Tumor Evasion of the Immune System by Converting CD4+CD25− T Cells into CD4+CD25+ T Regulatory Cells: Role of Tumor-Derived TGF-β

Use of Cell and Genome Modification Technologies to Generate Improved "Off-the-Shelf" CAR T and CAR NK Cells

The broad success of adoptive immunotherapy to treat human cancer has resulted in a paradigm shift in modern medicine. Modification of autologous and allogenic immune cells with chimeric antigen receptors (CAR) designed to target specific antigens on tumor cells has led to production of CAR T and CAR NK cell therapies, which are ever more commonly introduced into cancer patient treatment protocols. While allogenic T cells may offer advantages such as improved anti-tumor activity, they also carry the risk of adverse reactions like graft-versus-host disease. This risk can be mitigated by use of autologous immune cells, however, the time needed for T and/or NK cell isolation, modification and expansion may be too long for some patients. Thus, there is an urgent need for strategies to robustly produce “off-the-shelf” CAR T and CAR NK cells, which could be used as a bridging therapy between cancer diagnosis or relapse and allogeneic transplantation. Advances in genome modification technologies have accelerated the generation of designer cell therapy products, including development of “off-the-shelf” CAR T cells for cancer immunotherapy. The feasibility and safety of such approaches is currently tested in clinical trials. This review will describe cell sources for CAR-based therapies, provide background of current genome editing techniques and the applicability of these approaches for generation of universal “off-the-shelf” CAR T and NK cell therapeutics.

An IL6-Adenosine Positive Feedback Loop between CD73+ γδTregs and CAFs Promotes Tumor Progression in Human Breast Cancer

The tumor microenvironment induces immunosuppression via recruiting and expanding suppressive immune cells such as regulatory T cells (Treg) to promote cancer progression. In this study, we documented that tumor-infiltrating CD73⁺ γδTregs were the predominant Tregs in human breast cancer and exerted more potent immunosuppressive activity than CD4⁺ or CD8⁺ Tregs. We further demonstrated that cancer-associated fibroblast (CAF)-derived IL6, rather than TGFβ1, induced CD73⁺ γδTreg differentiation from paired normal breast tissues via the IL6/STAT3 pathway to produce more adenosine and become potent immunosuppressive T cells. CD73⁺ γδTregs could in turn promote IL6 secretion by CAFs through adenosine/A2BR/p38MAPK signaling, thereby forming an IL6-adenosine positive feedback loop. CD73⁺ γδTreg infiltration also impaired the tumoricidal functions of CD8⁺ T cells and significantly correlated with worse prognosis of patients. The data indicate that the IL6-adenosine loop between CD73⁺ γδTregs and CAFs is important to promote immunosuppression and tumor progression in human breast cancer, which may be critical for tumor immunotherapy.

Immunotherapy in Prostate Cancer

Immunotherapy encompasses a wide range of therapies to engage the immune system to target malignancies. In recent years, immunotherapy has made a major impact on treatment of metastatic cancer and has altered standard of care for many tumor types. However, predicting and understanding responses across tumor types has been challenging. While some metastatic cancers have shown dramatic responses to immunotherapy, such as melanoma, lung cancer, and renal cell carcinoma, prostate cancer has generally failed to show a significant response. However, small series of prostate cancer patients have shown impressive responses to cellular and immunotherapy. This review summarizes the current data for immunotherapy’s use in prostate cancer, as well as how currently available data might help predict patient responses to immunotherapy. Specifically, we will review vaccine-based therapies, immune checkpoint inhibitors, and future directions that are actively being explored.

TGFβ2 is a prognostic-related biomarker and correlated with immune infiltrates in gastric cancer

TGFβ2 is an essential regulator of immune cell functionality, but the mechanisms whereby it drives immune infiltration in gastric cancer remain uncertain. The Oncomine and Tumor Immunoassay Resource (TIMER) databases were used for assessing the expression of TGFβ2, after which TIMER was used to explore the relationship between TGFβ2 and tumour immune infiltration. Finally, we assessed how TGFβ2 expression correlated with the expression of a set of marker genes associated with immune infiltration using TIMER and GEPIA. We determined TGFβ2 expression to be significantly correlated with outcome in multiple types of cancer in the Cancer Genome Atlas (TCGA), with the effect being particularly pronounced in gastric cancer. Furthermore, elevated TGFβ2 expression was found to be significantly correlated with gastric cancer N staging, and with the expression of a variety of immune markers associated with particular immune cell subsets. These results indicate that TGFΒ2 is associated with patient outcome and tumour immune cell infiltration in multiple cancer types. This suggests that TGFβ2 is a key factor which governs immune cell recruitment to gastric cancer tumours, potentially playing a vital role in governing immune cell infiltration and thus representing a valuable prognostic biomarker in gastric cancer patients.

Regulation of CD4+CD25+FOXP3+ cells in Pediatric Acute Lymphoblastic Leukemia (ALL): Implication of cytokines and miRNAs

Regulatory T cells (Tregs) is one of the immunosuppressive subsets of CD4⁺ T cells characterized by transcription factor forkhead box protein P3 (FOXP3) expression which are involved in tumor development and progression. Identification of the factors that influence Treg cell function is extremely important. Our current study aimed to evaluate the frequency of Treg cells, cytokine secretion and the expression of microRNAs (miRNAs) in pediatric acute lymphoblastic leukemia (ALL) patients. The frequency of CD3⁺, CD4⁺ and CD4⁺CD25⁺FOXP3⁺ Treg was assessed by flow cytometry in 43 ALL patients versus 42 controls. Plasma levels of IL-10, transcription factor β (TGF-β), IL-6, IL-17, IL-23 and tumor necrosis factor (TNF-α) were measured by Enzyme-linked immunosorbent assay (ELISA). miR-21, miR-24, miR-26a, miR133b, miR-148a and miR-155 expression were analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). A slight insignificant increase in Treg cells in ALL patients compared to controls was observed. There was a significant elevation in IL-10 (p < 0.05), IL-6 (p < 0.01), IL-23 (p < 0.05) and TNF-α (p < 0.01) in ALL patients compared with controls. Meanwhile, a significant reduction in TGF-β (p < 0.001) was recorded. A slight insignificant decrease in IL-17 in ALL patients was observed.ALL patients showed a significant increase in miR-21 (p < 0.05), miR-148a (p < 0.01), miR-24 (p < 0.05) and a significant reduction in miR-155 (p < 0.01). In conclusion, the slight change in Treg cells frequency and alteration in related cytokines could possibly involve in the pathogenesis of ALL. Dysregulated miRNAs, as a regulatory mechanism of epigenetics, might contribute to these observed results. Further researches are required to confirm our interesting findings.

