Comparison of induced versus natural regulatory T cells of the same TCR specificity for induction of tolerance to an environmental antigen

Emerging strategies for treating autoimmune disease with genetically modified dendritic cells

Gene editing of living cells has become a crucial tool in medical research, enabling scientists to address fundamental biological questions and develop novel strategies for disease treatment. This technology has particularly revolutionized adoptive transfer cell therapy products, leading to significant advancements in tumor treatment and offering promising outcomes in managing transplant rejection, autoimmune disorders, and inflammatory diseases. While recent clinical trials have demonstrated the safety of tolerogenic dendritic cell (TolDC) immunotherapy, concerns remain regarding its effectiveness. This review aims to discuss the application of gene editing techniques to enhance the tolerance function of dendritic cells (DCs), with a particular focus on preclinical strategies that are currently being investigated to optimize the tolerogenic phenotype and function of DCs. We explore potential approaches for in vitro generation of TolDCs and provide an overview of emerging strategies for modifying DCs. Additionally, we highlight the primary challenges hindering the clinical adoption of TolDC therapeutics and propose future research directions in this field.

Enhancing Regulatory T Cells to Treat Inflammatory and Autoimmune Diseases

Regulatory T cells (Tregs) control immune responses and are essential to maintain immune homeostasis and self-tolerance. Hence, it is no coincidence that autoimmune and chronic inflammatory disorders are associated with defects in Tregs. These diseases have currently no cure and are treated with palliative drugs such as immunosuppressant and immunomodulatory agents. Thereby, there is a great interest in developing medical interventions against these diseases based on enhancing Treg cell function and numbers. Here, we give an overview of Treg cell ontogeny and function, paying particular attention to mucosal Tregs. We review some notable approaches to enhance immunomodulation by Tregs with therapeutic purposes including adoptive Treg cell transfer therapy and discuss relevant clinical trials for inflammatory bowel disease. We next introduce ways to expand mucosal Tregs in vivo using microbiota and dietary products that have been the focus of clinical trials in various autoimmune and chronic-inflammatory diseases.

Human Regulatory T Cells: Understanding the Role of Tregs in Select Autoimmune Skin Diseases and Post-Transplant Nonmelanoma Skin Cancers

Regulatory T cells (Tregs) play an important role in maintaining immune tolerance and homeostasis by modulating how the immune system is activated. Several studies have documented the critical role of Tregs in suppressing the functions of effector T cells and antigen-presenting cells. Under certain conditions, Tregs can lose their suppressive capability, leading to a compromised immune system. For example, mutations in the Treg transcription factor, Forkhead box P3 (FOXP3), can drive the development of autoimmune diseases in multiple organs within the body. Furthermore, mutations leading to a reduction in the numbers of Tregs or a change in their function facilitate autoimmunity, whereas an overabundance can inhibit anti-tumor and anti-pathogen immunity. This review discusses the characteristics of Tregs and their mechanism of action in select autoimmune skin diseases, transplantation, and skin cancer. We also examine the potential of Tregs-based cellular therapies in autoimmunity.

Regulatory T Cells, a Viable Target Against Airway Allergic Inflammatory Responses in Asthma

Asthma is a multifactorial disorder characterized by the airway chronic inflammation, hyper-responsiveness (AHR), remodeling, and reversible obstruction. Although asthma is known as a heterogeneous group of diseases with various clinical manifestations, recent studies suggest that more than half of the clinical cases are ‘‘T helper type 2 (Th2)-high’’ type, whose pathogenesis is driven by Th2 responses to an inhaled allergen from the environmental exposures. The intensity and duration of inflammatory responses to inhaled allergens largely depend on the balance between effector and regulatory cells, but many questions regarding the mechanisms by which the relative magnitudes of these opposing forces are remained unanswered. Regulatory T cells (Tregs), which comprise diverse subtypes with suppressive function, have long been attracted extensive attention owing to their capability to limit the development and progression of allergic diseases. In this review we seek to update the recent advances that support an essential role for Tregs in the induction of allergen tolerance and attenuation of asthma progression once allergic airway inflammation established. We also discuss the current concepts about Treg induction and Treg-expressed mediators relevant to controlling asthma, and the therapies designed based on these novel insights against asthma in clinical settings.

Your Regulatory T Cells Are What You Eat: How Diet and Gut Microbiota Affect Regulatory T Cell Development

Modern industrial practices have transformed the human diet over the last century, increasing the consumption of processed foods. Dietary imbalance of macro- and micro-nutrients and excessive caloric intake represent significant risk factors for various inflammatory disorders. Increased ingestion of food additives, residual contaminants from agricultural practices, food processing, and packaging can also contribute deleteriously to disease development. One common hallmark of inflammatory disorders, such as autoimmunity and allergies, is the defect in anti-inflammatory regulatory T cell (Treg) development and/or function. Treg represent a highly heterogeneous population of immunosuppressive immune cells contributing to peripheral tolerance. Tregs either develop in the thymus from autoreactive thymocytes, or in the periphery, from naïve CD4⁺ T cells, in response to environmental antigens and cues. Accumulating evidence demonstrates that various dietary factors can directly regulate Treg development. These dietary factors can also indirectly modulate Treg differentiation by altering the gut microbiota composition and thus the production of bacterial metabolites. This review provides an overview of Treg ontogeny, both thymic and peripherally differentiated, and highlights how diet and gut microbiota can regulate Treg development and function.

