Myeloid-derived suppressor cells: linking inflammation and cancer

Myeloid-derived suppressor cells in the peripheral blood of cancer patients contain a subset of immature neutrophils with impaired migratory properties

In tumor-bearing mice, immunosuppressive granulocytic and monocytic MDSC have been identified. The identity and function of MDSC in cancer patients are less clear and need further characterization. We analyzed the peripheral blood of 103 patients with HNC, lung cancer, or cancers of bladder and ureter. Based on sedimentation properties in density gradients, a subset of LD-PMN was identified and analyzed. LD-PMN were expanded in the peripheral blood of cancer patients, suppressed proliferation, and IFN-γ production of polyclonally stimulated T cells and thus, qualify as human MDSC. Immunophenotyping and morphological analysis revealed the accumulation of immature PMN in the MDSC fraction. Neutrophilic MDSC showed altered surface marker expression, prolonged survival, and impaired effector functions when compared with conventional, mature PMN of regular density. MDSC displayed markedly reduced chemotaxis toward tumor-conditioned medium and lacked expression of chemokine receptors CXCR1 and CXCR2, which are normally required for PMN extravasation from the bloodstream and subsequent tissue infiltration. Collectively, our data suggest the accumulation and persistence of long-lived, immature granulocytic MDSC with T cell-suppressive function and impaired migratory properties in the peripheral blood of cancer patients.

Ultraviolet irradiation of mice reduces the competency of bone marrow-derived CD11c+ cells via an indomethacin-inhibitable pathway

Direct UV irradiation of dendritic cells and Langerhans cells reduces their Ag presenting ability. However, the effects of UV on CD11c(+) cells located distally to the point of irradiation are poorly understood. Three days after UV irradiation (8 kJ/m(2)) of BALB/c mice, bone marrow cells were isolated and cultured for 7 d with IL-4 and GM-CSF for the propagation of CD11c(+) cells. Bone marrow-derived CD11c(+) cells from UV-irradiated or nonirradiated mice were loaded with dinitrobenzene sulfonic acid and injected into the ear pinnas of naive BALB/c mice. After 7 d, the ears were painted with 2,4-dinitro-1-fluorobenzene and the ear swelling determined 24 h later. A reduced contact hypersensitivity response was found in mice injected with CD11c(+) cells from the UV-irradiated animals compared with those injected with cells from the nonirradiated animals. Further, a long-lasting suppression of the memory response to 2,4-dinitro-1-fluorobenzene was created. This suppressed response corresponded to increased IL-10 and PGE(2) secretion by freshly isolated bone marrow cells from UV-irradiated mice, and to increased myelopoiesis. The reduction in competence of bone marrow-derived CD11c(+) cells from UV-irradiated mice was not due to delayed maturation, as it was maintained upon LPS exposure prior to CD11c(+) cell purification. The UV-induced effect was reversed by the administration of indomethacin to mice prior to UV irradiation and could be reproduced by s.c. PGE(2). These results show that UV irradiation of mice can affect the function of bone marrow-derived CD11c(+) cells via a mechanism inhibitable by indomethacin; this pathway is likely to contribute to systemic UV-induced immunosuppression.

A paradoxical role for myeloid-derived suppressor cells in sepsis and trauma

Myeloid-derived suppressor cells (MDSCs) are a heterogenous population of immature myeloid cells whose numbers dramatically increase in chronic and acute inflammatory diseases, including cancer, autoimmune disease, trauma, burns and sepsis. Studied originally in cancer, these cells are potently immunosuppressive, particularly in their ability to suppress antigen-specific CD8(+) and CD4(+) T-cell activation through multiple mechanisms, including depletion of extracellular arginine, nitrosylation of regulatory proteins, and secretion of interleukin 10, prostaglandins and other immunosuppressive mediators. However, additional properties of these cells, including increased reactive oxygen species and inflammatory cytokine production, as well as their universal expansion in nearly all inflammatory conditions, suggest that MDSCs may be more of a normal component of the inflammatory response ("emergency myelopoiesis") than simply a pathological response to a growing tumor. Recent evocative data even suggest that the expansion of MDSCs in acute inflammatory processes, such as burns and sepsis, plays a beneficial role in the host by increasing immune surveillance and innate immune responses. Although clinical efforts are currently underway to suppress MDSC numbers and function in cancer to improve antineoplastic responses, such approaches may not be desirable or beneficial in other clinical conditions in which immune surveillance and antimicrobial activities are required.

Naïve blood monocytes suppress T-cell function. A possible mechanism for protection from autoimmunity

In certain disease context, cells of the monocyte/macrophage lineage are known to exhibit T-cell suppressor function. However, whether naïve monocytes are also able to suppress T-cell responses has not been previously investigated. In this study, we have discovered that CD11b(+)Ly6G(-) mononuclear cells in the blood of naïve mice are potent suppressors of T-cell proliferation in vitro. The suppression of T-cell proliferation requires cell-cell contact and is partially dependent on nitric oxide production. Following the induction of experimental autoimmune encephalomyelitis in mice, the suppressor function of this blood CD11b(+)Ly6G(-) cell population is impaired. Therefore, blood CD11b(+)Ly6G(-) cells appear to be intrinsically suppressive and may have a key role in maintaining immune homoeostasis. Loss of this suppressive function may contribute to development of autoimmunity.

MHC II lung cancer vaccines prime and boost tumor-specific CD4+ T cells that cross-react with multiple histologic subtypes of nonsmall cell lung cancer cells

Nonsmall cell lung cancer (NSCLC) is the major cause of lung cancer-related deaths in the United States. We are developing cell-based vaccines as a new approach for the treatment of NSCLC. NSCLC is broadly divided into 3 histologic subtypes: adenocarcinoma, squamous cell carcinoma and large cell carcinoma. Since these subtypes are derived from the same progenitor cells, we hypothesized that they share common tumor antigens, and vaccines that induce immune reactivity against 1 subtype may also induce immunity against other subtypes. Our vaccine strategy has focused on activating tumor-specific CD4(+) T cells, a population of lymphocytes that facilitates the optimal activation of effector and memory cytotoxic CD8(+) T cells. We now report that our NSCLC MHC II vaccines prepared from adeno, squamous or large cell carcinomas each activate CD4(+) T cells that cross-react with the other NSCLC subtypes and do not react with HLA-DR-matched normal lung fibroblasts or other HLA-DR-matched nonlung tumor cells. Using MHC II NSCLC vaccines expressing the DR1, DR4, DR7 or DR15 alleles, we also demonstrate that antigens shared among the different subtypes are presented by multiple HLA-DR alleles. Therefore, MHC II NSCLC vaccines expressing a single HLA-DR allele activate NSCLC-specific CD4(+) T cells that react with the 3 major classes of NSCLC, and the antigens recognized by the activated T cells are presented by several common HLA-DR alleles, suggesting that the MHC II NSCLC vaccines are potential immunotherapeutics for a range of NSCLC patients.