Revisiting the role of CD4+ T cells in cancer immunotherapy-new insights into old paradigms

Cancer immunotherapy has revolutionised cancer treatment, with immune checkpoint blockade (ICB) therapy and adoptive cell therapy (ACT) increasingly becoming standard of care across a growing number of cancer indications. While the majority of cancer immunotherapies focus on harnessing the anti-tumour CD8⁺ cytotoxic T cell response, the potential role of CD4⁺ 'helper' T cells has largely remained in the background. In this review, we give an overview of the multifaceted role of CD4⁺ T cells in the anti-tumour immune response, with an emphasis on recent evidence that CD4⁺ T cells play a bigger role than previously thought. We illustrate their direct anti-tumour potency and their role in directing a sustained immune response against tumours. We further highlight the emerging observation that CD4⁺ T cell responses against tumours tend to be against self-derived epitopes. These recent trends raise vital questions and considerations that will profoundly affect the rational design of immunotherapies to leverage on the full potential of the immune system against cancer.

Ionizing radiation modulates the phenotype and function of human CD4+ induced regulatory T cells

BACKGROUND

The use of immunotherapy strategies for the treatment of advanced cancer is rapidly increasing. Most immunotherapies rely on induction of CD8+ tumor-specific cytotoxic T cells that are capable of directly killing cancer cells. Tumors, however, utilize a variety of mechanisms that can suppress anti-tumor immunity. CD4+ regulatory T cells can directly inhibit cytotoxic T cell activity and these cells can be recruited, or induced, by cancer cells allowing escape from immune attack. The use of ionizing radiation as a treatment for cancer has been shown to enhance anti-tumor immunity by several mechanisms including immunogenic tumor cell death and phenotypic modulation of tumor cells. Less is known about the impact of radiation directly on suppressive regulatory T cells. In this study we investigate the direct effect of radiation on human T_REG viability, phenotype, and suppressive activity.

RESULTS

Both natural and TGF-β1-induced CD4+ T_REG cells exhibited increased resistance to radiation (10 Gy) as compared to CD4+ conventional T cells. Treatment, however, decreased Foxp3 expression in natural and induced T_REG cells and the reduction was more robust in induced T_REGS. Radiation also modulated the expression of signature iT_REG molecules, inducing increased expression of LAG-3 and decreased expression of CD25 and CTLA-4. Despite the disconcordant modulation of suppressive molecules, irradiated iT_REGS exhibited a reduced capacity to suppress the proliferation of CD8+ T cells.

CONCLUSIONS

Our findings demonstrate that while human T_REG cells are more resistant to radiation-induced death, treatment causes downregulation of Foxp3 expression, as well as modulation in the expression of T_REG signature molecules associated with suppressive activity. Functionally, irradiated TGF-β1-induced T_REGS were less effective at inhibiting CD8+ T cell proliferation. These data suggest that doses of radiotherapy in the hypofractionated range could be utilized to effectively target and reduce T_REG activity, particularly when used in combination with cancer immunotherapies.

Characterization and antiproliferative activity of glioma-derived extracellular vesicles

Aim: To characterize a method to isolate glioma-derived extracellular vesicles (GEVs) and understand their role in immune system modulation and glioma progression. Materials & methods: GEVs were isolated by differential centrifugation from C6 cell supernatant and characterized by size and expression of CD9, HSP70, CD39 and CD73. The glioma model was performed by injecting C6 glioma cells into the right striatum of Wistar rats in the following groups: controls (C6 cells alone), coinjection (C6 cells + GEVs) and GEVs by intranasal administration followed by immune cells, tumor size and cells proliferation analyses. Results: GEVs presented uniform size (175 nm), expressed CD9, HSP70, CD39, CD73 and produced adenosine. In vivo, we observed a reduction in tumor size, in cell proliferation (Ki-67) and in a regulatory cell marker (FoxP3). Conclusion: GEVs, administered before or at tumor challenge, have antiproliferative properties and reduce regulatory cells in the glioma microenvironment.

Effect and Molecular Mechanisms of Traditional Chinese Medicine on Tumor Targeting Tumor-Associated Macrophages

Traditional Chinese medicine (TCM) has been used as a significant cancer treatment method for many years in China. It has been demonstrated that TCM could assist in inhibiting the growth of tumors and prolonging the survival rates of cancer patients. Although the mechanism of TCM are still not clear, accumulating evidence has shown that they may be related to the tumor microenvironment (TME). Tumor-associated macrophages (TAMs) play a significant role in TME and are polarized to two phenotypes, M1 (classically activated) and M2 (alternatively activated) TAMs. The two different phenotypes of TAMs play converse roles in the TME and M2-polarized tumor-associated macrophages (M2-TAMs) always lead to poor prognosis in cancer patients compared to M1-polarized tumor-associated macrophages (M1-TAMs). In this review, the potential correlation between TCM and TAMs (especially the M2 phenotype) in tumor progression and promising TCM strategies targeting TAMs in cancer are discussed.

Cell-mediated immune resistance in cancer

The genetic and epigenetic aberrations that underlie immune resistance lead to tumors that are refractory to clinically established and experimental immunotherapies, including monoclonal antibodies and T cell-based therapies. From various forms of cytotoxic T cells to small molecule inhibitors that revamp the tumor microenvironment, these therapies have demonstrated notable responses in cancer models and a resistant subset of cancer patients, used both alone and in combination. However, even current approaches, such as those targeting checkpoint molecules, tumor ligands, and involving gene-related therapies, present a challenge in non-responding patients. In this perspective, we discuss the most common mechanisms of immune resistance, including tumor heterogeneity, tumor ligand and major histocompatibility complex modulation, anti-apoptotic pathways, checkpoint inhibitory ligands, immunosuppressive cells and factors in the tumor microenvironment, and activation-induced cell death. In addition, we discuss the strategies designed to circumvent these resistance pathways to showcase the potential of emerging technologies in battling the rise of resistance.

Liver Tumor Microenvironment

The tumor microenvironment (TME) has recently been recognized as an important part of tumor development and growth. TME is a dynamic system orchestrated by immune, cancer and inflammatory cells, as well as the stromal tissue and surrounding extracellular matrix. While TME of primary hepatic tumors is usually characterized by a strong inflammatory background, the TME of liver metastases typically consists of otherwise healthy liver tissue. Chronic inflammation and hypoxia are key to the development and progression of primary liver cancer. The injury caused by chronic inflammation creates a condition of immune evasion that initiates a cascade of events that eventually leads to liver carcinogenesis.With liver metastases, primary tumors "prime" the target organs via secreting factors that induce expansion of myeloid cell populations and create a solid ground for successful cancer settlement. Once in the liver, metastatic cells begin a neovascularization process that is driven mainly by VEGF and FGF. Due to high mortality rates associated with liver cancer, as well as the limited effective treatment options for advanced disease, new therapies are urgently needed. Targeting a single molecule in a number of interactions between the tumor and the TME is highly unlikely to reduce tumor growth. Future trials should focus on combination therapies (i.e. targeted therapies combined with immunotherapy) to treat liver malignancies efficiently.

