Disruption of CCR5-dependent homing of regulatory T cells inhibits tumor growth in a murine model of pancreatic cancer

Nuclear FAK controls chemokine transcription, Tregs, and evasion of anti-tumor immunity

Focal adhesion kinase (FAK) promotes anti-tumor immune evasion. Specifically, the kinase activity of nuclear-targeted FAK in squamous cell carcinoma (SCC) cells drives exhaustion of CD8(+) T cells and recruitment of regulatory T cells (Tregs) in the tumor microenvironment by regulating chemokine/cytokine and ligand-receptor networks, including via transcription of Ccl5, which is crucial. These changes inhibit antigen-primed cytotoxic CD8(+) T cell activity, permitting growth of FAK-expressing tumors. Mechanistically, nuclear FAK is associated with chromatin and exists in complex with transcription factors and their upstream regulators that control Ccl5 expression. Furthermore, FAK's immuno-modulatory nuclear activities may be specific to cancerous squamous epithelial cells, as normal keratinocytes do not have nuclear FAK. Finally, we show that a small-molecule FAK kinase inhibitor, VS-4718, which is currently in clinical development, also drives depletion of Tregs and promotes a CD8(+) T cell-mediated anti-tumor response. Therefore, FAK inhibitors may trigger immune-mediated tumor regression, providing previously unrecognized therapeutic opportunities.

Immunosuppressive Mechanisms of Malignant Gliomas: Parallels at Non-CNS Sites

The central nervous system (CNS) possesses powerful local and global immunosuppressive capabilities that modulate unwanted inflammatory reactions in nervous tissue. These same immune-modulatory mechanisms are also co-opted by malignant brain tumors and pose a formidable challenge to brain tumor immunotherapy. Routes by which malignant gliomas coordinate immunosuppression include the mechanical and functional barriers of the CNS; immunosuppressive cytokines and catabolites; immune checkpoint molecules; tumor-infiltrating immune cells; and suppressor immune cells. The challenges to overcoming tumor-induced immunosuppression, however, are not unique to the brain, and several analogous immunosuppressive mechanisms also exist for primary tumors outside of the CNS. Ultimately, the immune responses in the CNS are linked and complementary to immune processes in the periphery, and advances in tumor immunotherapy in peripheral sites may therefore illuminate novel approaches to brain tumor immunotherapy, and vice versa.

A distinct chemokine axis does not account for enrichment of Foxp3(+) CD4(+) T cells in carcinogen-induced fibrosarcomas

The frequency of CD4⁺ Foxp3⁺ regulatory T (Treg) cells is often significantly increased in the blood of tumour-bearing mice and people with cancer. Moreover, Treg cell frequencies are often higher in tumours compared with blood and lymphoid organs. We wished to determine whether certain chemokines expressed within the tumour mass selectively recruit Treg cells, thereby contributing to their enrichment within the tumour-infiltrating lymphocyte pool. To achieve this goal, the chemokine profile of carcinogen-induced fibrosarcomas was determined, and the chemokine receptor expression profiles of both CD4⁺ Foxp3⁻ and CD4⁺ Foxp3⁺ T cells were compared. These analyses revealed that the tumours are characterized by expression of inflammatory chemokines (CCL2, CCL5, CCL7, CCL8, CCL12, CXCL9, CXCL10 and CX3CL1), reflected by an enrichment of activated Foxp3⁻ and Foxp3⁺ T cells expressing T helper type 1-associated chemokine receptors. Notably, we found that CXCR3⁺ T cells were significantly enriched in the tumours although curiously we found no evidence that CXCR3 was required for their recruitment. Instead, CXCR3 marks a population of activated Foxp3⁻ and Foxp3⁺ T cells, which use multiple and overlapping ligand receptor pairs to guide their migration to tumours. Collectively, these data indicate that enrichment of Foxp3⁺ cells in tumours characterized by expression of inflammatory chemokines, does not occur via a distinct chemokine axis, thus selective chemokine blockade is unlikely to represent a meaningful therapeutic strategy for preventing Treg cell accumulation in tumours.

CD4 T-cell subsets and tumor immunity: the helpful and the not-so-helpful

Research over the past decade has revealed the increasingly complex biologic features of the CD4(+) T-cell lineage. This T-cell subset, which was originally defined on the basis of helper activity in antibody responses, expresses receptors that recognize peptides that have been processed and presented by specialized antigen-presenting cells. At the core of the adaptive immune response, CD4 T cells display a large degree of plasticity and the ability to differentiate into multiple sublineages in response to developmental and environmental cues. These differentiated sublineages can orchestrate a broad range of effector activities during the initiation, expansion, and memory phase of an immune response. The contribution of CD4 cells to host defense against pathogenic invasion and regulation of autoimmunity is now well established. Emerging evidence suggests that CD4 cells also actively participate in shaping antitumor immunity. Here, we outline the biologic properties of CD4 T-cell subsets with an emphasis on their contribution to the antitumor response.

No Association between the CCR5Δ32 Polymorphism and Sporadic Esophageal Cancer in Punjab, North-West India

BACKGROUND

Chemokines and their receptors influence carcinogenesis and cysteine-cysteine chemokine receptor 5 (CCR5) directs spread of cancer to other tissues. A 32 base pair deletion in the coding region of CCR5 that might alter the expression or function of the protein has been implicated in a variety of immune-mediated diseases. The action of antiviral drugs being proposed as adjuvant therapy in cancer is dependent on CCR5 wild type status. In the present study, distribution of CCR5Δ32 polymorphism was assessed in North Indian esophageal cancer patients to explore the potential of using chemokine receptors antagonists as adjuvant therapy.

MATERIALS AND METHODS

DNA samples of 175 sporadic esophageal cancer patients (69 males and 106 females) and 175 unrelated healthy control individuals (69 males and 106 females) were screened for the CCR5Δ32 polymorphism by direct polymerase chain reaction (PCR).

RESULTS

The frequencies of wild type homozygous (CCR5/CCR5), heterozygous (CCR5/Δ32) and homozygous mutant (Δ32/Δ32) genotypes were 96.0 vs 97.72%, 4.0 vs 1.71% and 0 vs 0.57% in patients and controls respectively. There was no difference in the genotype and allele frequencies of CCR5Δ32 polymorphism in esophageal cancer patients and control group.

CONCLUSIONS

The CCR5Δ32 polymorphism is not associated with esophageal cancer in North Indians. As the majority of patients express the wild type allele, there is potential of using antiviral drug therapy as adjuvant therapy.

Cancer-associated mesenchymal stem cells aggravate tumor progression

Mesenchymal stem cells (MSCs) have both stemness and multi-modulatory activities on other cells, and the immunosuppressive and tumor-promotive mechanisms have been intensively investigated in cancer. The role of MSCs appears to be revealed in tumor aggravation, and targeting MSCs seems to be a promising strategy for treating cancer patients. However, it is still impractical in clinical therapy, since the precise MSCs are poorly understood in the in vivo setting. In previous studies, MSCs were obtained from different sources, and were prepared by ex vivo expansion for a long term. The inconsistent experimental conditions made the in vivo MSCs obscure. To define the MSCs in the host is a priority issue for targeting MSCs in cancer therapy. We recently identified a unique subpopulation of MSCs increasing in mice and human with cancer metastasis. These MSCs are specifically expanded by metastatic tumor cells, and promote tumor progression and dissemination accompanied by immune suppression and dysfunction in the host, more powerfully than normal MSCs growing without interference of cancer. In this review, we summarize current knowledge of the role of MSCs in tumor aggravation, along with our new findings of the bizarre MSCs.

