Induction Of Immunological Tolerance Research Articles

No significant association between mutations in exons 6 and 8 of the autoimmune regulator (AIRE) gene and inflammatory bowel disease.

Various autoantibodies have been described in patients with inflammatory bowel disease. The autoimmune regulator (AIRE) functions as a transcription factor in cells responsible for the induction and maintenance of immunological tolerance. In contrast to classic autoimmune disorders, polymorphisms of the AIRE gene are not associated with inflammatory bowel disease, despite the presence of disease-specific autoantibodies.

Polyreactivity of antibody molecules

The ’lock and key’ hypothesis of antigen–antibody interaction has long dominated immunological thinking. However, studies demonstrating the existence of a large number of monoclonal antibodies that can bind to a variety of totally unrelated self and foreign antigens (i.e. polyreactive antibodies) has modified this view. We argue that the best explanation for polyreactivity is that the antigen-binding ‘pocket’ of many antibody molecules is more flexible than previously thought and can change conformation to accommodate different antigens. In terms of biological function, we discuss the evidence for and against a role for polyreactive antibodies in immunological defense. We speculate that, paradoxically, because B cells that make polyreactive antibodies are capable of binding to many different endogenous host antigens, they might be involved in the induction and/or maintenance of immunological tolerance.

Facial transplantation: a working party report from the Royal College of Surgeons of England.

We are publishing this working party report on facial transplantation from the Royal College of Surgeons, England, in order to get opinions from the transplant community as to whether it is appropriate or not to perform this procedure at this point in time. There is no question that technically this can be done, but do the risks of failure, both technical and immunological, and the long-term risks of immunosuppression outweigh the potential benefits to the recipient who undoubtedly would be a severely burnt patient with a very scarred immobile face? The problems are not primarily technical but are immunological, psychological, and legal.

Bacterial Colonization in the Developing Gastrointestinal Tract: Role in the Pathogenesis of Intestinal Diseases

Bacterial colonization plays an important role in the normal development, differentiation, function and regulation of intestinal mucosal immune system. Through mechanisms that are still not fully understood, the intestinal mucosal immune system generates effective protective immunity against pathogen invasion and at the same time it develops immune tolerance, preventing the development of disease conditions, such as IBD and food allergy. The regulatory role of the intestinal flora in the development and function of the intestinal mucosal immune system is well established. Recent work has suggested that colonization with probiotics in the gut may play an essential role in balancing the intestinal mucosal immune system, which may contribute to the induction and maintenance of immunological tolerance to other luminal antigens in the normal host or to the inhibition of the dysregulated responses induced by luminal antigens in diseased hosts. A better understanding of the cellular and molecular mechanisms controlling the development and regulation of intestinal mucosal epithelial system by intestinal bacteria (commensal and probiotics) and their regulatory role in various diseases will help establish new strategies to prevent and control these disease conditions.

Induction of transgene-specific immunological tolerance in myeloablated nonhuman primates using lentivirally transduced CD34+ progenitor cells

Modeling human hematopoietic progenitor cell gene therapy in nonhuman primates allows long-term evaluation of safety, maintenance of gene expression, and potential immune response against transgene products. We transplanted autologous G-CSF/SCF-mobilized CD34+ cells transduced with lentiviral vectors expressing EGFP into myeloablated rhesus macaques. To date, more than 4 years posttransplantation, 0.5–8% EGFP expression is maintained in multiple cell lineages. The animals remain healthy with no evidence of hematopoietic abnormalities or malignancies. To assess immune functions, we actively immunized two of our transplanted animals with purified rEGFP proteins and CpG adjuvant and demonstrated stable levels of EGFP+ cell populations maintained for over 29 months despite four active immunizations. We did not detect a persistent anti-EGFP antibody response or anti-EGFP T cell response in these immunized animals. Immune response to an irrelevant antigen was normal. Taken together, our data provide formal support that transplantation of lentivirally transduced CD34+ progenitor cells in myeloablated rhesus macaques induces specific immunological tolerance toward a foreign transgene.

Optimizing anti-tumor necrosis factor strategies in inflammatory bowel disease.

