Induced and natural regulatory T cells in human cancer

Introduction: Evidence suggests that FOXP3(+)CD25(high)CD4(+) regulatory T cells (Treg) which accumulate in cancer may have beneficial or unfavorable effects on prognosis. The presence in tumor-associated inflammatory infiltrates of two subsets of Treg with distinct phenotypic and functional profiles might explain these conflicting observations. Areas covered: Human inducible (i) Treg arising by tumor-driven conversion of conventional CD4(+) T cells are highly suppressive, therapy-resistant Treg which down-regulate anti-tumor immune responses, promoting tumor growth. Natural (n) Treg, normally responsible for maintaining peripheral tolerance, control cancer-associated inflammation, which favors tumor progression. This division of labor between nTreg and iTreg is not absolute, and overlap may be common. Nevertheless, iTreg play a critical and major role in cancer and cancer therapy. The tumor microenvironment determines the type, frequency and suppression levels of accumulating Treg. Expert opinion: In cancer, a selective removal or silencing of iTreg and not of nTreg should be a therapeutic goal. However, the implementation of this challenging strategy requires further studies of cellular and molecular crosstalk among immune cells in the tumor microenvironment.     

T regulatory cells in cancer: recent advances and therapeutic potential

Importance of the field: The active suppression of immune responses against tumor is a major barrier to the likely success of cancer immunotherapy. There is now compelling evidence implicating T regulatory cells (Tregs) as being key players driving immune suppression. Elevated frequencies of Tregs within the peripheral circulation and tumor microenvironment of cancer patients correlate with poor prognosis and reduced survival. Understanding the mechanism of Treg elevation is critical for the development of new approaches aiming to modulate the frequency and function of Tregs to enhance the efficacy of cancer immune-based therapies.

Areas covered in this review: This review focuses on current knowledge concerning Tregs in cancer and discusses putative mechanisms which underlie the expansion of Tregs in cancer patients. Additionally, we review current strategies to deplete/suppress Treg activity, the limitations of these strategies and future perspective for improving their efficacy.

What the reader will gain: An insight of the current aspects concerning Treg subsets in cancer and an overview of recent advances in the identification of Treg-specific markers, in addition to the potential strategies to target Tregs for enhancing antitumor immunity.

Take home message: Mechanisms by which Treg functions modulate the immune response to tumors are becoming further understood. However, specific markers to tumor-specific/induced Tregs are yet to be clearly identified, which is a major limitation in optimizing strategies to specifically target Tregs in cancer. Despite this, strategies aimed at modulating Tregs in patients are providing some early encouraging results supporting the overall concept and indicating that further studies are clearly warranted.     

Expression of CD4+CD25highCD127low/− regulatory T cells in transitional cell carcinoma patients and its significance

To evaluate the expressions of CD4⁺CD25^highCD127^low/? regulatory T cells (Tregs) in peripheral blood from patients with transitional cell carcinoma (TCC) in urinary system, we investigated the proportion of Treg population in CD4⁺ T from 93 patients with TCC, 38 with benign urinary diseases, and 37 healthy subjects by using flow cytometric analysis and analyzing different clinicopathologic characteristics and the changes before and after operation. We found that the proportion of Treg in peripheral blood from patients with TCC was significantly increased as compared with the othertwo groups. There was a strong correlation between the proportion of Treg and tumor recurrence, quantity, lymph node metastasis (P<0.01), as well as pathological stage; no correlation was found between the proportion of Treg and clinical TNM stage (P>0.05). The proportion of Treg was also different before and after operation (P<0.05). This suggest that CD4⁺CD25⁺CD127^low/? regulatory T cells may be responsible for immune suppression in TCC patients. The resection of tumor can decrease the proportion of Treg in peripheral blood. J. Clin. Lab. Anal. 23:197–201, 2009. © 2009 Wiley‐Liss, Inc.     

