Biochemistry and therapeutic implications of mechanisms involved in FOXP3 activity in immune suppression

Transcriptional regulation of Treg homeostasis and functional specification

CD4+Foxp3+ regulatory T (Treg) cells are key players in keeping excessive inflammation in check. Mounting evidence has shown that Treg cells exert much more diverse functions in both immunological and non-immunological processes. The development, maintenance and functional specification of Treg cells are regulated by multilayered factors, including antigens and TCR signaling, cytokines, epigenetic modifiers and transcription factors (TFs). In the review, we will focus on TFs by summarizing their unique and redundant roles in Treg cells under physiological and pathophysiological conditions. We will also discuss the recent advances of Treg trajectories between lymphoid organs and non-lymphoid tissues. This review will provide an updated view of the newly identified TFs and new functions of known TFs in Treg biology.

Effects of tumor metabolic microenvironment on regulatory T cells

Recent studies have shown that on one hand, tumors need to obtain a sufficient energy supply, and on the other hand they must evade the body’s immune surveillance. Because of their metabolic reprogramming characteristics, tumors can modify the physicochemical properties of the microenvironment, which in turn affects the biological characteristics of the cells infiltrating them. Regulatory T cells (Tregs) are a subset of T cells that regulate immune responses in the body. They exist in large quantities in the tumor microenvironment and exert immunosuppressive effects. The main effect of tumor microenvironment on Tregs is to promote their differentiation, proliferation, secretion of immunosuppressive factors, and chemotactic recruitment to play a role in immunosuppression in tumor tissues. This review focuses on cell metabolism reprogramming and the most significant features of the tumor microenvironment relative to the functional effects on Tregs, highlighting our understanding of the mechanisms of tumor immune evasion and providing new directions for tumor immunotherapy.

SIRT1-Regulated Abnormal Acetylation of FOXP3 Induces Regulatory T-Cell Function Defect in Hashimoto's Thyroiditis

BACKGROUND

Hashimoto's thyroiditis (HT) is an autoimmune thyroid disease characterized by low expression of transcription factor Forkhead Box P3 (FOXP3) and functional deficiency of a cluster of differentiation regulatory T cells (Tregs). This study aimed to investigate the mechanism of Treg dysfunction in HT.

METHODS

The number of CD4⁺CD25⁺FOXP3⁺ T cells was determined by flow cytometry. Expression of FOXP3 and Sirtuin type 1 (SIRT1) was evaluated by Western blot analysis. Acetylation of FOXP3 was analyzed by immunoprecipitation and Western blot analysis. The suppressive function of Treg was analyzed by the 5,6-carboxyfluorescein diacetate succinimidyl ester (CFSE) assay.

RESULTS

The percentage of CD4⁺CD25⁺FOXP3⁺ T cells, expression of FOXP3, and FOXP3 acetylation level in the HT group were significantly lower than in the control groups. Conversely, SIRT1 expression was significantly higher in the HT group than in the other two groups. After Ex-527 treatment, the CD4⁺CD25⁺FOXP3⁺ T cells percentage, FOXP3 expression, and FOXP3 acetylation level in the HT group were significantly increased. HT Tregs exhibited less suppressive activity, but Ex-527 treatment significantly increased their suppressive activity.

CONCLUSIONS

The findings demonstrate that the reduced FOXP3 expression level and Treg function defect in HT patients are regulated by SIRT1-mediated abnormal FOXP3 acetylation. Ex-527 may upregulate the FOXP3 acetylation level and subsequently increase the number and suppressive function of Treg cells.

The role of inflammation in progression of breast cancer: Friend or foe? (Review)

There is a growing interest in the role of the microenvironment in cancer, however, it has been known for over one hundred years that the immune system plays a prominent role in cancer. Recent decades have revealed more and more data on how our own host response to cancer cells can help or hinder progression of the disease. Despite all this work it is surprising how little is known about the role of the immune system in human breast cancer development, as compared to other cancers. Recent successes of PD-1 blockade in treating multiple cancers, and new developments with other immune targets such as CTLA-4 and CSF-1 inhibitors, highlight that it is becoming ever more important that we understand the complexity of the immune and inflammatory systems in the development and progression of breast cancer. With this knowledge it may be possible to not only target therapy but also more accurately predict those patients that truly need it. This review summarises some of the most significant findings for the role of the immune system and inflammatory response in breast cancer progression. Focusing on how the inflammatory microenvironment may be involved in the progression of pre-invasive ductal carcinoma in situ to invasive breast cancer. It will also discuss the use of immune markers as diagnostic and prognostic tools and summarise the state of the art of immune-therapeutics in breast cancer treatment.