Regulation of chemokine expression in the tumor microenvironment

Chemokines are chemotactic cytokines critical for homeostatic and inflammation-induced trafficking of leukocytes during immune responses, hematopoesis, wound healing, and tumorigenesis. Despite three decades of intensive study of the chemokine network, the molecular mechanisms regulating chemokine expression during tumor growth are not well understood. In this review, we focus on the role of chemokines in both tumor growth and anti-tumor immune responses and on molecular mechanisms employed by tumor cells to regulate chemokine expression in the tumor microenvironment. Multiple mechanisms used by tumors to regulate chemokine production, including those revealed by very recent studies (such as DNA methylation or post-translational nitrosylation of chemokines) are discussed. Concluding the review, we discuss how understanding of these regulatory mechanisms can be used in cancer therapy to suppress tumor growth and/or to promote immune-mediated eradication of tumors.

Immune cell promotion of metastasis

Metastatic disease is the major cause of death from cancer, and immunotherapy and chemotherapy have had limited success in reversing its progression. Data from mouse models suggest that the recruitment of immunosuppressive cells to tumours protects metastatic cancer cells from surveillance by killer cells, which nullifies the effects of immunotherapy and thus establishes metastasis. Furthermore, in most cases, tumour-infiltrating immune cells differentiate into cells that promote each step of the metastatic cascade and thus are novel targets for therapy. In this Review, we describe how tumour-infiltrating immune cells contribute to the metastatic cascade and we discuss potential therapeutic strategies to target these cells.

Regulatory T-cell homeostasis: steady-state maintenance and modulation during inflammation

Regulatory T (Treg) cells play a vital role in the prevention of autoimmunity and the maintenance of self-tolerance, but these cells also have an active role in inhibiting immune responses during viral, bacterial, and parasitic infections. Although excessive Treg activity can lead to immunodeficiency, chronic infection, and cancer, too little Treg activity results in autoimmunity and immunopathology and impairs the quality of pathogen-specific responses. Recent studies have helped define the homeostatic mechanisms that support the diverse pool of peripheral Treg cells under steady-state conditions and delineate how the abundance and function of Treg cells changes during inflammation. These findings are highly relevant for developing effective strategies to manipulate Treg cell activity to promote allograft tolerance and treat autoimmunity, chronic infection, and cancer.

The effects of CCR5 inhibition on regulatory T-cell recruitment to colorectal cancer

BACKGROUND

Regulatory T cells (Treg) are enriched in human colorectal cancer (CRC) where they suppress anti-tumour immunity. The chemokine receptor CCR5 has been implicated in the recruitment of Treg from blood into CRC and tumour growth is delayed in CCR5-/- mice, associated with reduced tumour Treg infiltration.

METHODS

Tissue and blood samples were obtained from patients undergoing resection of CRC. Tumour-infiltrating lymphocytes were phenotyped for chemokine receptors using flow cytometry. The presence of tissue chemokines was assessed. Standard chemotaxis and suppression assays were performed and the effects of CCR5 blockade were tested in murine tumour models.

RESULTS

Functional CCR5 was highly expressed by human CRC infiltrating Treg and CCR5(high) Treg were more suppressive than their CCR5(low) Treg counterparts. Human CRC-Treg were more proliferative and activated than other T cells suggesting that local proliferation could provide an alternative explanation for the observed tumour Treg enrichment. Pharmacological inhibition of CCR5 failed to reduce tumour Treg infiltration in murine tumour models although it did result in delayed tumour growth.

CONCLUSIONS

CCR5 inhibition does not mediate anti-tumour effects as a consequence of inhibiting Treg recruitment. Other mechanisms must be found to explain this effect. This has important implications for anti-CCR5 therapy in CRC.

Functional dynamics of Foxp3⁺ regulatory T cells in mice and humans

Forkhead box protein 3 (Foxp3)(+) regulatory T (Treg) cells are critical mediators for the establishment of self-tolerance and immune homeostasis and for the control of pathology in various inflammatory responses. While Foxp3(+) Treg cells often control immune responses in secondary lymphoid tissues, they must also traffic to and persist within non-lymphoid tissues, where they integrate various environmental cues to coordinate and adapt their effector acitvities in these sites. In recent years, our group has made use of several mouse models, including the non-obese diabetic model of type 1 diabetes, to characterize the factors, which impact the homeostasis, function, and reprogramming potential of Foxp3(+) Treg cells in situ. In addition, our recent work shows that Foxp3(+) Treg cells possess distinct post-transcriptional mechanisms of gene regulation, namely mRNA translation, to modulate tissue-specific inflammatory responses. In humans, there is a pressing need for reliable markers of FOXP3(+) Treg cells and their related function in blood and tissue. Experimental progress in our group has enabled us to discover novel markers of FOXP3(+) Treg cell (dys)function and unique gene signatures that discriminate effector and Treg cells, as well as functional and dysfunctional FOXP3(+) Treg cells.

The potential to target CCL5/CCR5 in breast cancer

INTRODUCTION

Chemokines play a crucial role in breast cancer tumorigenesis and progression. Recently, the chemokine (C-C motif) ligand 5 (CCL5), which can be secreted either by tumor cells or by mesenchymal stromal cells recruited to the tumor, has been identified as a key node in the bidirectional communication between breast cancer and normal cells.

AREAS COVERED

In this review, the authors discuss the role of CCL5/chemokine receptor 5 (CCR5) axis in promoting breast cancer onset and progression. Interrogation of large clinical databases has demonstrated increased expression of the CCL5/CCR5 axis in specific subtypes of breast cancer. The activation of the receptor CCR5 in breast cancer cells controls their invasiveness serving as a driver for metastasis. Furthermore, the CCL5/CCR5 axis participates in the recruitment of specific immune cells into tumors, inducing local immunosuppression and favoring tumor progression.

EXPERT OPINION

The role of CCR5 in HIV infection led to the development of specific and potent CCR5 antagonists. The data reviewed here includes basic and translational studies that support the use of such CCR5 antagonists in breast cancer patients as adjuvant therapy to block the metastasis.

Complex role for the immune system in initiation and progression of pancreatic cancer

The immune system plays a complex role in the development and progression of pancreatic cancer. Inflammation can promote the formation of premalignant lesions and accelerate pancreatic cancer development. Conversely, pancreatic cancer is characterized by an immunosuppressive environment, which is thought to promote tumor progression and invasion. Here we review the current literature describing the role of the immune response in the progressive development of pancreatic cancer, with a focus on the mechanisms that drive recruitment and activation of immune cells at the tumor site, and our current understanding of the function of the immune cell types at the tumor. Recent clinical and preclinical data are reviewed, detailing the involvement of the immune response in pancreatitis and pancreatic cancer, including the role of specific cytokines and implications for disease outcome. Acute pancreatitis is characterized by a predominantly innate immune response, while chronic pancreatitis elicits an immune response that involves both innate and adaptive immune cells, and often results in profound systemic immune-suppression. Pancreatic adenocarcinoma is characterized by marked immune dysfunction driven by immunosuppressive cell types, tumor-promoting immune cells, and defective or absent inflammatory cells. Recent studies reveal that immune cells interact with cancer stem cells and tumor stromal cells, and these interactions have an impact on development and progression of pancreatic ductal adenocarcinoma (PDAC). Finally, current PDAC therapies are reviewed and the potential for harnessing the actions of the immune response to assist in targeting pancreatic cancer using immunotherapy is discussed.

