Forkhead-box transcription factors and their role in the immune system

Immune regulation by Foxo transcription factors

The Foxo subfamily of forkhead (Fox) transcription factors are mammalian homologues of the Caenorhabditis elegans DAF-16 longevity gene, and play key roles in cellular and organism survival, death, proliferation and metabolism. A growing body of evidence indicates that Foxo proteins furthermore play critical roles in immune cell homeostasis, modulating inflammation in some disease states such as inflammatory arthritis and systemic lupus erythematosus (SLE), via fundamental roles in T cells, B cells, neurophils and other myeloid lineages. This review summarizes current knowledge of the Foxo family members in general and in immunity, including their potential use as therapeutic targets.

Role of phosphoinositide 3-kinase signaling in autoimmunity

Activation of the phosphoinositide 3-kinase (PI3K) pathway promotes proliferation and survival in many different cell types of the immune system. PI3K acts downstream of receptors that mediate proliferation and survival in T cells, and required roles for individual class I PI3K catalytic isoforms have been established. Interestingly, mice with either augmented or diminished PI3K activity in T cells develop lymphoproliferation and signs of autoimmunity. Here, we summarize our current knowledge of mouse strains with hyperactive or reduced PI3K, different isoforms of class I PI3K in T cell-mediated immunity and autoimmunity, and the therapeutic implications for modulating this pathway for treatment of various autoimmune diseases.

Histone deacetylase inhibitors and transplantation

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.

Mucosa-associated lymphoid tissue lymphoma: molecular pathogenesis and clinicopathological significance

Mucosa-associated lymphoid tissue (MALT) lymphoma is a low-grade tumor closely associated with chronic inflammation such as that of Helicobacter pylori gastritis, Sjogren's syndrome, and Hashimoto's thyroiditis. Tumor regression by H. pylori eradication alone is well known in gastric MALT lymphoma, but some tumors occur in the absence of pre-existing chronic inflammation. The understanding of MALT lymphoma biology has significantly improved, and recurrent cytogenetic alterations have been detected. These include the trisomies 3 and 18, and the translocations t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21), and t(3;14)(p14.1;q32). At least some of these alterations result in the constitutive activation of the nuclear factor (NF)-kappaB pathway, and may exert anti-apoptotic action. Apoptosis inhibitor 2-MALT lymphoma-associated translocation 1 (API12-MALT1) fusion, resulting from t(11;18)(q21;q21), is specific to, and is the most common in, MALT lymphomas, and its clinicopathological significance has been studied extensively. The focus of the present review is on the recent progress made in elucidating MALT lymphomagenesis and its clinicopathological impact, especially in terms of the effect of API2-MALT1 fusion on this unique tumor.

Marginal-zone lymphoma

The term marginal-zone lymphoma (MZL) encompasses three closely related lymphoma subtypes, namely the "low-grade B-cell lymphoma of MALT type" currently named MALT lymphoma, the "nodal marginal-zone B-cell lymphoma" and a provisional entity in the REAL classification named "primary splenic MZL with or without villous lymphocytes". These entities display different characteristics, with evident clinical and biological variations according to the organ where the lymphoma arises. Marginal-zone B-cells are functionally heterogeneous and may differ with respect to the pattern of somatic hypermutation in their Ig variable genes. Sequence and mutation analysis of the rearranged Ig heavy chain variable genes and that somatic mutations pattern indicate that MZL may arise from different subsets of marginal-zone B-cells. Pathogenesis of these groups of lymphomas is correlated to chronic infections, like Helicobacter pylori, hepatitis C virus, Campylobacter jejuni, Chlamydia psittaci and Borrelia burgdorferi. Several therapeutic strategies against these malignancies exist. Surgical resection, radiotherapy and alkylating agent-based chemotherapy constitute standard approaches, while antimicrobial therapies, anti-CD20 therapy and new forms of immunotherapy constitute interesting experimental approaches. However, prospective trials on these malignancies are rare and universally accepted therapeutic guidelines do not exist. MZLs constitute an exciting investigational setting both from molecular and clinical points of view.

Foxp3 expression in pancreatic carcinoma cells as a novel mechanism of immune evasion in cancer

The forkhead transcription factor Foxp3 is highly expressed in CD4+CD25+ regulatory T cells (Treg) and was recently identified as a key player in mediating their inhibitory functions. Here, we describe for the first time the expression and function of Foxp3 in pancreatic ductal adenocarcinoma cells and tumors. Foxp3 expression was induced by transforming growth factor-beta2 (TGF-beta2), but not TGF-beta1 stimulation in these cells, and was partially suppressed following antibody-mediated neutralization of TGF-beta2. The TGF-beta2 effect could be mimicked by ectopic expression of a constitutively active TGF-beta type I receptor/ALK5 mutant. Down-regulation of Foxp3 with small interfering RNA (siRNA) in pancreatic carcinoma cells resulted in the up-regulation of interleukin 6 (IL-6) and IL-8 expression, providing evidence for a negative transcriptional activity of Foxp3 also in these epithelial cells. Coculture of Foxp3-expressing tumor cells with naive T cells completely inhibited T-cell proliferation, but not activation, and this antiproliferative effect was partially abrogated following specific inhibition of Foxp3 expression. These findings indicate that pancreatic carcinoma cells share growth-suppressive effects with Treg and suggest that mimicking Treg function may represent a new mechanism of immune evasion in pancreatic cancer.

Forkhead transcription factors regulate mosquito reproduction

Forkhead-box (Fox) genes encode a family of transcription factors defined by a 'winged helix' DNA-binding domain. In this study we aimed to identify Fox factors that are expressed within the fat body of the yellow fever mosquito Aedes aegypti, and determine whether any of these are involved in the regulation of mosquito yolk protein gene expression. The Ae. aegypti genome contains 18 loci that encode putative Fox factors. Our stringent cladistic analysis has profound implications for the use of Fox genes as phylogenetic markers. Twelve Ae. aegypti Fox genes are expressed within various tissues of adult females, six of which are expressed within the fat body. All six Fox genes expressed in the fat body displayed dynamic expression profiles following a blood meal. We knocked down the 'fat body Foxes' through RNAi to determine whether these 'knockdowns' hindered amino acid-induced vitellogenin gene expression. We also determined the effect of these knockdowns on the number of eggs deposited following a blood meal. Knockdown of FoxN1, FoxN2, FoxL, and FoxO, had a negative effect on amino acid-induced vitellogenin gene expression and resulted in significantly fewer eggs laid. Our analysis stresses the importance of Fox transcription factors in regulating mosquito reproduction.

FOXP1: a potential therapeutic target in cancer

Forkhead Box P1 (FOXP1) is a member of the FOX family of transcription factors which have a broad range of functions. Foxp1 is widely expressed and has been shown to have a role in cardiac, lung and lymphocyte development. FOXP1 is targeted by recurrent chromosome translocations and its overexpression confers a poor prognosis in a number of types of lymphomas, suggesting it may function as an oncogene. In contrast, FOXP1 localises to a tumour suppressor locus at 3p14.1 and loss of FOXP1 expression in breast cancer is associated with a worse outcome, suggesting FOXP1 may function as a tumour suppressor in other tissue types. These data suggest that FOXP1 may not only be useful in prognosis but also may be used to develop FOXP1-directed therapeutic strategies.

