Induction Of Specific Immunological Tolerance Research Articles

Mechanistic and Biomarker Studies to Demonstrate Immune Tolerance in Multiple Sclerosis.

The induction of specific immunological tolerance represents an important therapeutic goal for multiple sclerosis and other autoimmune diseases. Sound knowledge of the target antigens, the underlying pathomechanisms of the disease and the presumed mechanisms of action of the respective tolerance-inducing approach are essential for successful translation. Furthermore, suitable tools and assays to evaluate the induction of immune tolerance are key aspects for the development of such treatments. However, investigation of the mechanisms of action underlying tolerance induction poses several challenges. The optimization of sensitive, robust methods which allow the assessment of low frequency autoreactive T cells and the long-term reduction or change of their responses, the detection of regulatory cell populations and their immune mediators, as well as the validation of specific biomarkers indicating reduction of inflammation and damage, are needed to develop tolerance-inducing approaches successfully to patients. This short review focuses on how to demonstrate mechanistic proof-of-concept in antigen-specific tolerance-inducing therapies in MS.

Long-term prevention of chronic allograft rejection by regulatory T-cell immunotherapy involves host Foxp3-expressing T cells

AbstractDespite the use of immunosuppressive drugs, chronic allograft rejection remains a major hurdle in transplantation medicine. Induction of specific immunologic tolerance to antigens expressed by the graft would avoid its eventual functional loss and the severe side effects of paralyzing the immune system. We previously showed that donor-specific regulatory T-lymphocytes prevent rejection of fully allogeneic bone marrow (BM) grafts in mice. Thus generated hematopoietic chimeras then accepted skin and heart allografts of the same donor. We noticed that injected regulatory T-cells (Tregs) disappeared with time and investigated the mechanisms involved in the nevertheless long-term persistence of allograft tolerance. Using Tregs that can be depleted in vivo with diphtheria toxin, we show that injected cells are required for induction but not for maintenance of tolerance to BM allografts. We observed progressive deletion of donor-specific T-lymphocytes, accounting at least in part for maintenance of tolerance. Toxin-induced depletion of administered as well as host Tregs did not affect hematopoietic chimerism but it led to rapid loss of skin allografts. Therefore, our data show that newly generated host Tregs can prevent chronic allograft rejection. Long-lasting tolerance to allografts is thus achieved.

New cancer therapies based on the immune system

New cancer therapies based on the immune system

Tolerance-Inducing Immunosuppressive Strategies in Clinical Transplantation

The significant development of immunosuppressive drug therapies within the past 20 years has had a major impact on the outcome of clinical solid organ transplantation, mainly by decreasing the incidence of acute rejection episodes and improving short-term patient and graft survival. However, long-term results remain relatively disappointing because of chronic allograft dysfunction and patient morbidity or mortality, which is often related to the adverse effects of immunosuppressive treatment. Thus, the induction of specific immunological tolerance of the recipient towards the allograft remains an important objective in transplantation. In this article, we first briefly describe the mechanisms of allograft rejection and immune tolerance. We then review in detail current tolerogenic strategies that could promote central or peripheral tolerance, highlighting the promises as well as the remaining challenges in clinical transplantation. The induction of haematopoietic mixed chimerism could be an approach to induce robust central tolerance, and we describe recent encouraging reports of end-stage kidney disease patients, without concomitant malignancy, who have undergone combined bone marrow and kidney transplantation. We discuss current studies suggesting that, while promoting peripheral transplantation tolerance in preclinical models, induction protocols based on lymphocyte depletion (polyclonal antithymocyte globulins, alemtuzumab) or co-stimulatory blockade (belatacept) should, at the current stage, be considered more as drug-minimization rather than tolerance-inducing strategies. Thus, a better understanding of the mechanisms that promote peripheral tolerance has led to newer approaches and the investigation of individualized donor-specific cellular therapies based on manipulated recipient regulatory T cells.