Phenotypic alterations,clinical impact and therapeutic potential of regulatory T cells in cancer

Introduction: Regulatory T cells (Tregs) have been characterised in different cancers. They accumulate in peripheral blood and tumour microenvironments where they suppress tumour-specific immune responses, enabling tumours to develop without challenge. This tumour immune evasion represents a major obstacle to successful cancer therapies. Whilst Tregs are generally divided into thymic-derived and peripherally induced, Tregs exhibit a wide spectrum of phenotypes and functional capacity dependent on microenvironment. This phenotypic diversity is also reflected in tumour-infiltrating Treg (TI Treg) populations, which may explain the variable impact of Treg accumulation on prognosis in different cancers. Identifying TI Treg subsets is critical to understand TI Treg biology and for developing effective immunotherapies.

Areas covered: This review discusses current and potential markers, and the modulation of these markers in cancer. In addition, we systematically review the clinical impact of Tregs in cancer and their potential as a therapeutic target, with a focus on TI Tregs.

Expert opinion: TI Tregs represent dynamic and diverse subsets that are key in promoting tumour progression through their suppressive activities. Targeting specific TI Treg subpopulations and functional TI Treg markers represents a feasible therapeutic strategy that might allow reestablishment of antitumour immune responses without affecting physiological immune regulation.     

Induced regulatory T cells in inhibitory microenvironments created by cancer

Introduction: Regulatory T cells (Tregs) accumulating in the peripheral circulation and tumor sites of patients contribute to tumor escape from the host immune system. Tregs encompass subsets of immune cells with distinct phenotypic and functional properties. Whereas natural (n) or thymic-derived (t) Tregs regulate responses to self-antigens, inducible (i) or peripheral (p) Tregs generated and expanded in regulatory microenvironments control immune responses to a broad variety of antigens.

Areas covered: Tregs accumulating in the tumor microenvironment (TME) are contextually regulated. They acquire phenotypic and functional attributes imposed by the inhibitory molecular pathways operating in situ. Several molecular pathways active in human cancer are reviewed. The pathways may differ from one tumor to another, and environmentally induced Tregs may be functionally distinct. Potential therapeutic strategies for selective silencing of iTregs are considered in the light of the newly acquired understanding of their phenotypic and functional diversity.

Expert opinion: Human Tregs accumulating in cancer comprise ‘bad’ subsets, which inhibit antitumor immunity, and ‘good’ anti-inflammatory subsets, which maintain tolerance to self and benefit the host. Future therapeutic strategies targeting Tregs will need to discriminate between these Treg subsets and will need to consider reprogramming strategies instead of Treg elimination. Re-establishment of effective antitumor immune responses in cancer patients without disturbing a normal homeostatic T-cell balance will greatly benefit from insights into inhibitory pathways engaged by human tumors.     

Regulatory T cells in HBV and HCV liver diseases: implication of regulatory T lymphocytes in the control of immune response

Importance of the field: Hepatic cirrhosis is a frequent consequence of chronic hepatitis infection (HBV and HCV) or alcohol abuse and the most common cause of hepatocellular carcinoma (HCC). Currently, liver transplantation remains the only effective therapeutic approach for cirrhosis-related HCC patients. The evolution of the pathology strongly depends on immunological mechanisms.

Areas covered in this review: Despite the presence of specific T cells, viral chronic infection and continuous tumor growth suggest a failure of immune control. It appears that direct suppression of antiviral or antitumor effector cells by regulatory T cells plays a pivotal role in the impairment of immune response. Several types of regulatory T cells have been described, natural regulatory T cells (nTreg) and induced-type 1 regulatory T cells (Tr1) being the best characterized.

What the reader will gain: Currently, there is no evidence for a direct implication of regulatory T cells in the evolution of hepatitis, especially concerning chronic infection, cirrhosis late stage and HCC progress. However, recent studies show that regulatory T cells are implicated in the modulation of HBV- and HCV-associated immune response, thus, promoting HCC progress.

Take home message: Therefore, nTreg and Tr1 cells seem to play an important role in the control of immune response leading to chronic hepatitis infection and progression of the pathology to cirrhosis and HCC.     

