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The Wnt/β-catenin pathway regulates T-cell functions, including the repression of effector functions to the advantage of memory development via Tcf1. In a companion study, we demonstrate that, in human cancers, Wnt3a/β-catenin signaling maintains tumor-infiltrating T cells in a partially exhausted status. Here, we have investigated the effects of Wnt3a neutralization in vivo in a mouse tumor model. Abundant Wnt3a was released, mostly by stromal cells, in the tumor microenvironment. We tested whether Wnt3a neutralization in vivo could rescue the effector capacity of tumor-infiltrating T cells, by administering an antibody to Wnt3a to tumor-bearing mice. This therapy restrained tumor growth and favored the expansion of tumor antigen–specific CD8+ effector memory T cells with increased expression of Tbet and IFNγ and reduced expression of Tcf1. However, the effect was not attributable to the interruption of T-cell–intrinsic β-catenin signaling, because Wnt3a/β-catenin activation correlated with enhanced, not reduced, T-cell effector functions both ex vivo and in vitro. Adoptively transferred CD8+ T cells, not directly exposed to the anti-Wnt3a antibody but infiltrating previously Wnt3a-neutralized tumors, also showed improved functions. The rescue of T-cell response was thus secondary to T-cell–extrinsic changes that likely involved dendritic cells. Indeed, tumor-derived Wnt3a strongly suppressed dendritic cell maturation in vitro, and anti-Wnt3a treatment rescued dendritic cell activities in vivo. Our results clarify the function of the Wnt3a/β-catenin pathway in antitumor effector T cells and suggest that Wnt3a neutralization might be a promising immunotherapy for rescuing dendritic cell activities. Cancer Immunol Res; 6(8); 953–64. ©2018 AACR.

Metabolic inflammation, defined as a chronic low-grade inflammation, is implicated in numerous metabolic diseases. In recent years, the role of regulatory T cells (Tregs) as key controllers of metabolic inflammation has emerged, but our comprehension on how different metabolic pathways influence Treg functions needs a deeper understanding. Here we focus on how circulating and intracellular lipid metabolism, in particular cholesterol metabolism, regulates Treg homeostasis, expansion, and functions. Cholesterol is carried through the bloodstream by circulating lipoproteins (chylomicrons, very low-density lipoproteins, low-density lipoproteins). Tregs are equipped with a wide array of metabolic sensors able to perceive and respond to changes in the lipid environment through the activation of different intracellular pathways thus conferring to these cells a crucial metabolic and functional plasticity. Nevertheless, altered cholesterol transport, as observed in genetic dyslipidemias and atherosclerosis, impairs Treg proliferation and function through defective cellular metabolism. The intracellular pathway devoted to the cholesterol synthesis is the mevalonate pathway and several studies have shown that this pathway is essential for Treg stability and suppressive activity. High cholesterol concentrations in the extracellular environment may induce massive accumulation of cholesterol inside the cell thus impairing nutrients sensors and inhibiting the mevalonate pathway. This review summarizes the current knowledge regarding the role of circulating and cellular cholesterol metabolism in the regulation of Treg metabolism and functions. In particular, we will discuss how different pathological conditions affecting cholesterol transport may affect cellular metabolism in Tregs.

