T cell reactivity. Naturally occurring insulin-reactive T cells exhibited differing reactivities with the carboxyl-terminal amino acids, although various single residue changes in either the flanks or the core segments affected T cell responses. The insulin peptides represent another example of a weak MHC-binding ligand that is highly immunogenic, giving rise to distinct populations of autoimmune T cells.

Progress in the development of immune-based therapies for type 1 diabetes mellitus

Between ten and twenty million people worldwide have type 1 diabetes mellitus (T1DM), which has previously been called juvenile diabetes, childhood diabetes, and insulin-dependent diabetes mellitus. T1DM is undoubtedly a multifactorial disease affecting predisposed individuals with genetic susceptibilities; it is also associated with environmental factors leading to unbalanced immune responses. This chronic disorder is caused by auto-aggressive T lymphocytes entering the pancreatic islets of Langerhans where they destroy the insulin-producing beta-cells. A wide variety of immuno-interventions cure T1DM effectively in different animal models when given early in disease development. However, few of these interventions are efficacious in humans at a later stage of the disease. Indeed, only three immunotherapeutic compounds have demonstrated both safety and efficacy in phase II/III clinical trials. Although much time and resources have been spent on generating potent immune therapies, none of the patients enrolled in these trials have achieved normoglycemia in the absence of insulin injections. Many reasons can account for such a disappointing conclusion. Firstly, the dynamics of disease pathogenesis differs significantly from patient to patient, which directly impacts the therapeutic efficacy. Also, at trial entry, the percentage of remaining pancreatic beta-cells in T1DM patients often reflects the odds of responding positively to treatment. Based on the knowledge we have gained from preclinical studies and clinical trials, several steps have been made in the development of safer and more efficient immune-based therapies. There are, however, a number of concerns that should be addressed in order to improve future therapeutic strategies.

Translational mini-review series on type 1 diabetes: Immune-based therapeutic approaches for type 1 diabetes

Type 1 diabetes (T1D) is often considered the prototype organ-specific autoimmune disease in clinical immunology circles. The key disease features - precise destruction of a single endocrine cell type occurring on a distinct genetic and autoimmune background - have been unravelled in recent years to such an extent that there is a growing expectation that the disease should be curable. T1D is something of an orphan disease, currently managed by endocrinologists yet dependent upon the wit of immunologists, both basic and clinical, to find the best approaches to prevention and cure. Type 1 diabetes thus represents one of the most active arenas for translational research, as novel immune-based interventions find their way to the clinic. The first serious attempt at immune-based treatment for T1D was in 1984, the first at prevention in 1993; current and planned trials will take us into the next decade before reporting their results. This paper represents the first attempt at a comprehensive review of this quarter century of endeavour, documenting all the strategies that have emerged into clinical studies. Importantly, the intense clinical activity has established robust infrastructures for future T1D trials and frameworks for their design. The evident success of the monoclonal anti-CD3 antibody trials in established T1D demonstrate that modulation of islet autoimmunity in humans after the onset of overt disease can be achieved, and give some reason to be cautiously optimistic for the ability of these and other agents, alone and in combination, to provide an effective immunotherapy for the disease.

Mucosal exposure to antigen: cause or cure of type 1 diabetes?

The human gut offers more than 200 m2 of mucosal surface, where direct interactions between the immune system and foreign antigens take place to eliminate pathogens or induce immune tolerance toward food antigens or normal gut flora. Therefore, mucosally administered antigens can induce tolerance under certain circumstances. In autoimmune diabetes, mucosal vaccination with autoantigens elicits some efficacy in restoring tolerance in mice, but it never succeeded in humans. Furthermore, in some instances autoimmunity can be precipitated upon oral or intranasal autoantigen administration. Therefore, it is difficult to predict the effect of mucosal vaccination on autoimmunity and much effort should be put into establishing better assays to reduce the risk for possible adverse events in humans and enable a rapid and smooth translation.

Moving towards efficient therapies in type 1 diabetes: to combine or not to combine?