CD40 signaling augments IL-10 expression and the tolerogenicity of IL-10-induced regulatory dendritic cells

CD40 expressed on stimulatory dendritic cells (DC) provides an important accessory signal for induction of effector T cell responses. It is also expressed at lower levels on regulatory DC (DCreg), but there is little evidence that CD40 signaling contributes to the tolerogenic activity of these cells. Indeed, CD40 silencing within DCreg has been reported to induce T cell tolerance in multiple disease models, suggesting that CD40 is superfluous to DC-induced tolerance. We critically assessed whether CD40 does have a role in tolerance induced by IL-10-differentiated DC (DC10) by using DC10 generating from the bone marrow of wild-type (w.t.) or CD40^-/- donor mice, or IL-10-complemented CD40^-/- DC10 to treat asthmatic mice. Wild-type DC10 ablated the OVA-asthma phenotype via induction of Foxp3⁺ Treg responses, but CD40^-/- DC10 had no discernible effects on primary facets of the phenotype (e.g., IL-5, IL-9, IL-13 levels, IgE & IgG1 antibodies; p>0.05) and were ≤40% effective in reversal of others. Foxp3⁺ T cells from the lungs of CD40^-/- DC10-treated mice expressed reduced levels of a panel of six Treg-specific activation markers relative to Treg from w.t. DC10-treated mice. Coculture with effector T cells from asthmatic mice induced a marked upregulation of cell surface CD40 on w.t. DC10. While untreated CD40^-/- and w.t. DC10 secreted equally low levels of IL-10, stimulation of w.t. DC10 with anti-CD40 for 72 h increased their expression of IL-10 by ≈250%, with no parallel induction of IL-12. Complementing IL-10 expression in CD40^-/- DC10 by IL-10 mRNA transfection fully restored the cells’ abilities to suppress the asthma phenotype. In summary, CD40 signaling in DC10 contributes importantly to their expression of IL-10 and to a robust induction of tolerance, including activation of induced Treg.

Regulatory Dendritic Cells, T Cell Tolerance, and Dendritic Cell Therapy for Immunologic Disease

Dendritic cells (DC) are antigen-presenting cells that can communicate with T cells both directly and indirectly, regulating our adaptive immune responses against environmental and self-antigens. Under some microenvironmental conditions DC develop into anti-inflammatory cells which can induce immunologic tolerance. A substantial body of literature has confirmed that in such settings regulatory DC (DCreg) induce T cell tolerance by suppression of effector T cells as well as by induction of regulatory T cells (Treg). Many in vitro studies have been undertaken with human DCreg which, as a surrogate marker of antigen-specific tolerogenic potential, only poorly activate allogeneic T cell responses. Fewer studies have addressed the abilities of, or mechanisms by which these human DCreg suppress autologous effector T cell responses and induce infectious tolerance-promoting Treg responses. Moreover, the agents and properties that render DC as tolerogenic are many and varied, as are the cells’ relative regulatory activities and mechanisms of action. Herein we review the most current human and, where gaps exist, murine DCreg literature that addresses the cellular and molecular biology of these cells. We also address the clinical relevance of human DCreg, highlighting the outcomes of pre-clinical mouse and non-human primate studies and early phase clinical trials that have been undertaken, as well as the impact of innate immune receptors and symbiotic microbial signaling on the immunobiology of DCreg.

Stability of regulatory T cells in T helper 2-biased allergic airway diseases

Regulatory T (Treg) cells potentially suppress the deleterious activities of effector T cells and maintain a state of tolerance against antigens in the airway mucosa. A decrease in the number and function of Treg cells is observed in T helper 2 (Th2)-biased allergic airway diseases. However, adoptive transfer of naturally occurring Treg (tTreg) cells or peripherally derived Treg (pTreg) cells in asthmatic mouse models did not yield satisfactory results in any previous studies. Here, we review the recent progress in the identification and plasticity of tTreg and pTreg cells in Th2-biased airway diseases and summarize the factors affecting the stability and function of Treg cells. This review may serve as foundation for understanding the molecular mechanisms underlying the stability of tTreg and pTreg cells and development of effective strategies for treating allergic airway diseases.

