Redirecting in vivo elicited tumor infiltrating macrophages and dendritic cells towards tumor rejection

Intra-tumoral dendritic cells increase efficacy of peripheral vaccination by modulation of glioma microenvironment

Pilot data showed that adding intratumoral (IT) injection of dendritic cells (DCs) prolongs survival of patients affected by glioblastoma multiforme (GBM) treated by subcutaneous (SC) delivery of DCs. Using a murine model resembling GBM, we investigated the immunological mechanisms underlying this effect. C57BL6/N mice received brain injections of GL261 glioma cells. Seven days later, mice were treated by 3 SC injections of DCs with or without 1 IT injection of DCs. DC maturation, induced by pulsing with GL261 lysates, was necessary to develop effective immune responses. IT injection of pulsed (pDC), but not unpulsed DCs (uDC), increased significantly the survival, either per se or in combination with SC-pDC (P < .001 vs controls). Mice treated by IT-pDC plus SC-pDC survived longer than mice treated by SC-pDC only (P = .03). Injected pDC were detectable in tumor parenchyma, but not in cervical lymph nodes. In gliomas injected with IT-pDC, CD8+ cells were significantly more abundant and Foxp3+ cells were significantly less abundant than in other groups. Using real-time polymerase chain reaction, we also found enhanced expression of IFN-gamma and TNF-alpha and decreased expression of transforming growth factor-beta (TGF-beta) and Foxp3 in mice treated with SC-pDC and IT-pDC. In vitro, pDC produced more TNF-alpha than uDC: addition of TNF-alpha to the medium decreased the proliferation of glioma cells. Overall, the results suggest that IT-pDC potentiates the anti-tumor immune response elicited by SC-pDC by pro-immune modulation of cytokines in the tumor microenvironment, decrease of Treg cells, and direct inhibition of tumor proliferation by TNF-alpha.

Macrophages and NF-κB in cancer

Macrophages are tissue resident phagocytes with important roles in development, wound healing, and inflammation. There is enormous heterogeneity in macrophage phenotype, from 'classically' activated macrophages that have important roles in inflammation and innate immunity, to 'alternative' macrophage activation that is associated with wound healing, angiogenesis, and immune-suppression. Most, if not all, solid tumors have a significant macrophage population, clinical and experimental evidence suggests tumor-associated macrophages (TAM) are linked with tumor progression. The trophic functions of TAM are associated with increased angiogenesis, malignant cell invasion, and metastasis. NF-κB is s central regulator of inflammation and NF-κB activation particularly in TAM is linked with promotion of carcinogenesis in various experimental models of inflammation-associated cancer. NF-κB activation in TAM has, therefore, been suggested to represent a molecular link between inflammation and cancer. However, TAM frequently display an anti-inflammatory phenotype linked with immune-suppression that is not easily reconciled with a pro-inflammatory function for NF-κB in TAM. Here, I review the form and function of TAM and discuss the role of NF-κB activation in TAM in carcinogenesis.

Central role of IFNgamma-indoleamine 2,3-dioxygenase axis in regulation of interleukin-12-mediated antitumor immunity

Sustained intratumoral delivery of interleukin-12 (IL-12) and granulocyte macrophage colony-stimulating factor induces tumor regression via restoration of tumor-resident CD8+ T-effector/memory cell cytotoxicity and subsequent repriming of a secondary CD8+ T-effector cell response in tumor-draining lymph nodes (TDLN). However, treatment-induced T-effector activity is transient and is accompanied with a CD4+ CD25+ Foxp3+ T-suppressor cell rebound. Molecular and cellular changes in posttherapy tumor microenvironment and TDLN were monitored to elucidate the mechanism of counterregulation. Real-time PCR analysis revealed a 5-fold enhancement of indoleamine 2,3-dioxygenase (IDO) expression in the tumor and the TDLN after treatment. IDO induction required IFNgamma and persisted for up to 7 days. Administration of the IDO inhibitor D-1-methyl tryptophan concurrent with treatment resulted in a dramatic enhancement of tumor regression. Enhanced efficacy was associated with a diminished T-suppressor cell rebound, revealing a link between IDO activity and posttherapy regulation. Further analysis established that abrogation of the regulatory counterresponse resulted in a 10-fold increase in the intratumoral CD8+ T-cell to CD4+ Foxp3+ T-cell ratio. The ratio of proliferating CD8+ T-effector to CD4+ Foxp3+ T-suppressor cells was prognostic for efficacy of tumor suppression in individual mice. IFNgamma-dependent IDO induction and T-suppressor cell expansion were primarily driven by IL-12. These findings show a critical role for IDO in the regulation of IL-12-mediated antitumor immune responses.

Activated macrophages in the tumour microenvironment-dancing to the tune of TLR and NF-kappaB

A large number of variables have been identified which appear to influence macrophage phenotype within the tumour microenvironment. These include reciprocal chemical and physical interactions with tumour cells and with non-malignant cells of the tumour microenvironment, tissue oxygen tension, and the origin and prior experience of the particular macrophage population. In this review we outline the key evidence for these influences and consider how macrophage phenotype is acquired and the relevance of the TLR-NF-kappaB pathway.

The role of proto-oncogene Fra-1 in remodeling the tumor microenvironment in support of breast tumor cell invasion and progression

A growing body of evidence indicates that interactions between neoplastic cells and tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) are crucial in promoting tumor cell invasion and progression. Macrophages play an ambiguous role in these processes since this M1 phenotype correlates with tumoricidal capacity whereas TAMs of M2 phenotype exert tumor-promoting effects. Here, we provide evidence that interactions between mouse breast tumor cells and TAMs remodel the TME, leading to upregulation of Fra-1, a member of the FOS family of transcription factor. In turn, this proto-oncogene initiates activation of the IL-6/JAK/Stat3 signaling pathway. This creates a malignant switch in breast tumor cells, leading to increased release of pro-angiogenic factors MMP-9, VEGF and TGF-β from tumor cells and intensified invasion and progression of breast cancer. Proof of concept for the crucial role played by transcription factor Fra-1 in regulating these processes was established by specific knockdown of Fra-1 with siRNA which resulted in marked suppression of tumor cell invasion, angiogenesis and metastasis in a mouse breast cancer model. Such a strategy could eventually lead to future efficacious treatments of metastatic breast cancer.

