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Thirty years ago, one of the first types of CD4+ T regulatory cells was discovered and named T regulatory type 1 (Tr1) cells. Tr1 cells represent a distinct population of T cells, which are induced in the periphery upon antigen exposure under tolerogenic conditions. They produce the immunosuppressive cytokines interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β), do not constitutively express FOXP3, and suppress the function of effector immune cells. In this review, the key studies leading to the identification and biological characterization of Tr1 cells are recapitulated. The fundamental role of Tr1 cells in regulating immune responses to pathogenic and non-pathogenic antigens, as well as their use as cell therapeutics, is summarized.

Monogenic diseases of the immune system, also known as inborn errors of immunity, are caused by single-gene mutations resulting in immune deficiency and dysregulation. More than 350 diseases have been described to date, and the number is rapidly expanding, with increasing availability of next-generation sequencing facilitating the diagnosis. The spectrum of immune dysregulation is wide, encompassing deficiencies in humoral, cellular, innate, and adaptive immunity; phagocytosis; and the complement system, which lead to autoinflammation and autoimmunity. Multiorgan autoimmunity is a dominant symptom when genetic mutations lead to defects in molecules essential for the development, survival, and/or function of regulatory T (Treg) cells. Studies of "Tregopathies" are providing critical mechanistic information on Treg cell biology, the role of Treg cell-associated molecules, and regulation of peripheral tolerance in human subjects. The pathogenic immune networks underlying these diseases need to be dissected to apply and develop immunomodulatory treatments and design curative treatments using cell and gene therapy. Here we review the pathogenetic mechanisms, clinical presentation, diagnosis, and current and future treatments of major known Tregopathies caused by mutations in FOXP3, CD25, cytotoxic T lymphocyte-associated antigen 4 (CTLA4), LPS-responsive and beige-like anchor protein (LRBA), and BTB domain and CNC homolog 2 (BACH2) and gain-of-function mutations in signal transducer and activator of transcription 3 (STAT3). We also discuss deficiencies in genes encoding STAT5b and IL-10 or IL-10 receptor as potential Tregopathies.

Background Graft-vs-host-disease (GvHD) is a life-threatening complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT), limiting the use of this potentially curative treatment for hematological malignancies. To address this, we have developed T-allo10 cell therapy, which is enriched with type 1 regulatory T (Tr1) cells. Tr1 cells are peripherally inducible, CD49b+LAG3+IL-10+FOXP3- regulatory T cells that can confer alloantigen-specific tolerance, making them an attractive alternative to existing GvHD therapies, which non-discriminately impair both GvHD and protective immunity. T-allo10 cells are currently being evaluated in a phase I clinical trial in patients with hematological malignancies undergoing allo-HSCT (NCT03198234). Herein, we aimed to confirm that Tr1 cells are the active ingredient responsible for the T-allo10 suppressive function, and reveal the underlying molecular signatures to elucidate the mechanisms of Tr1 cell-mediated suppression. Methods T-allo10 cells were generated in a co-culture of healthy host or patient tolerogenic dendritic cells (DC-10) with allogeneic healthy donor CD4+ T cells, then tested for Tr1 phenotype, anergy, suppression and cytokine production. Sorted T-allo10-derived Tr1 cells and non-Tr1 cells, as well as control effector T cells (Teff) and parental CD4+ T cells, were analyzed by TCR- and RNA-seq. Protein expression for key differentially expressed genes were validated, and the functional roles for IL-10, CTLA-4 and PD-1 in T-allo10-mediated suppression were confirmed in a suppression assay. Results We show that the T-allo10 cell product is: i) enriched for Tr1 cells, ii) anergic in response to alloantigen re-challenge, but not to non-specific stimuli or 3rd party antigens, and iii) suppresses host-reactive T cells, but not T cell responses to other antigens. Furthermore, T-allo10-derived, isolated Tr1 cells had a restricted TCR repertoire, suggesting they clonally expand in response to alloantigens. T-allo10-derived Tr1 cells have a distinct signature compared to non-Tr1 cells, and, in addition to IL-10, express high levels of CTLA-4 and PD-1 (but not FOXP3). Notably, blockade of CTLA-4 and the PD-1 pathway completely abolishes T-allo10-mediated suppression of T cell responses. Conclusions Our data shows that Tr1 cells are the active, suppressive, and antigen-specific ingredient of T-allo10 cells. Furthermore, while the role of IL-10 in Tr1 cell-mediated suppression is well known, we uncover that Tr1 suppress in addition through CTLA-4 and PD-1. Collectively, these intriguing findings underscore the importance of CTLA-4 and PD-1 pathways in conferring cell-mediated immunological tolerance. Further, they define the key characteristics and modes of action of antigen-specific Tr1 cells, providing crucial information for the ongoing T-all10 trial and future design of novel Tr1 cell-based therapies. Ethics Approval The patient study was approved by Administrative Panels on Human Subjects in Medical Research, Stanford University, Tallo10 eProtocol # 38734. Healthy donor samples were purchased as deidentified human blood products from the Stanford Blood Center, and are thus exempt.

During their intrathymic development, nascent T cells are empowered to protect against pathogens and to be operative for a life-long acceptance of self. While autoreactive effector T (Teff) cell progenitors are eliminated by clonal deletion, the intrathymic mechanisms by which thymic regulatory T cell (tTreg) progenitors maintain specificity for self-antigens but escape deletion to exert their regulatory functions are less well understood. Both tTreg and Teff development and selection result from finely coordinated interactions between their clonotypic T cell receptors (TCR) and peptide/MHC complexes expressed by antigen-presenting cells, such as thymic epithelial cells and thymic dendritic cells. tTreg function is dependent on expression of the FOXP3 transcription factor, and induction of FOXP3 gene expression by tTreg occurs during their thymic development, particularly within the thymic medulla. While initial expression of FOXP3 is downstream of TCR activation, constitutive expression is fixed by interactions with various transcription factors that are regulated by other extracellular signals like TCR and cytokines, leading to epigenetic modification of the FOXP3 gene. Most of the understanding of the molecular events underlying tTreg generation is based on studies of murine models, whereas gaining similar insight in the human system has been very challenging. In this review, we will elucidate how inborn errors of immunity illuminate the critical non-redundant roles of certain molecules during tTreg development, shedding light on how their abnormal development and function cause well-defined diseases that manifest with autoimmunity alone or are associated with states of immune deficiency and autoinflammation.

Gene editing of FOXP3 ensures regulated expression and restored function in T cells, supporting clinical applicability., The prototypical genetic autoimmune disease is immune dysregulation polyendocrinopathy enteropathy X-linked (IPEX) syndrome, a severe pediatric disease with limited treatment options. IPEX syndrome is caused by mutations in the forkhead box protein 3 (FOXP3) gene, which plays a critical role in immune regulation. As a monogenic disease, IPEX is an ideal candidate for a therapeutic approach in which autologous hematopoietic stem and progenitor (HSPC) cells or T cells are gene edited ex vivo and reinfused. Here, we describe a CRISPR-based gene correction permitting regulated expression of FOXP3 protein. We demonstrate that gene editing preserves HSPC differentiation potential, and that edited regulatory and effector T cells maintain their in vitro phenotype and function. Additionally, we show that this strategy is suitable for IPEX patient cells with diverse mutations. These results demonstrate the feasibility of gene correction, which will be instrumental for the development of therapeutic approaches for other genetic autoimmune diseases.