Expression of CXC chemokine receptor-4 and forkhead box 3 in neuroblastoma cells and response to chemotherapy

Current evidence indicates that the abnormal expression of chemokines or their receptors, such as CXC chemokine receptor-4 (CXCR4), is positively correlated with the development, progression and metastasis of tumor cells. However, the role of CXCR4 in neuroblastoma and its response to chemotherapy remain largely unclear. In addition, forkhead box 3 (Foxp3), a transcription factor associated with T cell tolerance, is expressed in tumor cells and plays a role in the immune evasion of cancers. The present study aimed to examine the expression of CXCR4 and Foxp3 in the LAN-5 and SK-N-SH neuroblastoma cell lines. The effects of chemotherapy drugs, cyclophosphamide (CTX) and pirarubicin (THP), on the expression of these two genes were also investigated. Our findings indicated that CXCR4 and Foxp3 were highly expressed in LAN-5 and SK-N-SH cells. Following treatment with CTX and THP, the protein expression of CXCR4 in LAN-5 and SK-N-SH cells was significantly decreased (P<0.05). The expression of Foxp3 in LAN-5 cells was also significantly downregulated by CTX and THP treatment (P<0.05). Therefore, the high expression of CXCR4 and Foxp3 in LAN-5 and SK-N-SH cells and their subsequent downregulation following administration of the chemotherapy agents suggests that the chemokine receptors, CXCR4 and Foxp3, may be involved in the metastasis and tumor evasion of neuroblastoma. Further studies should investigate the expression of CXCR4 and Foxp3 in patient samples.

Modulation of Treg function improves adenovirus vector-mediated gene expression in the airway

Virus vector-mediated gene transfer has been developed as a treatment for cystic fibrosis (CF) airway disease, a lethal inherited disorder caused by somatic mutations in the cystic fibrosis transmembrane conductance regulator gene. The pathological proinflammatory environment of CF as well as the naïve and adaptive immunity induced by the virus vector itself limits the effectiveness of gene therapy for CF airway. Here, we report the use of an HDAC inhibitor, valproic acid (VPA), to enhance the activity of the regulatory T cells (T(reg)) and to improve the expression of virus vector-mediated gene transfer to the respiratory epithelium. Our study demonstrates the potential utility of VPA, a drug used for over 50 years in humans as an anticonvulsant and mood-stabilizer, in controlling inflammation and improving the efficacy of gene transfer in CF airway.

T-cell tolerance in cancer

T cells are the master regulators of adaptive immune responses and maintenance of their tolerance is critical to prevent autoimmunity. However, in the case of carcinogenesis, the tumor microenvironment aids T-cell tolerance, which contributes to uncontrolled tumor growth. Recently, there has been significant progress in understanding the intrinsic extracellular (positive and negative costimulatory molecules on APCs) and intracellular mechanisms (E3 ubiquitin ligases, transcriptional and epigenetic repressors), as well as extrinsic mechanisms (Tregs and tolerogenic dendritic cells) that are required for the implementation and maintenance of T-cell tolerance. Ultimately, understanding and manipulating T-cell tolerance will help to break the tolerance state in cancer.

BRG1-mediated immune tolerance: facilitation of Treg activation and partial independence of chromatin remodelling

Treg activation in response to environmental cues is necessary for regulatory T cells (Tregs) to suppress inflammation, but little is known about the transcription mechanisms controlling Treg activation. We report that despite the known proinflammatory role of the chromatin-remodelling factor BRG1 in CD4 cells, deleting Brg1 in all αβ T cell lineages led to fatal inflammation, which reflected essential roles of BRG1 in Tregs. Brg1 deletion impaired Treg activation, concomitant with the onset of the inflammation. Remarkably, as the inflammation progressed, Tregs became increasingly activated, but the activation levels could not catch up with the severity of inflammation. In vitro assays indicate that BRG1 regulates a subset of TCR target genes including multiple chemokine receptor genes. Finally, using a method that can create littermates bearing either a tissue-specific point mutation or deletion, we found the BRG1 ATPase activity partially dispensable for BRG1 function. Collectively, these data suggest that BRG1 acts in part via remodelling-independent functions to sensitize Tregs to inflammatory cues, thus allowing Tregs to promptly and effectively suppress autoimmunity.