Countering tumor-induced immunosuppression during immunotherapy for pancreatic cancer

Background: Vaccines for pancreatic cancer have been challenged by a number of factors, especially the immunosuppressive microenvironment within the tumor that allows for escape from immune surveillance. Objective/methods: We sought to identify results that define mechanisms of pancreatic-cancer-associated immunosuppression and strategies that might be useful to overcome them thereby resulting in effective immune responses to cancer vaccines capable of deleting pancreatic cancer cells. Results/conclusion: Immunosuppressive tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSC), and regulatory T cells (Treg) reside in tumors, and their products along with tumor derived products (such as VEGF, TGFβ and IL-10), create a microenvironment that counters immune activation and attack. Immunotherapy with cancer vaccines must include strategies to modulate these immunosuppressive cell types and tumor byproducts. Clinical trials are beginning to test these strategies.     

P38 MAP Kinase Signaling Is Required for the Conversion of CD4+CD25− T Cells into iTreg

CD4+CD25+ regulatory T cells (Treg) are important mediators of immune tolerance. A subset of Treg can be generated in the periphery by TGF-beta dependent conversion of conventional CD4+CD25− T cells into induced Treg (iTreg). In chronic viral infection or malignancy, such induced iTreg, which limit the depletion of aberrant or infected cells, may be of pathogenic relevance. To identify potential targets for therapeutic intervention, we investigated the TGF-beta signaling in Treg. In contrast to conventional CD4+ T cells, Treg exhibited marked activation of the p38 MAP kinase pathway. Inhibition of p38 MAP kinase activity prevented the TGF-beta-dependent conversion of CD4+CD25− T cells into Foxp3+ iTreg in vitro. Of note, the suppressive capacity of nTreg was not affected by inhibiting p38 MAP kinase. Our findings indicate that signaling via p38 MAP kinase seems to be important for the peripheral generation of iTreg; p38 MAP kinase could thus be a therapeutic target to enhance immunity to chronic viral infection or cancer.     

Immunophenotypic shift of memory CD8 T cells identifies the changes of immune status in the patients after liver transplantation

Abstract

Objective: Chronic or acute rejection is a leading cause of allograft loss after solid organ transplantation and the presence of memory T cells is associated with increased propensity for allograft rejection. The purpose of this study was to investigate the correlation between immunophenotypic shift of memory CD8⁺ T cells and immune status in the patients after liver transplantation. Material and methods: Seventy-three blood samples were collected and varied compartments of memory CD8⁺ T cells were analysed in non-rejected and rejected patients. Results: The results show that with time elapsed, the immunophenotypes of memory CD8⁺ cells shifted from naive T cells to central or intermediate memory cells, and then to effector or terminal memory cells in non-rejected patients. This course was correlated with the expression of CD127 on CD8⁺ T cells. In rejected patients, the main proportion of CD8⁺ cells were dominated by naive CD8⁺ cells and then rapidly restored to the immunophenotypes of memory T cells after effective treatment. Conclusion: These results demonstrated that immunophenotypic shift of memory CD8⁺ T cells was closely related to the change of the immune status in the patients after liver transplantation. Monitoring the immunophenotypic shift of memory CD8⁺ T cells is of great importance in the prediction for allograft rejection and treatment effectiveness after liver transplantation.     

Regulatory T cells and immunity to pathogens

Immune responses to pathogens are modulated by one or more types of cells that perform a regulatory function. Some cells with this function, such as CD4⁺Foxp3⁺ natural regulatory T cells (nTreg), pre-exist prior to infections whereas others may be induced as a consequence of infection (adaptive Treg). With pathogens that have a complex pathogenesis, multiple types of regulatory cells could influence the outcome. One major property of Treg is to help minimize collateral tissue damage that can occur during immune reactions to a chronic infection. The consequence is less damage to the host but in such situations the pathogen is likely to establish persistence. In some cases, a fine balance is established between Treg responses, effector components of immunity and the pathogen. Treg responses to pathogens may also act to hamper the efficacy of immune control. This review discusses these issues as well as the likely mechanisms by which various pathogens can signal the participation of Treg during infection.     