T Regulatory Cells and Priming the Suppressive Tumor Microenvironment

Treg play a central role in maintenance of self tolerance and homeostasis through suppression of self-reactive T cell populations. In addition to that role, Treg also survey cancers and suppress anti-tumor immune responses. Thus, understanding the unique attributes of Treg-tumor interactions may permit control of this pathologic suppression without interfering with homeostatic self-tolerance. This review will define the unique role of Treg in cancer growth, and the ways by which Treg inhibit a robust anti-tumor immune response. There will be specific focus placed on Treg homing to the tumor microenvironment (TME), TME formation of induced Treg (iTreg), mechanisms of suppression that underpin cancer immune escape, and trophic nonimmunologic effects of Treg on tumor cells.

Rebalancing Immune Homeostasis to Treat Autoimmune Diseases

During homeostasis, interactions between tolerogenic dendritic cells (DCs), self-reactive T cells, and T regulatory cells (Tregs) contribute to maintaining mammalian immune tolerance. In response to infection, immunogenic DCs promote the generation of proinflammatory effector T cell subsets. When complex homeostatic mechanisms maintaining the balance between regulatory and effector functions become impaired, autoimmune diseases can develop. We discuss some of the newest advances on the mechanisms of physiopathologic homeostasis that can be employed to develop strategies to restore a dysregulated immune equilibrium. Some of these designs are based on selectively activating regulators of immunity and inflammation instead of broadly suppressing these processes. Promising approaches include the use of nanoparticles (NPs) to restore Treg control over self-reactive cells, aiming to achieve long-term disease remission, and potentially to prevent autoimmunity in susceptible individuals.

The effect of regulatory T cells on tolerance to airborne allergens and allergen immunotherapy

Forkhead box P3-positive regulatory T (Treg) cells are essential mediators of tolerance against self-antigens and harmless exogenous antigens. Treg cell deficiencies result in multiple autoimmune and allergic syndromes in neonates. How Treg cells affect conventional allergies against aeroantigens, which are restricted to a few specific proteins released from inhaled particles, remains controversial. The hallmarks of antigen-specific loss of tolerance are allergen-specific T_H2 cells and IgE. However, difficulties in identifying the rare allergen-specific Treg cells have obscured the cellular basis of tolerance to aeroallergens, which is also a major obstacle for the rational design of novel and more efficient allergen-specific immunotherapies. Recent technological progress allowing characterization of allergen-specific effectors and Treg cells with minimal in vitro manipulation revealed their detailed contribution to tolerance. The data identified inhaled particles as immunodominant Treg cell targets in healthy and allergic subjects. Conversely, the supposed immunodominant major allergens being rapidly released from inhaled particles apparently do not actively induce tolerance but are ignored by the immune system. Here, the partially contradictory data on various allergen-specific T-cell types in healthy subjects, allergic patients, and patients undergoing allergen-specific immunotherapy are discussed and integrated into one model, postulating Treg cell-dependent and Treg cell-independent checkpoints of tolerance and allergy development.

EBV Latency III-Transformed B Cells Are Inducers of Conventional and Unconventional Regulatory T Cells in a PD-L1-Dependent Manner

EBV infects and immortalizes B cells in vitro and in vivo. It is the causative agent of most immune deficiency-related lymphoproliferative disorders and is associated with various lymphomas. EBV latency III-transformed B cells are known to express two immunosuppressive molecules, IL-10 and PD-L1, two characteristics of regulatory B cells (Bregs). In this study, we show that, in addition to secretion of the Breg immunosuppressive cytokines IL-10, IL-35, and TGF-β1, EBV latency III-transformed B cells were able to repress proliferation of their autologous T cells preactivated by CD2, CD3, and CD28. This inhibitory effect was likely caused by CD4⁺ T cells because EBV latency III-transformed B cells induced a strong proliferation of isolated autologous CD8 T cells. Indeed, EBV was able to promote expansion of autologous FOXP3⁺ CD39^high CTLA4⁺, Helios⁺, GITR⁺, LAG3⁺ CD4 T cells (i.e., regulatory T cells [Tregs]). Two types of Tregs were induced: unconventional CD25^neg and conventional CD25^pos Tregs. These Tregs expressed both the latency-associated peptide (LAP) and the PD-1 receptor, two markers of functional Tregs. Expansion of both Treg subtypes depended on PD-L1, whose expression was under the control of LMP1, the main EBV oncogene. These results demonstrate that, like Bregs, EBV latency III-transformed B cells exhibit strong immunoregulatory properties. These data provide clues to the understanding of how after EBV primo-infection, EBV-proliferating B cells can survive in an aggressive immunological environment and later emerge to give rise to EBV-associated B cell lymphomas such as in elderly patients.

Antigen-specific regulatory T-cell responses against aeroantigens and their role in allergy

The mucosal immune system of the respiratory tract is specialized to continuously monitor the external environment and to protect against invading pathogens, while maintaining tolerance to innocuous inhaled particles. Allergies result from a loss of tolerance against harmless antigens characterized by formation of allergen-specific Th2 cells and IgE. Tolerance is often described as a balance between harmful Th2 cells and various types of protective "regulatory" T cells. However, the identity of the protective T cells in healthy vs. allergic individuals or following successful allergen-specific therapy is controversially discussed. Recent technological progress enabling the identification of antigen-specific effector and regulatory T cells has significantly contributed to our understanding of tolerance. Here we discuss the experimental evidence for the various tolerance mechanisms described. We try to integrate the partially contradictory data into a new model proposing different mechanism of tolerance depending on the quality and quantity of the antigens as well as the way of antigen exposure. Understanding the basis of tolerance is essential for the rational design of novel and more efficient immunotherapies.