Graft-derived CCL2 increases graft injury during antibody-mediated rejection of cardiac allografts

The pathogenic role of macrophages in antibody-mediated rejection (AMR) remains unclear. Monocyte chemoattractant protein-1 (MCP-1/CCL2) is a potent chemotactic factor for monocytes and macrophages. The current studies used a murine model of AMR to investigate the role of graft-derived CCL2 in AMR and how macrophages may participate in antibody-mediated allograft injury. B6.CCR5−/−/CD8−/− recipients rejected MHC-mismatched WT A/J allografts with high donor-reactive antibody titers and diffuse C4d deposition in the large vessels and myocardial capillaries, features consistent with AMR. In contrast, A/J.CCL2−/− allografts induced low donor-reactive antibody titers and C4d deposition at Day 7 posttransplant. Decreased donor-reactive CD4 T cells producing interferon gamma were induced in response to A/J.CCL2−/− versus WT allografts. Consequently, A/J.CCL2−/− allograft survival was modestly but significantly longer than A/J allografts. Macrophages purified from WT allografts expressed high levels of IL-1β and IL-12p40 and this expression and the numbers of classically activated macrophages were markedly reduced in CCL2-deficient allografts on Day 7. The results indicate that allograft-derived CCL2 plays an important role in directing classically activated macrophages into allografts during AMR and that macrophages are important contributors to the inflammatory environment mediating graft tissue injury in this pathology, suggesting CCL2 as a therapeutic target for AMR.

Armed oncolytic virus enhances immune functions of chimeric antigen receptor-modified T cells in solid tumors

The clinical efficacy of chimeric antigen receptor (CAR)-redirected T cells remains marginal in solid tumors compared with leukemias. Failures have been attributed to insufficient T-cell migration and to the highly immunosuppressive milieu of solid tumors. To overcome these obstacles, we have combined CAR-T cells with an oncolytic virus armed with the chemokine RANTES and the cytokine IL15, reasoning that the modified oncolytic virus will both have a direct lytic effect on infected malignant cells and facilitate migration and survival of CAR-T cells. Using neuroblastoma as a tumor model, we found that the adenovirus Ad5Δ24 exerted a potent, dose-dependent, cytotoxic effect on tumor cells, whereas CAR-T cells specific for the tumor antigen GD2 (GD2.CAR-T cells) were not damaged. When used in combination, Ad5Δ24 directly accelerated the caspase pathways in tumor cells exposed to CAR-T cells, whereas the intratumoral release of both RANTES and IL15 attracted CAR-T cells and promoted their local survival, respectively, increasing the overall survival of tumor-bearing mice. These preclinical data support the use of this innovative biologic platform of immunotherapy for solid tumors. Cancer Res; 74(18); 5195-205. ©2014 AACR.

The role of chemoattractant receptors in shaping the tumor microenvironment

Chemoattractant receptors are a family of seven transmembrane G protein coupled receptors (GPCRs) initially found to mediate the chemotaxis and activation of immune cells. During the past decades, the functions of these GPCRs have been discovered to not only regulate leukocyte trafficking and promote immune responses, but also play important roles in homeostasis, development, angiogenesis, and tumor progression. Accumulating evidence indicates that chemoattractant GPCRs and their ligands promote the progression of malignant tumors based on their capacity to orchestrate the infiltration of the tumor microenvironment by immune cells, endothelial cells, fibroblasts, and mesenchymal cells. This facilitates the interaction of tumor cells with host cells, tumor cells with tumor cells, and host cells with host cells to provide a basis for the expansion of established tumors and development of distant metastasis. In addition, many malignant tumors of the nonhematopoietic origin express multiple chemoattractant GPCRs that increase the invasiveness and metastasis of tumor cells. Therefore, GPCRs and their ligands constitute targets for the development of novel antitumor therapeutics.

The fatal alliance of cancer and T cells: How pancreatic tumor cells gather immunosuppressive T cells

Immune evasion is a hallmark of cancer. We recently identified the adhesion molecule L1CAM as biomarker of pancreatic ductal adenocarcinoma (PDAC) associated with poor prognosis. During inflammation-associated carcinogenesis, L1CAM drives the enrichment of highly immunosuppressive CD4⁺CD25^-CD69⁺ T cells. Thus, L1CAM may serve as a target in immunomodulatory therapy for PDAC.

Stromal reengineering to treat pancreas cancer

Pancreatic ductal adenocarcinoma co-opts multiple cellular and extracellular mechanisms to create a complex cancer organ with an unusual proclivity for metastasis and resistance to therapy. Cell-autonomous events are essential for the initiation and maintenance of pancreatic ductal adenocarcinoma, but recent studies have implicated critical non-cell autonomous processes within the robust desmoplastic stroma that promote disease pathogenesis and resistance. Thus, non-malignant cells and associated factors are culprits in tumor growth, immunosuppression and invasion. However, even this increasing awareness of non-cell autonomous contributions to disease progression is tempered by the conflicting roles stromal elements can play. A greater understanding of stromal complexity and complicity has been aided in part by studies in highly faithful genetically engineered mouse models of pancreatic ductal adenocarcinoma. Insights gleaned from such studies are spurring the development of therapies designed to reengineer the pancreas cancer stroma and render it permissive to agents targeting cell-autonomous events or to reinstate immunosurveillance. Integrating conventional and immunological treatments in the context of stromal targeting may provide the key to a durable clinical impact on this formidable disease.

CCL5-403, CCR5-59029, and Delta32 polymorphisms and cancer risk: a meta-analysis based on 20,625 subjects

Associations between CCL5-403, CCR5-59029, and Delta32 polymorphisms and cancer risk are inconclusive. To derive a more precise estimation of the association, we performed a meta-analysis by searching PubMed, EMBASE, Google scholar, and WanFang databases. A total of 20 eligible articles with 39 studies were included. Of those studies, there were 21 studies for CCR5-Delta32 polymorphism, 9 studies for CCR5-59029 polymorphism, and 9 studies for CCL5-403 polymorphism. Combined analysis revealed no associations between these polymorphisms and cancer risk. However, subgroup analysis by ethnicity suggested that CCR5-59029 polymorphism was associated with the risk of cancer among Asian populations (A vs. G: odds ratio (OR)=1.36, 95 % confidence interval (CI) 1.13-1.65, P H=0.27; AA vs. GG: OR=2.07, 95 % CI 1.37-3.12, P H=0.17; GA+AA vs. GG: OR=1.35, 95 % CI 1.03-1.77, P H=0.92; AA vs. GA+GG: OR=1.98, 95 % CI 1.01-3.88, P H=0.08), but not among Caucasian populations. CCL5-403 polymorphism was associated with the risk of cancer among African populations (A vs. G: OR=0.68, 95 % CI 0.55-0.83, P H=0.14; AA vs. GG: OR=0.51, 95 % CI 0.33-0.77, P H=0.52; AG vs. GG: OR=0.58, 95 % CI 0.42-0.80, P H=0.14; AG+AA vs. GG: OR=0.56, 95 % CI 0.41-0.75, P H=0.13), but not among Caucasian populations and Asian populations. Overall, this meta-analysis indicated that CCR5-Delta32 was not associated with the risk of cancer. CCR5-59029 polymorphism contributed to cancer risk among Asian populations, and CCL5-403 polymorphism was associated with the decreased risk of cancer among African populations.