The introduction of infliximab, a mouse/human chimeric monoclonal antibody to tumor necrosis factor (TNF), is an important advance in the treatment of Crohn's disease. Infliximab is effective for induction and maintenance of remission in patients with inflammatory luminal and fistulizing disease. The development of human antichimeric antibodies (HACAs) has led to infusion reactions and loss of efficacy in patients treated with infliximab. Strategies to reduce the frequency of HACA formation include induction of immunologic tolerance with a three-dose regimen at 0, 2, and 6 weeks followed by systematic maintenance dosing every 8 weeks; concomitant immunosuppressive therapy with azathioprine, 6-mercaptopurine, or methotrexate; and premedication with intravenous corticosteroids. Humanized or fully human anti-TNF biotechnologic agents, including CDP571, CDP870, etanercept, adalimumab, and onercept, are theoretically less immunogenic than the chimeric antibody infliximab. Etanercept is not effective for Crohn's disease. CDP571 is not effective in unselected patients with active Crohn's disease, but it may be effective in patients with elevated C-reactive protein. The efficacy of CDP870, adalimumab, and onercept is under investigation. The different mechanisms of action of these anti-TNF agents may account for their variable efficacy. Their benefits, however, must be considered in the context of their risks, including infusion reaction; delayed hypersensitivity-like reaction; new onset of autoimmunity, with rare cases of drug-induced lupus and new-onset demyelination; and the potential for rare but serious infections.

Memory T cells: a hurdle to immunologic tolerance.

The induction of immunologic tolerance is an important clinical goal in transplantation and autoimmunity. Immunologic tolerance is traditionally defined as specific unresponsiveness to a self- or foreign antigen while maintaining reactivity to other (third party) antigens ([1,2][1][⇓][2]). In the

Immunological basis of septal fibrosis of the liver in Capillaria hepatica-infected rats.

Rats infected with the helminth Capillaria hepatica regularly develop septal fibrosis of the liver similar to that induced by repeated ip injections of pig serum. Fibrosis starts when the focal parasitic lesions begin to show signs of resorption, thus suggesting an immunologically mediated pathogenesis of this fibrosis. To explore this possibility, the development of C. hepatica-related hepatic fibrosis was observed in rats exposed to worm antigens from the first neonatal day onward. Wistar rats (150 g) were either injected ip with an extract of C. hepatica eggs (protein concentration: 1 mg/ml) or received immature eggs by gavage from the first neonatal day until adult life and were then infected with 500 embryonated eggs. Changes were monitored on the basis of serum levels of anti-worm antibodies and hepatic histopathology. Rats submitted to immunological oral tolerance markedly suppressed C. hepatica-related serum antibodies and septal fibrosis of the liver when infected with the helminth later on. Tolerance trials with ip injections of worm antigens gave essentially negative results. The partial suppression of septal fibrosis of the liver after the induction of immunological tolerance to C. hepatica antigens in rats indicates an immunological basis for the fibrosis and emphasizes the importance of immunological factors in the pathogenesis of hepatic fibrosis.

Clinical xenotransplantion—how close are we?

Xenotransplantation with pig organs offers a medium-term solution to the shortage of organs available for clinical transplantation. The immunological barriers to xenotransplantation have been, and remain, formidable. In the early 1990s, the identification of Galalpha1,3Gal (Gal) as the main target for human xenoreactive (anti-pig) antibodies and the development of pigs transgenic for a human complement regulatory protein, decay-accelerating factor (hDAF), were major advances. The presence of hDAF on the vascular endothelium of pig organs provided some protection against complement-mediated hyperacute rejection. This protection, however, was short-lived, and, until recently, the longest median time for organ survival that had been achieved (with combinations of biological and pharmacological immunosuppressants) in a series of pig-to-primate organ transplants was under a month. Christopher McGregor and colleagues recently reported to the International Society of Heart and Lung Transplantation (J Heart Lung Transplant 2003; 22: S89) that, by combining the use of organs which express hDAF with the administration of a soluble Gal glycoconjugate and other immunosuppressive agents, the survival of pig hearts in baboons can be extended to a median of 76 days. McGregor's work suggests that immunological barriers to xenotransplantation are not insurmountable. WHERE NEXT? The recent generation of pigs that do not express Gal epitopes (alpha1,3-galactosyltransferase gene-knockout pigs) might remove the need both for the expression of hDAF and the administration of a soluble Gal glycoconjugate. The absence of a natural antibody response will allow investigation of the cellular immune response and of any molecular incompatibilities between pig and primate that may be detrimental to graft survival. Furthermore, the absence of a humoral response may open the way for the induction of immunological tolerance (or unresponsiveness in the absence of exogenous immunosuppression) to a transplanted pig organ.

