MicroRNA-17 Modulates Regulatory T Cell Function by Targeting Co-regulators of the Foxp3 Transcription Factor.

Regulatory T (Treg) cells are important in maintaining self-tolerance and immune homeostasis. The Treg cell transcription factor Foxp3 works in concert with other co-regulatory molecules, including Eos, to determine the transcriptional signature and characteristic suppressive phenotype of Treg cells. Here, we report that the inflammatory cytokine interleukin-6 (IL-6) actively repressed Eos expression through microRNA-17 (miR-17). miR-17 expression increased in Treg cells in the presence of IL-6, and its expression negatively correlated with that of Eos. Treg cell suppressive activity was diminished upon overexpression of miR-17 in vitro and in vivo, which was mitigated upon co-expression of an Eos mutant lacking miR-17 target sites. Also, RNAi of miR-17 resulted in enhanced suppressive activity. Ectopic expression of miR-17 imparted effector-T-cell-like characteristics to Treg cells via the de-repression of genes encoding effector cytokines. Thus, miR-17 provides a potent layer of Treg cell control through targeting Eos and additional Foxp3 co-regulators.

TRAF6 directs FOXP3 localization and facilitates regulatory T-cell function through K63-linked ubiquitination.

Regulatory T cells (Tregs) are crucial mediators of immune control. The characteristic gene expression and suppressive functions of Tregs depend considerably on the stable expression and activity of the transcription factor FOXP3. Transcriptional regulation of the Foxp3 gene has been studied in depth, but both the expression and function of this factor are also modulated at the protein level. However, the molecular players involved in posttranslational FOXP3 regulation are just beginning to be elucidated. Here, we found that TRAF6-deficient Tregs were dysfunctional in vivo; mice with Treg-restricted deletion of TRAF6 were resistant to implanted tumors and displayed enhanced anti-tumor immunity. We further determined that FOXP3 undergoes K63-linked ubiquitination at lysine 262 mediated by the E3 ligase TRAF6. In the absence of TRAF6 activity or upon mutation of the ubiquitination site, FOXP3 displayed aberrant, perinuclear accumulation and disrupted regulatory function. Thus, K63-linked ubiquitination by TRAF6 ensures proper localization of FOXP3 and facilitates the transcription factor's gene-regulating activity in Tregs. These results implicate TRAF6 as a key posttranslational, Treg-stabilizing regulator that may be targeted in novel tolerance-breaking therapies.

The ubiquitin ligase Stub1 negatively modulates regulatory T cell suppressive activity by promoting degradation of the transcription factor Foxp3.

Regulatory T (Treg) cells suppress inflammatory immune responses and autoimmunity caused by self-reactive T cells. The key Treg cell transcription factor Foxp3 is downregulated during inflammation to allow for the acquisition of effector T cell-like functions. Here, we demonstrate that stress signals elicited by proinflammatory cytokines and lipopolysaccharides lead to the degradation of Foxp3 through the action of the E3 ubiquitin ligase Stub1. Stub1 interacted with Foxp3 to promote its K48-linked polyubiquitination in an Hsp70-dependent manner. Knockdown of endogenous Stub1 or Hsp70 prevented Foxp3 degradation. Furthermore, the overexpression of Stub1 in Treg cells abrogated their ability to suppress inflammatory immune responses in vitro and in vivo and conferred a T-helper-1-cell-like phenotype. Our results demonstrate the critical role of the stress-activated Stub1-Hsp70 complex in promoting Treg cell inactivation, thus providing a potential therapeutic target for the intervention against autoimmune disease, infection, and cancer.

Locoregional Therapy of Hepatocellular-Cholangiocarcinoma versus Hepatocellular Carcinoma: A Propensity Score-Matched Study.

PURPOSE: To compare outcomes of unresectable hepatocellular-cholangiocarcinoma (HCC-CC) with hepatocellular carcinoma (HCC) after locoregional therapy (LRT). MATERIALS AND METHODS: Consecutive patients with histologically confirmed HCC-CC or HCC treated with LRT between 2007 and 2017 were retrospectively reviewed. Ten patients (8 men; median age, 60 y) with 12 HCC-CCs (mean diameter, 4.2 cm ± 1.9; mean number, 3.7 ± 3.3) treated with chemoembolization (n = 6), yttrium-90 radioembolization (n = 2), RF ablation (n = 1), or chemoembolization/RF ablation (n = 1) were compared with 124 patients (92 men; median age, 59 y) with 134 HCCs (mean diameter, 4.8 cm ± 4.0; mean number, 2.6 ± 2.2) treated with chemoembolization (n = 51), yttrium-90 radioembolization (n = 17), RF ablation (n = 41), or chemoembolization/RF ablation (n = 15). Propensity score-matched analysis with conditional logistic regression adjusted for age, sex, LRT modality, tumor-specific features, and Child-Pugh class. Tumor-volume doubling time (TVDT) before LRT and objective response rates were compared by Kruskal-Wallis and Fisher exact test; progression-free survival (PFS) and transplant-free survival (TFS) were compared by Cox proportional hazards model. RESULTS: On univariate analysis, HCC-CC was associated with lower median TVDT (2.4 months vs 5.2 months, P = .03), objective response (30% vs 71%, P = .01), and median PFS (2.4 months vs 7.4 months, HR 4.3, 95% CI 2.2-8.4, P < .0001). Propensity score-matched analysis demonstrated greater distant progression (60% vs 30%, P = .003) and significantly shorter median PFS (2.4 months vs 6.0 months, HR 3.3, 95% CI 1.3-8.9, P = .017) for HCC-CC. No significant difference was observed in TFS (7.5 months vs 13.8 months, HR 1.5, 95% CI 0.4-6.1). CONCLUSIONS: HCC-CC was associated with reduced PFS and greater distant progression after LRT compared with HCC, indicating a need for adjunctive treatment strategies to improve outcomes.

