TNF optimally activatives regulatory T cells by inducing TNF receptor superfamily members TNFR2, 4-1BB and OX40

Regulation of Treg cells by cytokine signaling and co-stimulatory molecules

CD4+CD25+Foxp3+ regulatory T cells (Tregs), a vital component of the immune system, are responsible for maintaining immune homeostasis and preventing excessive immune responses. This review explores the signaling pathways of the cytokines that regulate Treg cells, including transforming growth factor beta (TGF-β), interleukin (IL)-2, IL-10, and IL-35, which foster the differentiation and enhance the immunosuppressive capabilities of Tregs. It also examines how, conversely, signals mediated by IL-6 and tumor necrosis factor -alpha (TNF-α) can undermine Treg suppressive functions or even drive their reprogramming into effector T cells. The B7 family comprises indispensable co-stimulators for T cell activation. Among its members, this review focuses on the capacity of CTLA-4 and PD-1 to regulate the differentiation, function, and survival of Tregs. As Tregs play an essential role in maintaining immune homeostasis, their dysfunction contributes to the pathogenesis of autoimmune diseases. This review delves into the potential of employing Treg-based immunotherapy for the treatment of autoimmune diseases, transplant rejection, and cancer. By shedding light on these topics, this article aims to enhance our understanding of the regulation of Tregs by cytokines and their therapeutic potential for various pathological conditions.

Aberrant frequency of TNFR2-expressing CD4+ FoxP3+ regulatory T cells in nasopharyngeal carcinoma patients

TNFR2 is a surface marker of highly suppressive subset of CD4+ FoxP3+ regulatory T cells (Tregs) in humans and mice. This study examined the TNFR2 expression by Tregs of nasopharyngeal carcinoma (NPC) patients and healthy controls. The proliferation, migration, survival of TNFR2+ Tregs, and association with clinicopathological characteristics were assessed. The expression levels of selected cytokines were also determined. The results demonstrated that in both peripheral blood (PB) (10.45 ± 5.71%) and tumour microenvironment (TME) (54.38 ± 16.15%) of NPC patients, Tregs expressed TNFR2 at noticeably greater levels than conventional T cells (Tconvs) (3.91 ± 2.62%, p < 0.0001), akin to healthy controls. Expression of TNFR2 (1.06 ± 0.99%) was correlated better than CD25+ (0.40 ± 0.46%) and CD127-/low (1.00 ± 0.83% ) with FoxP3 expression in NPC PB (p = 0.0005). Though there was no significant association between TNFR2 expression with the functional capacity (proliferation, migration and survival) of Tregs (p > 0.05), the proportions of PB and TME TNFR2+ Tregs in NPC patients showed more proliferative, higher migration capacity, and better survival ability, as compared to those in healthy controls. Furthermore, TNFR2+ Tregs from NPC patients expressed significantly higher amounts of IL-6 (p = 0.0077), IL-10 (p = 0.0001), IFN-γ (p = 0.0105) and TNF-α (p < 0.0001) than those from healthy controls. Most significantly, TNFR2 expression in maximally suppressive Tregs population were linked to WHO Type III histological type, distant metastasis, progressive disease status, and poor prognosis for NPC patients. Hence, our research implies that TNFR2 expression by PB and TME Tregs may be a useful predictive indicator in NPC patients.

Exosome-Modified Liposomes Targeted Delivery of Thalidomide to Regulate Treg Cells for Antitumor Immunotherapy

Thalidomide (THD), a synthetic derivative of glutamic acid, was initially used as a sedative and antiemetic until the 1960s, when it was found to cause devastating teratogenic effects. However, subsequent studies have clearly demonstrated the anti-inflammatory, anti-angiogenic, and immunomodulatory properties of thalidomide, thus providing a rationale for its current use in the treatment of various autoimmune diseases and cancers. Our group found that thalidomide can suppress the regulatory T cells (Tregs), a minor subset of CD4+ T cells (~10%) with unique immunosuppressive activity that have been shown to accumulate in the tumor microenvironment (TME) and represent a major mechanism of tumor immune evasion. Due to the low solubility of thalidomide in its present form of administration, coupled with its lack of specificity for targeted delivery and controlled drug release, it is an urgent need to find potent delivery methods that can significantly enhance its solubility, optimize the desired site of drug action, and mitigate its toxicity. In this study, the isolated exosomes were incubated with synthetic liposomes to form hybrid exosomes (HEs) that carried THD (HE-THD) with uniform size distribution. The results demonstrated that HE-THD could significantly abrogate the expansion and proliferation of Tregs induced by TNF, and this might result from blocking TNF-TNFR2 interaction. By encapsulating THD in hybrid exosomes, our drug delivery system successfully increased the solubility of THD, laying a foundation for future in vivo experiments that validate the antitumor activity of HE-THD by reducing the Treg frequency within the tumor microenvironment.

Allergen recognition by specific effector Th2 cells enables IL-2-dependent activation of regulatory T-cell responses in humans

Type 2 allergen-specific T cells are essential for the induction and maintenance of allergies to foods, and Tregs specific for these allergens are assumed to be involved in their resolution. However, it has not been convincingly demonstrated whether allergen-specific Treg responses are responsible for the generation of oral tolerance in humans. We observed that sustained food allergen exposure in the form of oral immunotherapy resulted in increased frequency of Tregs only in individuals with lasting clinical tolerance. We sought to identify regulatory components of the CD4+ T-cell response to food allergens by studying their functional activation over time in vitro and in vivo. Two subsets of Tregs expressing CD137 or CD25/OX40 were identified with a delayed kinetics of activation compared with clonally enriched pathogenic effector Th2 cells. Treg activation was dependent on IL-2 derived from effector T cells. In vivo exposure to peanut in the form of an oral food challenge of allergic subjects induced a delayed and persistent activation of Tregs after initiation of the allergen-specific Th2 response. The novel finding of our work is that a sustained wave of Treg activation is induced by the release of IL-2 from Th2 effector cells, with the implication that therapeutic administration of IL-2 could improve current OIT approaches.

The Immunosuppressive Effect of TNFR2 Expression in the Colorectal Cancer Microenvironment

Colorectal cancer (CRC) represents one of the most common causes of death among cancers worldwide. Its incidence has been increasing among the young population. Many risk factors contribute to the development and progression of CRC and about 70% of them are sporadic. The CRC microenvironment is highly heterogeneous and represents a very complex immunosuppressive platform. Many cytokines and their receptors are vital participants in this immunosuppressive microenvironment. Tumor necrosis factors (TNFs) and TNF receptor 2 (TNFR2) are critical players in the development of CRC. TNFR2 was observed to have increased the immunosuppressive activity of CRC cells via regulatory T cells (T regs) and myeloid-derived suppressor cells (MDSC) in the CRC microenvironment. However, the exact mechanism of TNFR2 in regulating the CRC prognosis remains elusive. Here, we discuss the role of TNFR2 in immune escape mechanism of CRC in the immunosuppressive cells, including Tregs and MDSCs, and the complex signaling pathways that facilitate the development of CRC. It is suggested that extensive studies on TNFR2 downstream signaling must be done, since TNFR2 has a high potential to be developed into a therapeutic agent and cancer biomarker in the future.

TNFR2 expression predicts the responses to immune checkpoint inhibitor treatments

Immune checkpoint inhibitors (ICIs) by targeting PD-1/PD-L1 or CTLA-4 have markedly improved the outcome of cancer patients. However, most solid tumor patients can't benefit from such therapy. Identification of novel biomarkers to predict the responses of ICIs is crucial to enhance their therapeutic efficacy. TNFR2 is highly expressed by the maximally immunosuppressive subset of CD4⁺Foxp3⁺ regulatory T cells (Tregs), especially those present in tumor microenvironment (TME). Since Tregs represent a major cellular mechanism in tumor immune evasion, TNFR2 may be a useful biomarker to predict the responses to ICIs therapy. This notion is supported by our analysis of the computational tumor immune dysfunction and exclusion (TIDE) framework from published single-cell RNA-seq data of pan-cancer databases. The results show that, as expected, TNFR2 is highly expressed by tumor-infiltrating Tregs. Interestingly, TNFR2 is also expressed by the exhausted CD8 T cells in breast cancer (BRCA), hepatocellular carcinoma (HCC), lung squamous cell carcinoma (LUSC), and melanoma (MELA). Importantly, high expression of TNFR2 is associated with poor responses to the treatment with ICIs in BRCA, HCC, LUSC, and MELA. In conclusion, the expression of TNFR2 in TME may be a reliable biomarker for the precision of ICIs treatment of cancer patients, and this idea merits further research.

Distepharinamide, a novel dimeric proaporphine alkaloid from Diploclisia glaucescens, inhibits the differentiation and proliferative expansion of CD4+Foxp3+ regulatory T cells

BACKGROUND

CD4⁺Foxp3⁺ regulatory T cells (Tregs) represent the primary cellular mechanism of tumor immune evasion. Elimination of Treg activity by the pharmacological agent may enhance anti-tumor immune responses. However, Treg-eliminating agents, especially those with small molecules, are rarely reported.

