Use of Foxp3-positive (Foxp3+) T-regulatory (Treg) cells as potential cellular therapy in patients with autoimmunity, or post-stem cell or -organ transplantation, requires a sound understanding of the transcriptional regulation of Foxp3. Conserved CpG dinucleotides in the Treg-specific demethylation region (TSDR) upstream of Foxp3 are demethylated only in stable, thymus-derived Foxp3+ Treg cells. Since methyl-binding domain (Mbd) proteins recruit histone-modifying and chromatin-remodeling complexes to methylated sites, we tested whether targeting of Mbd2 might promote demethylation of Foxp3 and thereby promote Treg numbers or function. Surprisingly, while chromatin immunoprecipitation (ChIP) analysis showed Mbd2 binding to the Foxp3-associated TSDR site in Treg cells, Mbd2 targeting by homologous recombination, or small interfering RNA (siRNA), decreased Treg numbers and impaired Treg-suppressive function in vitro and in vivo. Moreover, we found complete TSDR demethylation in wild-type (WT) Treg cells but >75% methylation in Mbd2−/− Treg cells, whereas reintroduction of Mbd2 into Mbd2-null Treg cells restored TSDR demethylation, Foxp3 gene expression, and Treg-suppressive function. Lastly, thymic Treg cells from Mbd2−/− mice had normal TSDR demethylation, but compared to WT Treg cells, peripheral Mbd2−/− Treg cells had a marked impairment of binding of Tet2, the DNA demethylase enzyme, at the TSDR site. These data show that Mbd2 has a key role in promoting TSDR demethylation, Foxp3 expression, and Treg-suppressive function.
Foxp3+ T-regulatory (Treg) cells maintain immune homeostasis and limit autoimmunity, but can also curtail host immune responses to various types of tumors1,2. Foxp3+ Tregs are therefore considered promising targets to enhance anti-tumor immunity, and efforts are underway to develop approaches for their therapeutic modulation. However, while studies showing that Foxp3+ Treg depletion experimentally can enhance anti-tumor responses provide proof-of-principle, they lack clear translational potential and have various shortcomings. Histone/protein acetyltransferases (HATs) promote chromatin accessibility, gene transcription and the function of multiple transcription factors and non-histone proteins3,4. We now report that conditional deletion or pharmacologic inhibition of one HAT, p300 (Ep300, KAT3B), in Foxp3+ Tregs, increased TCR-induced apoptosis in Tregs, impaired Treg suppressive function and peripheral Treg induction, and limited tumor growth in immunocompetent, but not in immunodeficient, hosts. Our data thereby demonstrate that p300 is important for Foxp3+ Treg function and homeostasis in vivo and in vitro, and identify novel mechanisms by which appropriate small molecule inhibitors can diminish Treg function without overtly impairing T-effector (Teff) cell responses or inducing autoimmunity. Collectively, these data suggest a new approach for cancer immunotherapy.
In a cross-sectional study, we assessed effects of calcineurin inhibitor (CNI) or rapamycin on T-regulatory (Treg) cells from children with stable liver (n=53) or kidney (n=9) allografts several years post-transplant. We analyzed Treg number, phenotype, suppressive function, and methylation at the Treg-specific demethylation region (TSDR) using Tregs and peripheral blood mononuclear cells. 48 patients received CNI (39 as monotherapy) and 12 patients received rapamycin (9 as monotherapy). Treg numbers diminished over time on either regimen, but reached significance only with CNI (r=−0.424, p=0.017). CNI levels inversely correlated with Treg number (r=−0.371, p=0.026), and positively correlated with CD127+ expression by Tregs (r=0.437, p=0.023). Patients with CNI levels >3.6 ng/ml had weaker Treg function than those with levels <3.6 ng/ml, whereas rapamycin therapy positively correlated with Treg numbers (r=0.628, p=0.029) and their expression of CTLA4 (r=0.726, p=0.041). Overall, CTLA4 expression, TSDR demethylation and an absence of CD127 were important for Treg suppressive function. We conclude that rapamycin has beneficial effects on Treg biology, whereas long-term and high dose CNI use may impair Treg number, function and phenotype, potentially acting as a barrier to attaining host hyporesponsiveness to an allograft.