Nanoparticle-delivered multimeric soluble CD40L DNA combined with Toll-Like Receptor agonists as a treatment for melanoma

Stimulation of CD40 or Toll-Like Receptors (TLR) has potential for tumor immunotherapy. Combinations of CD40 and TLR stimulation can be synergistic, resulting in even stronger dendritic cell (DC) and CD8+ T cell responses. To evaluate such combinations, established B16F10 melanoma tumors were injected every other day X 5 with plasmid DNA encoding a multimeric, soluble form of CD40L (pSP-D-CD40L) either alone or combined with an agonist for TLR1/2 (Pam₃CSK₄ ), TLR2/6 (FSL-1 and MALP2), TLR3 (polyinosinic-polycytidylic acid, poly(I:C)), TLR4 ( monophosphoryl lipid A, MPL), TLR7 (imiquimod), or TLR9 (Class B CpG phosphorothioate oligodeoxynucleotide, CpG). When used by itself, pSP-D-CD40L slowed tumor growth and prolonged survival, but did not lead to cure. Of the TLR agonists, CpG and poly(I:C) also slowed tumor growth, and the combination of these two TLR agonists was more effective than either agent alone. The triple combination of intratumoral pSP-D-CD40L + CpG + poly(I:C) markedly slowed tumor growth and prolonged survival. This treatment was associated with a reduction in intratumoral CD11c+ dendritic cells and an influx of CD8+ T cells. Since intratumoral injection of plasmid DNA does not lead to efficient transgene expression, pSP-D-CD40L was also tested with cationic polymers that form DNA-containing nanoparticles which lead to enhanced intratumoral gene expression. Intratumoral injections of pSP-D-CD40L-containing nanoparticles formed from polyethylenimine (PEI) or C32 (a novel biodegradable poly(B-amino esters) polymer) in combination with CpG + poly(I:C) had dramatic antitumor effects and frequently cured mice of B16F10 tumors. These data confirm and extend previous reports that CD40 and TLR agonists are synergistic and demonstrate that this combination of immunostimulants can significantly suppress tumor growth in mice. In addition, the enhanced effectiveness of nanoparticle formulations of DNA encoding immunostimulatory molecules such as multimeric, soluble CD40L supports the further study of this technology for tumor immunotherapy.

Regression of established AB1 murine mesothelioma induced by peritumoral injections of CpG oligodeoxynucleotide either alone or in combination with poly(I:C) and CD40 ligand plasmid DNA

INTRODUCTION

Stimulation of the CD40 receptor using an agonistic anti-CD40 antibody can slow the growth of AB1 tumors. Stimulation of the GITR receptor may also have antitumor activity by countering the immunosuppressive effects of regulatory CD4 T cells. Similarly, agonists for Toll-Like Receptors (TLR) such as CpG oligodeoxynucleotides (TLR9 agonist) have activity against AB1 tumors. Combinations of CpG with CD40 ligand and polyinosinic-polycytidylic acid (poly(I:C), TLR3 agonist) may be even stronger than CpG alone. The synergistic effects of these combinations have been tested in other tumor types but not in mesothelioma.

METHODS

Established AB1 mesothelioma tumors were injected with either plasmid DNA encoding a novel 4-trimer form of murine CD40 ligand (pSP-D-CD40L), GITR ligand (GITRL), or control plasmid DNA. In addition, CpG with or without poly(I:C) was also injected intratumorally.

RESULTS

Plasmid injections of pSP-D-CD40L or pSP-D-GITRL, had no significant antitumor effect, possibly reflecting the difficulty of administering DNA injections into this very dense tissue. However, the injection of CpG with or without poly(I:C) strongly suppressed tumor growth and led to long-term tumor-free survival. The response to a triple combination of pSP-D-CD40L + CpG + poly(I:C) was demonstrated by an increase in intratumoral CD8 T cells and a dramatic increase in F4/80 macrophages.

CONCLUSIONS

Intratumoral injections of plasmid DNAs encoding highly active forms of either CD40 ligand or GITR ligand had no significant antitumor effects in this model, although improved DNA delivery techniques could possibly improve this strategy. In contrast, intratumoral CpG injections had significant antitumor effects and there were indications that CpG plus poly(I:C) was even more effective. Taken together, these data confirm previous reports that immune stimulants, especially CpG TLR9 agonists, have potential as a treatment for mesothelioma.

Rapid release of cytoplasmic IL-15 from tumor-associated macrophages is an initial and critical event in IL-12-initiated tumor regression

This study reveals that the IL-15 rapidly released into serum upon IL-12 injection into tumor-bearing mice is critical for the subsequent leukocytic infiltration of the tumor and tumor-bearing tissue. The increase in serum IL-15 occurs within 2 h after IL-12 injection concomitantly with a decrease in cytoplasmic IL-15 in tumor-associated Mphi (TAM). Injection of anti-IL-15 one hour prior to IL-12 abrogates subsequent leukocytic infiltration into the tumor and prevents the IL-12-induced reduction of primary tumor mass and the clearance of metastases. Administration of anti-IL-15 18 h after IL-12 did not have a detectable impact on IL-12-induced leukocytic infiltration of the tumor. Deletion of NK cells had no impact on the IL-12-induced change in the functional phenotype of TAM or on the subsequent initiation of leukocytic infiltration of the tumor. In concert with our previous studies demonstrating that IL-12 reduces tumor-supportive activities of TAM, the current study supports the hypothesis that functional re-programming of TAM not only undermines Mphi support for tumor growth but also contributes to a critical step in the initiation of anti-tumor immune responses. In this context, the functional plasticity and pro-immunogenic potential of TAM may constitute a significant and unappreciated target in existing cytokine therapies.