Angiopoietin-like 3 (ANGPTL3) regulates lipid and glucose metabolism. Loss-of-function mutations in its gene, leading to ANGPTL3 deficiency, cause in humans the familial combined hypolipidemia type 2 (FHBL2) phenotype, characterized by very low concentrations of circulating lipoproteins and reduced risk of atherosclerotic cardiovascular disease. Whether this condition is accompanied by immune dysfunctions is unknown. Regulatory T cells (Tregs) are CD4 T lymphocytes endowed with immune suppressive and atheroprotective functions and sensitive to metabolic signals. By investigating FHBL2, we explored the hypothesis that Tregs expand in response to extreme hypolipidemia, through a modulation of the Treg-intrinsic lipid metabolism.Treg frequency, phenotype, and intracellular lipid content were assessed ex vivo from FHBL2 subjects and age- and sex-matched controls, through multiparameter flow cytometry. The response of CD4 T cells from healthy controls to marked hypolipidemia was tested in vitro in low-lipid culture conditions.The ex vivo analysis revealed that FHBL2 subjects showed higher percentages of Tregs with a phenotype undistinguishable from controls and with a lower lipid content, which directly correlated with the concentrations of circulating lipoproteins. In vitro, lipid restriction induced the upregulation of genes of the mevalonate pathway, including those involved in isoprenoid biosynthesis, and concurrently increased the expression of the Treg markers FOXP3 and Helios. The latter event was found to be prenylation-dependent, and likely related to increased IL-2 production and signaling.Our study demonstrates that FHBL2 is characterized by high Treg frequencies, a feature which may concur to the reduced atherosclerotic risk in this condition. Mechanistically, hypolipidemia may directly favor Treg expansion, through the induction of the mevalonate pathway and the prenylation of key signaling proteins.

The autoimmune immunopathology occurring in multiple sclerosis (MS) is sustained by myelin-specific and -nonspecific CD8+ T cells. We have previously shown that, in MS, activated T cells undergoing apoptosis induce a CD8+ T cell response directed against antigens that are unveiled during the apoptotic process, namely caspase-cleaved structural proteins such as non-muscle myosin and vimentin. Here, we have explored in vivo the development and the function of the immune responses to cryptic apoptosis-associated epitopes (AEs) in a well-established mouse model of MS, experimental autoimmune encephalomyelitis (EAE), through a combination of immunization approaches, multiparametric flow cytometry, and functional assays. First, we confirmed that this model recapitulated the main findings observed in MS patients, namely that apoptotic T cells and effector/memory AE-specific CD8+ T cells accumulate in the central nervous system of mice with EAE, positively correlating with disease severity. Interestingly, we found that AE-specific CD8+ T cells were present also in the lymphoid organs of unprimed mice, proliferated under peptide stimulation in vitro, but failed to respond to peptide immunization in vivo, suggesting a physiological control of this response. However, when mice were immunized with AEs along with EAE induction, AE-specific CD8+ T cells with an effector/memory phenotype accumulated in the central nervous system, and the disease severity was exacerbated. In conclusion, we demonstrate that AE-specific autoimmunity may contribute to immunopathology in neuroinflammation.

Background & aims During chronic viral infections, the apoptosis of activated T cell elicits a CD8+ T cell response directed to those cryptic epitopes that emerge from caspase-cleaved structural proteins. Such response directed to apoptosis-associated epitopes (AEs) contributes to the amplification of immunopathology. Methods Here, we have analysed through flow cytometry AE-specific CD8+ T cells in patients with chronic hepatitis B virus (HBV) infection, naive-to-treatment or undergoing nucleos(t)ide-analogue (NUC) therapy. Results We found that AE-specific CD8+ T cell frequencies were significantly increased only in those NUC-treated patients who also presented advanced hepatic fibrosis. Regulatory T cells were also expanded in those patients, and AE-specific, but not HBV-specific, CD8+ T cell frequency positively correlated with Treg percentages. Through multiparameter flow cytometry, multidimensionality reduction and unsupervised clustering analysis, we could identify novel subpopulations among effector memory (em) and emCD45RA+ T cell (Tem and Temra) subsets. CD8+ T cells with distinct specificities differentially populated the subpopulation map: while HBV-specific were mostly contained in the Tem subset, AE-specific CD8+ T cells encompassed naive, as well as T central memory, Tem and Temra cells. Conclusion All together, these findings indicate a link between AE-specific CD8+ T cells and advanced liver fibrosis in patients with chronic HBV infection, and suggest that virus-specific and AE-specific CD8+ T cells exhibit distinct differentiation states and contribute in distinct ways to immunopathology.