Immunosuppression; immunoregulation; clinical transplantation
Pirfenidone (PFD) is an anti-fibrotic agent with beneficial effects upon proinflammatory disorders. In this study, we further investigated PFD and long acting form, “deuterated (d)PFD” immune modulating properties by evaluating their effects on mouse dendritic cells (DCs).
The effects of PFD upon DCs were examined in vivo using an orthotopic mouse lung transplant model and in vitro utilizing isolated bone marrow derived DCs in response to lipopolysaccharide and allogeneic stimulation.
In mouse lung transplants, PFD and dPFD treatment improved allograft lung function based on peak airway pressure, less infiltrates/consolidation on microCT scan imaging, and reduced lung rejection/injury. DC activation from lung allografts was suppressed with PFD and there appeared to be a greater effect of PFD upon CD11c+CD11b−CD103+ lung DCs. In addition, PFD reduced the expression of a number of proinflammatory cytokines/chemokines from lung allografts. In vitro, DCs treated with PFD showed decreased expression of MHC class II and co-stimulatory molecules and impaired DC’s capacity to stimulate T cell activation while antigen uptake was preserved. PFD directly inhibited the release of inflammatory cytokines from isolated DCs, and was associated with a reduction of stress protein kinases and attenuated LPS-dependent MAPKp38 phosphorylation.
PFD has lung allograft protective properties and in addition to its known effects on T cell biology, PFD’s immune modulating activities encompass inhibitory effects upon DC activation and function.
pirfenidone; lung transplantation; dendritic cell; acute rejection; mouse
Lysine ε-acetylation is a post-translational modification that alters the biochemical properties of many proteins. The reaction is catalyzed by histone/protein acetyltransferases (HATs), and is reversed by histone/protein deacetylases (HDACs). As a result, HATs and HDACs constitute an important, though little recognized, set of proteins that control the functions of T-regulatory (Treg) cells. Targeting certain HDACs, especially HDAC6, HDAC9, and Sirtuin-1 (Sirt1), can augment Treg suppressive potency by several distinct and potentially additive mechanisms. These involve promoting Forkhead box p3 (Foxp3) gene expression and preserving Foxp3 lysine ε-acetylation, which infers resistance to ubiquitination and proteasomal degradation, and increases DNA binding. Moreover, depleting certain HDAC can enhance the heat shock response, which increases the tenacity of Treg to survive under stress, and helps preserve a suppressive phenotype. As a result, HDAC inhibitor therapy can be used to enhance Treg functions in vivo and have beneficial effects on allograft survival and autoimmune diseases.
transplantation; immunotherapy; HDAC6; HDAC9; Sirt1
BACKGROUND & AIMS
Foxp3+ T regulatory cells (Tregs) help prevent autoimmunity, and increases in their numbers of functions could decrease the development of inflammatory bowel disease. Like other cells, Foxp3+ Tregs express histone/protein deacetylases (HDACs), which regulate chromatin remodeling and gene expression. We investigated whether disruption of a specific class IIa HDAC, HDAC9, activity in Tregs affects the pathogenesis of colitis in mice.
We tested the effects of various HDAC inhibitors (HDACi) in models of colitis using wild-type mice. We also transferred Tregs and non-Treg cells from HDAC9−/− or wild-type mice to immunodeficient mice. HDAC9 contributions to the functions of Tregs were determined during development and progression of colitis.
Pan-HDACi, but not class I-specific HDACi, increased the functions of Foxp3+ Tregs, prevented colitis, and reduced established colitis in mice, indicating the role of class II HDACs in controlling Treg function. The abilities of pan-HDACi to prevent/reduce colitis were associated with increased numbers of Foxp3+ Tregs and their suppressive functions. Colitis was associated with increased local expression of HDAC9; HDAC9−/− mice resistant to development of colitis. HDAC9−/− Tregs expressed increased levels of the heat shock protein (HSP) 70, compared with controls. Immunoprecipitation experiments indicated an interaction between HSP70 and Foxp3. Inhibition of HSP70 reduced the suppressive functions of HDAC9−/− Tregs; Tregs that overexpressed HSP70 had increased suppressive functions.