Every year, thirty thousand people worldwide are diagnosed with type 1 diabetes mellitus (T1DM). T1DM, also called autoimmune diabetes, is a multifactorial disease affecting predisposed individuals and involving genetic susceptibilities, environmental triggers, as well as unbalanced immune responses. Auto-reactive T cells, produced during the pathogenesis, play an important role by specifically destroying the pancreatic insulin-producing beta-cells in the islets of Langerhans. Numerous therapeutic interventions have been tested, mostly in animal models, but also in humans. To date, only three phase II/III clinical trials have demonstrated safety and efficacy: anti-CD3 antibody, DiaPep277, and GAD65 (in patients with latent autoimmune diabetes in adults). Unfortunately, a significant number of patients did not respond positively and remained insulin-dependent after completion of therapy. Several reasons account for this. Firstly, the severity of the disease as well as the auto-aggressive T cell repertoire vary from patient to patient leading to a broad range of therapeutic efficacies, and secondly at the time of the treatment the number of remaining beta-cells will directly impact the level of insulin production post-treatment. In this review, we will provide some clues to enhance efficacy of future immuno-interventions in patients with T1DM. We suggest that combination therapies might be the best approach.

Potential of an altered peptide ligand of lipocalin allergen Bos d 2 for peptide immunotherapy

BACKGROUND

Peptide immunotherapy is a promising alternative for treating allergic diseases. One way to enhance the efficacy of peptide immunotherapy is to use altered peptide ligands (APLs) that contain amino acid substitutions compared with the natural peptide.

OBJECTIVE

To evaluate the potential of an APL of the immunodominant epitope of lipocalin allergen Bos d 2 for peptide immunotherapy.

METHODS

Peripheral blood CD4(+) T-cell responses of 8 HLA-DR4-positive subjects to the natural ligand of Bos d 2 (p127-142) or to an APL (pN135D) were analyzed by MHC class II tetramer staining after in vitro expansion with the peptides. Long-term T-cell lines (TCLs) were induced with the peptides, and the cytokine production, cross-reactivity, and T-cell receptor Vbeta subtype expression of the TCLs were analyzed.

RESULTS

CD4(+) T cells specific for both p127-142 and pN135D were readily detected in peripheral blood after a single in vitro stimulation. Whereas the TCLs induced with p127-142 were T(H)2/T(H)0-deviated, those induced with pN135D were T(H)1/T(H)0-deviated and highly cross-reactive with p127-142. Moreover, the pN135D-induced TCLs appeared to use a broader repertoire of T-cell receptor Vbeta subtypes than those induced with p127-142.

CONCLUSION

An APL of an immunodominant allergen epitope was able to induce a novel T(H)1-deviated T-cell population cross-reactive with the natural epitope in vitro. This cell population could have a therapeutic immunomodulatory function in vivo through bystander suppression.

CLINICAL IMPLICATIONS

These results support the idea that altered peptide ligands may be used to enhance the efficacy of peptide immunotherapy.

Strategies to treat autoimmune diabetes

Type 1 diabetes results from autoimmune destruction of insulin-producing β cells in the pancreatic islets, leading to deficiency in glucose uptake by the cells of the body. The resulting complications and mortality call into attention the need for therapeutic strategies to treat this disease. While general immunosuppressive treatment and antigen-based therapy have both proven effective in aborting the autoimmune attack on β cells, cellular therapy and synergistic combination of agents probably represent the most promising approaches for efficient targeting of autoreactive cells. The underlying challenge is fine tuning of immune therapy to avoid harmful side effects on the immune system or other host-defense functions. This should be rendered possible by identifying the optimal regimen and underlying mechanisms of action.

Long-term prevention of diabetes and marked suppression of insulin autoantibodies and insulitis in mice lacking native insulin B9-23 sequence

We analyzed double native insulin gene knockout NOD mice with a mutated (B16:alanine) proinsulin transgene at multiple ages for the development of insulin autoantibodies, insulitis, and diabetes. In contrast to mice with at least one copy of a native insulin gene that expressed insulin antibodies, only 2 out of 21 (10%) double native insulin gene knockout mice with a mutated insulin transgene developed insulin autoantibodies. Of 21 double insulin knockout mice sacrificed between 10 to 48 weeks of age, only 5 showed minimal insulitis versus 100% of wild-type NOD and more than 90% of insulin 1 knockout mice. Consistent with robust suppression of insulin autoantibodies and insulitis, no double insulin knockout mice developed diabetes. In that the B9-23 peptide with B16A is an altered peptide ligand inducing Th2 responses, we analyzed transfer of splenocytes into NOD.SCID mice. There was no evidence for regulatory T cells able to inhibit transfer of diabetes by diabetogenic NOD splenocytes. Insulin peptide B9-23 is likely a crucial target for initiation of islet autoimmunity and further mutation of the sequence will be tested to attempt to eliminate all anti-islet autoimmunity.