Selective blockade of CD28 and not CTLA-4 with a single-chain Fv–α1-antitrypsin fusion antibody

AbstractB7-1 and B7-2 are costimulatory molecules expressed on antigen-presenting cells. The CD28/B7 costimulation pathway is critical for T-cell activation, proliferation, and Th polarization. Blocking both cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4) and CD28 interactions with a CTLA-4/Ig fusion protein inhibits various immune-mediated processes in vivo, such as allograft rejection and autoimmunity. However, selective blockade of CD28 may represent a better strategy for immunosuppression than B7 blockade, because CTLA-4/B7 interactions have been shown to participate in the extinction of the T-cell receptor–mediated activation signal and to be required for the induction of immunologic tolerance. In addition, selective CD28 inhibition specifically decreases the activation of alloreactive and autoreactive T cells, but not the activation of T cells stimulated by exogenous antigens presented in the context of self major histocompatibility complex (MHC) molecules. CD28 blockade cannot be obtained with anti-CD28 dimeric antibodies, which cluster their target and promote T-cell costimulation, whereas monovalent Fab fragments can block CD28 and reduce alloreactivity. In this study, we report the construction of a monovalent single-chain Fv antibody fragment from a high-affinity antihuman CD28 antibody (CD28.3) that blocked adhesion of T cells to cells expressing the CD28 receptor CD80. Genetic fusion with the long-lived serum protein α1-antitrypsin led to an extended half-life without altering its binding characteristics. The anti-CD28 fusion molecule showed biologic activity as an immuno-suppressant by inhibiting T-cell activation and proliferation in a mixed lymphocyte reaction.

The cholera toxin B subunit is a mucosal adjuvant for oral tolerance induction in type 1 diabetes.

When conjugated to various proteins, the nontoxic B-chain of cholera toxin (CTB) significantly increases the ability of these proteins to induce immunological tolerance after oral administration. Here, we investigated if a nonconjugated form of CTB enhances the induction of immune tolerance after oral insulin administration. Induction of immunological tolerance was studied after oral administration of insulin preparations in three mouse models; an insulin/ovalbumin coimmunization model, a model of virus-induced diabetes in transgenic RIP-LCMV-NP mice and in nonobese diabetic (NOD) mice serving as a model of spontaneous diabetes. In the immunization model, we demonstrate that mixing with CTB increases the tolerogenic potential of insulin, approximately 10 fold. Titration of the CTB concentration in this system revealed that an insulin : CTB ratio of 100 : 1 was optimal for the induction of bystander suppression. Further studies revealed that this insulin : CTB ratio also was optimal for the prevention of diabetes in a virus-induced, transgenic diabetes model. In addition, the administration of this optimal insulin-CTB preparation significantly prevented the onset of diabetes in old NOD mice with established islet infiltration. The data presented here demonstrate that CTB, even in its unconjugated form, functions as a mucosal adjuvant, increasing the specific tolerogenic effect of oral insulin.

Induction of immunologic tolerance to cardiac allograft by simultaneous blockade of inducible co-stimulator and cytotoxic T-lymphocyte antigen 4 pathway.

Inducible co-stimulator (ICOS) is one of the most recently described members of the CD28 family, and it plays an important role in immune responses. To investigate the role of ICOS in allograft rejection, the authors studied graft survival after cardiac transplantation in mice. Hearts from BALB/c mice were transplanted into C3H/He mice. Immunohistochemical staining and flow cytometry were performed. Monoclonal antibody to ICOS or ICOS-immunoglobulin (Ig) was injected intraperitoneally. The authors performed mixed lymphocyte reaction (MLR). ICOS was expressed strongly by graft-infiltrating cells during rejection of the allograft. Blockade of the ICOS pathway with anti-ICOS antibody and ICOSIg significantly prolonged graft survival time relative to that in untreated mice; however, all cardiac allografts were eventually rejected by a single treatment. Treatment with both ICOSIg and cytotoxic T-lymphocyte antigen 4 (CTLA4) Ig induced not only long-term acceptance of the cardiac allograft but also donor-specific tolerance, which was shown by acceptance of donor but not third-party skin. Graft arterial intimal hyperplasia in these cardiac allografts was remarkably less than that in cardiac allografts treated with tacrolimus. Addition of anti-ICOS antibody or ICOSIg to MLR resulted in inhibition of T-cell proliferation. Inhibition of T-cell proliferation with ICOSIg and CTLA4Ig was more effective than that with ICOSIg alone. Thus, ICOS appears to be an important regulator of T-cell activation, and may be an effective therapy in clinical cardiac transplantation.

Neonatal toxic shock syndrome-like exanthematous disease (NTED).