PURPOSE

To identify small molecule inhibitors of Treg cells from natural products.

METHODS

Compounds from Diploclisia glaucescens were isolated by column chromatography, and structures were identified by spectroscopic evidence and quantum calculations. The tet-On system for Foxp3-GFP expression in Jurkat T cells was generated to screen Treg inhibitors based on Foxp3 expression. The effect of the compound on TNF-induced proliferative expansion of naturally occurring Tregs (nTregs) and TGF-β-induced generation of Tregs (iTregs) from naive CD4⁺ Tcells was further examined.

RESULTS

A novel dimeric proaporphine alkaloid, designated as distepharinamide (DSA) with a symmetric structure isolated from the stems of D. glaucescens, restrained the doxycycline (Doxy)-induced Foxp3-tGFP expression, decreased the half-life of Foxp3 mRNA as well as reduced the mRNA levels of chemokine receptors (CCR4, CCR8 and CCR10) in Jurkat T cells with inducible Foxp3-tGFP expression. In lymphocytes or purified Tregs from wild-type C57BL/6 mice or from C57BL/6-Tg(Foxp3-DTR/EGFP)23.2Spar/Mmjax mice, DSA markedly inhibited TNF-induced proliferative expansion of Tregs present in the unfractionated CD4⁺ T cells, accompanied by the down-regulation of TNFR2, CD25 and CTLA4 expression on Tregs. Furthermore, DSA potently inhibited TGF-β-induced differentiation of Foxp3-expressing iTregs. Importantly, the expression of Foxp3 mRNA by both nTregs and iTregs was decreased by DSA treatment. Nevertheless, DSA at the same concentrations did not inhibit the proliferation of conventional CD4⁺ and CD8⁺ T cells stimulated by anti-CD3/CD28 antibodies.

CONCLUSION

DSA, a novel dimeric proaporphine alkaloid, potently inhibited the expansion of nTregs and generation of iTregs. Therefore, DSA or its analogs may merit further investigation as novel immunotherapeutic agents.

Scutellarin enhances anti-tumor immune responses by reducing TNFR2-expressing CD4+Foxp3+ regulatory T cells

One characteristic of tumor-associated CD4⁺Foxp3⁺ regulatory T cells (Tregs) is the high expression of tumor necrosis factor receptor type II (TNFR2), a receptor that mediates the decisive effect of tumor necrosis factor (TNF) in the activation and expansion of Tregs. There is increasing evidence that inhibition of TNFR2 can enhance anti-tumor immune responses. Therefore, we screened Chinese herbal extracts for their capacity to block TNF-TNFR2 interaction. The results showed that the treatment with a Chinese herb extract could inhibit TNFR2-induced biological responses in vitro, including the proliferation of TNFR2⁺ Tregs. Our subsequent study led to the identification of flavonoid compound scutellarin was responsible for the activity. Our results showed that scutellarin is able to disrupt the interaction of TNF-TNFR2 and inhibited the phosphorylation of p38 MAPK, a down-stream signaling component of TNFR2. Importantly, in vivo scutellarin treatment markedly enhanced the efficacy of tumor immunotherapy with CpG oligodeoxynucleotide in mouse CT26 colon cancer model. This effect of scutellarin was associated with the reduction of the number of tumor-infiltrating TNFR2-expressing Tregs and increased tumor infiltration of interferon-γ-producing CD8⁺ T cells. Our result also suggests that scutellarin or its analogs may be used as an adjuvant to enhance the anti-tumor effect of immunotherapeutic agent by eliminating TNFR2⁺ Treg activity.

Effects of Spore-Displayed p75 Protein from Lacticaseibacillus rhamnosus GG on the Transcriptional Response of HT-29 Cells

A Lacticaseibacillus rhamnosus GG-derived protein, p75, is one of the key molecules exhibiting probiotic activity. However, the molecular mechanism and transcriptional response of p75 in human intestinal epithelial cells are not completely understood. To gain a deeper understanding of its potential probiotic action, this study investigated genome-wide responses of HT-29 cells to stimulation by spore-displayed p75 (CotG-p75) through a transcriptome analysis based on RNA sequencing. Analysis of RNA-seq data showed significant changes of gene expression in HT-29 cells stimulated by CotG-p75 compared to the control. A total of 189 up-regulated and 314 down-regulated genes was found as differentially expressed genes. Gene ontology enrichment analysis revealed that a large number of activated genes was involved in biological processes, such as epithelial cell differentiation, development, and regulation of cell proliferation. A gene–gene interaction network analysis showed that several DEGs, including AREG, EREG, HBEGF, EPGN, FASLG, GLI2, CDKN1A, FOSL1, MYC, SERPINE1, TNFSF10, BCL6, FLG, IVL, SPRR1A, SPRR1B, SPRR3, and MUC5AC, might play a critical role in these biological processes. RNA-seq results for selected genes were verified by reverse transcription-quantitative polymerase chain reaction. Overall, these results provide extensive knowledge about the transcriptional responses of HT-29 cells to stimulation by CotG-p75. This study showed that CotG-p75 can contribute to cell survival and epithelial development in human intestinal epithelial cells.

TNFR2 pathways are fully active in cancer regulatory T cells

Tumor necrosis factor receptor 2 (TNFR2), a membrane-bound tumor necrosis factor receptor expressed by regulatory T cells (Tregs), participates in Treg proliferation. Although a specific TNFR2 pathway has been reported, the signaling mechanism has not been completely elucidated. This study sought to clarify TNFR2 signaling in human Tregs using amplicon sequencing and single-cell RNA sequencing to assess Tregs treated with a TNFR2 agonist antibody. Pathway enrichment analysis based on differentially expressed genes highlighted tumor necrosis factor α signaling via nuclear factor kappa B, interleukin-2 signal transducer and activator of transcription 5 signaling, interferon-γ response, and cell proliferation-related pathways in Tregs after TNFR2 activation. TNFR2-high Treg-focused analysis found that these pathways were fully activated in cancer Tregs, showing high TNFR2 expression. Collectively, these findings suggest that TNFR2 orchestrates multiple pathways in cancer Tregs, which could help cancer cells escape immune surveillance, making TNFR2 signaling a potential anticancer therapy target.

IL-6 and TNFα Drive Extensive Proliferation of Human Tregs Without Compromising Their Lineage Stability or Function

Treg therapies are being tested in clinical trials in transplantation and autoimmune diseases, however, the impact of inflammation on Tregs remains controversial. We challenged human Tregs ex-vivo with pro-inflammatory cytokines IL-6 and TNFα and observed greatly enhanced proliferation stimulated by anti-CD3 and anti-CD28 (aCD3/28) beads or CD28 superagonist (CD28SA). The cytokine-exposed Tregs maintained high expression of FOXP3 and HELIOS, demethylated FOXP3 enhancer, and low IFNγ, IL-4, and IL-17 secretion. Blocking TNF receptor using etanercept or deletion of TNF receptor 2 using CRISPR/Cas9 blunted Treg proliferation and attenuated FOXP3 and HELIOS expression. These results prompted us to consider using CD28SA together with IL-6 and TNFα without aCD3/28 beads (beadless) as an alternative protocol for therapeutic Treg manufacturing. Metabolomics profiling revealed more active glycolysis and oxidative phosphorylation, increased energy production, and higher antioxidant potential during beadless Treg expansion. Finally, beadless expanded Tregs maintained suppressive functions in vitro and in vivo. These results demonstrate that human Tregs positively respond to proinflammatory cytokines with enhanced proliferation without compromising their lineage identity or function. This property can be harnessed for therapeutic Treg manufacturing.

The effects of TNF-α/TNFR2 in regulatory T cells on the microenvironment and progression of gastric cancer

TNFR2⁺ regulatory T cells preferentially accumulate in the tumor microenvironment, express high levels of immunosuppressive molecules and possess strong suppressive activity. Our study aimed to explore the characteristics and role of TNFR2⁺ Tregs in the microenvironment and progression of gastric cancer via polychromatic immunofluorescence, single-cell RNA sequencing and flow cytometry assays. The TNFR2⁺ Treg infiltration level in the tumor microenvironment increased significantly as gastric cancer progressed and was demonstrated to be a prognostic marker. Single-cell RNA sequencing revealed high levels of TNFR2 in tumor-infiltrating Tregs. The TNF-α/TNFR2 signaling pathway was activated, accompanied by the upregulation of costimulatory molecules. Unlike blood Tregs, tumor-infiltrating Tregs existed in activated and effector states. In addition to expressing costimulatory molecules such as TNFR2, 4-1BB, OX40 and GITR, tumor-infiltrating Tregs were also characterized by high expression levels of immune checkpoints such as CTLA-4 and TIGIT and chemokines such as CCR6. In vitro studies showed that the TNF-α/TNFR2 pathway increased the Foxp3 expression in CD4⁺ CD25⁺ T cells and the latent TGF-β production in Tregs as well as enhanced the immunosuppressive function of Tregs. In summary, our study revealed high infiltration levels of TNFR2⁺ Tregs that were in activated and effector states in the tumor microenvironment. The infiltration level of TNFR2⁺ Tregs is a prognostic marker and an independent risk factor for gastric cancer. Activation of the TNF-α/TNFR2 pathway promotes the immunosuppressive phenotype and function of Tregs. Our study provides a new theoretical basis for TNFR2⁺ Tregs as a therapeutic target in gastric cancer.