An immunologic homunculus for type 1 diabetes

Autoimmune diseases such as the diabetes that develops in NOD mice depend on immunologic recognition of specific autoantigens, but recognition can result in a pathogenic or protective T cell response. A study by Du et al. in this issue of the JCI demonstrates that TGF-beta signaling by T cells recognizing the insulin peptide B:9-23 is essential for such protection and that this inhibitory cytokine functions in both a paracrine and an autocrine manner (see the related article beginning on page 1360). We propose that the insulin peptide B:9-23 and a conserved TCR motif form an "immunologic homunculus" underlying the relatively common targeting of insulin by T cells that, as demonstrated by the study of Du and coworkers, results in a protective T cell response, or diabetes, as shown by other investigators, for related T cell receptors.

Anti-CD3 and nasal proinsulin combination therapy enhances remission from recent-onset autoimmune diabetes by inducing Tregs

Safe induction of autoantigen-specific long-term tolerance is the "holy grail" for the treatment of autoimmune diseases. In animal models of type 1 diabetes, oral or i.n. immunization with islet antigens induces Tregs that are capable of bystander suppression. However, such interventions are only effective early in the prediabetic phase. Here, we demonstrate that a novel combination treatment with anti-CD3epsilon-specific antibody and i.n. proinsulin peptide can reverse recent-onset diabetes in 2 murine diabetes models with much higher efficacy than with monotherapy with anti-CD3 or antigen alone. In vivo, expansion of CD25(+)Foxp3(+) and insulin-specific Tregs producing IL-10, TGF-beta, and IL-4 was strongly enhanced. These cells could transfer dominant tolerance to immunocompetent recent-onset diabetic recipients and suppressed heterologous autoaggressive CD8 responses. Thus, combining a systemic immune modulator with antigen-specific Treg induction is more efficacious in reverting diabetes. Since Tregs act site-specifically, this strategy should also be expected to reduce the potential for systemic side effects.

Immunomodulation in type 1 diabetes by NBI-6024, an altered peptide ligand of the insulin B epitope

NBI-6024 is an altered peptide ligand (APL) corresponding to the 9-23 amino acid region of the insulin B chain (B(9-23)), an epitope recognized by inflammatory interferon-gamma-producing T helper (Th)1 lymphocytes in type 1 diabetic patients. Immunomodulatory effects of NBI-6024 administration in recent-onset diabetic patients in a phase I clinical trial (NBI-6024-0003) were measured in peripheral blood mononuclear cells using the enzyme-linked immunosorbent spot assay. Analysis of the mean magnitude of cytokine responses to B(9-23) and NBI-6024 for each cohort showed significant increases in interleukin-5 responses (a Th2 regulatory phenotype) in cohorts that received APL relative to those receiving placebo. A responder analysis showed that Th1 responses to B(9-23) and NBI-6024 were observed almost exclusively in the placebo-treated diabetic population but not in nondiabetic control subjects and that APL administration (five biweekly subcutaneous injections) significantly and dose-dependently reduced the percentage of patients with these Th1 responses. The results of this phase I clinical study strongly suggest that NBI-6024 treatment shifted the Th1 pathogenic responses in recent-onset type 1 diabetic patients to a protective Th2 regulatory phenotype. The significance of these findings on the clinical outcome of disease is currently under investigation in a phase II multidose study.

Roles of dendritic cells and regulatory T cells in autoantigen-induced murine immune tolerance model

AIM: To investigate the important roles of dendritic cells (DC) and CD4⁺CD25⁺ regulatory T cells in immune prevention against insulin dependent diabetes (IDDM) by autoantigen insulin administration.

METHODS: The model of IDDM was established by intraperitoneal injection of low-dose streptozotocin (STZ) 40 mg/kg per day for 5 consecutive days in Balb/c mice. The bovine insulin (100 μg) in incomplete Freund's adjuvant (IFA, emulsified 1∶1) was given subcutaneously to the mice weekly for 4 wk. The blood glucose was examined once a week and all the mice were killed after 5 wk. Pancreas tissues were collected for histopathological examination. DC precursor cells from bone marrow and lymphocytes from spleen were isolated. The phenotype of DC and CD4⁺ CD25⁺ regulatory T cells were analyzed by fluorescence activated cell sorter (FACS). DC-stimulated proliferation of lymphacytes was determined by allo-mixed lymphocyte reaction (aMLR).