During chronic viral infections, the apoptosis of activated T cell elicits a CD8Here, we have analysed through flow cytometry AE-specific CD8We found that AE-specific CD8All together, these findings indicate a link between AE-specific CD8

In our study, we investigated the role of CD39 on tumor-infiltrating CD8

Regulatory T cells (Tregs), expressing the transcription factor Foxp3, are defined as immunosuppressive cells able to modulate a variety of immune cells in order to avoid unwanted and excessive immune responses; however, in the tumor context, Treg function contribute to inhibit immune surveillance, thus promoting cancer progression. In tumor microenvironment, where the availability of metabolic resources is strongly limited, Tregs are expanded and may exploit different metabolic routes to achieve a metabolic advantage, prevailing over effector cells. In this context an important role of lipid metabolism has been described thanks to the possibility to evaluate the intracellular lipid content selectively in tumor-infiltrating Tregs (TUM-Tregs). Taking into account the heterogeneous and complex build of tumor mass, we set-up a combined protocol that optimizes tumor-infiltrating lymphocytes (TIL) extraction from the tissue through a Percoll density gradient, and assesses ex vivo the lipid load in whole TUM-Treg population, evaluating by flow cytometry the incorporation of an intensely fluorescent lipophilic fluorophore able to specifically stain neutral lipids. This method provides an important advantage compared to the traditional technique based on microscopy, whose lipid level evaluation is limited to a tissue section, and hence may not be representative of the entire population.

Regulatory T cells (Tregs), expressing the transcription factor Foxp3, are defined as immunosuppressive cells able to modulate a variety of immune cells in order to avoid unwanted and excessive immune responses; however, in the tumor context, Treg function contribute to inhibit immune surveillance, thus promoting cancer progression. In tumor microenvironment, where the availability of metabolic resources is strongly limited, Tregs are expanded and may exploit different metabolic routes to achieve a metabolic advantage, prevailing over effector cells. In this context an important role of lipid metabolism has been described thanks to the possibility to evaluate the intracellular lipid content selectively in tumor-infiltrating Tregs (TUM-Tregs). Taking into account the heterogeneous and complex build of tumor mass, we set-up a combined protocol that optimizes tumor-infiltrating lymphocytes (TIL) extraction from the tissue through a Percoll density gradient, and assesses ex vivo the lipid load in whole TUM-Treg population, evaluating by flow cytometry the incorporation of an intensely fluorescent lipophilic fluorophore able to specifically stain neutral lipids. This method provides an important advantage compared to the traditional technique based on microscopy, whose lipid level evaluation is limited to a tissue section, and hence may not be representative of the entire population.

In our study, we investigated the role of CD39 on tumor-infiltrating CD8+ T lymphocytes (CD8+ TILs) in colorectal, head and neck and pancreatic cancers. Partially confirming recent observations correlating the CD39 expression with T-cell exhaustion, we demonstrated a divergent functional activity in CD39+ CD8+ TILs. On the one hand, CD39+ CD8+ TILs (as compared to their CD39- counterparts) produced significantly lower IFN-γ and IL-2 amounts, expressed higher PD-1, and inversely correlated with perforin and granzyme B expression. On the other, they displayed a significantly higher proliferative capacity ex vivo that was inversely correlated with the PD-1 expression. Therefore, CD39+ CD8+ TILs, including those co-expressing the CD103 (a marker of T resident memory [TRM] cells), were defined as partially dysfunctional T cells that correlate with tumor patients with initial progression stages. Interestingly, our results identified for the first time a single nucleotide polymorphism (SNP rs10748643 A>G), as a genetic factor associated with CD39 expression in CD8+ TILs. Finally, we demonstrated that compounds inhibiting CD39-related ATPases improved CD39+ CD8+ T-cell effector function ex vivo, and that CD39+ CD8+ TILs displayed effective suppression function in vitro. Overall these data suggest that the SNP analysis may represent a suitable predictor of CD39+ CD8+ T-cell expression in cancer patients, and propose the modulation of CD39 as a new strategy to restore partially exhausted CD8+ TILs.