Objectives Genetic or acquired defects in FOXP3+ regulatory T cells (Tregs) play a key role in many immune‐mediated diseases including immune dysregulation polyendocrinopathy, enteropathy, X‐linked (IPEX) syndrome. Previously, we demonstrated CD4+ T cells from healthy donors and IPEX patients can be converted into functional Treg‐like cells by lentiviral transfer of FOXP3 (CD4LVFOXP3). These CD4LVFOXP3 cells have potent regulatory function, suggesting their potential as an innovative therapeutic. Here, we present molecular and preclinical in vivo data supporting CD4LVFOXP3 cell clinical progression. Methods The molecular characterisation of CD4LVFOXP3 cells included flow cytometry, qPCR, RNA‐seq and TCR‐seq. The in vivo suppressive function of CD4LVFOXP3 cells was assessed in xenograft‐versus‐host disease (xeno‐GvHD) and FOXP3‐deficient IPEX‐like humanised mouse models. The safety of CD4LVFOXP3 cells was evaluated using peripheral blood (PB) humanised (hu)‐ mice testing their impact on immune response against pathogens, and immune surveillance against tumor antigens. Results We demonstrate that the conversion of CD4+ T cells to CD4LVFOXP3 cells leads to specific transcriptional changes as compared to CD4+ T‐cell transduction in the absence of FOXP3, including upregulation of Treg‐related genes. Furthermore, we observe specific preservation of a polyclonal TCR repertoire during in vitro cell production. Both allogeneic and autologous CD4LVFOXP3 cells protect from xeno‐GvHD after two sequential infusions of effector T cells. CD4LVFOXP3 cells prevent hyper‐proliferation of CD4+ memory T cells in the FOXP3‐deficient IPEX‐like hu‐mice. CD4LVFOXP3 cells do not impede in vivo expansion of antigen‐primed T cells or tumor clearance in the PB hu‐mice. Conclusion These data support the clinical readiness of CD4LVFOXP3 cells to treat IPEX syndrome and other immune‐mediated diseases caused by insufficient or dysfunctional FOXP3+ Tregs., In this study, we present novel molecular and preclinical in vivo data that support CD4LVFOXP3 clinical progression. These data support the clinical readiness of CD4LVFOXP3 to treat immune‐mediated diseases caused by insufficient or dysfunctional FOXP3+ Tregs.

FOXP3 is the transcription factor ruling regulatory T cell function and maintenance of peripheral immune tolerance, and mutations in its coding gene causes IPEX autoimmune syndrome. FOXP3 is also a cell-cycle inhibitor and onco-suppressor in different cell types. In this work, we investigate the effect of ectopic FOXP3 expression on HSC differentiation and we challenged this approach as a possible HSC-based gene therapy for IPEX. FOXP3-expressing HSC showed reduced proliferation ability and increased maintenance of primitive markers in vitro in both liquid and OP9-ΔL1 co-cultures. When transplanted into immunodeficient mice, FOXP3-expressing HSC showed significantly enhanced engraftment ability. This was due to a pronounced increase in the frequency of repopulating cells, as assessed by extreme limiting dilution assay. Likely underlying the increased repopulating ability, FOXP3 expressing HSC showed significantly enhanced expression of genes controlling stemness features. However, peripheral T cells developed in the FOXP3-humanized mice were quantitatively reduced and hyporesponsive to cytokine and polyclonal stimulation. Our findings reveal unpredicted effects of FOXP3 in the biology of HSC and may provide new tools to manipulate primitive features in HSC for clinical applications. Moreover, they formally prove the need of preserving endogenous FOXP3 regulation for an HSC-based gene therapy approach for IPEX syndrome.

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare disorder that increasingly has gained attention as a model of genetic autoimmunity. Numerous papers documenting the key clinical and molecular characteristics of IPEX have provided a detailed understanding of this devastating disease. IPEX is a primary immunodeficiency caused by mutations in the gene FOXP3, which encodes an essential transcription factor required for maintenance of thymus-derived regulatory T (tTreg) cells. tTreg cell dysfunction is the main pathogenic event leading to multiorgan autoimmunity in IPEX. In addition to the traditional clinical presentation (i.e., severe enteropathy, type 1 diabetes, and eczema), IPEX may encompass other variable and distinct clinical manifestations. As IPEX awareness and characterization have increased, so has identification of FOXP3 mutations, with at least 70 to date. Thus, while FOXP3 is the unifying gene, IPEX is a complex and diverse clinical continuum of disorders. Despite understanding IPEX pathogenesis, new treatment options have remained elusive, although early diagnosis led to hematopoietic stem cell transplantation (HSCT) and immunosuppression treatment and improved patient outcomes. Here, we review current knowledge about IPEX syndrome and highlight findings that could lead to novel targeted treatments.

Background & Aim Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is the prototypical primary immune regulatory disorder caused by mutations in the forkhead box protein 3 (FOXP3) gene, a critical transcription factor required for regulatory T cells (Tregs). Patients typically present with severe early onset autoimmune manifestations that can be fatal within the first year of life. Currently, the only cure for IPEX is allogeneic hematopoietic stem cell transplant (HSCT), but this comes with risk of complications and the survival probability at 15 years is 73.2% (F. Barzaghi et al 2018). Moreover, a suitable donor is not always available. As a monogenic immune disease with limited treatment options, IPEX is an ideal candidate for a gene therapy approach whereby patient hematopoietic stem cells are gene edited and reinfused for autologous transplant. Methods, Results & Conclusion We developed a CRISPR/Cas9 approach combined with AAV delivery of a donor template to restore FOXP3 expression at the endogenous locus, permitting regulated expression of wild-type FOXP3 irrespective of downstream mutations. We were able to edit CD4+ effector T cells (Teff) and Tregs, showing that they maintain characteristic phenotypic markers and are functional in vitro. IPEX patient Tregs edited with the construct had partial restoration of both FOXP3 expression and functional suppression upon co-culture with responder T cells. Gene edited cord blood hematopoietic stem and progenitor Cells (HSPCs) are capable of long-term engraftment in humanized mice and differentiate into multiple hematopoietic subsets (CD13, CD19, CD56, CD3) and partially reconstitute Tregs (CD4+CD25+FOXP3+). These results demonstrate the feasibility of using gene edited HSPCs and hold promise for autologous transplant in genetic autoimmune diseases such as IPEX syndrome.

[Background] Immune-dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a lethal disease caused by mutations in a transcription factor critical for the function of thymus-derived regulatory T (Treg) cells (ie, FOXP3), resulting in impaired Treg function and autoimmunity. At present, hematopoietic stem cell transplantation is the therapy of choice for patients with IPEX syndrome. If not available, multiple immunosuppressive regimens have been used with poor disease-free survival at long-term follow-up. Rapamycin has been shown to suppress peripheral T cells while sparing Treg cells expressing wild-type FOXP3, thereby proving beneficial in the clinical setting of immune dysregulation. However, the mechanisms of immunosuppression selective to Treg cells in patients with IPEX syndrome are unclear., [Objective] We sought to determine the cellular and molecular basis of the clinical benefit observed under rapamycin treatment in 6 patients with IPEX syndrome with different FOXP3 mutations., [Methods] Phenotype and function of FOXP3-mutated Treg cells from rapamycin-treated patients with IPEX syndrome were tested by flow cytometry and in vitro suppression assays, and the gene expression profile of rapamycin-conditioned Treg cells by droplet-digital PCR., [Results] Clinical and histologic improvements in patients correlated with partially restored Treg function, independent of FOXP3 expression or Treg frequency. Expression of TNF-receptor-superfamily-member 18 (TNFRSF18, glucocorticoid-induced TNF-receptor–related) and EBV-induced-3 (EBI3, an IL-35 subunit) in patients’ Treg cells increased during treatment as compared with that of Treg cells from untreated healthy subjects. Furthermore inhibition of glucocorticoid-induced TNF-receptor–related and Ebi3 partially reverted in vitro suppression by in vivo rapamycin-conditioned Treg cells., [Conclusions] Rapamycin is able to affect Treg suppressive function via a FOXP3-independent mechanism, thus sustaining the clinical improvement observed in patients with IPEX syndrome under rapamycin treatment.