Anti-inflammatory cytokines: important immunoregulatory factors contributing to chemotherapy-induced gastrointestinal mucositis

“Mucositis” is the clinical term used to describe ulceration and damage of the mucous membranes of the entire gastrointestinal tract (GIT) following cytotoxic cancer chemotherapy and radiation therapy common symptoms include abdominal pain, bloating, diarrhoea, vomiting, and constipation resulting in both a significant clinical and financial burden. Chemotherapeutic drugs cause upregulation of stress response genes including NFκB, that in turn upregulate the production of proinflammatory cytokines such as interleukin-1β (IL-1β), Interleukin-6 (IL-6), and tumour necrosis factor-α (TNF-α). These proinflammatory cytokines are responsible for initiating inflammation in response to tissue injury. Anti-inflammatory cytokines and specific cytokine inhibitors are also released to limit the sustained or excessive inflammatory reactions. In the past decade, intensive research has determined the role of proinflammatory cytokines in development of mucositis. However, a large gap remains in the knowledge of the role of anti-inflammatory cytokines in the setting of chemotherapy-induced mucositis. This critical paper will highlight current literature available relating to what is known regarding the development of mucositis, including the molecular mechanisms involved in inducing inflammation particularly with respect to the role of proinflammatory cytokines, as well as provide a detailed discussion of why it is essential to consider extensive research in the role of anti-inflammatory cytokines in chemotherapy-induced mucositis so that effective targeted treatment strategies can be developed.

Structural and biological features of FOXP3 dimerization relevant to regulatory T cell function

FOXP3 is a key transcription factor for regulatory T cell function. We report the crystal structure of the FOXP3 coiled-coil domain, through which a loose or transient dimeric association is formed and modulated, accounting for the activity variations introduced by disease-causing mutations or posttranslational modifications. Structure-guided mutagenesis revealed that FOXP3 coiled-coil-mediated homodimerization is essential for Treg function in vitro and in vivo. In particular, we identified human FOXP3 K250 and K252 as key residues for the conformational change and stability of the FOXP3 dimer, which can be regulated by protein posttranslational modifications such as reversible lysine acetylation. These studies provide structural and mechanistic explanations for certain disease-causing mutations in the coiled-coil domain of FOXP3 that are commonly found in IPEX syndrome. Overall, the regulatory machinery involving homooligomerization, acetylation, and heteroassociation has been dissected, defining atomic insights into the biological and pathological characteristics of the FOXP3 complex.

Regulatory T cells: mechanisms of differentiation and function

The immune system has evolved to mount an effective defense against pathogens and to minimize deleterious immune-mediated inflammation caused by commensal microorganisms, immune responses against self and environmental antigens, and metabolic inflammatory disorders. Regulatory T (Treg) cell-mediated suppression serves as a vital mechanism of negative regulation of immune-mediated inflammation and features prominently in autoimmune and autoinflammatory disorders, allergy, acute and chronic infections, cancer, and metabolic inflammation. The discovery that Foxp3 is the transcription factor that specifies the Treg cell lineage facilitated recent progress in understanding the biology of regulatory T cells. In this review, we discuss cellular and molecular mechanisms in the differentiation and function of these cells.

Immune regulation by histone deacetylases: a focus on the alteration of FOXP3 activity

Several histone deacetylases (HDACs) are involved in the regulation of forkhead box protein P3 (FOXP3) expression and function by affecting features of FOXP3 protein stability. FOXP3, a forkhead family transcription factor specially expressed in regulatory T (Treg) cells, controls the expression of many key immune-regulatory genes. Treg cells are a population of T lymphocytes that have critical roles in the immune system homeostasis and tolerance to self and foreign antigens, the body's response to cancer and infectious agents. FOXP3 forms oligomeric complexes with other proteins, the components of which are believed to be regulated dynamically. In addition, HDAC activities influence FOXP3 interactions with other partners to form transcriptional regulatory complexes. By understanding the details of the biochemical and structural basis of the regulation of FOXP3 acetylation, therapeutic strategies for diseases related to Treg cells may emerge.