RESULTS: The level of blood glucose was decreased significantly after insulin injection in comparison with that in the model control group (13.79 ± 2.71 mmol/L vs 20.98 ± 1.43 mmol/L, P < 0.05). Fewer lymphocytes infiltration was observed and pancreatic histological structure was intact. The surface marker CD11c on DC from bone marrow was decreased markedly in IDDM mice (26.4%) than that in normal mice (47.5%). DC differentiated abnormally, and the capacity of stimulating proliferation of allogeneic T cell was weakened as compared with that of normal mice (1.47 ± 0.01 vs 2.93 ± 0.01, P < 0.01, and 1.32 ± 0.01 vs 2.94 ± 0.02, P < 0.01, at DC/T ratios of 1∶10 and 1∶20, respectively). The percentage of CD4⁺CD25⁺ T cells were decreased to 1.43%, while it was 5.09% in normal mice. In contrast, blood glucose in mice given insulin subcutaneously was well controlled, and the amount of DC with CD11c was increased (50% approximately); the expression of CD86 and MHC-Ⅱ was low (26.6% and 28.8%, respectively) and MLR showed that DC capacity in stimulating T cell proliferation was lower than those from the normal mice, but higher than those from IDDM model mice (2.30 ± 0.06 and 2.17 ± 0.02, at DC/T ratios of 1∶10 and 1∶20, respectively); the percentage of CD4⁺CD25⁺ T cells from spleen was enhanced to 7.15%.

CONCLUSION: Subcutaneous administration of insulin can confer protection to mice against IDDM induced by STZ. The immune protection of autoantigen may be associated with the establishment of immune tolerance by improving the function of abnormal DC and promoting the production of CD4⁺CD25⁺ T cells in vivo.

Antigen-specific induction of regulatory T cells for type 1 diabetes therapy

Since their discovery decades ago, regulatory T (Treg) cells have prompted many investigations into their potential role in the generation or prevention of autoimmune disorders such as type 1 diabetes (T1D). Initially identified based on their ability to maintain tolerance to self-antigens in peripheral organs, Treg cells have since been efficiently induced therapeutically and shown to prevent the progression of T1D as well as other autoimmune diseases. Beneficial modification of immunity through the induction of Treg cells has been successfully achieved by antigen-based therapy as well as non-antigen-specific (systemic) treatments. In the current article, we review different strategies that have proved effective in preventing autoimmune diabetes and analyze them with respect to translation into clinical applications. Current evidence indicates that antigen-specific induction of potent regulatory mechanisms is influenced by the systemic milieu, suggesting that systemic modulation might be an essential prerequisite for antigen-based therapy and the successful maintenance or reestablishment of tolerance.

Immunotherapeutic approaches to prevent, ameliorate, and cure type 1 diabetes

Type 1A diabetes (T1D) is caused by autoimmune islet beta cell destruction precipitated by environmental triggers in genetically predisposed individuals. Islet beta cells produce insulin and are the primary target of this autoimmune disorder. Insulin, glutamic acid decarboxylase, and insulinoma associated-2 autoantibodies (IAA, GAD65, and IA-2) are the autoantibodies that have been associated most clearly with the development of T1D. Despite our current ability to predict T1D using genetic markers and detecting islet autoantibodies, we have yet to find a safe way to prevent the disease. However, there are more than 100 different therapies that prevent T1D in the nonobese diabetic (NOD) mouse model or the BioBreeding (BB) rats. This paper reviews a few select therapeutic approaches that have been or are being evaluated as possibilities for the prevention, amelioration, or cure of T1D.

Immunopathogenesis and immunotherapeutic approaches to type 1A diabetes

It is now clear that type 1A (immune-mediated) diabetes develops in genetically susceptible individuals where, prior to the onset of overt hyperglycaemia, there is usually a long prodrome characterised by the presence of autoimmunity directed at islet beta cells. It is the destruction of these insulin-producing cells that results in loss of metabolic regulation and the resultant hyperglycaemia and severe sequelae of type 1A diabetes. An extensive body of animal data and a developing body of human studies are now addressing therapies directed at this root immune cause of type 1A diabetes. Therapies can be considered in terms of the disease stage at which they are applied and in terms of their effects on the immune system (e.g., generalised immunosuppression, immunomodulation, antigen-specific therapies and tolerance-inducing therapies). As T cells are the primary mediators of islet beta cell destruction, it is likely that improved therapies and monitoring of T cell autoimmunity will be necessary to develop a safe and effective therapy for type 1A diabetes.