Vesicular stomatitis virus-induced immune suppressor cells generate antagonism between intratumoral oncolytic virus and cyclophosphamide

Despite having potent oncolytic activity, in vitro, direct intratumoral injection of oncolytic vesicular stomatitis virus (VSV) into established AE17ova mesothelioma tumors in C57Bl/6 mice had no therapeutic effect. During studies to combine systemic cyclophosphamide (CPA) with VSV to suppress the innate immune reaction against VSV, we observed that CPA alone had highly significant antitumor effects in this model. However, against our expectations, the combination of CPA and VSV consistently reduced therapeutic efficacy compared to CPA alone, despite the fact that the combination increased intratumoral VSV titers. We show here that CPA-mediated therapy against AE17ova tumors was immune-mediated and dependent upon both CD4 T cells and natural killer (NK) cells. However, intratumoral VSV induced a transforming growth factor-β (TGF-β)-dependent suppressive activity, mediated by CD11b(+)GR-1(+) cells that significantly inhibited both antigen-specific T-cell activation, and CPA-activated, NK-dependent killing of AE17ova tumor cells. Overall, our results show that treatment with oncolytic viruses can induce a variety of immune-mediated consequences in vivo with both positive, or negative, effects on antitumor therapy. These underexplored immune consequences of treatment with oncolytic viruses may have significant, and possibly unexpected, impacts on how virotherapy interacts in combination with other agents which modulate antitumor immune effectors.

Hoxa3 promotes the differentiation of hematopoietic progenitor cells into proangiogenic Gr-1+CD11b+ myeloid cells

Injury induces the recruitment of bone marrow-derived cells (BMDCs) that contribute to the repair and regeneration process. The behavior of BMDCs in injured tissue has a profound effect on repair, but the regulation of BMDC behavior is poorly understood. Aberrant recruitment/retention of these cells in wounds of diabetic patients and animal models is associated with chronic inflammation and impaired healing. BMD Gr-1(+)CD11b(+) cells function as immune suppressor cells and contribute significantly to tumor-induced neovascularization. Here we report that Gr-1(+)CD11b(+) cells also contribute to injury-induced neovascularization, but show altered recruitment/retention kinetics in the diabetic environment. Moreover, diabetic-derived Gr-1(+)CD11b(+) cells fail to stimulate neovascularization in vivo and have aberrant proliferative, chemotaxis, adhesion, and differentiation potential. Previously we demonstrated that gene transfer of HOXA3 to wounds of diabetic mice is taken up by and expressed by recruited BMDCs. This is associated with a suppressed inflammatory response, enhanced neovascularization, and accelerated wound healing. Here we show that sustained expression of Hoxa3 in diabetic-derived BMD Gr-1(+)CD11b(+) cells reverses their diabetic phenotype. These findings demonstrate that manipulation of adult stem/progenitor cells ex vivo could be used as a potential therapy in patients with impaired wound healing.

Anti-tumour synergy of cytotoxic chemotherapy and anti-CD40 plus CpG-ODN immunotherapy through repolarization of tumour-associated macrophages

We studied the effectiveness of monoclonal anti-CD40 + cytosine-phosphate-guanosine-containing oligodeoxynucleotide 1826 (CpG-ODN) immunotherapy (IT) in mice treated with multidrug chemotherapy (CT) consisting of vincristine, cyclophosphamide and doxorubicin. Combining CT with IT led to synergistic anti-tumour effects in C57BL/6 mice with established B16 melanoma or 9464D neuroblastoma. CT suppressed the functions of T cells and natural killer (NK) cells, but primed naïve peritoneal macrophages (Mφ) to in vitro stimulation with lipopolysaccharide (LPS), resulting in augmented nitric oxide (NO) production. IT, given after CT, did not restore the responsiveness of T cells and NK cells, but further activated Mφ to secrete NO, interferon-γ (IFN-γ) and interleukin (IL)-12p40 and to suppress the proliferation of tumour cells in vitro. These functional changes were accompanied by immunophenotype alterations on Mφ, including the up-regulation of Gr-1. CD11b(+) F4/80(+) Mφ comprised the major population of B16 tumour-infiltrating leucocytes. CT + IT treatment up-regulated molecules associated with the M1 effector Mφ phenotype [CD40, CD80, CD86, major histocompatibility complex (MHC) class II, IFN-γ, tumour necrosis factor-α (TNF-α) and IL-12] and down-regulated molecules associated with the M2 inhibitory Mφ phenotype (IL-4Rα, B7-H1, IL-4 and IL-10) on the tumour-associated Mφ compared with untreated controls. Together, the results show that CT and anti-CD40 + CpG-ODN IT synergize in the induction of anti-tumour effects which are associated with the phenotypic repolarization of tumour-associated Mφ.

Type 1 T helper cells induce the accumulation of myeloid-derived suppressor cells in the inflamed Tgfb1 knockout mouse liver

Immune-mediated liver injury in hepatitis is due to activated T cells producing interferon-γ (IFN-γ). It is important to identify negative feedback immune mechanisms that can regulate T cell activity. In this study, we demonstrate that liver inflammation mediated by type 1 T helper (Th1) cells can induce the accumulation of myeloid-derived suppressor cells (MDSCs), pleiomorphic cells capable of modulating T cell-mediated immunity, that heretofore have been studied almost exclusively in the context of tumor-associated inflammation. Mice deficient in the gene encoding transforming growth factor-β1 (Tgfb1(-/-) mice) acutely develop liver necroinflammation caused by IFN-γ-producing clusters of differentiation 4-positive (CD4(+)) T cells. Liver Th1 cell accumulation was accompanied by myeloid cells expressing CD11b and Gr1, phenotypic hallmarks of MDSCs. Isolated Tgfb1(-/-) liver CD11b(+)Gr1(+) cells were functional MDSCs, readily suppressing T cell proliferation in vitro. Pharmacologic inhibitors of inducible nitric oxide (NO) synthase completely eliminated suppressor function. Suppressor function and the production of NO were dependent on cell-cell contact between MDSCs and T cells, and upon IFN-γ, and were specifically associated with the "monocytic" CD11b(+)Ly6G(-) Ly6C(hi) subset of liver Tgfb1(-/-) CD11b(+) cells. The rapid accumulation of CD11b(+)Gr1(+) cells in Tgfb1(-/-) liver was abrogated when mice were either depleted of CD4(+) T cells or rendered unable to produce IFN-γ, showing that Th1 activity induces MDSC accumulation.

CONCLUSION

Th1 liver inflammation mobilizes an MDSC response that, through the production of NO, can inhibit T cell proliferation. We propose that MDSCs serve an important negative feedback function in liver immune homeostasis, and that insufficient or inappropriate activity of this cell population may contribute to inflammatory liver pathology.

HIF-1α regulates function and differentiation of myeloid-derived suppressor cells in the tumor microenvironment

Myeloid-derived suppressor cells (MDSCs) are a major component of the immune-suppressive network described in cancer and many other pathological conditions. We demonstrate that although MDSCs from peripheral lymphoid organs and the tumor site share similar phenotype and morphology, these cells display profound functional differences. MDSC from peripheral lymphoid organs suppressed antigen-specific CD8(+) T cells but failed to inhibit nonspecific T cell function. In sharp contrast, tumor MDSC suppressed both antigen-specific and nonspecific T cell activity. The tumor microenvironment caused rapid and dramatic up-regulation of arginase I and inducible nitric oxide synthase in MDSC, which was accompanied by down-regulation of nicotinamide adenine dinucleotide phosphate-oxidase and reactive oxygen species in these cells. In contrast to MDSC from the spleen, MDSC from the tumor site rapidly differentiated into macrophages. Exposure of spleen MDSC to hypoxia resulted in the conversion of these cells to nonspecific suppressors and their preferential differentiation to macrophages. Hypoxia-inducible factor (HIF) 1α was found to be primarily responsible for the observed effects of the tumor microenvironment on MDSC differentiation and function. Thus, hypoxia via HIF-1α dramatically alters the function of MDSC in the tumor microenvironment and redirects their differentiation toward tumor-associated macrophages, hence providing a mechanistic link between different myeloid suppressive cells in the tumor microenvironment.