CCR7 with S1P1 signaling through AP-1 for migration of Foxp3+ regulatory T-cells controls autoimmune exocrinopathy

Forkhead box p3-positive (Foxp3(+)) regulatory T cells (T(reg) cells) participate in maintaining peripheral immune tolerance and suppressing autoimmunity. We recently reported that in situ patrolling by C-C-chemokine receptor 7 (CCR7)(+) T(reg) cells in target organs is essential for controlling autoimmune lesions in Sjögren's syndrome. In the present study, the molecular mechanism underlying CCR7-mediated T(reg) cell migration was investigated in a mouse model. The impaired migratory response of Ccr7(-/-) T(reg) cells to sphingosine 1-phosphate (S1P) occurred because of defective association of S1P receptor 1 (S1P(1)) with a G coupled-protein. In addition, T-cell receptor (TCR)- and S1P(1)-mediated Ras-related C3 botulinum toxin substrate 1 (Rac-1), extracellular signal-related kinase (ERK), and c-Jun phosphorylation required for activator protein 1 (AP-1) transcriptional activity were significantly impaired in Ccr7(-/-) T(reg) cells. Surprisingly, the abnormal nuclear localization of Foxp3 was detected after abrogation of the c-Jun and Foxp3 interaction in the nucleus of Ccr7(-/-) T(reg) cells. These results indicate that CCR7 essentially controls the migratory function of T(reg) cells through S1P(1)-mediated AP-1 signaling, which is regulated through its interaction with Foxp3 in the nucleus.

Multipotent mesenchymal stromal cells express FoxP3: a marker for the immunosuppressive capacity?

Multipotent mesenchymal stromal cells (MSCs) have immunosuppressive capacity but the exact mechanism by which they suppress proliferation of T lymphocytes is not fully understood. Recently, the characteristics and function of regulatory T lymphocytes (Tregs) have become better defined. Tregs and MSCs have immunosuppressive features in common. Here, we looked for a common basis for immunosuppression in these distinct cell types. Forkhead box P3 (FoxP3) and CD39 expression in MSCs was measured by flow cytometry and real-time quantitative polymerase chain reaction. The importance of FoxP3 in MSC-mediated immunosuppression was investigated by siRNA technology and mixed lymphocyte culture (MLC). The effect of 5-azacytidine and other immunosuppressive drugs on FoxP3 expression and immunosuppression by MSCs was explored by flow cytometry, MLC, and real-time quantitative polymerase chain reaction. MSCs express FoxP3 at variable levels, but they do not express CD39. FoxP3 MSCs suppress MLC to a greater extent than cells with lower FoxP3 expression. However, FoxP3-decreased MSCs were found to retain their immunosuppressive properties. 5-azacytitine had no effect on FoxP3 expression or MLC suppression by MSCs. However, immunosuppressive drugs led to increased FoxP3 levels and MLC inhibition in FoxP3 MSCs. This is the first demonstration of FoxP3 expression by MSCs. Although MSCs share several features with Tregs, and FoxP3 MSCs tend to be more immunosuppressive, MSCs do not require functional FoxP3 for their immunosuppressive activity. The increased MSC-mediated suppression of immune responses by immunosuppressive drugs deserves further investigation.

Regulatory T cells and breast cancer: implications for immunopathogenesis

Current understanding of the role of several cancer risk factors is more comprehensive, as reported for a number of sites, including the brain, colon, breasts, and ovaries. Despite such advances, the incidence of breast cancer continues to increase worldwide. Signals from the microenviroment have a profound influence on the maintenance or progression cancers. Although T cells present the most important immunological response in tumor growth in the early stages of cancer, they become suppressive CD4(+) and CD8(+) regulatory T cells (Tregs) after chronic stimulation and interactions with tumor cells, thus promoting rather than inhibiting cancer development and progression. Tregs have an important marker protein which is FoxP3, though it does not necessarily confer a Treg phenotype when expressed in CD4(+) T lymphocytes. High Treg levels have been reported in peripheral blood, lymph nodes, and tumor specimens from patients with different types of cancer. The precise mechanisms by which Tregs suppress immune cell functions remain unclear, and there are reports of both direct inhibition through cell-cell contact and indirect inhibition through the secretion of anti-inflammatory mediators such as interleukin. In this review, we present the molecular and immunological aspects of Treg cells in the metastasis of breast cancer.