Pancreatic ductal adenocarcinoma: a review of immunologic aspects

With the continued failures of both early diagnosis and treatment options for pancreatic cancer, it is now time to comprehensively evaluate the role of the immune system on the development and progression of pancreatic cancer. It is important to develop strategies that harness the molecules and cells of the immune system to treat this disease. This review will focus primarily on the role of immune cells in the development and progression of pancreatic ductal adenocarcinoma and to evaluate what is known about the interaction of immune cells with the tumor microenvironment and their role in tumor growth and metastasis. We will conclude with a brief discussion of therapy for pancreatic cancer and the potential role for immunotherapy. We hypothesize that the role of the immune system in tumor development and progression is tissue specific. Our hope is that better understanding of this process will lead to better treatments for this devastating disease.

Pancreatic cancer, inflammation, and microbiome

Pancreatic cancer is one of the most lethal cancers worldwide. No effective screening methods exist, and available treatment modalities do not effectively treat the disease. Inflammatory conditions such as pancreatitis represent a well-known risk factor for pancreatic cancer development. Yet only in the past 2 decades has pancreatic cancer been recognized as an inflammation-driven cancer, and the precise mechanisms underlying the pathogenic role of inflammation are beginning to be explored in detail. A substantial amount of preclinical and clinical evidence suggests that bacteria are likely to influence this process by activating immune receptors and perpetuating cancer-associated inflammation. The recent explosion of investigations of the human microbiome have highlighted how perturbations of commensal bacterial populations can promote inflammation and promote disease processes, including carcinogenesis. The elucidation of the interplay between inflammation and microbiome in the context of pancreatic carcinogenesis will provide novel targets for intervention to prevent and treat pancreatic cancer more efficiently. Further studies toward this direction are urgently needed.

Synthetic control of mammalian-cell motility by engineering chemotaxis to an orthogonal bioinert chemical signal

Directed migration of diverse cell types plays a critical role in biological processes ranging from development and morphogenesis to immune response, wound healing, and regeneration. However, techniques to direct, manipulate, and study cell migration in vitro and in vivo in a specific and facile manner are currently limited. We conceived of a strategy to achieve direct control over cell migration to arbitrary user-defined locations, independent of native chemotaxis receptors. Here, we show that genetic modification of cells with an engineered G protein-coupled receptor allows us to redirect their migration to a bioinert drug-like small molecule, clozapine-N-oxide (CNO). The engineered receptor and small-molecule ligand form an orthogonal pair: The receptor does not respond to native ligands, and the inert drug does not bind to native cells. CNO-responsive migration can be engineered into a variety of cell types, including neutrophils, T lymphocytes, keratinocytes, and endothelial cells. The engineered cells migrate up a gradient of the drug CNO and transmigrate through endothelial monolayers. Finally, we demonstrate that T lymphocytes modified with the engineered receptor can specifically migrate in vivo to CNO-releasing beads implanted in a live mouse. This technology provides a generalizable genetic tool to systematically perturb and control cell migration both in vitro and in vivo. In the future, this type of migration control could be a valuable module for engineering therapeutic cellular devices.

L1CAM promotes enrichment of immunosuppressive T cells in human pancreatic cancer correlating with malignant progression

Regulatory T cell (T-reg) enrichment in the tumor microenvironment is regarded as an important mechanism of tumor immune escape. Hence, the presence of T-regs in highly malignant pancreatic ductal adenocarcinoma (PDAC) is correlated with short survival. Likewise, the adhesion molecule L1CAM is upregulated during PDAC progression in the pancreatic ductal epithelium also being associated with poor prognosis. To investigate whether L1CAM contributes to enrichment of T-regs in PDAC, human CD4(+)CD25(+)CD127(-)CD49d(-) T-regs and CD4(+)CD25(-) T-effector cells (T-effs) were isolated by magnetic bead separation from blood of healthy donors. Their phenotype and functional behavior were analyzed in dependence on human premalignant (H6c7) or malignant (Panc1) pancreatic ductal epithelial cells, either exhibiting or lacking L1CAM expression. T cells derived from blood and tumors of PDAC patients were analyzed by flow cytometry and findings were correlated with clinical parameters. Predominantly T-regs but not T-effs showed an increased migration on L1CAM expressing H6c7 and Panc1 cells. Whereas proliferation of T-regs did not change in the presence of L1CAM, T-effs proliferated less, exhibited a decreased CD25 expression and an increased expression of CD69. Moreover, these T-effs exhibited a regulatory phenotype as they inhibited proliferation of autologous T cells. Accordingly, CD4(+)CD25(-)CD69(+) T cells were highly abundant in PDAC tissues compared to blood being associated with nodal invasion and higher grading in PDAC patients. Overall, these data point to an important role of L1CAM in the enrichment of immunosuppressive T cells in particular of a CD4(+)CD25(-)CD69(+)-phenotype in PDAC providing a novel mechanism of tumor immune escape which contributes to tumor progression.

Concomitant gemcitabine therapy negatively affects DC vaccine-induced CD8(+) T-cell and B-cell responses but improves clinical efficacy in a murine pancreatic carcinoma model

BACKGROUND

Multiple studies have shown that dendritic cell (DC)-based vaccines can induce antitumor immunity. Previously, we reported that gemcitabine enhances the efficacy of DC vaccination in a mouse model of pancreatic carcinoma. The present study aimed at investigating the influence of gemcitabine on vaccine-induced anti-tumoral immune responses in a syngeneic pancreatic cancer model.

MATERIALS AND METHODS

Subcutaneous or orthotopic pancreatic tumors were induced in C57BL/6 mice using Panc02 cells expressing the model antigen OVA. Bone marrow-derived DC were loaded with soluble OVA protein (OVA-DC). Animals received gemcitabine twice weekly. OVA-specific CD8(+) T-cells and antibody titers were monitored by FACS analysis and ELISA, respectively.

RESULTS

Gemcitabine enhanced clinical efficacy of the OVA-DC vaccine. Interestingly, gemcitabine significantly suppressed the vaccine-induced frequency of antigen-specific CD8(+) T-cells and antibody titers. DC migration to draining lymph nodes and antigen cross-presentation were unaffected. Despite reduced numbers of tumor-reactive T-cells in peripheral blood, in vivo cytotoxicity assays revealed that cytotoxic T-cell (CTL)-mediated killing was preserved. In vitro assays revealed sensitization of tumor cells to CTL-mediated lysis by gemcitabine. In addition, gemcitabine facilitated recruitment of CD8(+) T-cells into tumors in DC-vaccinated mice. T- and B-cell suppression by gemcitabine could be avoided by starting chemotherapy after two cycles of DC vaccination.

CONCLUSIONS

Gemcitabine enhances therapeutic efficacy of DC vaccination despite its negative influence on vaccine-induced T-cell proliferation. Quantitative analysis of tumor-reactive T-cells in peripheral blood may thus not predict vaccination success in the setting of concomitant chemotherapy.

Maraviroc reduces the regulatory T-cell frequency in antiretroviral-naive HIV-infected subjects

BACKGROUND

Maraviroc is the first antiretroviral (ART) drug to target a human protein, the CCR5 coreceptor; however, the mechanisms of maraviroc-associated immunomodulation in human immunodeficiency virus (HIV)-infected subjects remain to be elucidated. Regulatory T cells (Tregs) play a key role in HIV-associated immunopathology and are susceptible to maraviroc-mediated CCR5 blockade. Our aim was to evaluate the effect of maraviroc on Tregs.