FOXP1: a potential therapeutic target in cancer

Forkhead Box P1 (FOXP1) is a member of the FOX family of transcription factors which have a broad range of functions. Foxp1 is widely expressed and has been shown to have a role in cardiac, lung and lymphocyte development. FOXP1 is targeted by recurrent chromosome translocations and its overexpression confers a poor prognosis in a number of types of lymphomas, suggesting it may function as an oncogene. In contrast, FOXP1 localises to a tumour suppressor locus at 3p14.1 and loss of FOXP1 expression in breast cancer is associated with a worse outcome, suggesting FOXP1 may function as a tumour suppressor in other tissue types. These data suggest that FOXP1 may not only be useful in prognosis but also may be used to develop FOXP1-directed therapeutic strategies.

Alterations of gene expression in the development of early hyperplastic precursors of breast cancer

Enlargement of normal terminal duct lobular units (TDLUs) by hyperplastic columnar epithelial cells is one of the most common abnormalities of growth in the adult female human breast. These hyperplastic enlarged lobular units (HELUs) are important clinically as the earliest histologically identifiable potential precursor of breast cancer. The causes of the hyperplasia are unknown but may include estrogen-simulated growth mediated by estrogen receptor-alpha, which is highly elevated in HELUs and may be fundamental to their development. The present study used DNA microarray technology and RNA from microdissected pure epithelial cells to examine changes in gene expression and molecular pathways associated with the development of HELUs from TDLUs. The results suggest that HELUs evolve from TDLUs primarily by reactivation of pathways involved in embryonic development and suppression of terminal differentiation. Changes in ERBB genes were particularly prominent, including a uniform switch in ligands for the ERBB1 receptor (14-fold decrease in epidermal growth factor and 10-fold increase in amphiregulin, respectively) in HELUs compared with TDLUs. Epidermal growth factor regulates terminal differentiation in adult breast and amphiregulin is critical to normal embryonic breast development. Because HELUs are such early potential precursors of breast cancer, targeting some of these alterations may be especially promising strategies for breast cancer prevention.

FoxP3 mRNA transcripts and regulatory cells in renal transplant recipients 10 years after donor marrow infusion

BACKGROUND

We update more favorable 10-year deceased donor kidney transplant survival in 63 recipients infused perioperatively with donor vertebral body bone marrow (DBMC-i) vs. 219 noninfused controls having equivalent immunosuppression and demographics. We questioned if this was associated with putatively regulatory FoxP3 mRNA and cell phenotypes (CD4+CD25+high percentages and high DC2:DC1 ratios) in DBMC-i vs. noninfused controls.

METHODS

Baseline studies were performed on peripheral blood lymphocytes (PBLs) vs. marrow in normal laboratory volunteers of CD4+CD25+high percentages and DC2:DC1 by flow cytometry, and FoxP3 mRNA in CD3+ cells by real-time polymerase chain reaction. Similar studies were performed on PBL of the majority of the 10-year patients remaining with graft function: 21 (of the remaining 37) DBMC-i vs. 55 (of the remaining 105) controls.

RESULTS

In normal subjects, all parameters were significantly higher in marrow than in PBL, supporting our previous reports of ex vivo DBMC immunoregulation. At 9.8+/-.02 years posttransplant in DBMC-i vs. controls, death-censored percent graft failure was 17.5% vs. 32.9% (P=0.02) with 247.6+/-24 vs. 79.9+/-3.1 (mean+/-SE) FoxP3 copies/5,000 CD3+ cells (P=0.0001). PBL CD4+CD25+high percentages were lower, but DC2:DC1 values higher in both recipient groups than in end-stage renal disease patients who had lower FoxP3 levels (40.8+/-5.9, P<0.0001), consistent with non-CD4+CD25+high T regulatory cells generated long-term posttransplant. Individual higher FoxP3 values correlated with higher iliac crest chimerism in DBMC-i, but not in controls (with 50-fold lower chimerism). In chronically rejecting controls, FoxP3 was further decreased.

CONCLUSIONS

Peritransplant DBMC-i has higher 10-year renal transplant acceptance, chimerism, and FoxP3 mRNA in thus-far unclarified regulatory cell phenotypes.

Sodium benzoate, a food additive and a metabolite of cinnamon, modifies T cells at multiple steps and inhibits adoptive transfer of experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is the animal model for multiple sclerosis. This study explores a novel use of sodium benzoate (NaB), a commonly used food additive and a Food and Drug Administration-approved nontoxic drug for urea cycle disorders, in treating the disease process of relapsing-remitting EAE in female SJL/J mice. NaB, administered through drinking water at physiologically tolerable doses, ameliorated clinical symptoms and disease progression of EAE in recipient mice and suppressed the generation of encephalitogenic T cells in donor mice. Histological studies reveal that NaB effectively inhibited infiltration of mononuclear cells and demyelination in the spinal cord of EAE mice. Consequently, NaB also suppressed the expression of proinflammatory molecules and normalized myelin gene expression in the CNS of EAE mice. Furthermore, we observed that NaB switched the differentiation of myelin basic protein-primed T cells from Th1 to Th2 mode, enriched regulatory T cell population, and down-regulated the expression of various contact molecules in T cells. Taken together, our results suggest that NaB modifies encephalitogenic T cells at multiple steps and that NaB may have therapeutic importance in multiple sclerosis.

CD4+ T Cells in Lymph Nodes of UVB-Irradiated Mice Suppress Immune Responses to New Antigens Both In Vitro and In Vivo

The mechanisms by which erythemal UVB irradiation modulates systemic immune responses to antigens applied to non-irradiated sites are poorly understood. In this study, regulatory CD4+ T cells were identified in the skin-draining lymph nodes (SDLNs) of UVB-irradiated, but otherwise naive mice. A transgenic mouse strain (DO11.10) was utilized in which the majority of CD4+ T cells expressed the ovalbumin (OVA(323-339)) T-cell receptor. Thus, T-cell responses could be examined following erythemal UVB irradiation without further antigen sensitization. CD4+ T cells from the SDLNs of UVB-irradiated mice had significantly reduced capacity to respond to presentation of the OVA(323-339) peptide in vitro. Transfer of CD4+ T cells from the SDLNs of UVB-irradiated antigen-naive mice significantly reduced both OVA sensitization and contact hypersensitivity responses to an experimental hapten in the recipient mice. Depletion of CD4+CD25+ cells abrogated this UVB-suppressive effect in the in vitro proliferation assay. There was also a significant increase in the proportion of CD4+CD25+Foxp3+ cells in the SDLNs of UVB-irradiated mice. The potential of these regulatory cells poised to regulate responses to incoming antigens at distant non-irradiated sites broadens the biological impact of UVB irradiation of skin on immunity.