Neutralization of IL-17 and treatment with IL-2 protects septic arthritis by regulating free radical production and antioxidant enzymes in Th17 and Tregs: An immunomodulatory TLR2 versus TNFR response

Septic arthritis is a destructive joint disease caused by Staphylococcus aureus. Synovial inflammation involved Th17 proliferation and down regulation of Treg population, thus resolution of inflammation targeting IL-17 may be important to control arthritis. Endogenous inhibition of IL-17 to regulate arthritic inflammation correlating with Th17/Treg cells TLR2 and TNFRs are not done. The role of SOD, CAT and GRx in relation to ROS production during arthritis along with expression of TLR2, TNFR1/TNFR2 in Th17/Treg cells of mice treated with IL-17A Ab/ IL-2 were studied. Increased ROS, reduced antioxidant enzyme activity was found in Th17 cells of SA infected mice whereas Treg cells of IL-17A Ab/ IL-2 treated group showed opposite effects. Neutralization of IL-17 after arthritis cause decreased TNFR1 and increased TNFR2 expression in Treg cells. Thus, neutralization of IL-17 or IL-2 treatment regulates septic arthritis by enhancing anti-inflammatory properties of Treg via antioxidant balance and modulating TLR2/TNFR response.

CD137 Costimulation Counteracts TGFβ Inhibition of NK-cell Antitumor Function

Enhancing natural killer (NK) cell-based cancer immunotherapy by overcoming immunosuppression is an area of intensive research. Here, we have demonstrated that the anti-CD137 agonist urelumab can overcome TGFβ-mediated inhibition of human NK-cell proliferation and antitumor function. Transcriptomic, immunophenotypic, and functional analyses showed that CD137 costimulation modified the transcriptional program induced by TGFβ on human NK cells by rescuing their proliferation in response to IL2, preserving their expression of activating receptors (NKG2D) and effector molecules (granzyme B, IFNγ) while allowing the acquisition of tumor-homing/retention features (CXCR3, CD103). Activated NK cells cultured in the presence of TGFβ1 and CD137 agonist recovered CCL5 and IFNγ secretion and showed enhanced direct and antibody-dependent cytotoxicity upon restimulation with cancer cells. Trastuzumab treatment of fresh breast carcinoma-derived multicellular cultures induced CD137 expression on tumor-infiltrating CD16⁺ NK cells, enabling the action of urelumab, which fostered tumor-infiltrating NK cells and recapitulated the enhancement of CCL5 and IFNγ production. Bioinformatic analysis pointed to IFNG as the driver of the association between NK cells and clinical response to trastuzumab in patients with HER2-positive primary breast cancer, highlighting the translational relevance of the CD137 costimulatory axis for enhancing IFNγ production. Our data reveals CD137 as a targetable checkpoint for overturning TGFβ constraints on NK-cell antitumor responses.

Insights into the biology and therapeutic implications of TNF and regulatory T cells

Treatments that block tumour necrosis factor (TNF) have major beneficial effects in several autoimmune and rheumatic diseases, including rheumatoid arthritis. However, some patients do not respond to TNF inhibitor treatment and rare occurrences of paradoxical disease exacerbation have been reported. These limitations on the clinical efficacy of TNF inhibitors can be explained by the differences between TNF receptor 1 (TNFR1) and TNFR2 signalling and by the diverse effects of TNF on multiple immune cells, including FOXP3⁺ regulatory T cells. This basic knowledge sheds light on the consequences of TNF inhibitor therapies on regulatory T cells in treated patients and on the limitations of such treatment in the control of diseases with an autoimmune component. Accordingly, the next generation of drugs targeting TNF is likely to be based on agents that selectively block the binding of TNF to TNFR1 and on TNFR2 agonists. These approaches could improve the treatment of rheumatic diseases in the future.

Differential transcriptional and functional properties of regulatory T cells in HIV-infected individuals on antiretroviral therapy and long-term non-progressors

OBJECTIVES

Regulatory T cells (Tregs) are widely recognised as a subset of CD4+CD25+FOXP3+ T cells that have a key role in maintaining immune homeostasis. The impact of HIV-1 infection on immunological properties and effector functions of Tregs has remained the topic of debate and controversy. In the present study, we investigated transcriptional profile and functional properties of Tregs in HIV-1-infected individuals either receiving antiretroviral therapy (ART, n = 50) or long-term non-progressors (LTNPs, n = 24) compared to healthy controls (HCs, n = 38).

METHODS

RNA sequencing (RNAseq), flow cytometry-based immunophenotyping and functional assays were performed to study Tregs in different HIV cohorts.

RESULTS

Our RNAseq analysis revealed that Tregs exhibit different transcriptional profiles in HIV-infected individuals. While Tregs from patients on ART upregulate pathways associated with a more suppressive (activated) phenotype, Tregs in LTNPs exhibit upregulation of pathways associated with impaired suppressive properties. These observations may explain a higher propensity for autoimmune diseases in LTNPs. Also, we found substantial upregulation of HLA-F mRNA and HLA-F protein in Tregs from HIV-infected subjects compared to healthy individuals. These observations highlight a potential role for this non-classical HLA in Tregs in the context of HIV infection, which should be investigated further in other chronic viral infections and cancer.

CONCLUSION

Our study has provided a novel insight into Tregs at the transcriptional and functional levels in different HIV-infected groups.

TNFR2: Role in Cancer Immunology and Immunotherapy

Immune checkpoint inhibitors (ICIs), including anti-CTLA-4 (cytotoxic T lymphocyte antigen-4) and anti-PD-1/PD-L1 (programmed death-1/programmed death-ligand 1), represent a turning point in the cancer immunotherapy. However, only a minor fraction of patients could derive benefit from such therapy. Therefore, new strategies targeting additional immune regulatory mechanisms are urgently needed. CD4⁺Foxp3⁺ regulatory T cells (Tregs) represent a major cellular mechanism in cancer immune evasion. There is compelling evidence that tumor necrosis factor (TNF) receptor type II (TNFR2) plays a decisive role in the activation and expansion of Tregs and other types of immunosuppressive cells such as myeloid-derived suppressor cells (MDSCs). Furthermore, TNFR2 is also expressed by some tumor cells. Emerging experimental evidence indicates that TNFR2 may be a therapeutic target to enhance naturally occurring or immunotherapeutic-triggered anti-tumor immune responses. In this article, we discuss recent advances in the understanding of the mechanistic basis underlying the Treg-boosting effect of TNFR2. The role of TNFR2-expressing highly suppressive Tregs in tumor immune evasion and their possible contribution to the non-responsiveness to checkpoint treatment are analyzed. Moreover, the role of TNFR2 expression on tumor cells and the impact of TNFR2 signaling on other types of cells that shape the immunological landscape in the tumor microenvironment, such as MDSCs, MSCs, ECs, EPCs, CD8⁺ CTLs, and NK cells, are also discussed. The reports revealing the effect of TNFR2-targeting pharmacological agents in the experimental cancer immunotherapy are summarized. We also discuss the potential opportunities and challenges for TNFR2-targeting immunotherapy.

Recruitment and Expansion of Tregs Cells in the Tumor Environment-How to Target Them?

Simple Summary

The immune response against cancer is generated by effector T cells, among them cytotoxic CD8⁺ T cells that destroy cancer cells and helper CD4⁺ T cells that mediate and support the immune response. This antitumor function of T cells is tightly regulated by a particular subset of CD4⁺ T cells, named regulatory T cells (Tregs), through different mechanisms. Even if the complete inhibition of Tregs would be extremely harmful due to their tolerogenic role in impeding autoimmune diseases in the periphery, the targeted blockade of their accumulation at tumor sites or their targeted depletion represent a major therapeutic challenge. This review focuses on the mechanisms favoring Treg recruitment, expansion and stabilization in the tumor microenvironment and the therapeutic strategies developed to block these mechanisms.

Abstract

Regulatory T cells (Tregs) are present in a large majority of solid tumors and are mainly associated with a poor prognosis, as their major function is to inhibit the antitumor immune response contributing to immunosuppression. In this review, we will investigate the mechanisms involved in the recruitment, amplification and stability of Tregs in the tumor microenvironment (TME). We will also review the strategies currently developed to inhibit Tregs’ deleterious impact in the TME by either inhibiting their recruitment, blocking their expansion, favoring their plastic transformation into other CD4⁺ T-cell subsets, blocking their suppressive function or depleting them specifically in the TME to avoid severe deleterious effects associated with Treg neutralization/depletion in the periphery and normal tissues.