The biology of FoxP3: a key player in immune suppression during infections, autoimmune diseases and cancer

The Transcription factor FoxP3 belongs to the forkhead/winged-helix family of transcriptional regulators and shares general structural features with other FoxP family members. FoxP3 functions as a master of transcription for the development of regulatory T-cells (Treg cells) both in humans and in mice. Natural genetic mutations ofFoxP3 that disrupt its function in humans result in an autoimmune syndrome called Immune Polyendocrinopathy, Enteropathy, X-linked (IPEX) and in mice, its deletion causes the Scurfy phenotype, with similar pathology. The finding that FoxP3 is required for the development and function of Tregs has led to an explosion of research in determining its regulation and function in the immune system. Understanding the biological properties of FoxP3 has a wide range of implications for immune tolerance, autoimmune disorders, inflammation and immune response to infectious diseases and cancer.

Foxp3 and Treg cells in HIV-1 infection and immuno-pathogenesis

FoxP3(+)CD4(+)CD25(+) regulatory T (Treg) cells are implicated in a number of pathologic processes including elevated levels in cancers and infectious diseases, and reduced levels in autoimmune diseases. Treg cells are activated to modulate immune responses to avoid over-reactive immunity. However, conflicting findings are reported regarding relative levels of Treg cells during HIV-1 infection and disease progression. The role of Treg cells in HIV-1 diseases (aberrant immune activation) is poorly understood due to lack of a robust model. We summarize here the regulation and function of Foxp3 in Treg cells and in modulating HIV-1 replication. Based on recent findings from SIV/monkey and HIV/humanized mouse models, a model of the dual role of Treg cells in HIV-1 infection and immuno-pathogenesis is discussed.

Structural aspects of the FOXP3 regulatory complex as an immunopharmacological target

The forkhead family transcription factor FOXP3 plays a fundamental role in immune homeostasis. FOXP3 dysfunction in regulatory T cells (Tregs) contributes to multiple disease processes such as autoimmunity, tumor development, and viral infection. FOXP3 cooperates and associates with a group of other transcriptional factors, co-repressors and co-activators in Tregs to form one or more dynamic regulatory complexes. These ensembles communicate with multiple key signaling pathways to either upregulate or downregulate the expression of downstream target genes such as cytokines and cell surface receptors, which are critical for the control of normal immune responses. Although the details of the underlying mechanism by which FOXP3 operates as a transcriptional repressor or an activator is largely undefined, FOXP3(+) Tregs based cellular therapies have been studied in animal models. Our recent studies concerning the FOXP3 complex ensemble provide structural and biochemical insights into FOXP3 function of Tregs, which are essential to the development of novel immunopharmacological agents for treating human immunological disease.

Using histone deacetylase inhibitors to enhance Foxp3(+) regulatory T-cell function and induce allograft tolerance

The histone/protein deacetylase inhibitor (HDACi), trichostatin A (TsA), increases the production and suppressive function of Foxp3(+) regulatory T cells (T(regs)), at least in part, by promoting the acetylation of Foxp3 protein itself. Acetylation of Foxp3 is required for effective binding of Foxp3 to the promoter of the interleukin-2 (IL-2) gene and the suppression of IL-2 expression. We have sought to identify agents that had similar effects on T(regs), but without the associated toxicity of TsA. This review summarizes the contrasting effects of various HDACis on T(reg) functions in vitro and in vivo. Agents that block primarily class I HDAC had minimal or no effect on T(reg) suppression, whereas multiple inhibitors of both class I and class II HDAC enhanced T(reg) suppression in vitro and in vivo. These data indicate tools for further analysis of T(reg) functions, and point to a critical role of class II HDAC in the regulation of T(regs). Such knowledge has direct implications for the development of in vivo approaches to treat autoimmune and other inflammatory diseases.

Identification of chromatin remodeling genes Arid4a and Arid4b as leukemia suppressor genes

Background

Leukemia evolves through a multistep process from premalignancy to malignancy. Epigenetic alterations, including histone modifications, have been proposed to play an important role in tumorigenesis. The involvement of two chromatin remodeling genes, retinoblastoma-binding protein 1 (Rbbp1/Arid4a) and Rbbp1-like 1 (Rbbp1l1/Arid4b), in leukemogenesis was not characterized.