Strategies to decrease HDAC9 expression or function in Tregs or to increase expression of HSP70 might be used to treat colitis and other autoimmune disorders.
Histone/protein deacetylases (HDACs) decrease histone and protein acetylation, typically leading to suppression of gene transcription and modulation of various protein functions. We found significant differences in expression of HDAC before and after stimulation of human T regulatory (Treg) and T effector cells, suggesting the potential for future selective targeting of Tregs with HDAC inhibitors (HDACi). Use of various HDACi small molecules enhanced, by up to 4.5-fold (average 2-fold), the suppressive functions of both freshly isolated and expanded human Tregs, consistent with our previous murine data. HDACi use increased Treg expression of CTLA-4, a key negative regulator of immune response, and we found a direct and significant correlation between CTLA-4 expression and Treg suppression. Hence, HDACi compounds are promising pharmacologic tools to increase Treg suppressive functions, and this action may potentially be of use in patients with autoimmunity or post-transplantation.
We previously showed that pirfenidone, an anti-fibrotic agent, reduces lung allograft injury/rejection. In this study, we tested the hypothesis that pirfenidone has immune modulating activities and evaluated its effects on the function of T cell subsets, which play important roles in allograft rejection.
We first evaluated whether pirfenidone alters T cell proliferation and cytokine release in response to T cell receptor (TCR) activation, and whether pirfenidone alters regulatory T cells (CD4+CD25+) suppressive effects using an in vitro assay. Additionally, pirfenidone effects on alloantigen-induced T cell proliferation in vivo were assessed by adoptive transfer of CFSE-labeled T cells across a parent->F1 MHC mismatch, as well as using a murine heterotopic cardiac allograft model (BALB/c->C57BL/6).
Pirfenidone was found to inhibit the responder frequency of TCR-stimulated CD4+ cell total proliferation in vitro and in vivo, whereas both CD4 and CD8 proliferation index were reduced by pirfenidone. Additionally, pirfenidone inhibited TCR-induced production of multiple pro-inflammatory cytokines and chemokines. Interestingly, there was no change on TGF-β production by purified T cells, and pirfenidone had no effect on the suppressive properties of naturally occurring regulatory T cells. Pirfenidone alone showed a small but significant (p < 0.05) effect on the in vivo allogeneic response while the combination of pirfenidone and low dose rapamycin had more remarkable effect in reducing the alloantigen response with prolonged graft survival.
Pirfenidone may be an important new agent in transplantation, with particular relevance to combating chronic rejection by inhibiting both fibroproliferative and alloimmune responses.
rodent; T cells; transplantation
Cellular proliferation in response to mitogenic stimuli is negatively regulated by the Cip/Kip and the Ink4 families of cyclin-dependent kinase (CDK) inhibitors. Several of these proteins are elevated in anergic T cells, suggesting a potential role in the induction or maintenance of tolerance. Our previous studies showed that p27kip1 is required for the induction of T cell anergy and transplantation tolerance by costimulatory blockade, but a role for Ink4 proteins in these processes has not been established. Here we show that CD4+ T cells from mice genetically deficient for p18ink4c divide more rapidly than wild-type cells in response to antigenic, costimulatory and growth factor signals. However, this gain of proliferative function was accompanied by a moderate increase in the rate of cell death, and was accompanied by an overall defect in the generation of alloreactive IFNγ-producing effector cells. Consistent with this, p18ink4c-deficient T cells were unable to induce graft-vs-host disease in vivo, and p18ink4c deficiency cooperated with costimulatory blockade to significantly increase the survival of fully mismatched allografts in a cardiac transplantation model. While both p18ink4c and p27kip1 act to restrict T cell proliferation, p18ink4c exerts an opposite effect from p27kip1 on alloimmunity and organ transplant rejection, most likely by sustaining T cell survival and the development of effector function. Our studies point to additional important links between the cell cycle machinery and the processes of T cell differentiation, survival and tolerance.