Cellular and molecular pathways linking inflammation and cancer

Several experimental and epidemiological evidence indicate that, irrespective of the trigger for the development (chronic infection/inflammation or genetic alteration), a "smouldering" inflammation is associated with the most of, if not all, tumours and supports their progression. Several evidence have highlighted that tumours promote a constant influx of myelomonocytic cells that express inflammatory mediators supporting pro-tumoral functions. Myelomonocytic cells are key orchestrators of cancer-related inflammation associated with proliferation and survival of malignant cells, subversion of adaptive immune response, angiogenesis, stroma remodelling and metastasis formation. Although the connection between inflammation and cancer is unequivocal the mechanistic basis of such association are largely unknown. Recent advances in the understanding of the cellular and molecular pathways involved in cancer-related inflammation as well as their potential relevance as diagnostic, prognostic and therapeutic targets are herein discussed.

Functional plasticity of macrophages: in situ reprogramming of tumor-associated macrophages

The extent to which the functional heterogeneity of Mvarphis is dependent on the differentiation of functional sublineages remains unresolved. One alternative hypothesis proposes that Mvarphis are functionally plastic cells, which are capable of altering their functional activities progressively in response to progressively changing signaling molecules generated in their microenvironment. This "functional plasticity" hypothesis predicts that the functionally polarized Mvarphis in chronic pathologies do not represent Mvarphi sublineages but rather, are mutable phenotypes sustained by chronic signaling from the pathological environment. Solid TAMvarphis are chronically polarized to provide activities that support tumor growth and metastasis and suppress adaptive immune responses. In support of the functional plasticity hypothesis, administration of slow-release microsphere-encapsulated IL-12 successfully reprogrammed TAMvarphis in situ, reducing Mvarphi support of tumor growth and metastasis and enhancing Mvarphi proimmunogenic activities. Increased knowledge of how Mvarphi function is regulated and how polarized Mvarphis can be reprogrammed in situ will increase our ability to control Mvarphi function in a variety of pathological states, including cancer and chronic inflammatory disease.

Alternatively activated RAW264.7 macrophages enhance tumor lymphangiogenesis in mouse lung adenocarcinoma

Tumor-associated macrophages (TAMs) have been implicated in promoting tumor progression and invasion. The onset and maintenance of tumor angiogenesis and lymphangiogenesis also seem to be partly driven by a group of polarized alternatively activated macrophages (aaMphi) in lung adenocarcinoma. Here, the aaMphi and classically activated macrophages (caMphi) were obtained using RAW264.7 cells via IL-4 and IFN-gamma + LPS treatment, respectively. Co-inoculation of aaMphi with Lewis lung carcinoma (LLC) cells promoted tumor growth, increased lymph node metastasis, and reduced the survival in C57BL/6 mice bearing LLC. Furthermore, the effects of the activated macrophages on the lymphangiogenesis-related properties of lymphatic endothelial cells (LECs) were investigated in vitro. When LECs were cultured in macrophages conditioned medium or in a co-culture system of macrophages and LECs, aaMphi significantly promoted proliferation, migration, and tube-like formation of LECs. We identified high VEGF-C expression in aaMphi and low expression in caMphi as well as unactivated macrophages by ELISA and Western blotting. In LECs, co-culture with aaMphi resulted in a significant increase of mRNA levels of specific lymphatic marker VEGF receptor-3 and the homeobox gene Prox-1, as well as lymphangiogenic factor VEGF-C rather than VEGF-D by quantitative RT-PCR. Furthermore, enhanced LECs migration and capillary formation by co-culture with aaMphi were significantly inhibited by rVEGF receptor-3/Fc chimera. In conclusion, these data show that aaMphi play a critical role in tumor-induced lymphangiogenesis through up-regulating VEGF-C and increasing lymphangiogenesis-related behavior of LECs, which may contribute to lymphatic invasion in lung adenocarcinoma.

Site-specific anti-tumor immunity: differences in DC function, TGF-beta production and numbers of intratumoral Foxp3+ Treg

Gliomas localized within the CNS are generally not rejected by the immune system despite being immunogenic. This failure of the immune system has been associated both with glioma-derived immunosuppressive molecules and the immune-privileged state of the CNS. However, the relative contribution of tumor location to the glioma-mediated immunosuppression, as well as the immune mechanisms involved in the failure of glioma rejection are not fully defined. We report here that syngeneic GL261 gliomas growing either intracranially or subcutaneously in mice are infiltrated by DC and T cells. However, only subcutaneous gliomas elicit an effective anti-tumor immune response. In contrast to DC infiltrating subcutaneously grown GL261 gliomas, tumor-infiltrating DC from intracranial gliomas do not activate antigen-dependent T-cell proliferation in vitro. In addition, brain-localized GL261 gliomas are characterized by significantly higher numbers of Foxp3(+) Treg and higher levels of TGF-beta1 mRNA and protein expression when compared with GL261 gliomas in the skin. Our data show that gliomas in the CNS, but not in the skin, give rise to TGF-beta production and accumulation of both Treg and functionally impaired DC. Thus, not the tumor itself, but its location dictates the efficiency of the anti-tumor immune response.