Alternatively activated macrophage possess antitumor cytotoxicity that is induced by IL-4 and mediated by arginase-1

Earlier studies have shown that the adoptive transfer of Th2-polarized CD4 T cells can clear established tumors from mice in an antigen-specific manner. Although eosinophils were implicated in this process, the exact mechanism of tumor clearance and which immune effector cells were involved, remain to be defined. Consequently, experiments were undertaken to elucidate the mechanism of Th2-mediated destruction of B16-F1 melanoma cells by examining the in vitro antitumor activity of leukocytes within a type-2 inflammatory infiltrate. The experimental data show that activation of alternatively activated macrophages (aaMacs) within type-2 infiltrates by IL-4 or IL-13 can inhibit B16-F1 melanoma cell proliferation through a mechanism that is dependent on arginase-1 depletion of L-arginine within the tumor cell microenvironment. Interestingly, whilst at higher E:T ratios aaMac exhibited antitumor activity, at lower E:T ratios aaMacs were observed to enhance rather than inhibit B16-F1 melanoma cell growth. This highlights the fine balance between stimulating the antitumorigenic and protumorigenic properties of aaMacs in tumor immunotherapy protocols.

The immunosuppressive tumor environment is the major impediment to successful therapeutic vaccination in Neu transgenic mice

We earlier showed that therapeutic vaccination of FVB/N mice with alphaviral replicon particles expressing rat neuET-VRP induced regression of established neu-expressing tumors. In this study, we evaluated the efficacy of neuET-VRPs in a tolerant mouse model using mice with transgenic expression of neu. Using the same approach that induced regression of 70 mm(2) tumors in FVB/N mice, we were unable to inhibit tumor growth in tolerant neu-N mice, despite showing neu-specific B-cell and T-cell responses post vaccination. As neu-N mice have a limited T-cell repertoire specific to neu, we hypothesized that the absence of these T cells led to differences in the vaccine response. However, transfer of neu-specific T cells from vaccinated FVB/N mice was not effective in inducing tumor regression, as these cells did not proliferate in the tumor-draining lymph node. Vaccination given with low-dose cyclophosphamide to deplete regulatory T cells delayed tumor growth but did not result in tumor regression. Finally, we showed that T cells given with vaccination were effective in inhibiting tumor growth, if administered with approaches to deplete myeloid-derived suppressor cells. Our data show that both central deletion of lymphocytes and peripheral immunosuppressive mechanisms are present in neu-N mice. However, the major impediment to successful vaccination is the peripheral tumor-induced immune suppression.

The defensive alliance between neutrophils and NK cells as a novel arm of innate immunity

The immune system is equipped with a plethora of mechanisms that protect the host from the harmful effects of environmental insults. However, the traditional "hierarchical" view of the immune response, in which innate, "nonspecific" cells are first recruited to the site of damage, before the highly "specific", adaptive immune response develops, has been questioned recently. First, the innate response is much more specific than recognized previously: indeed, each cell of the innate system is not only endowed with an ever-expanding array of germ-line-encoded receptors, which differentiate between distinct insults, but also is modulated continuously by other leukocytes that concomitantly interact with and respond to that particular insult. The other reason is that the cells of the innate system are instrumental for the adaptive system to accomplish its function, as they can also modulate the activity of lymphocytes reciprocally during the entire course of the immune response. This complex pattern of interactions is illustrated by recent advances on the functions of PMNs, clearly showing that unexpectedly, these cells also contribute to the regulation of the host immune response by crosstalk with innate and adaptive leukocytes, including NK cells. Herein, given the peculiar role of neutrophils and NK cells in inflammation, clearance of pathogens/viral-infected cells, and cancer immunosurveillance, we summarize the current knowledge about the mechanisms whereby neutrophils and NK cells interact and regulate the activities of one another, as well as discuss their potential implications involved in the pathogenesis of chronic, inflammatory pathologies, infections, and tumors.

Redirecting the immune response: role of adoptive T cell therapy

Adoptive T cell therapy is aimed at overcoming constraints of the endogenous immune response. In patients with malignancies, this approach is based on the possibility of administering sufficient numbers of tumor-reactive lymphocytes under conditions in which they will promote a therapeutic response. Although this strategy is potentially applicable to a vast number of malignancies, its efficacy, to date, has been limited. This is likely related to several factors including an insufficient persistence and reactivation of infused cells, insufficient tumor infiltration, and the presence of an immunosuppressive environment. Here, we review the importance of pretransplantation host conditioning and posttransplantation strategies that have been shown to contribute to the therapeutic efficacy of infused T lymphocytes.

Prognostic significance of regulatory T cells in tumor

Since entering the immunological stage several decades ago, regulatory T cell biology has been realized as fundamentally important in the prevention of autoimmune conditions, induction of transplant tolerance and the immune response to cancer. The role of regulatory T cells in tumor immunobiology is still being elucidated. Currently, regulatory T cells are implicated in the dampening of antitumor T-cell responses both through direct and indirect means. A number of investigators have demonstrated that regulatory T cell density and location may serve as independent prognostic factors in several types of cancer and are alternately detrimental or beneficial to patient survival. In this article, we will review the characteristics and functional phenotype of classical regulatory T cells, describe their distribution and quantification in tumor-bearing hosts and summarize recent studies investigating the prognostic significance of regulatory T cell number and locality in various cancers.

Alternatively activated macrophages inhibit T-cell proliferation by Stat6-dependent expression of PD-L2

Alternatively activated macrophages (AAM) accumulate in tissues during Th2-associated immune responses like helminth infections and allergic disorders. These cells differentiate in response to interleukin 4 (IL-4)/IL-13-mediated activation of Stat6 and possess potent inhibitory activity against T cells. The molecular mechanism that leads to T-cell suppression remains unclear and could involve soluble factors or inhibitory ligands. Microarray analysis revealed that the inhibitory ligand, programmed death ligand 2 (PD-L2) was strongly induced by IL-4 in macrophages from wild-type but not Stat6-deficient mice. PD-L2 expression correlated with other established markers for AAM-like Relm-α/Fizz1, arginase1, or Ym1 and thereby serves as useful surface marker to identify and isolate AAM from tissues. Antibodies against PD-L2 blocked the inhibitory activity of AAM and retroviral expression of PD-L2 in macrophages from Stat6(-/-) mice was sufficient to inhibit T-cell proliferation, which demonstrates that PD-L2 mediates potent and nonredundant inhibition of T cells independently of other Stat6-regulated genes. Infection of conditional IL-4/IL-13-deficient mice with the helminth Nippostrongylus brasiliensis further showed that PD-L2 expression was dependent on IL-4/IL-13 from Th2 cells. In vivo blockade of PD-L2 during N brasiliensis infection caused an enhanced Th2 response in the lung, indicating that AAM inhibit Th2 cells by expression of PD-L2.