Summary of recent advances
Simply detecting the presence or absence of Foxp3, a transcription factor characteristic of naturally occurring CD4+ CD25+ regulatory T cells (Tregs), now appears of minimal value in predicting the outcome of immunologic responses, since dividing human CD4+ effector T cells can induce Foxp3 without attaining repressive functions, and additional molecular interactions, as well epigenetic events, affect Foxp3-dependent Treg functions in humans and mice. Experimentally, in vivo and in vitro studies show histone deacetylase inhibitors (HDACi) can enhance the numbers and suppressive function of regulatory T cells (Tregs), by promoting Foxp3+ cell production, enhancing chromatin remodeling within Tregs, and inducing acetylation of Foxp3 protein itself. Human studies consistent with a role for HDACi in controlling Fox3-dependent Treg functions are also available. We review these molecular interactions and how they may be exploited therapeutically to enhance Treg-dependent functions, including post-transplantation.
Adaptive immunity requires signals from both the T cell antigen receptor and the costimulatory molecule CD28. These receptors activate multiple signaling pathways, including the cyclin-dependent kinase (CDK) cascade, and antigenic signals in the absence of costimulation results in a tolerant state that is enforced by the CDK inhibitory protein p27kip1. We find that CDK2, the major target of p27kip1, is highly active in T cells that infiltrate and reject cardiac allografts. To determine whether CDK2 is required for T cell alloimmunity, we utilized mice genetically deficient for CDK2. Blockade of CD28 costimulation alone was unable to inhibit the rejection of cardiac allografts by wild-type recipients, however, targeting this pathway in CDK2-deficient recipients led to long-term allograft survival. CDK2-deficient CD4+ T cells proliferated normally in response to stimulation in vitro and in vivo, however, genetic, shRNA, or small molecule-mediated antagonism of CDK2 resulted in decreased production of IL-2 and IFNγ. In addition, surviving grafts from CDK2-deficient recipients showed increased infiltration of Foxp3+ regulatory T cells (Treg), and Treg from CDK2-deficient mice exhibited increased suppressive activity in vitro and in an in vivo model of inflammatory bowel disease. These data suggest that that p27kip1 promotes peripheral tolerance through its ability to inhibit CDK2, which otherwise acts to promote conventional T cell differentiation and restrict Treg function.
Although certain chemokines and their receptors guide homeostatic recirculation of T cells and others promote recruitment of activated T cells to inflammatory sites, little is known of the mechanisms underlying a third function, migration of Foxp3+ regulatory T (T reg) cells to sites where they maintain unresponsiveness. We studied how T reg cells are recruited to cardiac allografts in recipients tolerized with CD154 monoclonal antibody (mAb) plus donor-specific transfusion (DST). Real-time polymerase chain reaction showed that intragraft Foxp3 levels in tolerized recipients were ∼100-fold higher than rejecting allografts or allografts associated with other therapies inducing prolonged survival but not tolerance. Foxp3+ cells were essential for tolerance because pretransplant thymectomy or peritransplant depletion of CD25+ cells prevented long-term survival, as did CD25 mAb therapy in well-functioning allografts after CD154/DST therapy. Analysis of multiple chemokine pathways showed that tolerance was accompanied by intragraft up-regulation of CCR4 and one of its ligands, macrophage-derived chemokine (CCL22), and that tolerance induction could not be achieved in CCR4−/− recipients. We conclude that Foxp3 expression is specifically up-regulated within allografts of mice displaying donor-specific tolerance, that recruitment of Foxp3-expressing T reg cells to an allograft tissue is dependent on the chemokine receptor, CCR4, and that, in the absence of such recruitment, tolerizing strategies such as CD154 mAb therapy are ineffectual.