Decreased up-regulation of the interleukin-12Rbeta2-chain and interferon-gamma secretion and increased number of forkhead box P3-expressing cells in patients with a history of chronic Lyme borreliosis compared with asymptomatic Borrelia-exposed individuals

Lyme borreliosis (LB) can, despite adequate antibiotic treatment, develop into a chronic condition with persisting symptoms such as musculoskeletal pain, subjective alteration of cognition and fatigue. The mechanism behind this is unclear, but it has been postulated that an aberrant immunological response might be the cause. In this study we investigated the expression of the T helper 1 (Th1) marker interleukin (IL)-12Rbeta2, the marker for T regulatory cells, forkhead box P3 (FoxP3) and the cytokine profile in patients with a history of chronic LB, subacute LB, previously Borrelia-exposed asymptomatic individuals and healthy controls. Fifty-four individuals (12 chronic LB, 14 subacute LB, 14 asymptomatic individuals and 14 healthy controls) were included in the study and provided a blood sample. Mononuclear cells were separated from the blood and stimulated with antigens. The IL-12Rbeta2 and FoxP3 mRNA expression was analysed with real-time reverse transcription-polymerase chain reaction (RT-PCR). The protein expression of IL-12Rbeta2 on CD3(+), CD4(+), CD8(+) and CD56(+) cells was assessed by flow cytometry. Furthermore, the secretion of interferon (IFN)-gamma, IL-4, IL-5, IL-10, IL-12p70 and IL-13 was analysed by enzyme-linked immunospot (ELISPOT) and/or enzyme-linked immunosorbent assay (ELISA). Chronic LB patients displayed a lower expression of Borrelia-specific IL-12Rbeta2 on CD8(+) cells and also a lower number of Borrelia-specific IFN-gamma-secreting cells compared to asymptomatic individuals. Furthermore, chronic LB patients had higher amounts of Borrelia-specific FoxP3 mRNA than healthy controls. We speculate that this may indicate that a strong Th1 response is of importance for a positive outcome of a Borrelia infection. In addition, regulatory T cells might also play a role, by immunosuppression, in the development of chronic LB.

Vav1 promotes T cell cycle progression by linking TCR/CD28 costimulation to FOXO1 and p27kip1 expression

Vav proteins play a critical role in T cell activation and proliferation by promoting cytoskeleton reorganization, transcription factor activation, and cytokine production. In this study, we investigated the role of Vav in T cell cycle progression. TCR/CD28-stimulated Vav1(-/-) T cells displayed a cell cycle block at the G0-G1 stage, which accounted for their defective proliferation. This defect was associated with impaired TCR/CD28-induced phosphorylation of Akt and the Forkhead family transcription factor, FOXO1. The cytoplasmic localization of FOXO1 and its association with 14-3-3tau were also reduced in Vav1(-/-) T cells. Consistent with the important role of FOXO1 in p27 kip1 transcription, stimulated Vav1(-/-) T cells failed to down-regulate the expression of p27 kip1, explaining their G0-G1 arrest. These defects were more pronounced in Vav1/Vav3 double-deficient T cells, suggesting partial redundancy between Vav1 and Vav3. Importantly, IL-2-induced p27 kip1 down-regulation and cyclin D3 up-regulation and FOXO1 phosphorylation were similar in Vav1(-/-) and wild-type T lymphoblasts, indicating that defective FOXO1 phosphorylation and p27 kip1 and cyclin D3 expression do not result from deficient IL-2 signaling in the absence of Vav1. Thus, Vav1 is a critical regulator of a PI3K/Akt/FOXO1 pathway, which controls T cell cycle progression and proliferation.

Human bladder carcinoma is dominated by T-regulatory cells and Th1 inhibitory cytokines

PURPOSE

Immunotherapy has faced limited success, although many solutions have been proposed. Recently regulatory T cells have made a comeback in the immunological arena and the role of these cells in patients with cancer is in focus. It is under evaluation whether the immunological status of patients with cancer may affect their sensitivity to immunotherapy. We are developing immunostimulating gene therapy for treating bladder cancer. In this study we constructed an immunological profile of patients with bladder carcinoma to understand which obstacles must be circumvented.

MATERIALS AND METHODS

Biopsies and blood were used to identify immune cell populations by FACS(R), histochemistry and proliferation assays, and cytokine production by polymerase chain reaction.

RESULTS

Results indicate that bladder carcinoma is a Tr1 dominated tumor, as shown by the infiltration of T-regulatory cells expressing FOXP3, and the presence of tumor necrosis factor-beta and interleukin-10 mRNA copies. We further noted that circulating patient T cells were unresponsive to polyclonal T-cell activation compared to healthy donor cells. Moreover, CD4+CD25+ T cells were increased in patient blood and could suppress the expansion of allogeneic T cells from healthy donors.

CONCLUSIONS

Patients with bladder carcinoma show an immunosuppressive regulatory profile, including nonresponsive T cells. Clinical protocols able to effectively counteract these mechanisms are warranted.

The negative regulators Foxj1 and Foxo3a are up-regulated by a peptide that inhibits systemic lupus erythematosus-associated T cell responses

A peptide (hCDR1) based on the complementarity determining region-1 of an anti-DNA antibody ameliorates systemic lupus erythematosus (SLE) in induced and spontaneous lupus models. Our objectives were to determine the effects of hCDR1 on TCR signaling and on its negative regulators, Foxj1 and Foxo3a. BALB/c mice were immunized with the SLE-inducing anti-DNA antibody, designated 16/6Id, and treated with hCDR1. hCDR1 treatment specifically inhibited IFN-gamma secretion by T cells in association with down-regulated T-bet expression and NF-kappaB activation; however, GATA-3 expression was not affected. Furthermore, TCR signaling (ZAP-70 phosphorylation) was inhibited, and the mRNA expression of the two modulators of Th1 activation, Foxj1 and Foxo3a, was significantly up-regulated. The latter were also elevated in SLE-afflicted (NZBxNZW)F1 mice that were treated with hCDR1. Addition of TGF-beta, which was elevated following treatment with hCDR1, to T cells from 16/6Id immunized mice, up-regulated Foxj1 and Foxo3a mRNA expression, similarly to hCDR1. In contrast, anti-TGF-beta antibodies added to hCDR1-treated T cells abrogated its effect. Thus, hCDR1 elevates TGF-beta, which contributes to the up-regulation of T cell Foxj1 and Foxo3a expression, leading to inhibition of NF-kappaB activation and IFN-gamma secretion, which is required for the maintenance of SLE.

FoxOs Are Critical Mediators of Hematopoietic Stem Cell Resistance to Physiologic Oxidative Stress

To understand the role of FoxO family members in hematopoiesis, we conditionally deleted FoxO1, FoxO3, and FoxO4 in the adult hematopoietic system. FoxO-deficient mice exhibited myeloid lineage expansion, lymphoid developmental abnormalities, and a marked decrease of the lineage-negative Sca-1+, c-Kit+ (LSK) compartment that contains the short- and long-term hematopoietic stem cell (HSC) populations. FoxO-deficient bone marrow had defective long-term repopulating activity that correlated with increased cell cycling and apoptosis of HSC. Notably, there was a marked context-dependent increase in reactive oxygen species (ROS) in FoxO-deficient HSC compared with wild-type HSC that correlated with changes in expression of genes that regulate ROS. Furthermore, in vivo treatment with the antioxidative agent N-acetyl-L-cysteine resulted in reversion of the FoxO-deficient HSC phenotype. Thus, FoxO proteins play essential roles in the response to physiologic oxidative stress and thereby mediate quiescence and enhanced survival in the HSC compartment, a function that is required for its long-term regenerative potential.

Convergence of TCR and cytokine signaling leads to FOXO3a phosphorylation and drives the survival of CD4+ central memory T cells

The molecular events involved in the establishment and maintenance of CD4⁺ central memory and effector memory T cells (T_CM and T_EM, respectively) are poorly understood. In this study, we demonstrate that ex vivo isolated T_CM are more resistant to both spontaneous and Fas-induced apoptosis than T_EM and have an increased capacity to proliferate and persist in vitro. Using global gene expression profiling, single cell proteomics, and functional assays, we show that the survival of CD4⁺ T_CM depends, at least in part, on the activation and phosphorylation of signal transducer and activator of transcription 5a (STAT5a) and forkhead box O3a (FOXO3a). T_CM showed a significant increase in the levels of phosphorylation of STAT5a compared with T_EM in response to both IL-2 (P < 0.04) and IL-7 (P < 0.002); the latter is well known for its capacity to enhance T cell survival. Moreover, ex vivo T_CM express higher levels of the transcriptionally inactive phosphorylated forms of FOXO3a and concomitantly lower levels of the proapoptotic FOXO3a target, Bim. Experiments aimed at blocking FOXO3a phosphorylation confirmed the role of this phosphoprotein in protecting T_CM from apoptosis. Our results provide, for the first time in humans, an insight into molecular mechanisms that could be responsible for the longevity and persistence of CD4⁺ T_CM.