The role of CD4+FoxP3+ regulatory T cells in the immunopathogenesis of COVID-19: implications for treatment

The severe cases of Coronavirus Disease 2019 (COVID-19) frequently exhibit excessive inflammatory responses, acute respiratory distress syndrome (ARDS), coagulopathy, and organ damage. The most striking immunopathology of advanced COVID-19 is cytokine release syndrome or "cytokine storm" that is attributable to the deficiencies in immune regulatory mechanisms. CD4+FoxP3+ regulatory T cells (Tregs) are central regulators of immune responses and play an indispensable role in the maintenance of immune homeostasis. Tregs are likely involved in the attenuation of antiviral defense at the early stage of infection and ameliorating inflammation-induced organ injury at the late stage of COVID-19. In this article, we review and summarize the current understanding of the change of Tregs in patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and discuss the potential role of Tregs in the immunopathology of COVID-19. The emerging concept of Treg-targeted therapies, including both adoptive Treg transfer and low dose of IL-2 treatment, is introduced. Furthermore, the potential Treg-boosting effect of therapeutic agents used in the treatment of COVID-19, including dexamethasone, vitamin D, tocilizumab and sarilumab, chloroquine, hydroxychloroquine, azithromycin, adalimumab and tetrandrine, is discussed. The problems in the current study of Treg cells in COVID-19 and future perspectives are also addressed.

AAV8 locoregional delivery induces long-term expression of an immunogenic transgene in macaques despite persisting local inflammation

Adeno-associated virus (AAV) vectors are considered efficient vectors for gene transfer, as illustrated by recent successful clinical trials targeting retinal or neurodegenerative disorders. However, limitations as host immune responses to AAV capsid or transduction of limited regions must still be overcome. Here, we focused on locoregional (LR) intravenous perfusion vector delivery that allows transduction of large muscular areas and is considered to be less immunogenic than intramuscular (IM) injection. To confirm this hypothesis, we injected 6 cynomolgus monkeys with an AAV serotype 8 (AAV8) vector encoding for the highly immunogenic GFP driven by either a muscle-specific promoter (n = 3) or a cytomegalovirus (CMV) promoter (n = 3). We report that LR delivery allows long-term GFP expression in the perfused limb (up to 1 year) despite the initiation of a peripheral transgene-specific immune response. The analysis of the immune status of the perfused limb shows that LR delivery induces persisting inflammation. However, this inflammation is not sufficient to result in transgene clearance and is balanced by resident regulatory T cells. Overall, our results suggest that LR delivery promotes persisting transgene expression by induction of Treg cells in situ and might be a safe alternative to IM route to target large muscle territories for the expression of secreted therapeutic factors.

Modulation of CD4 T Cell Response According to Tumor Cytokine Microenvironment

The advancement of knowledge on tumor biology over the past decades has demonstrated a close link between tumor cells and cells of the immune system. In this context, cytokines have a major role because they act as intermediaries in the communication into the tumor bed. Cytokines play an important role in the homeostasis of innate and adaptive immunity. In particular, they participate in the differentiation of CD4 T lymphocytes. These cells play essential functions in the anti-tumor immune response but can also be corrupted by tumors. The differentiation of naïve CD4 T cells depends on the cytokine environment in which they are activated. Additionally, at the tumor site, their activity can also be modulated according to the cytokines of the tumor microenvironment. Thus, polarized CD4 T lymphocytes can see their phenotype evolve, demonstrating functional plasticity. Knowledge of the impact of these cytokines on the functions of CD4 T cells is currently a source of innovation, for therapeutic purposes. In this review, we discuss the impact of the major cytokines present in tumors on CD4 T cells. In addition, we summarize the main therapeutic strategies that can modulate the CD4 response through their impact on cytokine production.

TNF-TNFR2 Signal Plays a Decisive Role in the Activation of CD4+Foxp3+ Regulatory T Cells: Implications in the Treatment of Autoimmune Diseases and Cancer

The puzzling biphasic or dual roles of tumor necrosis factor α (TNF) in the inflammatory and immune responses are likely to be mediated by distinct signaling pathways transduced by one of its two receptors, e.g., TNF receptor type I (TNFR1) and TNF receptor type II (TNFR2). Unlike TNFR1 that is ubiquitously expressed on almost all types of cells, the expression of TNFR2 is rather restricted to certain types of cells, such as T lymphocytes. There is now compelling evidence that TNFR2 is preferentially expressed by CD4⁺Foxp3⁺ regulatory T cells (Tregs), and TNFR2 plays a decisive role in the activation, expansion, in vivo function, and phenotypical stability of Tregs. In this chapter, the current understanding of the molecular basis and signaling pathway of TNF-TNFRs signal is introduced. Latest studies that have further supported and substantiated the pivotal role of TNF-TNFR2 interaction in Tregs biology and its molecular basis are discussed. The research progress regarding TNFR2-targeting treatment for autoimmune diseases and cancer is analyzed. Future study should focus on the further understanding of molecular mechanism underlying Treg-stimulatory effect of TNFR2 signal, as well as on the translation of research findings into therapeutic benefits of human patients with autoimmune diseases, allergy, allograft rejection, and cancer.

Accumulation of TNFR2-expressing regulatory T cells in malignant pleural effusion of lung cancer patients is associated with poor prognosis

Background

Regulatory T cells (Tregs) may represent a major cellular mechanism in immune suppression by dampening the anti-tumor response in malignant pleural effusion (MPE). Tumor necrosis factor receptor type II (TNFR2) has emerged as a novel identification for the maximally suppressive subset of Tregs in the tumor environment. At present, the significance of TNFR2 expression on Tregs in MPE remains unclear.

Methods

The distribution of TNFR2⁺cells in Tregs and effector T cells (Teffs) in MPE, peripheral blood (PB), and tuberculosis pleural effusion (TPE) were determined. The associations between TNFR2⁺Tregs frequencies present in MPE and the clinical and laboratorial characteristics of patients with lung cancer were investigated. The immunosuppressive phenotype of TNFR2⁺Tregs in MPE was analyzed. The effects of the TNF-TNFR2 interaction on the immunosuppressive function of Tregs was explored. The efficacy of targeting TNFR2 for MPE therapy was examined. The source of TNF in MPE was identified.

Results

We observed that markedly higher levels of TNFR2 were expressed in MPE Tregs compared with the levels expressed in MPE Teffs, PB Tregs, or in TPE Tregs. The frequencies of TNFR2⁺Tregs were positively correlated with the number of tumor cells in MPE, as well as the volume of MPE. High frequencies of TNFR2⁺Tregs in MPE indicated short survival time and poor performance status for MPE patients. Compared to TNFR2^-Tregs, TNFR2⁺Tregs expressed higher levels of immunosuppressive molecules cytotoxic T lymphocyte-associated protein 4 (CTLA-4), programmed cell death-ligand 1 (PD-L1), and replicating marker Ki-67. Consequently, the proportions of interferon gamma (IFN-γ)-producing cytotoxic T lymphocytes (CTLs) were significantly increased after TNFR2 blockade. Furthermore, tumor necrosis factor (TNF), through interaction with TNFR2, enhanced the suppressive capacity of Tregs by up-regulating CTLA-4 and PD-L1 expression. Interestingly, T helper 1 (Th1) and T helper 17 (Th17) cells are the major source of TNF in MPE, suggesting that MPE Teffs may paradoxically promote tumor growth by boosting MPE Treg activity via the TNF-TNFR2 pathway.

Conclusions

Our data expanded the immunosuppressive mechanism present in MPE induced by Tregs, and provides novel insight for the diagnosis, disease evaluation, and treatment of MPE patients.

Re-Examining the Role of TNF in MS Pathogenesis and Therapy

Multiple sclerosis (MS) is a common neurological disorder of putative autoimmune origin. Clinical and experimental studies delineate abnormal expression of specific cytokines over the course of the disease. One major cytokine that has been shown to play a pivotal role in MS is tumor necrosis factor (TNF). TNF is a pleiotropic cytokine regulating many physiological and pathological functions of both the immune system and the central nervous system (CNS). Convincing evidence from studies in human and experimental MS have demonstrated the involvement of TNF in various pathological hallmarks of MS, including immune dysregulation, demyelination, synaptopathy and neuroinflammation. However, due to the complexity of TNF signaling, which includes two-ligands (soluble and transmembrane TNF) and two receptors, namely TNF receptor type-1 (TNFR1) and type-2 (TNFR2), and due to its cell- and context-differential expression, targeting the TNF system in MS is an ongoing challenge. This review summarizes the evidence on the pathophysiological role of TNF in MS and in different MS animal models, with a special focus on pharmacological treatment aimed at controlling the dysregulated TNF signaling in this neurological disorder.

Viral Hepatitides, Inflammation and Tumour Microenvironment

In this chapter, we discuss the role of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections in the establishment of hepatocellular carcinoma (HCC), highlighting the key role of the multiple, non-mutually exclusive, pathways involved in the modulation of immune responses and in the orchestration of a chronic low-level inflammation state favouring HCC development. In particular, we discuss (i) HCC as a classical paradigm of inflammation-linked cancer; (ii) the role of the most relevant inflammatory cytokines involved (i.e. IL-6, TNF-α, IL-18, IL-1β, TGF-β IL-10); (iii) the role of T cell exhaustion by immune checkpoints; (iv) the role of the Wnt3a/β-catenin signalling pathway and (v) the role of different subsets of suppressor cells.