The author and colleagues recently discovered an emerging neonatal infectious disease: neonatal toxic shock syndrome-like exanthematous disease (NTED), which is induced by the superantigen toxic shock syndrome toxin-1 (TSST-1), produced by methicillin-resistant Staphylococcus aureus (MRSA). The massively expanded Vbeta2+ T cells were rapidly deleted in the peripheral blood of patients with NTED. A marked depletion of Vbeta2+ T cells was also observed in the peripheral blood before the expansion of these T cells. Anergy is specifically induced in the TSST-1 reactive T cells of patients with NTED. Rapid recovery from NTED without complications is expected to be related to the induction of immunologic tolerance in neonatal patients. Anti-TSST-1 IgG antibody of maternal origin was found to play a protective role in preventing the development of NTED. The number of hospitals that have experience caring for patients with NTED has increased threefold in the past 5 years. Most MRSA isolates from neonatal intensive care units in Japan were found to be a single clone of coagulase type II and to possess TSST-1 and staphylococcal enterotoxin C genes. The timing and increased incidence of NTED suggest the emergence of a new MRSA clone. By recognizing that TSST-1 can induce NTED, healthcare providers may give increased attention to this disease in neonatal wards.

Endogenous retroviruses related to jaagsiekte sheep retrovirus.

Ovine betaretroviruses consist of exogenous viruses [jaagsiekte sheep retrovirus (JSRV) and enzootic nasal tumor virus, (ENTV)] associated with neoplastic diseases of the respiratory tract and 15-20 endogenous viruses (enJSRV) stably integrated in the ovine and caprine genome. Phylogenetic analysis of this group of retroviruses suggests that the enJSRV can be considered as 'modern' endogenous retroviruses with active, exogenous counterparts. Sequence analysis of JSRV, ENTV and enJSRV suggests that enJSRV do not directly contribute to the pathogenesis of ovine pulmonary adenocarcinoma (OPA) or enzootic nasal tumor through large-scale recombination events, but small-scale recombination or complementation of gene function cannot be excluded; experiments involving enJSRV-free sheep, which have not been found, would be needed to investigate this possibility. Evidence of expression of enJSRV structural proteins in tissues of the reproductive tract and lung implies that they do not have a primary role in disease. However, experimental exploitation of exogenous/endogenous retrovirus sequence differences by producing chimeras has been useful in establishing the determinants of JSRV Env-induced transformation. Even if enJSRV do not have a direct role in OPA, their expression during ontogeny or in neonatal life may impact the likelihood of exogenous JSRV infection and disease outcome via the induction of immunological tolerance. Aside from any role in disease, enJSRV loci may serve as useful genetic markers in the sheep and their frequent expression in the reproductive tract of the ewe may portend an important physiologic role in sheep.

Efficacy of sublingual immunotherapy in asthma and eczema.

Sublingual immunotherapy (SLIT) is the local route of administration of allergen extracts investigated in several controlled clinical trials. In a number of countries, particularly Italy, France and Spain, this has become common in office practice. At variance with subcutaneous immunotherapy, the knowledge of mechanisms of action of SLIT is still at the beginning: some studies, in animal models, provided interesting information: the dendritic cells of oral mucosa act as efficient antigen-presenting cells and produce IL-12, which directs the immune response towards a Th1 profile away from IgE-Th2 profile. Its clinical efficacy (improvement of symptoms and reduction of drug intake) for both asthma and rhinitis has been assessed in detail for the most common allergens: house dust mites, grass pollen, Parietaria, birch pollen and olive tree. SLIT requires further evaluation concerning the treatment of the extrinsic form of atopic dermatitis. The induction of immunologic tolerance rather than immunoreactivity should be worth pursuing due to the immunologic pathway involved in the pathophysiology of atopic dermatitis. The safety profile of SLIT, derived from the clinical trials and postmarketing surveillance studies, turned out to be satisfactory in adults and children. SLIT represents an important step towards an efficacious and safe treatment of patients with allergic respiratory diseases; nevertheless, further studies are necessary to establish it as a viable alternative to subcutaneous immunotherapy.

Immunosuppression and immunological tolerance induction: lessons from a transplant model

Patients who receive organ transplants need life-long immunosuppression to prevent rejection of their grafts. Induction of immunological tolerance to the transplanted organs can solve this problem. However, according to the current opinion in clinical immunosuppression, administration of cyclosporin A (CyA) prevents tolerance induction. In our study, we attempted to find out whether immunosuppression with CyA is really so harmful for tolerance induction.