The enzyme indoleamine 2,3-dioxygenase (IDO) converts tryptophan into kynurenine metabolites that suppress effector T-cell function. In this study, we investigated IDO and its metabolite, 3-hydroxyanthranilic acid (3HAA), in regulating lung allograft rejection, using a murine orthotopic lung transplant model with a major mismatch (BALB/c donor and C57BL6 recipient). IDO was overexpressed in murine donor lungs, using an established nonviral (polyethylenimine carrier)–based gene transfer approach, whereas 3HAA was delivered daily via intraperitoneal injection. Increased IDO expression or its metabolite, 3HAA, resulted in a remarkable therapeutic effect with near normal lung function and little acute rejection, approximately A1, compared with A3 in untreated allografts (grading based on International Society for Heart and Lung Transplantation guidelines). We found that a high IDO environment for 7 days in lung allografts resulted in impaired T-cell activation, the production of multiple effector cytokines (IL-2, IL-4, IL-5, IL-6, IFN-γ, TNF-α, IL-12, and IL-13), and the generation of effector memory T cells (CD62LloCD44hi phenotype). In isolated murine splenocytes, we observed that IDO/3HAA impaired T-cell receptor (TCR)–mediated T-cell activation, and more importantly, a decrease of intracellular calcium, phospholipase C-γ1 phosphorylation, and mitochondrial mass was evident. This work further illustrates the potential role of a high IDO environment in lung transplantation, and that the high IDO environment directly impairs TCR activation via the disruption of calcium signaling.
3-hydroxyanthranilic acid; lung allograft rejection; nonviral gene transfer
LIGHT (TNFSF14), a tumor necrosis factor superfamily member expressed by activated T cells, binds to herpes virus entry mediator (HVEM) which is constitutively expressed by T cells and costimulates T cell activation in a CD28-independent manner. Given interest in regulating the effector functions of T cells in vivo, we examined the role of LIGHT-HVEM costimulation in a murine cardiac allograft rejection model. Normal hearts lacked LIGHT or HVEM mRNA expression, but allografts showed strong expression of both genes from day 3 after transplant, and in situ hybridization and immunohistology-localized LIGHT and HVEM to infiltrating leukocytes. To test the importance of LIGHT expression on allograft survival, we generated LIGHT−/− mice by homologous recombination. The mean survival of fully major histocompatibility complex–mismatched vascularized cardiac allografts in LIGHT−/− mice (10 days, P < 0.05) or cyclosporine A (CsA)-treated LIGHT+/+ mice (10 days, P < 0.05) was only slightly prolonged compared with LIGHT+/+ mice (7 days). However, mean allograft survival in CsA-treated LIGHT−/− allograft recipients (30 days) was considerably enhanced (P < 0.001) compared with the 10 days of mean survival in either untreated LIGHT−/− mice or CsA-treated LIGHT+/+ controls. Molecular analyzes showed that the beneficial effects of targeting of LIGHT in CsA-treated recipients were accompanied by decreased intragraft expression of interferon (IFN)-γ, plus IFN-γ–induced chemokine, inducible protein-10, and its receptor, CXCR3. Treatment of LIGHT+/+ allograft recipients with HVEM-Ig plus CsA also enhanced mean allograft survival (21 days) versus wild-type controls receiving HVEM-Ig (mean of 7 days) or CsA alone (P < 0.001). Our data suggest that T cell to T cell–mediated LIGHT/HVEM-dependent costimulation is a significant component of the host response leading to cardiac allograft rejection.
transplantation; allograft rejection; T cell activation; costimulation; TNF superfamily
Adoptive immunotherapy using cultured T cells holds promise for the treatment of cancer and infectious disease. Ligands immobilized on surfaces fabricated from hard materials such as polystyrene plastic are commonly employed for T cell culture. The mechanical properties of a culture surface can influence the adhesion, proliferation, and differentiation of stem cells and fibroblasts. We therefore explored the impact of culture substrate stiffness on the ex vivo activation and expansion of human T cells. We describe a simple system for the stimulation of the TCR/CD3 complex and the CD28 receptor using substrates with variable rigidity manufactured from poly(dimethylsiloxane) (PDMS), a biocompatible silicone elastomer. We show that softer (Young’s Modulus [E] < 100 kPa) substrates stimulate an average 4-fold greater IL-2 production and ex vivo proliferation of human CD4+ and CD8+ T cells compared with stiffer substrates (E >2 MPa). Mixed peripheral blood T cells cultured on the stiffer substrates also demonstrate a trend (non-significant) towards a greater proportion of CD62Lneg, effector-differentiated CD4+ and CD8+ T cells. Naïve CD4+ T cells expanded on softer substrates yield an average 3-fold greater proportion of IFN-γ producing TH1-like cells. These results reveal that the rigidity of the substrate used to immobilize T cell stimulatory ligands is an important and previously unrecognized parameter influencing T cell activation, proliferation and TH differentiation. Substrate rigidity should therefore be a consideration in the development of T cell culture systems as well as when interpreting results of T cell activation based upon solid-phase immobilization of TCR/CD3 and CD28 ligands.
