Antigen-based immunotherapy for autoimmune disease: from animal models to humans?

Transgenically induced GAD tolerance curtails the development of early beta-cell autoreactivities but causes the subsequent development of supernormal autoreactivities to other beta-cell antigens

OBJECTIVE

To study how tolerance to GAD65 affects the development of autoimmunity to other beta-cell autoantigens (beta-CAAs) in GAD65-transgenic (GAD-tg) NOD mice.

RESEARCH DESIGN AND METHODS

We used ELISPOT to characterize the frequency and functional phenotype of T-cell responses to GAD65 and other beta-CAAs at different ages in GAD-tg mice and their NOD mouse littermates.

RESULTS

In young GAD-tg mice, Th1 responses to GAD65's dominant determinants were 13-18% of those in young NOD mice. This coincided with a great reduction in Th1 responses to other beta-CAAs. Evidently, GAD65-reactive T-cells are important for activating and/or expanding early autoreactivities in NOD mice. As GAD-tg mice aged, their T-cell responses to GAD65 remained low, but they developed supernormal splenic and pancreatic lymph node T-cell autoimmunity to other beta-CAAs. Apparently, the elimination/impairment of many GAD65-reactive T-cells allowed other beta-CAA-reactive T-cells to eventually expand to a greater extent, perhaps by reducing competition for antigen-presenting cells, or homeostatic proliferation in the target tissue, which may explain the GAD-tg mouse's usual disease incidence.

CONCLUSIONS

Transgenically induced reduction of GAD65 autoreactivity curtailed the development of early T-cell responses to other beta-CAAs. However, later in life, beta-CAA-reactive T-cells expanded to supernormal levels. These data suggest that early beta-cell autoreactivities are mutually dependent for support to activate and expand, while later in the disease process, autoantigen-specific T-cell pools can expand autonomously. These findings have implications for understanding type 1 diabetes immunopathogenesis and for designing antigen-based immunotherapeutics.

Instant effect of soluble antigen on effector T cells in peripheral immune organs during immunotherapy of autoimmune encephalomyelitis

i.v. infusion of native autoantigen or its altered peptide variants is an important therapeutic option for the treatment of autoimmune diseases, because it selectively targets the disease-inducing T cells. To learn more about the mechanisms and kinetics of this approach, we visualized the crucial initial effects of i.v. infusion of peptides or intact protein on GFP-tagged autoaggressive CD4(+) effector T cells using live-video and two-photon in situ imaging of spleens in living animals. We found that the time interval between i.v. injection of intact protein to first changes in T cell behavior was extremely short; within 10 min after protein application, the motility of the T cells changed drastically. They slowed down and became tethered to local sessile stromal cells. A part of the cells aggregated to form clusters. Within the following 20 min, IFN-gamma mRNA was massively (>100-fold) up-regulated; surface IL-2 receptor and OX-40 (CD 134) increased 1.5 h later. These processes depleted autoimmune T cells in the blood circulation, trapping the cells in the peripheral lymphoid organs and thus preventing them from invading the CNS. This specific blockage almost completely abrogated CNS inflammation and clinical disease. These findings highlight the speed and efficiency of antigen recognition in vivo and add to our understanding of T cell-mediated autoimmunity.

Cell-based gene therapy experiments in murine experimental autoimmune encephalomyelitis

With the ultimate goal of developing a novel treatment for multiple sclerosis (MS), we have developed a cell-based gene therapy protocol for the treatment of murine experimental autoimmune encephalomyelitis (EAE), a powerful animal model for MS. We have determined that transduced fibroblasts secreting encephalogenic epitopes, when injected into mice with EAE, cause a striking abrogation of disease. Both myelin basic protein (MBP) and proteolipid protein mini-gene constructs expressed in syngeneic fibroblast cells were capable of ameliorating ongoing EAE induced by MBP protein. These experiments are crucial since they suggest that not all encephalogenic epitopes need be secreted for the control of disease. We also demonstrate the success of this protocol when transduced syngeneic, and most importantly, allogeneic cells are sequestered within an implantable chamber. Furthermore, we find that through modifying antigen expression by changing the signal sequence of the mini-gene construct, we were able to significantly reduce the dose of cells required for treatment. These improvements to the mini-gene delivery system are critical for the eventual translation of our protocol to the clinic.

