Smad-dependent cooperative regulation of interleukin 2 receptor alpha chain gene expression by T cell receptor and transforming growth factor-beta

Distinct use of super-enhancer elements controls cell type-specific CD25 transcription and function

The IL-2 receptor α chain (IL-2Rα/CD25) is constitutively expressed on double-negative (DN2/DN3 thymocytes and regulatory T cells (Tregs) but induced by IL-2 on T and natural killer (NK) cells, with Il2ra expression regulated by a STAT5-dependent super-enhancer. We investigated CD25 regulation and function using a series of mice with deletions spanning STAT5-binding elements. Deleting the upstream super-enhancer region mainly affected constitutive CD25 expression on DN2/DN3 thymocytes and Tregs, with these mice developing autoimmune alopecia, whereas deleting an intronic region decreased IL-2-induced CD25 on peripheral T and NK cells. Thus, distinct super-enhancer elements preferentially control constitutive versus inducible expression in a cell type-specific manner. The mediator-1 coactivator colocalized with specific STAT5-binding sites. Moreover, both upstream and intronic regions had extensive chromatin interactions, and deletion of either region altered the super-enhancer structure in mature T cells. These results demonstrate differential functions for distinct super-enhancer elements, thereby indicating previously unknown ways to manipulate CD25 expression in a cell type-specific fashion.

Regulatory T Cells-Related Genes Are under DNA Methylation Influence

Regulatory T cells (Tregs) exert a highly suppressive function in the immune system. Disturbances in their function predispose an individual to autoimmune dysregulation, with a predominance of the pro-inflammatory environment. Besides Foxp3, which is a master regulator of these cells, other genes (e.g., Il2ra, Ctla4, Tnfrsf18, Ikzf2, and Ikzf4) are also involved in Tregs development and function. Multidimensional Tregs suppression is determined by factors that are believed to be crucial in the action of Tregs-related genes. Among them, epigenetic changes, such as DNA methylation, tend to be widely studied over the past few years. DNA methylation acts as a repressive mark, leading to diminished gene expression. Given the role of increased CpG methylation upon Tregs imprinting and functional stability, alterations in the methylation pattern can cause an imbalance in the immune response. Due to the fact that epigenetic changes can be reversible, so-called epigenetic modifiers are broadly used in order to improve Tregs performance. In this review, we place emphasis on the role of DNA methylation of the genes that are key regulators of Tregs function. We also discuss disease settings that have an impact on the methylation status of Tregs and systematize the usefulness of epigenetic drugs as factors able to influence Tregs functions.

A gene co-association network regulating gut microbial communities in a Duroc pig population

BACKGROUND

Analyses of gut microbiome composition in livestock species have shown its potential to contribute to the regulation of complex phenotypes. However, little is known about the host genetic control over the gut microbial communities. In pigs, previous studies are based on classical "single-gene-single-trait" approaches and have evaluated the role of host genome controlling gut prokaryote and eukaryote communities separately.

RESULTS

In order to determine the ability of the host genome to control the diversity and composition of microbial communities in healthy pigs, we undertook genome-wide association studies (GWAS) for 39 microbial phenotypes that included 2 diversity indexes, and the relative abundance of 31 bacterial and six commensal protist genera in 390 pigs genotyped for 70 K SNPs. The GWAS results were processed through a 3-step analytical pipeline comprised of (1) association weight matrix; (2) regulatory impact factor; and (3) partial correlation and information theory. The inferred gene regulatory network comprised 3561 genes (within a 5 kb distance from a relevant SNP-P < 0.05) and 738,913 connections (SNP-to-SNP co-associations). Our findings highlight the complexity and polygenic nature of the pig gut microbial ecosystem. Prominent within the network were 5 regulators, PRDM15, STAT1, ssc-mir-371, SOX9 and RUNX2 which gathered 942, 607, 588, 284 and 273 connections, respectively. PRDM15 modulates the transcription of upstream regulators of WNT and MAPK-ERK signaling to safeguard naive pluripotency and regulates the production of Th1- and Th2-type immune response. The signal transducer STAT1 has long been associated with immune processes and was recently identified as a potential regulator of vaccine response to porcine reproductive and respiratory syndrome. The list of regulators was enriched for immune-related pathways, and the list of predicted targets includes candidate genes previously reported as associated with microbiota profile in pigs, mice and human, such as SLIT3, SLC39A8, NOS1, IL1R2, DAB1, TOX3, SPP1, THSD7B, ELF2, PIANP, A2ML1, and IFNAR1. Moreover, we show the existence of host-genetic variants jointly associated with the relative abundance of butyrate producer bacteria and host performance.

CONCLUSIONS

Taken together, our results identified regulators, candidate genes, and mechanisms linked with microbiome modulation by the host. They further highlight the value of the proposed analytical pipeline to exploit pleiotropy and the crosstalk between bacteria and protists as significant contributors to host-microbiome interactions and identify genetic markers and candidate genes that can be incorporated in breeding program to improve host-performance and microbial traits. Video Abstract.

