Subimmunogenic Conditions Research Articles

Vaccine-induced antigen-specific regulatory T cells attenuate the antiviral immunity against acute influenza virus infection.

Peptide-based T cell vaccines targeting the conserved epitopes of influenza virus can provide cross-protection against distantly related strains, but they are generally not immunogenic. Foreign antigen-specific regulatory T (Treg) cells are induced under subimmunogenic conditions peripherally, although their development and role in vaccine-mediated antiviral immunity is unclear. Here, we demonstrated primary vaccination with peptides alone significantly induced antigen-specific Foxp3+ Treg cells, which were further expanded by repeated vaccination with unadjuvanted peptides. Certain adjuvants, including CpG, suppressed the induction and expansion of antigen-specific Treg cells by peptide vaccination. Interestingly, secondary influenza virus infection significantly increased the frequency of preexisting antigen-specific Treg cells, although primary infection barely induced them. Importantly, specific depletion of vaccine-induced antigen-specific Treg cells promoted influenza viral clearance, indicating their inhibitory role in vivo. Immunization with CpG-adjuvanted peptides by the subcutaneous prime-intranasal-boost strategy restricted the recruitment and accumulation of antigen-specific Treg cells in lung, and stimulated robust T cell immunity. Finally, subcutaneous prime-intranasal-boost immunization with CpG-adjuvanted peptides or whole-inactivated influenza vaccines protected mice from heterosubtypic influenza virus infection. In conclusion, antigen-specific Treg cells induced by peptide vaccines attenuate the antiviral immunity against influenza virus infection. CpG-adjuvanted peptide vaccines provide heterosubtypic influenza protection probably by inhibiting Treg development and enhancing T cell immunity.

Bioconjugate Strategies for the Induction of Antigen-Specific Tolerance in Autoimmune Diseases.

Antigen-specific immunotherapy (ASI) holds great promise for the treatment of autoimmune diseases. In mice, administration of major histocompatibility complex (MHC) binding synthetic peptides which modulate T cell receptor (TCR) signaling under subimmunogenic conditions induces selective tolerance without suppressing the global immune responses. However, clinical translation has yielded limited success. It has become apparent that the TCR signaling pathway via synthetic peptide antigen alone is inadequate to induce an effective tolerogenic immunity in autoimmune diseases. Bioconjugate strategies combining additional immunomodulatory functions with TCR signaling can amplify the antigen-specific immune tolerance and possibly lead to the development of new treatments in autoimmune diseases. In this review, we provide a summary of recent advances in the development of bioconjugates to achieve antigen-specific immune tolerance in vivo, with the discussion focused on the underlying design principles and challenges that must be overcome to target these therapies to patients suffering from autoimmune diseases.

Reply to "Tolerogenic insulin peptide therapy precipitates type 1 diabetes".

In this issue of JEM, Bergman et al. (https://doi.org/10.1084/jem.20160471) challenge the data published in our previous JEM paper on the preventive effect of tolerogenic vaccination with a strong agonist insulin mimetope in type 1 diabetes. Here, we provide a response to these data and suggest that appropriate subimmunogenic conditions are required to induce Foxp3+ regulatory T cell conversion.

Treg Vaccination in Autoimmune Type 1 Diabetes

Foxp3⁺ regulatory T (Treg) cells are critical contributors to the establishment and maintenance of immunological self-tolerance. Autoimmune type 1 diabetes (T1D) is characterized by the loss of self-tolerance to the insulin-producing β cells in the pancreas and the destruction of β cells, resulting in the development of chronic hyperglycemia at diagnosis. The application of strong agonistic T-cell receptor ligands provided under subimmunogenic conditions functions as a critical means for the efficient de novo conversion of naive CD4⁺ T cells into Foxp3⁺ Treg cells. The specific induction of Treg cells upon supply of strong-agonistic variants of certain self-antigens could therefore function as a critical instrument in order to achieve safe and specific prevention of autoimmunity such as T1D via the restoration of self-tolerance. Such immunotherapeutic strategies are being developed, and in the case of T1D aim to restrict autoimmunity and β-cell destruction. In this review, we discuss the requirements and opportunities for Treg-based tolerance approaches with the goal of interfering with autoimmune T1D.

