Selective ablation of thymic and peripheral Foxp3+ regulatory T cell development

Foxp3+ regulatory T (Treg) cells of thymic (tTreg) and peripheral (pTreg) developmental origin are thought to synergistically act to ensure immune homeostasis, with self-reactive tTreg cells primarily constraining autoimmune responses. Here we exploited a Foxp3-dependent reporter with thymus-specific GFP/Cre activity to selectively ablate either tTreg (ΔtTreg) or pTreg (ΔpTreg) cell development, while sparing the respective sister populations. We found that, in contrast to the tTreg cell behavior in ΔpTreg mice, pTreg cells acquired a highly activated suppressor phenotype and replenished the Treg cell pool of ΔtTreg mice on a non-autoimmune C57BL/6 background. Despite the absence of tTreg cells, pTreg cells prevented early mortality and fatal autoimmunity commonly observed in Foxp3-deficient models of complete Treg cell deficiency, and largely maintained immune tolerance even as the ΔtTreg mice aged. However, only two generations of backcrossing to the autoimmune-prone non-obese diabetic (NOD) background were sufficient to cause severe disease lethality associated with different, partially overlapping patterns of organ-specific autoimmunity. This included a particularly severe form of autoimmune diabetes characterized by an early onset and abrogation of the sex bias usually observed in the NOD mouse model of human type 1 diabetes. Genetic association studies further allowed us to define a small set of autoimmune risk loci sufficient to promote β cell autoimmunity, including genes known to impinge on Treg cell biology. Overall, these studies show an unexpectedly high functional adaptability of pTreg cells, emphasizing their important role as mediators of bystander effects to ensure self-tolerance.

Genetic Tools for Analyzing Foxp3+ Treg Cells: Fluorochrome-Based Transcriptional Reporters and Genetic Fate-Mapping

The lack of unambiguous Foxp3⁺ Treg cell-specific surface markers has prompted the development of various transgenic mouse lines with Foxp3-dependent reporter activity, which involved different fluorochromes and transgenic strategies, including coexpression of multiple transgenes, such as Cre recombinase. Since then, Foxp3 transcriptional reporter has proven to be an indispensable tool to identify and isolate viable Foxp3⁺ Treg cell populations. However, the physiologic Treg cell pool is functionally heterogeneous and consists of intrathymically (tTreg) and peripherally (pTreg) induced Treg cells, which may confound interpretation of data relying on indiscriminatory Foxp3-fluorochrome reporter expressed in all Treg cells. In this chapter, we describe how the dual Foxp3^RFP/GFP reporter can be exploited to discriminate both developmental sublineages based on tTreg cell lineage-specific GFP/Cre recombinase activity, in conjunction with Foxp3-driven RFP expression in all Foxp3⁺ Treg cells, and provide guidelines for experimental design and implementation. We also elaborate on the possibility to exploit GFP/Cre expression of Foxp3^RFP/GFP reporter mice for the manipulation of gene expression (activation and inactivation), such as lineage tracing and in vivo ablation of tTreg cells, while sparing pTreg cells.

Role of Dynamic Actin Cytoskeleton Remodeling in Foxp3+ Regulatory T Cell Development and Function: Implications for Osteoclastogenesis

In T cells, processes such as migration and immunological synapse formation are accompanied by the dynamic reorganization of the actin cytoskeleton, which has been suggested to be mediated by regulators of RhoGTPases and by F-actin bundlers. SWAP-70 controls F-actin dynamics in various immune cells, but its role in T cell development and function has remained incompletely understood. CD4⁺ regulatory T (Treg) cells expressing the transcription factor Foxp3 employ diverse mechanisms to suppress innate and adaptive immunity, which is critical for maintaining immune homeostasis and self-tolerance. Here, we propose Swap-70 as a novel member of the Foxp3-dependent canonical Treg cell signature. We show that Swap-70^-/- mice have increased numbers of Foxp3⁺ Treg cells with an effector/memory-like phenotype that exhibit impaired suppressor function in vitro, but maintain overall immune homeostasis in vivo. Upon formation of an immunological synapse with antigen presenting cells in vitro, cytosolic SWAP-70 protein is selectively recruited to the interface in Treg cells. In this context, Swap-70^-/- Treg cells fail to downregulate CD80/CD86 on osteoclast precursor cells by trans-endocytosis and to efficiently suppress osteoclastogenesis and osteoclast function. These data provide first evidence for a crucial role of SWAP-70 in Treg cell biology and further highlight the important non-immune function of Foxp3⁺ Treg cells in bone homeostasis mediated through direct SWAP-70-dependent mechanisms.

Process Behavior of Special Mixing Elements in Twin-screw Extruders

Tightly intermeshing, co-rotating twin-screw extruders are commonly employed for tasks requiring good mixing. The modular structure of both barrel and screw makes it possible to optimize the extruder configuration for a given task. Increasing demands on polymers have resulted in the development of more sophisticated mixing elements. In the framework of this investigation we looked at the pressure-throughput behavior of mixing elements in a conveying, reconveying and conveying-reconveying configuration. Furthermore, the local residence time distribution within those elements was investigated. We developed physical-mathematical models to describe the pressure – throughput behavior observed in the experimental investigations.

Transient Depletion of Foxp3+ Regulatory T Cells Selectively Promotes Aggressive β Cell Autoimmunity in Genetically Susceptible DEREG Mice

Type 1 diabetes (T1D) represents a hallmark of the fatal multiorgan autoimmune syndrome affecting humans with abrogated Foxp3⁺ regulatory T (Treg) cell function due to Foxp3 gene mutations, but whether the loss of Foxp3⁺ Treg cell activity is indeed sufficient to promote β cell autoimmunity requires further scrutiny. As opposed to human Treg cell deficiency, β cell autoimmunity has not been observed in non-autoimmune-prone mice with constitutive Foxp3 deficiency or after diphtheria toxin receptor (DTR)-mediated ablation of Foxp3⁺ Treg cells. In the spontaneous nonobese diabetic (NOD) mouse model of T1D, constitutive Foxp3 deficiency did not result in invasive insulitis and hyperglycemia, and previous studies on Foxp3⁺ Treg cell ablation focused on Foxp3^DTR NOD mice, in which expression of a transgenic BDC2.5 T cell receptor (TCR) restricted the CD4⁺ TCR repertoire to a single diabetogenic specificity. Here we revisited the effect of acute Foxp3⁺ Treg cell ablation on β cell autoimmunity in NOD mice in the context of a polyclonal TCR repertoire. For this, we took advantage of the well-established DTR/GFP transgene of DEREG mice, which allows for specific ablation of Foxp3⁺ Treg cells without promoting catastrophic autoimmune diseases. We show that the transient loss of Foxp3⁺ Treg cells in prediabetic NOD.DEREG mice is sufficient to precipitate severe insulitis and persistent hyperglycemia within 5 days after DT administration. Importantly, DT-treated NOD.DEREG mice preserved many clinical features of spontaneous diabetes progression in the NOD model, including a prominent role of diabetogenic CD8⁺ T cells in terminal β cell destruction. Despite the severity of destructive β cell autoimmunity, anti-CD3 mAb therapy of DT-treated mice interfered with the progression to overt diabetes, indicating that the novel NOD.DEREG model can be exploited for preclinical studies on T1D under experimental conditions of synchronized, advanced β cell autoimmunity. Overall, our studies highlight the continuous requirement of Foxp3⁺ Treg cell activity for the control of genetically pre-installed autoimmune diabetes.