Activated monocytes in peritumoral stroma of hepatocellular carcinoma foster immune privilege and disease progression through PD-L1

Macrophages (Mφ) are prominent components of solid tumors and exhibit distinct phenotypes in different microenvironments. We have recently found that tumors can alter the normal developmental process of Mφ to trigger transient activation of monocytes in peritumoral stroma. We showed that a fraction of monocytes/Mφ in peritumoral stroma, but not in cancer nests, expresses surface PD-L1 (also termed B7-H1) molecules in tumors from patients with hepatocellular carcinoma (HCC). Monocytes activated by tumors strongly express PD-L1 proteins with kinetics similar to their activation status, and significant correlations were found between the levels of PD-L1⁺ and HLA-DR^high on tumor-infiltrating monocytes. Autocrine tumor necrosis factor α and interleukin 10 released from activated monocytes stimulated monocyte expression of PD-L1. The PD-L1⁺ monocytes effectively suppressed tumor-specific T cell immunity and contributed to the growth of human tumors in vivo; the effect could be reversed by blocking PD-L1 on those monocytes. Moreover, we found that PD-L1 expression on tumor-infiltrating monocytes increased with disease progression, and the intensity of the protein was associated with high mortality and reduced survival in the HCC patients. Thus, expression of PD-L1 on activated monocytes/Mφ may represent a novel mechanism that links the proinflammatory response to immune tolerance in the tumor milieu.

Anti-IL-10R antibody improves the therapeutic efficacy of targeted liposomal oligonucleotides

High-risk Neuroblastoma (NB) has still a poor prognosis. Liposomes targeted to NB cells and encapsulating antisense CpG-containing oligonucleotides (TL-asCpG) had increased anti-tumour efficacy in NB xenografts compared to free asCpG. Interleukin 10 (IL-10) suppresses antigen presenting cell activation contributing to tumour-mediated immune suppression. In principle, combination of TL-asCpG and antibodies against IL-10 receptor (aIL-10R) could prolong immune system activation, leading to better therapeutic results. Mice treated with TL-asCpG 4 h after human NB cell inoculation survived significantly longer than controls. An increased life span was achieved also in mice receiving TL-asCpG 24 and 72 h after NB cell challenge. The addition of aIL-10R to TL-asCpG in the 4-h protocol significantly increased the percentage of long term survivors compared to TL-asCpG only. Surviving mice treated with the combined strategy were completely cured. In contrast, long term surviving mice treated only with TL-asCpG presented lymph node infiltration with NB cells. TL-asCpG plus aIL-10R treatment was significantly superior to TL-asCpG alone also for the 24-h protocol. Ex vivo experiments demonstrated that the combined therapy evoked a stronger and more prolonged immune system activation compared to monotherapy. These results support the feasibility of a clinical trial with TL-asCpG and aIL-10R in advanced NB patients.

Tumor-specific bacteriophages induce tumor destruction through activation of tumor-associated macrophages

We recently reported that administration of tumor-specific bacteriophages initiates infiltration of neutrophilic granulocytes with subsequent regression of established B16 tumors. The aim of the current study was to investigate the mechanism of action of bacteriophage-induced tumor regression and to examine possible stimulatory effects of bacteriophages on macrophages. We observed that the mechanism of phage-induced tumor regression is TLR dependent as no signs of tumor destruction or neutrophil infiltration were observed in tumors in MyD88(-/-) mice in which TLR signaling is abolished. The microenvironment of bacteriophage-treated tumors was further analyzed by gene profiling through applying a low-density array preferentially designed to detect genes expressed by activated APCs, which demonstrated that the M2-polarized tumor microenvironment switched to a more M1-polarized milieu following phage treatment. Bacteriophage stimulation induced secretion of proinflammatory cytokines in both normal mouse macrophages and tumor-associated macrophages (TAMs) and increased expression of molecules involved in Ag presentation and costimulation. Furthermore, mouse neutrophils selectively migrated toward mediators secreted by bacteriophage-stimulated TAMs. Under these conditions, the neutrophils also exhibited increased cytotoxicity toward B16 mouse melanoma target cells. These results describe a close interplay of the innate immune system in which bacteriophages, located to the tumor microenvironment due to their specificity, stimulate TAMs to secrete factors that promote recruitment of neutrophils and potentiate neutrophil-mediated tumor destruction.

Alternatively activated macrophages elicited by helminth infection can be reprogrammed to enable microbial killing

The prime function of classically activated macrophages (activated by Th1-type signals, such as IFN-gamma) is microbial destruction. Alternatively activated macrophages (activated by Th2 cytokines, such as IL-4 and IL-13) play important roles in allergy and responses to helminth infection. We utilize a murine model of filarial infection, in which adult nematodes are surgically implanted into the peritoneal cavity of mice, as an in vivo source of alternatively activated macrophages. At 3 wk postinfection, the peritoneal exudate cell population is dominated by macrophages, termed nematode-elicited macrophages (NeMphi), that display IL-4-dependent features such as the expression of arginase 1, RELM-alpha (resistin-like molecule alpha), and Ym1. Since increasing evidence suggests that macrophages show functional adaptivity, the response of NeMphi to proinflammatory Th1-activating signals was investigated to determine whether a switch between alternative and classical activation could occur in macrophages differentiated in an in vivo infection setting. Despite the long-term exposure to Th2 cytokines and antiinflammatory signals in vivo, we found that NeMphi were not terminally differentiated but could develop a more classically activated phenotype in response to LPS and IFN-gamma. This was reflected by a switch in the enzymatic pathway for arginine metabolism from arginase to inducible NO synthase and the reduced expression of RELM-alpha and Ym1. Furthermore, this enabled NeMphi to become antimicrobial, as LPS/IFN-gamma-treated NeMphi produced NO that mediated killing of Leishmania mexicana. However, the adaptation to antimicrobial function did not extend to key regulatory pathways, such as IL-12 production, which remained unaltered.