CCL22 Signaling in the Tumor Environment

T cell-mediated elimination of malignant cells is one cornerstone of endogenous and therapeutically induced antitumor immunity. Tumors exploit numerous regulatory mechanisms to suppress T cell immunity. Regulatory T cells (T regs) play a crucial role in this process due to their ability to inhibit antitumoral immune responses and they are known to accumulate in various cancer entities. The chemokine CCL22, predominately produced by dendritic cells (DCs), regulates T reg migration via binding to its receptor CCR4. CCL22 controls T cell immunity, both by recruiting T regs to the tumor tissue and by promoting the formation of DC-T reg contacts in the lymph node. Here, we review the current knowledge on the role of CCL22 in cancer immunity. After revising the principal mechanisms of CCL22-induced immune suppression, we address the factors leading to CCL22 expression and ways of targeting this chemokine therapeutically. Therapeutic interventions to the CCL22-CCR4 axis may represent a promising strategy in cancer immunotherapy.

Chimeric antigen receptor T cells in solid tumors: a war against the tumor microenvironment

Chimeric antigen receptor (CAR) T cell is a novel approach, which utilizes anti-tumor immunity for cancer treatment. As compared to the traditional cell-mediated immunity, CAR-T possesses the improved specificity of tumor antigens and independent cytotoxicity from major histocompatibility complex molecules through a monoclonal antibody in addition to the T-cell receptor. CAR-T cell has proven its effectiveness, primarily in hematological malignancies, specifically where the CD 19 CAR-T cells were used to treat B-cell acute lymphoblastic leukemia and B-cell lymphomas. Nevertheless, there is little progress in the treatment of solid tumors despite the fact that many CAR agents have been created to target tumor antigens such as CEA, EGFR/EGFRvIII, GD2, HER2, MSLN, MUC1, and other antigens. The main obstruction against the progress of research in solid tumors is the tumor microenvironment, in which several elements, such as poor locating ability, immunosuppressive cells, cytokines, chemokines, immunosuppressive checkpoints, inhibitory metabolic factors, tumor antigen loss, and antigen heterogeneity, could affect the potency of CAR-T cells. To overcome these hurdles, researchers have reconstructed the CAR-T cells in various ways. The purpose of this review is to summarize the current research in this field, analyze the mechanisms of the major barriers mentioned above, outline the main solutions, and discuss the outlook of this novel immunotherapeutic modality.

A mathematical model for the immune-mediated theory of metastasis

Accumulating experimental and clinical evidence suggest that the immune response to cancer is not exclusively anti-tumor. Indeed, the pro-tumor roles of the immune system  -  as suppliers of growth and pro-angiogenic factors or defenses against cytotoxic immune attacks, for example  -  have been long appreciated, but relatively few theoretical works have considered their effects. Inspired by the recently proposed "immune-mediated" theory of metastasis, we develop a mathematical model for tumor-immune interactions at two anatomically distant sites, which includes both anti- and pro-tumor immune effects, and the experimentally observed tumor-induced phenotypic plasticity of immune cells (tumor "education" of the immune cells). Upon confrontation of our model to experimental data, we use it to evaluate the implications of the immune-mediated theory of metastasis. We find that tumor education of immune cells may explain the relatively poor performance of immunotherapies, and that many metastatic phenomena, including metastatic blow-up, dormancy, and metastasis to sites of injury, can be explained by the immune-mediated theory of metastasis. Our results suggest that further work is warranted to fully elucidate the pro-tumor effects of the immune system in metastatic cancer.

Exploring the key communicator role of exosomes in cancer microenvironment through proteomics

There have been many attempts to fully understand the mechanism of cancer behavior. Yet, how cancers develop and metastasize still remain elusive. Emerging concepts of cancer biology in recent years have focused on the communication of cancer with its microenvironment, since cancer cannot grow and live alone. Cancer needs to communicate with other cells for survival, and thus they secrete various messengers, including exosomes that contain many proteins, miRNAs, mRNAs, etc., for construction of the tumor microenvironment. Moreover, these intercellular communications between cancer and its microenvironment, including stromal cells or distant cells, can promote tumor growth, metastasis, and escape from immune surveillance. In this review, we summarized the role of proteins in the exosome as communicators between cancer and its microenvironment. Consequently, we present cancer specific exosome proteins and their unique roles in the interaction between cancer and its microenvironment. Clinically, these exosomes might provide useful biomarkers for cancer diagnosis and therapeutic tools for cancer treatment.

Conceptual Development of Immunotherapeutic Approaches to Gastrointestinal Cancer

Gastrointestinal (GI) cancer is one of the common causes of cancer-related death worldwide. Chemotherapy and/or immunotherapy are the current treatments, but some patients do not derive clinical benefits. Recently, studies from cancer molecular subtyping have revealed that tumor molecular biomarkers may predict the immunotherapeutic response of GI cancer patients. However, the therapeutic response of patients selected by the predictive biomarkers is suboptimal. The tumor immune-microenvironment apparently plays a key role in modulating these molecular-determinant predictive biomarkers. Therefore, an understanding of the development and recent advances in immunotherapeutic pharmacological intervention targeting tumor immune-microenvironments and their potential predictive biomarkers will be helpful to strengthen patient immunotherapeutic efficacy. The current review focuses on an understanding of how the host-microenvironment interactions and the predictive biomarkers can determine the efficacy of immune checkpoint inhibitors. The contribution of environmental pathogens and host immunity to GI cancer is summarized. A discussion regarding the clinical evidence of predictive biomarkers for clinical trial therapy design, current immunotherapeutic strategies, and the outcomes to GI cancer patients are highlighted. An understanding of the underlying mechanism can predict the immunotherapeutic efficacy and facilitate the future development of personalized therapeutic strategies targeting GI cancers.

Tumor Hypoxia As an Enhancer of Inflammation-Mediated Metastasis: Emerging Therapeutic Strategies

Metastasis is the leading cause of cancer-related deaths. Recent research has implicated tumor inflammation as a promoter of metastasis. Myeloid, lymphoid, and mesenchymal cells in the tumor microenvironment promote inflammatory signaling amongst each other and together with cancer cells to modulate sustained inflammation, which may enhance cancer invasiveness. Tumor hypoxia, a state of reduced available oxygen present in the majority of solid tumors, acts as a prognostic factor for a worse outcome and is known to have a role in tumor inflammation through the regulation of inflammatory mediator signals in both cancer and neighboring cells in the microenvironment. Multiple methods to target tumor hypoxia have been developed and tested in clinical trials, and still more are emerging as the impacts of hypoxia become better understood. These strategies include mechanistic inhibition of the hypoxia inducible factor signaling pathway and hypoxia activated pro-drugs, leading to both anti-tumor and anti-inflammatory effects. This prompts a need for further research on the prevention of hypoxia-mediated inflammation in cancer. Hypoxia-targeting strategies seem to have the most potential for therapeutic benefit when combined with traditional chemotherapy agents. This paper will serve to summarize the role of the inflammatory response in metastasis, to discuss how hypoxia can enable or enhance inflammatory signaling, and to review established and emerging strategies to target the hypoxia-inflammation-metastasis axis.