Immune cell profiles provide valuable diagnostic information for hematologic and immunologic diseases. Although it is the most widely applied analytical approach, flow cytometry is limited to liquid blood. Moreover, either analysis must be performed with fresh samples or cell integrity needs to be guaranteed during storage and transport. We developed epigenetic real-time quantitative polymerase chain reaction (qPCR) assays for analysis of human leukocyte subpopulations. After method establishment, whole blood from 25 healthy donors and 97 HIV+ patients as well as dried spots from 250 healthy newborns and 24 newborns with primary immunodeficiencies were analyzed. Concordance between flow cytometric and epigenetic data for neutrophils and B, natural killer, CD3+ T, CD8+ T, CD4+ T, and FOXP3+ regulatory T cells was evaluated, demonstrating substantial equivalence between epigenetic qPCR analysis and flow cytometry. Epigenetic qPCR achieves both relative and absolute quantifications. Applied to dried blood spots, epigenetic immune cell quantification was shown to identify newborns suffering from various primary immunodeficiencies. Using epigenetic qPCR not only provides a precise means for immune cell counting in fresh-frozen blood but also extends applicability to dried blood spots. This method could expand the ability for screening immune defects and facilitates diagnostics of unobservantly collected samples, for example, in underdeveloped areas, where logistics are major barriers to screening.

Anti-cytokine autoantibodies (ACAAs) have been described in a growing number of primary immunodeficiencies with autoimmune features including Autoimmune Polyendocrine Syndrome Type I (APS-1), a prototypical disease of defective T cell central tolerance. Whether defects in peripheral tolerance lead to similar ACAAs is unknown. Immunodysregulation Polyendocrinopathy Enteropathy X-linked (IPEX) is caused by mutations in FOXP3, a master regulator of T regulatory cells (Treg), and consequently results in defective T cell peripheral tolerance. Unique autoantibodies have previously been described in IPEX. To test the hypothesis that ACAAs are present in IPEX, we designed and fabricated antigen microarrays. We discovered elevated levels of IgG ACAAs against interferon-alpha (IFN-alpha) in a cohort of IPEX patients. Serum from IPEX patients blocked IFN-alpha signaling in vitro, and blocking activity was tightly correlated with ACAA titer. To show that blocking activity was mediated by IgG and not other serum factors, we purified IgG and showed that blocking activity was contained entirely in the immunoglobulin fraction. We also screened for ACAAs against IFN-alpha in a second geographically distinct cohort. In these samples, ACAAs against IFN-alpha were elevated in a post-hoc analysis. In summary, we report the discovery of ACAAs against IFN-alpha in IPEX, an experiment of nature demonstrating the important role of peripheral T cell tolerance in preventing the development of IFN-alpha ACAAs.

The development of novel approaches to control immune responses to self- and allogenic tissues/organs represents an ambitious goal for the management of autoimmune diseases and in transplantation. Regulatory T cells (Tregs) are recognized as key players in the maintenance of peripheral tolerance in physiological and pathological conditions, and Treg-based cell therapies to restore tolerance in T cell-mediated disorders have been designed. However, several hurdles, including insufficient number of Tregs, their stability, and their antigen specificity, have challenged Tregs clinical applicability. In the past decade, the ability to engineer T cells has proven a powerful tool to redirect specificity and function of different cell types for specific therapeutic purposes. By using lentivirus-mediated gene transfer of the thymic-derived Treg transcription factor forkhead-box-P3 (FOXP3) in conventional CD4+ T cells, we converted effector T cells into Treg-like cells, endowed with potent in vitro and in vivo suppressive activity. The resulting CD4FOXP3 T-cell population displays stable phenotype and suppressive function. We showed that this strategy restores Treg function in T lymphocytes from patients carrying mutations in FOXP3 [immune-dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX)], in whom CD4FOXP3 T cell could be used as therapeutics to control autoimmunity. Here, we will discuss the potential advantages of using CD4FOXP3 T cells for in vivo application in inflammatory diseases, where tissue inflammation may undermine the function of natural Tregs. These findings pave the way for the use of engineered Tregs not only in IPEX syndrome but also in autoimmune disorders of different origin and in the context of stem cell and organ transplantation.

Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) syndrome is a rare autoimmune disease due to mutations in the gene encoding for Forkhead box P3 (FOXP3), a transcription factor fundamental for the function of thymus-derived (t) regulatory T (Treg) cells. The dysfunction of Treg cells results in the development of devastating autoimmune manifestations affecting multiple organs, eventually leading to premature death in infants, if not promptly treated by hematopoietic stem cell transplantation (HSCT). Novel gene therapy strategies can be developed for IPEX syndrome as more definitive cure than allogeneic HSCT. Here we describe the therapeutic approaches, alternative to HSCT, currently under development. We described that effector T cells can be converted in regulatory T cells by LV-mediated FOXP3-gene transfer in differentiated T lymphocytes. Despite FOXP3 mutations mainly affect a highly specific T cell subset, manipulation of stem cells could be required for long-term remission of the disease. Therefore, we believe that a more comprehensive strategy should aim at correcting FOXP3-mutated stem cells. Potentials and hurdles of both strategies will be highlighted here.

Background & Aim FOXP3 is an essential transcription factor for the regulatory T cell (Treg) function and therefore is a key regulator for the tolerance maintenance. Treg cell therapy, either with freshly isolated or expanded in vitro, has been proven to be safe but still challenging because of difficulties in isolating sufficient number of pure Treg cells, stability of the expanded preparations and Treg plasticity in vivo under pro-inflammatory conditions. The key role of FOXP3 and Treg cells in immune function is exemplified by immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX), a monogenic primary immune regulatory disease caused by mutations in FOXP3, that lead to impaired Treg cell function and early onset autoimmune manifestations. Our recent international retrospective study demonstrated suboptimal disease-free survival from current therapeutic options such as immunosuppression and allogeneic hematopoietic stem cell transplantation. Therefore, there is a great unmet medical need in patients with IPEX syndrome. Methods, Results & Conclusion We investigated lentiviral FOXP3 gene transfer (LV-FOXP3) in CD4+ T cells as an innovative approach to generate in large number stable Treg cells that could provide therapeutic benefit to IPEX patients lacking functional Treg. We have shown that LV-FOXP3 can converts IPEX patients-derived CD4+ effector T cells into Treg-like cells (CD4LV-FOXP3 T cells). To better investigate the safety and efficacy of this approach and to make it suitable for large scale GMP generation of CD4LV-FOXP3 T cells, we optimized the original lentiviral vector and we assessed the phenotype and function of CD4LV-FOXP3 T cells both in vitro using transcriptome analysis and in vivo in different humanized mice models. CD4LV-FOXP3 T cells express key molecules in common with freshly isolated Treg cells. CD4LV-FOXP3 T cells can significantly extend the survival of xeno GVHD model mice, both in autologous and allogenic conditions and they can suppress xeno GVHD reaction caused by secondary infusion of responder cells. These data indicated CD4LV-FOXP3 T cells have a sustained suppressive function in the various autologous in vivo mice models. In conclusion, we completed the preclinical requirement for the use of the CD4LV-FOXP3 cell product in IPEX syndrome. The Proof-of-concept trial in a severe monogenic pediatric disease will open to future clinical applications of CD4LV-FOXP3 cell therapy in other autoimmune and immunodysregulatory disorders of different origin.