Objectives Type I interferons (IFNs) inhibit regulatory T‐cell (Treg) expansion and activation, making them beneficial in antiviral responses, but detrimental in autoimmune diseases. Herein, we investigate the role of ISG15 in human Tregs in the context of refractoriness to type I IFN stimulation. Methods ISG15 expression and Treg dynamics were analysed in vitro and ex vivo from patients with chronic hepatitis C, with lupus and ISG15 deficiency. Results ISG15 is expressed at high levels in human Tregs, renders them refractory to the IFN‐STAT1 signal, and protects them from IFN‐driven contraction. In vitro, Tregs from healthy controls upregulate ISG15 upon activation to higher levels than conventional CD4 T cells, and ISG15‐silenced Tregs are more susceptible to IFNα‐induced contraction. In human ISG15 deficiency, patient Tregs display an elevated IFN signature relative to Tregs from healthy control. In vivo, in patients with chronic hepatitis C, 2 days after starting pegIFN/ribavirin therapy, a stronger ISG15 inducibility correlates with a milder Treg depletion. Ex vivo, in systemic lupus erythematosus patients, higher levels of ISG15 are associated to reduced STAT1 phosphorylation in response to IFNα, and also to increased frequencies of Tregs, characterising active disease. Conclusion Our results reveal a Treg‐intrinsic role of ISG15 in dictating their refractoriness to the IFN signal, thus preserving the Treg population under inflammatory conditions., Tregs are particularly sensitive to the detrimental effects of type I IFNs. Here, we show that an IFN‐stimulated gene, ISG15, mediates Treg refractoriness to IFN‐induced contraction in vitro. In lupus patients, high ISG15 expression sustains high Treg frequencies in active disease. In human ISG15 deficiency, Tregs show an elevated IFN signature.

The Wnt/β-catenin pathway regulates T-cell functions, including the repression of effector functions to the advantage of memory development via Tcf1. In a companion study, we demonstrate that, in human cancers, Wnt3a/β-catenin signaling maintains tumor-infiltrating T cells in a partially exhausted status. Here, we have investigated the effects of Wnt3a neutralization in vivo in a mouse tumor model. Abundant Wnt3a was released, mostly by stromal cells, in the tumor microenvironment. We tested whether Wnt3a neutralization in vivo could rescue the effector capacity of tumor-infiltrating T cells, by administering an antibody to Wnt3a to tumor-bearing mice. This therapy restrained tumor growth and favored the expansion of tumor antigen–specific CD8+ effector memory T cells with increased expression of Tbet and IFNγ and reduced expression of Tcf1. However, the effect was not attributable to the interruption of T-cell–intrinsic β-catenin signaling, because Wnt3a/β-catenin activation correlated with enhanced, not reduced, T-cell effector functions both ex vivo and in vitro. Adoptively transferred CD8+ T cells, not directly exposed to the anti-Wnt3a antibody but infiltrating previously Wnt3a-neutralized tumors, also showed improved functions. The rescue of T-cell response was thus secondary to T-cell–extrinsic changes that likely involved dendritic cells. Indeed, tumor-derived Wnt3a strongly suppressed dendritic cell maturation in vitro, and anti-Wnt3a treatment rescued dendritic cell activities in vivo. Our results clarify the function of the Wnt3a/β-catenin pathway in antitumor effector T cells and suggest that Wnt3a neutralization might be a promising immunotherapy for rescuing dendritic cell activities. Cancer Immunol Res; 6(8); 953–64. ©2018 AACR.