Therapeutic cancer vaccines in combination with conventional therapy

The clinical efficacy of most therapeutic vaccines against cancer has not yet met its promise. Data are emerging that strongly support the notion that combining immunotherapy with conventional therapies, for example, radiation and chemotherapy may improve efficacy. In particular combination with chemotherapy may lead to improved clinical efficacy by clearing suppressor cells, reboot of the immune system, by rendering tumor cells more susceptible to immune mediated killing, or by activation of cells of the immune system. In addition, a range of tumor antigens have been characterized to allow targeting of proteins coupled to intrinsic properties of cancer cells. For example, proteins associated with drug resistance can be targeted, and form ideal target structures for use in combination with chemotherapy for killing of surviving drug resistant cancer cells. Proteins associated with the malignant phenotype can be targeted to specifically target cancer cells, but proteins targeted by immunotherapy may also simultaneously target cancer cells as well as suppressive cells in the tumor stroma.

A multi-functional role of interferon regulatory factor-8 in solid tumor and myeloid cell biology

Understanding mechanisms of tumor escape are critically important not only to improving our knowledge of cancer biology, but also for the overall development of more effective anti-neoplastic therapies. Our laboratory focuses on mechanisms of apoptotic resistance, with emphasis on Fas loss of function as an important determinant of tumor progression. Our work in solid tumor systems has led to the identification of interferon regulatory factor-8 (IRF-8) as a differentially expressed gene important for tumor cell response to cytotoxicity, including Fas-mediated apoptosis and host-anti-tumor immunosurveillance mechanisms. Although IRF-8 was originally identified in the regulation of normal and neoplastic myeloid cell development, these findings revealed a new functional role for IRF-8 in non-hematopoietic malignancies and establish a molecular basis for its potential manipulation during cancer therapy.

Tim-3/galectin-9 pathway: regulation of Th1 immunity through promotion of CD11b+Ly-6G+ myeloid cells

IFN-gamma plays a central role in antitumor immunity. T cell Ig and mucin domain (Tim-3) is expressed on IFN-gamma-producing Th1 cells; on interaction with its ligand, galectin-9, Th1 immunity is terminated. In this study, we show that transgenic overexpression of Tim-3 on T cells results in an increase in CD11b(+)Ly-6G(+) cells and inhibition of immune responses. Molecular characterization of CD11b(+)Ly-6G(+) cells reveals a phenotype consistent with granulocytic myeloid-derived suppressor cells. Accordingly, we find that modulation of the Tim-3/galectin-9 (Gal-9) pathway impacts on tumor growth. Similarly, overexpression of Tim-3 ligand, Gal-9, results in an increase in CD11b(+)Ly-6G(+) cells and inhibition of immune responses. Loss of Tim-3 restores normal levels of CD11b(+)Ly-6G(+) cells and normal immune responses in Gal-9 transgenic mice. Our data uncover a novel mechanism by which the Tim-3/Gal-9 pathway regulates immune responses and identifies this pathway as a therapeutic target in diseases where myeloid-derived suppressor cells are disadvantageous.

Different tumor microenvironments contain functionally distinct subsets of macrophages derived from Ly6C(high) monocytes

Tumor-associated macrophages (TAM) form a major component of the tumor stroma. However, important concepts such as TAM heterogeneity and the nature of the monocytic TAM precursors remain speculative. Here, we show for the first time that mouse mammary tumors contained functionally distinct subsets of TAMs and provide markers for their identification. Furthermore, in search of the TAM progenitors, we show that the tumor-monocyte pool almost exclusively consisted of Ly6C(hi)CX(3)CR1(low) monocytes, which continuously seeded tumors and renewed all nonproliferating TAM subsets. Interestingly, gene and protein profiling indicated that distinct TAM populations differed at the molecular level and could be classified based on the classic (M1) versus alternative (M2) macrophage activation paradigm. Importantly, the more M2-like TAMs were enriched in hypoxic tumor areas, had a superior proangiogenic activity in vivo, and increased in numbers as tumors progressed. Finally, it was shown that the TAM subsets were poor antigen presenters, but could suppress T-cell activation, albeit by using different suppressive mechanisms. Together, our data help to unravel the complexities of the tumor-infiltrating myeloid cell compartment and provide a rationale for targeting specialized TAM subsets, thereby optimally "re-educating" the TAM compartment.

Tolerogenic dendritic cells and myeloid-derived suppressor cells: potential for regulation and therapy of liver auto- and alloimmunity

Organ transplantation is now established as an accepted treatment for end-stage liver disease, acute fulminant hepatic liver failure and hepatocellular carcinoma. While early graft acceptance rates have increased markedly due to improved immunosuppressive drug regimens, rates of late graft failure remain largely unchanged. Recent findings suggest that in addition to alloimmunity, chronic rejection of liver allografts may also reflect de novo autoimmune hepatitis or recurrence of pre-existing hepatic autoimmune disease. Dendritic cell (DC)- based therapy is a promising experimental approach to promotion of transplant tolerance and the treatment of autoimmune diseases. Newly emerging evidence also demonstrates the potential efficacy of myeloid-derived suppressor cells (MDSC) in the antigen (Ag)-specific regulation of T-cell responses. Herein, we discuss current understanding of liver autoimmunity post-transplantation, along with current approaches for the development of tolerogenic DC, and the potential use of MDSC for the development of stable, Ag-specific tolerance.

Kinetics of host cell recruitment during dissemination of diffuse malignant peritoneal mesothelioma

Diffuse malignant mesothelioma is an aggressive tumor which displays a median survival of 11.2 months and a 5-year survival of less than 5% emphasizing the need for more effective treatments. This study uses an orthotopic model of malignant mesothelioma established in syngeneic, immunocompetent C57Bl/6 mice which produce malignant ascites and solid tumors that accurately replicate the histopathology of the human disease. Host stromal and immune cell accumulation within malignant ascites and solid tumors was determined using immunofluorescent labeling with confocal microscopy and fluorescence-activated cell sorting. An expression profile of cytokines and chemokines was produced using quantitative real-time PCR arrays. Tumor spheroids and solid tumors show progressive growth and infiltration with host stromal and immune cells including macrophages, endothelial cells, CD4(+) and CD8(+) lymphocytes, and a novel cell type, myeloid derived suppressor cells (MDSCs). The kinetics of host cell accumulation and inflammatory mediator expression within the tumor ascites divides tumor progression into two distinct phases. The first phase is characterized by progressive macrophage and T lymphocyte recruitment, with a cytokine profile consistent with regulatory T lymphocytes differentiation and suppression of T cell function. The second phase is characterized by decreased expression of macrophage chemotactic and T-cell regulating factors, an increase in MDSCs, and increased expression of several cytokines which stimulate differentiation of MDSCs. This cellular and expression profile suggests a mechanism by which host immune cells promote diffuse malignant mesothelioma progression.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12307-010-0048-1) contains supplementary material, which is available to authorized users.