Leptin favors Th17/Treg cell subsets imbalance associated with allergic asthma severity

BackgroundObesity has often been associated with severe allergic asthma (AA). Here, we analyzed the frequency of different circulating CD4⁺T‐cell subsets from lean, overweight and obese AA patients.MethodsMononuclear cells from peripheral blood were obtained from 60 AA patients and the frequency of different CD4⁺T‐cell subsets and type 1 regulatory B cells (Br1) was determined by cytometry. The effect of obese‐related leptin dose on cytokine production and Treg cell function in AA‐derived CD4⁺ T cell cultures was evaluated by ELISA and 3H thymidine uptake, respectively. Leptin levels were quantified in the plasma by ELISA. According to the BMI, patients were stratified as lean, overweight and obese.ResultsAA severity, mainly among obese patients, was associated with an expansion of hybrid Th2/Th17 and Th17‐like cells rather than classic Th2‐like cells. On the other hand, the frequencies of Th1‐like, Br1 cells and regulatory CD4⁺ T‐cell subsets were lower in patients with severe AA. While percentages of the hybrid Th2/Th17 phenotype and Th17‐like cells positively correlated with leptin levels, the frequencies of regulatory CD4⁺ T‐cell subsets and Br1 cells negatively correlated with this adipokine. Interestingly, the obesity‐related leptin dose not only elevated Th2 and Th17 cytokine levels, but also directly reduced the Treg function in CD4⁺ T cell cultures from lean AA patients.ConclusionIn summary, our results indicated that obesity might increase AA severity by favoring the expansion of Th17‐like and Th2/Th17 cells and decreasing regulatory CD4⁺T cell subsets, being adverse effects probably mediated by leptin overproduction.     

Overexpression of CD155 is associated with PD-1 and PD-L1 expression on immune cells,rather than tumor cells in the breast cancer microenvironment

BACKGROUNDCD155 is an immune checkpoint protein in cancers and interacts with ligands to regulate the immune microenvironment. The expression of CD155 is correlated with the prognosis and pathological features of breast cancer.AIMTo investigate the expression status of CD155 and the association with exhausted CD4⁺ helper and CD8⁺ cytotoxic tumor infiltrating lymphocytes (TILs) and PD-L1 in the breast cancer microenvironment.METHODSOne hundred and twenty-six breast cancer patients with invasive ductal breast cancer were consecutively recruited into this study. Immunohistochemistry was used to detect the expression CD155, PD-L1 and PD-1 on tumor-infiltrating immune cells and tumor cells in the microenvironment.RESULTSThe proportion of patients with CD155 expression was higher in triple negative breast cancer (72.7%) than in Luminal A patients (22.2%, P < 0.05). Patients with positive CD155 expression had a higher percentage of CD4⁺/PD-1⁺ helper TILs (30%) than patients with negative CD155 expression (21%, P < 0.05). Patients with positive CD155 expression also had higher cell counts of exhausted CD4⁺ TILs [47 vs 20/high-power fields (HPF)] and unexhausted CD8⁺ TILs (30 vs 17/HPF) than patients with negative expression (P < 0.05). CD155 expression was correlated with increased PD-L1 expression in immune cells, 0.8% and 0.02% immune cells expressed PD-L1 in patients with positive and negative CD155 expression, respectively (P < 0.05).CONCLUSIONCD155 was related to an inhibitory immune breast cancer microenvironment. CD155 was associated with a high proportion of exhausted CD4⁺ and unexhausted CD8⁺ TILs and high PD-L1 expression in immune cells.     

Targeting human inducible regulatory T cells (Tr1) in patients with cancer: blocking of adenosine–prostaglandin E2 cooperation

Introduction: Emerging data suggest that human inducible regulatory T cells (Tr1) produce adenosine and prostaglandin E₂ and that these factors cooperate in mediating immune suppression.