The role of pathogenic B-cell clones in antibody mediated autoimmune disorders

Our understanding of the role of B-cells in the immunopathogenesis of certain antibody mediated diseases has developed remarkably in the past few years. In this review, autoantibody mediated immune disorders associated with pathogenic B-cell clones are discussed. We have focused on the roles and pathogenic mechanisms of B-cell clones in autoantibodyimmune diseases. The roles of pathogenic B-cells in Castleman's disease in PNP patients is used as one example. The developments in the treatment of B-cell mediated autoimmune diseases, such as intravenous immunoglobulin (IVIg), targets the regulatory pathway of B-cells, using anti-CD20, CD19, CD22 and, CD95 monoclonal antibody therapy, etc. are also discussed. Immunotherapy, targeting specific pathogenic B-cells, is believed to be one approach in the management of autoimmune diseases.

Gene therapy in a murine model for clinical application to multiple sclerosis

Female SJL/J mice, suffering from experimental autoimmune encephalomyelitis (EAE), were injected with 1 x 10(7) cells from a syngeneic fibroblast line transduced with a retroviral vector designed to encode proteolipid protein (101-157) targeted for secretion. A striking abrogation of both clinical and histological signs of disease resulted. The treatment was efficacious when given after the first or the third relapses, protected naive mice from challenge with spinal cord homogenate, and was dose dependent. This strategy was devised to provide a systemic, antigen-specific signal to pathogenic T cells in the absence of costimulation and, hence, render them anergic. Cytokine analyses of brain and spinal cord lymphocytes demonstrate that the treatment induces an antiinflammatory Th2 profile, indicating that this antigen-specific therapy acts by a cytokine-induced pathway. This study was designed for translation to the clinic. We envision using allogeneic transduced fibroblasts, encapsulated in a chamber, to deliver the antigen-specific signal. This will enable us to use one therapeutic cell line for all patients and to remove the device should the therapy exacerbate disease.

Therapeutic approaches in multiple sclerosis: lessons from failed and interrupted treatment trials

The therapy for multiple sclerosis (MS) has changed dramatically over the past decade. Recent immunobiological findings and current pathophysiological concepts together with advances in biotechnology, improvements in clinical trial design and development of magnetic resonance imaging have led to a variety of evaluable therapeutic approaches in MS. However, in contrast to the successfully introduced and established immunomodulatory therapies (e.g. interferon-beta and glatiramer acetate), there have been a remarkable number of therapeutic failures as well. Despite convincing immunological concepts, impressive data from animal models and promising results from phase I/II studies, the drugs and strategies investigated showed no benefit or even turned out to have unexpectedly severe adverse effects. Although to date there is no uniformly accepted model for MS, there is agreement on the significance of inflammatory events mediated by autoreactive T cells in the CNS. These can be modified therapeutically at the individual steps of a hypothetical pathogenetic cascade. Crucial corners like: the prevalence and peripheral activation of CNS-autoreactive T cells in the periphery;adhesion and penetration of T cells into the CNS;local activation and proliferation and;de- and remyelination processes can be targeted through their putative mediators. Like a 'specificity pyramid', therapeutic approaches therefore cover from general immunosuppression up to specific targeting of T-cell receptor peptide major histocompatibility (MHC) complex. We discuss in detail clinical MS trials that failed or were discontinued for other reasons. These trials include cytokine modulators [tumour necrosis factor (TNF)-alpha antagonists, interleukin-10, interleukin-4, transforming growth factor-beta2], immunosuppressive agents (roquinimex, gusperimus, sulfasalazine, cladribine), inducers of remyelination [intravenous immunoglobulins (IVIg)], antigen-derived therapies [oral tolerance, altered peptide ligands (APL), MHC-Peptide blockade], T cell and T-cell receptor directed therapies (T cell vaccination, T-cell receptor peptide vaccination), monoclonal antibodies against leucocyte differentiation molecules (anti-CD3, anti-CD4), and inactivation of circulating T cells (extracorporeal photopheresis). The main conclusions that can be drawn from these 'negative' experiences are as follows. Theoretically promising agents may paradoxically increase disease activity (lenercept, infliximab), be associated with unforeseen adverse effects (e.g. roquinimex) or short-term favourable trends may reverse with prolonged follow-up (e.g. sulfasalzine). One should not be too enthusiastic about successful trials in animal models (TNFalpha blockers; oral tolerance; remyelinating effect of IVIg) nor be irritated by non-scientific media hype (deoxyspergualine; bone marrow transplantation). More selectivity can imply less efficacy (APL, superselective interventions like T-cell receptor vaccination) and antigen-related therapies can stimulate rather than inhibit encephalitogenic cells. Failed strategies are of high importance for a critical revision of assumed immunopathological mechanisms, their neuroimaging correlates, and for future trial design. Since failed trials add to our growing understanding of multiple sclerosis, 'misses' are nearly as important to the scientific process as the 'hits'.