Background Forkhead box P3 (FOXP3) is a key transcription factor in regulatory T (Treg) cell function. FOXP3 gene mutations cause immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, a fatal autoimmune syndrome. FOXP3 has also been proposed to act in effector T (Teff) cells, but to date, this role has not been confirmed. Objective We sought to evaluate the effect of reduced FOXP3 expression on human Treg and Teff cell development and correlate it with IPEX syndrome immune pathology. Methods We developed a model of humanized mice (huMice) in which the human hematopoietic system is stably knocked down or knocked out for the FOXP3 gene (knockdown [KD]/knockout [KO] huMice). Results Because FOXP3-KD/KO was not 100% effective, residual FOXP3 expression in hematopoietic stem progenitor cells was sufficient to give rise to Treg cells with normal expression of FOXP3. However, numerous defects appeared in the Teff cell compartment. Compared with control mice, FOXP3-KD/KO huMice showed altered thymocyte differentiation, with KD/KO thymocytes displaying significantly reduced T-cell receptor (TCR) signaling strength and increased TCR repertoire diversity. Peripheral KD/KO Teff cells were expanded and showed signs of homeostatic proliferation, such as a significantly contracted TCR repertoire, a severely reduced naive compartment, decreased telomeric repeat-binding factor 2 expression, and a skew toward a TH2 profile, resembling an aged immune system. Consistent with results in FOXP3-KD/KO huMice, analysis of patients with IPEX syndrome provided evidence of defects in the Teff cell compartment at both the thymic and peripheral levels. Conclusions These findings support an intrinsic role for human FOXP3 in controlling thymocyte maturation and peripheral expansion of Teff cells and reveal a previously undescribed pathogenic mechanism through an altered Teff cell compartment in patients with IPEX syndrome.

Cell-surface CD25 expression is critical for maintaining immune function and homeostasis. As in few reported cases, CD25 deficiency manifests with severe autoimmune enteritis and viral infections. To dissect the underlying immunological mechanisms driving these symptoms, we analyzed the regulatory and effector T cell functions in a CD25 deficient patient harboring a novel IL2RA mutation. Pronounced lymphoproliferation, mainly of the CD8+ T cells, was detected together with an increase in T cell activation markers and elevated serum cytokines. However, Ag-specific responses were impaired in vivo and in vitro. Activated CD8+STAT5+ T cells with lytic potential infiltrated the skin, even though FOXP3+ Tregs were present and maintained a higher capacity to respond to IL-2 compared to other T-cell subsets. Thus, the complex pathogenesis of CD25 deficiency provides invaluable insight into the role of IL2/IL-2RA-dependent regulation in autoimmunity and inflammatory diseases., Highlights ► CD25 deficiency leads to profound immune dysregulation. ► Preferential CD8+ T cell expansion and high cytokine serum levels were present. ► Proliferating CD8+ T cells infiltrated the skin but failed to respond to pathogens. ► CD4+FOXP3+CD127lowCD25null Tregs could be detected. ► Altered IL2 signaling events and failure of IL2 consumption contribute to autoimmunity.

The role of forkhead box P3 (FOXP3) is well-established in T-regulatory cells, but the function of transient FOXP3 expression in activated human conventional T (Tconv) cells is unknown. In the present study, we used 2 approaches to determine the role of FOXP3 in human Tconv cells. First, we obtained Tconv clones from a female subject who is hemizygous for a null mutation in FOXP3, allowing the comparison of autologous T-cell clones that do or do not express FOXP3. Second, we knocked down activation-induced FOXP3 in Tconv cells from healthy donors with small interfering RNAagainst FOXP3. We found that FOXP3-deficient Tconv cells proliferate more and produce more cytokines than wild-type Tconv cells and have differential expression of 274 genes. We also investigated the role of FOXP3 in Th1 and Th17 cells and found that the expression of activation-induced FOXP3 was higher and more sustained in Th17 cells compared with Th1 cells. Knocking down FOXP3 expression in Th17 cells significantly increased the production of IFN-γ and decreased the expression of CCR4, but had no effect on IL-17 expression. These data reveal a novel function of FOXP3 in Tconv cells and suggest that expression of this protein is important in the function of multiple CD4(+) T-cell lineages.

Immune dysregulation, Polyendocrinopathy, Enteropathy X-linked (IPEX) syndrome is a unique example of primary immunodeficiency characterized by autoimmune manifestations due to defective regulatory T (Treg) cells, in the presence of FOXP3 mutations. However, autoimmune symptoms phenotypically resembling IPEX often occur in the absence of detectable FOXP3 mutations. The cause of this “IPEX-like” syndrome presently remains unclear. To investigate whether a defect in Treg cells sustains the immunological dysregulation in IPEX-like patients, we measured the amount of peripheral Treg cells within the CD3+ T cells by analysing demethylation of the Treg cell-Specific-Demethylated-Region (TSDR) in the FOXP3 locus and demethylation of the T cell-Specific-Demethylated-Region (TLSDR) in the CD3 locus, highly specific markers for stable Treg cells and overall T cells, respectively. TSDR demethylation analysis, alone or normalized for the total T cells, showed that the amount of peripheral Treg cells in a cohort of IPEX-like patients was significantly reduced, as compared to both healthy subjects and unrelated disease controls. This reduction could not be displayed by flow cytometric analysis, showing highly variable percentages of FOXP3+ and CD25+FOXP3+ T cells. These data provide evidence that a quantitative defect of Treg cells could be considered a common biological hallmark of IPEX-like syndrome. Since Treg cell suppressive function was not impaired, we propose that this reduction per se could sustain autoimmunity., Highlights ► FOXP3 (TSDR) and CD3 (TLSDR) demethylation assays allow Treg cell quantification. ► TSDR/TLSDR ratio is altered in the majority of patients with immune dysregulation. ► IPEX-like syndromes share a quantitative but not functional defect of Treg cells.

Mutations of forkhead box p3 (FOXP3), the master gene for naturally occurring regulatory T cells (nTregs), are responsible for the impaired function of nTregs, resulting in an autoimmune disease known as the immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. The relevance of other peripheral tolerance mechanisms, such as the presence and function of type 1 regulatory T (Tr1) cells, the major adaptive IL-10-producing Treg subset, in patients with IPEX syndrome remains to be clarified. FOXP3(mutated) Tr1-polarized cells, differentiated in vitro from CD4(+) T cells of four IPEX patients, were enriched in IL-10 1 IL-4(+) IFN-gamma(+) T cells, a cytokine production profile specific for Tr1 cells, and expressed low levels of FOXP3 and high levels of Granzyme-B. IPEX Tr1 cells were hypoproliferative and suppressive, thus indicating that FOXP3 mutations did not impair their function. Furthermore, we isolated Tr1 cell clones from the peripheral blood of one FOXP3(null) patient, demonstrating that Tr1 cells are present in vivo and they can be expanded in vitro in the absence of WT FOXP3. Overall, our results (i) show that functional Tr1 cells differentiate independently of FOXP3, (ii) confirm that human Tr1 and nTregs are distinct T-cell lineages, and (iii) suggest that under favorable conditions Tr1 cells could exert regulatory functions in IPEX patients.