Intercellular Crosstalk Via Extracellular Vesicles in Tumor Milieu as Emerging Therapies for Cancer Progression

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Increasing evidence has suggested that extracellular vesicles (EV) mediated bidirectional transfer of functional molecules (such as proteins, different types of RNA, and lipids) between cancer cells and tumor stromal cells (immune cells, endothelial cells, fibroblasts, stem cells) and strongly contributed to the reinforcement of cancer progression. Thus, intercellular EV-mediated signaling in tumor microenvironment (TME) is essential in the modulation of all processes that support and promote tumor development like immune suppression, angiogenesis, invasion and metastasis, and resistance of tumor cells to anticancer treatments.

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Besides EV potential to revolutionize our understanding of the cancer cell-stromal cells crosstalk in TME, their ability to selectively transfer different cargos to recipient cells has created excitement in the field of tumortargeted delivery of specific molecules for anticancer treatments. Therefore, in tight connection with previous findings, this review brought insight into the dual role of EV in modulation of TME. Thus, on one side EV create a favorable phenotype of tumor stromal cells for tumor progression; however, as a future new class of anticancer drug delivery systems EV could re-educate the TME to overcome main supportive processes for malignancy progression.

CD4+ T cell help in cancer immunology and immunotherapy

Cancer immunotherapy aims to promote the activity of cytotoxic T lymphocytes (CTLs) within a tumour, assist the priming of tumour-specific CTLs in lymphoid organs and establish efficient and durable antitumour immunity. During priming, help signals are relayed from CD4⁺ T cells to CD8⁺ T cells by specific dendritic cells to optimize the magnitude and quality of the CTL response. In this Review, we highlight the cellular dynamics and membrane receptors that mediate CD4⁺ T cell help and the molecular mechanisms of the enhanced antitumour activity of CTLs. We outline how deficient CD4⁺ T cell help reduces the response of CTLs and how maximizing CD4⁺ T cell help can improve outcomes in cancer immunotherapy strategies.

Blockade of TGF-β signaling to enhance the antitumor response is accompanied by dysregulation of the functional activity of CD4+CD25+Foxp3+ and CD4+CD25-Foxp3+ T cells

Background

The pleiotropic cytokine, transforming growth factor (TGF)-β, and CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) play a critical role in actively suppressing antitumor immune responses. Evidence shows that TGF-β produced by tumor cells promotes tolerance via expansion of Tregs. Our group previously demonstrated that blockade of TGF-β signaling with a small molecule TGF-β receptor I antagonist (SM16) inhibited primary and metastatic tumor growth in a T cell dependent fashion. In the current study, we evaluated the effect of SM16 on Treg generation and function.

Methods

Using BALB/c, FoxP3eGFP and Rag^−/− mice, we performed FACS analysis to determine if SM16 blocked de novo TGF-β-induced Treg generation in vitro and in vivo. CD4⁺ T cells from lymph node and spleen were isolated from control mice or mice maintained on SM16 diet, and flow cytometry analysis was used to detect the frequency of CD4⁺CD25⁻FoxP3⁺ and CD4⁺CD25⁺FoxP3⁺ T cells. In vitro suppression assays were used to determine the ability to suppress naive T cell proliferation in vitro of both CD4⁺CD25⁺FoxP3⁺ and CD4⁺CD25⁻FoxP3⁺ T cell sub-populations. We then examined whether SM16 diet exerted an inhibitory effect on primary tumor growth and correlated with changes in FoxP3⁺expression. ELISA analysis was used to measure IFN-γ levels after 72 h co-culture of CD4⁺CD25⁺ T cells from tumor-bearing mice on control or SM16 diet with CD4⁺CD25⁻ T cells from naive donors.

Results

SM16 abrogates TGF-β-induced Treg generation in vitro but does not prevent global homeostatic expansion of CD4⁺ T cell sub-populations in vivo. Instead, SM16 treatment causes expansion of a population of CD4⁺CD25⁻Foxp3⁺ Treg-like cells without significantly altering the overall frequency of Treg in lymphoreplete naive and tumor-bearing mice. Importantly, both the CD4⁺CD25⁻Foxp3⁺ T cells and the CD4⁺CD25⁺Foxp3⁺ Tregs in mice receiving SM16 diet exhibited diminished ability to suppress naive T cell proliferation in vitro compared to Treg from mice on control diet.

Conclusions

These findings suggest that blockade of TGF-β signaling is a potentially useful strategy for blunting Treg function to enhance the anti-tumor response. Our data further suggest that the overall dampening of Treg function may involve the expansion of a quiescent Treg precursor population, which is CD4⁺CD25⁻Foxp3⁺.

An Oncolytic Adenovirus Targeting Transforming Growth Factor β Inhibits Protumorigenic Signals and Produces Immune Activation: A Novel Approach to Enhance Anti-PD-1 and Anti-CTLA-4 Therapy

In an effort to develop a new therapy for cancer and to improve antiprogrammed death inhibitor-1 (anti-PD-1) and anticytotoxic T lymphocyte-associated protein (anti-CTLA-4) responses, we have created a telomerase reverse transcriptase promoter-regulated oncolytic adenovirus rAd.sT containing a soluble transforming growth factor receptor II fused with human IgG Fc fragment (sTGFβRIIFc) gene. Infection of breast and renal tumor cells with rAd.sT produced sTGFβRIIFc protein with dose-dependent cytotoxicity. In immunocompetent mouse 4T1 breast tumor model, intratumoral delivery of rAd.sT inhibited both tumor growth and lung metastases. rAd.sT downregulated the expression of several transforming growth factor β (TGFβ) target genes involved in tumor growth and metastases, inhibited Th2 cytokine expression, and induced Th1 cytokines and chemokines, and granzyme B and perforin expression. rAd.sT treatment also increased the percentage of CD8⁺ T lymphocytes, promoted the generation of CD4⁺ T memory cells, reduced regulatory T lymphocytes (Tregs), and reduced bone marrow-derived suppressor cells. Importantly, rAd.sT treatment increased the percentage of CD4⁺ T lymphocytes, and promoted differentiation and maturation of antigen-presenting dendritic cells in the spleen. In the immunocompetent mouse Renca renal tumor model, similar therapeutic effects and immune activation results were observed. In the 4T1 mammary tumor model, rAd.sT improved the inhibition of tumor growth and lung and liver metastases by anti-PD-1 and anti-CTLA-4 antibodies. Analysis of the human breast and kidney tumors showed that a significant number of tumor tissues expressed high levels of TGFβ and TGFβ-inducible genes. Therefore, rAd.sT could be a potential enhancer of anti-PD-1 and anti-CTLA-4 therapy for treating breast and kidney cancers.

Regulation of regulatory T cells in cancer

The inflammatory response to transformed cells forms the cornerstone of natural or therapeutically induced protective immunity to cancer. Regulatory T (Treg) cells are known for their critical role in suppressing inflammation, and therefore can antagonize effective anti-cancer immune responses. As such, Treg cells can play detrimental roles in tumour progression and in the response to both conventional and immune-based cancer therapies. Recent advances in our understanding of Treg cells reveal complex niche-specific regulatory programmes and functions, which are likely to extrapolate to cancer. The regulation of Treg cells is reliant on upstream cues from haematopoietic and non-immune cells, which dictates their genetic, epigenetic and downstream functional programmes. In this review we will discuss how Treg cells are themselves regulated in normal and transformed tissues, and the implications of this cross talk on tumour growth.