RelB Deficiency in Dendritic Cells Protects from Autoimmune Inflammation Due to Spontaneous Accumulation of Tissue T Regulatory Cells

Foxp3⁺ regulatory T cells are well-known immune suppressor cells in various settings. In this study, we provide evidence that knockout of the relB gene in dendritic cells (DCs) of C57BL/6 mice results in a spontaneous and systemic accumulation of Foxp3⁺ T regulatory T cells (Tregs) partially at the expense of microbiota-reactive Tregs. Deletion of nfkb2 does not fully recapitulate this phenotype, indicating that alternative NF-κB activation via the RelB/p52 complex is not solely responsible for Treg accumulation. Deletion of RelB in DCs further results in an impaired oral tolerance induction and a marked type 2 immune bias among accumulated Foxp3⁺ Tregs reminiscent of a tissue Treg signature. Tissue Tregs were fully functional, expanded independently of IL-33, and led to an almost complete Treg-dependent protection from experimental autoimmune encephalomyelitis. Thus, we provide clear evidence that RelB-dependent pathways regulate the capacity of DCs to quantitatively and qualitatively impact on Treg biology and constitute an attractive target for treatment of autoimmune diseases but may come at risk for reduced immune tolerance in the intestinal tract.

Inducible IL-7 Hyperexpression Influences Lymphocyte Homeostasis and Function and Increases Allograft Rejection

The IL-7/IL-7R pathway is essential for lymphocyte development and disturbances in the pathway can lead to immune deficiency or T cell mediated destruction. Here, the effect of transient hyperexpression of IL-7 was investigated on immune regulation and allograft rejection under immunosuppression. An experimental in vivo immunosuppressive mouse model of IL-7 hyperexpression was developed using transgenic mice (C57BL/6 background) carrying a tetracycline inducible IL-7 expression cassette, which allowed the temporally controlled induction of IL-7 hyperexpression by Dexamethasone and Doxycycline treatment. Upon induction of IL-7, the B220⁺ c-kit⁺ Pro/Pre-B I compartment in the bone marrow increased as compared to control mice in a serum IL-7 concentration-correlated manner. IL-7 hyperexpression also preferentially increased the population size of memory CD8⁺ T cells in secondary lymphoid organs, and reduced the proportion of CD4⁺Foxp3⁺ T regulatory cells. Of relevance to disease, conventional CD4⁺ T cells from an IL-7-rich milieu escaped T regulatory cell-mediated suppression in vitro and in a model of autoimmune diabetes in vivo. These findings were validated using an IL-7/anti-IL7 complex treatment mouse model to create an IL-7 rich environment. To study the effect of IL-7 on islet graft survival in a mismatched allograft model, BALB/c mice were rendered diabetic by streptozotocin und transplanted with IL-7-inducible or control islets from C57BL/6 mice. As expected, Dexamethasone and Doxycycline treatment prolonged graft median survival as compared to the untreated control group in this transplantation mouse model. However, upon induction of local IL-7 hyperexpression in the transplanted islets, graft survival time was decreased and this was accompanied by an increased CD4⁺ and CD8⁺ T cell infiltration in the islets. Altogether, the findings show that transient elevations of IL-7 can impair immune regulation and lead to graft loss also under immune suppression.

Foxp3+ Regulatory T Cells in Bone and Hematopoietic Homeostasis

The bone represents surprisingly dynamic structures that are subject to constant remodeling by the concerted action of bone-forming osteoblasts and bone-resorbing osteoclasts - two cell subsets of distinct developmental origin that are key in maintaining skeletal integrity throughout life. In general, abnormal bone remodeling due to dysregulated bone resorption and formation is an early event in the manifestation of various human bone diseases, such as osteopetrosis/osteoporosis and arthritis. But bone remodeling is also closely interrelated with lympho-hematopoietic homeostasis, as the bone marrow niche is formed by solid and trabecular bone structures that provide a framework for the long-term maintenance and differentiation of HSCs (>blood lineage cells and osteoclasts) and MSCs (>osteoblasts). Numerous studies in mice and humans have implicated innate and adaptive immune cells in the dynamic regulation of bone homeostasis, but despite considerable clinical relevance, the exact mechanisms of such immuno-bone interplay have remained incompletely understood. This holds particularly true for CD4⁺ regulatory T (Treg) cells expressing the lineage specification factor Foxp3: Foxp3⁺ Treg cells have been shown to play an indispensable role in maintaining immune homeostasis, but may also exert critical non-immune functions, which includes the control of metabolic and regenerative processes, as well as the differentiation of HSCs and function of osteoclasts. Here, we summarize our current knowledge on the T cell/bone interplay, with a particular emphasis on our own efforts to dissect the role of Foxp3⁺ Treg cells in bone and hematopoietic homeostasis, employing experimental settings of gain- and loss-of-Treg cell function. These data make a strong case that Foxp3⁺ Treg cells impinge on lympho-hematopoiesis through indirect mechanisms, i.e., by acting on osteoclast development and function, which translates into changes in niche size. Furthermore, we propose that, besides disorders that involve inflammatory bone loss, the modulation of Foxp3⁺ Treg cell function in vivo may represent a suitable approach to reinstate bone homeostasis in non-autoimmune settings of aberrant bone remodeling.