Background: Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) is a primary immunodeficiency with autoimmunity caused by mutations in forkhead box P3 (FOXP3), which encodes a transcription factor involved in regulatory T (Treg) cell function. The mechanistic basis for how different mutations in FOXP3 cause distinct manifestations of IPEX remains unclear. Objective: To determine whether 3 different point mutants of FOXP3 that cause severe or mild IPEX differ in their ability to reprogram conventional T cells into Treg cells. Methods: Human CD4(+) T cells were transduced with wild-type or point mutant forms of FOXP3, and changes in cell surface marker expression, cytokine production, proliferation and suppressive capacity were assessed. Ex vivo T H 17 cells were also transduced with different forms of FOXP3 to monitor changes in IL-17 production. Results: The forkhead mutant F373A failed to upregulate CD25 and CCR4, did not suppress cytokine production, and induced suppressive activity less effectively than wild-type FOXP3. In contrast, although the forkhead mutant R347H was also defective in upregulation of CD25, it suppressed the production of cytokines, conferred suppressive capacity on CD4(+) T cells, and suppressed IL-17 production. F324L, a mutant outside the forkhead domain associated with mild IPEX, was equivalent to wild-type FOXP3 in all aspects tested. Conclusion: Mutations in FOXP3 that cause IPEX do not uniformly abrogate the ability of FOXP3 to regulate transcription and drive the development of Treg cells. These data support the notion that factors in addition to functional changes in Treg cells, such as alterations in conventional T cells, are involved in the pathogenesis of IPEX. (J Allergy Clin Immunol 2010;126:1242-51.)

Background Peanut allergy (PA) is a life-threatening condition that lacks regulator-approved treatment. Regulatory T type 1 (T R 1) cells are potent suppressors of immune responses and can be induced in vivo upon repeated antigen exposure or in vitro by using tolerogenic dendritic cells. Whether oral immunotherapy (OIT) leads to antigen-specific T R 1 cell induction has not been established. Objectives We sought to determine whether peanut-specific T R 1 cells can be generated in vitro from peripheral blood of patients with PA at baseline or during OIT and whether they are functional compared with peanut-specific T R 1 cells induced from healthy control (HC) subjects. Methods Tolerogenic dendritic cells were differentiated in the presence of IL-10 from PBMCs of patients with PA and HC subjects pulsed with the main peanut allergens of Arachis hypogaea , Ara h 1 and 2, and used as antigen-presenting cells for autologous CD4 + T cells (CD4 + T cells coincubated with tolerogenic dendritic cells pulsed with the main peanut allergens [pea-T10 cells]). Pea-T10 cells were characterized by the presence of CD49b + lymphocyte-activation gene 3 (LAG3) + T R 1 cells, antigen-specific proliferative responses, and cytokine production. Results CD49b + LAG3 + T R 1 cells were induced in pea-T10 cells at comparable percentages from HC subjects and patients with PA. Despite their antigen specificity, pea-T10 cells of patients with PA with or without OIT, as compared with those of HC subjects, were not anergic and had high T H 2 cytokine production upon peanut-specific restimulation. Conclusions Peanut-specific T R 1 cells can be induced from HC subjects and patients with PA, but those from patients with PA are functionally defective independent of OIT. The unfavorable T R 1/T H 2 ratio is discussed as a possible cause of PA T R 1 cell impairment.

Forkhead box P3 (FOXP3) is constitutively expressed by CD4+CD25hi regulatory T cells (nTregs). Mutations of FOXP3 cause a severe autoimmune syndrome known as immune dysregulation polyendocrinopathy enteropathy X-linked, in which nTregs are absent or dysfunctional. Whether FOXP3 is essential for both differentiation and function of human nTreg cells remains to be demonstrated. Because FOXP3 is an X-linked gene subject to X-chromosome inactivation (XCI), we studied 9 healthy female carriers of FOXP3 mutations to investigate the role of wild-type (WT) versus mutated FOXP3 in different cell subsets. Analysis of active WT versus mutated (mut)–FOXP3 allele distribution revealed a random pattern of XCI in peripheral blood lymphocytes and in naive and memory CD4+T cells, whereas nTregs expressed only the active WT-FOXP3. These data demonstrate that expression of WT-FOXP3 is indispensable for the presence of a normal nTreg compartment and suggest that FOXP3 is not necessary for effector T-cell differentiation in humans.

Mice reconstituted with a human immune system provide a tractable in vivo model to assess human immune cell function. To date, reconstitution of murine strains with human hematopoietic stem cells (HSCs) from patients with monogenic immune disorders have not been reported. One obstacle precluding the development of immune-disease specific “humanized” mice is that optimal adaptive immune responses in current strains have required implantation of autologous human thymic tissue. To address this issue, we developed a mouse strain that lacks murine major histocompatibility complex class II (MHC II) and instead expresses human leukocyte antigen DR1 (HLA-DR1). These mice displayed improved adaptive immune responses when reconstituted with human HSCs including enhanced T-cell reconstitution, delayed-type hypersensitivity responses, and class-switch recombination. Following immune reconstitution of this novel strain with HSCs from a patient with immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, associated with aberrant FOXP3 function, mice developed a lethal inflammatory disorder with multiorgan involvement and autoantibody production mimicking the pathology seen in affected humans. This humanized mouse model permits in vivo evaluation of immune responses associated with genetically altered HSCs, including primary immunodeficiencies, and should facilitate the study of human immune pathobiology and the development of targeted therapeutics.

Little is known about the molecules that control the development and function of CD4(+)CD25(+)Tregs. Recently, it was shown that the transcription factor FOXP3 is necessary and sufficient for the generation of CD4(+)CD25(+) Tregs in mice. We investigated the capacity of FOXP3 to drive the generation of suppressive CD4(+)CD25(+) Tregs in humans. Surprisingly, although ectopic expression of FOXR3 in human CD4(+) T cells resulted in induction of hyporesponsiveness and suppression of IL-2 production, it,did not lead to acquisition of significant suppressor activity in vitro. Similarly, ectopic expression of FOXP3 Delta 2, an isoform found in human CD4(+)CD25(+) Tregs that lacks exon 2, also failed to induce the development of suppressor T cells. Moreover, when FOXP3 and FOXP3 Delta 2 were simultaneously overexpressed, although the expression of several Treg-associated cell surface markers was significantly increased, only a modest suppressive activity was induced. These data indicate that in humans, overexpression of FOXP3 alone or together with FOXP3 Delta 2 is not an effective method to generate potent suppressor T cells in vitro and suggest that factors in addition to FOXP3 are required during the process of activation and/or differentiation for the development of bona fide Tregs.

The main function of the immune system is to fight off potential infections, but also to maintain its activity below a level that would trigger self-reactivity. Regulatory T cells (Tregs) such as forkhead box P3(+) (FOXP3) Tregs and type 1 regulatory T cells (Tr1) play an essential role in this active process, using several distinct suppressive mechanisms. A wide range of pathologies have been associated with altered Treg cell function. This is best exemplified by the impact of mutations of genes essential for Treg function and the associated autoimmune syndromes. This review summarizes the main features of different subtypes of Tregs and focuses on the clinical implications of their altered function in human studies. More specifically, we discuss abnormalities affecting FOXP3(+) Tregs and Tr1 cells that will lead to autoimmune manifestations and/or allergic reactions, and the potential therapeutic use of Tregs.

Signal transducer and activator of transcription (STAT) comprises a family of universal transcription factors that help cells sense and respond to environmental signals. STAT5 refers to two highly related proteins, STAT5A and STAT5B, with critical function: their complete deficiency is lethal in mice; in humans, STAT5B deficiency alone leads to endocrine and immunological problems, while STAT5A deficiency has not been reported. STAT5A and STAT5B show peptide sequence similarities greater than 90%, but subtle structural differences suggest possible non-redundant roles in gene regulation. However, these roles remain unclear in humans. We applied chromatin immunoprecipitation followed by DNA sequencing using human CD4(+) T cells to detect candidate genes regulated by STAT5A and/or STAT5B, and quantitative-PCR in STAT5A or STAT5B knock-down (KD) human CD4(+) T cells to validate the findings. Our data show STAT5A and STAT5B play redundant roles in cell proliferation and apoptosis via SGK1 interaction. Interestingly, we found a novel, unique role for STAT5A in binding to genes involved in neural development and function (NDRG1, DNAJC6, and SSH2), while STAT5B appears to play a distinct role in T cell development and function via DOCK8, SNX9, FOXP3 and IL2RA binding. Our results also suggest that one or more co-activators for STAT5A and/or STAT5B may play important roles in establishing different binding abilities and gene regulation behaviors. The new identification of these genes regulated by STAT5A and/or STAT5B has major implications for understanding the pathophysiology of cancer progression, neural disorders, and immune abnormalities.