EphB4/ TNFR2/ERK/MAPK signaling pathway comprises a signaling axis to mediate the positive effect of TNF-α on osteogenic differentiation

BACKGROUND

Low concentrations of tumor necrosis factor-alpha (TNF-α) and its receptor TNFR2 are both reported to promote osteogenic differentiation of osteoblast precursor cells. Moreover, low concentrations of TNF-α up-regulate the expression of EphB4. However, the molecular mechanisms underlying TNF-α-induced osteogenic differentiation and the roles of TNFR2 and EphB4 have not been fully elucidated.

RESULTS

The ALP activity, as well as the mRNA and protein levels of RUNX2, BSP, EphB4 and TNFR2, was significantly elevated in MC3T3-E1 murine osteoblast precursor cells when stimulated with 0.5 ng/ml TNF-α. After TNFR2 was inhibited by gene knockdown with lentivirus-mediated shRNA interference or by a neutralizing antibody against TNFR2, the pro-osteogenic effect of TNF-α was partly reversed, while the up-regulation of EphB4 by TNF-α remained unchanged. With EphB4 forward signaling suppressed by a potent inhibitor of EphB4 auto-phosphorylation, NVP-BHG712, TNF-α-enhanced expressions of TNFR2, BSP and Runx2 were significantly decreased. Further investigation into the signaling pathways revealed that TNF-α significantly increased levels of p-JNK, p-ERK and p-p38. However, only the p-ERK level was significantly inhibited in TNFR2-knockdown cells. In addition, the ERK pathway inhibitor, U0126 (10 μM), significantly reversed the positive effect of TNF-α on the protein levels of RUNX2 and BSP.

CONCLUSIONS

The EphB4, TNFR2 and ERK/MAPK signaling pathway comprises a signaling axis to mediate the positive effect of TNF-α on osteogenic differentiation.

Preferential Expansion of CD4+Foxp3+ Regulatory T Cells (Tregs) In Vitro by Tumor Necrosis Factor

CD4⁺Foxp3⁺ regulatory T cells (Tregs) are a distinct subset of CD4 T cells that play indispensable role in the maintenance of immune homeostasis and prevention of deleterious immune responses to self-antigens. Tumor necrosis factor (TNF) is a key cytokine in the autoimmune inflammatory responses. The effect of TNF on Treg activity was extensively studied in the past decade. We for the first time reported that TNF through TNFR2 preferentially activates and expands Tregs. Our discovery is increasingly supported by the research community; however, some controversial results were reported. The differential results are likely caused by different experimental condition. A standard experiment protocol can help researchers to obtain more consistent results. In this chapter, we detail methods used to examine in vitro effect of exogenous TNF on the proliferative expansion of Tregs in unfractionated mouse CD4⁺ T cells. The related technic issues are analyzed and discussed.

OX40 ligand is inhibitory during the effector phase of crescentic glomerulonephritis

BACKGROUND

The functional relevance of OX40 ligand (OX40L) in the effector phase of crescentic glomerulonephritis (GN) is unknown. These studies defined the role of endogenous OX40L during the effector stage of murine crescentic GN.

METHODS

GN was induced by immunization with sheep globulin/adjuvant on Day 0 and injection of sheep anti-mouse glomerular basement membrane immunoglobulin (Ig) on Day 10. Rat IgG or neutralizing anti-OX40L antibody was administered on Days 10-18 and immune responses and renal injury assessed on Day 20.

RESULTS

Compared with naïve animals, OX40L was upregulated in the lymph nodes (LNs) and on leucocytes and resident non-immune cells in the kidneys of mice with GN. Inhibition of OX40L in GN augmented renal injury, as indicated by increased crescent formation, proteinuria and glomerular leucocyte accumulation. In line with increased injury, anti-OX40L treatment increased proliferation and decreased apoptosis of CD4 T cells in the LNs, without affecting LN CD4 cytokine production and CD8 T-cell responses. Blockade of OX40L decreased LN regulatory T-cell (Treg) proliferation, transforming growth factor β production and foxp3 expression. OX40L inhibition did not affect B cell expansion or circulating antibody levels. In the kidney, neutralization of OX40L augmented interferon γ (IFNγ) expression by CD4 and CD8 T cells and shifted macrophage polarization towards the pro-inflammatory M1 phenotype.

CONCLUSIONS

OX40L is protective during the effector phase of murine crescentic GN by reducing the expansion of CD4 T cells and enhancing Treg responses in the LNs, and by locally inhibiting T-cell IFNγ production and pro-inflammatory macrophage phenotype in the kidney.

Dysfunctional and Proinflammatory Regulatory T-Lymphocytes Are Essential for Adverse Cardiac Remodeling in Ischemic Cardiomyopathy

BACKGROUND

Heart failure (HF) is a state of inappropriately sustained inflammation, suggesting the loss of normal immunosuppressive mechanisms. Regulatory T-lymphocytes (Tregs) are considered key suppressors of immune responses; however, their role in HF is unknown. We hypothesized that Tregs are dysfunctional in ischemic cardiomyopathy and HF, and they promote immune activation and left ventricular (LV) remodeling.

METHODS

Adult male wild-type C57BL/6 mice, Foxp3-diphtheria toxin receptor transgenic mice, and tumor necrosis factor (TNF) α receptor-1 (TNFR1)^-/- mice underwent nonreperfused myocardial infarction to induce HF or sham operation. LV remodeling was assessed by echocardiography as well as histological and molecular phenotyping. Alterations in Treg profile and function were examined by flow cytometry, immunostaining, and in vitro cell assays.

RESULTS

Compared with wild-type sham mice, CD4⁺Foxp3⁺ Tregs in wild-type HF mice robustly expanded in the heart, circulation, spleen, and lymph nodes in a phasic manner after myocardial infarction, beyond the early phase of wound healing, and exhibited proinflammatory T helper 1-type features with interferon-γ, TNFα, and TNFR1 expression, loss of immunomodulatory capacity, heightened proliferation, and potentiated antiangiogenic and profibrotic properties. Selective Treg ablation in Foxp3-diphtheria toxin receptor mice with ischemic cardiomyopathy reversed LV remodeling and dysfunction, alleviating hypertrophy and fibrosis, while suppressing circulating CD4⁺ T cells and systemic inflammation and enhancing tissue neovascularization. Tregs reconstituted after ablation exhibited restoration of immunosuppressive capacity and normalized TNFR1 expression. Treg dysfunction was also tightly coupled to Treg-endothelial cell contact- and TNFR1-dependent inhibition of angiogenesis and the mobilization and tissue infiltration of CD34⁺Flk1⁺ circulating angiogenic cells in a C-C chemokine ligand 5/C-C chemokine receptor 5-dependent manner. Anti-CD25-mediated Treg depletion in wild-type mice imparted similar benefits on LV remodeling, circulating angiogenic cells, and tissue neovascularization.

CONCLUSIONS

Proinflammatory and antiangiogenic Tregs play an essential pathogenetic role in chronic ischemic HF to promote immune activation and pathological LV remodeling. The restoration of normal Treg function may be a viable approach to therapeutic immunomodulation in this disease.

MicroRNA expression profiling provides novel insights into immune-related pathways involved in gastric cancer

Gastric cancer is one of the most common cancers, and an increasing number of studies have found that microRNAs (miRNAs) play essential roles in gastric cancer progression; however, the roles of specific miRNAs involved in the immune response to this disease remain unclear. We compared the miRNA expression in tissues from primary gastric cancer patients and healthy controls to find miRNAs dysregulated in gastric cancer and used bioinformatics tools to determine potential roles of these miRNAs in the immune system. We evaluated 25 primary gastric cancer tissues and five healthy gastric tissues. Quantitative real-time polymerase chain reaction was performed for a set of miRNAs, followed by the prediction of their target genes and functional enrichment analysis of these targets. Analysis of a microarray dataset showed that the miRNA miR-196a-5p was significantly upregulated, while miR-374a-5p and miR-375 were downregulated in gastric cancer patients. In addition, miR-374-5p was significantly downregulated in patients with metastasis compared with its expression levels in non-metastatic patients (p = 0.03). Bioinformatics analysis suggested that the pathways regulated by these differentially expressed miRNAs were related to the immune response, cell adhesion, and cell migration. Most importantly, this study provides a new insight into the potential use of multiple miRNAs to find distinct pathways of immune regulation in gastric cancer.

Allergen-specific immunotherapy enhances CD8+ CD25+ CD137+ regulatory T cells and decreases nasal nitric oxide

BACKGROUND

4-1BB (CD137), a member of the inducible tumor necrosis factor receptor (TNFR) family, is expressed on regulatory T (Treg) cells and regulates Treg cells to control allergic inflammation. Pam3CSK4, a synthetic TLR2 ligand that can expand CD8⁺ Treg function, is a promising adjuvant for allergen immunotherapy (IT). We examined whether Dermatophagoides pteronyssinus (Der p) IT and Pam3CSK4 could enhance CD8⁺  CD25⁺  CD137⁺ Treg suppressive function to decrease nasal nitric oxide (nNO) levels.