Chimeric antigen receptors designed to overcome transforming growth factor-β-mediated repression in the adoptive T-cell therapy of solid tumors

Adoptive cell therapy with chimeric antigen receptor (CAR)-engineered T cells produced lasting remissions in the treatment of advanced, so far refractory B-cell malignancies; however, the elimination of solid tumors remains so far elusive. The low efficacy of CAR T cells is thought to be due to the immune-repressive milieu within the tumor lesion, predominantly mediated by transforming growth factor-β (TGF-β) that represses effector T-cell activities and drives differentiation towards regulatory T cells (Tregs). Seeking to boost antitumor immunity, TGF-β is currently targeted by different means in pre-clinical studies. While a recent clinical trial showed the utility of shielding CAR T cells from TGF-β repression, further strategies in counteracting TGF-β in the adoptive cell therapy warrant exploration. We here discuss the most recent advances in the field and draw future developments to make CAR T-cell therapy more potent in the treatment of solid cancer.

Cryptotanshinone has curative dual anti-proliferative and immunotherapeutic effects on mouse Lewis lung carcinoma

Lung cancer is currently the leading cause of cancer-related mortality with very limited effective therapy. Screening of a variety of traditional Chinese medicines (TCMs) for their capacity to inhibit the proliferation of human lung cancer A549 cells and to induce the in vitro maturation of human DCs led to the identification of cryptotanshinone (CT), a compound purified from the TCM Salvia miltiorrhiza Bunge. Here, CT was shown to inhibit the proliferation of mouse Lewis lung carcinoma (LLC) cells by upregulating p53, downregulating cyclin B1 and Cdc2, and, consequently, inducing G2/M cell-cycle arrest of LLC cells. In addition, CT promoted maturation of mouse and human DCs with upregulation of costimulatory and MHC molecules and stimulated DCs to produce TNFα, IL-1β, and IL-12p70, but not IL-10 in vitro. CT-induced maturation of DCs depended on MyD88 and also involved the activation of NF-κB, p38, and JNK. CT was effective in the treatment of LLC tumors and, when used in combination with low doses of anti-PD-L1, cured LLC-bearing mice with the induction of subsequent anti-LLC long-term specific immunity. CT treatment promoted T-cell infiltration and elevated the expression of genes typical of Th1 polarization in LLC tumor tissue. The therapeutic effect of CT and low doses of anti-PD-L1 was reduced by depletion of CD4 and CD8 T cells. This paper provides the first report that CT induces immunological antitumor activities and may provide a new promising antitumor immunotherapeutic.

Combined Inhibition of TGF-β Signaling and the PD-L1 Immune Checkpoint Is Differentially Effective in Tumor Models

Antibodies blocking the programmed death-ligand 1 (PD-L1) have shown impressive and durable responses in clinical studies. However, this type of immunotherapy is only effective in a subset of patients and not sufficient for rejection of all tumor types. In this study, we explored in two mouse tumor models whether the antitumor effect could be enhanced by the combined blockade of PD-L1 and transforming growth factor-β (TGF-β), a potent immunosuppressive cytokine. The effect of anti-PD-L1 mouse monoclonal (mAb) and a TGF-β type I receptor small molecule kinase inhibitor (LY364947) was evaluated in the highly immunogenic mouse MC38 colon adenocarcinoma and the poorly immunogenic mouse KPC1 pancreatic tumor model. In the MC38 tumor model, LY364947 monotherapy did not show any antitumor effect, whereas treatment with anti-PD-L1 mAb significantly delayed tumor outgrowth. However, combination therapy showed the strongest therapeutic efficacy, resulting in improved long-term survival compared with anti-PD-L1 mAb monotherapy. This improved survival was associated with an increased influx of CD8⁺ T cells in the tumor microenvironment. In the KPC1 tumor model, LY364947 did not enhance the antitumor effect of anti-PD-L1 mAb. Despite this, delayed KPC1 tumor outgrowth was observed in the LY364947-treated group and this treatment led to a significant reduction of CD4⁺ T cells in the tumor microenvironment. Together, our data indicate that an additive anti-tumor response of dual targeting PD-L1 and TGF-β is dependent on the tumor model used, highlighting the importance of selecting appropriate cancer types, using in-depth analysis of the tumor microenvironment, which can benefit from combinatorial immunotherapy regimens.

T cell-inflamed phenotype and increased Foxp3 expression in infiltrating T-cells of mismatch-repair deficient endometrial cancers

Mismatch repair-deficient endometrial cancers have a high somatic mutation burden, suggesting that patients with these tumors may benefit from immunotherapy. Elucidating the immune suppressive mechanisms of mismatch repair-deficient endometrial cancers is fundamental to developing future immune-based interventions. This study aimed to determine the immune cell populations associated with mismatch repair-deficient endometrial cancers, especially focusing on targetable regulatory pathways of the immune response. A total of 76 endometrial cancer hysterectomy specimens were evaluated for tumor-infiltrating immune cells by immunohistochemistry. Immune specific markers were used to evaluate each specimen for the number of CD8 + cytotoxic T lymphocytes, forkhead-box P3 (FoxP3) + regulatory T cells, CD68 + tumor-associated macrophages, as well as programmed death-1 (PD-1) + immune cells, and the percentage of programmed death ligand-1 (PD-L1) + immune cells. Mismatch repair-deficient tumors exhibited a significantly higher number of CD8 + cytotoxic T lymphocytes (p = 0.0006), FoxP3 + regulatory T cells (p = 0.0003), PD-1 + immune cells (p = 0.0069), and a higher percentage of PD-L1 + immune cells (p = 0.0007) occupying the tumor compared to mismatch repair-proficient endometrial cancers. There was no significant difference in CD68 + tumor-associated macrophages infiltration between the two groups. Endometrial cancers with tumor PD-L1 expression also showed significantly increased infiltration of CD8 + cytotoxic T lymphocytes (p = 0.0002), FoxP3 + regulatory T cells (p = 0.0003), PD-1 + immune cells (p < 0.0001), and PD-L1 + immune cells (p < 0.0001). Endometrial cancers showing mismatch repair-deficiency and PD-L1 expression in tumor cells exhibit a prominent T cell-inflamed phenotype. More importantly, the increased number of FoxP3 + regulatory T cells in mismatch repair-deficient endometrial cancers suggests that combination therapy by targeting both regulatory T cells and immune checkpoints may be warranted to improve clinical efficacy.

