Antigen-specific Immunological Tolerance Research Articles

Lymph Node-Targeted Synthetically Glycosylated Antigen Leads to Antigen-Specific Immunological Tolerance.

Inverse vaccines that tolerogenically target antigens to antigen-presenting cells (APCs) offer promise in prevention of immunity to allergens and protein drugs and treatment of autoimmunity. We have previously shown that targeting hepatic APCs through intravenous injection of synthetically glycosylated antigen leads to effective induction of antigen-specific immunological tolerance. Here, we demonstrate that targeting these glycoconjugates to lymph node (LN) APCs under homeostatic conditions leads to local and increased accumulation in the LNs compared to unmodified antigen and induces a tolerogenic state both locally and systemically. Subcutaneous administration directs the polymeric glycoconjugate to the draining LN, where the glycoconjugated antigen generates robust antigen-specific CD4+ and CD8+ T cell tolerance and hypo-responsiveness to antigenic challenge via a number of mechanisms, including clonal deletion, anergy of activated T cells, and expansion of regulatory T cells. Lag-3 up-regulation on CD4+ and CD8+ T cells represents an essential mechanism of suppression. Additionally, presentation of antigen released from the glycoconjugate to naïve T cells is mediated mainly by LN-resident CD8+ and CD11b+ dendritic cells. Thus, here we demonstrate that antigen targeting via synthetic glycosylation to impart affinity for APC scavenger receptors generates tolerance when LN dendritic cells are the cellular target.

Polymeric nanoparticles containing rapamycin and autoantigen induce antigen-specific immunological tolerance for preventing vitiligo in mice

ABSTRACT Vitiligo is an autoimmune disease in which pigment is lost in patches of the skin. CD4+ T cells are implicated in vitiligo while regulatory T cells (Tregs) could ameliorate vitiligo. Rapamycin together with autoantigen have been shown to induce immunological tolerance and promote Tregs in multiple autoimmune diseases. In the current study, we synthesized nanoparticles containing rapamycin and autoantigen HEL46-61 (NPHEL46-61/Rapa) and investigated their effects on vitiligo. We treated bone marrow-derived dendritic cells (BMDCs) from TrpHEL mice with NPHEL46-61/Rapa and monitored the phenotype of BMDCs. We investigated the effects of NPHEL46-61/Rapa-treated BMDCs on CD4+ T cell proliferation and differentiation. We administrated NPHEL46-61/Rapa to TCR-TrpHEL mice and investigated the effects on vitiligo. We found that BMDCs can uptake the NPHEL46-61/Rapa, which resulted in decreased expression of costimulation molecules CD80 and CD86 in BMDCs. BMDCs treated with NPHEL46-61/Rapa suppressed antigen-specific CD4+ T cell proliferation while promoted the differentiation of these CD4+ T cell to Tregs in vitro. Administration of NPHEL46-61/Rapa to TCR-TrpHEL mice ameliorated vitiligo, promoted Treg production, and suppressed IFN-γ and IL-6 production, while induced IL-10 production. Therefore, our study provides experimental evidence that nanoparticles containing rapamycin and autoantigen could induce antigen-specific immunological tolerance and prevent vitiligo.

Extracorporeal photopheresis as a non-specific immune therapy of autoimmune diseases and skin T-cell lymphoma (a review of the literature and own studies)