Ten years ago Forkhead box P3 (FOXP3) was discovered as master gene driving CD4(+)CD25(+) T cell regulatory (Treg) function. Since then, several layers of complexity have emerged in the regulation of its expression and function, which is not only exerted in Treg cells. While the mechanisms leading to the highly selective expression of FOXP3 in thymus-derived Treg cells still remain to be elucidated, we review here the current knowledge on the role of FOXP3 in the development of Treg cells and the direct and indirect consequences of FOXP3 mutations on multiple arms of the immune response. Finally, we summarize the newly acquired knowledge on the epigenetic regulation of FOXP3, still largely undefined in human cells.

In humans, mutations in the gene encoding for forkhead box P3 (FOXP3), a critically important transcription factor for CD4⁺CD25⁺ regulatory T (T(reg)) cell function, lead to a life-threatening systemic poly-autoimmune disease, known as immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. Severe autoimmunity results from the inborn dysfunction and instability of FOXP3-mutated T(reg) cells. Hematopoietic stem cell transplantation is the only current curative option for affected patients. We show here that when CD4⁺ T cells are converted into T(reg) cells after lentivirus-mediated FOXP3 gene transfer, the resulting CD4(FOXP3) T cell population displays stable phenotype and suppressive function, especially when naive T cells are converted. We further demonstrate that CD4(FOXP3) T cells are stable in inflammatory conditions not only in vitro but also in vivo in a model of xenogeneic graft-versus-host disease. We therefore applied this FOXP3 gene transfer strategy for the development of a T(reg) cell-based therapeutic approach to restore tolerance in IPEX syndrome. IPEX-derived CD4(FOXP3) T cells mirrored T(reg) cells from healthy donors in terms of cellular markers, anergic phenotype, cytokine production, and suppressive function. These findings pave the way for the treatment of IPEX patients by adoptive cell therapy with genetically engineered T(reg) cells and are seminal for future potential application in patients with autoimmune disorders of different origin.

To the editor: Mutations of FoxP3 result in the disturbance of FoxP3 expression and lack of functional CD4+CD25high regulatory T cells in humans, causing immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. The only curative approach for IPEX syndrome, which is fatal

The association of immunodeficiency and autoimmunity may represent a paradox, yet it has been described in an increasing number of conditions. Use of unbiased genomic approach to identify novel forms of primary immunodeficiencies (PIDs), along with in-depth functional studies in biological samples from affected individuals continue to unravel novel mechanisms underlying immune dysregulation in patients with altered ability of fighting pathogens. In particular, it has been clearly established that genetic defects that affect T and B cell development compromise not just the ability to generate a diversified repertoire of lymphocytes capable of recognizing multiple pathogens, but also impinge on mechanisms of central and peripheral tolerance, hence favoring autoimmune and inflammatory manifestations. Yet, the diagnosis of autoimmune symptoms in the context of PIDs is troublesome, the prognosis unclear, and the treatment challenging. In the present collection of manuscripts, several experts in the field provide an overview of the spectrum of different forms of monogenic defects of the immune system manifesting also with autoimmunity, and discuss established and novel mechanisms involved in immune dysregulation. Studies on patients with Immunedysregulation-Polyendocrinopathy Enteropathy-X-linked (IPEX) Syndrome, have paved the way to understand the phenotype arising from impaired peripheral tolerance due to dysfunctional regulatory T cells (Treg) expressing mutated FOXP3. However, this important T cell subpopulation can also be affected in other forms of PID, such as Wiskott–Aldrich syndrome (WAS) and adenosine deaminase (ADA) deficiency. In these disorders, the underlying genetic defect affects multiple cell types, resulting in impaired immune defense, but also poor Treg function. Similarly, STAT5B mutations disrupt an essential intracellular transcriptional activator for Treg cells, causing reduction of Treg number in affected individuals. Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is an autosomal recessive condition due to mutation of the Autoimmune regulator (AIRE) gene. Patients with APECED present with predominant organ specific autoimmunity and autoantibodies with multiple specificities. AIRE has been shown to play a critical role in allowing expression of self-antigens in the thymus, thereby permitting deletion of self-reactive T lymphocytes or their diversion to Treg cells. Thus APECED stands as the prototypic monogenic disorder of central T cell tolerance. While it is still questionable whether deficiency of AIRE also affects peripheral tolerance, recent data indicate that the autoimmune-associated tissue damage may not be primarily due to autoantibodies, but rather to autoreactive CD8+ T cells. Moreover, recent studies in patients affected with Common Variable Immunodeficiency, a condition in which proper specific antibody production is deficient in favor of pathogenic autoantibody secretion, have highlighted the importance of mechanisms that control B cell development and receptor editing in maintaining immune homeostasis. Finally, two manuscripts call the attention to the dual role of certain cell types and their ability to acquire different immunological functions depending on the environment in which they differentiate, as described for Th17 cells and dendritic cells, at the end of the Topic. Possibly, the future of medicine should aim to implement physiological plasticity and to empower epigenetics modifications in order to recover from inborn errors of Nature.

Regulatory T cells (Tregs) play an essential role in preventing autoimmunity. Mutations in the forkhead box protein 3 (FOXP3) gene, which encodes a transcription factor critical for Treg function, result in a severe autoimmune disorder and the production of various autoantibodies in mice and in IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) patients. However, it is unknown whether Tregs normally suppress autoreactive B cells. To investigate a role for Tregs in maintaining human B-cell tolerance, we tested the reactivity of recombinant antibodies isolated from single B cells isolated from IPEX patients. Characteristics and reactivity of antibodies expressed by new emigrant/transitional B cells from IPEX patients were similar to those from healthy donors, demonstrating that defective Treg function does not impact central B-cell tolerance. In contrast, mature naive B cells from IPEX patients often expressed autoreactive antibodies, suggesting an important role for Tregs in maintaining peripheral B-cell tolerance. T cells displayed an activated phenotype in IPEX patients, including their Treg-like cells, and showed up-regulation of CD40L, PD-1, and inducibl T-cell costimulator (ICOS), which may favor the accumulation of autoreactive mature naive B cells in these patients. Hence, our data demonstrate an essential role for Tregs in the establishment and the maintenance of peripheral B-cell tolerance in humans.

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Children carrying mutations in the forkhead box p3 (FOXP3) gene are affected by the syndrome known as Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX). Early onset severe enteropathy, Type-1 diabetes (T1D) and eczema with elevated IgE serum levels are the hallmarks of the disease. Mortality is generally high within the first year of life, although some patients can partially respond to conventional immunosuppression showing clinical improvement. Progress in understanding the pathogenesis of IPEX have been made possible by the recognition that FOXP3 is the driving force for the function of naturally occurring regulatory T cells, a T-cell subset specialized in controlling immune responses. However, many open questions concerning the disease mechanisms, the indications for genetic screening and appropriate treatment of IPEX syndrome remain unanswered. In addition, several patients presenting IPEX-like symptoms do not carry mutations in the FOXP3 gene. In the present chapter, we will (1) summarize the latest findings on the biologic function of FOXP3 and its role in immune regulation, (2) highlight the most relevant signs for a correct diagnosis of IPEX syndrome, and (3) provide indications for the development of more targeted therapeutic strategies for the treatment of this devastating pediatric autoimmune disease.