Immunostimulatory silica nanoparticle boosts innate immunity in brain tumors

The high mortality associated with glioblastoma multiforme (GBM) is attributed to its invasive nature, hypoxic core, resistant cell subpopulations and a highly immunosuppressive tumor microenvironment (TME). To support adaptive immune function and establish a more robust antitumor immune response, we boosted the local innate immune compartment of GBM using an immunostimulatory mesoporous silica nanoparticle, termed immuno-MSN. The immuno-MSN was specifically designed for systemic and proficient delivery of a potent innate immune agonist to dysfunctional antigen-presenting cells (APCs) in the brain TME. The cargo of the immuno-MSN was cyclic diguanylate monophosphate (cdGMP), a Stimulator of Interferon Gene (STING) agonist. Studies showed the immuno-MSN promoted the uptake of STING agonist by APCs in vitro and the subsequent release of the pro-inflammatory cytokine interferon β, 6-fold greater than free agonist. In an orthotopic GBM mouse model, systemically administered immuno-MSN particles were taken up by APCs in the near-perivascular regions of the brain tumor with striking efficiency. The immuno-MSNs facilitated the recruitment of dendritic cells and macrophages to the TME while sparing healthy brain tissue and peripheral organs, resulting in elevated circulating CD8+ T cell activity (2.5-fold) and delayed GBM tumor growth. We show that an engineered immunostimulatory nanoparticle can support pro-inflammatory innate immune function in GBM and subsequently augment current immunotherapeutic interventions and improve their therapeutic outcome.

Deciphering epigenomic code for cell differentiation using deep learning

Background

Although DNA sequence plays a crucial role in establishing the unique epigenome of a cell type, little is known about the sequence determinants that lead to the unique epigenomes of different cell types produced during cell differentiation. To fill this gap, we employed two types of deep convolutional neural networks (CNNs) constructed for each of differentially related cell types and for each of histone marks measured in the cells, to learn the sequence determinants of various histone modification patterns in each cell type.

Results

We applied our models to four differentially related human CD₄⁺ T cell types and six histone marks measured in each cell type. The cell models can accurately predict the histone marks in each cell type, while the mark models can also accurately predict the cell types based on a single mark. Sequence motifs learned by both the cell or mark models are highly similar to known binding motifs of transcription factors known to play important roles in CD₄⁺ T cell differentiation. Both the unique histone mark patterns in each cell type and the different patterns of the same histone mark in different cell types are determined by a set of motifs with unique combinations. Interestingly, the level of sharing motifs learned in the different cell models reflects the lineage relationships of the cells, while the level of sharing motifs learned in the different histone mark models reflects their functional relationships. These models can also enable the prediction of the importance of learned motifs and their interactions in determining specific histone mark patterns in the cell types.

Conclusion

Sequence determinants of various histone modification patterns in different cell types can be revealed by comparative analysis of motifs learned in the CNN models for multiple cell types and histone marks. The learned motifs are interpretable and may provide insights into the underlying molecular mechanisms of establishing the unique epigenomes in different cell types. Thus, our results support the hypothesis that DNA sequences ultimately determine the unique epigenomes of different cell types through their interactions with transcriptional factors, epigenome remodeling system and extracellular cues during cell differentiation.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-6072-8) contains supplementary material, which is available to authorized users.

JunB plays a crucial role in development of regulatory T cells by promoting IL-2 signaling

The AP-1 transcription factor JunB plays crucial roles in multiple biological processes, including placental formation and bone homeostasis. We recently reported that JunB is essential for development of Th17 cells, and thus Junb-deficient mice are resistant to experimental autoimmune encephalomyelitis. However, the role of JunB in CD4⁺ T cells under other inflammatory disease conditions is unknown. Here we show that mice lacking JunB in CD4⁺ T cells (Junb^fl/flCd4-Cre mice) were more susceptible to dextran sulfate sodium (DSS)-induced colitis because of impaired development of regulatory T (Treg) cells. Production of interleukin (IL)-2 and expression of CD25, a high affinity IL-2 receptor component, were decreased in Junb-deficient CD4⁺ T cells in vitro and in vivo. Naive CD4⁺ T cells from Junb^fl/flCd4-Cre mice failed to differentiate into Treg cells in the absence of exogenously added IL-2 in vitro. A mixed bone marrow transfer experiment revealed that defective Treg development of Junb-deficient CD4⁺ T cells was not rescued by co-transferred wild-type cells, indicating a significance of the cell-intrinsic defect. Injection of IL-2-anti-IL-2 antibody complexes induced expansion of Treg cells and alleviated DSS-induced colitis in Junb^fl/flCd4-Cre mice. Thus JunB plays a crucial role in the development of Treg cells by facilitating IL-2 signaling.