T cells; Cell Activation; Cell Proliferation; Cytokines; Human
Although mononuclear cell infiltration is a hallmark of cellular rejection of a vascularized allograft, efforts to inhibit rejection by blocking leukocyte-endothelial cell adhesion have proved largely unsuccessful, perhaps in part because of persistent generation of chemokines within rejecting grafts. We now provide, to our knowledge, the first evidence that in vivo blockade of specific chemokine receptors is of therapeutic significance in organ transplantation. Inbred mice with a targeted deletion of the chemokine receptor CCR1 showed significant prolongation of allograft survival in 4 models. First, cardiac allografts across a class II mismatch were rejected by CCR1+/+ recipients but were accepted permanently by CCR1–/– recipients. Second, CCR1–/– mice rejected completely class I– and class II–mismatched BALB/c cardiac allografts more slowly than control mice. Third, levels of cyclosporin A that had marginal effects in CCR1+/+ mice resulted in permanent allograft acceptance in CCR1–/– recipients. These latter allografts showed no sign of chronic rejection 50–200 days after transplantation, and transfer of CD4+ splenic T cells from these mice to naive allograft recipients significantly prolonged allograft survival, whereas cells from CCR1+/+ mice conferred no such benefit. Finally, both CCR1+/+ and CCR1–/– allograft recipients, when treated with a mAb to CD4, showed permanent engraftment, but these allografts showed florid chronic rejection in the former strain and were normal in CCR1–/– mice. We conclude that therapies to block CCR1/ligand interactions may prove useful in preventing acute and chronic rejection clinically.
During the development of nephrotoxic nephritis (NTN) in the mouse, we find that a variety of chemokines and chemokine receptors are induced: CCR1 (RANTES, MIP-1α), CCR2 (MCP-1), CCR5 (RANTES, MIP-1α, MIP-1β), CXCR2 (MIP-2), and CXCR3 (IP-10). Their timing of expression indicated that CXCR2 and CCR1 are probably important in the neutrophil-dependent heterologous phase of the disease, whereas CCR1, CCR2, CCR5, and CXCR3 accompany the subsequent mononuclear cell infiltration characteristic of autologous disease. We therefore assessed the role of CCR1 in NTN using CCR1–/– mice. We found that neutrophil accumulation in CCR1–/– mice was comparable to that in wild-type animals but that renal recruitment of CD4+ and CD8+ T cells and macrophages increased significantly. Moreover, CCR1–/– mice developed more severe glomerulonephritis than did controls, with greater proteinuria and blood urea nitrogen, as well as a higher frequency of crescent formation. In addition, CCR1–/– mice showed enhanced Th1 immune responses, including titers of antigen-specific IgG2a antibody, delayed-type hypersensitivity responses, and production of IFN-γ and TNF-α. Lastly, using recombinant proteins and transfected cells that overexpressed CCR1, we demonstrated that MIP-1α, but not RANTES, bound CCR1 and induced cell chemotaxis. Thus, rather than simply promoting leukocyte recruitment during NTN, CCR1 expression profoundly alters the effector phase of glomerulonephritis. Therapeutic targeting of chemokine receptors may, on occasion, exacerbate underlying disease.