METHODS

We compared the effect of maraviroc-containing or -sparing combination ART (cART) on Tregs in ART-naive, HIV-infected subjects. Tregs were characterized as CD4(+)CD25(hi)FoxP3(+) on day 0, 8, and 30. Additional analysis on week 48 was performed in a subgroup of patients. The potential reduction in the frequency of Tregs among maraviroc-treated peripheral blood mononuclear cells (PBMCs) was also tested in vitro. The suppressive function of Tregs was also analyzed in maraviroc-treated Tregs.

RESULTS

We found that maraviroc significantly reduced the Treg frequency in both the short term and 1 year after treatment initiation. In vitro experiments showed a dose-dependent reduction in the Treg frequency after treatment of PBMCs with maraviroc, although their in vitro suppressive function was not altered.

CONCLUSIONS

These findings partially explain maraviroc-associated immunomodulatory effects and open new therapeutic expectations for the development of Treg-depleting immunotherapies.

Fallen angels or risen apes? A tale of the intricate complexities of imbalanced immune responses in the pathogenesis and progression of immune-mediated and viral cancers

Excessive immune responses directed against foreign pathogens, self-antigens, or commensal microflora can cause cancer establishment and progression if the execution of tight immuno-regulatory mechanisms fails. On the other hand, induction of potent tumor antigen-specific immune responses together with stimulation of the innate immune system is a pre-requisite for effective anti-tumor immunity, and if suppressed by the strong immuno-regulatory mechanisms can lead to cancer progression. Therefore, it is crucial that the inevitable co-existence of these fundamental, yet conflicting roles of immune-regulatory cells is carefully streamlined as imbalances can be detrimental to the host. Infection with chronic persistent viruses is characterized by severe immune dysfunction resulting in T cell exhaustion and sometimes deletion of antigen-specific T cells. More often, this is due to increased immuno-regulatory processes, which are triggered to down-regulate immune responses and limit immunopathology. However, such heightened levels of immune disruption cause a concomitant loss of tumor immune-surveillance and create a permissive microenvironment for cancer establishment and progression, as demonstrated by increased incidences of cancer in immunosuppressed hosts. Paradoxically, while some cancers arise as a consequence of increased immuno-regulatory mechanisms that inhibit protective immune responses and impinge on tumor surveillance, other cancers arise due to impaired immuno-regulatory mechanisms and failure to limit pathogenic inflammatory responses. This intricate complexity, where immuno-regulatory cells can be beneficial in certain immune settings but detrimental in other settings underscores the need for carefully formulated interventions to equilibrate the balance between immuno-stimulatory and immuno-regulatory processes.

Modification of the tumor microenvironment as a novel target of renal cell carcinoma therapeutics

To move forward with immunotherapy, it is important to understand how the tumor microenvironment generates systemic immunosuppression in patients with renal cell carcinoma (RCC) as well as in patients with other types of solid tumors. Even though antigen discovery in RCC has lagged behind melanoma, recent clinical trials have finally authenticated that RCC is susceptible to vaccine-based therapy. Furthermore, judicious coadministration of cytokines and chemotherapy can potentiate therapeutic responses to vaccine in RCC and prolong survival, as has already proved possible for melanoma. Although high-dose interleukin 2 immunotherapy has been superseded as first-line therapy for RCC by promiscuous receptor tyrosine kinase inhibitors (rTKIs) such as sunitinib, sunitinib itself is a potent immunoadjunct in animal tumor models. A reasonable therapeutic goal is to unite antiangiogenic strategies with immunotherapy as first-line therapy for RCC. This strategy is equally appropriate for testing in all solid tumors in which the microenvironment generates immunosuppression. A common element of RCC and pancreatic, colon, breast, and other solid tumors is large numbers of circulating myeloid-derived suppressor cells (MDSCs), and because MDSCs elicit regulatory T cells rather than vice versa, gaining control over MDSCs is an important initial step in any immunotherapy. Although rTKIs like sunitinib have a remarkable capacity to deplete MDSCs and restore normal T-cell function in peripheral body compartments such as the bloodstream and the spleen, such rTKIs are effective only against MDSCs, which are engaged in phospho-STAT3-dependent programming (pSTAT3+). Unfortunately, rTKI-resistant pSTAT3- MDSCs are especially apt to arise within the tumor microenvironment itself, necessitating strategies that do not rely exclusively on STAT3 disruption. The most utilitarian strategy to gain control of both pSTAT3+ and pSTAT3- MDSCs may be to exploit the natural differentiation pathway, which permits MDSCs to mature into tumoricidal macrophages (TM1) via such stimuli as Toll-like receptor agonists, interferon γ, and CD40 ligation. Overall, this review highlights the mechanisms of immune suppression used by the different regulatory cell types operative in RCC as well as other tumors. It also describes the different therapeutic strategies to overcome the suppressive nature of the tumor microenvironment.

CC chemokine receptor 5: the interface of host immunity and cancer

Solid tumors are embedded in a stromal microenvironment consisting of immune cells, such as macrophages and lymphocytes, as well as nonimmune cells, such as endothelial cells and fibroblasts. Chemokines are a type of small secreted chemotactic cytokine and together with their receptors play key roles in the immune defense. Critically, they regulate cancer cellular migration and also contribute to their proliferation and survival. The CCR5 chemokine receptor is involved in leucocytes chemotaxis to sites of inflammation and plays an important role in the macrophages, T cells, and monocytes recruitment. Additionally, CCR5 may have an indirect effect on cancer progression by controlling the antitumor immune response, since it has been demonstrated that its expression could promote tumor growth and contribute to tumor metastasis, in different types of malignant tumors. Furthermore, it was demonstrated that a CCR5 antagonist may inhibit tumor growth, consisting of a possible therapeutic target. In this context, the present review focuses on the establishment of CCR5 within the interface of host immunity, tumor microenvironment, and its potential as a targeting to immunotherapy.

A requirement of dendritic cell-derived interleukin-27 for the tumor infiltration of regulatory T cells

Tregs (Foxp3⁺CD4⁺) are enriched in tumors to foster a tolerant microenvironment that inhibits antitumor immune response. IL-27 is reported to regulate the development and function of Tregs in vitro and in vivo; however, the effects of endogenous IL-27 on Tregs in the tumor microenvironment remain elusive. We demonstrated that in the absence of DC-derived IL-27, Tregs were decreased significantly in transplanted B16 melanoma, transplanted EL-4 lymphoma, and MCA-induced fibrosarcoma by using IL-27p28 conditional KO mice. Further studies revealed that IL-27 promoted the expression of CCL22, which is established to mediate the recruitment of peripheral Tregs into tumors. Tumor-associated DCs were identified as the major source of CCL22 in tumor sites, and IL-27 could induce CCL22 expression in an IL-27R-dependent manner. Intratumoral reconstitution of rmCCL22 or rmIL-27, but not rmIL-27p28, significantly restored the tumor infiltration of Tregs in IL-27p28 KO mice. Correlated with a decreased number of Tregs, tumor-infiltrating CD4 T cells were found to produce much more IFN-γ in IL-27p28 KO mice, which highlighted the physiological importance of Tregs in suppressing an antitumor immune response. Overall, our results identified a novel mechanism of action of IL-27 on Tregs in the context of cancers.