Cord Blood Dendritic Cells: Subsets, Functional Characteristics and In Vitro Generation

Dendritic cells (DCs) form a heterogeneous population of cells capable of stimulating naive T cells and initiating primary immune responses. This well-known function of DCs has offered the possibility of developing clinical protocols for their use in immunotherapy to tumours. DCs may also play a critical role in the induction of peripheral immunological tolerance, which could have important implications in the treatment of autoimmunity or in the outcome of clinical transplantation. Recent reports have indicated that cord blood transplantation is associated with a reduced incidence of graft versus host disease. Thus studies on the identification and characterisation of DCs present in, or derived from cord blood will help to understand their role, not only in neonatal immunity, but also in the outcome of cord blood transplantation.

Transplantation of Amniotic Epithelial Cells into Fetal Rat Liver by In Utero Manipulation

It has been hoped that amniotic epithelial cells would be a gene carrier to neural and hepatic tissue, because of 1) the presence of neural and hepatic stem-like cells, 2) the ability to cryopreserve them, 3) long-term survival in the transplanted site, and 4) few ethical problems concerning procurement. But transplantation of a sufficient number of cells to adult tissue needs large-scale cell supply and may lead to vascular embolism. We attempted transplantation of amniotic epithelial cells into fetal liver, because 1) the fetal liver is at the proliferative stage, 2) the number of cells required is small, and 3) the fetal stage is advantageous for the induction of immunological tolerance. Amniotic epithelial cells from day 18.5-20.5 fetuses were transfected with adenoviral AdlacZ and harvested to inject into fetal rat liver of the syngeneic strain (day 18.5-20.5). The efficacy of cell transplantation into the liver increased in the order: intraplacental < intraumbilical vein < intrahepatic route. LacZ-transfected amniotic cells (1-8 x 10(5) cells), hepatocytes (5 x 10(5) cells), or AdlacZ vector solution (1.7 x 10(7) pfu) were injected through the uterine membrane into the liver. Transplanted cells formed a cellular mass and survived for up to 14 days after birth, whereas lacZ-transfected cells were rapidly decreased after the injection of AdlacZ vector or rat hepatocytes as a gene carrier so that the use of amniotic epithelial cells as a gene carrier will result in long-term expression of exogenous genes in the liver.

Induction of T-cell tolerance to an MHC class I alloantigen by gene therapy

Induction of immunologic tolerance to alloantigens is a major goal in the field of transplantation. Here, we demonstrate that efficient transduction and expression of a retrovirally transduced major histocompatibility complex (MHC) class I gene (H-2K(b)) in bone marrow (BM)-derived cells, resulting in a permanent state of hematopoietic molecular chimerism, induces stable tolerance to the transduced gene product. Reconstitution of lethally irradiated syngeneic recipients with BM transduced with virus encoding H-2K(b) resulted in life-long expression of the retroviral gene product on the surface of BM-derived hematopoietic lineages including Sca-1(+), lineage negative, hematopoietic progenitors. T cells from mice receiving MHC-transduced BM were unable to kill targets expressing H-2K(b) but were able to respond to third-party controls. Mice reconstituted with H-2K(b)-transduced BM exhibited long-term acceptance of H-2K(b) mismatched skin grafts but were able to rapidly reject third-party control grafts. Thus, gene therapy approaches may be used to induce T-cell tolerance.

Mucosal tolerance to a bacterial superantigen indicates a novel pathway to prevent toxic shock.

Enterotoxins with superantigenic properties secreted during systemic Staphylococcus aureus infection are responsible for toxic shock. We show that intranasal administration of staphylococcal enterotoxin A (SEA), but not a recombinant SEA lacking superantigenic activity, protected mice against lethal systemic SEA challenge. Protection was superantigen specific since intranasal exposure to SEA would not protect against death caused by subsequent toxic shock syndrome toxin 1 systemic challenge. Protection was neither due to selective depletion of SEA-specific T-cell receptor Vbeta families nor due to production of neutralizing anti-SEA antibodies. Importantly, the production of interleukin 10 (IL-10) induced by "tolerization" (that is, by the induction of immunological tolerance) contributed to the observed protection against lethal superantigen-triggered disease. In support of this notion we found that (i) significantly increased levels of IL-10 in sera of "tolerized" animals (that is, animals rendered tolerant) and (ii) IL-10(-/-) mice could not be tolerized by mucosal SEA administration. Altogether, this is the first study to show that mucosal tolerance to a superantigen is readily triggered by means of immunodeviation.