J. Clin. Invest. 104:1549–1557 (1999).
Therapeutic targeting of histone/protein deacetylase 6 (HDAC6), HDAC9, or the sirtuin-1 (Sirt1) augments the suppressive functions of regulatory T cells (Tregs) that contain the transcription factor Foxp3. However, it is unclear whether distinct mechanisms are involved or whether combined inhibition of these targets would be more beneficial. We compared the suppressive functions of Tregs from wild-type C57BL/6 mice with those from mice with either global (HDAC6−/−, HDAC9−/−, and HDAC6−/−HDAC9−/−), or conditional (fl-Sirt1/CD4-Cre or fl-Sirt1/Foxp3-Cre) HDAC deletion, as well as treatment with isoform-selective HDAC inhibitors. We found that the heat shock response was important for the improvement of Treg suppressive function mediated by HDAC6 inhibition, but not Sirt1 inhibition. Furthermore, although HDAC6, HDAC9, and Sirt1 all deacetylated Foxp3, each protein had diverse effects on transcription factors controlling Foxp3 gene expression. For example, loss of HDAC9 was associated with stabilization of the acetylation of signal transducer and activator of transcription 5 (STAT5) and of its transcriptional activity. Hence, targeting different HDACs increased Treg function by multiple and additive mechanisms, which indicates the therapeutic potential for combinations of HDAC inhibitors in the management of autoimmunity and organ transplantation.
Early allograft dysfunction (EAD) occurring in the first week post-liver transplantation is associated with increased graft failure and mortality and is believed to be largely due to ischemia/reperfusion injury. We anticipated that the presence of EAD would be reflected by alterations in expression of serum proteins associated with an inflammatory response in the peri-operative period, and hypothesized that a specific pattern of expression might correlate with the development of EAD. The serum levels of 25 cytokines, chemokines, and immunoreceptors were measured by Luminex multiplex assays pre- and post-liver transplantation. Levels of each cytokine biomarker were compared in adult recipients with or without EAD at serial time points using samples collected pre-operatively and at 1, 7, 14, and 30 days post-transplant. EAD was defined according to standard criteria as maximum alanine transferase (ALT) or aspartate transferase (AST) levels on days 1–7 of >2000 U/ml, day 7 bilirubin level ≥10 mg/dl, or a day 7 international normalized ratio (INR) ≥1.7. Multivariable analyses showed that patients experiencing EAD had lower pre-operative IL-6 and higher IL-2R levels. Patients with EAD also showed higher MCP-1 (CCL2), IL-8 (CXCL8), and RANTES (CCL5) chemokine levels in the early post-operative period, suggesting up-regulation of the NF-κB pathway, in addition to higher levels of chemokines and cytokines associated with T cell immunity, including Mig (CXCL9), IP-10 (CXCL10) and IL-2R. These findings identify several possible biomarkers and pathways associated with EAD, that may guide future validation studies and investigation of specific cellular and molecular mechanisms of graft dysfunction. Furthermore, if validated, our findings may contribute to perioperative prediction of the occurrence of EAD and ultimately lead to identification of potential interventional therapies.
immune monitoring; multiplex analysis; chemokines; immunobiology
FOXP3 is a key transcription factor for regulatory T cell function. We report the crystal structure of the FOXP3 coiled coil domain, through which a loose or transient dimeric association is formed and modulated, accounting for the activity variations introduced by disease-causing mutations or posttranslational modifications. Structure-guided mutagenesis revealed that FOXP3 coiled coil mediated homo-dimerization is essential for Treg function in vitro and in vivo. In particular, we identified human FOXP3 K250 and K252 as key residues for the conformational change and stability of the FOXP3 dimer, which can be regulated by protein posttranslational modifications such as reversible lysine acetylation. These studies provide structural and mechanistic explanations for certain disease-causing mutations in the coiled coil domain of FOXP3 that are commonly found in IPEX syndrome. Overall the regulatory machinery involving homo-oligomerization, acetylation, and hetero-association has been dissected, defining atomic insights into the biological and pathological characteristics of the FOXP3 complex.