Methods

The leukemic phenotype of mice deficient for Arid4a with or without haploinsufficiency for Arid4b was investigated by serially monitoring complete blood counts together with microscopic histologic analysis and flow cytometric analysis of bone marrow and spleen from the Arid4a^−/− mice or Arid4a^−/−Arid4b^+/− mice. Regulation in bone marrow cells of downstream genes important for normal hematopoiesis was analyzed by reverse transcription–polymerase chain reaction. Genotypic effects on histone modifications were examined by western blotting and immunofluorescence analysis. All statistical tests were two-sided.

Results

Young (2–5 months old) Arid4a-deficient mice had ineffective blood cell production in all hematopoietic lineages. Beyond 5 months of age, the Arid4a^−/− mice manifested monocytosis, accompanied by severe anemia and thrombocytopenia. These sick Arid4a^−/− mice showed bone marrow failure with myelofibrosis associated with splenomegaly and hepatomegaly. Five of 42 Arid4a^−/− mice and 10 of 12 Arid4a^−/−Arid4b^+/− mice progressed to acute myeloid leukemia (AML) and had rapid further increases of leukocyte counts. Expression of Hox genes (Hoxb3, Hoxb5, Hoxb6, and Hoxb8) was decreased in Arid4a-deficient bone marrow cells with or without Arid4b haploinsufficiency, and FoxP3 expression was reduced in Arid4a^−/−Arid4b^+/− bone marrow. Increases of histone trimethylation of H3K4, H3K9, and H4K20 (fold increases in trimethylation = 32, 95% confidence interval [CI] = 27 to 32; 45, 95% CI = 41 to 49; and 2.2, 95% CI = 1.7 to 2.7, respectively) were observed in the bone marrow of Arid4a-deficient mice.

Conclusions

Arid4a-deficient mice initially display ineffective hematopoiesis, followed by transition to chronic myelomonocytic leukemia (CMML)–like myelodysplastic/myeloproliferative disorder, and then transformation to AML. The disease processes in the Arid4a-deficient mice are very similar to the course of events in humans with CMML and AML. This mouse model has the potential to furnish additional insights into the role of epigenetic alterations in leukemogenesis, and it may be useful in developing novel pharmacological approaches to treatment of preleukemic and leukemic states.

CD28 costimulation is essential for human T regulatory expansion and function

The costimulatory requirements required for peripheral blood T regulatory cells (Tregs) are unclear. Using cell-based artificial APCs we found that CD28 but not ICOS, OX40, 4-1BB, CD27, or CD40 ligand costimulation maintained high levels of Foxp3 expression and in vitro suppressive function. Only CD28 costimulation in the presence of rapamycin consistently generated Tregs that consistently suppressed xenogeneic graft-vs-host disease in immunodeficient mice. Restimulation of Tregs after 8-12 days of culture with CD28 costimulation in the presence of rapamycin resulted in >1000-fold expansion of Tregs in <3 wk. Next, we determined whether other costimulatory pathways could augment the replicative potential of CD28-costimulated Tregs. We observed that while OX40 costimulation augmented the proliferative capacity of CD28-costimulated Tregs, Foxp3 expression and suppressive function were diminished. These studies indicate that the costimulatory requirements for expanding Tregs differ from those for T effector cells and, furthermore, they extend findings from mouse Tregs to demonstrate that human postthymic Tregs require CD28 costimulation to expand and maintain potent suppressive function in vivo.

Regulatory T cells and treatment of cancer

CD4+CD25+FOXP3+ regulatory T cells (Tregs) are elevated in cancers and can thwart protective antitumor immunity. Recent human cancer trials suggest that depleting Tregs can be clinically beneficial. Additional types of deleterious regulatory cells are also increased in cancer. Tregs also play unanticipated roles in cancer therapy in that some drugs unexpectedly increase (e.g. cancer vaccines or IL-2 treatment) or decrease (e.g. antineoangiogenesis agents or receptor tyrosine kinase inhibitors) their numbers or function. Managing deleterious effects of regulatory cells represents a novel and potentially effective way to give immunotherapy for cancer. New insights into molecular mechanisms governing trafficking, differentiation, and function of these cells suggest novel approaches to manipulating them as treatment strategies.