A look to the future: prediction, prevention, and cure including islet transplantation and stem cell therapy

Type 1 diabetes mellitus (T1DM) is characterized by the almost complete absence of insulin secretion, which is secondary to an autoimmune destruction or dysfunction of the insulin-producing cells of the pancreatic islets of Langerhans. Because T1DM is an autoimmune disease with a long preclinical course, the predictive testing of individuals before the clinical onset of the disease has provided a real opportunity for the identification of risk markers and the design of therapeutic intervention. With such a high degree of predictability using a combination of immunologic markers, strategies to prevent T1DM may become possible. A number of novel therapeutic strategies are under investigation in newly diagnosed T1DM patients and might ultimately be applied to prevent T1DM.

Thymic expression of mutated B16:A preproinsulin messenger RNA does not reverse acceleration of NOD diabetes associated with insulin 2 (thymic expressed insulin) knockout

We detected insulin2 mRNA but not insulin1 in thymus using real-time PCR analysis. Transgenic expression of a mutated insulin message (alanine rather than tyrosine at insulin B chain amino acid 16) was variably induced in thymus of four transgenic founder strains. The transgenic message levels were as high or higher than native insulin2 message. Lack of the insulin2 gene resulted in the enhancement of anti-insulin autoantibodies (regular NOD vs insulin2-knockout NOD, P<0.001) and in the presence of the B16:A insulin transgenes, levels of insulin autoantibodies remained elevated (regular NOD vs insulin2-knockout NOD with B16:A insulin, P<0.01). Diabetes acceleration by the knockout of the insulin2 gene was not influenced by the presence of the B16:A insulin transgenes. These data suggest that the B16:A insulin does not compensate for lack of native insulin expression in thymus. If lack of thymic insulin message of the insulin2 knockout is the cause of diabetes acceleration, this suggests that native insulin B:9-23 sequences may be crucial in thymus for insulin mediated immunomodulation. Further experiments varying native insulin message expression in thymus is necessary for direct comparison, but the current study provides additional evidence of the potential important role of a specific insulin B chain epitope.

The stages of type 1A diabetes: 2005

Type 1A diabetes is a chronic autoimmune disease usually preceded by a long prodrome during which autoantibodies to islet autoantigens are present. These antibodies are directed to a variety of antigens, but the best characterized are glutamic acid decarboxylase-65, insulinoma-associated antigen-2, and insulin. We hypothesize that the natural history of type 1A diabetes can be represented by several stages, starting from genetic susceptibility and ending in complete beta-cell destruction and overt diabetes. Type 1A diabetes probably results from a balance between genetic susceptibility and environmental influences. In both humans and animal models, the major determinants of the disease are genes within the major histocompatibility complex. The next best-characterized susceptibility locus is the insulin gene, the variable nucleotide tandem repeat locus. This gene affects the expression of insulin in the thymus and thus may play a role in the modulation of tolerance to this molecule. In a subset of genetically susceptible individuals, the activation of autoimmunity may be triggered by environmental factors such as viruses and/or diet. However, no conclusive association has been established between type 1A diabetes and specific environmental triggers. In this review, we provide evidence that insulin has a fundamental role in anti-islet autoimmunity.

Establishment of native insulin-negative NOD mice and the methodology to distinguish specific insulin knockout genotypes and a B:16 alanine preproinsulin transgene

We hypothesize that NOD mice without native insulin, but with an altered insulin B:9-23 sequence, will be completely protected from diabetes/insulitis if insulin B:9-23 is an essential T cell epitope. To investigate this hypothesis, we have established initial insulin 1- and 2-negative NOD mice with a transgene directing production of preproinsulin with alanine at position B:16 rather than the native tyrosine of both insulin 1 and insulin 2. Sets of primers for PCR-based assays have been created and validated. They are able to distinguish the presence or absence of the insulin gene knockouts and of both native insulin 1 and insulin 2 (and thus distinguish heterozygous versus homozygous knockouts), as well as the presence of the altered insulin transgene, B:16 alanine preproinsulin. Four B:16 alanine transgenic founders were produced directly in NOD mice and, by intercrossing, initial live native insulin-negative B:16 alanine transgenic mice have been generated.