Aim:To present well-known and disputable mechanisms of the effects of extracorporeal photopheresis (ECP) in heterogeneous clinical conditions, as well as to demonstrate its advantages over conventional hormonal, immunosuppressive and cytostatic treatments, with a recommendation to widely implement it into practical management of autoimmune disease and cutaneous T-cell lymphomas (CTCLs).Key points:Despite convincing evidence of the ECP efficacy in the treatment of T-cell mediated disorders, a unifying concept of its mechanism has not been established so far. In this review, we attempted to determine the value of multiple, sometimes contradictory and equivocal points of view to immunobiochemical processes underlying the restoration of mechanism of immune tolerance in some autoimmune diseases and CTCLs. We focused our attention on our own clinical and immunological data obtained during a 20-years' experience with the use of ECP in clinical departments of MONIKI (Russia). Based on this, we have shown that ECP is more effective in autoimmune diseases than conventional treatment approaches with hormones, immunosuppressants and cytostatics. Unlike them, ECP is selectively targeted to auto-aggressive T-cells without induction of systemic immunosuppression. The leading role is played by the transformation of activated (immunogenic) myeloid dendrite cells (DC) into tolerogenic cell associated with their synthesis of inhibitor cytokines. The interplay of the cytokines with an antigen results in polarization of CD4+ Т lymphocytes via the Th2 pathway with restoration of the Th1/Th2 balance and their cytokine production. ECP triggers regulatory anti-clonotypic effector memory cells at the end stage of CD3+/CD8+/CD27-/CD28-/CD62L+ differentiation, that provide and maintain the peripheral immune tolerance, by deletion of the clone of auto-reactive cytotoxic lymphocytes and inducing their apoptosis. In autoimmune disorders, ECP results in reduction of the expression of integrin adhesion molecules on auto-reactive cell membranes with subsequent loss of their ability to migrate through the endothelium to their target cells. In its turn, it leads to decreasing immunoinflammatory response in the lesion. Both clinical and experimental data indicate that the mechanism of ECP action against CTCLs is characterized by activation of tumor cell apoptosis, unblocking of co-activation receptors on the antigen-presenting DC providing the functioning of the second signaling pathway for T lymphocyte activation. This results in proliferation of anti-tumor effector cells pool, production of DC activating cytokines that participate in the CD4+ polarization via Th1 pathway. In addition, this review considers the mechanism of the immunomodulating effect of ECP in the context of its influence at the levels of transcription and translation of proteins contributing to the pathophysiology of the disorders, based on molecular immunogenetic studies. Thus, ECP is able to induce antigen-specific immunological tolerance through the transformation of antigen-presenting cells, modulation of cytokine profile, adhesion and activation molecules, as well as through formatting of the regulatory T cells (Tregs).Conclusion:Undoubtedly, the immunobiological ECP technique has significant advantages over well-known conventional hormonal, immunosuppressive, and cytostatic therapies of autoimmune diseases and CTCLs.

Synthetically glycosylated antigens induce antigen-specific tolerance and prevent the onset of diabetes.

Homeostatic antigen presentation by hepatic antigen-presenting cells, which results in tolerogenic T-cell education, could be exploited to induce antigen-specific immunological tolerance. Here we show that antigens modified with polymeric forms of either N-acetylgalactosamine or N-acetylglucosamine target hepatic antigen-presenting cells, increase their antigen presentation and induce antigen-specific tolerance, as indicated by CD4+ and CD8+ T-cell deletion and anergy. These synthetically glycosylated antigens also expanded functional regulatory T cells, which are necessary for the durable suppression of antigen-specific immune responses. In an adoptive-transfer mouse model of type-1 diabetes, treatment with the glycosylated autoantigens prevented T-cell-mediated diabetes, expanded antigen-specific regulatory T cells and resulted in lasting tolerance to a subsequent challenge with activated diabetogenic T cells. Glycosylated autoantigens targeted to hepatic antigen-presenting cells might enable therapies that promote immune tolerance in patients with autoimmune diseases.

APVO210: A Bispecific Anti-CD86-IL-10 Fusion Protein (ADAPTIR™) to Induce Antigen-Specific T Regulatory Type 1 Cells.

IL-10 is a potent immunosuppressive cytokine that promotes the differentiation of tolerogenic dendritic cells (DC-10), and the subsequent induction of antigen-specific T regulatory type 1 (Tr1) cells, which suppress immune responses. However, IL-10 acts on multiple cell types and its effects are not solely inhibitory, therefore, limiting its use as immunomodulant. APVO210 is a bispecific fusion protein composed of an anti-CD86 antibody fused with monomeric IL-10 (ADAPTIR™ from Aptevo Therapeutics). APVO210 specifically induces IL-10R signaling in CD86+ antigen-presenting cells, but not in T and B cells. In this study, we tested whether APVO210 promotes the differentiation of tolerogenic DC-10 and the differentiation of antigen-specific CD4+ Tr1 cells in vitro. We compared the effect of APVO210 with that of recombinant human (rh) IL-10 on the in vitro differentiation of DC-10, induction of alloantigen-specific anergic CD4+ T cells, enrichment in CD49b+LAG3+ Tr1 cells mediating antigen-specific suppression, and stability upon exposure to inflammatory cytokines. APVO210 induced the differentiation of tolerogenic DC (DC-A210) that produced high levels of IL-10, expressed CD86, HLA-G, and intermediate levels of CD14 and CD16. These DC-A210 induced alloantigen-specific anergic T-cell cultures (T-alloA210) that were enriched in CD49b+ LAG3+ Tr1 cells, produced high levels of IL-10, and had suppressive properties. The phenotype and high IL-10 production by DC-A210, and the alloantigen-specific anergy of T-alloA210 were preserved upon exposure to the inflammatory cytokines IL-1β, IL-6, and TNF-α. The effects of APVO210 were comparable to that of dimeric rh IL-10. In conclusion, our data demonstrate that APVO210 drives the differentiation of tolerogenic DC and functional alloantigen-specific Tr1 cells in vitro. Since APVO210 specifically targets CD86+ cells, we hypothesize that it will specifically target CD86+ DC to induce Tr1 cells in vivo, and mediate antigen-specific immunological tolerance by induction of tolerogenic DC and Tr1 cells.