METHODS

Nasal symptom scores, nNO levels, PBMCs, and inferior turbinate biopsies were obtained from 40 mite-sensitive perennial allergic rhinitis (PAR) patients before and after one year of Der p IT and 30 non-allergic control subjects. CD137 expression on CD8⁺  CD25⁺ T cells and suppressive function of CD8⁺  CD25⁺  CD137⁺ Tregs was measured using flow cytometry. Cytokine levels were analyzed by ELISA. Inducible nitric oxide synthase production by nasal epithelial cells after co-culturing with CD8⁺  CD25⁺  CD137⁺ T cells was analyzed by Western blotting.

RESULTS

Der p IT improved nasal symptom scores, decreased nNO levels, and increased CD137 expression on CD8⁺ T cells in PBMCs and nasal mucosa. Pam3CSK4 expanded the CD8⁺  CD25⁺  CD137⁺ population in PBMCs. Pam3CSK4-stimulated CD8⁺  CD25⁺  CD137⁺ Tregs induced IL-10 and TGF-β and suppressed CD4⁺  CD25- T-cell proliferation mainly by cell contact inhibition. CD8⁺  CD25⁺  CD137⁺ Tregs cultured with nasal epithelial cells suppressed Der p 2-induced iNOS production. Silencing CD137 in sorted CD8⁺  CD25⁺ T cells decreased Pam3CSK4-activated Foxp3 expression.

CONCLUSION

Der p IT expanded CD8⁺  CD25⁺  CD137⁺ Tregs and decreased nNO levels. Induced CD137 expression on CD8⁺  CD25⁺ Tregs by Pam3CSK4 stimulation may help suppress allergic inflammation during IT.

Expression of costimulatory and inhibitory receptors in FoxP3+ regulatory T cells within the tumor microenvironment: Implications for combination immunotherapy approaches

The unprecedented success of immune checkpoint inhibitors has given rise to a rapidly growing number of immuno-oncology agents undergoing preclinical and clinical development and an exponential increase in possible combinations. Defining a clear rationale for combinations by identifying synergies between immunomodulatory pathways has therefore become a high priority. Immunosuppressive regulatory T cells (Tregs) within the tumor microenvironment (TME) represent a major roadblock to endogenous and therapeutic tumor immunity. However, Tregs are also essential for the maintenance of immunological self-tolerance, and share many molecular pathways with conventional T cells including cytotoxic T cells, the primary mediators of tumor immunity. Hence the inability to specifically target and neutralize Tregs within the TME of cancer patients without globally compromising self-tolerance poses a significant challenge. Here we review recent advances in the characterization of tumor-infiltrating Tregs with a focus on costimulatory and inhibitory receptors. We discuss receptor expression patterns, their functional role in Treg biology and mechanistic insights gained from targeting these receptors in preclinical models to evaluate their potential as clinical targets. We further outline a framework of parameters that could be used to refine the assessment of Tregs in cancer patients and increase their value as predictive biomarkers. Finally, we propose modalities to integrate our increasing knowledge on Treg phenotype and function for the rational design of checkpoint inhibitor-based combination therapies. Such combinations have great potential for synergy, as they could concomitantly enhance cytotoxic T cells and inhibit Tregs within the TME, thereby increasing the efficacy of current cancer immunotherapies.

TNFR2-expressing CD4+Foxp3+ regulatory T cells in cancer immunology and immunotherapy

CD4⁺Foxp3⁺ regulatory T cells (Tregs) represent a major cellular mechanism in tumor immune evasion. Elimination of Treg activity has become a strategy to devise an effective tumor immunotherapy. We reported that TNF receptor type II (TNFR2), one of two receptors transducing TNF biological activity, is preferentially expressed by the most suppressive subset of Tregs. By interaction with TNFR2, TNF plays a decisive role in the activation, expansion and phenotype stability of Tregs. We also found that highly suppressive TNFR2-expressing Tregs appear to be tumor-associated Tregs. This finding has been supported by recent studies in mouse tumor models and in cancer patients. In this chapter, published data revealing the important role of TNFR2⁺ Tregs in tumor development and metastasis in different tumor types are reviewed and analyzed. The therapeutic potential of targeting TNF-TNFR2 interaction as means to eliminate Treg activity, and consequently to enhance anti-tumor immune responses, also is discussed.

Tumor necrosis factor receptor-2 (TNFR2): an overview of an emerging drug target

INTRODUCTION

Tumor necrosis factor (TNF) receptor 2 (TNFR2) is one of two receptors of the cytokines, TNF and lymphotoxin-α. TNFR1 is a strong inducer of proinflammatory activities. TNFR2 has proinflammatory effects too, but it also elicits strong anti-inflammatory activities and has protective effects on oligodendrocytes, cardiomyocytes, and keratinocytes. The protective and anti-inflammatory effects of TNFR2 may explain why TNF inhibitors failed to be effective in diseases such as heart failure or multiple sclerosis, where TNF has been strongly implicated as a driving force. Stimulatory and inhibitory TNFR2 targeting hence attracts considerable interest for the treatment of autoimmune diseases and cancer. Areas covered: Based on a brief description of the pathophysiological importance of the TNF-TNFR1/2 system, we discuss the potential applications of TNFR2 targeting therapies. We also debate TNFR2 activation as a way forward in the search for TNFR2-specific agents. Expert opinion: The use of TNFR2 to target regulatory T-cells is attractive, but this approach is just one amongst many suitable targets. With respect to its preference for Treg stimulation and protection of non-immune cells, TNFR2 is more unique and thus offers opportunities for translational success.

Essential and non-overlapping IL-2Rα-dependent processes for thymic development and peripheral homeostasis of regulatory T cells

IL-2R signaling is essential for regulatory T cell (Treg) function. However, the precise contribution of IL-2 during Treg thymic development, peripheral homeostasis and lineage stability remains unclear. Here we show that IL-2R signaling is required by thymic Tregs at an early step for expansion and survival, and a later step for functional maturation. Using inducible, conditional deletion of CD25 in peripheral Tregs, we also find that IL-2R signaling is indispensable for Treg homeostasis, whereas Treg lineage stability is largely IL-2-independent. CD25 knockout peripheral Tregs have increased apoptosis, oxidative stress, signs of mitochondrial dysfunction, and reduced transcription of key enzymes of lipid and cholesterol biosynthetic pathways. A divergent IL-2R transcriptional signature is noted for thymic Tregs versus peripheral Tregs. These data indicate that IL-2R signaling in the thymus and the periphery leads to distinctive effects on Treg function, while peripheral Treg survival depends on a non-conventional mechanism of metabolic regulation.

Interleukin-2 (IL-2) signaling is required for regulatory T (Treg) cell differentiation in the thymus, but its function in peripheral Tregs is still unclear. Here the authors show, using inducible deletion of IL-2 receptor subunit CD25, that IL-2 signaling is essential for maintaining peripheral Treg homeostasis, but dispensable for lineage stability.

Regulatory T Cells: From Discovery to Autoimmunity

Multiple sclerosis (MS) is a genetically mediated autoimmune disease of the central nervous system. Allelic variants lead to lower thresholds of T-cell activation resulting in activation of autoreactive T cells. Environmental factors, including, among others, diet, vitamin D, and smoking, in combination with genetic predispositions, play a substantial role in disease development and activation of autoreactive T cells. FoxP3⁺ regulatory T cells (Tregs) have emerged as central in the control of autoreactive T cells. A consistent finding in patients with MS is defects in Treg cell function with reduced suppression of effector T cells and production of proinflammatory cytokines. Emerging data suggests that functional Tregs become effector-like T cells with loss of function associated with T-bet expression and interferon γ (IFN-γ) secretion.

The Key Role of TNF-TNFR2 Interactions in the Modulation of Allergic Inflammation: A Review

Tumor necrosis factor-alpha (TNF) is a pleiotropic cytokine, which is thought to play a major role in the pathogenesis of inflammatory diseases, including allergy. TNF is produced at the early stage of allergen sensitization, and then continues to promote the inflammation cascade in the effector phase of allergic reactions. Consequently, anti-TNF treatment has been proposed as a potential therapeutic option. However, recent studies reveal anti-intuitive effects of TNF in the activation and proliferative expansion of immunosuppressive Tregs, tolerogenic DCs and MDSCs. This immunosuppressive effect of TNF is mediated by TNFR2, which is preferentially expressed by immunosuppressive cells. These findings redefine the role of TNF in allergic reaction, and suggest that targeting TNF-TNFR2 interaction itself may represent a novel strategy in the treatment of allergy.