Areas covered: Human Tr1 present in human tumors or blood of cancer patients express ectonucleotidases, CD39 and/or CD73, hydrolyze ATP to adenosine and are COX-2 positive. Expression of CD39 and/or CD73 on human tumors favors expansion and suppressor functions of Tr1. Adenosine and PGE₂ signal via adenosine 2A receptor (A_2AR) and prostaglandin E₂ receptor 2 (EP₂R) expressed on effector T (Teff) cells, suppressing their anti-tumor functions by a common mechanism involving upregulation of cytosolic cAMP levels and protein kinase A (PKA) type I activation. The frequency and activity of circulating CD4⁺CD39⁺ and CD4⁺COX-2⁺ Treg subsets increase in advanced disease and also following oncologic therapies.

Expert opinion: Pharmacologic blocking of adenosine–PGE₂ collaboration provides a clinically-feasible strategy for disarming of Treg. Used in conjunction with conventional anti-cancer drugs or immune interventions, pharmacologic inhibitors could improve outcome of oncologic therapies.     

Transforming growth factor‐beta1 inhibits tissue engineering cartilage absorption via inducing the generation of regulatory T cells

The objective of the present study was to explore the mechanisms of transforming growth factor (TGF)‐β1 inhibiting the absorption of tissue engineering cartilage. We transfected TGF‐β1 gene into bone marrow mesenchymal stem cells (BMMSCs) and co‐cultured with interferon (IFN)‐γ and tumour necrosis factor (TNF)‐α and CD4⁺CD25^? T lymphocytes. We then characterized the morphological changes, apoptosis and characterization of chondrogenic‐committed cells from TGF‐β1⁺BMMSCs and explored their mechanisms. Results showed that BMMSCs apoptosis and tissue engineering cartilage absorption in the group with added IFN‐γ and TNF‐α were greater than in the control group. In contrast, there was little BMMSC apoptosis and absorption by tissue engineering cartilage in the group with added CD4⁺CD25^? T lymphocytes; Foxp3⁺T cells and CD25⁺CD39⁺ T cells were found. In contrast, no type II collagen or Foxp3⁺T cells or CD25⁺CD39⁺ T cells was found in the TGF‐β1^–BMMSC group. The data suggest that IFN‐γ and TNF‐α induced BMMSCs apoptosis and absorption of tissue engineering cartilage, but the newborn regulatory T (Treg) cells inhibited the function of IFN‐γ and TNF‐α and protected BMMSCs and tissue engineering cartilage. TGF‐β1not only played a cartilage inductive role, but also inhibited the absorption of tissue engineering cartilage. The pathway proposed in our study may simulate the actual reaction procedure after implantation of BMMSCs and tissue engineering cartilage in vivo. Copyright © 2013 John Wiley & Sons, Ltd.     

The immune microenvironment in vulvar (pre)cancer: review of literature and implications for immunotherapy

ABSTRACT

Introduction: Vulvar squamous cell carcinoma (VSCC) develops via two different pathways: TP53 mutations in a background of lichen sclerosus or a persistent infection with high-risk human papilloma virus (HPV). The latter group of tumor responds better to treatment than the non-virally induced VSCC. This may be explained by a difference in the tumor immune microenvironment (TME).

Areas covered: This review summarizes literature on TME of VSCC and its precursors, and extrapolates this to foster the development of new therapeutic strategies.

Expert opinion: Both types of VSCC and their precursors are infiltrated with variable numbers of M2 macrophages, regulatory T cells and CD8+ T cells, indicating that they express targetable tumor antigens. Type 1 T cell immunity in precursor lesions is associated with fewer recurrences and better clinical responses to immunotherapy. Escape of these lesions and progression toward VSCC is associated with the downregulation of HLA Class I, increased expression of co-inhibitory molecules, infiltration with immunosuppressive cells and the local production of immunosuppressive enzymes and cytokines. More in-depth studies of the VSCC TME are required to fully comprehend the impact of the immune system on VSCC, and subsequently to identify patients who will benefit from immunotherapeutic strategies.     