Dexamethasone promotes durable factor VIII-specific tolerance in hemophilia A mice via thymic mechanisms.

The development of inhibitory antibodies to factor VIII is the most serious complication of replacement therapy in hemophilia A. Activation of the innate immune system during exposure to this protein contributes to inhibitor development. However, avoidance of factor VIII exposure during innate immune system activation by external stimuli (e.g., vaccines) has not been consistently shown to prevent inhibitors. We hypothesized that dexamethasone, a drug with potent anti-inflammatory effects, could prevent inhibitors by promoting immunologic tolerance to factor VIII in hemophilia A mice. Transient dexamethasone treatment during ainitial factor VIII exposure reduced the incidence of anti-factor VIII immunoglobulin G in both a conventional hemophilia A mouse model (E16KO, 77% vs. 100%, P=0.048) and a hemophilia A mouse model with a humanized major histocompatibility complex type II transgene (E17KO/hMHC, 6% vs. 33%, P=0.0048). More importantly, among E17KO/hMHC mice that did not develop anti-factor VIII immunoglobulin G after initial exposure, dexamethasone-treated mice were less likely to develop a response after re-exposure six (7% vs. 52%, P=0.005) and 16 weeks later (7% vs. 50%, P=0.097). Similar results were obtained even when factor VIII re-exposure occurred in the context of lipopolysaccharide (30% vs. 100%, P=0.069). The ability of these mice to develop immunoglobulin G to human von Willebrand factor, a structurally unrelated antigen, remained unaffected by treatment. Transient dexamethasone administration therefore promotes antigen-specific immunologic tolerance to factor VIII. This effect is associated with an increase in the percentage of thymic regulatory T cells (12.06% vs. 4.73%, P<0.001) and changes in the thymic messenger ribonucleic acid transcription profile.

Partial retinal photoreceptor loss in a transgenic mouse model associated with reduced levels of interphotoreceptor retinol binding protein (IRBP, RBP3)

Organ-specific transgenic membrane expression of hen egg lysozyme (HEL) as a “neo-self antigen” has been used in several models to study immunological tolerance. In this study we report the changes which occur in the B10.BR mouse retina when membrane-bound HEL is expressed in photoreceptors under the control of the promoter for interphotoreceptor retinoid binding protein (IRBP, RBP3). On direct clinical examination of the single transgenic (sTg-IRBP:HEL) mouse fundus, a low-level increase in retinal degeneration compared to non-transgenic controls was observed, presenting as drusenoid deposits and occasional small patches of atrophy. On histological examination, there was an overall shortening of outer segments and loss of photoreceptor nuclei in sTg-IRBP:HEL mice, which was more pronounced in the retinal periphery, particularly inferiorly. The fundoscopically observed lesions did not correlate with the photoreceptor shortening/loss but appeared to be located at the level of the retinal pigment epithelium/choriocapillaris layer and were an exaggeration in size and number of similar age-related changes found in wild type (WT) mice. In addition, neither the atrophic lesions nor the photoreceptor shortening were associated with common retinal degeneration genes, nor were they caused by exposure to light damage since mice housed at both high and low ambient light levels had similar degrees of retinal degeneration. Instead, sTg-IRBP:HEL mice expressed reduced levels of soluble retinal IRBP compared to WT mice which were present from postnatal day16 (P16) and preceded development of photoreceptor shortening (onset P21). We propose that insertion of the HEL transgene in the photoreceptor membrane disrupted normal photoreceptor function and led to reduced levels of soluble IRBP and retinal thinning. A similar phenotype has been observed in IRBP deficient mice. Despite the retinal thinning, the amount of HEL expressed in the retina was sufficient to act as an autoantigenic target when the mice were crossed to the HEL T cell receptor Tg mouse, since double transgenic (dTg-IRBP:HEL) mice spontaneously developed a severe uveoretinitis with onset at weaning. We suggest that, although membrane expression of foreign transgene products is likely to modify the structure and function of tissues and cells, the technology provides useful models to investigate mechanisms of antigen-specific immunological tolerance.