T Lymphocytes Contribute to the Control of Baseline Neural Precursor Cell Proliferation but Not the Exercise-Induced Up-Regulation of Adult Hippocampal Neurogenesis

Cross-talk between the peripheral immune system and the central nervous system is important for physiological brain health. T cells are required to maintain normal baseline levels of neural precursor proliferation in the hippocampus of adult mice. We show here that neither T cells, B cells, natural killer cells nor natural killer T cells are required for the increase in hippocampal precursor proliferation that occurs in response to physical exercise. In addition, we demonstrate that a subpopulation of T cells, regulatory T cells, is not involved in maintaining baseline levels of neural precursor proliferation. Even when applied at supraphysiological numbers, populations of both naive and stimulated lymphocytes had no effect on hippocampal precursor proliferation in vitro. In addition, physical activity had no effect on peripheral immune cells in terms of distribution in the bone marrow, lymph nodes or spleen, activation state or chemokine receptor (CXCR4 and CCR9) expression. Together these results suggest that lymphocytes are not involved in translating the peripheral effects of exercise to the neurogenic niche in the hippocampus and further support the idea that the exercise-induced regulation of adult neurogenesis is mechanistically distinct from its baseline control.

Induced B Cell Development in Adult Mice

We employed the B-Indu-Rag1 model in which the coding exon of recombination-activating gene 1 (Rag1) is inactivated by inversion. It is flanked by inverted loxP sites. Accordingly, B cell development is stopped at the pro/pre B-I cell precursor stage. A B cell-specific Cre recombinase fused to a mutated estrogen receptor allows the induction of RAG1 function and B cell development by application of Tamoxifen. Since Rag1 function is recovered in a non-self-renewing precursor cell, only single waves of development can be induced. Using this system, we could determine that B cells minimally require 5 days to undergo development from pro/preB-I cells to the large and 6 days to the small preB-II cell stage. First immature transitional (T) 1 and T2 B cells could be detected in the bone marrow at day 6 and day 7, respectively, while their appearance in the spleen took one additional day. We also tested a contribution of adult bone marrow to the pool of B-1 cells. Sublethally irradiated syngeneic WT mice were adoptively transferred with bone marrow of B-Indu-Rag1 mice and B cell development was induced after 6 weeks. A significant portion of donor derived B-1 cells could be detected in such adult mice. Finally, early VH gene usage was tested after induction of B cell development. During the earliest time points the VH genes proximal to D/J were found to be predominantly rearranged. At later time points, the large family of the most distal VH prevailed.

Targeting DEC-205-DCIR2+ dendritic cells promotes immunological tolerance in proteolipid protein-induced experimental autoimmune encephalomyelitis

Background

Dendritic cells (DC) induce adaptive responses against foreign antigens, and play an essential role in maintaining peripheral tolerance to self-antigens. Therefore they are involved in preventing fatal autoimmunity. Selective delivery of antigens to immature DC via the endocytic DEC-205 receptor on their surface promotes antigen-specific T cell tolerance, both by recessive and dominant mechanisms. We provide evidence that the induction of antigen-specific T cell tolerance is not a unique property of CD11c⁺CD8⁺DEC-205⁺ DCs.

Methods

We employed a fusion between αDCIR2 antibodies and the highly encephalitogenic peptide 139–151 of myelin-derived proteolipid protein (PLP_139–151), to target CD11c ⁺CD8^- DCs with a DEC-205−DCIR2⁺ phenotype in vivo, and to substantially improve clinical symptoms in the PLP_139–151-induced model of experimental autoimmune encephalomyelitis (EAE).

Results

Consistent with previous studies targeting other cell surface receptors, EAE protection mediated by αDCIR2-PLP_139–151 fusion antibody (Ab) depended on an immature state of targeted DCIR2⁺ DCs. The mechanism of αDCIR2-PLP_139–151 mAb function included the deletion of IL-17- and IFN-γ-producing pathogenic T cells, as well as the enhancement of regulatory T (Treg) cell activity. In contrast to the effect of αDEC-205⁺ fusion antibodies, which involves extrathymic induction of a Foxp3⁺ Treg cell phenotype in naïve CD4⁺Foxp3^- T cells, treatment of animals with DCIR2⁺ fusion antibodies resulted in antigen-specific activation and proliferative expansion of natural Foxp3⁺ Treg cells.

Conclusions

These results suggest that multiple mechanisms can lead to the expansion of the Treg population, depending on the DC subset and receptor targeted.

Electronic supplementary material

The online version of this article (10.1186/s10020-018-0017-6) contains supplementary material, which is available to authorized users.

Critical Role of TGF-β and IL-2 Receptor Signaling in Foxp3 Induction by an Inhibitor of DNA Methylation

Under physiological conditions, CD4⁺ regulatory T (Treg) cells expressing the transcription factor Foxp3 are generated in the thymus [thymus-derived Foxp3⁺ Treg (tTregs) cells] and extrathymically at peripheral sites [peripherally induced Foxp3⁺ Treg (pTreg) cell], and both developmental subsets play non-redundant roles in maintaining self-tolerance throughout life. In addition, a variety of experimental in vitro and in vivo modalities can extrathymically elicit a Foxp3⁺ Treg cell phenotype in peripheral CD4⁺Foxp3⁻ T cells, which has attracted much interest as an approach toward cell-based therapy in clinical settings of undesired immune responses. A particularly notable example is the in vitro induction of Foxp3 expression and Treg cell activity (iTreg cells) in initially naive CD4⁺Foxp3⁻ T cells through T cell receptor (TCR) and IL-2R ligation, in the presence of exogenous TGF-β. Clinical application of Foxp3⁺ iTreg cells has been hampered by the fact that TGF-β-driven Foxp3 induction is not sufficient to fully recapitulate the epigenetic and transcriptional signature of in vivo induced Foxp3⁺ tTreg and pTreg cells, which includes the failure to imprint iTreg cells with stable Foxp3 expression. This hurdle can be potentially overcome by pharmacological interference with DNA methyltransferase activity and CpG methylation [e.g., by the cytosine nucleoside analog 5-aza-2′-deoxycytidine (5-aza-dC)] to stabilize TGF-β-induced Foxp3 expression and to promote a Foxp3⁺ iTreg cell phenotype even in the absence of added TGF-β. However, the molecular mechanisms of 5-aza-dC-mediated Foxp3⁺ iTreg cell generation have remained incompletely understood. Here, we show that in the absence of exogenously added TGF-β and IL-2, efficient 5-aza-dC-mediated Foxp3⁺ iTreg cell generation from TCR-stimulated CD4⁺Foxp3⁻ T cells is critically dependent on TGF-βR and IL-2R signaling and that this process is driven by TGF-β and IL-2, which could either be FCS derived or produced by T cells on TCR stimulation. Overall, these findings contribute to our understanding of the molecular mechanisms underlying the process of Foxp3 induction and may provide a rational basis for generating phenotypically and functionally stable iTreg cells.