The immune system is responsible for not only eliminating threats to the body, but also for protecting the body from its own immune responses that would cause harm if left unchecked. Forkhead box protein 3 (FOXP3) is a forkhead family member with an important role in the development and function of a type of CD4+ T cell called T regulatory cells that is fundamental for maintaining immune tolerance to self. This chapter reviews the structure of FOXP3 and how its role in the immune system was discovered. Studies ofpatients with mutations in FOXP3 who suffer from a syndrome known as IPEX (immune dysregulation, polyendocrinopathy, enteropathy, x-linked) are also discussed. Investigation into howexpression of FOXP3 is regulated and how it interacts with other proteins have recently provided considerable insight into mechanisms bywhich the lack of this protein could cause disease. We also discuss how FOXP3 is involved in the reciprocal development of T regulatory cellsand proinflammatory T-cells that produce IL-17. A better understanding ofhow FOXP3 is regulated and the molecular basis for its function will ultimately contribute to the development of T regulatory cell-based cellular therapies that could be used to restore dysregulated immune responses.

T-regulatory cells (Tregs) have a fundamental role in the establishment and maintenance of peripheral tolerance. There is now compelling evidence that deficits in the numbers and/or function of different types of Tregs can lead to autoimmunity, allergy, and graft rejection, whereas an over-abundance of Tregs can inhibit anti-tumor and anti-pathogen immunity. Experimental models in mice have demonstrated that manipulating the numbers and/or function of Tregs can decrease pathology in a wide range of contexts, including transplantation, autoimmunity, and cancer, and it is widely assumed that similar approaches will be possible in humans. Research into how Tregs can be manipulated therapeutically in humans is most advanced for two main types of CD4(+) Tregs: forkhead box protein 3 (FOXP3)(+) Tregs and interleukin-10-producing type 1 Tregs (Tr1 cells). The aim of this review is to highlight current information on the characteristics of human FOXP3(+) Tregs and Tr1 cells that make them an attractive therapeutic target. We discuss the progress and limitations that must be overcome to develop methods to enhance Tregs in vivo, expand or induce them in vitro for adoptive transfer, and/or inhibit their function in vivo. Although many technical and theoretical challenges remain, the next decade will see the first clinical trials testing whether Treg-based therapies are effective in humans.

BACKGROUND: Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is an autoimmune genetic disorder caused by mutation of the forkhead box protein 3 gene (FOXP3), a key regulator of immune tolerance. OBJECTIVE: We sought to provide clinical and molecular indicators that facilitate the understanding and diagnosis of IPEX syndrome. METHODS: In 14 unrelated affected male subjects who were given diagnoses of IPEX syndrome based on FOXP3 gene sequencing, we determined whether particular FOXP3 mutations affected FOXP3 protein expression and correlated the molecular and clinical data. RESULTS: Molecular analysis of FOXP3 in the 14 subjects revealed 13 missense and splice-site mutations, including 7 novel mutations. Enteropathy, generally associated with endocrinopathy and eczema, was reported in all patients, particularly in those carrying mutations within FOXP3 functional domains or mutations that altered protein expression. However, similar genotypes did not always result in similar phenotypes in terms of disease presentation and severity. In addition, FOXP3 protein expression did not correlate with disease severity. CONCLUSION: Severe autoimmune enteropathy, which is often associated with increased IgE levels and eosinophilia, is the most prominent early manifestation of IPEX syndrome. Nevertheless, the disease course is variable and somewhat unpredictable. Therefore genetic analysis of FOXP3 should always be performed to ensure an accurate diagnosis, and FOXP3 protein expression analysis should not be the only diagnostic tool for IPEX syndrome. OI RONCAROLO, Maria Grazia/0000-0002-2193-9186 ZS 1 ZR 2 ZB 47 Z8 7

Therapies based on enhancing the numbers and/or function of T regulatory cells (Tregs) represent one of the most promising approaches to restoring tolerance in many immune-mediated diseases. Several groups have investigated whether human Tregs suitable for cellular therapy can be obtained by in vitro expansion, in vitro conversion of conventional T cells into Tregs, or gene transfer of the FOXP3 transcription factor. To date, however, none of these approaches has resulted in a homogeneous and stable population of cells that is as potently suppressive as ex vivo Tregs. We developed a lentivirus-based strategy to ectopically express high levels of FOXP3 that do not fluctuate with the state of T-cell activation. This method consistently results in the development of suppressive cells that are as potent as Tregs and can be propagated as a homogeneous population. Moreover, using this system, both naïve and memory CD4(+) T cells can be efficiently converted into Tregs. To date, this is the most efficient and reliable protocol for generating large numbers of suppressive CD4(+) Tregs, which can be used for further biological study and developed for antigen-specific cellular therapy applications.

Forkhead box P3 (FOXP3) is considered a specific marker for CD4(+)CD25(+) regulatory T (Treg) cells, but increasing evidence suggests that human CD4(+)CD25(-) effector T (Teff) cells can transiently express FOXP3 upon activation. We demonstrate that the signal transducer and activator of transcription 5 (STAT5)-signaling cytokines, IL-2, IL-15 and to a lesser extent IL-7, induce FOXP3 up-regulation in vitro in activated human Teff cells. In contrast, cytokines which do not activate STAT5, such as IL-4 or transforming growth factor-beta alone, do not directly induce FOXP3 expression in activated Teff cells. Moreover, expression of a constitutively active form of STAT5a is sufficient to induce FOXP3 expression in Teff cells. Expression of FOXP3 in activated Teff cells requires both TCR-mediated activation and endogenous IL-2, but is not dependent on cell division and does not induce suppressive function. The presence of STAT5-activating cytokines is also required to maintain high FOXP3 expression and suppressive activity of Treg cells in vitro. These data indicate that activation of STAT5 sustains FOXP3 expression in both Treg and Teff cells and contribute to our understanding of how cytokines affect the expression of FOXP3.

Forkhead box P3 (FOXP3) is currently thought to be the most specific marker for naturally occurring CD4(+)CD25(+) T regulatory cells (nTregs). In mice, expression of FoxP3 is strictly correlated with regulatory activity, whereas increasing evidence suggests that in humans, activated T effector cells (Teffs) may also express FOXP3. In order to better define the role of FOXP3 in human Teff cells, we investigated the intensity and kinetics of expression in ex vivo Teff cells, suppressed Teff cells and Teff cell lines. We found that all dividing Teff cells expressed FOXP3, but only transiently, and at levels that were significantly lower than those in suppressive nTregs. This temporary expression in Teff cells was insufficient to suppress expression of reported targets of FOXP3 repressor activity, including CD127, IL-2 and IFN-gamma, and was not correlated with induction of a nTreg phenotype. Thus expression of FOXP3 is a normal consequence of CD4(+) T cell activation and, in humans, it can no longer be used as an exclusive marker of nTregs. These data indicate that our current understanding of how FOXP3 contributes to immune tolerance in humans needs to be re-evaluated.

Immune regulation and tolerance are specific functions of the immune system, meaning at prevention or limitation of effector immune responses against inner and external insults. Regulatory T (Treg) cells are crucial players in this immune balance network. Research over the last 10 years has significantly contributed to characterizing Treg cell features, their mechanisms of function, and their role in human pathologies. The discovery of FOXP3 as an essential transcription factor not only for differentiation and function of naturally occurring Treg cells but also for regulation of intracellular molecules related to effector T-cell responses has provided new insights into the pathogenesis of immune-mediated diseases. Interestingly, there is increasing evidence that the individual signature of genes relevant for immune regulation definitely influences the final outcome of an immune response.