Nanoparticles for the Induction of Antigen-Specific Immunological Tolerance.

Antigen-specific immune tolerance has been a long-standing goal for immunotherapy for the treatment of autoimmune diseases and allergies and for the prevention of allograft rejection and anti-drug antibodies directed against biologic therapies. Nanoparticles have emerged as powerful tools to initiate and modulate immune responses due to their inherent capacity to target antigen-presenting cells (APCs) and deliver coordinated signals that can elicit an antigen-specific immune response. A wide range of strategies have been described to create tolerogenic nanoparticles (tNPs) that fall into three broad categories. One strategy includes tNPs that provide antigen alone to harness natural tolerogenic processes and environments, such as presentation of antigen in the absence of costimulatory signals, oral tolerance, the tolerogenic environment of the liver, and apoptotic cell death. A second strategy includes tNPs that carry antigen and simultaneously target tolerogenic receptors, such as pro-tolerogenic cytokine receptors, aryl hydrocarbon receptor, FAS receptor, and the CD22 inhibitory receptor. A third strategy includes tNPs that carry a payload of tolerogenic pharmacological agents that can “lock” APCs into a developmental or metabolic state that favors tolerogenic presentation of antigens. These diverse strategies have led to the development of tNPs that are capable of inducing antigen-specific immunological tolerance, not just immunosuppression, in animal models. These novel tNP technologies herald a promising approach to specifically prevent and treat unwanted immune reactions in humans. The first tNP, SEL-212, a biodegradable synthetic vaccine particle encapsulating rapamycin, has reached the clinic and is currently in Phase 2 clinical trials.

Multipeptide-coupled nanoparticles induce tolerance in 'humanised' HLA-transgenic mice and inhibit diabetogenic CD8+ T cell responses in type 1 diabetes.

Induction of antigen-specific immunological tolerance may provide an attractive immunotherapy in the NOD mouse model but the conditions that lead to the successful translation to human type 1 diabetes are limited. In this study, we covalently linked 500nm carboxylated polystyrene beads (PSB) with a mixture of immunodominant HLA-A*02:01-restricted epitopes (peptides-PSB) that may have high clinical relevance in humans as they promote immune tolerance; we then investigated the effect of the nanoparticle-peptide complexes on T cell tolerance. PSB-coupled mixtures of HLA-A*02:01-restricted epitopes were administered to HHD II mice via intravenous injection. The effects on delaying the course of the disease were verified in NOD.β2m null HHD mice. The diabetogenic HLA-A*02:01-restricted cytotoxic lymphocyte (CTL) responses to treatment with peptides-PSB were validated in individuals with type 1 diabetes. We showed that peptides-PSB could induce antigen-specific tolerance in HHD II mice. The protective immunological mechanisms were mediated through the function of CD4+CD25+ regulatory T cells, suppressive T cell activation and T cell anergy. Furthermore, the peptides-PSB induced an activation and accumulation of regulatory T cells and CD11c+ dendritic cells through a rapid production of CD169+ macrophage-derived C-C motif chemokine 22 (CCL22). Peptides-PSB also prevented diabetes in 'humanised' NOD.β2m null HHD mice and suppressed pathogenic CTL responses in people with type 1 diabetes. Our findings demonstrate for the first time the potential for using multipeptide-PSB complexes to induce T cell tolerance and halt the autoimmune process. These findings represent a promising platform for an antigen-specific tolerance strategy in type 1 diabetes and highlight a mechanism through which metallophilic macrophages mediate the early cell-cell interactions required for peptides-PSB-induced immune tolerance.

Immune Tolerance for Autoimmune Disease and Cell Transplantation.