Induction of allograft tolerance in nonhuman primates and humans

Despite remarkable improvement in short-term survival following organ transplantation, long-term results have been less satisfactory, mainly due to chronic rejection or toxicities induced by immunosuppressive drugs. Therefore, induction of specific immunologic tolerance remains an important goal in organ transplantation. Although numerous regimens for the induction of allograft tolerance have been developed in rodents, their application to large animal models has been limited. The mechanisms of action of the approaches that have been successfully applied in monkey models can be divided into three major categories: 1) deletion, 2) co-stimulatory blockade and 3) regulation. Long-term allograft survival has now been achieved in several nonhuman primate models; however, late-onset chronic rejection as well as the toxicity of some of these regimens remain as significant limitations that hamper clinical application.

Suppression of Experimental Autoimmune Encephalomyelitis by Inducing Immunologic Tolerance Via Peritoneal

Objective To investigate the method and mechanism of immunologic tolerance induction via peritoneal on experimental autoimmune encephalomyelitis（EAE） Methods The animals were administrated with the soluble myelin basic protein (MBP) or transferred MBP sensitizing antigen presenting cells (MBP-APC) by intraperitoneal (I.p.). The clinical symptoms of EAE were observed. The delayed type hypersensitivity(DTH) and proliferative responses to MBP in vitro were tested. Results The incidence of EAE and severity of the disease were decreased in the I.p. Injection of MBP group and I.p. Injection of MBP-APC group contrast to the EAE group, In addition, DTH responses and the antigen specific proliferative responses to MBP in vitro were markedly suppressed. Conclusions EAE can be inhibited by intraperitoneal administration of MBP or MBP-APC via induction of specific immunologic tolerance. Key words: Myelin basic protein; Antigen-presenting cells; Experimental autoimmune encephalomyelitis; Intraperitoneal injection; Immunologic tolerance

T cell receptor peptides for the vaccination therapy of multiple sclerosis.

Current options for treatment of diseases with a presumed autoimmune etiology such as multiple sclerosis (MS) are far from satisfactory. Most treatments are associated with undesirable side effects due to toxicity and lack of immunological specificity. For these reasons, one of the primary goals in the development of immunotherapies has been to achieve selective inactivation of disease-inducing lymphocytes in the absence of general immunosuppression. It appears that the peripheral immune system can be divided into two compartments: one in which positive responses are initiated and another one where tolerance is induced (Mitchison 1998). Augmenting of tolerance by immunoregulation ranks prominently among the various approaches studied for the treatment of autoimmune disorders. Strategies in this direction include induction of specific immunological tolerance via anergizing, deletion, or suppression of autoreactive clones (Van Paris et al. 1998). The role of some of these mechanisms in maintaining peripheral tolerance in vivo is still very much a matter of debate.

New concepts concerning the clinical control of IgE synthesis.

Prospects for new therapeutic approaches to IgE-mediated allergic diseases have arisen from (1) recent experimental observations that have suggested new concepts concerning the pathogenesis of the allergic phenotype, and (2) adaptation of previously described methods for induction of specific immunological tolerance to problems to allergy. The bases for these new approaches to allergic diseases are summarized herein.

Failure to Induce Tolerance to Mechlorethamine Hydrochloride

In view of the contradictory results reported in the literature regarding induction of specific immunologic tolerance to mechlorethamine hydrochloride (HN2), the problem was reinvestigated using a "tolerogenic" schedule that had been reported to be effective. Mechlorethamine hydrochloride, 200 microgram, intravenously, was given weekly for five weeks before beginning topical therapy with it. In the test group, five of 13 patients (11 with mycosis fungoides and two with psoriasis) became contact sensitized to mechlorethamine. In another patient, what was probably a contact urticarial reaction developed. In the control group, five of 13 patients (12 with mycosis fungoides, one with parapsoriasis) became contact sensitized to mechlorethamine. Thus, 38% of the patients in both groups became contact sensitized to mechlorethamine. It is concluded that this tolerogenic schedule, just as others previously tried, was not effective in inducing specific tolerance to mechlorethamine.

Mechanism of Inhibition of immunization with irradiated tumour cells by a large dose of Corynebacterium parvum.