Notch ligand Delta-like 4 induces epigenetic regulation of Treg cell differentiation and function in viral infection

Notch ligand Delta-like ligand 4 (DLL4) has been shown to regulate CD4 T-cell differentiation, including regulatory T cells (T_reg). Epigenetic alterations, which include histone modifications, are critical in cell differentiation decisions. Recent genome-wide studies demonstrated that T_reg have increased trimethylation on histone H3 at lysine 4 (H3K4me3) around the T_reg master transcription factor, Foxp3 loci. Here we report that DLL4 dynamically increased H3K4 methylation around the Foxp3 locus that was dependent upon upregulated SET and MYDN domain containing protein 3 (SMYD3). DLL4 promoted Smyd3 through the canonical Notch pathway in iT_reg differentiation. DLL4 inhibition during pulmonary respiratory syncytial virus (RSV) infection decreased Smyd3 expression and Foxp3 expression in T_reg leading to increased Il17a. On the other hand, DLL4 supported Il10 expression in vitro and in vivo, which was also partially dependent upon SMYD3. Using genome-wide unbiased mRNA sequencing, novel sets of DLL4- and Smyd3-dependent differentially expressed genes were discovered, including lymphocyte-activation gene 3 (Lag3), a checkpoint inhibitor that has been identified for modulating Th cell activation. Together, our data demonstrate a novel mechanism of DLL4/Notch-induced Smyd3 epigenetic pathways that maintain regulatory CD4 T cells in viral infections.

Contributions of direct versus indirect mechanisms for regulatory dendritic cell suppression of asthmatic allergen-specific IgG1 antibody responses

IL-10-differentiated dendritic cells (DC10) can reverse the asthma phenotype in mice, but how they suppress the asthmatic B cell response is unclear. Herein we assessed the mechanism(s) by which DC10 and DC10-induced Treg affect IgG1 production in asthma. We observed a rapid decline in lung-resident OVA-specific IgG1-secreting B cells on cessation of airway allergen challenge, and intraperitoneal DC10 therapy did not amplify that (p>0.05). It did however increase the loss of IgG1-B cells from the bone marrow (by 45+/-7.2%; p≤0.01) and spleen (by 65+/-17.8%; p≤0.05) over 2 wk. Delivery of OVA-loaded DC10 directly into the airways of asthmatic mice decreased the lung IgG1 B cell response assessed 2 dy later by 33+/-9.7% (p≤0.01), while their co-culture with asthmatic lung cell suspensions reduced the numbers of IgG1-secreting cells by 56.5+/-9.7% (p≤0.01). This effect was dependent on the DC10 carrying intact allergen on their cell surface; DC10 that had phagocytosed and fully processed their allergen were unable to suppress B cell responses, although they did suppress asthmatic Th2 cell responses. We had shown that therapeutic delivery of DC10-induced Treg can effectively suppress asthmatic T and B cell (IgE and IgG1) responses; herein CD4⁺ cells or Treg from the lungs of DC10-treated OVA-asthmatic mice suppressed in vitro B cell IgG1 production by 52.2+/-8.7% (p≤0.001) or 44.6+/-12.2% (p≤0.05), respectively, but delivery of DC10-induced Treg directly into the airways of asthmatic mice had no discernible impact over 2 dy on the numbers of lung IgG1-secreting cells (p≥0.05). In summary, DC10 treatment down-regulates OVA-specific B cell responses of asthmatic mice. While DC10 that carry intact allergen on their cell surface can dampen this response, DC10-induced Treg are critical for full realization of this outcome. This suggests that infectious tolerance is an essential element in regulatory DC control of the B cell response in allergic asthma.

Regulatory T cells and type 2 innate lymphoid cell-dependent asthma

Group 2 innate lymphoid cells (ILC2s) are a recently identified group of cells with the potent capability to produce Th2-type cytokines such as interleukin (IL)-5 and IL-13. Several studies suggest that ILC2s play an important role in the development of allergic diseases and asthma. Activation of pulmonary ILC2s in murine models lacking T and B cells induces eosinophilia and airway hyper-reactivity (AHR), which are cardinal features of asthma. More importantly, numerous recent studies have highlighted the role of ILC2s in asthma persistence and exacerbation among human subjects, and thus, regulation of pulmonary ILC2s is a major area of investigation aimed at curbing allergic lung inflammation and exacerbation. Emerging evidence reveals that a group of regulatory T cells, induced Tregs (iTregs), effectively suppress the production of ILC2-driven, pro-inflammatory cytokines IL-5 and IL-13. The inhibitory effects of iTregs are blocked by preventing direct cellular contact or by inhibiting the ICOS-ICOS-ligand (ICOSL) pathway, suggesting that both direct contact and ICOS-ICOSL interaction are important in the regulation of ILC2 function. Also, cytokines such as IL-10 and TGF-β1 significantly reduce cytokine secretion by ILC2s. Altogether, these new findings uncover iTregs as potent regulators of ILC2 activation and implicate their utility as a therapeutic approach for the treatment of ILC2-mediated allergic asthma and respiratory disease.