The undesired destruction of healthy cells, either endogenous or transplanted, by the immune system results in the loss of tissue function or limits strategies to restore tissue function. Current therapies typically involve nonspecific immunosuppression that may prevent the appropriate response to an antigen, thereby decreasing humoral immunity and increasing the risks of patient susceptibility to opportunistic infections, viral reactivation, and neoplasia. The induction of antigen-specific immunological tolerance to block undesired immune responses to self- or allogeneic antigens, while maintaining the integrity of the remaining immune system, has the potential to transform the current treatment of autoimmune disease and serve as a key enabling technology for therapies based on cell transplantation.

Abatacept Inhibition of T Cell Priming in Mice by Induction of a Unique Transcriptional Profile That Reduces Their Ability to Activate Antigen-Presenting Cells.

To determine at the phenotypic, functional, and transcriptional levels whether abatacept, a CTLA-4Ig molecule that binds with high affinity to CD80/86 on antigen-presenting cells (APCs) and is used to treat rheumatoid arthritis, induces a state of immunologic tolerance in T cells and dendritic cells in mice. We investigated the capacity of abatacept to regulate the development of antigen-specific immunologic tolerance in vivo using murine models of priming and tolerance to generate highly purified antigen-specific T cell populations and CD11c+ APCs. These were combined with detailed immunologic and full genome transcriptional analyses. We found that abatacept inhibited T cell activation, but did not render T cells anergic or lead to the generation of Treg cells. However, it induced a sustained inhibition of T cell activation due to the inability of these cells to progress through the cell cycle following T cell receptor stimulation. We also observed that this state was accompanied by an inhibition of dendritic cell activation due to their reduced licensing by T cells. This study provides detailed insight into the mode of action of abatacept, demonstrating that its effectiveness is not due to the induction of T cell tolerance, but rather to a sustained inhibition of T cell activation that results in reduced functionality of APCs, with significant implications for its clinical application.

Memory of tolerance and induction of regulatory T cells by erythrocyte-targeted antigens.

New approaches based on induction of antigen-specific immunological tolerance are being explored for treatment of autoimmunity and prevention of immunity to protein drugs. Antigens associated with apoptotic debris are known to be processed tolerogenically in vivo. Our group is exploring an approach toward antigen-specific tolerization using erythrocyte-binding antigens, based on the premise that as the erythrocytes circulate, age and are cleared, the erythrocyte surface-bound antigen payload will be cleared tolerogenically along with the eryptotic debris. Here, we characterized the phenotypic signatures of CD8+ T cells undergoing tolerance in response to soluble and erythrocyte-targeted antigen. Signaling through programmed death-1/programmed death ligand-1 (PD-1/PD-L1), but not through cytotoxic T lymphocyte antigen 4 (CTLA4), was shown to be required for antigen-specific T cell deletion, anergy and expression of regulatory markers. Generation of CD25+FOXP3+ regulatory T cells in response to erythrocyte-targeted antigens but not soluble antigen at an equimolar dose was observed, and these cells were required for long-term maintenance of immune tolerance in both the CD4+ and CD8+ T cell compartments. Evidence of infectious tolerance was observed, in that tolerance to a one antigenic epitope was able to regulate responses to other epitopes in the same protein antigen.

Proinsulin multi-peptide immunotherapy induces antigen-specific regulatory T cells and limits autoimmunity in a humanized model.

Peptide immunotherapy (PIT) is a targeted therapeutic approach, involving administration of disease-associated peptides, with the aim of restoring antigen-specific immunological tolerance without generalized immunosuppression. In type 1 diabetes, proinsulin is a primary antigen targeted by the autoimmune response, and is therefore a strong candidate for exploitation via PIT in this setting. To elucidate the optimal conditions for proinsulin-based PIT and explore mechanisms of action, we developed a preclinical model of proinsulin autoimmunity in a humanized HLA-DRB1*0401 transgenic HLA-DR4 Tg mouse. Once proinsulin-specific tolerance is broken, HLA-DR4 Tg mice develop autoinflammatory responses, including proinsulin-specific T cell proliferation, interferon (IFN)-γ and autoantibody production. These are preventable and quenchable by pre- and post-induction treatment, respectively, using intradermal proinsulin-PIT injections. Intradermal proinsulin-PIT enhances proliferation of regulatory [forkhead box protein 3 (FoxP3(+))CD25(high) ] CD4 T cells, including those capable of proinsulin-specific regulation, suggesting this as its main mode of action. In contrast, peptide delivered intradermally on the surface of vitamin D3-modulated (tolerogenic) dendritic cells, controls autoimmunity in association with proinsulin-specific IL-10 production, but no change in regulatory CD4 T cells. These studies define a humanized, translational model for in vivo optimization of PIT to control autoimmunity in type 1 diabetes and indicate that dominant mechanisms of action differ according to mode of peptide delivery.