Corrupt policemen: inflammatory cells promote tumor angiogenesis

PURPOSE OF REVIEW

The last decade has seen a paradigm change in that tumor stroma contributes to malignant tumor progression in a manner comparable to genetic and epigenetic changes within cancer cells. This review summarizes recent novel insights into how inflammatory conditions stimulate the formation and expansion of blood and lymphatic vessels within tumors and, thus, allow tumors to grow, to gain invasive capabilities, and to finally seed metastasis in distant organs.

RECENT FINDINGS

Different cancer types have a highly defined microenvironment, which is composed of cancer-associated fibroblasts, blood vessel and lymphatic endothelial cells, pericytes, and a heterogeneous infiltrate of cells of the immune system. In addition to the local stimulation of tumor angiogenesis and tumor lymphangiogenesis, cytokines released by the primary tumor and by the immune cell infiltrate also instruct bone marrow-derived cells to colonize distant organs and to prepare these sites for future metastasis.

SUMMARY

Inflammatory reactions coinciding with carcinogenesis can be visualized by the presence of specific bone marrow-derived, inflammatory cells in patients' peripheral blood. Recent findings suggest that such inflammatory fingerprints may better define the inflammatory nature of the primary malignancy and, thus, allow the design of therapeutic strategies targeting the protumorigenic immune cell stroma compartment.

Regulation of macrophage function in tumors: the multifaceted role of NF-kappaB

The pivotal role of tumor-associated macrophages (TAMs) in tumor progression is now well established. TAMs have been shown to influence multiple steps in tumor development including the growth, survival, invasion, and metastasis of tumor cells as well as angiogenesis and lymphangiogenesis in tumors. The molecular circuits that polarize TAMs toward such a protumoral phenotype are now the focus of intense investigation. The transcription factor, nuclear factor-kappaB (NF-kappaB), is a master regulator of many cellular processes and been shown to regulate various pathways that impact on the function of TAMs. Much evidence for this has come from the use of elegant transgenic murine tumor models in which modification of single components of the NF-kappaB signaling pathway has been shown to regulate the pro-tumor repertoire of TAMs. Here, we outline this evidence and attempt to reconcile the various views that have emerged recently over the exact role of NF-kappaB in this phenomenon.

Chemokine–chemokine receptors in cancer immunotherapy

A surge in interest in the chemokine–chemokine receptor network is probably related to the expanding roles that chemokines have now been identified to play in human biology, particularly immunity. Specific tissue microenvironments express distinct chemokines and both hematopoietic and nonhematopoietic cells have receptor expression profiles that permit the coordinated trafficking and organization of cells within these specific tissues. Since the chemokine network plays critical roles in both the function of the immune system and the progression of cancer, it is an attractive target for therapeutic manipulation. This review will focus on chemokine and chemokine receptor network-related therapeutic interventions that utilize host–tumor interactions particularly involving the immune system.

Signalling pathways leading to IFN-alpha production in human plasmacytoid dendritic cell and the possible use of agonists or antagonists of TLR7 and TLR9 in clinical indications

Plasmacytoid dendritic cells (PDC) are highly specialized immune cells capable of producing large amounts of type I and III IFN in response to viral infection. This response is mediated through TLR7 and TLR9 signalling pathways. In addition, PDC can differentiate into fully mature dendritic cells able to efficiently crosspresent viral antigens, thus playing an important role in adaptive immunity. This dual property of PDC is being used in clinical settings where synthetic TLR7 and TLR9 ligands are currently evaluated in clinical trials for the treatment of viral infections, allergies and cancers. Interestingly, there is evidence suggesting that chronic activation of PDC by endogenous RNA and DNA containing immune complexes maybe an important mechanism of driving autoimmunity and significant efforts to develop bi-functional antagonists of TLR7 and TLR9 are currently underway.

CD4+CD25+ Tregs control the TRAIL-dependent cytotoxicity of tumor-infiltrating DCs in rodent models of colon cancer

Tumors that progress do so via their ability to escape the antitumor immune response through several mechanisms, including developing ways to induce the differentiation and/or recruitment of CD4(+)CD25(+) Tregs. The Tregs, in turn, inhibit the cytotoxic function of T cells and NK cells, but whether they have an effect on the cytotoxic function of tumor-infiltrating DCs (TIDCs) has not been determined. Here we have shown, in 2 rodent models of colon cancer, that CD4(+)CD25(+) Tregs inhibit the ability of CD11b(+) TIDCs to mediate TNF-related apoptosis-inducing ligand-induced (TRAIL-induced) tumor cell death. In both models of cancer, combination treatment with Mycobacterium bovis Bacillus Calmette-Guérin (BCG), which activates the innate immune system via TLR2, TLR4, and TLR9, and cyclophosphamide (CTX), which depletes Tregs, eradicated the tumors. Further analysis revealed that the treatment led to a marked increase in the number of CD11b(+) TIDCs that killed the tumor cells via a TRAIL-dependent mechanism. Furthermore, acquisition of TRAIL expression by the CD11b(+) TIDCs was induced by BCG and dependent on signaling through TLR2, TLR4, and TLR9. In vivo transfer of Tregs abrogated the ability of BCG to induce CD11b(+) TIDCs to express TRAIL and thereby nullified the efficacy of the CTX-BCG treatment. Our data have therefore delineated what we believe to be a novel mechanism by which Tregs inhibit the antitumor immune response.

Will advances in fish immunology change vaccination strategies?

This review will discuss some of the recent advances in discovering immune genes in fish, in terms of their relevance to vaccine design and development. Particular emphasis will be placed on the many cytokine and costimulatory molecules now known, with examples drawn from the mammalian literature as to their potential value for fish vaccinology. A new area of vaccine research will also be touched upon, where efficacious responses are elicited by inhibiting the natural negative regulators of immune responses, such as Treg cell products and SOCS proteins.