Induced Regulatory T Cells Superimpose Their Suppressive Capacity with Effector T Cells in Lymph Nodes via Antigen-Specific S1p1-Dependent Egress Blockage

Regulatory T cells (Tregs) restrict overexuberant lymphocyte activation. While close proximity between Tregs and their suppression targets is important for optimal inhibition, and literature indicates that draining lymph nodes (LNs) may serve as a prime location for the suppression, signaling details orchestrating this event are not fully characterized. Using a protocol to enable peripheral generation of inducible antigen-specific Tregs (asTregs) to control allergen-induced asthma, we have identified an antigen-specific mechanism that locks asTregs within hilar LNs which in turn suppresses airway inflammation. The suppressive asTregs, upon antigen stimulation in the LN, downregulate sphingosine-1-phosphate receptor 1 egress receptor expression. These asTregs in turn mediate the downregulation of the same receptor on incoming effector T cells. Therefore, asTregs and effector T cells are locked in these draining LNs for prolonged interactions. Disruption of individual steps of this retention sequence abolishes the inflammation controlled by asTregs. Collectively, this study identifies a new requirement of spatial congregation with their suppression targets essential for asTreg functions and suggests therapeutic programs via Treg traffic control.

Lung CD103+ dendritic cells restrain allergic airway inflammation through IL-12 production

DCs are necessary and sufficient for induction of allergic airway inflammation. CD11b+ DCs direct the underlying Th2 immunity, but debate surrounds the function of CD103+ DCs in lung immunity and asthma after an allergic challenge. We challenged Batf3-/- mice, which lacked lung CD103+ DCs, with the relevant allergen house dust mite (HDM) as a model to ascertain their role in asthma. We show that acute and chronic HDM exposure leads to defective Th1 immunity in Batf3-deficient mice. In addition, chronic HDM challenge in Batf3-/- mice results in increased Th2 and Th17 immune responses and exacerbated airway inflammation. Mechanistically, Batf3 absence does not affect induction of Treg or IL-10 production by lung CD4+ T cells following acute HDM challenge. Batf3-dependent CD103+ migratory DCs are the main source of IL-12p40 in the mediastinal lymph node DC compartment in the steady state. Moreover, CD103+ DCs selectively increase their IL-12p40 production upon HDM administration. In vivo IL-12 treatment reverts exacerbated allergic airway inflammation upon chronic HDM challenge in Batf3-/- mice, restraining Th2 and Th17 responses without triggering Th1 immunity. These results suggest a protective role for lung CD103+ DCs to HDM allergic airway inflammation through the production of IL-12.

Type 2 innate lymphoid cell suppression by regulatory T cells attenuates airway hyperreactivity and requires inducible T-cell costimulator-inducible T-cell costimulator ligand interaction

BACKGROUND

Atopic diseases, including asthma, exacerbate type 2 immune responses and involve a number of immune cell types, including regulatory T (Treg) cells and the emerging type 2 innate lymphoid cells (ILC2s). Although ILC2s are potent producers of type 2 cytokines, the regulation of ILC2 activation and function is not well understood.

OBJECTIVE

In the present study, for the first time, we evaluate how Treg cells interact with pulmonary ILC2s and control their function.

METHODS

ILC2s and Treg cells were evaluated by using in vitro suppression assays, cell-contact assays, and gene expression panels. Also, human ILC2s and Treg cells were adoptively transferred into NOD SCID γC-deficient mice, which were given isotype or anti-inducible T-cell costimulator ligand (ICOSL) antibodies and then challenged with IL-33 and assessed for airway hyperreactivity.

RESULTS

We show that induced Treg cells, but not natural Treg cells, effectively suppress the production of the ILC2-driven proinflammatory cytokines IL-5 and IL-13 both in vitro and in vivo. Mechanistically, our data reveal the necessity of inducible T-cell costimulator (ICOS)-ICOS ligand cell contact for Treg cell-mediated ILC2 suppression alongside the suppressive cytokines TGF-β and IL-10. Using a translational approach, we then demonstrate that human induced Treg cells suppress syngeneic human ILC2s through ICOSL to control airway inflammation in a humanized ILC2 mouse model.

CONCLUSION

These findings suggest that peripheral expansion of induced Treg cells can serve as a promising therapeutic target against ILC2-dependent asthma.