Minimum Information about T Regulatory Cells: A Step toward Reproducibility and Standardization

Cellular therapies with CD4+ T regulatory cells (Tregs) hold promise of efficacious treatment for the variety of autoimmune and allergic diseases as well as posttransplant complications. Nevertheless, current manufacturing of Tregs as a cellular medicinal product varies between different laboratories, which in turn hampers precise comparisons of the results between the studies performed. While the number of clinical trials testing Tregs is already substantial, it seems to be crucial to provide some standardized characteristics of Treg products in order to minimize the problem. We have previously developed reporting guidelines called minimum information about tolerogenic antigen-presenting cells, which allows the comparison between different preparations of tolerance-inducing antigen-presenting cells. Having this experience, here we describe another minimum information about Tregs (MITREG). It is important to note that MITREG does not dictate how investigators should generate or characterize Tregs, but it does require investigators to report their Treg data in a consistent and transparent manner. We hope this will, therefore, be a useful tool facilitating standardized reporting on the manufacturing of Tregs, either for research purposes or for clinical application. This way MITREG might also be an important step toward more standardized and reproducible testing of the Tregs preparations in clinical applications.

Distinct roles of β-cell mass and function during type 1 diabetes onset and remission

Cure of type 1 diabetes (T1D) by immune intervention at disease onset depends on the restoration of insulin secretion by endogenous β-cells. However, little is known about the potential of β-cell mass and function to recover after autoimmune attack ablation. Using a longitudinal in vivo imaging approach, we show how functional status and mass of β-cells adapt in response to the onset and remission of T1D. We demonstrate that infiltration reduces β-cell mass prior to onset and, together with emerging hyperglycemia, affects β-cell function. After immune intervention, persisting hyperglycemia prevents functional recovery but promotes β-cell mass increase in mouse islets. When blood glucose levels return to normoglycemia β-cell mass expansion stops, and subsequently glucose tolerance recovers in combination with β-cell function. Similar to mouse islets, human islets exhibit cell exhaustion and recovery in response to transient hyperglycemia. However, the effect of hyperglycemia on human islet mass increase is minor and transient. Our data demonstrate a major role of functional exhaustion and recovery of β-cells during T1D onset and remission. Therefore, these findings support early intervention therapy for individuals with T1D.

DEC205+ Dendritic Cell-Targeted Tolerogenic Vaccination Promotes Immune Tolerance in Experimental Autoimmune Arthritis

Previous studies in mouse models of autoimmune diabetes and encephalomyelitis have indicated that the selective delivery of self-antigen to the endocytic receptor DEC205 on steady-state dendritic cells (DCs) may represent a suitable approach to induce Ag-specific immune tolerance. In this study, we aimed to examine whether DEC205(+) DC targeting of a single immunodominant peptide derived from human cartilage proteoglycan (PG) can promote immune tolerance in PG-induced arthritis (PGIA). Besides disease induction by immunization with whole PG protein with a high degree of antigenic complexity, PGIA substantially differs from previously studied autoimmune models not only in the target tissue of autoimmune destruction but also in the nature of pathogenic immune effector cells. Our results show that DEC205(+) DC targeting of the PG peptide 70-84 is sufficient to efficiently protect against PGIA development. Complementary mechanistic studies support a model in which DEC205(+) DC targeting leads to insufficient germinal center B cell support by PG-specific follicular helper T cells. Consequently, impaired germinal center formation results in lower Ab titers, severely compromising the development of PGIA. Overall, this study further corroborates the potential of prospective tolerogenic DEC205(+) DC vaccination to interfere with autoimmune diseases, such as rheumatoid arthritis.

Induced miR-99a expression represses Mtor cooperatively with miR-150 to promote regulatory T-cell differentiation

Peripheral induction of regulatory T (Treg) cells provides essential protection from inappropriate immune responses. CD4(+) T cells that lack endogenous miRNAs are impaired to differentiate into Treg cells, but the relevant miRNAs are unknown. We performed an overexpression screen with T-cell-expressed miRNAs in naive mouse CD4(+) T cells undergoing Treg differentiation. Among 130 candidates, the screen identified 29 miRNAs with a negative and 10 miRNAs with a positive effect. Testing reciprocal Th17 differentiation revealed specific functions for miR-100, miR-99a and miR-10b, since all of these promoted the Treg and inhibited the Th17 program without impacting on viability, proliferation and activation. miR-99a cooperated with miR-150 to repress the expression of the Th17-promoting factor mTOR. The comparably low expression of miR-99a was strongly increased by the Treg cell inducer "retinoic acid", and the abundantly expressed miR-150 could only repress Mtor in the presence of miR-99a. Our data suggest that induction of Treg cell differentiation is regulated by a miRNA network, which involves cooperation of constitutively expressed as well as inducible miRNAs.

Fluorochrome-based definition of naturally occurring Foxp3(+) regulatory T cells of intra- and extrathymic origin

Under physiological conditions, studies on the biology of naturally induced Foxp3(+) Treg cells of intra- and extrathymic origin have been hampered by the lack of unambiguous markers to discriminate the mature progeny of such developmental Treg-cell sublineages. Here, we report on experiments in double-transgenic mice, in which red fluorescent protein (RFP) is expressed in all Foxp3(+) Treg cells, whereas Foxp3-dependent GFP expression is exclusively confined to intrathymically induced Foxp3(+) Treg cells. This novel molecular genetic tool enabled us to faithfully track and characterize naturally induced Treg cells of intrathymic (RFP(+) GFP(+) ) and extrathymic (RFP(+) GFP(-) ) origin in otherwise unmanipulated mice. These experiments directly demonstrate that extrathymically induced Treg cells substantially contribute to the overall pool of mature Foxp3(+) Treg cells residing in peripheral lymphoid tissues of steady-state mice. Furthermore, we provide evidence that intra- and extrathymically induced Foxp3(+) Treg cells represent distinct phenotypic and functional sublineages.