High prevalence of Streptococcus pyogenes Cas9-reactive T cells within the adult human population

The discovery of the highly efficient site-specific nuclease system CRISPR-Cas9 from Streptococcus pyogenes has galvanized the field of gene therapy^1,2. The immunogenicity of Cas9 nuclease has been demonstrated in mice^3,4. Preexisting immunity against therapeutic gene vectors or their cargo can decrease the efficacy of a potentially curative treatment and may pose significant safety issues^3-6. S. pyogenes is a common cause for infectious diseases in humans, but it remains unclear whether it induces a T cell memory against the Cas9 nuclease^7,8. Here, we show the presence of a preexisting ubiquitous effector T cell response directed toward the most widely used Cas9 homolog from S. pyogenes (SpCas9) within healthy humans. We characterize SpCas9-reactive T cells within the CD4/CD8 compartments for multi-effector potency, cytotoxicity, and lineage determination. In-depth analysis of SpCas9-reactive T cells reveals a high frequency of SpCas9-reactive regulatory T cells that can mitigate SpCas9-reactive effector T cell proliferation and function in vitro. Our results shed light on T cell-mediated immunity toward CRISPR-associated nucleases and offer a possible solution to overcome the problem of preexisting immunity.

The p38 MAPK Inhibitor SB203580 Abrogates Tumor Necrosis Factor-Induced Proliferative Expansion of Mouse CD4+Foxp3+ Regulatory T Cells

There is now compelling evidence that tumor necrosis factor (TNF) preferentially activates and expands CD4⁺Foxp3⁺ regulatory T cells (Tregs) through TNF receptor type II (TNFR2). However, it remains unclear which signaling transduction pathway(s) of TNFR2 is required for the stimulation of Tregs. Previously, it was shown that the interaction of TNF–TNFR2 resulted in the activation of a number of signaling pathways, including p38 MAPK, NF-κB, in T cells. We thus examined the role of p38 MAPK and NF-κB in TNF-mediated activation of Tregs, by using specific small molecule inhibitors. The results show that treatment with specific p38 MAPK inhibitor SB203580, rather than NF-κB inhibitors (Sulfasalazine and Bay 11-7082), abrogated TNF-induced expansion of Tregs in vitro. Furthermore, upregulation of TNFR2 and Foxp3 expression in Tregs by TNF was also markedly inhibited by SB203580. The proliferative expansion and the upregulation of TNFR2 expression on Tregs in LPS-treated mice were mediated by TNF–TNFR2 interaction, as shown by our previous study. The expansion of Tregs in LPS-treated mice were also markedly inhibited by in vivo treatment with SB203580. Taken together, our data clearly indicate that the activation of p38 MAPK is attributable to TNF/TNFR2-mediated activation and proliferative expansion of Tregs. Our results also suggest that targeting of p38 MAPK by pharmacological agent may represent a novel strategy to up- or downregulation of Treg activity for therapeutic purposes.

Transmembrane TNF and Partially TNFR1 Regulate TNFR2 Expression and Control Inflammation in Mycobacterial-Induced Pleurisy

Pleural tuberculosis is one of the most frequent forms of extra-pulmonary tuberculosis observed in patients infected with Mycobacterium tuberculosis. Tumor Necrosis Factor (TNF) is a crucial cytokine needed to control tuberculosis infection that remains a leading cause of morbidity and mortality worldwide. TNF blockade compromises host immunity and may increase the risk of reactivation of latent infection resulting in overt pulmonary, pleural and extra-pulmonary tuberculosis. While TNF signaling is mainly considered pro-inflammatory, its requirement for the anti-inflammation process involved in the resolution of infection and tissue repair is less explored. Our study analyzes the role of TNF and TNF receptors in the control of the inflammatory process associated with Bacillus Calmette-Guérin (BCG)-induced pleurisy. This study shows that the absence of TNF causes exacerbated inflammation in the pleural cavity of BCG-infected mice which is controlled by the transmembrane TNF (tmTNF) expression. The lack of TNF is associated with an impaired cellular expression and shedding of TNFR2 in the pleural cavity. The presence of tmTNF restores the normal expression of TNFR2 on myeloid cells during BCG-induced pleurisy. We also show that absence of TNFR1 affects the expression of TNFR2 on pleural cells and inflammation in the pleural cavity of BCG-infected mice. In conclusion, tmTNF but not soluble TNF prevents pleural cavity inflammation leading to attenuation and the resolution of the inflammatory process caused by mycobacterial pleurisy in association with the expression of TNFR2 on myeloid cells.

An Autocrine TNFα-Tumor Necrosis Factor Receptor 2 Loop Promotes Epigenetic Effects Inducing Human Treg Stability In Vitro

A crucial issue for Treg-based immunotherapy is to maintain a bona fide Treg phenotype as well as suppressive function during and after ex vivo expansion. Several strategies have been applied to harness Treg lineage stability. For instance, CD28 superagonist stimulation in vitro, in the absence of CD3 ligation, is more efficient in promoting Treg proliferation, and prevention of pro-inflammatory cytokine expression, such as IL-17, as compared to CD3/CD28-stimulated Treg. Addition of the mTOR inhibitor rapamycin to Treg cultures enhances FOXP3 expression and Treg stability, but does impair proliferative capacity. A tumor necrosis factor receptor 2 (TNFR2) agonist antibody was recently shown to favor homogenous expansion of Treg in vitro. Combined stimulation with rapamycin and TNFR2 agonist antibody enhanced hypo-methylation of the FOXP3 gene, and thus promoting Treg stability. To further explore the underlying mechanisms of rapamycin and TNFR2 agonist-mediated Treg stability, we here stimulated FACS-sorted human Treg with a CD28 superagonist, in the presence of rapamycin and a TNFR2 agonist. Phenotypic analysis of expanded Treg revealed an autocrine loop of TNFα-TNFR2 underlying the maintenance of Treg stability in vitro. Addition of rapamycin to CD28 superagonist-stimulated Treg led to a high expression of TNFR2, the main TNFR expressed on Treg, and additional stimulation with a TNFR2 agonist enhanced the production of soluble as well as membrane-bound TNFα. Moreover, our data showed that the expression of histone methyltransferase EZH2, a crucial epigenetic modulator for potent Treg suppressor function, was enhanced upon stimulation with CD28 superagonist. Interestingly, rapamycin seemed to downregulate CD28 superagonist-induced EZH2 expression, which could be rescued by the additional addition of TNFR2 agonist antibody. This process appeared TNFα-dependent manner, since depletion of TNFα using Etanercept inhibited EZH2 expression. To summarize, we propose that an autocrine TNFα-TNFR2 loop plays an important role in endorsing Treg stability.

Tumor Necrosis Factor α and Regulatory T Cells in Oncoimmunology

Tumor necrosis factor α (TNF) is a potent pro-inflammatory cytokine that has deleterious effect in some autoimmune diseases, which led to the use of anti-TNF drugs in some of these diseases. However, some rare patients treated with these drugs paradoxically develop an aggravation of their disease or new onset autoimmunity, revealing an immunosuppressive facet of TNF. A possible mechanism of this observation is the direct and positive effect of TNF on regulatory T cells (Tregs) through its binding to the TNF receptor type 2 (TNFR2). Indeed, TNF is able to increase expansion, stability, and possibly function of Tregs via TNFR2. In this review, we discuss the role of TNF in graft-versus-host disease as an example of the ambivalence of this cytokine in the pathophysiology of an immunopathology, highlighting the therapeutic potential of triggering TNFR2 to boost Treg expansion. We also describe new targets in immunotherapy of cancer, emphasizing on the putative suppressive effect of TNF in antitumor immunity and of the interest of blocking TNFR2 to regulate the Treg compartment.

Engrafting human regulatory T cells with a flexible modular chimeric antigen receptor technology

As regulatory T cells (Tregs) play a fundamental role in immune homeostasis their adoptive transfer emerged as a promising treatment strategy for inflammation-related diseases. Preclinical animal models underline the superiority of antigen-specific Tregs compared to polyclonal cells. Here, we applied a modular chimeric antigen receptor (CAR) technology called UniCAR for generation of antigen-specific human Tregs. In contrast to conventional CARs, UniCAR-endowed Tregs are indirectly linked to their target cells via a separate targeting module (TM). Thus, transduced Tregs can be applied universally as their antigen-specificity is easily adjusted by TM exchange. Activation of UniCAR-engrafted Tregs occurred in strict dependence on the TM, facilitating a precise control over Treg activity. In order to augment efficacy and safety, different intracellular signaling domains were tested. Both 4-1BB (CD137) and CD28 costimulation induced strong suppressive function of genetically modified Tregs. However, in light of safety issues, UniCARs comprising a CD137-CD3ζ signaling domain emerged as constructs of choice for a clinical application of redirected Tregs. In that regard, Tregs isolated from patients suffering from autoimmune or inflammatory diseases were, for the first time, successfully engineered with UniCAR 137/ζ and efficiently suppressed patient-derived effector cells. Overall, the UniCAR platform represents a promising approach to improve Treg-based immunotherapies for tolerance induction.