Generation and Immune Regulation of CD4+CD25-Foxp3+ T Cells in Chronic Obstructive Pulmonary Disease

The imbalance of CD4⁺Foxp3⁺ T cell subsets is reportedly involved in abnormal inflammatory immune responses in patients with chronic obstructive pulmonary disease (COPD). However, the possible role of CD4⁺CD25^-Foxp3⁺ T cells in immune regulation in COPD remains to be investigated. In the current study, distribution and phenotypic characteristics of CD4⁺CD25^-Foxp3⁺ T cells from peripheral blood were determined by flow cytometry; the origin, immune function and ultimate fate of CD4⁺CD25^-Foxp3⁺ T cells were further explored in vitro. It was observed that circulating CD4⁺CD25^-Foxp3⁺ T cells were significantly increased in stable COPD patients (SCOPD) and resembled central memory or effector memory T cells. Compared with peripheral CD4⁺CD25⁺Foxp3⁺ T cells, peripheral CD4⁺CD25^-Foxp3⁺ T cells showed a lower expression of Foxp3, CTLA-4, HELIOS, and TIGIT, but a higher expression of CD127 and KI-67, suggesting that CD4⁺CD25^-Foxp3⁺ T cells lost the expression of Tregs-associated molecules following the reduction in CD25. Unexpectedly, our study found that transforming growth factor-β1 (TGFβ1) decreased CD25 expression and played a critical role in the generation of CD4⁺CD25^-Foxp3⁺ T cells from CD4⁺CD25⁺Foxp3⁺ T cells. Phenotypic analysis further revealed that both inducible and peripheral CD4⁺CD25^-Foxp3⁺ T cells exhibited the features of activated conventional T cells. Importantly, memory CD4⁺CD25^-Foxp3⁺ T cells facilitated the proliferation and differentiation of naïve CD4⁺ T cells into Th17 cells in the presence of IL-1β, IL-6, IL-23, and TGFβ1. Finally, a fraction of CD4⁺CD25^-Foxp3⁺ T cells, exhibiting instability and plasticity, were converted to Th17 cells when subjected to Th17 cell-polarizing condition. Taken together, we propose that TGFβ1 is responsible for the generation of CD4⁺CD25^-Foxp3⁺ T cells, and these cells functionally exert an auxiliary effect on Th17 cells generation and might perpetuate chronic inflammation in COPD.

Cytokine-induced alterations of BAMBI mediate the reciprocal regulation of human Th17/Treg cells in response to cigarette smoke extract

In CD4+ T helper (Th) cells, transforming growth factor β (TGF‑β) is indispensable for the induction of both regulatory T (Treg) and interleukin‑17‑producing effector T helper (Th17) cells. Although BMP and activin membrane‑bound inhibitor (BAMBI) is part of a rheostat‑like mechanism for the regulation of TGF‑β signalling and autoimmune arthritis in mouse models, the underlying activity of BAMBI on the human Th17/Treg cell axis, particularly during exposure to cigarette smoke, remains to be elucidated. The present study aimed to further characterize BAMBI expression in human CD4+ cells, as well as immune imbalance during activation and cigarette smoke exposure. Results from the present study indicated that exposure to cigarette smoke extract partially suppressed Treg differentiation and promoted Th17 cell generation under stimulation by anti‑CD3/28 antibodies and TGF‑β1. Additionally, exposure to cigarette smoke induced an inhibition of phosphorylated‑Smad2/Smad3, which may have arisen from a concomitant enhancement of BAMBI expression. In conclusion, human BAMBI may function as a molecular switch to control TGF‑β signalling strength and the Th17/Treg cell balance, which may be used not only as a biomarker but also as a target of new treatment strategies for maintaining immune tolerance and for the treatment of smoking‑induced immune disorders.

Dynamic demethylation of the IL2RA promoter during in vitro CD4+ T cell activation in association with IL2RA expression

IL2RA, a subunit of the high affinity receptor for interleukin-2 (IL2), plays a crucial role in immune homeostasis. Notably, IL2RA expression is induced in CD4+ T cells in response to various stimuli and is constitutive in regulatory T cells (Tregs). We selected for our study 18 CpGs located within cognate regulatory regions of the IL2RA locus and characterized their methylation in naive, regulatory, and memory CD4+ T cells. We found that 5/18 CpGs (notably CpG + 3502) show dynamic, active demethylation during the in vitro activation of naive CD4+ T cells. Demethylation of these CpGs correlates with appearance of IL2RA protein at the cell surface. We found no influence of cis located SNP alleles upon CpG methylation. Treg cells show constitutive demethylation at all studied CpGs. Methylation of 9/18 CpGs, including CpG +3502, decreases with age. Our data thus identify CpG +3502 and a few other CpGs at the IL2RA locus as coordinated epigenetic regulators of IL2RA expression in CD4+ T cells. This may contribute to unravel how the IL2RA locus can be involved in immune physiology and pathology.

Bone Morphogenetic Protein and Activin Membrane-Bound Inhibitor, a Transforming Growth Factor β Rheostat That Controls Murine Treg Cell/Th17 Cell Differentiation and the Development of Autoimmune Arthritis by Reducing Interleukin-2 Signaling

OBJECTIVE

Transforming growth factor β (TGFβ) plays a prominent role in the establishment of immunologic tolerance, and mice lacking TGFβ1 die of multiorgan inflammation early in life. TGFβ controls the differentiation of CD4+ lymphocytes into Treg cells or proinflammatory Th17 cells. Although this dual capacity is modulated by the presence of additional cytokines around the activated cells, TGFβ also dissociates Th17/Treg cell differentiation in a dose-dependent manner by mechanisms still unknown. The purpose of this study was to explore the contribution of bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) to the modulation of TGFβ activity during the differentiation of CD4+ cells and in the control of immunologic tolerance in mice with collagen-induced arthritis (CIA).