Foxp3 controls autoreactive T cell activation through transcriptional regulation of early growth response genes and E3 ubiquitin ligase genes, independently of thymic selection

To elucidate the mechanisms of autoreactive T cell activation and expansion, we used endogenous viral superantigens (VSAg)-reactive T cells as a model of self-antigens in two strains of Foxp3-mutant mice. These two strains, together with wild-type mice, provided us with an advantage to simultaneously study the positively and negatively selected as well as rescued autoreactive T cells. We show here that while both VSAg-reactive and non-VSAg-reactive T cells are equally activated in Foxp3-mutant mice, only the VSAg-reactive T cells are preferentially expanded independently of their selected states in the thymus. The T cell activation appears to be controlled by Foxp3 through transcriptional regulation of early growth response (Egr) genes Egr-2 and Egr-3, and E3 ubiquitin (Ub) ligase genes Cblb, Itch and GRAIL, subsequently affecting degradation of two key signaling proteins, PLCgamma1 and PKC-theta. Physiologically, the positively, but not negatively selected VSAg-reactive T cells are spontaneously activated without significant expansion. The results suggest that autoreactive T cell activation is controlled by Foxp3 through transcriptional regulation of early growth response genes and E3 ubiquitin ligase genes, independently of thymic selection.

Guarding the immune system: Suppression of autoimmunity by CD4+CD25+immunoregulatory T cells

CD4+CD25+Foxp3+ T cells (CD25+ T regulatory [Treg] cells) are a naturally occurring suppressor T-cell population that regulates a wide variety of immune responses. A major function of CD25+ Treg cells is to inhibit the activity of self-reactive T cells that can potentially cause autoimmune disease. This review examines the recent advances in CD25+ Treg cell biology, with particular focus on the thymic and peripheral development of CD25+ Treg cells, the signals that promote their expansion and maintenance in the periphery and the mechanism by which they mediate their suppressor activity in peripheral lymphoid tissues. An understanding of these issues is likely to facilitate the development of CD25+ Treg-cell-based therapies for the treatment of autoimmune disease.

Analysis of FOXP3 reveals multiple domains required for its function as a transcriptional repressor

Foxp3 has been shown to be both necessary and sufficient for the development and function of naturally arising CD4+ CD25+ regulatory T cells in mice. Mutation of Foxp3 in Scurfy mice and FOXP3 in humans with IPEX results in fatal, early onset autoimmune disease and demonstrates the critical role of FOXP3 in maintaining immune homeostasis. The FOXP3 protein encodes several functional domains, including a C2H2 zinc finger, a leucine zipper, and a winged-helix/forkhead (FKH) domain. We have shown previously that FOXP3 functions as a transcriptional repressor and inhibits activation-induced IL-2 gene transcription. To characterize the role of each predicted functional domain on the in vivo activity of FOXP3, we have evaluated the location of point mutations identified in a large cohort of patients with the immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX) and found them to cluster primarily within the FKH domain and the leucine zipper, but also present within the poorly defined N-terminal portion of the protein. The molecular functions of each of the IPEX-targeted domains were investigated. We show that FOXP3 is constitutively localized to the nucleus and this localization requires sequences at both the amino and C-terminal ends of its FKH domain. Moreover, FOXP3 was found to homodimerize through its leucine zipper. We also identify a novel functional domain within the N-terminal half of FOXP3, which is required for FOXP3-mediated repression of transcription from both a constitutively active and a NF-AT-inducible promoter. Furthermore, we demonstrate that IPEX mutations in these domains correlate with deficiencies in FOXP3 repressor function, corroborating their in vivo relevance.

Ionizing radiation activates expression of FOXO3a, Fas ligand, and Bim, and induces cell apoptosis

Genotoxic stress such as ionizing radiation can induce DNA damage and promote cell-cycle arrest or apoptosis through either a p53-dependent or -independent pathway. Recently, members of the FOXO Forkhead transcription factor family have been implicated in playing a role in both DNA repair and apoptosis in mammalian cells that promoted us to examine the role of FOXO transcription factors in ionizing radiation-induced apoptosis. Here, we show that ionizing radiation can promote FOXO3a (FKHRL1) transcriptional activity and protein expression level, and induce nuclear translocation of FOXO3a in Saos2, a p53-null osteosarcoma cell line. Ionizing radiation stimulates expression of apoptosis-inducing proteins such as Fas ligand and the Bcl-2 interacting mediator of cell death (Bim) leading to cellular apoptosis. The observed upregulation of proapoptotic genes and apoptosis in cells without p53 in response to ionizing radiation suggests a novel p53-independent mechanism underlying ionizing radiation-induced apoptosis in cancer cells.

Trafficking on serpentines: molecular insight on how maturating T cells find their winding paths in the thymus

Maintenance of the peripheral T-cell pool throughout the life requires uninterrupted generation of T cells. The majority of peripheral T cells are generated in the thymus. However, the thymus does not contain hematopoietic progenitors with unlimited self-renewing potential, and continuous production of T cells requires importation of such progenitors from the bone marrow into the thymus. Thymus-homing progenitors enter the thymus and subsequently migrate throughout distinct intrathymic microenvironments while differentiating into mature T cells. At each step of this scheduled journey, developing thymocytes interact intimately with the local stroma, which allow them to proceed to the next stage of their differentiation and maturation program. Undoubtedly, thymocyte/stroma interactions are instrumental for both thymocytes and stroma, because only their ongoing interplay generates and maintains a fully operational thymus, able to guarantee unimpaired T-cell supply. Therefore, proper T-cell generation intrinsically involves polarized cell migration during both adult life and embryogenesis when the thymus primordium develops into a functional thymus. The molecular mechanisms controlling cell migration during thymus development and postnatal T-cell differentiation are beginning to be defined. This review focuses on recent data regarding the role of cell migration in both colonization of the fetal thymus and T-cell development during postnatal life in mice.

p38 MAPK regulates expression of immune response genes and contributes to longevity in C. elegans

The PMK-1 p38 mitogen-activated protein kinase pathway and the DAF-2–DAF-16 insulin signaling pathway control Caenorhabditis elegans intestinal innate immunity. pmk-1 loss-of-function mutants have enhanced sensitivity to pathogens, while daf-2 loss-of-function mutants have enhanced resistance to pathogens that requires upregulation of the DAF-16 transcription factor. We used genetic analysis to show that the pathogen resistance of daf-2 mutants also requires PMK-1. However, genome-wide microarray analysis indicated that there was essentially no overlap between genes positively regulated by PMK-1 and DAF-16, suggesting that they form parallel pathways to promote immunity. We found that PMK-1 controls expression of candidate secreted antimicrobials, including C-type lectins, ShK toxins, and CUB-like genes. Microarray analysis demonstrated that 25% of PMK-1 positively regulated genes are induced by Pseudomonas aeruginosa infection. Using quantitative PCR, we showed that PMK-1 regulates both basal and infection-induced expression of pathogen response genes, while DAF-16 does not. Finally, we used genetic analysis to show that PMK-1 contributes to the enhanced longevity of daf-2 mutants. We propose that the PMK-1 pathway is a specific, indispensable immunity pathway that mediates expression of secreted immune response genes, while the DAF-2–DAF-16 pathway appears to regulate immunity as part of a more general stress response. The contribution of the PMK-1 pathway to the enhanced lifespan of daf-2 mutants suggests that innate immunity is an important determinant of longevity.