A novel nanoparticle drug delivery system: the anti-inflammatory activity of curcumin is enhanced when encapsulated in exosomes

Monocyte-derived myeloid cells play vital roles in inflammation-related autoimmune/inflammatory diseases and cancers. Here, we report that exosomes can deliver anti-inflammatory agents, such as curcumin, to activated myeloid cells in vivo. This technology provides a means for anti-inflammatory drugs, such as curcumin, to target the inflammatory cells as well as to overcome unwanted off-target effects that limit their utility. Using exosomes as a delivery vehicle, we provide evidence that curcumin delivered by exosomes is more stable and more highly concentrated in the blood. We show that the target specificity is determined by exosomes, and the improvement of curcumin activity is achieved by directing curcumin to inflammatory cells associated with therapeutic, but not toxic, effects. Furthermore, we validate the therapeutic relevance of this technique in a lipopolysaccharide (LPS)-induced septic shock mouse model. We further show that exosomes, but not lipid alone, are required for the enhanced anti-inflammatory activity of curcumin. The specificity of using exosomes as a drug carrier creates opportunities for treatments of many inflammation-related diseases without significant side effects due to innocent bystander or off-target effects.

Immature immunosuppressive CD14+HLA-DR-/low cells in melanoma patients are Stat3hi and overexpress CD80, CD83, and DC-sign

Myeloid-derived suppressor cells (MDSC) have emerged as key immune modulators in various tumor models and human malignancies, but their characteristics in humans remain to be unequivocally defined. In this study, we have examined circulating CD14(+)HLA-DR(-/low) MDSC in 34 advanced malignant melanoma (MM) patients. Their frequency is significantly increased and associated with disease activity. Contrary to the common notion that MDSC are a heterogeneous population of exclusively immature cells, we find the coexpression of markers associated with mature phenotype. We show for the first time the overexpression of CD80, CD83, and DC-Sign in human MDSC. Further, increased levels of signal transducer and activator of transcription 3 (Stat3), an important regulator in MDSC development and function, were noted in MM-MDSC. Stat3 was altered toward an active, phosphorylated state in the HLA-DR(-) population of CD14(+) cells and was more reactive to activating stimuli in patients. Importantly, inhibition of Stat3 abolished their suppressive activity almost completely. The described MM-MDSC use arginase in conjunction with other yet undefined mechanisms to suppress CD4(+) and CD8(+) T cells. Several observations suggest a redox imbalance in MDSC and indicate an important role of Stat3-dependent oxidative stress in MDSC-mediated T-cell suppression. These results emphasize the diversity of MDSC in human cancer and provide potential targets for therapeutic interventions.

Immune regulation of cancer

Innate and adaptive immune system cells play a major role in regulating the growth of cancer. Although it is commonly thought that an immune response localized to the tumor will inhibit cancer growth, it is clear that some types of inflammation induced in a tumor may also lead to cancer proliferation, invasion, and dissemination. Recent evidence suggests, however, that some patients with cancer can mount an antitumor immune response that has the potential to control or eliminate cancer. Indeed, a so-called "immune response" signature has been described in malignancy that is associated with improved outcomes in several tumor types. Moreover, the presence of specific subsets of T cells, which have the capability to penetrate tumor stroma and infiltrate deep into the parenchyma, identifies patients with an improved prognosis. Immune-based therapies have the potential to modulate the tumor microenvironment by eliciting immune system cells that will initiate acute inflammation that leads to tissue destruction.

Nrf2-deficiency creates a responsive microenvironment for metastasis to the lung

The Nrf2 transcription factor is crucial for regulating the cellular defense against various carcinogens. However, relationship between host Nrf2 and cancer metastasis remains unexplored. To address this issue, we examined susceptibility of Nrf2-deficient mice to pulmonary cancer metastasis following implantation of the mouse Lewis lung carcinoma (3LL) cell line. Nrf2-deficient mice reproducibly exhibited a higher number of pulmonary metastatic nodules than wild-type mice did. The lung and bone marrow (BM) of cancer-bearing Nrf2-deficient mice contained increased numbers of inflammatory cells, including myeloid-derived suppressor cells (MDSCs), a potent population of immunosuppressive cells. MDSCs can attenuate CD8(+) T-cell immunity through modification of the T-cell receptor complex exploiting reactive oxygen species (ROS). MDSCs of Nrf2-deficient mice retained elevated levels of ROS relative to wild-type mice. BM transplantation experiments revealed functional disturbance in the hematopoietic and immune systems of Nrf2-deficient mice. Wild-type recipient mice with Nrf2-deficient BM cells showed increased levels of lung metastasis after cancer cell inoculation. These mice exhibited high-level accumulation of ROS in MDSCs, which showed very good coincidence to the decrease of splenic CD8(+) T-cells. In contrast, Keap1-knockdown mutant mice harboring high-level Nrf2 expression displayed increased resistance against the cancer cell metastasis to the lung, accompanied by a decrease in ROS in the MDSCs fraction. Our results thus reveal a novel function for Nrf2 in the prevention of cancer metastasis, presumably by its ability to preserve the redox balance in the hematopoietic and immune systems.

Myeloid cells in the tumor microenvironment: modulation of tumor angiogenesis and tumor inflammation

Myeloid cells are a heterogeneous population of bone marrow-derived cells that play a critical role during growth and metastasis of malignant tumors. Tumors exhibit significant myeloid cell infiltrates, which are actively recruited to the tumor microenvironment. Myeloid cells promote tumor growth by stimulating tumor angiogenesis, suppressing tumor immunity, and promoting metastasis to distinct sites. In this review, we discuss the role of myeloid cells in promoting tumor angiogenesis. Furthermore, we describe a subset of myeloid cells with immunosuppressive activity (known as myeloid-derived suppressor cells). Finally, we will comment on the mechanisms regulating myeloid cell recruitment to the tumor microenvironment and on the potential of myeloid cells as new targets for cancer therapy.

Identification of a novel antigen cross-presenting cell type in spleen

Antigen-presenting cells (APC), like dendritic cells (DC), are essential for T-cell activation, leading to immunity or tolerance. Multiple DC subsets each play a unique role in the immune response. Here, a novel splenic dendritic-like APC has been characterized in mice that has immune function and cell surface phenotype distinct from other, described DC subsets. These were identified as a cell type continuously produced in spleen long-term cultures (LTC) and have an in vivo equivalent cell type in mice, namely 'L-DC'. This study characterizes LTC-DC in terms of marker phenotype and function, and compares them with L-DC and other known splenic DC and myeloid subsets. L-DC display a myeloid dendritic-like phenotype equivalent to LTC-DC as CD11c(lo) CD11b(hi) MHC-II(-) CD8α(-) cells, distinct by high accessibility and endocytic capacity for blood-borne antigen. Both LTC-DC and L-DC have strong antigen cross-presentation ability leading to strong activation of CD8(+) T cells, particularly after exposure to lipopolysaccharide. However, they have weak ability to stimulate CD4(+) T cells in antigen-specific responses. Evidence is presented here for a novel DC type produced by in vitro haematopoiesis which has distinct antigen-presenting potential and reflects a DC subset present also in vivo in spleen.