METHODS

The in vitro and in vivo Treg cell and Th17 cell differentiation and the development of CIA were compared in wild-type mice and BAMBI-deficient mice.

RESULTS

BAMBI was induced after activation by TGFβ and fixed the appropriate intensity level of TGFβ signaling in CD4+ cells. Its deficiency protected mice against the development of CIA by a Treg cell- and TGFβ-dependent mechanism. Mechanistically, BAMBI was found to regulate CD25 expression and interleukin-2 (IL-2) signaling in Treg cells and in IL-2- and/or TGFβ-activated CD4+ cells and modulated Treg cell and Th17 cell differentiation both in vitro and in vivo.

CONCLUSION

Taken together, the results indicate that BAMBI is a component of a rheostat-like mechanism that, through the control of TGFβ and IL-2 signaling strength, regulates the differentiation of CD4+ lymphocytes and the development of autoimmune arthritis.

Engagement of SLAMF3 enhances CD4+ T-cell sensitivity to IL-2 and favors regulatory T-cell polarization in systemic lupus erythematosus

Signaling lymphocytic activation molecule family 3 (SLAMF3/Ly9) is a coregulatory molecule implicated in T-cell activation and differentiation. Systemic lupus erythematosus (SLE) is characterized by aberrant T-cell activation and compromised IL-2 production, leading to abnormal regulatory T-cell (Treg) development/function. Here we show that SLAMF3 functions as a costimulator on CD4(+) T cells and influences IL-2 response and T helper cell differentiation. SLAMF3 ligation promotes T-cell responses to IL-2 via up-regulation of CD25 in a small mothers against decapentaplegic homolog 3 (Smad3)-dependent mechanism. This augments the activation of the IL-2/IL-2R/STAT5 pathway and enhances cell proliferation in response to exogenous IL-2. SLAMF3 costimulation promotes Treg differentiation from naïve CD4(+) T cells. Ligation of SLAMF3 receptors on SLE CD4(+) T cells restores IL-2 responses to levels comparable to those seen in healthy controls and promotes functional Treg generation. Taken together, our results suggest that SLAMF3 acts as potential therapeutic target in SLE patients by augmenting sensitivity to IL-2.

Epigenetic silencing of the MUPCDH gene as a possible prognostic biomarker for cyst growth in ADPKD

Although autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease, and is characterized by the formation of multiple fluid-filled cysts, which results in renal failure, early diagnosis and treatment of ADPKD have yet to be defined. Herein, we observed that the promoter region of the gene encoding mucin-like protocadherin (MUPCDH) was hypermethylated in the renal tissue of patients with ADPKD compared to non-ADPKD controls. Inversely, MUPCDH was significantly repressed in ADPKD, especially in cyst-lining cells. Our results indicate that aberrant methylation of MUPCDH promoter CpG islands may be negatively correlated with reduced expression level of MUPCDH and that this contributes to abnormal cell proliferation in ADPKD. It suggests that methylation status of MUPCDH promoter can be used as a novel epigenetic biomarker and a therapeutic target in ADPKD.

Galectin-9-CD44 interaction enhances stability and function of adaptive regulatory T cells

The β-galactoside-binding protein galectin-9 is critical in regulating the immune response, but the mechanism by which it functions remains unclear. We have demonstrated that galectin-9 is highly expressed by induced regulatory T cells (iTreg) and was crucial for the generation and function of iTreg cells, but not natural regulatory T (nTreg) cells. Galectin-9 expression within iTreg cells was driven by the transcription factor Smad3, forming a feed-forward loop, which further promoted Foxp3 expression. Galectin-9 increased iTreg cell stability and function by directly binding to its receptor CD44, which formed a complex with transforming growth factor-β (TGF-β) receptor I (TGF-βRI), and activated Smad3. Galectin-9 signaling was further found to regulate iTreg cell induction by dominantly acting through the CNS1 region of the Foxp3 locus. Our data suggest that exogenous galectin-9, in addition to being an effector molecule for Treg cells, acts synergistically with TGF-β to enforce iTreg cell differentiation and maintenance.

Interleukin-2 at the crossroads of effector responses, tolerance, and immunotherapy

Interleukin-2 (IL-2) is a pleiotropic cytokine produced after antigen activation that plays pivotal roles in the immune response. Discovered as a T cell growth factor, IL-2 additionally promotes CD8(+) T cell and natural killer cell cytolytic activity and modulates T cell differentiation programs in response to antigen, promoting naïve CD4(+) T cell differentiation into T helper 1 (Th1) and T helper 2 (Th2) cells while inhibiting T helper 17 (Th17) and T follicular helper (Tfh) cell differentiation. Moreover, IL-2 is essential for the development and maintenance of T regulatory cells and for activation-induced cell death, thereby mediating tolerance and limiting inappropriate immune reactions. In this review, we focus on the molecular mechanisms and complex cellular actions of IL-2, its cooperative and opposing effects with other cytokines, and how both promoting and blocking the actions of IL-2 are being utilized in clinical medicine.