Suppression of Tregs by anti-glucocorticoid induced TNF receptor antibody enhances the antitumor immunity of interferon-α gene therapy for pancreatic cancer

We have reported that interferon (IFN)-α can attack cancer cells by multiple antitumor mechanisms including the induction of direct cancer cell death and the enhancement of an immune response in several pancreatic cancer models. However, an immunotolerant microenvironment in the tumors is often responsible for the failure of the cancer immunotherapy. Here we examined whether the suppression of regulatory T cells (Tregs) within tumors can enhance an antitumor immunity induced by an intratumoral IFN-α gene transfer. First we showed that an intraperitoneal administration of an agonistic anti-glucocorticoid induced TNF receptor (GITR) monoclonal antibody (mAb), which is reported to suppress the function of Tregs, significantly inhibited subcutaneous tumor growth in a murine pancreatic cancer model. The anti-GITR mAb was then combined with the intratumoral injection of the IFN-α-adenovirus vector. The treatment with the antibody synergistically augmented the antitumor effect of IFN-α gene therapy not only in the vector-injected tumors but also in the vector-uninjected tumors. Immunostaining showed that the anti-GITR mAb decreased Foxp3⁺ cells infiltrating in the tumors, while the intratumoral IFN-α gene transfer increased CD4⁺ and CD8⁺ T cells in the tumors. Therefore, the combination therapy strongly inclined the immune balance of the tumor microenvironment in an antitumor direction, leading to a marked systemic antitumor effect. The CCR5 expression on Tregs was downregulated in the antibody-treated mice, which may explain the decrease of tumor-infiltrating Tregs. The combination of Treg-suppression by GITR mAb and the tumor immunity induction by IFN-α gene therapy could be a promising therapeutic strategy for pancreatic cancer.

The chemokine system, and its CCR5 and CXCR4 receptors, as potential targets for personalized therapy in cancer

Chemokines and their receptors regulate the trafficking of leukocytes in hematopoiesis and inflammation, and thus are fundamental to the immune integrity of the host. In parallel, members of the chemokine system exert a large variety of functions that dictate processes of cancer development and progression. Chemokines can act as pro-tumoral or anti-tumoral regulators of malignancy by affecting cells of the tumor microenvironment (leukocytes, endothelial cells, fibroblasts) and the tumor cells themselves (migration, invasion, proliferation, resistance to chemotherapy). Several of the chemokines are generally skewed towards the cancer-promoting direction, including primarily the CCR5-CCL5 (RANTES) and the CXCR4-CXCL12 (SDF-1) axes. This review provides a general view of chemokines and chemokine receptors as regulators of malignancy, describing their multi-faceted activities in cancer. The tumor-promoting activities of the CCR5-CCL5 and CXCR4-CXCL12 pathways are enlightened, emphasizing their potential use as targets for personalized therapy. Indeed, novel blockers of chemokines and their receptors are constantly emerging, and two chemokine receptor inhibitors were recently approved for clinical use: Maraviroc for CCR5 and Plerixafor for CXCR4. The review addresses ongoing pre-clinical and clinical trials using these modalities and others in cancer. Then, challenges and opportunities of personalized therapy directed against chemokines and their receptors in malignancy are discussed, demonstrating that such novel personalized cancer therapies hold many challenges, but also offer hope for cancer patients.

Low-molecular-mass secretome profiling identifies C-C motif chemokine 5 as a potential plasma biomarker and therapeutic target for nasopharyngeal carcinoma

Cancer cell secretome profiling has been shown to be a promising strategy for identifying potential body fluid-accessible cancer biomarkers and therapeutic targets. However, very few reports have investigated low-molecular-mass (LMr) proteins (<15kDa) in the cancer cell secretome. In the present study, we applied tricine-SDS-gel-assisted fractionation in conjunction with LC-MS/MS to systemically identify LMr proteins in the secretomes of three nasopharyngeal carcinoma (NPC) cell lines. We examined two NPC tissue transcriptome datasets to identify LMr genes/proteins that are highly upregulated in NPC tissues and also secreted/released from NPC cells, obtaining 35 candidates. We verified the overexpression of four targets (LSM2, SUMO1, RPL22, and CCL5) in NPC tissues by immunohistochemistry and demonstrated elevated plasma levels of two targets (S100A2 and CCL5) in NPC patients by ELISA. Notably, plasma CCL5 showed good power (AUC 0.801) for discriminating NPC patients from healthy controls. Additionally, functional assays revealed that CCL5 promoted migration of NPC cells, an effect that was effectively blocked by CCL5-neutralizing antibodies and maraviroc, a CCL5 receptor antagonist. Collectively, our data indicate the feasibility of the tricine-SDS-gel/LC-MS/MS approach for efficient identification of LMr proteins from cancer cell secretomes, and suggest that CCL5 is a potential plasma biomarker and therapeutic target for NPC.

BIOLOGICAL SIGNIFICANCE

Both LMr proteome and cancer cell secretome represent attractive reservoirs for discovery of cancer biomarkers and therapeutic targets. Our present study provides evidence for the practicality of using the tricine-SDS-PAGE/LC-MS/MS approach for in-depth identification of LMr proteins from the NPC cell secretomes, leading to the discovery of CCL5 as a potential plasma biomarker and therapeutic target for NPC. We believe that the modified GeLC-MS/MS approach used here can be further applied to explore extremely low-abundance, extracellular LMr proteins with important biological functions in other cell lines and biospecimens.

Regulatory T cells in nonlymphoid tissues

Both Foxp3(+)CD4(+) regulatory T cells (Treg cells) and local immune responses in nonlymphoid tissues have long been recognized as important elements of a well-orchestrated immune system, but only recently have these two fields of study begun to intersect. There is growing evidence that Treg cells are present in various nonlymphoid tissues in health and disease, that they have a unique phenotype and that their functions go beyond the classical modulation of immune responses. Thus, tissue Treg cells might add yet another level to classification of the Treg cell compartment into functional and/or phenotypic subtypes. In this Review, we summarize recent findings in this new field, discussing knowns and unknowns about the origin, phenotype, function and memory of nonlymphoid tissue-resident Treg cells.

STAT3 in epithelial cells regulates inflammation and tumor progression to malignant state in colon

Chronic inflammation is an important risk factor for the development of colorectal cancer; however, the mechanism of tumorigenesis especially tumor progression to malignancy in the inflamed colon is still unclear. Our study shows that epithelial signal transducer and activator of transcription 3 (STAT3), persistently activated in inflamed colon, is not required for inflammation-induced epithelial overproliferation and the development of early-stage tumors; however, it is essential for tumor progression to advanced malignancy. We found that one of the mechanisms that epithelial STAT3 regulates in tumor progression might be to modify leukocytic infiltration in the large intestine. Activation of epithelial STAT3 promotes the infiltration of the CD8+ lymphocyte population but inhibits the recruitment of regulatory T (Treg) lymphocytes. The loss of Stat3 in epithelial cells promoted the expression of cytokines/chemokines including CCL19, CCL28, and RANTES, which are known to be able to recruit Treg lymphocytes. Linked to these changes was the pathway mediated by sphingosine 1-phosphate receptor 1 and sphingosine 1-phosphate kinases, which is activated in colonic epithelial cells in inflamed colon with functional STAT3 but not in epithelial cells deleted of STAT3. Our data suggest that epithelial STAT3 plays a critical role in inflammation-induced tumor progression through regulation of leukocytic recruitment especially the infiltration of Treg cells in the large intestine.