Continuous T cell receptor signals maintain a functional regulatory T cell pool

Regulatory T (Treg) cells maintain immune homeostasis and prevent inflammatory and autoimmune responses. During development, thymocytes bearing a moderately self-reactive T cell receptor (TCR) can be selected to become Treg cells. Several observations suggest that also in the periphery mature Treg cells continuously receive self-reactive TCR signals. However, the importance of this inherent autoreactivity for Treg cell biology remains poorly defined. To address this open question, we genetically ablated the TCR of mature Treg cells in vivo. These experiments revealed that TCR-induced Treg lineage-defining Foxp3 expression and gene hypomethylation were uncoupled from TCR input in mature Treg cells. However, Treg cell homeostasis, cell-type-specific gene expression and suppressive function critically depend on continuous triggering of their TCR.

Advantages of Foxp3(+) regulatory T cell depletion using DEREG mice

Several mechanisms enable immunological self-tolerance. Regulatory T cells (Tregs) are a specialized T cell subset that prevents autoimmunity and excessive immune responses, but can also mediate detrimental tolerance to tumors and pathogens in a Foxp3-dependent manner. Genetic tools exploiting the foxp3 locus including bacterial artificial chromosome (BAC)-transgenic DEREG mice have provided essential information on Treg biology and the potential therapeutic modulation of tolerance. In DEREG mice, Foxp3(+) Tregs selectively express eGFP and diphtheria toxin (DT) receptor, allowing for the specific depletion of Tregs through DT administration. We here provide a detailed overview about important considerations such as DT toxicity, which affects any mouse strain treated with DT, and Treg rebound after depletion. Additionally, we point out the specific advantages of BAC-transgenic DEREG mice including their suitability to study organ-specific autoimmunity such as type I diabetes. Moreover, we discuss recent insights into the role of Tregs in viral infections. In summary, DEREG mice are an important tool to study Treg-mediated tolerance and its therapeutic circumvention.

Myelin-specific T helper 17 cells promote adult hippocampal neurogenesis through indirect mechanisms

CD4 ⁺ T cells provide a neuro-immunological link in the regulation of adult hippocampal neurogenesis, but the exact mechanisms underlying enhanced neural precursor cell proliferation and the relative contribution of different T helper (Th) cell subsets have remained unclear. Here, we explored the pro-proliferative potential of interleukin 17-producing T helper (Th17) cells, a developmentally and functionally distinct Th cell subset that is a key mediator of autoimmune neurodegeneration. We found that base-line proliferation of hippocampal precursor cells in a T cell-deficient mouse model of impaired hippocampal neurogenesis can be restored upon adoptive transfer with homogeneous Th17 populations enriched for myelin-reactive T cell receptors (TCR). In these experiments, enhanced proliferation was independent of direct interactions of infiltrating Th17 cells with precursor cells or neighboring cells in the hippocampal neurogenic niche. Complementary studies in immunocompetent mice identified several receptors for Th17 cell-derived cytokines with mRNA expression in hippocampal precursor cells and dentate gyrus tissue, suggesting that Th17 cell activity in peripheral lymphoid tissues might promote hippocampal neurogenesis through secreted cytokines.

Myelin-specific T helper 17 cells promote adult hippocampal neurogenesis through indirect mechanisms

CD4 ⁺ T cells provide a neuro-immunological link in the regulation of adult hippocampal neurogenesis, but the exact mechanisms underlying enhanced neural precursor cell proliferation and the relative contribution of different T helper (Th) cell subsets have remained unclear. Here, we explored the pro-proliferative potential of interleukin 17-producing T helper (Th17) cells, a developmentally and functionally distinct Th cell subset that is a key mediator of autoimmune neurodegeneration. We found that base-line proliferation of hippocampal precursor cells in a T cell-deficient mouse model of impaired hippocampal neurogenesis can be restored upon adoptive transfer with homogeneous Th17 populations enriched for myelin-reactive T cell receptors (TCR). In these experiments, enhanced proliferation was independent of direct interactions of infiltrating Th17 cells with precursor cells or neighboring cells in the hippocampal neurogenic niche. Complementary studies in immunocompetent mice identified several receptors for Th17 cell-derived cytokines with mRNA expression in hippocampal precursor cells and dentate gyrus tissue, suggesting that Th17 cell activity in peripheral lymphoid tissues might promote hippocampal neurogenesis through secreted cytokines.

Small-molecule RORγt antagonists inhibit T helper 17 cell transcriptional network by divergent mechanisms

We identified three retinoid-related orphan receptor gamma t (RORγt)-specific inhibitors that suppress T helper 17 (Th17) cell responses, including Th17-cell-mediated autoimmune disease. We systemically characterized RORγt binding in the presence and absence of drugs with corresponding whole-genome transcriptome sequencing. RORγt acts as a direct activator of Th17 cell signature genes and a direct repressor of signature genes from other T cell lineages; its strongest transcriptional effects are on cis-regulatory sites containing the RORα binding motif. RORγt is central in a densely interconnected regulatory network that shapes the balance of T cell differentiation. Here, the three inhibitors modulated the RORγt-dependent transcriptional network to varying extents and through distinct mechanisms. Whereas one inhibitor displaced RORγt from its target loci, the other two inhibitors affected transcription predominantly without removing DNA binding. Our work illustrates the power of a system-scale analysis of transcriptional regulation to characterize potential therapeutic compounds that inhibit pathogenic Th17 cells and suppress autoimmunity.

A repertoire of peptide tags for controlled drug release from injectable noncovalent hydrogel

A repertoire of conjugable tags for controlling the release of drugs from biomaterials is highly interesting for the development of combinatorial drug administration techniques. This paper describes such a system of 11 peptide tags derived from our previous work on a physical hydrogel system cross-linked through peptide-heparin interactions. The release kinetics of the tags correlate well with their affinity to heparin and obey Fick's second law of diffusion, with the exception of the ATIII peptide, which displays a stable release profile close to a zero-order reaction. A system for release experiments over seven months was built, using the hydrogel matrix as a barrier between the reservoirs of tagged compounds and supernatant. The gel matrix can be injected without affecting the releasing properties. A tagged cyclosporin A derivative was also tested, and its release was monitored by measuring its biological activity. This work represents a design of biomaterials with an integral system of drug delivery, where both the assembly process of the matrix and affinity capture/release of tagged compounds are based on the noncovalent interaction of heparin with one class of peptides.