Experimental autoimmune diabetes: a new tool to study mechanisms and consequences of insulin-specific autoimmunity

(Prepro)insulin is considered a central antigenic determinant in diabetic autoimmunity. Insulin has been used to modify diabetes development in NOD mice and prediabetic individuals. We have recently shown that (prepro)insulin can adversely promote diabetes development in murine type 1 diabetes. Based on these findings we have developed experimental autoimmune diabetes (EAD), a new mouse model characterized by (1) CD4(+)/CD8(+) insulitis, induced by (2) (prepro)insulin DNA vaccination, leading to (3) beta cell damage and insulin deficiency in (4) RIP-B7.1 transgenic mice (H-2(b)). EAD develops rapidly in 60-95% of mice after intramuscular, but not intradermal ("gene gun"), vaccination; and DNA plasmids expressing insulin or the insulin analogues glargine, aspart, and lispro are equally potent to induce EAD. Similar to NOD mice, diabetes is adoptively transferred into syngeneic recipients by spleen cell transplantation in a dose-dependent fashion. We have devised a two-stage concept of EAD in which T cell activation and expansion is driven by in vivo autoantigen expression, followed by islet damage that requires beta cell expression of costimulatory B7.1 for disease manifestation. Taken together, EAD is a novel, genetically defined animal model of type 1 diabetes suitable to analyze mechanisms and consequences of insulin-specific T cell autoimmunity.

Identification of CD4+ T Cell-Specific Epitopes of Islet-Specific Glucose-6-Phosphatase Catalytic Subunit-Related Protein: A Novel β Cell Autoantigen in Type 1 Diabetes

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) has been identified as a novel CD8(+) T cell-specific autoantigen in NOD mice. This study was undertaken to identify MHC class II-specific CD4(+) T cell epitopes of IGRP. Peptides named P1, P2, P3, P4, P5, P6, and P7 were synthesized by aligning the IGRP protein amino acid sequence with peptide-binding motifs of the NOD MHC class II (I-A(g7)) molecule. Peptides P1, P2, P3, and P7 were immunogenic and induced both spontaneous and primed responses. IGRP peptides P1-, P2-, P3-, and P7-induced responses were inhibited by the addition of anti-MHC class II (I-A(g7)) Ab, confirming that the response is indeed I-A(g7) restricted. Experiments using purified CD4(+) and CD8(+) T cells from IGRP peptide-primed mice also showed a predominant CD4(+) T cell response with no significant activation of CD8(+) T cells. T cells from P1-, P3-, and P7-primed mice secreted both IFN-gamma and IL-10 cytokines, whereas P2-primed cells secreted only IFN-gamma. Peptides P3 and P7 prevented the development of spontaneous diabetes and delayed adoptive transfer of diabetes. Peptides P1 and P2 delayed the onset of diabetes in both these models. In summary, we have identified two I-A(g7)-restricted CD4(+) T cell epitopes of IGRP that can modulate and prevent the development of diabetes in NOD mice. These results provide the first evidence on the role of IGRP-specific, MHC class II-restricted CD4(+) T cells in disease protection and may help in the development of novel therapies for type 1 diabetes.

Inhibition of altered peptide ligand-mediated antagonism of human GAD65-responsive CD4+ T?cells by non-antagonizable T?cells

Altered peptide ligands derived from T cell-reactive self antigens have been shown to be protective therapeutic agents in animal models of autoimmunity. In this study we identified several altered peptide ligands derived from the type 1 diabetes-associated autoantigen human glutamic acid decarboxylase 65 (hGAD65) epitope that were capable of antagonizing a subset of a panel of human CD4(+) GAD65 (555-567)-responsive T cell clones derived from a diabetic individual. While no altered peptide ligand was able to antagonize all six clones in the T cell panel, a single-substituted peptide of isoleucine to methionine at position 561, which resides at the TCR contact p5 position, was able to antagonize five out of the six hGAD65-responsive clones. In a mixed T cell culture system we observed that altered peptide ligand-mediated antagonism is inhibited in a dose-dependent manner by the presence of non-antagonizable hGAD65 (555-567)-responsive T cells. From an analysis of the cytokines present in the mixed T cell cultures, interleukin-2 was sufficient to inhibit altered peptide ligand-induced antagonism. The inhibition of altered peptide ligand-mediated antagonism of self-antigen-responsive T cells by non-antagonizable T cells has implications in altered peptide ligand therapy where T cell antagonism is the goal.

Allogeneic core amino acids of an immunodominant allopeptide are important for MHC binding and TCR recognition

The indirect alloimmune response seems to be restricted to a few dominant major histocompatibility complex (MHC)-derived peptides responsible for T-cell activation in allograft rejection. The molecular mechanisms of indirect T-cell activation have been studied using peptide analogues derived from the dominant allopeptide in vitro, whereas the in vivo effects of peptide analogues have not been well characterized yet. In the present study, we generated allochimeric peptide analogues by replacing the three allogeneic amino acids 5L, 9L, and 10T in the sequence of the dominant MHC class I allopeptide P1. These allochimeric peptide analogues were used to define the allogeneic amino acids critical for the MHC binding and TCR recognition. We found that position 5 (5L) of the dominant allopeptide acts as an MHC-binding residue, while the other two allogeneic positions, 9 and 10, are important for the T-cell receptor (TCR) recognition. A peptide containing the MHC-binding residue 5L, as the only different amino acid between donor (RT1.A(u)) and recipient (RT1.A(l)) sequences, did not induce proliferation of lymph node cells primed with the dominant peptide and prevented dominant peptide-induced acceleration of allograft rejection. Identification of MHC and TCR contact residues should facilitate the development of antigen-specific therapies to inhibit or regulate the indirect alloimmune response.