Critical role of kinase activity of hematopoietic progenitor kinase 1 in anti-tumor immune surveillance

Immunotherapy has fundamentally changed the landscape of cancer treatment. Despite the encouraging results with the checkpoint modulators, response rates vary widely across tumor types, with a majority of patients exhibiting either primary resistance without a significant initial response to treatment or acquired resistance with subsequent disease progression. Hematopoietic progenitor kinase 1 (HPK1) is predominantly expressed in hematopoietic cell linages and serves as a negative regulator in T cells and dendritic cells (DC). While HPK1 gene knockout (KO) studies suggest its role in anti-tumor immune responses, the involvement of kinase activity and thereof its therapeutic potential remain unknown. To investigate the potential of pharmacological intervention using inhibitors of HPK1, we generated HPK1 kinase dead (KD) mice which carry a single loss-of-function point mutation in the kinase domain and interrogated the role of kinase activity in immune cells in the context of suppressive factors or the tumor microenvironment (TME). Our data provide novel findings that HKP1 kinase activity is critical in conferring suppressive functions of HPK1 in a wide range of immune cells including CD4+, CD8+, DC, NK to Tregs, and inactivation of kinase domain was sufficient to elicit robust anti-tumor immune responses. These data support the concept that an HPK1 small molecule kinase inhibitor could serve as a novel agent to provide additional benefit in combination with existing immunotherapies, particularly to overcome resistance to current treatment regimens.

Liquid Biopsies and Cancer Immunotherapy

Cancer immunotherapy has recently undergone rapid advances and has become an integral part of the treatment armamentarium in various malignancies. However, tissue-based biomarker development in this arena has been slow, and valid biomarker identification to guide immunotherapeutic management is desperately needed. "Liquid" or blood-based biopsies potentially offer more convenient and efficient means to judge the immune milieu of individual patients and identify who will benefit most from immunotherapy. The following review highlights the current literature regarding the application of liquid biopsies to cancer immunotherapy.

Cancer Metabolism Drives a Stromal Regenerative Response

The metabolic reprogramming associated with malignant transformation has led to a growing appreciation of the nutrients required to support anabolic cell growth. Less well studied is how cancer cells satisfy those demands in vivo, where they are dispersed within a complex microenvironment. Tumor-associated stromal components can support tumor growth by providing nutrients that supplement those provided by the local vasculature. These non-malignant stromal cells are phenotypically similar to those that accumulate during wound healing. Owing to their immediate proximity, stromal cells are inevitably affected by the metabolic activity of their cancerous neighbors. Until recently, a role for tumor cell metabolism in influencing the cell fate decisions of neighboring stromal cells has been underappreciated. Here, we propose that metabolites consumed and released by tumor cells act as paracrine factors that regulate the non-malignant cellular composition of a developing tumor by driving stromal cells toward a regenerative response that supports tumor growth.

Regulatory T Cells for More Targeted Immunosuppressive Therapies

There has been a prolific amount of research dedicated to the T-regulatory cells (Tregs) and their role in achieving immune homeostasis. Here, the authors briefly discuss the known biology, utilization, and potential of Tregs, for current trials and future immunotherapy. Most current trials of Treg therapies include either ex vivo expanded Tregs transferred into the peripheral blood of patients with diseases of immunologic origin or interleukin 2 injected to stimulate Tregs directly. Ongoing trials designed to measure the clinical efficacy and safety profile of these novel therapeutic approaches have resulted in largely favorable outcomes in a variety of autoimmune and alloimmune diseases.

Autocrine TGFβ Is a Survival Factor for Monocytes and Drives Immunosuppressive Lineage Commitment

Transforming growth factor β (TGFβ) is an effector of immune suppression and contributes to a permissive tumor microenvironment that compromises effective immunotherapy. We identified a correlation between TGFB1 and genes expressed by myeloid cells, but not granulocytes, in The Cancer Genome Atlas lung adenocarcinoma data, in which high TGFB1 expression was associated with poor survival. To determine whether TGFβ affected cell fate decisions and lineage commitment, we studied primary cultures of CD14⁺ monocytes isolated from peripheral blood of healthy donors. We discovered that TGFβ was a survival factor for CD14⁺ monocytes, which rapidly executed an apoptotic program in its absence. Continued exposure to TGFβ in combination with granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin 6 (IL6) amplified HLA-DR^lowCD14⁺CD11b⁺CD33⁺ myeloid-derived suppressor cells (MDSCs) at the expense of macrophage and dendritic cell (DC) differentiation. MDSCs generated in the presence of TGFβ were more effective in suppressing T-cell proliferation and promoted the T regulatory cell phenotype. In contrast, inhibition of TGFβ signaling using a small-molecule inhibitor of receptor kinase activity in CD14⁺ monocytes treated with GM-CSF and IL6 decreased MDSC differentiation and increased differentiation to proinflammatory macrophages and antigen-presenting DCs. The effect of autocrine and paracrine TGFβ on myeloid cell survival and lineage commitment suggests that pharmacologic inhibition of TGFβ-dependent signaling in cancer would favor antitumor immunity.

Does the Immunocompetent Status of Cancer Patients Have an Impact on Therapeutic DC Vaccination Strategies?

Although different types of therapeutic vaccines against established cancerous lesions in various indications have been developed since the 1990s, their clinical benefit is still very limited. This observed lack of effectiveness in cancer eradication may be partially due to the often deficient immunocompetent status of cancer patients, which may facilitate tumor development by different mechanisms, including immune evasion. The most frequently used cellular vehicle in clinical trials are dendritic cells (DCs), thanks to their crucial role in initiating and directing immune responses. Viable vaccination options using DCs are available, with a positive toxicity profile. For these reasons, despite their limited therapeutic outcomes, DC vaccination is currently considered an additional immunotherapeutic option that still needs to be further explored. In this review, we propose potential actions aimed at improving DC vaccine efficacy by counteracting the detrimental mechanisms recognized to date and implicated in establishing a poor immunocompetent status in cancer patients.

Blockade of TGF-β signaling with novel synthetic antibodies limits immune exclusion and improves chemotherapy response in metastatic ovarian cancer models

Epithelial ovarian cancer (EOC) is a leading cause of cancer-related death in women. EOC is often diagnosed at late stages, with peritoneal metastases and ascites production. Current surgery and platinum-based chemotherapy regimes fail to prevent recurrence in most patients. High levels of Transforming growth factor-β (TGF-β) within ascites has been linked to poor prognosis. TGF-β signaling promotes epithelial-mesenchymal transition (EMT) in EOC tumor cells, and immune suppression within the tumor microenvironment, with both contributing to chemotherapy resistance and metastasis. The goal of this study was to develop specific synthetic inhibitory antibodies to the Type II TGF-β receptor (TGFBR2), and test these antibodies in EOC cell and tumor models. Following screening of a phage-displayed synthetic antigen-binding fragment (Fab) library with the extracellular domain of TGFBR2, we identified a lead inhibitory Fab that suppressed TGF-β signaling in mouse and human EOC cell lines. Affinity maturation of the lead inhibitory Fab resulted in several derivative Fabs with increased affinity for TGFBR2 and efficacy as suppressors of TGF-β signaling, EMT and EOC cell invasion. In EOC xenograft and syngeneic tumor models, blockade of TGFBR2 with our lead antibodies led to improved chemotherapy response. This correlated with reversal of EMT and immune exclusion in these tumor models with TGFBR2 blockade. Together, these results describe new inhibitors of the TGF-β pathway that improve antitumor immunity, and response to chemotherapy in preclinical EOC models.