Physico-Mathematical Model for the Description of the Temperature Development and the Power Consumption in Co-Rotating Twin Screw Extruders

Tightly intermeshing, co-rotating twin-screw extruders are commonly employed for tasks requiring good mixing. The modular constitution of both barrel and screw makes it possible to optimise the extruder configuration for a given task. Even today this optimisation is frequently done by applying the “Trial and Error”-method. Physico-mathematical models enable the process engineer to predict the process behaviour of a chosen extruder configuration and to optimise existing extrusion processes.

Increasing demands in mixing quality and efficiency of the processing unit result in efforts to optimise existing extruders with respect to those factors. For this reason knowledge concerning the temperature profile along the screw and the power consumption is essential. We present a new physico-mathematical model for the description of the temperature development. At stages where the analytical solution itself would result in a not satisfying degree of accuracy we used descriptions based on finite element simulation results to achieve the desired exactness. As a result we got a model to describe the temperature development in the screw channel and a model to describe the power consumption in different screw sections. Applying these models it is possible to optimise the process parameters and the screw configuration with only a minimum of preceding experimental investigations.

Active demethylation of the Foxp3 locus leads to the generation of stable regulatory T cells within the thymus

Stable expression of Foxp3 in regulatory T cells (Tregs) depends on DNA demethylation at the Treg-specific demethylated region (TSDR), a conserved, CpG-rich region within the Foxp3 locus. The TSDR is selectively demethylated in ex vivo Tregs purified from secondary lymphoid organs, but it is unclear at which stage of Treg development demethylation takes place. In this study, we show that commitment to a stable lineage occurred during early stages of murine thymic Treg development by engraving of lineage-specific epigenetic marks in parallel with establishment of a Treg-specific gene expression profile. TSDR demethylation was achieved through an active mechanism and involved enzymes of the ten-eleven-translocation family and hydroxylation of methylated cytosines, a modification that is implicated as an initiating step of mitosis-independent DNA demethylation pathways and has not yet been observed at specific loci during immune cell differentiation. Together, our results demonstrate that initiating TSDR demethylation during early stages of thymic Treg development commences stabilization of Foxp3 expression and guarantees full functionality and long-term lineage stability of Tregs.

Regulatory T Cell-Based Immunotherapy

CD4+CD25+ regulatory T (Treg) cells expressing the forkhead box transcription factor Foxp3 have a vital function in the maintenance of immune homeostasis and the prevention of fatal multi-organ autoimmunity throughout life. In the last decade, Foxp3+ Treg cells have raised the hope for novel cell-based therapies to achieve tolerance in clinical settings of unwanted immune responses such as autoimmunity and graft rejection. Conceptually, the antigen-specific enhancement of Treg cell function is of particular importance because such strategies will minimize the requirements for pharmaceutical immunosuppression, sparing desired protective host immune responses to infectious and malignant insults. This chapter discusses current concepts of Treg cell-based immunotherapy with particular emphasis on antigen-specific Treg cell induction from conventional CD4+ T cells to deal with organ-specific autoimmunity.

Foxp3(+) regulatory T cells in mouse models of type 1 diabetes

Studies on human type 1 diabetes (T1D) are facilitated by the availability of animal models such as nonobese diabetic (NOD) mice that spontaneously develop autoimmune diabetes, as well as a variety of genetically engineered mouse models with reduced genetic and pathogenic complexity, as compared to the spontaneous NOD model. In recent years, increasing evidence has implicated CD4(+)CD25(+) regulatory T (Treg) cells expressing the transcription factor Foxp3 in both the breakdown of self-tolerance and the restoration of immune homeostasis in T1D. In this paper, we provide an overview of currently available mouse models to study the role of Foxp3(+) Treg cells in the control of destructive β cell autoimmunity, including a novel NOD model that allows specific and temporally controlled deletion of Foxp3(+) Treg cells.

Targeted antigen delivery to DEC-205⁺ dendritic cells for tolerogenic vaccination

Dendritic cells (DCs) and Foxp3-expressing CD4⁺ regulatory T (Treg) cells play non-redundant roles in the maintenance of peripheral tolerance to self-antigens, thereby preventing fatal autoimmunity. A common hallmark of intra- and extra-thymic Treg cell lineage commitment is the induction of Foxp3 expression as a consequence of appropriate T cell receptor engagement with MHC class II:agonist ligand. It has now become increasingly clear that agonist ligand presentation by immature DCs in the steady state induces T cell tolerance by both recessive and dominant mechanisms, rather than promoting productive T helper cell responses. In this context, the ability of steady-state DCs to promote the extrathymic conversion of initially naïve CD4⁺Foxp3⁻ T cells into Foxp3⁺ Treg cells is of particular interest as it provides novel perspectives to enhance antigen-specific Treg cell function in clinical settings of unwanted immunity, such as β-cell autoimmunity.

IL-7 abrogates suppressive activity of human CD4+CD25+FOXP3+ regulatory T cells and allows expansion of alloreactive and autoreactive T cells

CD4(+)CD25(+)FOXP3(+) regulatory T cells (Tregs) control the activation and expansion of alloreactive and autoreactive T cell clones. Because uncontrolled activation and expansion of autoreactive T cells occur in an IL-7-rich environment, we explored the possibility that IL-7 may affect the function of Treg. We show that the functional high-affinity IL-7R is expressed on both naive and memory Tregs, and exposure to IL-7 results in STAT-5 phosphorylation. Naive, but not memory, Tregs proliferated greatly and acquired a memory phenotype in the setting of a suppression assay when IL-7 was present. Importantly, the presence of IL-7 abrogated the capacity of Tregs to suppress proliferation of conventional T cells in response to TCR activators, including alloantigens and autoantigens. Removal of IL-7 restored the suppressive function of Tregs. Preblocking of the IL-7R on the Tregs also restored suppressor function, indicating that IL-7 directly affected Treg function. Thus, prolonged periods of homeostatic expansion can temporarily release natural regulatory brakes on T cells, thereby providing an additional mechanism for activating and expanding alloreactive and autoreactive T cells.