Polymeric synthetic nanoparticles for the induction of antigen-specific immunological tolerance

Current treatments to control pathological or unwanted immune responses often use broadly immunosuppressive drugs. New approaches to induce antigen-specific immunological tolerance that control both cellular and humoral immune responses are desirable. Here we describe the use of synthetic, biodegradable nanoparticles carrying either protein or peptide antigens and a tolerogenic immunomodulator, rapamycin, to induce durable and antigen-specific immune tolerance, even in the presence of potent Toll-like receptor agonists. Treatment with tolerogenic nanoparticles results in the inhibition of CD4+ and CD8+ T-cell activation, an increase in regulatory cells, durable B-cell tolerance resistant to multiple immunogenic challenges, and the inhibition of antigen-specific hypersensitivity reactions, relapsing experimental autoimmune encephalomyelitis, and antibody responses against coagulation factor VIII in hemophilia A mice, even in animals previously sensitized to antigen. Only encapsulated rapamycin, not the free form, could induce immunological tolerance. Tolerogenic nanoparticle therapy represents a potential novel approach for the treatment of allergies, autoimmune diseases, and prevention of antidrug antibodies against biologic therapies.

Die Leber als immunologisches Organ

In many species, liver transplants induce antigen-specific immunological tolerance. Furthermore, the liver seems to play an important role in oral tolerance although the exact mechanisms as to how the liver induces immunological tolerance still need to be defined. Apart from the presence of an unusual subset of effector cells of the innate immune system, the liver is rich in CD 8+ T cells with an activated and preapoptotic phenotype. In this article, we discuss the suggested hypothesis to explain this phenotype. In addition, we discuss the different cell types that have been suggested to serve as antigen-presenting cells (APC) for naïve T cells. Interestingly, different APCs seem to use different mechanisms to induce tolerance while hepatic stellate cells were reported to induce an effective immune response.

In vivo delivery of a microRNA-regulated transgene induces antigen-specific regulatory T cells and promotes immunologic tolerance

AbstractWe previously showed that incorporating target sequences for the hematopoietic-specific microRNA miR-142 into an antigen-encoding transgene prevents antigen expression in antigen-presenting cells (APCs). To determine whether this approach induces immunologic tolerance, we treated mice with a miR-142–regulated lentiviral vector encoding green fluorescent protein (GFP), and subsequently vaccinated the mice against GFP. In contrast to control mice, no anti-GFP response was observed, indicating that robust tolerance to the transgene-encoded antigen was achieved. Furthermore, injection of the miR-142–regulated vector induced a population of GFP-specific regulatory T cells. Interestingly, an anti-GFP response was observed when microRNA miR-122a was inserted into the vector and antigen expression was detargeted from hepatocytes as well as APCs. This demonstrates that, in the context of lentiviral vector-mediated gene transfer, detargeting antigen expression from professional APCs, coupled with expression in hepatocytes, can induce antigen-specific immunologic tolerance.

A GMCSF-neuroantigen fusion protein is a potent tolerogen in experimental autoimmune encephalomyelitis (EAE) that is associated with efficient targeting of neuroantigen to APC