Interleukin-10-mediated regulatory T-cell responses to epitopes on a human red blood cell autoantigen

Regulatory T cells have been shown to control animal models of immune-mediated pathology by inhibitory cytokine production, but little is known about such cells in human disease. Here we characterize regulatory T-cell responses specific for a human red blood cell autoantigen in patients with warm-type autoimmune hemolytic anemia. Peripheral blood mononuclear cells from patients with autoimmune hemolytic anemia were found either to proliferate and produce interferon-gamma or to secrete the regulatory cytokine interleukin 10 when stimulated in vitro with a major red blood cell autoantigen, the RhD protein. Flow cytometric analysis confirmed that the majority of the responding cells were of the CD4(+) phenotype. Serial results from individual patients demonstrated that this bias toward proliferative or interleukin-10 responses was unstable over time and could reverse in subsequent samples. Epitope mapping studies identified peptides from the sequence of the autoantigen that preferentially induced interleukin-10 production, rather than proliferation, and demonstrated that many contain naturally processed epitopes. Responses to such peptides suppressed T-cell proliferation against the RhD protein, an inhibition that was mediated largely by interleukin 10 and dependent on cytotonic T lymphocyte-associated antigen (CTLA-4) costimulation. Antigenic peptides with the ability to stimulate specific regulatory cells may represent a new class of therapeutic agents for immune-mediated disease.

Antigen-based immunotherapy drives the precocious development of autoimmunity

During the development of type I diabetes mellitus in nonobese diabetic (NOD) mice, T cell autoimmunity gradually spreads among beta cell Ags. Little is known about how autoantigen-based immunotherapies affect this spreading hierarchy. We treated newborn NOD mice with different autoantigenic beta cell peptides (in adjuvant) and characterized their T cell responses at 4 wk of age, when autoimmunity is usually just beginning to arise to a few beta cell Ag determinants. Surprisingly, we found that regardless of whether an early, or late target determinant was administered, autoimmunity had already arisen to all tested beta cell autoantigen determinants, far in advance of when autoimmunity would have naturally arisen to these determinants. Thus, rather than limiting the loss of self-tolerance, immunotherapy caused the natural spreading hierarchy to be bypassed and autoreactivities to develop precociously. Evidently, young NOD mice have a broad array of beta cell-reactive T cells whose activation/expansion can occur rapidly after treatment with a single beta cell autoantigen. Notably, the precocious autoreactivities were Th2 type, with the exception that a burst of precocious Th1 responses was also induced to the injected autoantigen and there were always some Th1 responses to glutamic acid decarboxylase. Similarly treated type 1 diabetes mellitus-resistant mouse strains developed Th2 responses only to the injected Ag. Thus, autoantigen administration can induce a cascade of autoimmune responses in healthy (preautoimmune) mice that are merely genetically susceptible to spontaneous autoimmune disease. Such phenomena have not been observed in experimental autoimmune disease models and may have important clinical implications.