Vagaries of fluorochrome reporter gene expression in Foxp3+ regulatory T cells

CD4⁺CD25⁺ regulatory T (Treg) cell lineage commitment and expression of the transcription factor Foxp3 can be induced at the CD4⁺CD8⁺ double-positive (DP) and CD4⁺CD8^? single-positive stages of thymic development, as well as in postthymic CD4⁺ T cells in peripheral lymphoid tissues. The availability of transgenic mice with Foxp3-dependent fluorochrome reporter gene expression has greatly facilitated studies on the intra- and extrathymic generation of murine Foxp3⁺ Treg cells. Here, we performed a comparative analysis of thymic Treg cell development and peripheral compartments of mature Treg cells in various transgenic strains with gene targeted and bacterial artificial chromosome (BAC)-driven Foxp3-fluorochrome expression. These studies revealed a relative deficiency of Foxp3⁺ DP thymocytes selectively in mice with targeted insertion of the fluorochrome reporter gene coding sequence into the endogenous Foxp3 gene. While Foxp3 BAC-driven fluorochrome expression in ex vivo CD4⁺ T cells was found to faithfully reflect Foxp3 protein expression, we provide evidence that Foxp3 BAC transgenesis can result in sizable populations of Foxp3⁺ Treg cells that lack fluorochrome reporter expression. This could be attributed to both timely delayed up-regulation of BAC expression in developing Treg cells and the accumulation of peripheral Foxp3⁺ Treg cells with continuous transcriptional inactivity of the Foxp3 BAC transgene.

Severe Developmental B Lymphopoietic Defects in Foxp3-Deficient Mice are Refractory to Adoptive Regulatory T Cell Therapy

The role of Foxp3-expressing regulatory T (T_reg) cells in tolerance and autoimmunity is well-established. However, although of considerable clinical interest, the role of T_reg cells in the regulation of hematopoietic homeostasis remains poorly understood. Thus, we analysed B and T lymphopoiesis in the scurfy (Sf) mouse model of T_reg cell deficiency. In these experiments, the near-complete block of B lymphopoiesis in the BM of adolescent Sf mice was attributed to autoimmune T cells. We could exclude a constitutive lympho-hematopoietic defect or a B cell-intrinsic function of Foxp3. Efficient B cell development in the BM early in ontogeny and pronounced extramedullary B lymphopoietic activity resulted in a peripheral pool of mature B cells in adolescent Sf mice. However, marginal zone B and B-1a cells were absent throughout ontogeny. Developmental B lymphopoietic defects largely correlated with defective thymopoiesis. Importantly, neonatal adoptive T_reg cell therapy suppressed exacerbated production of inflammatory cytokines and restored thymopoiesis but was ineffective in recovering defective B lymphopoiesis, probably due to a failure to compensate production of stroma cell-derived IL-7 and CXCL12. Our observations on autoimmune-mediated incapacitation of the BM environment in Foxp3-deficient mice will have direct implications for the rational design of BM transplantation protocols for patients with severe genetic deficiencies in functional Foxp3⁺ T_reg cells.

Identification of an immediate Foxp3(-) precursor to Foxp3(+) regulatory T cells in peripheral lymphoid organs of nonmanipulated mice

CD4⁺CD25⁺ regulatory T cells (T reg cells) expressing the transcription factor Foxp3 can be induced from peripheral T cell receptor (TCR) transgenic CD4⁺CD25⁻Foxp3⁻ T cells stimulated with noninflammatory dendritic cells presenting low amounts of agonist cognate antigen. However, limited evidence exists for extra-thymic T reg cell generation from non-TCR transgenic T cells in unmanipulated mice. We compared events early during agonist-driven generation of Foxp3⁺ TCR transgenic T cells to polyclonal CD4⁺ T cell populations in unmanipulated mice. We identified an interleukin-2– and phosphatidylinositol-3-kinase–dependent precommitted Foxp3⁻ precursor to Foxp3⁺ T reg cells in peripheral lymphoid organs. Transforming growth factor β signaling played a minor role in the generation and subsequent differentiation of these T reg precursor cells.

Dendritic cell-targeted pancreatic beta-cell antigen leads to conversion of self-reactive CD4(+) T cells into regulatory T cells and promotes immunotolerance in NOD mice

Studies employing T cell receptor transgenic T cells have convincingly shown that selective delivery of non-self model antigens to DEC-205(+) dendritic cells (DCs) in the steady-state can induce Foxp3-expressing CD4(+)CD25(+) regulatory T (Treg) cells from conventional CD4(+)CD25(-)Foxp3(-) T cells. Although of considerable clinical interest, the concept of DC-targeted de novo generation of antigen-specific Treg cells has not yet been evaluated for self-antigens and self-reactive CD4(+) T cells in the non-obese diabetic (NOD) mouse model of type 1 diabetes (T1D). Here, we show in proof-of-principle experiments that targeting a mimotope peptide to the endocytic receptor DEC-205 on DCs in NOD mice induces efficient conversion of pancreatic beta-cell-reactive BDC2.5 CD4(+) T cells into long-lived Foxp3(+) Treg cells. Of note, conversion efficiency in normoglycemic and hyperglycemic mice with early diabetes onset was indistinguishable. While de novo generation of BDC2.5 Treg cells did not interfere with disease progression, anti-DEC-205-mediated targeting of whole proinsulin in prediabetic NOD mice substantially reduced the incidence of diabetes. These results suggest that promoting antigen-specific Treg cells in vivo might be a feasible approach towards cellular therapy in T1D.

Retinoic acid can enhance conversion of naive into regulatory T cells independently of secreted cytokines

It has been reported that retinoic acid (RA) enhances regulatory T (T reg) cell conversion by inhibiting the secretion of cytokines that interfere with conversion. This report shows that these conclusions provide a partial explanation at best. First, RA not only interfered with cytokine secretion but also with the ability of these cytokines to inhibit T reg cell conversion of naive T cells. Furthermore, RA enhanced conversion even in the absence of inhibitory cytokines. The latter effect depended on the RA receptor α (RARα) but did not require Smad3, despite the fact that RA enhanced Smad3 expression. The RARα1 isoform was not essential for RA-dependent enhancement of transforming growth factor β–driven conversion, suggesting that conversion can also be mediated by RARα2. Interleukin (IL)-6 strongly reduced RARα expression levels such that a deficiency of the predominant RARα1 isoform leaves too little RARα2 for RA to inhibit the generation of Th17 cells in the presence of IL-6.