Immunogenic chemotherapy with cyclophosphamide and doxorubicin against established murine carcinoma

Mitigation of regulatory T cell-mediated immunosuppression and elicitation of immunogenic tumor cell death are crucial events for optimal anti-tumor immune activity in vivo. This study was designed to investigate the potential synergistic activity of the combined use of cyclophosphamide (CP) and doxorubicin (DR), both of which are known to resolve these two issues. BALB/c mice were inoculated subcutaneously with CT-26 carcinoma cells in the bilateral flank and treated with an intraperitoneal injection of a low dose of CP followed by an intratumoral injection of DR into one side of the tumor. We found that, in addition to a significant suppression of growth on the DR-treated side of the tumor, combination therapy suppressed the growth of DR-untreated remote tumors in both tumor-specific and T cell-dependent manners. Mitomycin C showed no such synergistic anti-tumor activity with CP treatment. Combination therapy increased the frequency of interferon (IFN)-gamma-producing T lymphocytes specific to a CT-26-associated class I-binding tumor peptide in the tumor-draining lymph nodes. Real-time PCR analysis revealed that combination therapy led to an increase in IFN-gamma and tumor necrosis factor-alpha mRNA expression; however, levels of Foxp3 and transforming growth factor-beta within the remote tumor tissues were decreased. In addition, knock down of calreticulin expression in CT-26 cells using small interfering RNA attenuated anti-tumor vaccine effects induced by DR-treated CT-26 cells. These results provide an immunological rationale for the combined use of chemotherapeutic drugs, i.e., CP and DR, and further recommend their use with current cancer vaccines.

Treatment with imiquimod enhances antitumor immunity induced by therapeutic HPV DNA vaccination

BACKGROUND

There is an urgent need to develop new innovative therapies for the control of advanced cancer. The combination of antigen-specific immunotherapy with the employment of immunomodulatory agents has emerged as a potentially plausible approach for the control of advanced cancer.

METHODS

In the current study, we explored the combination of the DNA vaccine encoding calreticulin (CRT) linked to human papillomavirus type 16 (HPV-16) E7 antigen (CRT/E7) with the TLR7 agonist imiquimod for their ability to generate E7-specific immune responses and antitumor effects in tumor-bearing mice.

RESULTS

We observed that treatment with CRT/E7 DNA in combination with imiquimod leads to an enhancement in the E7-specific CD8+ T cell immune responses and a decrease in the number of myeloid-derived suppressor cells in the tumor microenvironment of tumor-bearing mice. Furthermore, treatment with CRT/E7 DNA in combination with imiquimod leads to significantly improved antitumor effects and prolonged survival in treated mice. In addition, treatment with imiquimod led to increased number of NK1.1+ cells and F4/80+ cells in the tumor microenvironment. Macrophages and NK1.1+ cells were found to play an important role in the antitumor effects mediated by treatment with CRT/E7 DNA in combination with imiquimod.

CONCLUSIONS

Thus, our data suggests that the combination of therapeutic HPV DNA vaccination with topical treatment with the TLR7 agonist imiquimod enhances the antitumor immunity induced by DNA vaccination. The current study has significant implications for future clinical translation.

Molecularly defined vaccines for cancer immunotherapy, and protective T cell immunity

Malignant cells are frequently recognized and destroyed by T cells, hence the development of T cell vaccines against established tumors. The challenge is to induce protective type 1 immune responses, with efficient Th1 and CTL activation, and long-term immunological memory. These goals are similar as in many infectious diseases, where successful immune protection is ideally induced with live vaccines. However, large-scale development of live vaccines is prevented by their very limited availability and vector immunogenicity. Synthetic vaccines have multiple advantages. Each of their components (antigens, adjuvants, delivery systems) contributes specifically to induction and maintenance of T cell responses. Here we summarize current experience with vaccines based on proteins and peptide antigens, and discuss approaches for the molecular characterization of clonotypic T cell responses. With carefully designed step-by-step modifications of innovative vaccine formulations, T cell vaccination can be optimized towards the goal of inducing therapeutic immune responses in humans.

Direct and differential suppression of myeloid-derived suppressor cell subsets by sunitinib is compartmentally constrained

The antiangiogenic drug sunitinib is a receptor tyrosine kinase inhibitor with significant, yet not curative, therapeutic effects in metastatic renal cell carcinoma (RCC). Sunitinib is also an immunomodulator, potently reversing myeloid-derived suppressor cell (MDSC) accumulation and T-cell inhibition in the blood even of nonresponder RCC patients. We observed that sunitinib similarly prevented MDSC accumulation and restored normal T-cell function to the spleens of tumor-bearing mice, independent of the capacity of sunitinib to inhibit tumor progression (RENCA>CT26>4T1). Both monocytic and neutrophilic splenic MDSC were highly repressible by sunitinib. In contrast, MDSC within the microenvironment of 4T1 tumors or human RCC tumors proved highly resistant to sunitinib and ambient T-cell function remained suppressed. Proteomic analyses comparing tumor to peripheral compartments showed that granulocyte macrophage colony-stimulating factor (GM-CSF) predicted sunitinib resistance and recombinant GM-CSF conferred sunitinib resistance to MDSC in vivo and in vitro. MDSC conditioning with GM-CSF uniquely inhibited signal transducers and activators of transcription (STAT3) and promoted STAT5 activation. STAT5ab(null/null) MDSC were rendered sensitive to sunitinib in the presence of GM-CSF in vitro. We conclude that compartment-dependent GM-CSF exposure in resistant tumors may account for the regionalized effect of sunitinib upon host MDSC modulation and hypothesize that ancillary strategies to decrease such regionalized escape will enhance the potency of sunitinib as an immunomodulator and a cancer therapy.

Increased adenosine triphosphate production by peripheral blood CD4+ cells in patients with hematologic malignancies treated with stem cell mobilization agents

Hematopoietic stem cell (HSC) transplantation is an important therapeutic option for patients with hematologic malignancies. To explore the immunomodulatory effects of HSC mobilization agents, we studied the function and phenotype of CD4(+) T cells from 16 adult patients with hematologic malignancies undergoing HSC mobilization treatment for autologous transplantation. Immune cell function was determined using the Immuknow (Cylex) assay by measuring the amount of adenosine triphosphate (ATP) produced by CD4(+) cells from whole blood. ATP activity measured in G-CSF-treated patients was significantly higher than that measured in healthy individuals or "nonmobilized" patients. In patients treated with G-CSF, CD4(+) T cells were predominantly CD25(low)FOXP3(low), consistent with an activated phenotype. However, T-cell depletion did not abrogate ATP production in blood samples from G-CSF-treated patients, indicating that CD4(+) myeloid cells contributed to the increased ATP levels observed in these patients. There was a significant correlation between ATP activity and patient survival, suggesting that efficient activation of CD4(+) cells during mobilization treatment predicts a low risk of disease relapse. Monitoring immune cell reactivity using the Immuknow assay may assist in the clinical management of patients with hematologic malignancies and optimization of HSC mobilization protocols.

Myeloid cells in cancer progression: unique subtypes and their roles in tumor growth, vascularity, and host immune suppression

Leukocytic infiltrates, particularly myeloid cells, can stimulate an anti-tumor immune response, but more often they stimulate tumor development, including promoting invasion, tumor growth, angiogenesis, and metastasis. Distinct myeloid phenotypes are being characterized that have been shown to promote tumor growth, angiogenesis, and metastasis. This review provides an overview of myeloid differentiation and spotlights specific pro-tumorogenic myeloid populations and their role in cancer progression. Efforts to characterize these pro-tumorogenic myeloid cell immunophenotypes may lead to novel targets for cancer therapy.