Accessible chromatin structure permits factors Sp1 and Sp3 to regulate human TGFBI gene expression

Transforming growth factor beta 1-induced (TGFBI) protein is an extracellular matrix (ECM) protein that is associated with other ECM proteins and functions as a ligand for various types of integrins. In this study, we investigated how human TGFBI expression is regulated in lung and breast cancer cells. We observed that the TGFBI promoter in A549 and MBA-MD-231 cells, which constitutively express TGFBI, existed in an open chromatin conformation associated with transcriptionally permissive histone modifications. Moreover, we found that TGFBI expression required Sp1 transcription elements that can bind transcription factors Sp1 and Sp3 in vitro. Occupancy of the TGFBI promoter by Sp1 and Sp3 in vivo was only observed in TGFBI-expressing cells, indicating that open chromatin conformation might facilitate the binding of Sp1 and Sp3 to the TGFBI promoter region. TGFBI promoter activity was impaired when Sp1 elements were mutated, but was increased when Sp1 or Sp3 factors was overexpressed. Furthermore, Sp1 inhibition in vivo by mithramycin A, as well as knockdown of Sp1 and/or Sp3 expression by short interfering RNA, significantly reduced TGFBI mRNA and protein levels. Thus, our data demonstrated that the expression of TGFBI is well correlated with chromatin conformation at the TGFBI promoter, and that factors Sp1 and Sp3 are the primary determinants for the control of constitutive expression of TGFBI gene.

Interleukin (IL)-10 induced by CD11b(+) cells and IL-10-activated regulatory T cells play a role in immune modulation of mesenchymal stem cells in rat islet allografts

Mesenchymal stem cells (MSCs) are suggested to be immune modulators because of their therapeutic potential in transplantation. In the present study, we evaluated the therapeutic potential of autologous MSCs for preventing graft rejection after allogeneic rat islet transplantation. We assessed the ability of MSCs to elicit an antiproliferative response in alloreactive lymphocytes and tested the immunosuppressive effect of MSCs in allogeneic islet transplantation. In islet allotransplantation, injection of autologous MSCs or a subtherapeutic dose of cyclosporine A (CsA; 5 mg/kg) alone did not prolong allograft survival. However, graft survival was attained for >100 d in 33% of autologous MSC-plus-CsA-treated recipients, indicating that graft acceptance was achieved in a subgroup of allograft recipients. Splenocytes from autologous MSC-plus-CsA-treated rats exhibited a reduced mixed lymphocyte reaction (MLR)-proliferative response to donor stimulators and increased interleukin (IL)-10 release. Interestingly, after excluding host CD11b(+) cells, splenic T cells from autologous MSC-plus-CsA-treated rats did not produce IL-10 or did not inhibit proliferative responses under the same conditions. The use of autologous MSC-plus-CsA downregulated immune responses, inducing donor-specific T-cell hyporesponsiveness by reducing the production of proinflammatory cytokines and inducing antiinflammatory cytokine production, especially that of IL-10, during the early posttransplantation period. T-regulatory cells made a contribution at a later phase. In conclusion, the combined use of autologous MSCs and low-dose CsA exerted a synergistic immunosuppressive effect in an islet allograft model, suggesting a role for autologous MSCs as an immune modulator.

Transforming growth factor beta 1 (TGF-beta1) and rapamycin synergize to effectively suppress human T cell responses via upregulation of FoxP3+ Tregs

BACKGROUND

The major obstacle faced by patients with type 1 diabetes who undergo islet transplantation is a gradual decline in insulin independence. This decline may reflect alloimmune rejection, autoimmune recurrence and toxicity of drugs such as rapamycin to islet beta cells. Thus, there is a pressing need to refine immunosuppressive protocols in order to reduce toxicity to islet grafts and yet prevent rejection. Recent studies demonstrated that TGF-beta1 is a critical cytokine for the regulation of immune responses. In naive T cells, TGF-beta1 induces FoxP3(+) regulatory T cells and thus could promote transplant tolerance. In this study, in vitro experiments were performed to determine whether TGF-beta1 could synergize with low-dose rapamycin and inhibit T cell activation and production of inflammatory cytokines, as well as enhance FoxP3 expression for potential application in islet transplantation.

METHODS

Human peripheral blood mononuclear cells were stimulated with either anti-CD3/CD28 or anti-CD3 during TGF-beta1 and rapamycin treatment.

RESULTS

TGF-beta1 inhibited T cell proliferation induced with anti-CD3 stimulation, but not with anti-CD3/CD28 stimulation. The combination of these reagents produced a synergistic inhibition of T cell proliferation induced with both anti-CD3/CD28 and anti-CD3 stimulations. Moreover, TGF-beta1 and rapamycin significantly suppressed cytokine production and induced regulatory T cells by upregulating FoxP3 expression.