Cytokine-NAg fusion proteins represent an emerging platform for specific targeting of self-antigen to particular APC subsets as a means to achieve antigen-specific immunological tolerance. This study focused on cytokine-NAg fusion proteins that targeted NAg to myeloid APC. Fusion proteins contained GM-CSF or the soluble extracellular domain of M-CSF as the N-terminal domain and the encephalitogenic 69-87 peptide of MBP as the C-terminal domain. GMCSF-NAg and MCSF-NAg fusion proteins were approximately 1000-fold and 32-fold more potent than NAg in stimulating antigenic proliferation of MBP-specific T cells, respectively. The potentiated antigenic responses required cytokine-NAg covalent linkage and receptor-mediated uptake. That is, the respective cytokines did not potentiate antigenic responses when cytokine and NAg were added as separate molecules, and the potentiated responses were inhibited specifically by the respective free cytokine. Cytokine-dependent targeting of NAg was specific for particular subsets of APC. GMCSF-NAg and MCSF-NAg targeted NAg to DC and macrophages; conversely, IL4-NAg and IL2-NAg fusion proteins, respectively, induced an 1000-fold enhancement in NAg reactivity in the presence of B cell and T cell APC. GMCSF-NAg significantly attenuated severity of EAE when treatment was completed before encephalitogenic challenge or alternatively, when treatment was initiated after onset of EAE. MCSF-NAg also had significant tolerogenic activity, but GMCSF-NAg was substantially more efficacious as a tolerogen. Covalent GMCSF-NAg linkage was required for prevention and treatment of EAE. In conclusion, GMCSF-NAg was highly effective for targeting NAg to myeloid APC and was a potent, antigen-specific tolerogen in EAE.

Anti-CD3 prevents factor VIII inhibitor development in hemophilia A mice by a regulatory CD4+CD25+-dependent mechanism and by shifting cytokine production to favor a Th1 response

AbstractNon–Fc-receptor binding anti-CD3 Ab therapy, in the setting of several different autoimmune disorders, can induce antigen-specific and long-lasting immunologic tolerance. Because factor VIII (FVIII) inhibitor formation is the most serious treatment-related complication for hemophilia A patients, we tested the efficacy of anti-CD3 to prevent FVIII inhibitor formation in hemophilia A BALB/c and C57BL/6 mice. A short course of low-dose anti-CD3 significantly increased expression of CD25 and the proportion of CD4+CD25+ regulatory T cells in the spleen and potently prevented the production of inhibitory and non-neutralizing anti-FVIII antibodies in both strains of mouse. Depleting the CD4+CD25+ cells during anti-CD3 therapy completely ablated tolerance to FVIII. Further phenotypic characterization of regulatory cells in tolerant mice showed a consistently higher number of CD4+GITR+ and CD4+FoxP3+ cells in both strains of mice. In addition, in tolerant C57BL/6 mice we observed an increase in CD4+CD25+CTLA-4+ and CD4+CD25+mTGF-β1+ cells. Finally, in vitro cytokine profiling demonstrated that splenocytes from tolerant BALB/c and C57BL/6 were polarized toward a Th1-immune response. Taken together, these findings indicate that anti-CD3 induces tolerance to FVIII and that the mechanism(s) regulating this response almost certainly occurs through the generation of several distinct regulatory T-cell lineages and by influencing cytokine production and profile.

Pancreatic Islets Induce CD4+CD25−Foxp3+ T-Cell Regulated Tolerance to HY-Mismatched Skin Grafts

The ability to induce and maintain antigen-specific immunologic tolerance is the ultimate goal in allo-transplantation. Here, we report that the transplantation of unmanipulated murine pancreatic islets across the HY disparity induced transplantation tolerance that prevented HY-mismatched skin grafts being rejected. Three hundred islet equivalent of freshly isolated islets from male C57BL/6 donor mice was transplanted underneath the kidney capsule of syngeneic female recipients rendered diabetic by streptozotocin. Nephrectomy was carried out to remove the islet graft and retransplantation was performed using the contralateral kidney. For skin transplantation, donor tail skin was transplanted onto the lateral thorax. Islets from male C57BL/6 donors transplanted to syngeneic female recipients cured diabetes and the mice survived indefinitely. The acceptance of second grafts and rejection of third party islet grafts indicated antigen-specific transplantation tolerance. However, flow cytometry and ELISPOT analysis demonstrated that the HY-specific T cells were not deleted or anergized. A 2-fold increase of CD4+Foxp3+ regulatory T cells (Tregs) was observed in spleen and lymph nodes. Notably, CD25- Tregs increased threefold over levels in naïve mice. Adoptive transfer of CD4+ T cells to neonatal mice could transfer tolerance. At the graft site in long-term tolerant mice, CD4+ T cells, 40% of which were CD4+Foxp3+ Tregs (43% CD25-, 57% CD25+) infiltrated the peri-islet spaces. Unmanipulated pancreatic islets can induce immunologic tolerance associated with peripherally induced CD4+Foxp3+ Tregs, a significant proportion of which notably are CD25-.