The Effect of TNF-α on Regulatory T Cell Function in Graft-versus-Host Disease

FoxP3⁺ regulatory T cells (Tregs) are a subset of CD4⁺ T cells that can suppress proliferation and effector functions of T cells, B cells, NK cells, and antigen-presenting cells. Treg deficiency causes dramatic immunologic disease in both animal models and humans. As they are capable to suppress the function and the proliferation of conventional CD4⁺ and CD8⁺ T cells, Treg-based cell therapies are under evaluation for the treatment of various autoimmune diseases and are currently employed to prevent graft-versus-host disease (GvHD) in clinical trials of hematopoietic stem cell transplantation. Even though tumor necrosis factor-α (TNF-α) is well known for its pro-inflammatory role, recent studies show that it promotes Treg activation and suppressive function. In the present review, we discuss the role of TNF-α in Treg function and the possible implications on the actual treatments for immune-mediated diseases, with a particular attention to GvHD.

GARP: a surface molecule of regulatory T cells that is involved in the regulatory function and TGF-β releasing

There are many molecules that define regulatory T cells (Tregs) phenotypically and functionally. Glycoprotein A repetitions predominant (GARP) is a transmembrane protein containing leucine rich repeats. Recently, GARP is found to express highly on the surface of activated Tregs. The combination of GARP and other surface molecules isolates Tregs with higher purity. Besides, GARP is a cell surface molecule of Tregs that maintains their regulatory function and homeosatsis. GARP has also been proved to promote the activation and secretion of transforming growth factor β (TGF-β). Moreover, its potential value in cancer immunotherapy is also discussed in this work.

Blockade of TNFR2 signaling enhances the immunotherapeutic effect of CpG ODN in a mouse model of colon cancer

Through the tumor necrosis factor (TNF) receptor type II (TNFR2), TNF preferentially activates, expands, and promotes the phenotypic stability of CD4⁺Foxp3⁺ regulatory T (T_reg) cells. Those T_reg cells that have a high abundance of TNFR2 have the maximal immunosuppressive capacity. We investigated whether targeting TNFR2 could effectively suppress the activity of T_reg cells and consequently enhance the efficacy of cancer immunotherapy. We found that, relative to a suboptimal dose of the immunostimulatory Toll-like receptor 9 ligand CpG oligodeoxynucleotide (ODN), the combination of the suboptimal dose of CpG ODN with the TNFR2-blocking antibody M861 more markedly inhibited the growth of subcutaneously grafted mouse CT26 colon tumor cells. This resulted in markedly fewer TNFR2⁺ T_reg cells and more interferon-γ-positive (IFN-γ⁺) CD8⁺ cytotoxic T lymphocytes infiltrating the tumor and improved long-term tumor-free survival in the mouse cohort. Tumor-free mice were resistant to rechallenge by the same but not unrelated (4T1 breast cancer) cells. Treatment with the combination of TNFR2-blocking antibody and a CD25-targeted antibody also resulted in enhanced inhibition of tumor growth in a syngeneic 4T1 mouse model of breast cancer. Thus, the combination of a TNFR2 inhibitor and an immunotherapeutic stimulant may represent a more effective treatment strategy for various cancers.

Interleukin 6 Present in Inflammatory Ascites from Advanced Epithelial Ovarian Cancer Patients Promotes Tumor Necrosis Factor Receptor 2-Expressing Regulatory T Cells

Background

Epithelial ovarian cancer (EOC) remains a highly lethal gynecological malignancy. Ascites, an accumulation of peritoneal fluid present in one-third of patients at presentation, is linked to poor prognosis. High levels of regulatory T cells (Tregs) in ascites are correlated with tumor progression and reduced survival. Malignant ascites harbors high levels of Tregs expressing the tumor necrosis factor receptor 2 (TNFR2), as well as pro-inflammatory factors such as interleukin 6 (IL-6) and tumor necrosis factor (TNF). IL-6 is also associated with poor prognosis. Herein, we study the effect of IL-6 and TNF present in ascites on the modulation of TNFR2 expression on T cells, and specifically Tregs.

Methods

Ascites and respective peripheral blood sera were collected from 18 patients with advanced EOC and soluble biomarkers, including IL-6, sTNFR2, IL-10, TGF-β, and TNF, were quantified using multiplexed bead-based immunoassay. Peripheral blood mononuclear cells (PBMC) from healthy donors were incubated with cell-free ascites for 48 h (or media as a negative control). In some experiments, IL-6 or TNF within the ascites were neutralized by using monoclonal antibodies. The phenotype of TNFR2⁺ Tregs and TNFR2⁻ Tregs were characterized post incubation in ascites. In some experiments, cell sorted Tregs were utilized instead of PBMC.

Results

High levels of immunosuppressive (sTNFR2, IL-10, and TGF-β) and pro-inflammatory cytokines (IL-6 and TNF) were present in malignant ascites. TNFR2 expression on all T cell subsets was higher in post culture in ascites and highest on CD4⁺CD25^hiFoxP3⁺ Tregs, resulting in an increased TNFR2⁺ Treg/effector T cell ratio. Furthermore, TNFR2⁺ Tregs conditioned in ascites expressed higher levels of the functional immunosuppressive molecules programmed cell death ligand-1, CTLA-4, and GARP. Functionally, TNFR2⁺ Treg frequency was inversely correlated with interferon-gamma (IFN-γ) production by effector T cells, and was uniquely able to suppress TNFR2⁺ T effectors. Blockade of IL-6, but not TNF, within ascites decreased TNFR2⁺ Treg frequency. Results indicating malignant ascites promotes TNFR2 expression, and increased suppressive Treg activity using PBMC were confirmed using purified Treg subsets.

Conclusion

IL-6 present in malignant ovarian cancer ascites promotes increased TNFR2 expression and frequency of highly suppressive Tregs.

Transmembrane Tumor Necrosis Factor Controls Myeloid-Derived Suppressor Cell Activity via TNF Receptor 2 and Protects from Excessive Inflammation during BCG-Induced Pleurisy

Pleural tuberculosis (TB) is a form of extra-pulmonary TB observed in patients infected with Mycobacterium tuberculosis. Accumulation of myeloid-derived suppressor cells (MDSC) has been observed in animal models of TB and in human patients but their role remains to be fully elucidated. In this study, we analyzed the role of transmembrane TNF (tmTNF) in the accumulation and function of MDSC in the pleural cavity during an acute mycobacterial infection. Mycobacterium bovis BCG-induced pleurisy was resolved in mice expressing tmTNF, but lethal in the absence of tumor necrosis factor. Pleural infection induced MDSC accumulation in the pleural cavity and functional MDSC required tmTNF to suppress T cells as did pleural wild-type MDSC. Interaction of MDSC expressing tmTNF with CD4 T cells bearing TNF receptor 2 (TNFR2), but not TNFR1, was required for MDSC suppressive activity on CD4 T cells. Expression of tmTNF attenuated Th1 cell-mediated inflammatory responses generated by the acute pleural mycobacterial infection in association with effective MDSC expressing tmTNF and interacting with CD4 T cells expressing TNFR2. In conclusion, this study provides new insights into the crucial role played by the tmTNF/TNFR2 pathway in MDSC suppressive activity required during acute pleural infection to attenuate excessive inflammation generated by the infection.

PKC-ѳ is dispensable for OX40L-induced TCR-independent Treg proliferation but contributes by enabling IL-2 production from effector T-cells

We have previously shown that OX40L/OX40 interaction is critical for TCR-independent selective proliferation of Foxp3⁺ Tregs, but not Foxp3^- effector T-cells (Teff), when CD4⁺ T-cells are co-cultured with GM-CSF derived bone marrow dendritic cells (G-BMDCs). Events downstream of OX40L/OX40 interaction in Tregs responsible for this novel mechanism are not understood. Earlier, OX40L/OX40 interaction has been shown to stimulate CD4⁺ T-cells through the formation of a signalosome involving TRAF2/PKC-Ѳ leading to NF-kB activation. In this study, using CD4⁺ T-cells from WT and OX40^-/- mice we first established that OX40 mediated activation of NF-kB was critical for this Treg proliferation. Although CD4⁺ T-cells from PKC-Ѳ^-/- mice were also defective in G-BMDC induced Treg proliferation ex vivo, this defect could be readily corrected by adding exogenous IL-2 to the co-cultures. Furthermore, by treating WT, OX40^-/-, and PKC-Ѳ^-/- mice with soluble OX40L we established that OX40L/OX40 interaction was required and sufficient to induce Treg proliferation in vivo independent of PKC-Ѳ status. Although PKC-Ѳ is dispensable for TCR-independent Treg proliferation per se, it is essential for optimum IL-2 production by Teff cells. Finally, our findings suggest that OX40L binding to OX40 likely results in recruitment of TRAF1 for downstream signalling.

Molecular mechanisms underlying Th1-like Treg generation and function

Since their ‘re-discovery’ more than two decades ago, FOXP3⁺ regulatory T cells (Tregs) have been an important subject of investigation in the biomedical field and our understanding of the mechanisms that drive their phenotype and function in health and disease has advanced tremendously. During the past few years it has become clear that Tregs are not a terminally differentiated population but show some degree of plasticity, and can, under specific environmental conditions, acquire the phenotype of effector T cells. In particular, recent works have highlighted the acquisition of a Th1-like phenotype by Tregs in several pathological environments. In this review we give an update on the concept of Treg plasticity and the advances in defining the molecular mechanisms that underlie the generation of Th1-like Tregs during an immune response and in different disease settings.