Tissue Injury-Induced Initiation of the Adaptive Immune Response

We read, with great pleasure, the article by Wood and Goto (1) and agree with the scientific content of their article, especially with their statement “Activation of elements of the innate immune system, triggered as a consequence of tissue injury sustained during cell isolation or organ retrieval and ischemia-reperfusion, will initiate and amplify the adaptive response.” We particularly enjoyed their article because it is in full agreement with our Injury Hypothesis posed in 1994/1996 (2, 3). The original Injury Hypothesis, as published in Transplantation in 1994 (2), held that the postischemic reperfusion injury to an allograft (in addition to its degree of foreignness) initiates and induces the adaptive alloimmune response, predominantly through injury-induced activation of antigen-presenting cells. The theory was extended and modified several times during subsequent years (4–7). Along with these modifications, we coined the terms Innate Alloimmunity in 2002 (4) and DAMPs in the sense of damage-associated molecular patterns in 2003 (5). In particular, we proposed that oxidative stress to the brain-dead donor organism and generation of reactive oxygen species during reperfusion of the allograft represent acute injurious events to the donor organ that, in turn, lead to acute rejection. By activation of donor/recipient Toll-like receptor-bearing dendritic cells of the innate immune system through interaction of damage-associated molecular patterns with Toll-like receptors, these events lead to initiation of adaptive alloimmunity (6). In a recently published review article, evidence is provided in support of the notion that prevention of oxidative allograft injury may operate as an efficient tool in the clinical situation to present alloantigens under subimmunogenic conditions within an intragraft noninflammatory milieu, thereby potentially generating tolerogenic dendritic cells able to induce regulatory T-cell-mediated innate allotolerance (7). Finally, the whole concept of the Injury Hypothesis, in light of the international literature on innate immunity currently available, has been thoroughly and comprehensively discussed in a monograph that was recently published (8). We thought it would be worthwhile to provide the reader of Transplantation with this information about the scientific history of the Injury Hypothesis: a note that may serve as a useful addendum to the excellent article by Wood and Goto. Walter G. Land 1 Konrad MeAmer2 1German Academy of Munich, Germany 2Former Institute for Surgical Research University of Munich Munich, Germany

The danger theory in view of the injury hypothesis: 20 years later

The danger theory in view of the injury hypothesis: 20 years later

Emerging role of innate immunity in organ transplantation part III: the quest for transplant tolerance via prevention of oxidative allograft injury and its consequences

In parts I and II of this tripartite review, the innate immune system was briefly described, focusing on its emerging role in organ transplantation and by emphasizing the oxidative injury-induced allograft inflammation that promotes the generation of immunostimulatory donor- and recipient-derived dendritic cells (DCs) translating innate immune events into adaptive alloimmunity. This part III of the review discusses the possibility to induce adaptive antigen-specific T regulatory cells (Tregs) in the clinical situation by harnessing donor- and recipient-derived tolerogenic DCs (tolDCs) as inducers for alloantigen-specific adaptive Tregs, an effort that follows current trends to harnessing DCs for immunotherapy. This challenge is based on accumulating evidence from basic immunological work in support of the notion that presentation of antigens, including weak transplantation antigens under subimmunogenic conditions within a noninflammatory microenvironment, promotes generation of tolDCs. With respect to these basic immunological studies, which are expressively reviewed, prevention of oxidative allograft injury can be regarded as an efficient tool in the clinical situation to present alloantigens under subimmunogenic conditions within an intragraft noninflammatory milieu, thereby potentially generating tolDCs able to induce Tregs-mediated innate allotolerance. Various therapeutic strategies to prevent oxidative allograft injury occurring in both the brain-dead donor before/during organ removal and the recipient during/after donor organ reperfusion as well as therapeutic options to inhibit injury-induced molecular and cellular consequences are finally discussed.