As reported previously, the resistance to subsequent isogeneic live challenge with a highly immunogenic murine fibrosarcoma, which is normally evoked by prior subcutaneous injection of 10 6 irradiated tumour cells, is completely abrogated if a large dose (1.4 mg) of Corynebacterium parvum (strain CN6134) is mixed with the irradiated cells. New experiments designed to elucidate the mechanism underlying this phenomenon have revealed no evidence of humoral inhibitory factors or of an increase in suppressor T cells following injection of C . parvum and irradiated cells. The results suggest, on the other hand, that the abrogation of immunization is due to the induction of specific immunological tolerance of tumour antigens since it can be largely reversed by adoptive immunization, and are consistent with the hypothesis that in this model tolerance is due to prolonged trapping and eventual destruction in the regional nodes of lymphocytes which have responded to tumour antigen.

Studies on Tolerance Induction in Vitro

Abstract The induction of specific immunologic tolerance and its transfer has been studied in the in vitro response of unprimed rabbit spleen cells to solubilized phage antigens. Evidence presented shows that only viable cells transfer tolerance and that the responsible cells appear devoid of membrane-bound antigen but are sensitive to anti-thymocyte serum. It appears, therefore, that although the in vitro response to solubilized S-T2 has no demonstrable requirement for T “helper” cells, it is subject to the action of T “suppressor” cells.

Complete remissions of mycosis fungoides lymphoma induced by topical nitrogen mustard (HN2). Control of delayed hypersensitivity to HN2 by desensitization and by induction of specific immunologic tolerance.

Sustained complete remissions have been achieved with whole body continuous topical applications of aqueous solutions of mechlorethamine (HN2), and supplemental intralesional injections of tumors. Of 76 patients entered into the treatment study over a 4-year period, approximately 50% are free of detectable disease, 13 of whom have had remissions extending now beyond 2 years. Most patients experiencing complete remissions had disease confined to skin, without lymph node or visceral involvement, when topical therapy was initiated. Delayed hypersensitivity to HN2, a frequent occurrence, has been abolished in sensitized patients by means of daily minute I.V. doses of the drug. Induction of specific immunologic tolerance to HN2, prior to topical treatment, has been achieved by means of several weekly I.V. injections of similarly minute doses of the drug.

Induction of immunological tolerance in neonatal and adult rabbits differences in the cellular events

A transient production of antibody does not occur in the induction of specific immunological tolerance to soluble BSA in neonatal rabbits. The newborn rabbit, however, has the immunologic potential to respond to BSA when it is given in adjuvant. These results suggest that a normal complement of specific B cells is present in the newborn rabbit and that the immunoincompetence to the soluble protein, that permits the induction of tolerance without a phase of antibody formation, may be a function of either T cells or macrophages. In contrast to the newborn, the induction of tolerance in adult rabbits following daily injections with large doses of BSA is preceded by a transient production of antibody-producing cells. In this situation, at least, one of the events involved in the induction of unresponsiveness appears to be interpretable as an exhaustive differentiation of competent cells capable of being stimulated. Therefore, two differing cellular patterns can be observed in the completion of seemingly identical end states of immunological tolerance.

Effect of a DNA tumour virus on antibody forming cells in neonatally infected hamsters.

LEUKAEMOGENIC viruses, such as Friend, Rauscher or Moloney virus, may markedly suppress the immune responses of infected mice, both at the cellular and humoral levels1–10. AKR mice developing spontaneous leukaemia also have a marked suppression of serum antibody formation preceding clinical symptoms11. Several current theories of carcinogenesis suggest that such deficiencies of specific immunological competence may be a necessary but not exclusive prerequisite for tumour development12–16. In this regard, the induction of tumours by viruses other than those associated with murine leukaemia may also depend on an inadequate immune system and/or induction of specific immunological tolerance. Because most tumour viruses induce neoantigens in infected cells, it seems probable that an immunocompetent individual would respond to the virus induced antigens15. Loss of immunological competence could be related to development of the tumours. This study was undertaken to determine if a non-leukaemia DNA tumour virus could affect the immunological responsiveness of experimental animals. For this purpose, SV40 tumour virus was inoculated into newborn hamsters and their subsequent immune response to sheep erythrocytes was determined at the serum and cell level, using the haemolytic plaque assay in agar gel and serological procedures. The responses of non-infected hamsters were determined simultaneously.