Immunomodulatory effect of statins on Regulatory T Lymphocytes in human colorectal cancer is determined by the stage of disease

Colorectal cancer (CRC) is a public health problem worldwide and in Jordan. Statins are cholesterol lowering agents. Beyond their effects, statins use has been reported to reduced risk of several malignances, including CRC. This study aimed to assess the effect of statins on CRC by studying cellular infiltration of Regulatory T Lymphocytes (Tregs) into CRC tissues and their effect on Transforming growth factor beta 1 (TGF-β₁) level and on angiogenesis. Fourty seven specimens (25 statins users vs. 22 non-users) were used. Immunohistochemistry was performed to study Tregs infiltration using their marker, fork head transcription factor, and angiogenesis using CD31 as a marker. TGF-β₁ levels were measured using ELISA. Results revealed that statins use was associated with more Tregs infiltration, less angiogenesis but no difference in TGF-β₁ content in tumor tissue. When results were further stratified according to stage of disease, more Tregs infiltration was significantly noticed in advanced disease but not in early disease. In addition, more angiogenesis inhibition was noticed in early disease but not in advanced disease. Same stage-dependence wasn’t noticed with TGF-β₁ expression. In early disease, reduction of angiogenesis mediated by statins might lead to reduction of tumor aggressiveness. On the other hand, Tregs infiltration into tumor mediated by statins might reduce cancer aggressiveness in advanced disease. These results suggest that statins might be used in the treatment of CRC.

The roles of FOX proteins in virus-associated cancers

Forkhead box (FOX) proteins play a crucial role in regulating the expression of genes involved in multiple biological processes, such as metabolism, development, differentiation, proliferation, apoptosis, migration, invasion, and longevity. Deregulation of FOX proteins is commonly associated with cancer initiation, progression, and chemotherapeutic drug resistance in many human tumors. FOX proteins deregulate through genetic events and the perturbation of posttranslational modification. The purpose of the present review is to describe the deregulation of FOX proteins by oncoviruses. Oncoviruses utilize various mechanisms to deregulate FOX proteins, including alterations in posttranslational modifications, cellular localization independently of posttranslational modifications, virus-encoded miRNAs, activation or suppression of a series of cell signaling pathways. This deregulation can affect proliferation, metastasis, chemotherapy resistance, and immunosuppression in virus-induced cancers and help to chronic viral infection, development of gluconeogenic responses, and inflammation. Since the PI3K/Akt/mTOR signaling pathway is the upstream FOXO, suppressing it can cause FOXO function to return, and this can be one of the reasons for patients to recover from the infection of the viruses used to treat these inhibitors. Hence, FOX proteins could serve as prognosis markers and target therapy specifically in cancers caused by oncoviruses.

Oncolytic Adenovirus rAd.DCN Inhibits Breast Tumor Growth and Lung Metastasis in an Immune-Competent Orthotopic Xenograft Model

The majority of advanced breast cancer patients develop distal metastasis, including lung and bone metastasis. However, effective therapeutic strategies to prevent metastasis are still lacking. Decorin is a natural inhibitor of transforming growth factor β, which plays a pivotal role in tumor metastasis. An oncolytic adenovirus expressing decorin, rAd.DCN, has been developed previously. In an immune-competent breast tumor (4T1) model, intratumoral (i.t.) as well as intravenous (i.v.) delivery of rAd.DCN inhibited growth of orthotopic tumors and spontaneous lung metastasis. It was shown that i.t. delivery of rAd.DCN produced higher levels of transgene expression and evoked stronger oncolysis of the tumors compared to i.v. delivery. However, i.v. delivery resulted in higher amount of virus accumulation in the lungs and produced stronger responses to prevent tumor lung metastasis. Oncolytic adenovirus-mediated decorin expression in the tumors downregulated the decorin target genes and decreased epithelial mesenchymal transition markers. Decorin expression in lung tissues also increased Th1 cytokine expression, such as interleukin (IL)-2, IL-12, and tumor necrosis factor α, and decreased Th2 cytokines, such as transforming growth factor β and IL-6. Moreover, rAd.DCN treatment induced strong systemic inflammatory responses and upregulated CD8⁺ T lymphocytes. In conclusion, rAd.DCN inhibits tumor growth and lung metastasis of breast cancer via regulating wnt/β-catenin, vascular endothelial growth factor (VEGF), and Met pathways, and modulating the antitumor inflammatory and immune responses. Considering that i.v. delivery was much more effective in preventing lung metastasis, systemic delivery of rAd.DCN might be a promising strategy to treat breast cancer lung metastasis.

Oncogenic BRAFV600E Governs Regulatory T-cell Recruitment during Melanoma Tumorigenesis

Regulatory T cells (Treg) are critical mediators of immunosuppression in established tumors, although little is known about their role in restraining immunosurveillance during tumorigenesis. Here, we employ an inducible autochthonous model of melanoma to investigate the earliest Treg and CD8 effector T-cell responses during oncogene-driven tumorigenesis. Induction of oncogenic BRAFV600E and loss of Pten in melanocytes led to localized accumulation of FoxP3+ Tregs, but not CD8 T cells, within 1 week of detectable increases in melanocyte differentiation antigen expression. Melanoma tumorigenesis elicited early expansion of shared tumor/self-antigen-specific, thymically derived Tregs in draining lymph nodes, and induced their subsequent recruitment to sites of tumorigenesis in the skin. Lymph node egress of tumor-activated Tregs was required for their C-C chemokine receptor 4 (Ccr4)-dependent homing to nascent tumor sites. Notably, BRAFV600E signaling controlled expression of Ccr4-cognate chemokines and governed recruitment of Tregs to tumor-induced skin sites. BRAFV600E expression alone in melanocytes resulted in nevus formation and associated Treg recruitment, indicating that BRAFV600E signaling is sufficient to recruit Tregs. Treg depletion liberated immunosurveillance, evidenced by CD8 T-cell responses against the tumor/self-antigen gp100, which was concurrent with the formation of microscopic neoplasia. These studies establish a novel role for BRAFV600E as a tumor cell-intrinsic mediator of immune evasion and underscore the critical early role of Treg-mediated suppression during autochthonous tumorigenesis.Significance: This work provides new insights into the mechanisms by which oncogenic pathways impact immune regulation in the nascent tumor microenvironment. Cancer Res; 78(17); 5038-49. ©2018 AACR.

TGF-β-responsive CAR-T cells promote anti-tumor immune function

A chimeric antigen receptor (CAR) that responds to transforming growth factor beta (TGF‐β) enables the engineering of T cells that convert this immunosuppressive cytokine into a potent T‐cell stimulant. However, clinical translation of TGF‐β CAR‐T cells for cancer therapy requires the ability to productively combine TGF‐β responsiveness with tumor‐targeting specificity. Furthermore, the potential concern that contaminating, TGF‐β?producing regulatory T (Treg) cells may preferentially expand during TGF‐β CAR‐T cell manufacturing and suppress effector T (Teff) cells demands careful evaluation. Here, we demonstrate that TGF‐β CAR‐T cells significantly improve the anti‐tumor efficacy of neighboring cytotoxic T cells. Furthermore, the introduction of TGF‐β CARs into mixed T‐cell populations does not result in the preferential expansion of Treg cells, nor do TGF‐β CAR‐Treg cells cause CAR‐mediated suppression of Teff cells. These results support the utility of incorporating TGF‐β CARs in the development of adoptive T‐cell therapy for cancer.