CXCR3, a double-edged sword in tumor progression and angiogenesis

CXC chemokines are involved in chemotaxis, regulation of cell growth, induction of apoptosis and modulation of angiostatic effects. CXCL9, CXCL10, CXCL11, CXCL4 and its variant CXCL4L1 are members of the CXC chemokine family, which bind to the CXCR3 receptor to exert their biological effects. These chemokines are associated with a variety of human diseases including chronic inflammation, immune dysfunction, cancer and metastasis. In this review, we focus on accumulating evidence demonstrating the pivotal role of CXCR3 in tumor progression. Its effects are mediated directly in tumor cells or indirectly through the regulation of angiogenesis and tumor immunity. Understanding the emerging role of CXCR3 and its signaling mechanisms further validates this receptor as a biomarker and therapeutic target for tumor progression and tumor angiogenesis.

Specific recruitment of γδ regulatory T cells in human breast cancer

Understanding the role of different subtypes of tumor-infiltrating lymphocytes (TIL) in the immunosuppressive tumor microenvironment is essential for improving cancer treatment. Enriched γδ1 T-cell populations in TILs suppress T-cell responses and dendritic cell maturation in breast cancer, where their presence is correlated negatively with clinical outcomes. However, mechanism(s) that explain the increase in this class of regulatory T cells (γδ Treg) in patients with breast cancer have yet to be elucidated. In this study, we show that IP-10 secreted by breast cancer cells attracted γδ Tregs. Using neutralizing antibodies against chemokines secreted by breast cancer cells, we found that IP-10 was the only functional chemokine that causes γδ Tregs to migrate toward breast cancer cells. In a humanized NOD-scid IL-2Rγ(null) (NSG) mouse model, human breast cancer cells attracted γδ Tregs as revealed by a live cell imaging system. IP-10 neutralization in vivo inhibited migration and trafficking of γδ Tregs into breast tumor sites, enhancing tumor immunity mediated by tumor-specific T cells. Together, our studies show how γδ Tregs accumulate in breast tumors, providing a rationale for their immunologic targeting to relieve immunosuppression in the tumor microenvironment.

Natural and induced T regulatory cells in cancer

CD4+Foxp3+ T regulatory (Treg) cells control many facets of immune responses ranging from autoimmune diseases, to inflammatory conditions, and cancer in an attempt to maintain immune homeostasis. Natural Treg (nTreg) cells develop in the thymus and constitute a critical arm of active mechanisms of peripheral tolerance particularly to self antigens. A growing body of knowledge now supports the existence of induced Treg (iTreg) cells which may derive from a population of conventional CD4+ T cells. The fork-head transcription factor (Foxp3) typically is expressed by natural CD4+ Treg cells, and thus serves as a marker to definitively identify these cells. On the contrary, there is less consensus on what constitutes iTreg cells as their precise definition has been somewhat elusive. This is in part due to their distinct phenotypes which are shaped by exposure to certain inflammatory or "assault" signals stemming from the underlying immune disorder. The "policing" activity of Treg cells tends to be uni-directional in several pathological conditions. On one end of the spectrum, Treg cell suppressive activity is beneficial by curtailing T cell response against self-antigens and allergens thus preventing autoimmune diseases and allergies. On the other end however, their inhibitory roles in limiting immune response against pseudo-self antigens as in tumors often culminates into negative outcomes. In this review, we focus on this latter aspect of Treg cell immunobiology by highlighting the involvement of nTreg cells in various animal models and human tumors. We further discuss iTreg cells, relationship with their natural counterpart, and potential co-operation between the two in modulating immune response against tumors. Lastly, we discuss studies focusing on these cells as targets for improving anti-tumor immunity.

Home sweet home: the tumor microenvironment as a haven for regulatory T cells

CD4⁺Foxp3⁺ regulatory T cells (T_regs) have a fundamental role in maintaining immune balance by preventing autoreactivity and immune-mediated pathology. However this role of T_regs extends to suppression of anti-tumor immune responses and remains a major obstacle in the development of anti-cancer vaccines and immunotherapies. This feature of T_reg activity is exacerbated by the discovery that T_reg frequencies are not only elevated in the blood of cancer patients, but are also significantly enriched within tumors in comparison to other sites. These observations have sparked off the quest to understand the processes through which T_regs become elevated in cancer-bearing hosts and to identify the specific mechanisms leading to their accumulation within the tumor microenvironment. This manuscript reviews the evidence for specific mechanisms of intra-tumoral T_reg enrichment and will discuss how this information may be utilized for the purpose of manipulating the balance of tumor-infiltrating T cells in favor of anti-tumor effector cells.

The immune network in pancreatic cancer development and progression

The presence of stromal desmoplasia is a hallmark of spontaneous pancreatic ductal adenocarcinoma, forming a unique microenvironment that comprises many cell types. Only recently, the immune system has entered the pathophysiology of pancreatic ductal adenocarcinoma development. Tumor cells in the pancreas seem to dysbalance the immune system, thus facilitating spontaneous cancer development. This review will try to assemble all relevant data to demonstrate the implications of the immune network on spontaneous cancer development.

Natural and induced T regulatory cells in cancer

CD4+Foxp3+ T regulatory (Treg) cells control many facets of immune responses ranging from autoimmune diseases, to inflammatory conditions, and cancer in an attempt to maintain immune homeostasis. Natural Treg (nTreg) cells develop in the thymus and constitute a critical arm of active mechanisms of peripheral tolerance particularly to self antigens. A growing body of knowledge now supports the existence of induced Treg (iTreg) cells which may derive from a population of conventional CD4+ T cells. The fork-head transcription factor (Foxp3) typically is expressed by natural CD4+ Treg cells, and thus serves as a marker to definitively identify these cells. On the contrary, there is less consensus on what constitutes iTreg cells as their precise definition has been somewhat elusive. This is in part due to their distinct phenotypes which are shaped by exposure to certain inflammatory or “assault” signals stemming from the underlying immune disorder. The “policing” activity of Treg cells tends to be uni-directional in several pathological conditions. On one end of the spectrum, Treg cell suppressive activity is beneficial by curtailing T cell response against self-antigens and allergens thus preventing autoimmune diseases and allergies. On the other end however, their inhibitory roles in limiting immune response against pseudo-self antigens as in tumors often culminates into negative outcomes. In this review, we focus on this latter aspect of Treg cell immunobiology by highlighting the involvement of nTreg cells in various animal models and human tumors. We further discuss iTreg cells, relationship with their natural counterpart, and potential co-operation between the two in modulating immune response against tumors. Lastly, we discuss studies focusing on these cells as targets for improving anti-tumor immunity.

Myeloid-derived suppressor cells in cancer: recent progress and prospects

Immunosuppressive cells, mainly myeloid-derived suppressor cells (MDSCs) and T regulatory cells, downregulate antitumour immunity and cancer immunotherapy. MDSCs are a heterogeneous group of immature myeloid cells that negatively regulate the immune responses during tumour progression, inflammation and infection. Whilst there have been extensive laboratory investigations aimed at characterising the MDSC subsets in cancer, there remains a significant gap in our understanding of their phenotypical and functional heterogeneity. In this article, we review data concerning the phenotypical and functional role of MDSCs in cancers. Importantly, we analyse the value of MDSCs as a prognostic factor in various clinical settings and the possible therapeutic approaches towards elimination of their immunosuppressive activity and enhancement of beneficial antitumour immune responses. MDSCs promote tumour immune evasion by inhibiting T-cell responses, as well as by supporting tumour progression. Accumulation of MDSCs is associated with the progression of human cancers, and their elimination was shown to improve anti-tumour immune responses. Phenotypical characterisation of MDSCs has been poorly investigated in many human cancers and lacks comprehensive clinicopathological correlation data. Although the need for effective therapeutic agents to eliminate the MDSC suppressive effect is immense, their role has been examined only in a few clinical settings.