Cytokine-induced killer (CIK) cells as feasible and effective adoptive immunotherapy for the treatment of solid tumors

Introduction: Cytokine-induced killer (CIK) cells are heterogeneous ex vivo-expanded T lymphocytes with mixed T-NK phenotype and endowed with a wide MHC-unrestricted antitumor activity. CIK cells can be expanded from peripheral blood mononuclear cells (PBMC) cultured with the timed addition of IFN-γ, Ab anti-CD3 and IL2. A consistent subset of mature CIK cells presents a CD3⁺CD56⁺ phenotype. The CD3⁺CD56⁺ cellular subset is the main responsible for the tumor-killing activity, mostly mediated by the interaction of NKG2D receptor with MHC-unrestricted ligands (MIC A/B; ULBPs) on tumor cells.

Areas covered: In the present work, we described the biologic characteristics of CIK cells, focusing on those aspects that may favor their clinical translation. We reviewed preclinical data and analyzed reports from clinical trials. A specific paragraph is dedicated to future research perspectives in the field.

Expert opinion: CIK cells represent a realistic new option in the field of cancer immunotherapy. Crucial issues, favoring their clinical translation, are the easy availability of large amounts of expanded CIK cells and their MHC-unrestricted tumor killing, potentially effective against many tumor types. Intriguing future perspectives and open challenges are the investigation of synergisms with other immunotherapy approaches, targeted therapies or even conventional chemotherapy.     

Identification of heme oxygenase-1–specific regulatory CD8+ T cells in cancer patients

Treg deficiencies are associated with autoimmunity. Conversely, CD4⁺ and CD8⁺ Tregs accumulate in the tumor microenvironment and are associated with prevention of antitumor immunity and anticancer immunotherapy. Recently, CD4⁺ Tregs have been much studied, but little is known about CD8⁺ Tregs and the antigens they recognize. Here, we describe what we believe to be the first natural target for CD8⁺ Tregs. Naturally occurring HLA-A2–restricted CD8⁺ T cells specific for the antiinflammatory molecule heme oxygenase-1 (HO-1) were able to suppress cellular immune responses with outstanding efficacy. HO-1–specific CD8⁺ T cells were detected ex vivo and in situ among T cells from cancer patients. HO-1–specific T cells isolated from the peripheral blood of cancer patients inhibited cytokine release, proliferation, and cytotoxicity of other immune cells. Notably, the inhibitory effect of HO-1–specific T cells was far more pronounced than that of conventional CD4⁺CD25⁺CD127^– Tregs. The inhibitory activity of HO-1–specific T cells seemed at least partly to be mediated by soluble factors. Our data link the cellular stress response to the regulation of adaptive immunity, expand the role of HO-1 in T cell–mediated immunoregulation, and establish a role for peptide-specific CD8⁺ T cells in regulating cellular immune responses. Identification of potent antigen-specific CD8⁺ Tregs may open new avenues for therapeutic interventions in both autoimmune diseases and cancer.     

T regulatory cells as an immunotherapy for transplantation

Advances in immunosuppressive therapies have made tissue and organ transplantation a common procedure in clinical medicine. However, true donor and recipient tolerance is not regularly achieved and almost all transplant recipients continue to require immunosuppressants throughout life, which is associated with side effects of the drugs. The identification and characterisation of regulatory T cells (Tregs) has recently opened up exciting opportunities for new ways of adoptive immunotherapy in transplantation. CD4⁺CD25⁺ Tregs of thymic origin have been shown to be key regulators of unseasoned immune responses in mice and in humans, preventing graft-versus-host disease and organ graft rejection in the transplantation setting. Although these cells can be found in the peripheral blood of healthy individuals, their isolation to a satisfying degree of purity is time-consuming and ineffective. Therefore, a variety of different methods to expand or induce regulatory T cells ex vivo have been advocated. Antigen-specific activation of Tregs is a prerequisite for their optimal function, making the design of new strategies to create and expand antigen-specific Tregs highly desirable. This review will focus on recent advances achieved in the field of transplantation tolerance using naturally occurring Tregs (CD4⁺CD25⁺), as well as other Tregs, and will discuss future applications of these cells in immunotherapy.