Kruppel-like factor KLF10 targets transforming growth factor-beta1 to regulate CD4(+)CD25(-) T cells and T regulatory cells

CD4(+)CD25(+) regulatory T cells (T regs) play a major role in the maintenance of self-tolerance and immune suppression, although the mechanisms controlling T reg development and suppressor function remain incompletely understood. Herein, we provide evidence that Kruppel-like factor 10 (KLF10/TIEG1) constitutes an important regulator of T regulatory cell suppressor function and CD4(+)CD25(-) T cell activation through distinct mechanisms involving transforming growth factor (TGF)-beta1 and Foxp3. KLF10 overexpressing CD4(+)CD25(-) T cells induced both TGF-beta1 and Foxp3 expression, an effect associated with reduced T-Bet (Th1 marker) and Gata3 (Th2 marker) mRNA expression. Consistently, KLF10(-/-) CD4(+)CD25(-) T cells have enhanced differentiation along both Th1 and Th2 pathways and elaborate higher levels of Th1 and Th2 cytokines. Furthermore, KLF10(-/-) CD4(+)CD25(-) T cell effectors cannot be appropriately suppressed by wild-type T regs. Surprisingly, KLF10(-/-) T reg cells have reduced suppressor function, independent of Foxp3 expression, with decreased expression and elaboration of TGF-beta1, an effect completely rescued by exogenous treatment with TGF-beta1. Mechanistic studies demonstrate that in response to TGF-beta1, KLF10 can transactivate both TGF-beta1 and Foxp3 promoters, implicating KLF10 in a positive feedback loop that may promote cell-intrinsic control of T cell activation. Finally, KLF10(-/-) CD4(+)CD25(-) T cells promoted atherosclerosis by approximately 2-fold in ApoE(-/-)/scid/scid mice with increased leukocyte accumulation and peripheral pro-inflammatory cytokines. Thus, KLF10 is a critical regulator in the transcriptional network controlling TGF-beta1 in both CD4(+)CD25(-) T cells and T regs and plays an important role in regulating atherosclerotic lesion formation in mice.

Peripherally induced Treg: mode, stability, and role in specific tolerance

Foxp3-expressing regulatory T cells (Treg) have an essential function of preventing autoimmune disease in man and mouse. Foxp3 binds to forkhead motifs of about 1,100 genes and the strength of binding increases upon phorbol 12-myristate 13-acetate/ionomycin stimulation. In Foxp3-expressing T cell hybridomas, Foxp3 promoter binding does not lead to activation or suppression of genes which becomes only visible after T cell activation. These findings are in line with observations by others that Foxp3 exerts important functions in collaboration with T cell receptor (TCR)-dependent transcription factors in a DNA-binding complex. Tregs can be generated when developing T cells encounter TCR agonist ligands in the thymus. This process apparently depends on costimulatory signals. In contrast, extrathymic conversion of naïve T cells into Tregs appears to depend on transforming growth factor (TGF)-beta and is inhibited by costimulation. In fact, dendritic cell-derived retinoic acid helps the conversion process by counteracting the negative impact of costimulation. Tregs induced by subimmunogenic antigen delivery in vivo are much more stable than Tregs induced by antigenic stimulation in the presence of TGF-beta in vitro which correlates with the extent of demethylation of the Foxp3 locus. Tregs can be induced by conversion of antigen-specific T cells that occur with a very low frequency in wt mice. Conversion of naïve cluster of differentiation (CD)4 T cells into Tregs by a single peptide of HY antigens results in complete antigen-specific tolerance to an entire set of HY epitopes recognized by CD4 as well as CD8 T cells when presented with male skin or hemopoietic grafts.

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.

B-1a cells are imprinted by the microenvironment in spleen and peritoneum

B-1a cells are found mainly in the peritoneal cavity of mice but are also present in the spleen. Gene expression profiling defined many genes differentially expressed in B-1a cells from these two sites. To see whether this gene expression pattern was imprinted by the particular microenvironment, peritoneal or spleen cells from recombinant L2 mice mainly consisting of B-1a cells were adoptively transferred into Rag1-/- mice. Re-isolated peritoneal and splenic B-1a cells were analyzed for expression of three indicator genes--vcam-1, adamdec1 and spi-c. The expression of these genes was up-regulated in splenic and down-regulated in peritoneal cells. This particular pattern was observed for peritoneal or splenic donor cells transferred either intraperitoneally or intravenously. Similar results were obtained when levels of surface IgM or frequencies of Mac-1+ B-1 cells were compared after transfer. This suggests that the environment induces the particular genetic program of B-1a cells and argues against an independent ontogeny.

Foxp3 occupancy and regulation of key target genes during T-cell stimulation

Foxp3+CD4+CD25+ regulatory T (T(reg)) cells are essential for the prevention of autoimmunity. T(reg) cells have an attenuated cytokine response to T-cell receptor stimulation, and can suppress the proliferation and effector function of neighbouring T cells. The forkhead transcription factor Foxp3 (forkhead box P3) is selectively expressed in T(reg) cells, is required for T(reg) development and function, and is sufficient to induce a T(reg) phenotype in conventional CD4+CD25- T cells. Mutations in Foxp3 cause severe, multi-organ autoimmunity in both human and mouse. FOXP3 can cooperate in a DNA-binding complex with NFAT (nuclear factor of activated T cells) to regulate the transcription of several known target genes. However, the global set of genes regulated directly by Foxp3 is not known and consequently, how this transcription factor controls the gene expression programme for T(reg) function is not understood. Here we identify Foxp3 target genes and report that many of these are key modulators of T-cell activation and function. Remarkably, the predominant, although not exclusive, effect of Foxp3 occupancy is to suppress the activation of target genes on T-cell stimulation. Foxp3 suppression of its targets appears to be crucial for the normal function of T(reg) cells, because overactive variants of some target genes are known to be associated with autoimmune disease.

Making regulatory T cells with defined antigen specificity: role in autoimmunity and cancer

There is increasing evidence that agonist ligand presentation either intrathymically or extrathymically plays a crucial if not essential role in the generation of regulatory T cells (Tregs). Thus, it is possible to induce Tregs of any desired specificity in vivo. The same goal can be achieved in vitro by expanding antigen-specific CD4+ T cells and retrovirally transducing them. In contrast, in vitro expansion of Tregs is limited to antigens that have resulted in Treg generation in vivo. Antigen-specific Tregs can be used in cellular therapy with the goal to prevent autoimmune disease or even to interfere with established autoimmunity. The latter requires that the Tregs can suppress effector cells that have already caused harm, which is possible because of the antigen-dependent homing properties of Tregs, i.e. these cells can accumulate in antigen-draining lymph nodes and exit into inflamed tissue. Generally, the in vivo interference is dependent on cytokines such as transforming growth factor-beta and interleukin-10 that were dispensable in in vivo analysis of immunosuppression. The precise mechanisms of suppression remain enigmatic, however, but may be further elucidated by the molecular analysis of suppressed versus non-suppressed T cells.