Ovarian transplantation: Graft-host interactions in corneal encapsulated homografts

Ovarian homografts encapsulated in corneal tissue may survive by the induction of specific immunologic tolerance in the host by the graft or the adaptation of the graft to the host. To test these hypotheses, these grafts were challenged in a series of experiments. Despite challenge grafts of ovarian tissue and skin from the original donor and of ovarian tissue from a “third party” donor, the ovarian tissue within the capsule remained viable for periods up to 30 weeks. A “backgraft” of encapsulated ovarian tissue removed from the recipient after 11 weeks and stripped of its capsule was not rejected after 6 weeks’ residence in the original donor. Rejection times for homografts of ear skin in animals with ovarian homografts were the same as controls. These data indicate that (a) survival was not due to immunologic tolerance and (b) the surviving ovarian tissue was nonantigenic in relation to the host but had not undergone adaptation. It is suggested that the less antigenic cells within the capsules had been “passively” selected for survival by prolonged incubation in an immunologically unfavorable environment.

Induction of specific immunological tolerance of homografts in adult mice by sublethal irradiation and injection of donor-type spleen cells in high dosage

AdultA-strain mice in the weight-range 15 to 20 g were irradiated to 350 or 500 r, followed by the injection, divided between the intravenous and intraperitoneal routes, of suspensions of spleen cells obtained fromCBAor (CBAxA)F1mice, donors and recipients being matched for sex. After the lapse of 18 to 25 days all mice, including control batches which had received irradiation but not spleen cells, were challenged with donor-type skin grafts. Mice irradiated to 500 r which receivedCBAspleen cells in doses from 500 to 1500 million developed severe graft-versus-host disease, fatal in most cases. Rejection of the grafts occurred in irradiated controls after periods ranging from 8 to 23 days. Mice receiving 500r followed by (CBAxA)F1spleen cells showed prolonged survival of skin grafts, amounting to 90 days or more in animals which had received the highest dose of cells (12 x 109). Analysis of the phenomenon by means of Simonsen’s discriminant spleen assay showed that approximately 85% of the immunologically competent spleen cells of the graft-bearing animals were replaced by cells of donor origin; the remainder, however, retained the power to react immunologically against third-party (C57BL) antigens. It was also possible to secure adoptive rejection of grafts by injection of 60 to 90 millionA-strain lymph node cells pre-sensitized againstCBA. It is concluded that the state of specific unresponsiveness induced in the adultAstrain mice represented a specific central inhibition of the mechanism of immunological response and could thus be equated to immunological tolerance as classically defined. Prior splenectomy not only abolished the tolerance phenomenon, but actually reversed it, there being clear signs of an immunity resulting from the irradiation and injection procedure. This result is discussed in terms of the significance of antigen dose-level for the induction of tolerance.

Qualitative differences in the immune response.

There are four types of response to an antigen: the production of classical antibody; the induction of hay fever type of hypersensitivity; the induction of tuberculin type of hypersensitivity; and the induction of specific immunological tolerance. Since the formation of antibody of some kind appears to be associated with the first three types of response, and the inhibition of antibody formation with immunological tolerance, any hypothesis of antibody formation must be consistent with what is known about all four responses. A reasonable consistency may be achieved by postulating the existence in the cell of endogenously produced 'genocopies' of certain proteins, which act as templates and determine the configuration of the proteins as they are synthesized; when a genocopy is modified by contact with antigen, protein will be synthesized with the specific complementary pattern of an antibody. The interference with this synthesis during embryonic life by entry into the cell of macromolecules objectionable to it, results in intracellular antibody and self-replicating mechanism for its further production—a system that can deal with all such macromolecules at the intracellular level; this corresponds to specific immune tolerance. When antigenic material enters body cells after birth, the same response occurs but there is in addition a transfer of the self-replicating mechanisms to cells of the lymphoid system with a consequent output of extracellular antibody—the classical antibody response. The hypersensitivity responses are intermediate in kind, and differ according to the transferability of the self-replicating mechanism, the amount of antibody released into the body fluids, and the readiness with which the antibody becomes attached to the tissue cells.