The innate immune system provides the first line of defense against pathogen infection and relies upon pathways conserved across mammals, insects, and nematodes. Here, the authors have analyzed the transcriptional response of the nematode Caenorhabditis elegans to infection by the human pathogen Pseudomonas aeruginosa. They investigated this transcriptional response in the context of two conserved pathways involved in pathogen defense: the PMK-1 p38 mitogen-activated protein kinase (p38 MAPK) pathway and the DAF-2–DAF-16 insulin-signaling pathway. Specifically, the authors found that the p38 MAPK pathway plays a critical role in the infection-induced expression of secreted immune response genes. These genes include C-type lectins, lysozymes, and antimicrobial peptides that fight off infection in many species. In contrast, they found that the DAF-16 pathway is not required for immune response gene expression and may regulate immunity as part of a general stress response that functions in parallel to p38 MAPK. In addition, the authors observed that p38 MAPK contributes to the enhanced longevity of daf-2 mutants, implicating p38 MAPK signaling in the regulation of longevity, possibly through its role in immunity.

FOXP3 controls regulatory T cell function through cooperation with NFAT

Antigen stimulation of immune cells activates the transcription factor NFAT, a key regulator of T cell activation and anergy. NFAT forms cooperative complexes with the AP-1 family of transcription factors and regulates T cell activation-associated genes. Here we show that regulatory T cell (Treg) function is mediated by an analogous cooperative complex of NFAT with the forkhead transcription factor FOXP3, a lineage specification factor for Tregs. The crystal structure of an NFAT:FOXP2:DNA complex reveals an extensive protein-protein interaction interface between NFAT and FOXP2. Structure-guided mutations of FOXP3, predicted to progressively disrupt its interaction with NFAT, interfere in a graded manner with the ability of FOXP3 to repress expression of the cytokine IL2, upregulate expression of the Treg markers CTLA4 and CD25, and confer suppressor function in a murine model of autoimmune diabetes. Thus by switching transcriptional partners, NFAT converts the acute T cell activation program into the suppressor program of Tregs.

Addition of the CD28 signaling domain to chimeric T-cell receptors enhances chimeric T-cell resistance to T regulatory cells

T cells can be engineered to target tumor cells by transduction of tumor-specific chimeric receptors, consisting of an extracellular antigen-binding domain and an intracellular signaling domain. However, the peripheral blood of cancer patients frequently contains an increased number of T regulatory cells, which appear to inhibit immune reactivity. We have investigated the effects of T regulatory cells on chimeric T cells specific for the B-cell antigen CD19, as B-cell malignancies are attractive targets for chimeric T-cell therapy. When a CD19 single-chain Fv antibody was coupled to the CD3 zeta (zeta) chain, there was sharply reduced activity on exposure to T regulatory cells, measured by CD19+ target-induced proliferation and cytotoxicity. By contrast, expression in T cells of a chimeric receptor consisting of the intracellular portion of the CD28 molecule fused to the zeta-chain and CD19 single-chain Fv not only produced a higher proliferative response and an increased nuclear factor kappaB activation but also sustained these activities in the presence of T regulatory cells. These effects are seen whether the chimeric T cells are derived from normal donors or from patients with B-cell chronic lymphocytic leukemia, indicating the potential for clinical application in B cell malignancies.

Th17: an effector CD4 T cell lineage with regulatory T cell ties

The naive CD4 T cell is a multipotential precursor with defined antigen recognition specificity but substantial plasticity for development down distinct effector or regulatory lineages, contingent upon signals from cells of the innate immune system. The range of identified effector CD4 T cell lineages has recently expanded with description of an IL-17-producing subset, called Th17, which develops via cytokine signals distinct from, and antagonized by, products of the Th1 and Th2 lineages. Remarkably, Th17 development depends on the pleiotropic cytokine TGF-beta, which is also linked to regulatory T cell development and function, providing a unique mechanism for matching CD4 T cell effector and regulatory lineage specification. Here, we review Th17 lineage development, emphasizing similarities and differences with established effector and regulatory T cell developmental programs that have important implications for immune regulation, immune pathogenesis, and host defense.

FOXP3 ensembles in T-cell regulation

Our recent studies have identified dynamic protein ensembles containing forkhead box protein 3 (FOXP3) that provide insight into the molecular complexity of suppressor T-cell activities, and it is our goal to determine how these ensembles regulate FOXP3's transcriptional activity in vivo. In this review, we summarize our current understanding of how FOXP3 expression is induced and how FOXP3 functions in vivo as a transcriptional regulator by assembling a multisubunit complex involved in histone modification as well as chromatin remodeling.

In control of biology: of mice, men and Foxes

Forkhead proteins comprise a highly conserved family of transcription factors, named after the original forkhead gene in Drosophila. To date, over 100 forkhead genes have been identified in a large variety of species, all sharing the evolutionary conserved 'forkhead' DNA-binding domain, and the cloning and characterization of forkhead genes have continued in recent years. Forkhead transcription factors regulate the expression of countless genes downstream of important signalling pathways in most, if not all, tissues and cell types. Recent work has provided novel insights into the mechanisms that contribute to their functional diversity, including functional protein domains and interactions of forkheads with other transcription factors. Studies using loss- and gain-of-function models have elucidated the role of forkhead factors in developmental biology and cellular functions such as metabolism, cell division and cell survival. The importance of forkhead transcription factors is underlined by the developmental defects observed in mutant model organisms, and multiple human disorders and cancers which can be attributed to mutations within members of the forkhead gene family. This review provides a comprehensive overview of current knowledge on forkhead transcription factors, from structural organization and regulatory mechanisms to cellular and developmental functions in mice and humans. Finally, we will discuss how novel insights gained from involvement of 'Foxes' in the mechanisms underlying human pathology may create new opportunities for treatment strategies.

FOXP3: of mice and men

The immune system has evolved mechanisms to recognize and eliminate threats, as well as to protect against self-destruction. Tolerance to self-antigens is generated through two fundamental mechanisms: (a) elimination of self-reactive cells in the thymus during selection and (b) generation of a variety of peripheral regulatory cells to control self-reactive cells that escape the thymus. It is becoming increasing apparent that a population of thymically derived CD4+ regulatory T cells, exemplified by the expression of the IL-2Ralpha chain, is essential for the maintenance of peripheral tolerance. Recent work has shown that the forkhead family transcription factor Foxp3 is critically important for the development and function of the regulatory T cells. Lack of Foxp3 leads to development of fatal autoimmune lymphoproliferative disease; furthermore, ectopic Foxp3 expression can phenotypically convert effector T cells to regulatory T cells. This review focuses on Foxp3 expression and function and highlights differences between humans and mice regarding Foxp3 regulation.