Background Data on T regulatory (T reg) cells number and functions in patients with Systemic Lupus Erythematosus (SLE) are conflicting (1). Type I interferon (IFN) decreases Treg proliferation and induces Treg apoptosis (2). IFN stimulated gene 15 (ISG15) is an IFN-induced protein with a negative effect on IFN pathway. Objectives Aim of the study was to evaluate the effect of IFN alpha and ISG15 on Treg number and on STAT1 phosphorilation in patients with SLE. Methods We recruited patients with SLE classified according to 1997 ACR criteria. We collected demographic and clinical data including disease duration, disease activity scored according to Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) 2K. Peripheral blood mononuclear cells (PBMC) were isolated from whole blood samples. Intracellular phosphorilated STAT1 (pSTAT) levels were evaluated in Treg (CD4+FOXP3+CD127 low cells) and conventional T cell (Tconv, CD4+FOXP3- cells) by multiparametric flow cytometry, ex vivo or after stimulation with recombinant IFN alpha. PBMC were cultured for 48 hours with anti-CD3 or anti-CD3 and IFN alpha; the frequency of Treg was analysed by multiparametric flow cytometry. ISG15 mRNA expression was evaluated by RT-PCR on PBMC from SLE patients. Data were expressed as mean ± standard deviation or median (interquartile range(according) to the distribution; Mann-Whitney and Spearman tests were applied. P value Results We enrolled 21 SLE patients [F:M 20:1; mean age 45.2 ± 12.9 years; mean disease duration 157.5± 103 months; median SLEDAI 2(4)] Overall, median baseline ISG15 mRNA expression was 0.06 (IQR 0.16); patients were divided into ISG15-high (n=9) and ISG15-low (n=12), according to the mean mRNA expression. Ex vivo, after short-term treatment with IFN alpha (15 and 25 minutes), we observed a significant increase in STAT1 phosphorilation compared to baseline both in Treg and Tconv (p 4 vs SLEDAI Conclusion ISG15 protects T conventional cells from STAT1 phosphorilation and induces resistance to T regulatory cells depletion. The results of the study suggest that ISG15, a protein induced by IFN in the acute phase of the disease, exerts a negative feedback, allowing the recovery of T reg. References [1] Zhang SX, et al. J Immunol res. 2018 [2] Piconese S, et al. Cytokine Growth Factor rev. 2014 Disclosure of Interests None declared

Background The PDE4-inhibitor apremilast has been recently introduced in the treatment of Psoriatic Arthritis (PsA). It acts by down-regulating intracellular inflammatory mediators synthesis by elevating cAMP levels. Tregs, a subset of FOXP3+ CD4 T cells, play a key role in preventing immune responses and could exert their suppressive function via cAMP (1). Reduced frequencies of circulating Tregs have been observed in inflammatory disorders, nonetheless very few data are available on PsA patients. Objectives We evaluated peripheral Tregs in a cohort of PsA patients treated by apremilast. Methods Seventeen PsA patients (M/F 3/14; median age 56.0 years, IQR 20.0; median disease duration 15.0 years, IQR 11.0) with polyarticular subset treated by apremilast, were evaluated at baseline (T0) and after 6 (T1) and 12 weeks (T1). Clinimetric evaluation included DAS28, DAPSA, CDAI, and SDAI. Moreover, US assessment was performed at wrists, metacarpophalangeal (MCP), and proximal interphalangeal (PIP) joints: synovial effusion/hypertrophy and power Doppler were scored by a semi-quantitative scale (0-3), obtaining a total score (0-198). Treg frequency was assessed in peripheral blood mononuclear cells by flow cytometry, as the percentage of CD127low FOXP3+ in live CD4+ T cells (%Treg). Results At baseline we identified a median%Tregs of 4.6 (IQR 1.1), inversely correlating with DAS28 (r=-0.5, p=0.02), DAPSA (r=-0.7, p=0.003), CDAI (r=-0.6, p=0.01), SDAI (r=-0.6, p=0.003 and US inflammatory score (r=-0.6, p=0.01) (Figure 1). Treatment with apremilast was able to induce a significant improvement in all activity indices at T1 (DAS28, P=0.009; DAPSA, P=0.01; CDAI, P=0.005; SDAI, P=0.006; US score, P Conclusion The results of our study demonstrate that%Treg is a marker of disease activity in PsA patients. Moreover, the baseline value of Tregs could predict the response to apremilast after 12 weeks of treatment. Reference: [1] Chavele KMet al, FEBS Lett2011. Disclosure of Interests Fulvia Ceccarelli: None declared, Ilenia Pacella: None declared, Ramona Lucchetti: None declared, Arianna Forniti: None declared, francesca spinelli: None declared, enrica cipriano: None declared, Carlo Perricone Speakers bureau: BMS; Lilly, Celgene, Sanofi, Simona Truglia: None declared, Francesca Miranda: None declared, Rossana Scrivo: None declared, cristiano alessandri: None declared, Vincenzo Barnaba: None declared, Guido Valesini: None declared, Silvia Piconese: None declared, fabrizio conti: None declared