Inducible and naturally occurring regulatory T cells enhance lung allergic responses through divergent transcriptional pathways

BACKGROUND

Regulatory T cells attenuate development of asthma in wild-type (WT) mice, with both naturally occurring regulatory T (nTreg) cells and inducible regulatory T (iTreg) cells exhibiting suppressive activity. When transferred into CD8-deficient (CD8^-/-) recipients, both cell types enhanced development of allergen-induced airway hyperresponsiveness.

OBJECTIVE

We sought to determine whether the pathways leading to enhancement of lung allergic responses by transferred nTreg and iTreg cells differed.

METHODS

nTreg cells (CD4⁺CD25⁺) were isolated from WT mice and iTreg cells were generated from WT CD4⁺CD25^- T cells after activation in the presence of TGF-β and transferred into sensitized CD8^-/- recipients before challenge. Development of airway hyperresponsiveness, cytokine levels, and airway inflammation were monitored.

RESULTS

Transfer of nTreg cells enhanced lung allergic responses, as did transfer of iTreg cells. Although anti-IL-13 reduced nTreg cell-mediated enhancement, it was ineffective in iTreg cell-mediated enhancement; conversely, anti-IL-17, but not anti-IL-13, attenuated the enhancement by iTreg cells. Recovered iTreg cells from the lungs of CD8^-/- recipients were capable of IL-17 production and expressed high levels of signature genes of the T_H17 pathway, RORγt and Il17, whereas reduced expression of the Treg cell key transcription factor forkhead box p3 (Foxp3) was observed. In vitro exogenous IL-6-induced IL-17 production in iTreg cells, and in vivo conversion of transferred iTreg cells was dependent on recipient IL-6.

CONCLUSIONS

iTreg cells, similar to nTreg cells, exhibit functional plasticity and can be converted from suppressor cells to pathogenic effector cells, enhancing lung allergic responses, but these effects were mediated through different pathways.

Tolerogenic dendritic cells for reprogramming of lymphocyte responses in autoimmune diseases

Dendritic cells (DCs) control immune responses by driving potent inflammatory actions against external and internal threats while generating tolerance to self and harmless components. This duality and their potential to reprogram immune responses in an antigen-specific fashion have made them an interesting target for immunotherapeutic strategies to control autoimmune diseases. Several protocols have been described for in vitro generation of tolerogenic DCs (tolDCs) capable of modulating adaptive immune responses and restoring tolerance through different mechanisms that involve anergy, generation of regulatory lymphocyte populations, or deletion of potentially harmful inflammatory T cell subsets. Recently, the capacity of tolDCs to induce interleukin (IL-10)-secreting regulatory B cells has been demonstrated. In vitro assays and rodent models of autoimmune diseases provide insights to the molecular regulators and pathways enabling tolDCs to control immune responses. Here we review mechanisms through which tolDCs modulate adaptive immune responses, particularly focusing on their suitability for reprogramming autoreactive CD4⁺ effector T cells. Furthermore, we discuss recent findings establishing that tolDCs also modulate B cell populations and discuss clinical trials applying tolDCs to patients with autoimmune diseases.

Diffuse traumatic brain injury induces prolonged immune dysregulation and potentiates hyperalgesia following a peripheral immune challenge

Background

Nociceptive and neuropathic pain occurs as part of the disease process after traumatic brain injury (TBI) in humans. Central and peripheral inflammation, a major secondary injury process initiated by the traumatic brain injury event, has been implicated in the potentiation of peripheral nociceptive pain. We hypothesized that the inflammatory response to diffuse traumatic brain injury potentiates persistent pain through prolonged immune dysregulation.

Results

To test this, adult, male C57BL/6 mice were subjected to midline fluid percussion brain injury or to sham procedure. One cohort of mice was analyzed for inflammation-related cytokine levels in cortical biopsies and serum along an acute time course. In a second cohort, peripheral inflammation was induced seven days after surgery/injury with an intraplantar injection of carrageenan. This was followed by measurement of mechanical hyperalgesia, glial fibrillary acidic protein and Iba1 immunohistochemical analysis of neuroinflammation in the brain, and flow cytometric analysis of T-cell differentiation in mucosal lymph. Traumatic brain injury increased interleukin-6 and chemokine ligand 1 levels in the cortex and serum that peaked within 1–9 h and then resolved. Intraplantar carrageenan produced mechanical hyperalgesia that was potentiated by traumatic brain injury. Further, mucosal T cells from brain-injured mice showed a distinct deficiency in the ability to differentiate into inflammation-suppressing regulatory T cells (Tregs).

Conclusions

We conclude that traumatic brain injury increased the inflammatory pain associated with cutaneous inflammation by contributing to systemic immune dysregulation. Regulatory T cells are immune suppressors and failure of T cells to differentiate into regulatory T cells leads to unregulated cytokine production which may contribute to the potentiation of peripheral pain through the excitation of peripheral sensory neurons. In addition, regulatory T cells are identified as a potential target for therapeutic rebalancing of peripheral immune homeostasis to improve functional outcome and decrease the incidence of peripheral inflammatory pain following traumatic brain injury.