The mutant leucine-zipper domain impairs both dimerization and suppressive function of Foxp3 in T cells

Regulatory T cells that express the Foxp3 transcription factor play important roles in preventing autoimmune diseases. Although several studies have demonstrated that the lack of the forkhead DNA-binding domain of Foxp3 caused severe autoimmune disease in scurfy mutant mice, the other functional domains of Foxp3 are less well characterized. Here, we show that the deletion of glutamic acid (DeltaE250) in the leucine-zipper domain of Foxp3 causes a loss of hyporesponsiveness when compared with wild-type Foxp3 upon antigenic stimulation. CD4 T cells that ectopically express the glutamic acid mutant show significant losses of suppressor activity both in vitro and in vivo. We also demonstrate that regulation of both Th1- and Th2-type cytokine secretion in CD4 T cells that express wild-type Foxp3 is significantly altered by the deletion of glutamic acid. Defects are also observed in the expression of adhesion molecules, such as l-selectin (CD62L) and CD103, suggesting an important role of glutamic acid in the migratory behavior of regulatory T cells. Finally, this mutation reduces transcriptional repressor activity and impairs the homodimerization of Foxp3. Taken together, our results provide insight into the mechanism that controls autoimmune diseases via the deletion of this single glutamic acid residue in the leucine-zipper domain of Foxp3.

Coordination of NF-kappaB and NFAT antagonism by the forkhead transcription factor Foxd1

Forkhead transcription factors play critical roles in the maintenance of immune homeostasis. In this study, we demonstrate that this regulation most likely involves intricate interactions between the forkhead family members and inflammatory transcription factors: the forkhead member Foxd1 coordinates the regulation of the activity of two key inflammatory transcription factors, NF-AT and NF-kappaB, with Foxd1 deficiency resulting in multiorgan, systemic inflammation, exaggerated Th cell-derived cytokine production, and T cell proliferation in autologous MLRs. Foxd1-deficient T cells possess increased activity of both NF-AT and NF-kappaB: the former correlates with the ability of Foxd1 to regulate casein kinase 1, an NF-AT inhibitory kinase; the latter with the ability of Foxd1 to regulate Foxj1, which regulates the NF-kappaB inhibitory subunit IkappaB beta. Thus, Foxd1 modulates inflammatory reactions and prevents autoimmunity by directly regulating anti-inflammatory regulators of the NF-AT pathway, and by coordinating the suppression of the NF-kappaB pathway via Foxj1. These findings indicate the presence of a general network of forkhead proteins that enforce T cell quiescence.

Foxp3 represses retroviral transcription by targeting both NF-kappaB and CREB pathways

Forkhead box (Fox)/winged-helix transcription factors regulate multiple aspects of immune responsiveness and Foxp3 is recognized as an essential functional marker of regulatory T cells. Herein we describe downstream signaling pathways targeted by Foxp3 that may negatively impact retroviral pathogenesis. Overexpression of Foxp3 in HEK 293T and purified CD4+ T cells resulted in a dose-dependent and time-dependent decrease in basal levels of nuclear factor-kappaB (NF-kappaB) activation. Deletion of the carboxyl-terminal forkhead (FKH) domain, critical for nuclear localization and DNA-binding activity, abrogated the ability of Foxp3 to suppress NF-kappaB activity in HEK 293T cells, but not in Jurkat or primary human CD4+ T cells. We further demonstrate that Foxp3 suppressed the transcription of two human retroviral promoters (HIV-1 and human T cell lymphotropic virus type I [HTLV-I]) utilizing NF-kappaB-dependent and NF-kappaB-independent mechanisms. Examination of the latter identified the cAMP-responsive element binding protein (CREB) pathway as a target of Foxp3. Finally, comparison of the percent Foxp3+CD4+CD25+ T cells to the HTLV-I proviral load in HTLV-I-infected asymptomatic carriers and patients with HTLV-I-associated myelopathy/tropical spastic paraparesis suggested that high Foxp3 expression is associated with low proviral load and absence of disease. These results suggest an expanded role for Foxp3 in regulating NF-kappaB- and CREB-dependent cellular and viral gene expression.

Identification of novel genes and transcription factors involved in spleen, thymus and immunological development and function

We constructed and analyzed six serial analysis of gene expression (SAGE) libraries to identify genes with previously uncharacterized roles in spleen or thymus development. A total of 625 070 tags were sequenced from the three spleen (embryonic day (E)15.5, E16.5 and adult) and three thymus (E15.5, E18.5 and adult) libraries. These tags corresponded to 83 182 tag types, which mapped unambiguously to 36 133 different genes. Genes over-represented in these libraries, compared to 115 mouse SAGE libraries (www.mouseatlas.org), included genes of known and unknown immunological or developmental relevance. The expression profiles of 11 genes with unknown roles in spleen and thymus development were validated using reverse transcription-qPCR. We further characterized the expression of one of these candidates, RIKEN cDNA 9230105E10 that encodes a murine homolog of Trim5alpha, in numerous adult tissues and immune cell types. In addition, we demonstrate that transcript levels are upregulated in response to TLR stimulation of plasmacytoid dendritic cells and macrophages. This work provides the first evidence of regulated and cell type-specific expression of this gene. In addition, these observations suggest that the SAGE libraries provide an important resource for further investigations into the molecular mechanisms regulating spleen and thymus organogenesis, as well as the development of immunological competence.

Antigen-induced, tolerogenic CD11c+,CD11b+ dendritic cells are abundant in Peyer's patches during the induction of oral tolerance to type II collagen and suppress experimental collagen-induced arthritis

OBJECTIVE

Although oral tolerance is a well-known phenomenon, the role of dendritic cells (DCs) is not well characterized. This study was conducted to better understand the differential role played by each Peyer's patch DC subset in the induction of oral tolerance to type II collagen (CII) in murine collagen-induced arthritis (CIA).

METHODS

CII was fed 6 times to DBA/1 mice beginning 2 weeks before immunization, and the effect on arthritis was assessed. We compared the proportion of CD11c+,CD11b+ DCs and CD11c+,CD8alpha+ DCs in the Peyer's patches of CII-fed tolerized and phosphate buffered saline-fed nontolerized mice after the induction of CIA. The immunosuppressive properties of each DC subset were determined using fluorescence-activated cell sorter analysis for intracellular interleukin-10 (IL-10) and IL-12 and mixed lymphocyte culture. The ability of each DC subset to induce CD4+,CD25+ T regulatory cells was also examined. Mice were injected with CII-pulsed CD11c+,CD11b+ DCs isolated from Peyer's patches of tolerized mice, and the effect on CIA was examined.

RESULTS

The severity of arthritis was significantly lower in tolerized mice. The proportion of CD11c+,CD11b+ DCs was increased in the Peyer's patches of tolerized mice and those DCs exhibited immunosuppressive characteristics, such as increased IL-10 production, inhibition of T cell proliferative responses to CII, and CD4+,CD25+ regulatory T cell induction. Furthermore, the CD11c+,CD11b+ DCs suppressed the severity of arthritis upon adoptive transfer.

CONCLUSION

Our observations demonstrate that CD11c+,CD11b+ DCs, which are abundant in Peyer's patches during the induction of oral tolerance to CII, are crucial for the suppression of CIA and could be exploited for immunotherapy of autoimmune diseases.

Cutting edge: Foxj1 protects against autoimmunity and inhibits thymocyte egress

Previous studies suggest that the forkhead transcription factor Foxj1 inhibits spontaneous autoimmunity in part by antagonizing NF-kappaB activation. To test this hypothesis, we ectopically expressed Foxj1 in the T cells of lupus-prone MRL/lpr mice by backcrossing a CD2-Foxj1 transgene against the MRL/lpr background. Strikingly, CD2-Foxj1-MRL/lpr animals showed a significant reduction in lymphadenopathy, pathogenic autoantibodies, and end-organ disease-but surprisingly, reversion of autoimmunity was not attributable to modulation of NF-kappaB. Instead, CD2-Foxj1 transgenic mice exhibited a peripheral T cell lymphopenia, associated with an accumulation of mature single-positive thymocytes. Transgenic thymocytes demonstrated unimpaired lymphoid organ entry in adoptive transfer studies but demonstrated impaired thymic exodus in response to CCL19, apparently independent of CCR7, S1P1, and NF-kappaB. These findings confirm the importance of Foxj1 in the regulation of T cell tolerance but furthermore suggest a novel and specific role for Foxj1 in regulating thymic egress.