International audience; The tumor microenvironment restrains conventional T cell (Tconv) activation while facilitating the expansion of Tregs. Here we showed that Tregs' advantage in the tumor milieu relies on supplemental energetic routes involving lipid metabolism. In murine models, tumor-infiltrating Tregs displayed intracellular lipid accumulation, which was attributable to an increased rate of fatty acid (FA) synthesis. Since the relative advantage in glucose uptake may fuel FA synthesis in intratumoral Tregs, we demonstrated that both glycolytic and oxidative metabolism contribute to Tregs' expansion. We corroborated our data in human tumors showing that Tregs displayed a gene signature oriented toward glycolysis and lipid synthesis. Our data support a model in which signals from the tumor microenvironment induce a circuitry of glycolysis, FA synthesis, and oxidation that confers a preferential proliferative advantage to Tregs, whose targeting might represent a strategy for cancer treatment.

Summary Mitochondria are key players in the regulation of T cell biology by dynamically responding to cell needs, but how these dynamics integrate in T cells is still poorly understood. We show here that the mitochondrial pro-fission protein Drp1 fosters migration and expansion of developing thymocytes both in vitro and in vivo. In addition, we find that Drp1 sustains in vitro clonal expansion and cMyc-dependent metabolic reprogramming upon activation, also regulating effector T cell numbers in vivo. Migration and extravasation defects are also exhibited in Drp1-deficient mature T cells, unveiling its crucial role in controlling both T cell recirculation in secondary lymphoid organs and accumulation at tumor sites. Moreover, the observed Drp1-dependent imbalance toward a memory-like phenotype favors T cell exhaustion in the tumor microenvironment. All of these findings support a crucial role for Drp1 in several processes during T cell development and in anti-tumor immune-surveillance., Graphical Abstract, Highlights • The pro-fission protein Drp1 sustains correct thymocyte maturation • Drp1 promotes T cell metabolic reprogramming and expansion upon activation • Drp1 allows efficient T cell extravasation from blood and infiltration into tumors • An optimal T cell anti-tumor response requires Drp1, Mitochondria are emerging as key players for optimal T cell functionality. Simula et al. demonstrate that the mitochondrial pro-fission factor Drp1 controls thymocyte maturation and plays multiple roles in mature T cells by promoting their proliferation, migration, and cMyc-dependent metabolic reprogramming upon activation; this activity sustains efficient anti-tumor immune-surveillance.

Type I IFNs are pleiotropic cytokines that exert concerted activities in the development of antiviral responses. Regulatory T cells represent a physiologic checkpoint in the balance between immunity and tolerance, requiring fine and rapid controls. Here, we show that human regulatory T cells are particularly sensitive to the sequential effects of IFN-α. First, IFN-α exerts a rapid, antiproliferative and proapoptotic effect in vitro and in vivo, as early as after 2 d of pegylated IFN/ribavirin therapy in patients with chronic hepatitis C. Such activities result in the decline, at d 2, in circulating regulatory T cell frequency and specifically of the activated regulatory T cell subset. Later, IFN-based therapy restrains the fraction of regulatory T cells that can be polarized into IFN-γ-producing Th1-like regulatory T cells known to contribute to chronic immune activation in type 1 inflammation. Indeed, Th1-like regulatory T cell frequency significantly declines after 30 d of therapy in vivo in relation to the persistent decline of relevant IL-12 sources, namely, myeloid and 6-sulfo LacNAc-expressing dendritic cells. This event is recapitulated by experiments in vitro, providing evidence that it may be attributable to the inhibitory effect of IFN-α on IL-12-induced, Th1-like regulatory T cell polarization. In summary, our results suggest that IFN-α-driven, early regulatory T cell depletion contributes to the development of antiviral immunity, ultimately resulting in the resolution of type 1 inflammation.