CONCLUSIONS

These results suggest that the combination of TGF-beta1 and low-dose rapamycin can potently inhibit T cell responses in vivo and would be beneficial in supporting islet graft survival by limiting toxicity and preventing immune rejection.

CD4+ T cell-derived IL-2 signals during early priming advances primary CD8+ T cell responses

Stimulating naïve CD8⁺ T cells with specific antigens and costimulatory signals is insufficient to induce optimal clonal expansion and effector functions. In this study, we show that the activation and differentiation of CD8⁺ T cells require IL-2 provided by activated CD4⁺ T cells at the initial priming stage within 0–2.5 hours after stimulation. This critical IL-2 signal from CD4⁺ cells is mediated through the IL-2Rβγ of CD8⁺ cells, which is independent of IL-2Rα. The activation of IL-2 signaling advances the restriction point of the cell cycle, and thereby expedites the entry of antigen-stimulated CD8⁺ T-cell into the S phase. Besides promoting cell proliferation, IL-2 stimulation increases the amount of IFNγ and granzyme B produced by CD8⁺ T cells. Furthermore, IL-2 at priming enhances the ability of P14 effector cells generated by antigen activation to eradicate B16.gp33 tumors in vivo. Therefore, our studies demonstrate that a full CD8⁺ T-cell response is elicited by a critical temporal function of IL-2 released from CD4⁺ T cells, providing mechanistic insights into the regulation of CD8⁺ T cell activation and differentiation.

Signaling cross-talk between TGF-beta/BMP and other pathways

Transforming growth factor-beta (TGF-beta)/bone morphogenic protein (BMP) signaling is involved in the vast majority of cellular processes and is fundamentally important during the entire life of all metazoans. Deregulation of TGF-beta/BMP activity almost invariably leads to developmental defects and/or diseases, including cancer. The proper functioning of the TGF-beta/BMP pathway depends on its constitutive and extensive communication with other signaling pathways, leading to synergistic or antagonistic effects and eventually desirable biological outcomes. The nature of such signaling cross-talk is overwhelmingly complex and highly context-dependent. Here we review the different modes of cross-talk between TGF-beta/BMP and the signaling pathways of Mitogen-activated protein kinase, phosphatidylinositol-3 kinase/Akt, Wnt, Hedgehog, Notch, and the interleukin/interferon-gamma/tumor necrosis factor-alpha cytokines, with an emphasis on the underlying molecular mechanisms.

Combinatorial patterns of histone acetylations and methylations in the human genome

Histones are characterized by numerous posttranslational modifications that influence gene transcription. However, because of the lack of global distribution data in higher eukaryotic systems, the extent to which gene-specific combinatorial patterns of histone modifications exist remains to be determined. Here, we report the patterns derived from the analysis of 39 histone modifications in human CD4(+) T cells. Our data indicate that a large number of patterns are associated with promoters and enhancers. In particular, we identify a common modification module consisting of 17 modifications detected at 3,286 promoters. These modifications tend to colocalize in the genome and correlate with each other at an individual nucleosome level. Genes associated with this module tend to have higher expression, and addition of more modifications to this module is associated with further increased expression. Our data suggest that these histone modifications may act cooperatively to prepare chromatin for transcriptional activation.

The biology of interleukin-2

Much data support an essential role for interleukin (IL)-2 in immune tolerance. This idea is much different from the early paradigm in which IL-2 is central for protective immune responses. This change in thinking occurred when a T regulatory cell defect was shown to be responsible for the lethal autoimmunity associated with IL-2/IL-2R deficiency. This realization allowed investigators to explore immune responses in IL-2-nonresponsive mice rendered autoimmune-free. Such studies established that IL-2 sometimes contributes to optimal primary immune responses, but it is not mandatory. Emerging findings, however, suggest an essential role for IL-2 in immune memory. Here, the current understanding of the dual role of IL-2 in maintaining tolerance and contributing to immunity in vivo is reviewed with some emphasis on T regulatory cell production and homeostasis. Also discussed are implications of this new appreciation concerning the immunobiology of IL-2 with respect to targeting IL-2 or its receptor in immunotherapy.

TGF-beta inhibits IL-2 production and promotes cell cycle arrest in TCR-activated effector/memory T cells in the presence of sustained TCR signal transduction