Zoledronic acid modulates antitumoral responses of prostate cancer-tumor associated macrophages

Macrophages are considered a key component of the immunosuppressive environment present in solid tumors, where they support tumor growth through the production of pro-angiogenic factors and active suppression of effector immune responses. Zoledronic acid (ZA), an aminobisphosphonate clinically approved for treatment of symptomatic skeletal events, has recently been shown to have immunomodulatory properties that can be exploited in cancer immunotherapy. Here, we utilize an in vitro model of prostate cancer cell-macrophage interaction to dissect the effect of ZA, on the function of prostate cancer tumor-associated macrophages (PC-TAM). We show that prostate cancer cells recruit macrophages, which in turn express a variety of proangiogenic and immunosuppressive mediators. ZA selectively suppressed the expression of MMP-9 by PC-TAM, whereas the expression of other mediators was not limited. PC-TAM treated with ZA, on the other hand, could effectively drive the proliferation of activated Tgammadelta lymphocytes, which lysed bisphosphonate-pulsed prostate cancer cells. Moreover, ZA boosted the production of type-1 cytokines by PC-TAM in response to immunomodulators such as IL-12 and polyI:C, which are known to polarize macrophages towards an anti-tumoral M1 phenotype. Overall, we provide evidence that ZA shifts the balance of PC-TAM from a tumor promoting to a tumor-eliminating phenotype and also suggest a potential use of this pharmacological agent as an immunotherapeutic adjuvant.

Tumor-educated tolerogenic dendritic cells induce CD3epsilon down-regulation and apoptosis of T cells through oxygen-dependent pathways

Defects in the CD3/TCR complex and impairment of T cell function are necessary for tumor evasion, but the underlying mechanisms are incompletely understood. We found that culture supernatants from several types of solid tumor cell lines drove human monocytes to become tolerogenic semimature dendritic cells (TDCs). Upon encountering T cells, the TDCs triggered rapid down-regulation of CD3epsilon and TCR-alpha/beta and subsequent apoptosis in autologous T cells. Consistent with these results, accumulation of immunosuppressive DCs coincided with CD3epsilon down-regulation and T cell deletion in cancer nests of human tumors. The impaired T cell function was mediated by factor(s) released by live TDCs after direct interaction with lymphocytes. Also, the TDC-induced effect on T cells was markedly reduced by blocking of NADPH oxidase but not by inhibition of arginase, inducible NO synthase (iNOS), IDO, or IFN-gamma. Moreover, we found that hyaluronan fragments constituted a common factor produced by a variety of human tumor cell lines to induce formation of TDCs. These observations indicate that tumor microenvironments, including hyaluronan fragments derived from cancer cells, educate DCs to adopt a semimature phenotype, which in turn aids tumor immune escape by causing defects in the CD3/TCR complex and deletion of T cells.

Cytokines as a key component of cancer-related inflammation

Inflammatory conditions in some tissues increase the risk of cancer. Cytokines and chemokines are components of an intensive dialog promoting angiogenesis, metastasis, subversion of adaptive immunity and changing response to hormones and to chemotherapeutic agents. Cytokines involved in cancer-related inflammation represent a target for innovative diagnostic and therapeutic strategies, and a future challenge for scientists and clinicians.

Optimization of antibody binding to FcgammaRIIa enhances macrophage phagocytosis of tumor cells

The contribution of Fc-mediated effector functions to the therapeutic efficacy of some monoclonal antibodies has motivated efforts to enhance interactions with Fcgamma receptors (FcgammaR). Although an early goal has been enhanced FcgammaRIIIa binding and natural killer (NK) cell antibody-dependent cell-mediated cytotoxicity (ADCC), other relevant cell types such as macrophages are dependent on additional activating receptors such as FcgammaRIIa. Here, we describe a set of engineered Fc variants with diverse FcgammaR affinities, including a novel substitution G236A that provides selectively enhanced binding to FcgammaRIIa relative to FcgammaRIIb. Variants containing this substitution have up to 70-fold greater FcgammaRIIa affinity and 15-fold improvement in FcgammaRIIa/FcgammaRIIb ratio and mediate enhanced phagocytosis of antibody-coated target cells by macrophages. Specific double and triple combination variants with this substitution are simultaneously capable of exhibiting high NK-mediated ADCC and high macrophage phagocytosis. In addition, we have used this unique set of variants to quantitatively probe the relative contributions of individual FcgammaR to effector functions mediated by NK cells and macrophages. These experiments show that FcgammaRIIa plays the most influential role for macrophages and, surprisingly, that the inhibitory receptor FcgammaRIIb has little effect on effector function. The enhancements in phagocytosis described here provide the potential to improve the performance of therapeutic antibodies targeting cancers.

Recombinant vesicular stomatitis virus targeted to Her2/neu combined with anti-CTLA4 antibody eliminates implanted mammary tumors

Vesicular stomatitis virus (VSV) is being developed for cancer therapy. We created a recombinant replicating VSV (rrVSV) that preferentially infected Her2/neu expressing breast cancer cells. We now used this rrVSV to treat macroscopic peritoneal tumor implants of a mouse mammary tumor cell line stably transfected to express Her2/neu. rrVSV therapy alone prolonged survival but did not cure any animals. rrVSV therapy combined with antibody to TGFb or antibody to IL-10 receptor (IL-10R) each produced cure in one of six animals. Strikingly, rrVSV therapy combined with anti-CTLA4 monoclonal antibody (MAb) produced cure in four of five animals. Anti-CTLA4 MAb was only effective when administered within one day of rrVSV therapy. Cure required CD4 T-cells early (<7 days) and late (>7 days) after rrVSV therapy whereas CD8 T-cells were required only late (>7 days) after rrVSV therapy. Surviving animals were resistant to re-challenge with D2F2/E2 suggesting a memory immune response. Histopathologic analysis demonstrated a dense inflammatory infiltrate of tumor nodules within days of therapy and foamy histiocytes replacing the tumor nodules 2 weeks following therapy. These studies demonstrate that targeted rrVSV combined with anti-CTLA4 MAb can eliminate established macroscopic tumor implants by eliciting an anti-tumor CD4 and CD8 T-cell immunologic response.