Tregs can contribute to tumor progression by suppressing antitumor immunity. Exceptionally, in human colorectal cancer (CRC), Tregs are thought to exert beneficial roles in controlling pro-tumor chronic inflammation. The goal of our study was to characterize CRC-infiltrating Tregs at multiple levels, by phenotypical, molecular and functional evaluation of Tregs from the tumor site, compared to non-tumoral mucosa and peripheral blood of CRC patients. The frequency of Tregs was higher in mucosa than in blood, and further significantly increased in tumor. Ex vivo, those Tregs suppressed the proliferation of tumor-infiltrating CD8(+) and CD4(+) T cells. A differential compartmentalization was detected between Helios(high) and Helios(low) Treg subsets (thymus-derived versus peripherally induced): while Helios(low) Tregs were enriched in both sites, only Helios(high) Tregs accumulated significantly and specifically in tumors, displayed a highly demethylated TSDR region and contained high proportions of cells expressing CD39 and OX40, markers of activation and suppression. Besides the suppression of T cells, Tregs may contribute to CRC progression also through releasing IL-17, or differentiating into Tfr cells that potentially antagonize a protective Tfh response, events that were both detected in tumor-associated Tregs. Overall, our data indicate that Treg accumulation may contribute through multiple mechanisms to CRC establishment and progression.

Regulatory T cells (Treg) exert a dominant role in the protection of unwanted immune responses and in the resolution of inflammation. To ensure the proper mounting of protective immune responses, Treg should be finely modulated by microenvironmental signals, mostly conveyed by cytokines. Type-I interferons are pleiotropic cytokines, best known for their anti-viral activities but also playing relevant immunostimulatory as well as immunomodulatory functions. The impact of type-I interferons on Treg homeostasis and functions is quite controversial, as some studies indicate that interferons sustain Treg stability and suppression, while other reports describe a null or even negative role for interferons in Treg activities. Interferons may also establish alternative routes of suppression, through the induction of other suppressive populations, such as Tr1 and the recently discovered FoxA1+ Treg. Discrepant results about Treg behavior in vivo emerge also from data collected in patients with multiple sclerosis, chronic hepatitis C or cancer undergoing interferon therapy. Concurrent events, such as Treg-extrinsic interferon activities, desensitization to chronic interferon exposure, and changes in microenvironmental signals during the evolution of diseases, may contribute to depict such a complex scenario, in which short-term and long-term effects of interferon exposure may give rise to apparently opposite conclusions.

International audience; Regulatory T cells (Tregs) can be considered as a mixed population of distinct subsets, endowed with a diverse extent and quality of adaptation to microenvironmental signals. Here, we uncovered an opposite distribution of Treg expansion, phenotype, and plasticity in different microenvironments in the same organ (liver) derived from patients with chronic hepatitis C: On the one side, cirrhotic and tumor fragments were moderately and highly infiltrated by Tregs, respectively, expressing OX40 and a T-bet high IFN-c – " T-helper (Th)1-suppressing " phenotype; on the other side, noncirrhotic liver specimens contained low frequencies of Tregs that expressed low levels of OX40 and highly produced interferon-gamma (IFN-c; T-bet 1 IFN-c 1), thus becoming " Th1-like " cells. OX40-expressing and Th1-suppressing Tregs were enriched in the Helios-positive subset, carrying highly demethylated Treg cell-specific demethylated region that configures committed Tregs stably expressing forkhead box protein 3. OX40 ligand, mostly expressed by M2-like monocytes and macrophages, boosted OX40 1 Treg proliferation and antagonized the differentiation of Th1-like Tregs. However, this signal is counteracted in non-cirrhotic liver tissue (showing various levels of inflammation) by high availability of interleukin-12 and IFN-c, ultimately leading to complete, full Th1-like Treg differentiation. Conclusion: Our data demonstrate that Tregs can finely adapt, or even subvert, their classical inhibitory machinery in distinct microenvironments within the same organ. (HEPATOLOGY 2014;60:1494-1507)