Identification of single nucleotide polymorphisms in FOXJ1 and their association with allergic rhinitis

Forkhead-box J1 (FOXJ1) is a presumed transcription factor that can suppress T cell activity, at least partially, through the repression of NFkappaB activity. Thus, dysregulation of FOXJ1 is thought to be associated with autoimmune diseases and/or other inflammatory diseases. To investigate the association between single nucleotide polymorphisms (SNPs) of human FOXJ1 and allergic rhinitis, we scanned the whole human FOXJ1 gene, including the promoter region, by direct sequencing of DNA from 32 individuals. We identified seven SNPs, three of which (g.-460C>T, g.1805G>T, and g.3375G>C) were chosen for large sample size genotyping (n=713), and to assess the genotype frequencies of these SNPs between controls and allergic rhinitis patients. We also investigated the relationships of each genotype with serum total IgE levels in allergic rhinitis patients, and compared the frequencies of haplotypes constructed by these SNPs between the two groups. Our results suggest that the SNPs g.-460C>T, g.1805G>T and g.3375G>C in the human FOXJ1 gene might be associated with susceptibility to allergic rhinitis (P=0.0184, 0.0076, and 0.0143, respectively). The main haplotype, CGG, also revealed a significant association with allergic rhinitis (P=0.000018). However, no significant association was found between serum total IgE levels and the genotypes of these polymorphisms.

The molecular immunology of mucositis: implications for evidence-based research in alternative and complementary palliative treatments

The terms 'mucositis' and 'stomatitis' are often used interchangeably. Mucositis, however, pertains to pharyngeal-esophago-gastrointestinal inflammation that manifests as red, burn-like sores or ulcerations throughout the mouth. Stomatitis is an inflammation of the oral tissues proper, which can present with or without sores, and is made worse by poor dental hygiene. Mucositis is observed in a variety of immunosuppressed patients, but is most often consequential to cancer therapy. It appears as early as the third day of intervention, and is usually established by Day 7 of treatment. Mucositis increases mortality and morbidity and contributes to rising health care costs. The precise immune components involved in the etiology of mucositis are unclear, but evidence-based research (EBR) data has shown that applications of granulocyte-macrophage-colony stimulating factor prevent the onset or the exacerbation of oropharyngeal mucositis. The molecular implications of this observation are discussed from the perspective of future developments of complementary and alternative treatments for this condition. It must be emphasized that this article is meant to be neither a review on mucositis and the various treatments for it, nor a discussion paper on its underlying molecular immunology. It is a statement of the implications of EBR for CAM-based interventions for mucositis. It explores and discusses the specific domain of molecular immunology in the context of mucositis and its direct implications for EBR research in CAM-based treatments for mucositis.

The role of the FOXP3 transcription factor in the immune regulation of allergic asthma

Unbalanced immune reactions against allergens are caused by Th2 cells, which are the basis of immunoglobulin E (IgE)-mediated symptoms of allergy and asthma. Although Th2 cells are essential for allergy, they are not sufficient to cause disease, because regulatory T cells (Tregs) control their activity and expansion. Therefore, Tregs are assumed to play an important role not only in the sensitization but also in established allergic disease under therapy. A key factor of Tregs is FOXP3, which, upon expression, is sufficient to induce regulatory T-cell phenotypes. The initiation and suppressive function of FOXP3 and Tregs in the context of allergic asthma are discussed in this review.

The mouse forkhead gene Foxc1 is required for primordial germ cell migration and antral follicle development

Foxc1 encodes a forkhead/winged helix transcription factor expressed in many embryonic tissues. Previous studies have investigated defects in the urogenital system of Foxc1 null mutants, but the mechanisms underlying the abnormal development of the gonad have not been explored. From earliest stages, the mutant ovaries are smaller than normal, with fewer germ cells and disorganized somatic issue. No bursa membrane is formed, and the oviduct remains uncoiled. Although germ cells are specified correctly, many of them do not migrate to the gonadal ridge, remaining trapped in the hindgut. Consequently, the number initially reaching the gonad is less than 25% of normal. Once in the ovary, germ cells proliferate normally, but the supporting somatic cells are not organized correctly. Since mutant embryos die at birth, further development was followed in ovaries grafted underneath the kidney capsule of ovariectomized females. Transplanted ovaries display normal folliculogenesis up to preantral stages. However, no follicles develop beyond early antral stages. Mutant follicles are often polyovulatory and have disrupted theca and granulosa cell layers. We conclude that alongside its previously known roles in kidney, cardiovascular and eye development, Foxc1 has essential functions during at least two stages of gonad development-germ cell migration and folliculogenesis.

Functional analysis of HGF/MET signaling and aberrant HGF-activator expression in diffuse large B-cell lymphoma

Inappropriate activation of MET, the receptor tyrosine kinase for hepatocyte growth factor (HGF), has been implicated in tumorigenesis. Although we have previously shown that HGF/MET signaling controls survival and proliferation of multiple myeloma (MM), its role in the pathogenesis of other B-cell malignancies has remained largely unexplored. Here, we have examined a panel of 110 B-cell malignancies for MET expression, which, apart from MM (48%), was found to be largely confined to diffuse large B-cell lymphomas (DLBCLs) (30%). No amplification of the MET gene was found; however, mutational analysis revealed 2 germ-line missense mutations: R1166Q in the tyrosine kinase domain in 1 patient, and R988C in the juxtamembrane domain in 4 patients. The R988C mutation has recently been shown to enhance tumorigenesis. In MET-positive DLBCL cells, HGF induces MEK-dependent activation of ERK and PI3K-dependent phosphorylation of PKB, GSK3, and FOXO3a. Furthermore, HGF induces PI3K-dependent α4β1 integrin-mediated adhesion to VCAM-1 and fibronectin. Within the tumor microenvironment of DLBCL, HGF is provided by macrophages, whereas DLBCL cells themselves produce the serine protease HGF activator (HGFA), which autocatalyzes HGF activation. Taken together, these data indicate that HGF/MET signaling, and secretion of HGFA by DLBCL cells, contributes to lymphomagenesis in DLBCL. (Blood. 2006;107:760-768)

CHES1/FOXN3 interacts with Ski-interacting protein and acts as a transcriptional repressor

Checkpoint Suppressor 1 (CHES1; FOXN3) encodes a member of the forkhead/winged-helix transcription factor family. The human CHES1 cDNA was originally identified by its ability to function as a high-copy suppressor of multiple checkpoint mutants of Saccharomyces cerevisiae. Accumulating expression profile data suggest that CHES1 plays a role in tumorigenicity and responses to cancer treatments, though nothing is known regarding the transcriptional function of CHES1 or other FOXN proteins in human cells. In this report, we find that the carboxyl terminus of CHES1 fused to a heterologous DNA binding domain consistently represses reporter gene transcription in cell lines derived from tumor tissues. Using a cytoplasmic two-hybrid screening approach, we find that this portion of CHES1 interacts with Ski-interacting protein (SKIP; NCoA-62), which is a transcriptional co-regulator known to associate with repressor complexes. We verify this interaction through co-immunoprecipitation experiments performed in mammalian cells. Further analysis of the CHES1/SKIP interaction indicates that CHES1 binds to a region within the final 66 hydrophobic residues of SKIP thus defining a new protein-protein interaction domain of SKIP. These data suggest that CHES1 recruits SKIP to repress genes important for tumorigenesis and the response to cancer treatments.