Understanding autoimmune diabetes: insights from mouse models

Type 1 or insulin-dependent diabetes is an autoimmune disease that causes the selective destruction of insulin-secreting beta cells in the pancreatic islets. Although this is a polygenic disease, with at least 20 genes implicated, the dominant susceptibility locus maps to the major histocompatibility complex (MHC), both in humans and in rodent models. However, in spite of progress on several fronts, the molecular pathology of autoimmune diabetes remains incompletely defined. Major areas of research include environmental trigger factors, the identification and role of beta-cell antigens in inducing and maintaining the autoimmune response, and the nature of the pathogenic and protective lymphocytes involved. In this review, we will focus on these areas to highlight recent advances in understanding the pathogenesis of autoimmune diabetes, drawing extensively on insights gained by studying the non-obese diabetic (NOD) mouse.

Plasmid DNAs encoding insulin and glutamic acid decarboxylase 65 have distinct effects on the progression of autoimmune diabetes in nonobese diabetic mice

We previously demonstrated that administration of plasmid DNAs (pDNAs) encoding IL-4 and a fragment of glutamic acid decarboxylase 65 (GAD65) fused to IgGFc induces GAD65-specific Th2 cells and prevents insulin-dependent diabetes mellitus (IDDM) in nonobese diabetic (NOD) mice. To assess the general applicability of pDNA vaccination to mediate Ag-specific immune deviation, we examined the immunotherapeutic efficacy of recombinants encoding murine insulin A and B chains fused to IgGFc. Insulin was chosen based on studies demonstrating that administration of insulin or insulin B chain by a variety of strategies prevents IDDM in NOD mice. Surprisingly, young NOD mice receiving i.m. injections of pDNA encoding insulin B chain-IgGFc with or without IL-4 exhibited an accelerated progression of insulitis and developed early diabetes. Exacerbation of IDDM correlated with an increased frequency of IFN-gamma-secreting CD4(+) and CD8(+) T cells in response to insulin B chain-specific peptides compared with untreated mice. In contrast, treatment with pDNAs encoding insulin A chain-IgGFc and IL-4 elicited a low frequency of IL-4-secreting Th cells and had no effect on the progression of IDDM. Vaccination with pDNAs encoding GAD65-IgGFc and IL-4, however, prevented IDDM. These results demonstrate that insulin- and GAD65-specific T cell reactivity induced by pDNA vaccination has distinct effects on the progression of IDDM.

Activated T lymphocytes from patients with high risk of type I diabetes mellitus have different ability to produce interferon-gamma, interleukin-6 and interleukin-10 and undergo anti-CD95 induced apoptosis after insulin stimulation

Type I Diabetes mellitus (DM1) is the effect of T cell dependent autoimmune destruction of insulin producing beta cells in the pancreas islet. T cells are activated in response to islet dominant autoantigens, the result being the development of DM1. Insulin is one of the islet autoantigens responsible for activation of T lymphocyte functions, inflammatory cytokine production and development of DM1. The experiments reported in this study have shown the spontaneous increase of CD95 molecule expression on lymphocytes of the first-degree relatives of DM1 patients. The autoantigen insulin is responsible for stimulation in vitro of potentially hazardous 'memory' lymphocytes to produce interleukin-6 (IL-6) and interleukin-10 (IL-10) interleukins. Insulin induced stimulation of lymphocytes in vitro was observed in patients at high risk of developing diabetes mellitus (prediabetics). Phytohaemagglutinin (PHA) stimulates lymphocytes of all groups in the same way. Stimulated lymphocytes in second cultures undergo apoptosis induced with anti-Fas specific antibodies. The deletion in vitro of resting peripheral lymphocytes is nonfunctional. Insulin activated T lymphocytes, which undergo apoptosis were not observed in peripheral blood of healthy people and in patients with DM1. This observation suggests that insulin is involved as autoantigen in DM1 progression in patients with high risk of diabetes type I. The autoreactive T lymphocytes may persist in peripheral blood of patients with high risk DM1. Defective elimination of autoreactive T cells may result in autodestructive damage of islets beta cells in the prediabetic stage and disease progression to DM1.