5-Fluorouracil selectively kills tumor-associated myeloid-derived suppressor cells resulting in enhanced T cell-dependent antitumor immunity

Myeloid-derived suppressor cells (MDSC) accumulate in the spleen and tumor bed during tumor growth. They contribute to the immune tolerance of cancer notably by inhibiting the function of CD8(+) T cells. Thus, their elimination may hamper tumor growth by enhancing antitumor T-cell functions. We have previously reported that some anticancer agents relied on T cell-dependent anticancer responses to achieve maximal efficacy. However, the effect of anticancer agents on MDSC has remained largely unexplored. In this study, we observed that gemcitabine and 5-fluorouracil (5FU) were selectively cytotoxic on MDSC. In vivo, the treatment of tumor-bearing mice with 5FU led to a major decrease in the number of MDSC in the spleens and tumor beds of animals whereas no significant effect on T cells, natural killer cells, dendritic cells, or B cells was noted. Interestingly, 5FU showed a stronger efficacy over gemcitabine to deplete MDSC and selectively induced MDSC apoptotic cell death in vitro and in vivo. The elimination of MDSC by 5FU increased IFN-gamma production by tumor-specific CD8(+) T cells infiltrating the tumor and promoted T cell-dependent antitumor responses in vivo. Altogether, these findings suggest that the antitumor effect of 5FU is mediated, at least in part, by its selective cytotoxic action on MDSC.

Critical roles of lysosomal acid lipase in myelopoiesis

Lysosomal acid lipase (LAL) is a key enzyme that cleaves cholesteryl esters and triglycerides to generate free fatty acids and cholesterol in lysosomes. Genetic ablation of the lal gene (lal(-/-)) in mice has resulted in a systemic increase of macrophages and neutrophils, causing severe inflammation and pathogenesis in multiple organs. We hypothesized that aberrant growth and differentiation of myeloid cells in lal(-/-) mice arises from dysregulated production of progenitor cells in the bone marrow. Indeed, lal(-/-) mice displayed increased numbers of primitive lin(-)Sca-1(+)c-Kit(+) (LSK) cells and granulocyte-macrophage precursors (GMP). Increased high proliferative potential colony-forming cells (HPP-CFC) were enumerated from cultured lal(-/-) bone marrow cells, as were significantly more CFU-GM, CFU-G, and CFU-M colonies. As a consequence, lal(-/-) mice developed significant myeloid infiltration, particularly with CD11b+/Gr-1+ myeloid-derived suppressive cells in multiple organs. Both decreased apoptosis and increased proliferation contribute to the systemic increase of myeloid cells in lal(-/-) myeloid cells. These lal(-/-) CD11b(+)/Gr-1(+) cells displayed suppressive activity on T cell proliferation and function in vitro. Bone marrow chimeras confirmed that the myeloproliferative disorder in lal(-/-) mice was primarily attributable to autonomous defects in myeloid progenitor cells, although the hematopoietic microenvironment in the lal(-/-) mice did not support hematopoiesis normally. These results provide evidence that LAL is an important regulator of myelopoiesis during hematopoietic development, differentiation, and homeostasis.

Homeostatic and pathogenic extramedullary hematopoiesis

Extramedullary hematopoiesis (EH) is defined as hematopoiesis occurring in organs outside of the bone marrow; it occurs in diverse conditions, including fetal development, normal immune responses, and pathological circumstances. During fetal development, before formation of mature marrow, EH occurs in the yolk sac, fetal liver, and spleen. EH also occurs during active immune responses to pathogens. Most frequently, this response occurs in the spleen and liver for the production of antigen-presenting cells and phagocytes. EH also occurs when the marrow becomes inhabitable for stem and progenitor cells in certain pathological conditions, including myelofibrosis, where marrow cells are replaced with collagenous connective tissue fibers. Thus, EH occurs either actively or passively in response to diverse changes in the hematopoietic environment. This article reviews the key features and regulators of the major types of EH.

Immunotherapy for prostate cancer: an emerging treatment modality

This article examines prostate cancer as a target for immunotherapy and investigates active immunotherapy for prostate cancer, combining conventional therapy with active immunotherapy, immune modulators (brakes and accelerators), and monoclonal antibodies.

Anti-inflammatory triterpenoid blocks immune suppressive function of MDSCs and improves immune response in cancer

PURPOSE

Myeloid-derived suppressor cells (MDSC) are one of the major factors responsible for immune suppression in cancer. Therefore, it would be important to identify effective therapeutic means to modulate these cells.

EXPERIMENTAL DESIGN

We evaluated the effect of the synthetic triterpenoid C-28 methyl ester of 2-cyano-3,12-dioxooleana-1,9,-dien-28-oic acid (CDDO-Me; bardoxolone methyl) in MC38 colon carcinoma, Lewis lung carcinoma, and EL-4 thymoma mouse tumor models, as well as blood samples from patients with renal cell cancer and soft tissue sarcoma. Samples were also analyzed from patients with pancreatic cancer treated with CDDO-Me in combination with gemcitabine.

RESULTS

CDDO-Me at concentrations of 25 to 100 nmol/L completely abrogated immune suppressive activity of MDSC in vitro. CDDO-Me reduced reactive oxygen species in MDSCs but did not affect their viability or the levels of nitric oxide and arginase. Treatment of tumor-bearing mice with CDDO-Me did not affect the proportion of MDSCs in the spleens but eliminated their suppressive activity. This effect was independent of antitumor activity. CDDO-Me treatment decreased tumor growth in mice. Experiments with severe combined immunodeficient-beige mice indicated that this effect was largely mediated by the immune system. CDDO-Me substantially enhanced the antitumor effect of a cancer vaccines. Treatment of pancreatic cancer patients with CDDO-Me did not affect the number of MDSCs in peripheral blood but significantly improved the immune response.

CONCLUSIONS

CDDO-Me abrogated the immune suppressive effect of MDSCs and improved immune responses in tumor-bearing mice and cancer patients. It may represent an attractive therapeutic option by enhancing the effect of cancer immunotherapy.

IL-17 promotes tumor development through the induction of tumor promoting microenvironments at tumor sites and myeloid-derived suppressor cells

The role of immune responses in tumor development is a central issue for tumor biology and immunology. IL-17 is an important cytokine for inflammatory and autoimmune diseases. Although IL-17-producing cells are detected in cancer patients and tumor-bearing mice, the role of IL-17 in tumor development is controversial, and mechanisms remain to be fully elucidated. In the current study, we found that the development of tumors was inhibited in IL-17R-deficient mice. A defect in IFN-gammaR increased tumor growth, whereas tumor growth was inhibited in mice that were deficient in both IL-17R and IFN-gammaR compared with wild-type animals. Further experiments showed that neutralization of IL-17 by Abs inhibited tumor growth in wild-type mice, whereas systemic administration of IL-17 promoted tumor growth. The IL-17R deficiency increased CD8 T cell infiltration, whereas it reduced the infiltration of myeloid-derived suppressor cells (MDSCs) in tumors. In contrast, administration of IL-17 inhibited CD8 T cell infiltration and increased MDSCs in tumors. Further analysis indicated that IL-17 was required for the development and tumor-promoting activity of MDSCs in tumor-bearing mice. These data demonstrate that IL-17-mediated responses promote tumor development through the induction of tumor-promoting microenvironments at tumor sites. IL-17-mediated regulation of MDSCs is a primary mechanism for its tumor-promoting effects. The study provides novel insights into the role of IL-17 in tumor development and has major implications for targeting IL-17 in treatment of tumors.