Glycogen synthase kinase 3β inhibition promotes human iTreg differentiation and suppressive function

Induced regulatory T cells (iTregs) are essential to maintain immunological tolerance, immune homeostasis and prevention of autoimmunity. Some studies suggest that glycogen synthase kinase 3β (GSK3β) is involved in the mouse iTreg differentiation; however, whether GSK3β inhibits or enhances iTreg differentiation is still a matter of controversy. To address this issue, we have utilized human naïve CD4(+) T cells and investigated whether GSK3 activity changes during iTreg differentiation and whether altering GSK3 activity influences the development of iTregs and its suppressive function. As a constitutively activated kinase, during iTreg differentiation GSK3β became quickly deactivated (phosphorylated at serine 9), which is dependent on MAPK pathway rather than PI3-kinase/Akt pathway. Our results indicated that inhibition of GSK3β by specific inhibitors, SB216763 or TDZD-8, promoted the differentiation of iTreg and increased their suppressive activity. In contrast, overexpression of GSK3β significantly inhibited iTreg differentiation. Furthermore, GSK3β inhibition enhanced iTreg differentiation through the TGF-β/Smad3 pathway. Taken together, this study demonstrates that inhibition of GSK3β enhances human iTreg differentiation and its suppressive activity, and provides a rationale to target GSK3β as a novel immunotherapeutic strategy.

T cell epitope redundancy: cross-conservation of the TCR face between pathogens and self and its implications for vaccines and autoimmunity

T cells are extensively trained on 'self' in the thymus and then move to the periphery, where they seek out and destroy infections and regulate immune response to self-antigens. T cell receptors (TCRs) on T cells' surface recognize T cell epitopes, short linear strings of amino acids presented by antigen-presenting cells. Some of these epitopes activate T effectors, while others activate regulatory T cells. It was recently discovered that T cell epitopes that are highly conserved on their TCR face with human genome sequences are often associated with T cells that regulate immune response. These TCR-cross-conserved or 'redundant epitopes' are more common in proteins found in pathogens that have co-evolved with humans than in other non-commensal pathogens. Epitope redundancy might be the link between pathogens and autoimmune disease. This article reviews recently published data and addresses epitope redundancy, the "elephant in the room" for vaccine developers and T cell immunologists.

Scientific foundations of allergen-specific immunotherapy for allergic disease

Allergen-specific immunotherapy (AIT) was described as a therapeutic option for the treatment of allergies > 100 years ago. It is based on administration of allergen extracts and leads to the development of clinical allergen tolerance in selected patients. According to current knowledge, AIT results in the restoration of immune tolerance toward the allergen of interest. It is mainly accompanied by the induction of regulatory and suppressive subsets of T and B cells, the production of IgG4 isotype allergen-specific blocking antibodies, and decreased inflammatory responses to allergens by effector cells in inflamed tissues. Currently, AIT is mainly applied subcutaneously or sublingually and is suitable for both children and adults for pollen, pet dander, house dust mite, and venom allergies. It not only affects rhinoconjunctival symptoms but also has documented short- and long-term benefits in asthma treatment. Clinically, a fast onset of tolerance is achieved during desensitization, with a tolerable amount of side effects. The disease modification effect leads to decreased disease severity, less drug usage, prevention of future allergen sensitizations, and a long-term curative effect. Increasing safety while maintaining or even augmenting efficiency is the main goal of research for novel vaccine development and improvement of treatment schemes in AIT. This article reviews the principles of allergen-specific immune tolerance development and the effects of AIT in the clinical context.

Mechanisms of immune tolerance to allergens: role of IL-10 and Tregs

During the past 20 years, major advances have been made in understanding the molecular and cellular mechanisms of allergen tolerance in humans. The demonstration of T cell tolerance, particularly that mediated by the immune-suppressive functions of IL-10, led to a major conceptual change in this area. Currently, the known essential components of allergen tolerance include the induction of allergen-specific regulatory subsets of T and B cells, the immune-suppressive function of secreted factors, such as IL-10 and TGF-β, the production of IgG4 isotype allergen-specific blocking antibodies, and decreased allergic inflammatory responses by mast cells, basophils, and eosinophils in inflamed tissues.

Interleukin-2 drives immature double negative thymocytes into γδ T cells expressing Foxp3 on a stromal cell line in vitro

γδ T cells are exported from the thymus as innate-like lymphocytes that can immediately respond to antigens. In the thymus, γδ T cells diverge into functionally distinct lineages. It is not known whether γδ T cells differentiate into regulatory cells that express Foxp3, which is an essential transcription factor for CD4(+) regulatory T cells. In this study, we analyzed CD25(+) immature thymocytes that give rise to both αβ and γδ thymocytes. These precursor cells have the potential to differentiate into Foxp3(+) γδ T cells on a stromal cell line, TSt4-Dll1. Development of Foxp3(+) γδ thymocytes in this culture was dependent on IL-2. IL-2 stimulation induced Id3, Egr1, and Egr3 expression in CD25(+) immature thymocytes, suggesting that it could activate signaling molecules that are downstream of TCR signaling. The induction of Foxp3 in precursor γδ T cells suggested that IL-2 could activate the Foxp3 gene early in thymocyte development.