FOXP3; IPEX Syndrome; Dimerization; Acetylation; Complex Assembly
The forkhead box transcription factor, Foxp3, is master regulator of the development and function of CD4+CD25+ T regulatory (Treg) cells that limit autoimmunity and maintain immune homeostasis. The carboxyl-terminal forkhead (FKH) domain is required for the nuclear localization and DNA binding of Foxp3. We assessed how individual FKH lysines contribute to the functions of Foxp3 in Treg cells.
We found that mutation of FKH lysines at position 382 (K17) and at position 393 (K18) impaired Foxp3 DNA binding and inhibited Treg suppressive function in vivo and in vitro. These lysine mutations did not affect the level of expression of Foxp3 but inhibited IL-2 promoter remodeling and had important and differing effects on Treg-associated gene expression.
These data point to complex effects of post-translational modifications at individual lysines within the Foxp3 FKH domain that affect Treg function. Modulation of these events using small molecule inhibitors may allow regulation of Foxp3+ Treg function clinically.
Erythropoiesis, the production of red blood cells, must be tightly controlled to ensure adequate oxygen delivery to tissues without causing thrombosis or stroke. Control of physiologic and pathologic erythropoiesis is dependent predominantly on erythropoietin (EPO), the expression of which is regulated by hypoxia-inducible factor (HIF) activity in response to low oxygen tension. Accumulating evidence indicates that oxygen-independent mediators, including inflammatory stimuli, cytokines, and growth factors, also upregulate HIF activity, but it is unclear whether these signals also result in EPO production and erythropoiesis in vivo. Here, we found that signaling through herpesvirus entry mediator (HVEM), a molecule of the TNF receptor superfamily, promoted HIF-1α activity in the kidney and subsequently facilitated renal Epo production and erythropoiesis in vivo under normoxic conditions. This Epo upregulation was mediated by increased production of NO by renal macrophages. Hvem-deficient mice displayed impaired Epo expression and aggravated anemia in response to erythropoietic stress. These data reveal that HVEM signaling functions to promote HIF-1α activity and Epo production, and thus to regulate erythropoiesis. Furthermore, our findings suggest that this molecular mechanism could represent a therapeutic target for Epo-responsive diseases, including anemia.
Foxp3+ T-regulatory cells (Tregs) are key to immune homeostasis such that their diminished numbers or function can cause autoimmunity and allograft rejection. Foxp3+ Tregs express multiple histone/protein deacetylases (HDACs) that regulate chromatin remodeling, gene expression, and protein function. Pan-HDAC inhibitors developed for oncologic applications enhance Treg production and Treg suppression function but have limited nononcologic utility given their broad actions and various side effects. We show, using HDAC6-deficient mice and wild-type (WT) mice treated with HDAC6-specific inhibitors, that HDAC6 inhibition promotes Treg suppressive activity in models of inflammation and autoimmunity, including multiple forms of experimental colitis and fully major histocompatibility complex (MHC)-incompatible cardiac allograft rejection. Many of the beneficial effects of HDAC6 targeting are also achieved by inhibition of the HDAC6-regulated protein heat shock protein 90 (HSP90). Hence, selective targeting of a single HDAC isoform, HDAC6, or its downstream target, HSP90, can promote Treg-dependent suppression of autoimmunity and transplant rejection.
Regulatory T cells (Tregs) are required for the maintenance of immune homeostasis as first clearly described by Herman Waldmann’s laboratory. Dysfunction of Treg cells also leads to fatal autoimmunity in humans and mice. Conversely, the activation of different classes of Tregs operative systemically and within the cancer microenvironment can suppress host anti-tumor immune responses and promote tumor progression. Therefore, the development of new therapeutic approaches to regulate the activity of Treg cells may have considerable clinical potential.
FOXP3 is the key transcriptional regulator of Treg development and function. The activity of FOXP3 is regulated by acetylation, a process catalyzed by distinct types of histone/protein acetyltransferases (HATs) that regulate the functions of many transcription factors, independently of FOXP3, as well as non-histone proteins, in addition to their effects on chromatin accessibility. Interactions between FOXP3 and these enzymes determine the suppressive function of FOXP3. Clearly, small molecules targeting these enzymes are candidates for the regulation of Treg function in vaccines and tumor therapies.