Cancer related inflammation: the macrophage connection

Tumor-associated macrophages (TAM) are key regulators of the link between inflammation and cancer. In the tumor microenvironment neoplastic cells shape the differentiation and functional orientation of TAM which, in turn, express several protumoral functions, including secretion of growth factors and matrix-proteases, promotion of angiogenesis and suppression of adaptive immunity. This review analyzes our current knowledge of TAM and their involvement in tumor development and progression. The interplay between TAM and neoplastic cells represents a promising target of future therapeutic approaches.

Plasticity of macrophage function during tumor progression: regulation by distinct molecular mechanisms

Recent studies have shown that macrophages play an important part in both tumor initiation and various key steps in growth and metastasis. These cells show a remarkable degree of plasticity during tumor development with a "switch" in macrophage phenotypes occurring during the course of tumor progression. During chronic inflammation they appear to predispose a given tissue to tumor initiation by the release of factors that promote neoplastic transformation. Following this, their phenotype shifts more toward one that is immunosuppressive and supports tumor growth, angiogenesis, and metastasis. In this review, we discuss the evidence for this plasticity of macrophage functions, the specific signaling mechanisms that may be regulating it, and the new targets for anticancer therapies highlighted by these findings.

Macrophage polarization in tumour progression

Macrophages are a fundamental part of the innate defense mechanisms, which can promote specific immunity by inducing T cell recruitment and activation. Despite this, their presence within the tumour microenvironment has been associated with enhanced tumour progression and shown to promote cancer cell growth and spread, angiogenesis and immunosuppression. This paradoxical role of macrophages in cancer finds an explanation in their functional plasticity, that may result in the polarized expression of either pro- or anti-tumoural functions. Key players in the setting of their phenotype are the microenvironmental signals to which macrophages are exposed, which selectively tune their functions within a functional spectrum encompassing the M1 and M2 extremes. Here, we discuss recent findings suggesting that targeting tumour-associated macrophages (TAMs) polarization may represent a novel therapeutic strategy against cancer.

Endosomal translocation of CpG-oligodeoxynucleotides inhibits DNA-PKcs-dependent IL-10 production in macrophages

Synthetic oligodeoxynucleotides containing unmethylated CpG motifs (CpG-ODNs) function as powerful immune adjuvants by activating macrophages, dendritic cells, and B cells. However, the molecular recognition mechanism that initiates signaling in response to CpG-ODN has not fully been identified. We show in this study that peritoneal macrophages from SCID mice having mutations in the catalytic subunit of DNA-protein kinase (DNA-PKcs) were almost completely defective in the production of IL-10 and in ERK activation when treated with CpG-ODN. In contrast, IL-12 p70 production significantly increased. Furthermore, small interfering RNA (siRNA)-mediated knockdown of DNA-PKcs expression in the mouse monocyte/macrophage cell line RAW264.7 led to reduced IL-10 production and ERK activation by CpG-ODN. IL-10 and IL-12 p70 production, but not ERK activation, are blocked by chloroquine, an inhibitor of endosomal acidification. Endosomal translocation of CpG-ODN in a complex with cationic liposomes consisting of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) (CpG-DOTAP-liposomes) decreased IL-10 production and ERK activation, whereas the endosomal escape of CpG-ODN in a complex with cationic liposomes consisting of DOTAP and dioleyl-phosphatidylethanolamine (DOPE) (CpG-DOTAP/DOPE-liposomes) increased. In contrast, IL-12 p70 production was increased by CpG-DOTAP-liposomes and decreased by CpG-DOTAP/DOPE-liposomes. IL-10 production induced by CpG-DOTAP/DOPE-liposomes was not observed in macrophages from SCID mice. Thus, our findings suggest that DNA-PKcs in the cytoplasm play an important role in CpG-ODN-induced production of IL-10 in macrophages. In addition, DNA-PKcs-mediated production of IL-10 and IL-12 p70 can be regulated by manipulating the intracellular trafficking of CpG-ODN in macrophages.

Colonization of experimental murine breast tumours by Escherichia coli K-12 significantly alters the tumour microenvironment

The successful application of live bacteria in cancer therapy requires a more detailed understanding of bacterial interaction with the tumour microenvironment. Here, we analysed the effect of Escherichia coli K-12 colonization on the tumour microenvironment by immunohistochemistry and fluorescence microscopy in the murine 4T1 breast carcinoma model. We described the colonization of tumour-bearing mice, as well as the spatiotemporal distribution of E. coli K-12 in the 4T1 tumour tissue over a period of 14 days. The colonization resulted within 3 days in large avascular necrotic tissue, redistribution of hypoxic areas and an enhanced collagen IV deposition within the colonized tumour tissue, which changed the tumoral perfusion of systemically injected immunoglobulins. In addition, E. coli K-12 colonization led to the redistribution of tumour-associated macrophages, forming a granulation tissue around bacterial colonies, and also to an increase in TNFalpha and matrix metalloproteinase 9 expression. Colonization of 4T1 tumours by E. coli K-12 resulted in strong reduction of pulmonary metastatic events. These new insights will contribute to the general understanding of the tumour-microbe cross-talk and to the design of bacterial strains with enhanced anticancer efficiency.