Homeostasis and function of regulatory T cells (Tregs) in vivo: lessons from TCR-transgenic Tregs

The identification of CD25 and subsequently Forkhead box protein 3 (Foxp3) as markers for regulatory T cells (Tregs) has revolutionized our ability to explore this population experimentally. In a similar vein, our understanding of antigen-specific Treg responses in vivo owes much to the fortuitous generation of T-cell receptor (TCR)-transgenic Tregs. This has permitted tracking of Tregs with a defined specificity in vivo, facilitating analysis of how encounter with cognate antigen shapes Treg homeostasis and function. Here, we review the key lessons learned from a decade of analysis of TCR-transgenic Tregs and set this in the broader context of general progress in the field. Use of TCR-transgenic Tregs has led to an appreciation that Tregs are a highly dynamic proliferative population in vivo, rather than an anergic population as they were initially portrayed. It is now clear that Treg homeostasis is positively regulated by encounter with self-antigen expressed on peripheral tissues, which is likely to be relevant to the phenomenon of peripheral repertoire reshaping that has been described for Tregs and the observation that the Treg TCR specificities vary by anatomical location. Substantial evidence has also accumulated to support the role of CD28 costimulation and interleukin-2 in Treg homeostasis. The availability of TCR-transgenic Tregs has enabled analysis of Treg populations that are sufficient or deficient in particular genes, without the comparison being confounded by repertoire alterations. This approach has yielded insights into genes required for Treg function in vivo, with particular progress being made on the role of ctla-4 in this context. As the prospect of manipulating Treg populations in the clinic becomes reality, a full appreciation of the rules governing their homeostasis will prove increasingly important.

Exogenous interleukin-10 alleviates allergic inflammation but inhibits local interleukin-10 expression in a mouse allergic rhinitis model

Background

Interleukin-10 (IL-10) has an important anti-inflammatory and immunoregulatory function, and its expression is negatively correlated with the development and severity of allergic rhinitis (AR). However, the in vivo effects of exogenous IL-10 on AR have not been studied and the mechanisms underlying the effects of IL-10 have not been fully understood. Here, we investigated the effects of intranasal administration of recombinant mouse (rm) IL-10 on the expression of Th responses and local IL-10 in a mouse model of AR induced by ovalbumin.

Results

Administration of rmIL-10 during challenge significantly reduced the number of eosinophils and mast cells, as well as Type 2 helper T (Th2) and Th17 cell related cytokine and transcription factor levels in the nasal mucosa and nasal lavage fluid in AR mice. The rmIL-10 treatment significantly inhibited the number of IL-10-positive cells and IL-10 mRNA expression in the nasal mucosa in AR mice.

Conclusion

Our results show that exogenous IL-10 administrated in challenge phase alleviates nasal allergic inflammation in AR mice, most likely by inhibiting Th2 and Th17 responses. It can also inhibit local IL-10 levels in the nasal mucosa. Our findings indicate that IL-10 may have the potential as an inhibitor of AR.

Regulatory dendritic cells for immunotherapy in immunologic diseases

We recognize well the abilities of dendritic cells to activate effector T cell (Teff cell) responses to an array of antigens and think of these cells in this context as pre-eminent antigen-presenting cells, but dendritic cells are also critical to the induction of immunologic tolerance. Herein, we review our knowledge on the different kinds of tolerogenic or regulatory dendritic cells that are present or can be induced in experimental settings and humans, how they operate, and the diseases in which they are effective, from allergic to autoimmune diseases and transplant tolerance. The primary conclusions that arise from these cumulative studies clearly indicate that the agent(s) used to induce the tolerogenic phenotype and the status of the dendritic cell at the time of induction influence not only the phenotype of the dendritic cell, but also that of the regulatory T cell responses that they in turn mobilize. For example, while many, if not most, types of induced regulatory dendritic cells lead CD4⁺ naïve or Teff cells to adopt a CD25⁺Foxp3⁺ Treg phenotype, exposure of Langerhans cells or dermal dendritic cells to vitamin D leads in one case to the downstream induction of CD25⁺Foxp3⁺ regulatory T cell responses, while in the other to Foxp3⁻ type 1 regulatory T cells (Tr1) responses. Similarly, exposure of human immature versus semi-mature dendritic cells to IL-10 leads to distinct regulatory T cell outcomes. Thus, it should be possible to shape our dendritic cell immunotherapy approaches for selective induction of different types of T cell tolerance or to simultaneously induce multiple types of regulatory T cell responses. This may prove to be an important option as we target diseases in different anatomic compartments or with divergent pathologies in the clinic. Finally, we provide an overview of the use and potential use of these cells clinically, highlighting their potential as tools in an array of settings.