TGF-beta signaling is critical for controlling naive T cell homeostasis and differentiation; however, the biological and biochemical changes induced by TGF-beta in effector/memory T cells are poorly defined. We show that although TGF-beta inhibits effector/memory peripheral blood T lymphoblast proliferation and IL-2 production, the intensity and kinetics for TCR-induced global tyrosine phosphorylation are markedly increased compared with that in untreated cells or naive T cells. After TCR ligation, tyrosine phosphorylation of proximal tyrosine kinases and docking proteins like linker for activation of T cells is maintained for >30 min in TGF-beta-primed cells compared with untreated cells where phosphorylation of these targets returned to basal levels by 10 min. Extended phosphorylation of linker for activation of T cells in treated peripheral blood T selectively prolongs ERK 1/2 signaling and phospholipase C-gamma1 activation leading to increased Ca(2+) flux. A kinase/phosphatase imbalance could not account for extended phosphorylation as CD45R, SHP-1, and SHP-2 expression remains unaltered. The contradiction between prolonged signal transduction and inhibition of proliferation is partially explained by the observation that TGF-beta priming results in ERK 1/2-independent p21 induction and decreased cyclin D1 expression leading to accumulation of T cells in G(0)/G(1) phases of the cell cycle and cell cycle arrest. Despite inhibition of T cell function by TGF-beta priming, TCR and cytokine signaling pathways are intact and selectively extended, suggesting that suppression in the effector/memory T cell is mediated by reprogramming signal transduction, rather than its inhibition as in the naive T cell.

'Yin-Yang' functions of transforming growth factor-beta and T regulatory cells in immune regulation

Transforming growth factor-beta (TGF-beta) and forkhead box p3-expressing T-regulatory (Treg) cells are critical in maintaining self-tolerance and immune homeostasis. The immune suppressive functions of TGF-beta and Treg cells are widely acknowledged and extensively studied. Nonetheless, recent studies revealed the positive roles of TGF-beta and Treg cells in shaping the immune system and the inflammatory responses. This review discusses our and other's efforts in understanding the negative (Yin) as well as the positive (Yang) roles for TGF-beta and Treg cells in immune regulation.

CREB/ATF-dependent T cell receptor-induced FoxP3 gene expression: a role for DNA methylation

Regulatory T cells (T reg cells) are a population of CD4⁺ T cells that limit immune responses. FoxP3 is a master control transcription factor for development and function of these cells, but its regulation is poorly understood. We have identified a T cell receptor–responsive enhancer in the FoxP3 first intron that is dependent on a cyclic-AMP response element binding protein (CREB)/activating transcription factor (ATF) site overlapping a CpG island. Methylation of this island inversely correlates with CREB binding and FoxP3 expression. Interestingly, transforming growth factor-β, which induces T reg cell formation, decreases methylation of the CpG island and increases FoxP3 expression. Similarly, inhibiting methylation with 5-azacytidine or knocking down the DNA methyltransferase Dnmt1 also induces FoxP3 expression. Conversely, methylation of the CpG island, which decreases CREB binding or expression of dominant-negative CREB, decreases FoxP3 gene expression. Thus, T cell receptor–induced FoxP3 expression in T reg cells is controlled both by sequence-specific binding of CREB/ATF and by DNA methylation of a CpG island.

CD28 costimulation overcomes transforming growth factor-beta-mediated repression of proliferation of redirected human CD4+ and CD8+ T cells in an antitumor cell attack

The T-cell-mediated antitumor immune response is frequently repressed in the tumor environment by an immunologic barrier, the predominant mediators of which are thought to be interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta). We explored the effect of these cytokines on the individual T-cell effector functions on antigen engagement during an antitumor cell attack. Isolated CD4+ and CD8+ T cells were antigen-specifically redirected toward carcinoembryonic antigen (CEA)-positive tumor cells by expression of a recombinant T-cell receptor (immunoreceptor), which triggers T-cell activation via CD3zeta on binding to CEA. Immunoreceptor-activated T cells secrete IFN-gamma, proliferate, and lyse CEA+ but not CEA- tumor cells. Whereas IL-10 has no direct effect on immunoreceptor-triggered effector functions, TGF-beta represses proliferation of both CD4+ and CD8+ T cells but neither IFN-gamma secretion nor specific cytolytic activities. CD28 costimulation, however, overcomes TGF-beta-mediated repression in T-cell proliferation. Consequently, T cells redirected by a combined CD28-CD3zeta signaling immunoreceptor are largely resistant to TGF-beta-mediated repression. This is reflected in vivo by a more pronounced antitumor activity of T cells against TGF-beta-secreting tumors when redirected by a costimulatory CD28-CD3zeta than by a CD3zeta signaling immunoreceptor.

IL-2 is essential for TGF-beta to convert naive CD4+CD25- cells to CD25+Foxp3+ regulatory T cells and for expansion of these cells

IL-2 and TGF-beta both have important roles in the induction and maintenance of immunologic tolerance, but whether these cytokines act separately or together to achieve this effect is poorly understood. Although others have reported that IL-2 can directly enhance forkhead box protein P3 (Foxp3) transcription factor expression by natural CD4(+)CD25(+) regulatory T cells, in this study, we report that the role of IL-2 on the generation of peripheral regulatory CD4(+) cells is indirect. Ab neutralization studies and experiments with IL-2-deficient mice have revealed that IL-2 is required for TGF-beta to induce naive CD4(+)CD25(-) cells to become CD25(+) and express Foxp3, and develop the characteristic properties of CD4(+)CD25(+) regulatory cells. This effect of IL-2 on the generation and expansion of these adaptive Foxp3(+) regulatory cells is nonredundant, but IL-4, IL-7, and IL-15, other common gamma-chain cytokines, could sustain Foxp3 expression. Because subjects with autoimmune diseases often have defects in the production of IL-2 and/or TGF-beta, the generation of autologous T regulatory cells ex vivo with these cytokines for transfer in vivo may have considerable therapeutic potential.