Immunosuppressive CD14+HLA-DRlow/- monocytes in prostate cancer

OBJECTIVE

To determine if the levels of circulating myeloid-derived suppressor cells increase with progression of prostate cancer (PCa); to determine if such cells could contribute to the relative inefficiency of PCa immunotherapy.

MATERIALS AND METHODS

We analyzed peripheral blood mononuclear cells isolated from untreated PCa patients (uPCa; N = 18; mean age +/- SD: 72.1 +/- 6.9 years), tPCa (N = 22; 72.8 +/- 9.8 years) and age matched controls (AMC; N = 12; 68.8 +/- 7.5 years). We quantified surface marker phenotype, differentiation potential, effects on T cell proliferation and intracellular cytokines.

RESULTS

We observed an unexpectedly high percentage of a type of myeloid-derived suppressor cells, CD14(+)HLA-DR(low/-) monocytes, in tPCa (30.7 +/- 15.0% of CD14(+) cells) relative to AMC (4.1 +/- 6.5%, P < 0.0001) and uPCa (10.6 +/- 14.3%, P = 0.0001). The levels of CD14(+) HLA-DR(low/-) cells were significantly correlated with circulating PSA levels and treatment with LHRH-agonist leuprolide in combination with either an antiandrogen or dexamethasone. Monocytes from tPCa inhibited autologous T cell proliferation statistically significantly more effectively than AMC monocytes and were defective in their ability to differentiate into phenotypically mature dendritic cells. Isolated CD14(+)HLA-DR(low/-) cells expressed higher levels of intracellular interleukin-10 and suppressed T cell proliferation more effectively than isolated CD14(+)HLA-DR(+) cells.

CONCLUSIONS

This is the first report of CD14(+) cells exhibiting reduced expression of HLA-DR molecules in PCa patients. These cells suppress immune cell function in vitro and, plausibly, in vivo, a finding that must be factored into the design of immunotherapy protocols for PCa patients.

IL-1-induced inflammation promotes development of leishmaniasis in susceptible BALB/c mice

The role of host-derived IL-1 on the course of Leishmania major infection in susceptible BALB/c mice was assessed. Manifestations of the disease were more severe in mice deficient in the physiological inhibitor of IL-1, the IL-1 receptor antagonist (IL-1Ra) in comparison with control mice. In mice lacking one of the IL-1 genes (IL-1alpha or IL-1beta), there was delayed development of the disease and more attenuated systemic inflammatory responses. IL-1alpha-deficient mice were slightly more resistant to L. major infection compared with IL-1beta-knockout mice. During disease progression in IL-1Ra KO and control mice, myeloid-derived suppressor cells invaded the spleen, concomitant to suppression of T cell-mediated immunity and expression of systemic high levels of pro-inflammatory cytokines. In IL-1-deficient mice, T(h)1 responses were still apparent, even at late stages of the disease. Thus, dose-dependent effects of IL-1 were shown to influence the pathogenesis of murine leishamaniasis in susceptible BALB/c mice. Physiological and supra-physiological levels of IL-1 in the microenvironment promoted an exacerbated form of disease, whereas sub-physiological doses of IL-1 induced a less progressive disease. Thus, manipulation of IL-1 levels in the host, using the IL-1Ra or specific antibodies, has the potential to alleviate symptoms of visceral manifestations of leishmaniasis.

Elusive identities and overlapping phenotypes of proangiogenic myeloid cells in tumors

It is now established that bone marrow-derived myeloid cells regulate tumor angiogenesis. This was originally inferred from studies of human tumor biopsies in which a positive correlation was seen between the number of tumor-infiltrating myeloid cells, such as macrophages and neutrophils, and tumor microvessel density. However, unequivocal evidence was only provided once mouse models were used to examine the effects on tumor angiogenesis by genetically or pharmacologically targeting myeloid cells. Since then, identifying the exact myeloid cell types involved in this process has proved challenging because of myeloid cell heterogeneity and the expression of overlapping phenotypic markers in tumors. As a result, investigators often simply refer to them now as "bone marrow-derived myeloid cells." Here we review the findings of various attempts to phenotype the myeloid cells involved and discuss the therapeutic implications of correctly identifying-and thus being able to target-this proangiogenic force in tumors.

Immune-based therapeutics for pediatric cancer

IMPORTANCE OF THE FIELD

Although most children with cancer are cured, there remain significant limitations of standard treatment, most notably chemotherapy resistance and non-specific toxicities. Novel immune-based therapies that target pediatric malignancies offer attractive adjuncts and/or alternatives to commonly employed cytotoxic regimens of chemotherapy or radiotherapy. Elucidation of the principles of tumor biology and the development of novel laboratory technologies over the last decade have led to substantial progress in bringing immunotherapies to the bedside.

AREAS COVERED IN THIS REVIEW

Current immunotherapeutic clinical trials in pediatric oncology and the science behind their development are reviewed.

WHAT THE READER WILL GAIN

Most of the immune-based therapies studied to date have been well tolerated, and some have shown promise in the setting of refractory or high-risk malignancies, demonstrating that immunotherapy has the potential to overcome resistance to conventional chemotherapy.

TAKE HOME MESSAGE

Some immune-based therapies, such as ch14.18 and MTP-PE, have already been proven effective in phase III randomized trials. Further studies are needed to optimize and integrate other therapies into standard regimens, and to test them in randomized trials for patients with childhood cancer.

Mast cells mobilize myeloid-derived suppressor cells and Treg cells in tumor microenvironment via IL-17 pathway in murine hepatocarcinoma model

Tumor immunosuppression is commonly braided with chronic inflammation during tumor development. However, the relationship between immunosuppression and inflammation in tumor microenvironment is still unclear. We have demonstrated that mast cells are accumulated and exacerbate the inflammation and immunosuppression in tumor microenvironment via SCF/c-kit signaling pathway. Here, we further elucidate the underlying mechanism, which involves both myeloid-derived suppressor cells (MDSCs) and regulatory T (Treg) cells. Our data showed that mast cells mobilized the infiltration of MDSCs to tumor and induced the production of IL-17 by MDSCs; MDSCs-derived IL-17 indirectly attracted Treg cells, enhanced their suppressor function, and induced the IL-9 production by Treg cells; in turn, IL-9 strengthened the survival and protumor effect of mast cells in tumor microenvironment. Our findings disclose a closed loop among mast cells, MDSCs and Treg cells in tumor microenvironment, which provides a new insight into the paralleled developments of inflammation and immunosuppression in tumor microenvironment. Based on these findings, we propose that targeting tumor inflammation might be a potential strategy to reverse the immunosuppression of tumor microenvironment, thus facilitating cancer immunotherapy.