Histology of Hepatocellular Carcinoma: Association with Clinical Features, Radiological Findings, and Locoregional Therapy Outcomes.

OBJECTIVE: The objective of the study was to investigate whether hepatocellular carcinoma (HCC) histology is associated with clinical and computed tomographic/magnetic resonance imaging features and locoregional therapy (LRT) outcomes. SUBJECTS AND METHODS: This single-center retrospective study included 124 consecutive patients (92 men, median age 59 years) with 132 HCC diagnosed by biopsy between 2008 and 2017 before LRT. Patients underwent chemoembolization (n = 51, 41%), ablation (n = 41, 33%), yttrium-90 radioembolization (n = 17, 13%), and chemoembolization/ablation (n = 15, 12%). Barcelona clinic liver cancer (BCLC) stage was 0/A (n = 48, 38%), B (n = 33, 26%), C (n = 27, 22%), and D (n = 16, 13%). Edmondson-Steiner (ES) grade and cytology were correlated with baseline features and radiologic response using logistic regression. Time to progression (TTP) and transplant-free survival (TFS) were analyzed using Cox proportional hazard models. RESULTS: High ES grade was associated with α-fetoprotein (AFP) >50 ng/ml (odds ratio [OR] 4.6, 95% confidence interval [CI]: 1.5-13.9; P < 0.01), tumor diameter >5 cm (OR 3.1, 95% CI: 1.1-9.0; P < 0.05), infiltrative appearance (OR 5.0, 95% CI: 1.5-16.2; P < 0.01), and BCLC Stage C (OR 4.5, 95% CI: 1.3-16.4; P = 0.02). Clear-cell subtype was associated with non-viral cirrhosis (OR 5.3, 95% CI: 1.6-17.2; P < 0.01) and atypical enhancement (OR 3.1, 95% CI: 1.0-9.3; P < 0.05). AFP, BCLC Stage B, and diameter were associated with reduced TTP and TFS (P < 0.05). Neither ES grade nor clear-cell subtype was associated with objective response (OR 2.3, 95% CI: 0.7- 7.4; P = 0.15 and OR 1.1, 95% CI: 0.4-3.4; P = 0.87, respectively), TTP (P > 0.20), or TFS (P > 0.90) on univariate or stratified analysis. CONCLUSION: Histologic grade is associated with aggressive tumor features, while clear-cell HCC is associated with non-viral cirrhosis and atypical enhancement. Unlike AFP, BCLC stage, and tumor size, histologic features were not associated with LRT outcomes, supporting biopsy deferral for imaging diagnosed HCC.

A biologic scaffold-associated type 2 immune microenvironment inhibits tumor formation and synergizes with checkpoint immunotherapy.

Biomaterials in regenerative medicine are designed to mimic and modulate tissue environments to promote repair. Biologic scaffolds (derived from decellularized tissue extracellular matrix) promote a wound-healing (proregenerative) immune phenotype and are used clinically to treat tissue loss, including in the context of tumor resection. It is unknown whether a biomaterial microenvironment that encourages tissue formation may also promote tumor development. We implanted a urinary bladder matrix (UBM) scaffold, which is used clinically for wound management, with syngeneic cancer cell lines in mice to study how wound-healing immune responses affect tumor formation and sensitivity to immune checkpoint blockade. The UBM scaffold created an immune microenvironment that inhibited B16-F10 melanoma tumor formation in a CD4+ T cell-dependent and macrophage-dependent manner. In-depth immune characterization revealed an activated type 2-like immune response that was distinct from the classical tumor microenvironment, including activated type 2 T helper T cells, a unique macrophage phenotype, eosinophil infiltration, angiogenic factors, and complement. Tumor growth inhibition by PD-1 and PD-L1 checkpoint blockade was potentiated in the UBM scaffold immune microenvironment. Engineering the local tumor microenvironment to promote a type 2 wound-healing immune signature may serve as a therapeutic target to improve immunotherapy efficacy.