Autoimmune diabetes: ongoing development of immunological intervention strategies targeted directly against autoreactive T cells

It is well known that autoimmunity associated with the onset of insulin-dependent diabetes mellitus (IDDM) involves the generation of autoreactive T and B cells. The findings that diabetics mount humoral and cellular immune responses against islet cell antigens (ICAs) have led to the testing of ICAs and their analogs as candidates for therapeutic agents for better treatment of IDDM at its prediabetic and diabetic stages. Apart from this type of approach, various immunological intervention strategies aimed at direct targeting of the autoreactive T cells have also been investigated. The present review covers the ongoing aspects of these developments focusing on the preclinical findings made in NOD (nonobese diabetic) mice which have been commonly used as a disease model for human autoimmune diabetes. Other types of approaches involving the mobilization of regulatory T cells to indirectly control or modulate the pathological activity of autoreactive T cells will not be discussed within this scope.

HLA-DQ8-Associated T Cell Responses to the Diabetes Autoantigen Phogrin (IA-2β) in Human Prediabetes

Susceptibility to type 1A autoimmune diabetes is linked to expression of particular MHC class II molecules, notably HLA-DQ8 in man and the orthologous I-Ag7 in the nonobese diabetic mouse. In the present study, we analyzed two peptide epitopes (peptides 2 and 7) from the diabetes autoantigen phogrin (IA-2beta), in the context of their presentation by the I-Ag7 and HLA-DQ8 molecules and their role as potential T cell antigenic epitopes in human diabetes. Both of these peptides are targets of diabetogenic CD4+ T cell clones in the nonobese diabetic mouse. Transgenic mice expressing HLA-DQ8 as the sole class II molecule generated a robust T cell-proliferative response when primed with peptide 2 or peptide 7 in CFA. Analysis of the IL-2 secretion from peptide 2-reactive T cell hybridomas stimulated with alanine-substituted peptides identified three residues that were crucial to the response. Among 41 islet cell Ag-positive prediabetic human subjects, 36.5% showed PBMC-proliferative responses to peptide 7, 17.1% to peptide 2, and 17.1% to both peptides; no response was seen among 20 matched healthy controls. Stratification of the data based upon HLA haplotype suggested that peptide 7 could be presented by at least one HLA-DR molecule in addition to HLA-DQ8, a finding that was supported by blocking studies with monomorphic mAbs. The results indicate that common phogrin peptides are targeted by autoreactive T cells in human and murine type 1A diabetes, and that the responses may in part be associated with the similar peptide-binding specificities of I-Ag7 and HLA-DQ8.

An Altered Self-Peptide with Superagonist Activity Blocks a CD8-Mediated Mouse Model of Type 1 Diabetes

T cell tolerance can be experimentally induced through administration of self-peptides with single amino acid substitution (altered peptide ligands or APLs). However, little is known about the effects of APLs on already differentiated autoreactive CD8+ T cells that play a pivotal role in the pathogenesis of autoimmune diabetes. We generated a panel of APLs derived from an influenza virus hemagglutinin peptide exhibiting in vitro functions ranging from antagonism to superagonism on specific CD8+ T cells. A superagonist APL was further characterized for its therapeutic activity in a transgenic mouse model of type 1 diabetes. When injected i.v. 1 day after the transfer of diabetogenic hemagglutinin-specific CD8+ T cells into insulin promoter-hemagglutinin transgenic mice, the superagonist APL proved more effective than the native hemagglutinin peptide in blocking diabetes. This protective effect was associated with an inhibition of CD8+ T cell cytotoxicity in vivo and with a decreased accumulation of these cells in the pancreas, leading to a marked reduction of intrainsulitis. In conclusion, a superagonist "self-peptide" APL was more effective than the native peptide in treating a CD8+ T cell-mediated diabetes model.