The autoimmune disease immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) is caused by mutations in the forkhead box protein P3 (FOXP3) gene. In the mouse model of FOXP3 deficiency, the lack of CD4(+)CD25(+) Tregs is responsible for lethal autoimmunity, indicating that FOXP3 is required for the differentiation of this Treg subset. We show that the number and phenotype of CD4(+)CD25(+) T cells from IPEX patients are comparable to those of normal donors. CD4(+)CD25(high) T cells from IPEX patients who express FOXP3 protein suppressed the in vitro proliferation of effector T cells from normal donors, when activated by "weak" TCR stimuli. In contrast, the suppressive function of CD4(+)CD25(high) T cells from IPEX patients who do not express FOXP3 protein was profoundly impaired. Importantly, CD4(+)CD25(high) T cells from either FOXP3(+) or FOXP3(-) IPEX patients showed altered suppression toward autologous effector T cells. Interestingly, IL-2 and IFN-gamma production by PBMCs from IPEX patients was significantly decreased. These findings indicate that FOXP3 mutations in IPEX patients result in heterogeneous biological abnormalities, leading not necessarily to a lack of differentiation of CD4(+)CD25(high) Tregs but rather to a dysfunction in these cells and in effector T cells.

he main subsets of CD4(+) regulatory T (Tr) cells are the CD4(+) CD25(+) Tr cells and the type 1 regulatory (Tr1) cells. Both subsets are essential for the maintenance of peripheral tolerance. CD4(+) CD25(+) Tr cells control immune homeostasis (e.g., in autoimmunity) mainly by cell contact-dependent interactions. In contrast, Tr1 cells regulate immune responses in transplantation, allergy, and autoirnmune diseases, via an IL-10- and TGF-beta-dependent mechanism. Identification of the mechanisms responsible for the induction of the different Tr subsets in vivo is a matter of intense investigation. Studies on dendritic cells (DC), performed in the last years by several groups, have significantly contributed to clarify this point. Indeed, it is now clear that the role of DCs is not only to sense danger, but also to tolerize the immune system to antigens (Ags) encountered in the absence of maturation/inflammatory stimuli. Therefore, if a naive T cell encounters the antigen on immature DCs (iDCs), it differentiates into a Tr cell rather than an effector T cell. A better understanding of the mechanisms underlying the induction and functions of Tr cells in controlling the immune system is critical in view of a future cellular therapy to modulate immune-mediated pathologies.

T regulatory cells (Tregs) play a pivotal role in promoting and maintaining tolerance. Several subsets of Tregs have been identified but, to date, the best characterized are the CD4+FOXP3+ Tregs (FOXP3+Tregs), thymic-derived or induced in the periphery, and the CD4+ IL-10-producing T regulatory type 1 (Tr1) cells. In the past decade much effort has been dedicated to develop methods for the in vitro induction and expansion of FOXP3+Tregs and of Tr1 cells for Treg-based cell therapy to promote and restore tolerance in T-cell mediated diseases, and for expanding antigen (Ag)-specific Tregs in vivo. FOXP3+Tregs constitutively express high levels of CD25 and of the transcription factor FOXP3. FOXP3+Tregs are distinguished from activated CD4+ T cells by the low expression of CD127, and by the DNA demethylation of a specific region of the FOXP3 gene called Treg-specific demethylated region (TSDR). FOXP3+Tregs suppress effector T-cell responses through cell-to-cell contact-dependent mechanisms and suppression requires activation via TCR and is IL-2 dependent. In vitro protocols to expand FOXP3+Tregs for adoptive transfer in vivo have been established. We demonstrated that rapamycin permits the in vitro expansion of FOXP3+Tregs while impairing the proliferation of non-Tregs. Moreover, rapamycin-expanded FOXP3+Tregs maintain their regulatory phenotype in a proinflammatory environment and Th17 cells do not expand in the presence of rapamycin. Despite the progress in FOXP3+Tregs expansion protocols, adoptive transfer of FOXP3+Tregs in humans remains a difficult experimental procedure due to the ability to expand a sufficient number of Ag-specific FOXP3+Tregs in vitro. To propagate a homogenous population of FOXP3+Tregs we developed a lentiviral vector (LV)-based strategy to ectopically express FOXP3 in CD4+ T cells. This method results in the development of suppressive cells that are super-imposable to FOXP3+Tregs. Conversion of effector T cells into FOXP3+Tregs upon LV-mediated gene transfer of wild-type FOXP3 was also obtained in CD4+T cells from immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX) patients. We also developed a LV platform, which selectively targets expression of the transgene in hepatocytes, to induce tolerance to self or exogenous Ags. Using this approach we showed that systemic administration of LV encoding for the gene of interest leads to the induction of Ag-specific FOXP3+ Tregs, which mediate tolerance even in pre-immunized hosts. Tr1 cells are identified by their cytokine profile (IL-10+TGF-b+IL-4-IL-17-). Tr1 cells express transiently FOXP3 upon activation; but FOXP3 expression never reaches the high levels characteristic of FOXP3+Tregs. Tr1 cell differentiation and function is independent of FOXP3 since suppressive Tr1 cells can be isolated or generated from peripheral blood of IPEX patients. Tr1 cells were first discovered in peripheral blood of patients who developed tolerance after HLA-mismatched fetal liver hematopoietic stem cell transplant (HSCT). Since their discovery, Tr1 cells have proven to be important in mediating tolerance in several immune-mediated diseases. The immuno-regulatory mechanisms of Tr1 cells have been studied over the years thanks to the possibility to generate these cells in vitro. Tr1 cells suppress T-cell responses via the secretion of IL-10 and TGF-β and by the specific killing of myeloid APC via Granzyme B and perforin. Tr1 cells can be induced in vitro in an Ag-specific manner in the presence of IL-10 or of DC-10. Proof-of-principle clinical trials in allogeneic HSCT demonstrated the safety of Treg-based cell therapy with these polarized Tr1 cells. We are currently planning a phase I/II trial using in vitro polarized Tr1 cells with DC-10 in patients after kidney transplantation. An alternative strategy for the induction of high numbers of human Tr1 cells is the LV-mediated gene transfer of human IL-10 into conventional CD4+ T cells. Stable ectopic expression of IL-10 leads to the differentiation of homogeneous populations of Tr1-like cells displaying potent suppressive functions both in vitro and in vivo. A major hurdle, which limited the studies and the clinical use of Tr1 cells, was the lack of specific biomarkers. By gene expression profiling of human Tr1 cell clones we identified two surface markers (CD49b and LAG-3), which are stably and selectively co-expressed on murine and human Tr1 cells induced in vitro or in vivo. The co-expression of CD49b and LAG-3 enables the isolation of highly suppressive Tr1 cells from in vitro IL-10-polarized Tr1 cells and allows tracking of Tr1 cells in peripheral blood of patients who developed tolerance after allogeneic HSCT. The identification of CD49b and LAG-3 as Tr1-specific biomarkers will facilitate the study of Tr1 cells in vivo in healthy and pathological conditions and the use of Tr1 cells for forthcoming therapeutic interventions. In conclusion, Tregs play a key role in maintaining immunological homeostasis in the periphery. Several open questions regarding FOXP3+ Tregs or Tr1 cell-based therapy in humans remain: how long do Tregs survive after transfer? Is their phenotype stable in pathological conditions and inflammatory environments? Is their mechanism of suppression in vivo Ag-specific? Carefully designed and standardized future clinical protocols reflecting a concerted action among different investigators will help to address these questions and to advance the field. Disclosures: No relevant conflicts of interest to declare.