YAP Is Essential for Treg-Mediated Suppression of Antitumor Immunity.

Regulatory T cells (Treg) are critical for maintaining self-tolerance and immune homeostasis, but their suppressive function can impede effective antitumor immune responses. FOXP3 is a transcription factor expressed in Tregs that is required for their function. However, the pathways and microenvironmental cues governing FOXP3 expression and Treg function are not completely understood. Herein, we report that YAP, a coactivator of the Hippo pathway, is highly expressed in Tregs and bolsters FOXP3 expression and Treg function in vitro and in vivo. This potentiation stemmed from YAP-dependent upregulation of activin signaling, which amplifies TGFß/SMAD activation in Tregs. YAP deficiency resulted in dysfunctional Tregs unable to suppress antitumor immunity or promote tumor growth in mice. Chemical YAP antagonism and knockout or blockade of the YAP-regulated activin receptor similarly improved antitumor immunity. Thus, we identify YAP as an unexpected amplifier of a Treg-reinforcing pathway with significant potential as an anticancer immunotherapeutic target.Significance: Tregs suppress antitumor immunity, and pathways supporting their function can be novel immunotherapy targets. Here, the selective expression of YAP by Tregs, its importance for their function, and its unexpected enhancement of pro-Treg Activin/SMAD signaling are reported, as are validations of potential cancer-fighting antagonists of YAP and its regulatory targets. Cancer Discov; 8(8); 1026-43. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 899.

TGFß1-Mediated SMAD3 Enhances PD-1 Expression on Antigen-Specific T Cells in Cancer.

Programmed death-1 (PD-1) is a coinhibitory receptor that downregulates the activity of tumor-infiltrating lymphocytes (TIL) in cancer and of virus-specific T cells in chronic infection. The molecular mechanisms driving high PD-1 expression on TILs have not been fully investigated. We demonstrate that TGFß1 enhances antigen-induced PD-1 expression through SMAD3-dependent, SMAD2-independent transcriptional activation in T cells in vitro and in TILs in vivo The PD-1hi subset seen in CD8+ TILs is absent in Smad3-deficient tumor-specific CD8+ TILs, resulting in enhanced cytokine production by TILs and in draining lymph nodes and antitumor activity. In addition to TGFß1's previously known effects on T-cell function, our findings suggest that TGFß1 mediates T-cell suppression via PD-1 upregulation in the tumor microenvironment (TME). They highlight bidirectional cross-talk between effector TILs and TGFß-producing cells that upregulates multiple components of the PD-1 signaling pathway to inhibit antitumor immunity. SIGNIFICANCE: Engagement of the coinhibitory receptor PD-1 or its ligand, PD-L1, dramatically inhibits the antitumor function of TILs within the TME. Our findings represent a novel immunosuppressive function of TGFß and demonstrate that TGFß1 allows tumors to evade host immune responses in part through enhanced SMAD3-mediated PD-1 expression on TILs. Cancer Discov; 6(12); 1366-81. ©2016 AACRThis article is highlighted in the In This Issue feature, p. 1293.

The role of nuclear receptors in regulation of Th17/Treg biology and its implications for diseases.

Nuclear receptors in the cell play essential roles in environmental sensing, differentiation, development, homeostasis,and metabolism and are thus highly conserved across multiple species. The anti-inflammatory role of nuclear receptors in immune cells has recently gained recognition. Nuclear receptors play critical roles in both myeloid and lymphoid cells, particularly in helper CD41 T-cell type 17 (Th17) and regulatory T cells (Treg). Th17 and Treg are closely related cell fates that are determined by orchestrated cytokine signaling. Recent studies have emphasized the interactions between nuclear receptors and the known cytokine signals and how such interaction affects Th17/Treg development and function.This review will focus on the most recent discoveries concerning the roles of nuclear receptors in the context of therapeutic applications in autoimmune diseases.

Metabolic regulation of T cell differentiation and function.

Upon encountering pathogens, T cells mount immune responses by proliferating, increasing cellular mass and differentiating. These cellular changes impose significant energetic challenges on T cells. It was believed that TCR and cytokine-mediated signaling are dominant dictators of T cell-mediated immune responses. Recently, it was recognized that T cells utilize metabolic transporters and metabolic sensors that allow them to rapidly respond to nutrient-limiting inflammatory environments. Metabolic sensors allow T cells to find a balance between energy consumption (anabolic metabolism) and production (catabolic metabolism) in order to mount effective immune responses. Also, metabolic regulators interact with cytokine-dependent transcriptional regulators, suggesting a more integrative and advanced model of T cell activation and differentiation. In this review, we will discuss recent discoveries regarding the roles of metabolic regulators in effector and memory T cell development and their interaction with canonical transcription factors.