Nondepleting anti-CD4 monoclonal antibody prevents diabetes and blocks induction of insulin autoantibodies following insulin peptide B:9-23 immunization in the NOD mouse

INTRODUCTION

Insulin peptide B:9-23 is a major autoantigen in type 1 diabetes that induces insulin autoantibodies and prevents diabetes in the NOD. However, immunization with peptide without adjuvant may be insufficient to reverse disease or induce long-term tolerance. Furthermore, recent experience has demonstrated the potential dangers of disease exacerbation or anaphylaxis with peptide immunotherapy.

METHODS

Combination therapy of B:9-23 with a nondepleting anti-CD4 monoclonal antibody (YTS 177.9) was studied in female NOD mice from 4 through 6 weeks of age. Injections of either B:9-23 in saline, YTS 177.9 antibody, or both peptide and antibody were given to mice.

RESULTS

By 52 weeks follow-up, 40% of B:9-23-treated, 100% of YTS177.9-treated, and 70% of B:9-23 and YTS177.9 combination-treated mice remained diabetes-free. IAA, both spontaneous and induced by B:9-23, was almost completely suppressed in mice receiving YTS 177.9. In addition to suppression of IAA expression, anti-B:9-23 peptide antibodies are also suppressed in mice receiving B:9-23 with YTS 177.9, compared to B:9-23 alone.

CONCLUSION

A brief course of the nondepleting anti-CD4 monoclonal antibody (YTS 177.9) in NOD mice confers long-term protection from diabetes and insulitis and profoundly blocks spontaneous and B:9-23 peptide-induced insulin autoantibodies.

Role of the thymus in the development of tolerance and autoimmunity towards the neuroendocrine system

The thymus is the unique lymphoid organ inside which a confrontation occurs throughout life between neuroendocrine self-antigens and a recently evolved system with original recombination machinery driving random generation of immune response diversity. Through transcription of neuroendocrine genes in the thymus stromal network and expression of cognate receptors by immature T cells, the neuroendocrine system regulates early T cell differentiation. In addition and more specifically, intrathymic presentation of neuroendocrine self-antigens by, or in close association with, major histocompatibility complex (MHC) proteins is responsible for the establishment of central immune self-tolerance of neuroendocrine principles. All members of the insulin gene (INS) family are expressed in the thymus stroma according to a precise hierarchy and cell topography: IGF2 (thymic epithelial cells) > IGF1 (thymic macrophages) >> INS (thymic medullary epithelial cells and/or dendritic cells). Given this hierarchical pattern in gene expression, the protein IGF-2 is more tolerated than INS. Igf2 transcription is defective in the thymus of bio-breeding (BB) rat, one animal model of type 1 diabetes (T1DM). This thymus-specific defect in Igf2 expression may explain both the absence of central tolerance to INS-secreting beta cells and the lymphopenia (including lack of regulatory RT6(+) T cells) in diabetes-prone BB rats. INS B:9-23 and the homologous sequence of IGF-2 compete for binding to DQ8, an MHC class II allele conferring major susceptibility to T1DM. In young DQ8(+) T1DM patients, INS B:9-23 presentation by DQ8 elicits a dominant IFN-gamma secretion by isolated PBMCs, whereas presentation of the IGF-2 self-antigen promotes a dominant regulatory interleukin-10 secretion. These data demonstrate that opposite immune responses are driven by MHC presentation of a self-antigen (here, IGF-2) and an autoantigen (INS, as "altered" self). The important tolerogenic properties of thymic self-antigens deserve now to be exploited for prevention and/or cure of devastating autoimmune diseases such as T1DM.

Development of new strategies to prevent type 1 diabetes: the role of animal models

Type 1 diabetes is an immune-mediated disease typically preceded by a long preclinical stage during which a growing number of islet-cell-specific autoantibodies appear in the serum. Although antigen-specific T lymphocytes and cytokines rather than these autoantibodies are the likely executors of beta-cell-destruction, these autoantibodies reflect the existence of autoimmunity that targets islet beta-cells. Abrogation of this autoimmunity during the preclinical stage would be the key to the prevention of type 1 diabetes. However, the quest of protecting islet-cells from the immune attack requires detailed knowledge of mechanisms that control islet-inflammation and beta-cell-destruction, and of mechanisms that control immune tolerance to peripheral self-antigens in general. This knowledge can only be obtained through further innovative research in experimental animal models. In this review, we will first examine how research in non-obese diabetic mice has already led to promising new strategies of diabetes prevention now being tested in human clinical trials. Thereafter, we will discuss how recent advances in understanding the mechanisms that control immune response to peripheral self-antigens such as beta-cell antigens may help to develop even more selective and effective strategies to prevent diabetes in the future.