Anti-CD3 Therapy Expands the CD4+CD25+ Compartment in Hemophilia a Mice Inducing Tregs That Potently Prevent Factor VIII Inhibitor Formation

Non-Fc-Receptor binding anti-CD3 Ab therapy, in the setting of several different autoimmune disorders, can induce antigen-specific and long-lasting immunological tolerance. As FVIII inhibitor formation is the most serious treatmentrelated complication for hemophilia A patients, we tested the efficacy of anti-CD3 to prevent FVIII inhibitor formation in hemophilia A Balb/c and C57Bl/6 mice. Mice were treated intravenously with 50 μg anti-CD3 daily for 5 consecutive days. One, 8 and 15 days after the final anti-CD3 treatment spleens were harvested (n=5/time point) and total splenocytes were analyzed by flow cytometry. One day after anti-CD3 treatment the effector CD4+ and CD8+ populations decreased by >2- fold (p<0.00009), while CD4+CD25+ Treg cells increased 2.2-fold (p=0.0002) compared to untreated control mice. This was maintained at 8 days post anti-CD3 treatment, and by day 15, all T cell populations returned to pre-treatment levels. Interestingly, we observed that smaller doses of anti-CD3 were the most effective at preventing FVIII inhibitor formation. In four separate experiments this optimized dose of anti-CD3 (10 μg/d for 5 d), was administered to Balb/c hemophilia A mice, and 3 days later these mice were immunized with 0.2 μg FVIII (50 U/kg) weekly for 4 weeks. By 1 week after the final FVIII immunization, 98% of the HBSS-treated control (n = 30) and 22% of anti-CD3-treated mice (n = 33) were inhibitor positive. Twenty-seven of 33 anti-CD3-treated mice were inhibitor negative (p = 0.000065). Importantly, the mean inhibitor titer in the anti-CD3-treated mice was 1.6 ± 1.1 BU/mL compared to the HBSS-treated mice at 50.1 ± 14.9 BU/mL (p = 0.0014). We depleted CD4+CD25+ T cells in vivo to test their importance in the FVIII tolerogenic process. Hemophilia A Balb/c mice were injected intraperitoneally with anti-CD25 (clone PC61) or isotype control (Rat IgG1) on days 0 and 5. Next, mice received 10 μg/d anti- CD3 on days 3–7 and on day 10, the first of 4 weekly FVIII immunizations was begun. One week after the 4th FVIII immunization, plasma was assessed for inhibitor formation by the Bethesda assay. Tolerance to FVIII was completely ablated in the anti-CD25/anti-CD3- treated mice (mean titer 110 ± 36 BU/mL), while the isotype control/anti-CD3-treated mice continued to show markedly reduced inhibitor levels (1.2 ± 1.9 BU/mL, p = 0.00003). To directly test the tolerogenic capacity of CD4+CD25+ population from tolerant animals, this population was cocultured, in the presence of FVIII, with splenocytes from FVIII immunized mice that were not treated with anti-CD3. Cells were either in direct contact or were physically separated by a transwell membrane. We observed a contact-dependent 30% and 20% reduction of IFN-γ and IL-10, respectively, in the coculture studies when compared to cytokine secretion by splenocytes cultured alone. The suppressive function was localized to the CD4+CD25+ compartment because coculture of CD4+CD25− cells from tolerant animals with splenocytes caused a 6.5- and 1.9-fold increase in IFN-γ and IL-10, respectively, compared to splenocytes alone. Phenotypic characterization of regulatory cells in tolerant mice showed a consistently higher number of CD4+GITR+ and CD4+FoxP3+ cells in both strains of mouse compared to HBSS-treated control mice. Additionally, in tolerant C57Bl/6 mice we observed an increase in CD4+CD25+CTLA-4+ and CD4+CD25+mTGF-β1+ cells. In vitro cytokine profiling demonstrated that splenocytes from tolerant Balb/c and C57Bl/6 were polarized toward a Th1 immune response. Taken together, these findings indicate that anti-CD3 induces tolerance to FVIII, and that the mechanism(s) regulating this response occurs through the generation of several distinct regulatory T cell lineages and by influencing cytokine production and profile. In light of these results, a short course of low-dose anti-CD3 treatment in patients at high risk of inhibitor development, with concomitant FVIII exposure administered prophylactically, in the absence of potentially “inflammatory” bleeding, may reduce the likelihood of inhibitor development.