TGF-β in T Cell Biology: Implications for Cancer Immunotherapy

Transforming Growth Factor beta (TGF-&beta;) is a pleiotropic cytokine produced in large amounts within cancer microenvironments that will ultimately promote neoplastic progression, notably by suppressing the host&rsquo;s T-cell immunosurveillance. This effect is mostly due to the well-known inhibitory effect of TGF-&beta; on T cell proliferation, activation, and effector functions. Moreover, TGF-&beta; subverts T cell immunity by favoring regulatory T-cell differentiation, further reinforcing immunosuppression within tumor microenvironments. These findings stimulated the development of many strategies to block TGF-&beta; or its signaling pathways, either as monotherapy or in combination with other therapies, to restore anti-cancer immunity. Paradoxically, recent studies provided evidence that TGF-&beta; can also promote differentiation of certain inflammatory populations of T cells, such as Th17, Th9, and resident-memory T cells (Trm), which have been associated with improved tumor control in several models. Here, we review current advances in our understanding of the many roles of TGF-&beta; in T cell biology in the context of tumor immunity and discuss the possibility to manipulate TGF-&beta; signaling to improve cancer immunotherapy.

TGF-β in T Cell Biology: Implications for Cancer Immunotherapy

Transforming Growth Factor beta (TGF-&beta;) is a pleiotropic cytokine produced in large amounts within cancer microenvironments that will ultimately promote neoplastic progression, notably by suppressing the host&rsquo;s T-cell immunosurveillance. This effect is mostly due to the well-known inhibitory effect of TGF-&beta; on T cell proliferation, activation, and effector functions. Moreover, TGF-&beta; subverts T cell immunity by favoring regulatory T-cell differentiation, further reinforcing immunosuppression within tumor microenvironments. These findings stimulated the development of many strategies to block TGF-&beta; or its signaling pathways, either as monotherapy or in combination with other therapies, to restore anti-cancer immunity. Paradoxically, recent studies provided evidence that TGF-&beta; can also promote differentiation of certain inflammatory populations of T cells, such as Th17, Th9, and resident-memory T cells (Trm), which have been associated with improved tumor control in several models. Here, we review current advances in our understanding of the many roles of TGF-&beta; in T cell biology in the context of tumor immunity and discuss the possibility to manipulate TGF-&beta; signaling to improve cancer immunotherapy.

Prostate cancer immunotherapy: the path forward

PURPOSE OF REVIEW

To provide an overview of current strategies being investigated in the development of immunotherapy in prostate cancer.

RECENT FINDINGS

Development of immunotherapy in prostate cancer actually began in 2010 with FDA approval of sipuleucel-T. Given that immune checkpoint inhibitor trials have either been negative at the phase III level or underwhelming in smaller studies, it is likely that combination strategies will be required to further maximize the impact immune-based therapies on the clinical course of the disease. Emerging data suggests the presence of multiple checkpoint inhibitors in the prostate cancer tumor microenvironment highlighting the need for combination immunotherapy platforms that would potentially include androgen deprivation, chemotherapy, or radiation.

SUMMARY

Preclinical and clinical data support immune-based combinations in prostate cancer and several trials are underway to better define the future of immunotherapy in prostate cancer.

The opposing roles of CD4+ T cells in anti-tumour immunity

Cancer immunotherapy focuses mainly on anti-tumour activity of CD8+ cytotoxic T lymphocytes (CTLs). CTLs can directly kill all tumour cell types, provided they carry recognizable antigens. However, CD4+ T cells also play important roles in anti-tumour immunity. CD4+ T cells can either suppress or promote the anti-tumour CTL response, either in secondary lymphoid organs or in the tumour. In this review, we highlight opposing mechanisms of conventional and regulatory T cells at both sites. We outline how current cancer immunotherapy strategies affect both subsets and how selective modulation of each subset is important to maximize the clinical response of cancer patients.

Contribution to Tumor Angiogenesis From Innate Immune Cells Within the Tumor Microenvironment: Implications for Immunotherapy

The critical role of angiogenesis in promoting tumor growth and metastasis is strongly established. However, tumors show considerable variation in angiogenic characteristics and in their sensitivity to antiangiogenic therapy. Tumor angiogenesis involves not only cancer cells but also various tumor-associated leukocytes (TALs) and stromal cells. TALs produce chemokines, cytokines, proteases, structural proteins, and microvescicles. Vascular endothelial growth factor (VEGF) and inflammatory chemokines are not only major proangiogenic factors but are also immune modulators, which increase angiogenesis and lead to immune suppression. In our review, we discuss the regulation of angiogenesis by innate immune cells in the tumor microenvironment, specific features, and roles of major players: macrophages, neutrophils, myeloid-derived suppressor and dendritic cells, mast cells, γδT cells, innate lymphoid cells, and natural killer cells. Anti-VEGF or anti-inflammatory drugs could balance an immunosuppressive microenvironment to an immune permissive one. Anti-VEGF as well as anti-inflammatory drugs could therefore represent partners for combinations with immune checkpoint inhibitors, enhancing the effects of immune therapy.

A novel highly potent trivalent TGF-β receptor trap inhibits early-stage tumorigenesis and tumor cell invasion in murine Pten-deficient prostate glands

The effects of transforming growth factor beta (TGF-β) signaling on prostate tumorigenesis has been shown to be strongly dependent on the stage of development, with TGF-β functioning as a tumor suppressor in early stages of disease and as a promoter in later stages. To study in further detail the paradoxical tumor-suppressive and tumor-promoting roles of the TGF-β pathway, we investigated the effect of systemic treatment with a TGF-β inhibitor on early stages of prostate tumorigenesis. To ensure effective inhibition, we developed and employed a novel trivalent TGF-β receptor trap, RER, comprised of domains derived from the TGF-β type II and type III receptors. This trap was shown to completely block TβRII binding, to antagonize TGF-β1 and TGF-β3 signaling in cultured epithelial cells at low picomolar concentrations, and it showed equal or better anti-TGF-β activities than a pan TGF-β neutralizing antibody and a TGF-β receptor I kinase inhibitor in various prostate cancer cell lines. Systemic administration of RER inhibited prostate tumor cell proliferation as indicated by reduced Ki67 positive cells and invasion potential of tumor cells in high grade prostatic intraepithelial neoplasia (PIN) lesions in the prostate glands of Pten conditional null mice. These results provide evidence that TGF-β acts as a promoter rather than a suppressor in the relatively early stages of this spontaneous prostate tumorigenesis model. Thus, inhibition of TGF-β signaling in early stages of prostate cancer may be a novel therapeutic strategy to inhibit the progression as well as the metastatic potential in patients with prostate cancer.