Introduction to immune cell signalling

The dynamic interaction of cells of the immune system with other cells, antigens and secreted factors determines the nature of an immune response. The response of individual cells is governed by the sequence of intracellular signalling events triggered following the association of cell surface molecules during cell-cell contact or the detection of soluble molecules of host or pathogen origin. In this review we will first outline the general principles of intracellular signal transduction. We will then describe the signalling pathways triggered following the recognition of antigen, as well as the detection of cytokines, and discuss how the signalling pathways activated regulate the effector response.

Factors that regulate naturally occurring T regulatory cell–mediated suppression

T regulatory (Treg) cells play a key role in the modulation of allergic and autoimmune responses. This review will discuss the factors that regulate naturally occurring Treg (nTreg) cell-mediated suppression. The involvement of cytokines, costimulatory molecules, and ligands on antigen-presenting cells in the inhibition of nTreg cell-mediated suppression in vitro is summarized. Understanding the events that control suppressive function of nTreg cells will allow manipulation of these cells to inhibit or enhance their functions in the development of novel therapies for autoimmune and allergic diseases.

Human skin cells support thymus-independent T cell development

Thymic tissue has previously been considered a requirement for the generation of a functional and diverse population of human T cells. We report that fibroblasts and keratinocytes from human skin arrayed on a synthetic 3-dimensional matrix support the development of functional human T cells from hematopoietic precursor cells in the absence of thymic tissue. Newly generated T cells contained T cell receptor excision circles, possessed a diverse T cell repertoire, and were functionally mature and tolerant to self MHC, indicating successful completion of positive and negative selection. Skin cell cultures expressed the AIRE, Foxn1, and Hoxa3 transcription factors and a panel of autoantigens. Skin and bone marrow biopsies can thus be used to generate de novo functional and diverse T cell populations for potential therapeutic use in immunosuppressed patients.

Molecular pathogenesis of mucosa-associated lymphoid tissue lymphoma

Extranodal marginal zone B-cell lymphomas of mucosa-associated lymphoid tissue (MALT) type occur in a number of anatomic sites, but share overlapping morphologic and immunophenotypic features. Helicobacter pylori infection has been identified as an etiologic factor in gastric MALT lymphoma, and a growing list of other infectious organisms have recently been shown to be associated with MALT lymphomas at other anatomic sites. Although cause and effect has not been established for most of these infectious agents, our understanding of the biology has significantly improved, in part through the application of standard cytogenetic analyses. The common karyotypic alterations that characterize MALT lymphomas include the trisomies 3 and 18, the translocations t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21), t(3;14)(q27;q32), and the recently described t(3;14)(p14.1;q32). This apparent complexity of cytogenetic alterations that have now been implicated in the pathogenesis of extranodal MALT lymphoma serves as a paradigm for molecular cross talk in neoplastic disease. Recent data have shown that at least three of the disparate translocations affect a common signaling mechanism, and thus unify all three under a common pathogenesis, resulting in the constitutive activation of the nuclear factor kappa B (NF-kappaB) pathway. It may be that the new MALT-related translocation involving the FOXP1 gene and other as yet undiscovered translocations may all have in common increased NF-kappaB signaling.

Axotrophin and leukaemia inhibitory factor (LIF) in transplantation tolerance

Immune self-tolerance is controlled by a subset of T lymphocytes that are regulatory (Treg) and epigenetically programmed to suppress auto-reactive immune effector cells in vivo. By extrapolation, donor-specific transplantation tolerance might be controlled by donor-specific Treg that have acquired the appropriate epigenetic program for tolerance. Although such tolerance has yet to be achieved in man, proof of concept comes from mouse models where regulatory transplantation tolerance can be induced within the complex micro-environment of the spleen or draining lymph node. By studying whole spleen cell populations in a murine model of transplantation tolerance we have incorporated a complexity of environmental factors when looking for specific features that characterize tolerance versus aggression. This approach has revealed unexpected patterns of gene activity in tolerance and most notably that a novel stem cell gene, axotrophin, regulates T lymphocyte responsiveness both in terms of proliferation and in release of leukaemia inhibitory factor (LIF). Since LIF is a regulator of stem cells in addition to being a key neuropoietic cytokine, these preliminary results linking both axotrophin and LIF to transplantation tolerance lead us to propose that regulatory pathways encoded during the epigenetic development of Treg cells are related to pathways that regulate fate determination of stem cells.

FOXP1, a gene highly expressed in a subset of diffuse large B-cell lymphoma, is recurrently targeted by genomic aberrations

The transcription factor Forkhead box protein P1 (FOXP1) is highly expressed in a proportion of diffuse large B-cell lymphoma (DLBCL). In this report, we provide cytogenetic and fluorescence in situ hybridization (FISH) data showing that FOXP1 (3p13) is recurrently targeted by chromosome translocations. The genomic rearrangement of FOXP1 was identified by FISH in three cases with a t(3;14)(p13;q32) involving the immunoglobulin heavy chain (IGH) locus, and in one case with a variant t(2;3) affecting sequences at 2q36. These aberrations were associated with strong expression of FOXP1 protein in tumor cells, as demonstrated by immunohistochemistry (IHC). The cases with t(3p13) were diagnosed as DLBCL ( x 1), gastric MALT lymphoma ( x 1) and B-cell non-Hodgkin's lymphoma, not otherwise specified ( x 2). Further IHC and FISH studies performed on 98 cases of DLBCL and 93 cases of extranodal marginal zone lymphoma showed a high expression of FOXP1 in approximately 13 and 12% of cases, respectively. None of these cases showed, however, FOXP1 rearrangements by FISH. However, over-representation of the FOXP1 locus found in one additional case of DLBCL may represent another potential mechanism underlying an increased expression of this gene.

Antigen-dependent suppression of alloresponses byFoxp3-induced regulatory T cells in transplantation

Adoptive transfer of polyclonal CD4+CD25+ regulatory T cells (Treg) can tolerize transplantation alloresponses. Treg are activated via their specific TCR, but the antigen specificity of wild-type Treg remains elusive, and therefore controlling potency and duration of Treg activity in the transplantation setting is still not feasible. In this study, we used murine graft-versus-host disease (GVHD) as a model system to show that antigen-specific Treg suppress the response of T effector cells to alloantigens in vitro and prevent GVHD in vivo. The suppressive potential of antigen-specific Treg was much greater than that of polyclonal Treg. To acquire large numbers of antigen-specific Treg, we transduced CD4+CD25- cells with foxp3, and found that these foxp3-induced Treg suppress alloresponses in vitro and prevent GVHD in vivo as effectively as naturally derived CD4+CD25+ Treg. Furthermore, we used an antigen-specific CD4 Th1 clone as a source of foxp3-induced Treg after transduction with foxp3, and found those Treg to effectively prevent GVHD in an antigen-dependent manner. The findings of this study provide a basis for the concept that the onset and potency of the suppression by Treg can be regulated, and suggest a novel approach to enhance the feasibility and effectiveness of inducing tolerance by Treg as an adoptive immunotherapy in transplantation.