Role of tolerogen conformation in induction of oral tolerance in experimental autoimmune myasthenia gravis

We recently demonstrated that oral or nasal administration of recombinant fragments of the acetylcholine receptor (AChR) prevents the induction of experimental autoimmune myasthenia gravis (EAMG) and suppresses ongoing EAMG in rats. We have now studied the role of spatial conformation of these recombinant fragments in determining their tolerogenicity. Two fragments corresponding to the extracellular domain of the human AChR alpha-subunit and differing in conformation were tested: Halpha1-205 expressed with no fusion partner and Halpha1-210 fused to thioredoxin (Trx), and designated Trx-Halpha1-210. The conformational similarity of the fragments to intact AChR was assessed by their reactivity with alpha-bungarotoxin and with anti-AChR mAbs, specific for conformation-dependent epitopes. Oral administration of the more native fragment, Trx-Halpha1-210, at the acute phase of disease led to exacerbation of EAMG, accompanied by an elevation of AChR-specific humoral and cellular reactivity, increased levels of Th1-type cytokines (IL-2, IL-12), decreased levels of Th2 (IL-10)- or Th3 (TGF-beta)-type cytokines, and higher expression of costimulatory factors (CD28, CTLA4, B7-1, B7-2, CD40L, and CD40). On the other hand, oral administration of the less native fragments Halpha1-205 or denatured Trx-Halpha1-210 suppressed ongoing EAMG and led to opposite changes in the immunological parameters. It thus seems that native conformation of AChR-derived fragments renders them immunogenic and immunopathogenic and therefore not suitable for treatment of myasthenia gravis. Conformation of tolerogens should therefore be given careful attention when considering oral tolerance for treatment of autoimmune diseases.

Novel therapeutic approaches to Guillain-Barré syndrome

Guillain-Barré syndrome is an autoimmune disease which occurs throughout the world. Whilst the majority of patients can expect a reasonable recovery, about 10% die and 10% are left disabled with current therapy. The standard treatment is a five day course of iv. immunoglobulin, given at a dose of 0.4 g/kg/day, with plasma exchange as an equally efficacious alternative. Steroids are ineffective in Guillain-Barré syndrome. All new potential therapeutic agents need to be tested in addition to the standard agents available. Future potential therapies are suggested by the study of the animal model experimental autoimmune neuritis in the Lewis rat. Whilst in theory it is possible to target the different stages of the immune response, in practice not all of the steps at which experimental autoimmune neuritis can be prevented will be translatable to human Guillain-Barré syndrome. This is because Guillain-Barré syndrome probably presents after the immune reaction has been ongoing for some time and therefore early aspects of the immune response cannot be prevented. Many of the possible measures would have widespread immunosuppressive effects which would be unacceptable to patients. Interfering with the immune response by attempting to block antigen binding or inducing tolerance may not be practical, owing to the possibility of exacerbating disease. Once we have a more thorough understanding of the pathogenesis of Guillain-Barré syndrome, then immune-specific therapy for Guillain-Barré syndrome may become a possibility, rather than general immunosuppressive measures. Trials of beta-interferon and of a combination of steroid and i.v. immunoglobulin are underway. A trial of a second course of i.v. immunoglobulin is planned.

Attenuation of Inducible Th2 Immunity with Autoimmune Disease Progression

Autoantigen-based immunotherapeutics have been shown to activate regulatory responses capable of inhibiting T cell-mediated autoimmune disease in animal models. However, their efficacy generally declines, as treatment occurs later in the disease process, and their mechanism of action is a matter of intense debate. Here, we report that the early administration of β cell autoantigens (βCAAs) to nonobese diabetic (NOD) mice broadly diverts the natural development of potentially pathogenic Th1-biased autoimmune responses toward the Th2 phenotype through Th2 spreading. With disease progression, there was a steady decline in the ability of βCAA treatment to promote Th2-type cellular and humoral autoimmunity. Late in the disease process, some βCAAs were still able to induce Th2 responses and Th2 spreading (although to a much lesser extent), while other autoantigens were not. This attenuation of inducible Th2 immunity with disease progression is likely to reflect a reduction in the availability of uncommitted autoantigen-reactive precursor T cells. These findings suggest that there are inherent differences in the frequency of βCAA-reactive T cells and that, in advanced stages of autoimmune disease, regulatory responses may be best elicited with target tissue Ags against which large uncommitted T cell pools are still available. Since individuals presenting the first signs of autoimmune disease are likely to already have an advanced disease process, these findings may be useful for the rational design of Ag-based immunotherapeutics.