Adenosine as an endogenous immunoregulator in cancer pathogenesis: where to go?

Cancer is a chronic disease and its pathogenesis is well correlated with infection and inflammation. Adenosine is a purine nucleoside, which is produced under metabolic stress like hypoxic conditions. Acute or chronic inflammatory conditions lead to the release of precursor adenine nucleotides (adenosine triphosphate (ATP), adenosien diphosphate (ADP) and adenosine monophosphate (AMP)) from cells, which are extracellularly catabolized into adenosine by extracellular ectonucleotidases, i.e., CD39 or nucleoside triphosphate dephosphorylase (NTPD) and CD73 or 5'-ectonucleotidase. It is now well-known that adenosine is secreted by cancer as well as immune cells during tumor pathogenesis under metabolic stress or hypoxia. Once adenosine is released into the extracellular environment, it exerts various immunomodulatory effects via adenosine receptors (A1, A2A, A2B, and A3) expressed on various immune cells (i.e., macrophages, myeloid-derived suppressor cells (MDSCs), natural killer (NK) cells, dendritic cells (DCs), T cells, regulatory T cell (Tregs), etc.), which play very important roles in the pathogenesis of cancer. This review is intended to summarize the role of inflammation and adenosine in the immunopathogenesis of tumor along with regulation of tumor-specific immune response and its modulation as an adjunct approach to tumor immunotherapy.

Expanding roles for CD4 T cells and their subpopulations in tumor immunity and therapy

The importance of CD4 T cells in orchestrating the immune system and their role in inducing effective T cell-mediated therapies for the treatment of patients with select established malignancies are undisputable. Through a complex and balanced array of direct and indirect mechanisms of cellular activation and regulation, this functionally diverse family of lymphocytes can potentially promote tumor eradication, long-term tumor immunity, and aid in establishing and/or rebalancing immune cell homeostasis through interaction with other immune cell populations within the highly dynamic tumor environment. However, recent studies have uncovered additional functions and roles for CD4 T cells, some of which are independent of other lymphocytes, that can not only influence and contribute to tumor immunity but paradoxically promote tumor growth and progression. Here, we review the recent advances in our understanding of the various CD4 T cell lineages and their signature cytokines in disease progression and/or regression. We discuss their direct and indirect mechanistic interplay among themselves and with other responding cells of the antitumor response, their potential roles and abilities for "plasticity" and memory cell generation within the hostile tumor environment, and their potentials in cancer treatment and immunotherapy.

Suppression, subversion and escape: the role of regulatory T cells in cancer progression

Regulatory T cells (T(regs) ) are crucial in mediating immune homeostasis and promoting the establishment and maintenance of peripheral tolerance. However, in the context of cancer their role is more complex, and they are thought to contribute to the progress of many tumours. As cancer cells express both self- and tumour-associated antigens, T(regs) are key to dampening effector cell responses, and therefore represent one of the main obstacles to effective anti-tumour responses. Suppression mechanisms employed by T(regs) are thought to contribute significantly to the failure of current therapies that rely on induction or potentiation of anti-tumour responses. This review will focus on the current evidence supporting the central role of T(regs) in establishing tumour-specific tolerance and promoting cancer escape. We outline the mechanisms underlying their suppressive function and discuss the potential routes of T(regs) accumulation within the tumour, including enhanced recruitment, in-situ or local proliferation, and de-novo differentiation. In addition, we review some of the cancer treatment strategies that act, at least in part, to eliminate or interfere with the function of T(regs) . The role of T(regs) is being recognized increasingly in cancer, and controlling the function of these suppressive cells in the tumour microenvironment without compromising peripheral tolerance represents a significant challenge for cancer therapies.

CC chemokine receptors and chronic inflammation--therapeutic opportunities and pharmacological challenges

Chemokines are a family of low molecular weight proteins with an essential role in leukocyte trafficking during both homeostasis and inflammation. The CC class of chemokines consists of at least 28 members (CCL1-28) that signal through 10 known chemokine receptors (CCR1-10). CC chemokine receptors are expressed predominantly by T cells and monocyte-macrophages, cell types associated predominantly with chronic inflammation occurring over weeks or years. Chronic inflammatory diseases including rheumatoid arthritis, atherosclerosis, and metabolic syndrome are characterized by continued leukocyte infiltration into the inflammatory site, driven in large part by excessive chemokine production. Over years or decades, persistent inflammation may lead to loss of tissue architecture and function, causing severe disability or, in the case of atherosclerosis, fatal outcomes such as myocardial infarction or stroke. Despite the existence of several clinical strategies for targeting chronic inflammation, these diseases remain significant causes of morbidity and mortality globally, with a concomitant economic impact. Thus, the development of novel therapeutic agents for the treatment of chronic inflammatory disease continues to be a priority. In this review we introduce CC chemokine receptors as critical mediators of chronic inflammatory responses and explore their potential role as pharmacological targets. We discuss functions of individual CC chemokine receptors based on in vitro pharmacological data as well as transgenic animal studies. Focusing on three key forms of chronic inflammation--rheumatoid arthritis, atherosclerosis, and metabolic syndrome--we describe the pathologic function of CC chemokine receptors and their possible relevance as therapeutic targets.

Basic principles of tumor-associated regulatory T cell biology

Due to the critical role of forkhead box (Fox)p3(+) regulatory T cells (Tregs) in the regulation of immunity and the enrichment of Tregs within many human tumors, several emerging therapeutic strategies for cancer involve the depletion or modulation of Tregs, with the aim of eliciting enhanced antitumor immune responses. Here, we review recent advances in understanding of the fundamental biology of Tregs, and discuss the implications of these findings for current models of tumor-associated Treg biology. In particular, we discuss the context-dependent functional diversity of Tregs, the developmental origins of these cells, and the nature of the antigens that they recognize within the tumor environment. In addition, we highlight critical areas of focus for future research.

Homing of regulatory T cells to human skin is important for the prevention of alloimmune-mediated pathology in an in vivo cellular therapy model

Regulatory T cell (Treg) therapy for immune modulation is a promising therapeutic strategy for the treatment and prevention of autoimmune disease and graft-versus-host disease (GvHD) after bone marrow transplantation. However, Treg are heterogeneous and express a variety of chemokine receptor molecules. The optimal subpopulation of Treg for therapeutic use may vary according to the pathological target. Indeed, clinical trials of Treg for the prevention of GvHD where the skin is a major target of the anti-host response have employed Treg derived from a variety of different sources. We postulated that for the effective treatment of GvHD-related skin pathology, Treg must be able to migrate to skin in order to regulate local alloimmune responses efficiently. To test the hypothesis that different populations of Treg display distinct efficacy in vivo based on their expression of tissue-specific homing molecules, we evaluated the activity of human Treg derived from two disparate sources in a model of human skin transplantation. Treg were derived from adult blood or cord blood and expanded in vitro. While Treg from both sources displayed similar in vitro suppressive efficacy, they exhibited marked differences in the expression of skin homing molecules. Importantly, only adult-derived Treg were able to prevent alloimmune-mediated human skin destruction in vivo, by virtue of their improved migration to skin. The presence of Treg within the skin was sufficient to prevent its alloimmune-mediated destruction. Additionally, Treg expressing the skin homing cutaneous lymphocyte antigen (CLA) were more efficient at preventing skin destruction than their CLA-deficient counterparts. Our findings highlight the importance of the careful selection of an effective subpopulation of Treg for clinical use according to the pathology of interest.