Transforming growth factor-beta in cancer and metastasis

Transforming growth factor-beta (TGF-beta) is a multifunctional regulatory polypeptide that is the prototypical member of a large family of cytokines that controls many aspects of cellular function, including cellular proliferation, differentiation, migration, apoptosis, adhesion, angiogenesis, immune surveillance, and survival. The actions of TGF-beta are dependent on several factors including cell type, growth conditions, and the presence of other polypeptide growth factors. One of the biological effects of TGF-beta is the inhibition of proliferation of most normal epithelial cells using an autocrine mechanism of action, and this suggests a tumor suppressor role for TGF-beta. Loss of autocrine TGF-beta activity and/or responsiveness to exogenous TGF-beta appears to provide some epithelial cells with a growth advantage leading to malignant progression. This suggests a pro-oncogenic role for TGF-beta in addition to its tumor suppressor role. During the early phase of epithelial tumorigenesis, TGF-beta inhibits primary tumor development and growth by inducing cell cycle arrest and apoptosis. In late stages of tumor progression when tumor cells become resistant to growth inhibition by TGF-beta due to inactivation of the TGF-beta signaling pathway or aberrant regulation of the cell cycle, the role of TGF-beta becomes one of tumor promotion. Resistance to TGF-beta-mediated inhibition of proliferation is frequently observed in multiple human cancers, as are various alterations in the complex TGF-beta signaling and cell cycle pathways. TGF-beta can exert effects on tumor and stromal cells as well as alter the responsiveness of tumor cells to TGF-beta to stimulate invasion, angiogenesis, and metastasis, and to inhibit immune surveillance. Because of the dual role of TGF-beta as a tumor suppressor and pro-oncogenic factor, members of the TGF-beta signaling pathway are being considered as predictive biomarkers for progressive tumorigenesis, as well as molecular targets for prevention and treatment of cancer and metastasis.

The roles for cytokines in the generation and maintenance of regulatory T cells

As an essential mechanism for self-tolerance, immune suppression has attracted much attention since the discovery of suppressor T cells, now called regulatory T cells (Tregs), in the 1990s. Different types of Tregs have been described based on distinct expression patterns of surface markers and cytokines. Cytokines are not only essential for function but also important for the generation of Tregs. Interleukin-2 (IL-2), transforming growth factor-beta, IL-10, and other immunoregulatory molecules have been shown to control the generation of Tregs. The presence of other types of cells, in particular antigen-presenting cells (APCs), is critical for the generation of Tregs. Cytokines can serve as either initiators or intermediates for the interactions between APCs and Tregs. This review discusses our current knowledge of how cytokines regulate the generation and maintenance of Tregs.

Both integrated and differential regulation of components of the IL-2/IL-2 receptor system

Interleukin-2 was discovered in 1976 as a T-cell growth factor. It was the first type I cytokine cloned and the first for which a receptor component was cloned. Its importance includes its multiple actions, therapeutic potential, and lessons for receptor biology, with three components differentially combining to form high, intermediate, and low-affinity receptors. IL-2Ralpha and IL-2Rbeta, respectively, are markers for double-negative thymocytes and regulatory T-cells versus memory cells. gamma(c), which is shared by six cytokines, is mutated in patients with X-linked severe-combined immunodeficiency. We now cover an under-reviewed area-the regulation of genes encoding IL-2 and IL-2R components, with an effort to integrate/explain this knowledge.

TGF-beta requires CTLA-4 early after T cell activation to induce FoxP3 and generate adaptive CD4+CD25+ regulatory cells

Although positive CD28 costimulation is needed for the generation of natural CD4+CD25+ regulatory T cells, we report that negative CTLA-4 costimulation is necessary for generating phenotypically and functionally similar adaptive CD4+CD25+ suppressor cells. TGF-beta could not induce CD4+CD25- cells from CTLA-4(-/-) mice to express normal levels of FoxP3 or to develop suppressor activity. Moreover, blockade of CTLA-4 following activation of wild-type CD4+ cells abolished the ability of TGF-beta to induce FoxP3-expressing mouse suppressor cells. TGF-beta accelerated expression of CTLA-4, and time course studies suggested that CTLA-4 ligation of CD80 shortly after T cell activation enables TGF-beta to induce CD4+CD25- cells to express FoxP3 and develop suppressor activity. TGF-beta also enhanced CD4+ cell expression of CD80. Thus, CTLA-4 has an essential role in the generation of acquired CD4+CD25+ suppressor cells in addition to its other inhibitory effects. Although natural CD4+CD25+ cells develop normally in CTLA-4(-/-) mice, the lack of TGF-beta-induced, peripheral CD4+CD25+ suppressor cells in these mice may contribute to their rapid demise.