Setting the threshold for extra-thymic differentiation of Foxp3+ Tregs: TGF-β-dependent and T-cell autonomous

There is a lack of clarity regarding the conditions supporting de novo induction of Tregs. While there is widespread agreement in the literature over the need for optimal stimulation conditions and exogenous TGF-β in vitro, a number of studies indicate that sub-immunogenic conditions induce Tregs in vivo. These seemingly disparate findings have hindered the ability to pin down the conditions promoting Treg induction, including the role of co-stimulation and even the necessity for TGF-β. Two studies in this issue of the European Journal of Immunology re-examine these previous findings in detail and shed some light on the controversy. These studies demonstrate that Treg induction depends on reaching a certain threshold of signal strength: the requirement for co-stimulation is therefore not absolute but dictated by the strength of other signals received by the T cell. Furthermore, these studies demonstrate that the only source of TGF-β required for the induction of Tregs under sub-optimal condition is the T cells themselves. Overall, the picture that emerges is one where sub-immunogenicity, rather than a requirement for exogenous TGF-β, defines the conditions that support TGF-β-dependent Foxp3 induction in a T-cell autonomous fashion. The next challenge lies in utilizing this knowledge for the purpose of inducing Tregs for therapeutic gain.

Enhancement of antigen-specific Treg vaccination in vivo.

The conversion of naive T cells into Treg can be achieved in vivo by delivery of antigen under subimmunogenic conditions. Here we have examined several drugs for their ability to enhance the conversion process in vivo and have found that the rapamycin analog everolimus potently enhances Treg conversion by interfering with T-cell costimulation, reducing cell division and thereby activation of DNA methyltransferase 1 as well as by reducing T-cell activation through the ATP-gated P2×7 receptor controlling Ca2(+) influx. The resulting Tregs exhibit increased stability of Foxp3 expression even when generated in TGFβ-containing media in vitro. Thus the mammalian target of rapamycin (mTOR) inhibitor everolimus in addition to inhibiting immune responses enhances Treg conversion by several distinct pathways. The converted Tregs can be further expanded by injection of IL-2/IL-2ab complexes. These complexes also increase the number of CD25(+)Foxp3(-) cells that, however, do not represent cytokine secreting effector cells but anergic cells, some of which can secrete IL-10 and can themselves be considered regulatory T cells as well. The combined use of everolimus and IL-2/IL-2ab complexes in vivo makes it feasible to achieve highly effective antigen-driven conversion of naive T cells into Treg and their expansion in vivo and thereby the described protocols constitute important tools to achieve immunological tolerance by Treg vaccination.

De novo production of antigen-specific suppressor cells in vivo

Foxp3-expressing regulatory T cells (Treg) play an essential role in maintaining tolerance to self antigens and are generated under physiological conditions when developing T cells encounter antigens expressed by thymic epithelial cells. We have addressed the possibility that Treg can be exploited to prevent or even suppress ongoing immune responses to foreign antigens. To this end, one must develop methods that permit the de novo generation of Treg specific for foreign antigens in peripheral lymphoid tissue. This report describes the methodology of generating Treg by delivering minute doses of peptide contained in fusion Abs directed against the DEC-205 endocytic receptor on steady-state dendritic cells. The process, from cloning and production of fusion Abs to antigen-specific Treg induction in vivo, takes approximately 2 months. The results show that delivery of T-cell receptor agonist ligands under subimmunogenic conditions represents a suitable approach for converting naive T cells into Treg.

Inducing and expanding regulatory T cell populations by foreign antigen

Evidence suggests that regulatory T cells expressing the transcription factor Foxp3 develop extrathymically and intrathymically. Mechanisms of extrathymic induction require further scrutiny, especially as proliferation and/or phenotypic changes of preexisting suppressor cells must be distinguished from true de novo generation. Here we report the conversion of truly naive CD4(+) T cells into suppressor cells expressing Foxp3 by targeting of peptide-agonist ligands to dendritic cells and by analysis of Foxp3 expression at the level of single cells. We show that conversion was achieved by minute antigen doses with suboptimal dendritic cell activation. The addition of transforming growth factor-beta or the absence of interleukin 2 production, which reduces proliferation, enhanced the conversion rate. In addition, regulatory T cell populations induced in subimmunogenic conditions could subsequently be expanded by delivery of antigen in immunogenic conditions. The extrathymic generation and proliferation of regulatory T cells may contribute to self-tolerance as well as the poor immunogenicity of tumors and may be exploited clinically to prevent or reverse unwanted immunity.