[Immunotherapy against peritoneal dissemination by immunostimulatory CpG DNA]

Peritoneal dissemination is one of the most common causes of metastasis from malignancies in the abdominal cavity. However, the treatment of peritoneal dissemination is difficult; patients receiving normal chemotherapy have a 0-1% chance of surviving for 5 years. Milky spots in the greater omentum are considered to facilitate the adhesion and invasion of abdominal free cancer cells, and subsequently lymph node metastasis occurs. Since immune cells such as macrophages and lymphocytes are present in the greater omentum and lymph nodes, the activation of immune cells would be a promising strategy for treatment. Single-stranded oligonucleotides containing CpG dinucleotides (CpG DNA) are recognized by Toll-like receptor-9 on antigen-presenting cells such as macrophages to stimulate Th-1-type immune responses. However, a delivery system for CpG DNA to immune cells is essential to develop effective therapy against peritoneal dissemination. Here we review the pathophysiologic basis of peritoneal dissemination and introduce our approach that employs cationic liposomes as a carrier for CpG DNA as a new approach in the treatment of peritoneal dissemination.

The inflammatory micro-environment in tumor progression: the role of tumor-associated macrophages

The link between inflammation and cancer proposed more than a century ago by Rudolf Virchow, who noticed the infiltration of leukocytes in malignant tissues, has recently found a number of genetic and molecular confirmations. Experimental, clinical and epidemiological studies have revealed that chronic inflammation contributes to cancer progression and even predisposes to different types of cancer. Cancer-associated inflammation includes: the presence of leukocyte infiltration; the expression of cytokines such as tumor necrosis factor (TNF) or interleukin (IL)-1; chemokines such as CCL2 and CXCL8; active tissue remodelling and neo-angiogenesis. Tumor-associated macrophages (TAM) are key regulators of the link between inflammation and cancer. Many observations indicate that, in the tumor micro-environment, TAM have several protumoral functions, including expression of growth factors, matrix proteases, promotion of angiogenesis and suppression of adaptive immunity. In this review we will discuss the role of TAM in the inflammatory micro-environment of solid tumors and will try to identify potential target for future therapeutic approaches.

Targeting tumour-associated macrophages

Clinical and experimental evidence have highlighted that a major leukocyte population present in tumours, the so-called tumour-associated macrophages (TAM), is the principal component of the leukocyte infiltrate supporting tumour growth. Over the years the mechanisms supporting the protumoural functions of TAM have become increasingly clear and in several experimental tumour models, the activation of an inflammatory response (most frequently mediated by macrophages) has been shown to play an essential role for full neoplastic transformation and progression. This evidence strongly supports the idea that TAM are central orchestrators of the inflammatory networks expressed in the tumour microenvironment, and suggest these cells as possible targets of anticancer therapies.

Cross-talk between myeloid-derived suppressor cells and macrophages subverts tumor immunity toward a type 2 response

Although the immune system has the potential to protect against malignancies, many individuals with cancer are immunosuppressed. Myeloid-derived suppressor cells (MDSC) are elevated in many patients and animals with tumors, and contribute to immune suppression by blocking CD4(+) and CD8(+) T cell activation. Using the spontaneously metastatic 4T1 mouse mammary carcinoma, we now demonstrate that cross-talk between MDSC and macrophages further subverts tumor immunity by increasing MDSC production of IL-10, and by decreasing macrophage production of IL-12. Cross-talk between MDSC and macrophages requires cell-cell contact, and the IL-12 decrease is dependent on MDSC production of IL-10. Treatment with the chemotherapeutic drug gemcitabine, which reduces MDSC, promotes rejection of established metastatic disease in IL-4Ralpha(-/-) mice that produce M1 macrophages by allowing T cell activation, by maintaining macrophage production of IL-12, and by preventing increased production of IL-10. Therefore, MDSC impair tumor immunity by suppressing T cell activation and by interacting with macrophages to increase IL-10 and decrease IL-12 production, thereby promoting a tumor-promoting type 2 response, a process that can be partially reversed by gemcitabine.

Manipulating the chemokine-chemokine receptor network to treat cancer

Chemokines are chemoattractant cytokines that regulate the trafficking and activation of leukocytes and other cell types under a variety of inflammatory and noninflammatory conditions. Over the past few years, studies have increasingly shown that chemokines play an important role in several aspects of tumor progression. Tumor cells express functional chemokine receptors, which can sustain proliferation, angiogenesis, and survival and promote organ-specific localization of distant metastases. Chemokine expression in human malignancies is associated with a leukocyte infiltration favoring the establishment of immune escape mechanisms. A literature review of relevant publications on preclinical testing of cancer therapies based on interference with the cancer chemokine network was performed. The feasibility, potential advantages, and limitations of the clinical translation of the results of such studies in treatment of different tumor types and settings are discussed. The chemokine network is a key player in the establishment of metastases. In the preclinical setting, blocking agents and antibodies directed against CXCR4 prevent metastasis of different cancers. In mouse models, overexpression of selected chemokines causes tumor infiltration by distinct leukocyte subsets, resulting in tumor regression and tumor-specific immunity generation. Researchers have also successfully used chemokines as carriers and/or adjuvants for cancer vaccines. The cancer chemokine network is a multifaceted therapeutic target.

Altered macrophage differentiation and immune dysfunction in tumor development

Tumors require a constant influx of myelomonocytic cells to support the angiogenesis and stroma remodeling needed for their growth. This is mediated by tumor-derived factors, which cause sustained myelopoiesis and the accumulation and functional differentiation of myelomonocytic cells, most of which are macrophages, at the tumor site. An important side effect of the accumulation and functional differentiation of these cells is that they can induce lymphocyte dysfunction. A complete understanding of the complex interplay between neoplastic and myelomonocytic cells might offer novel targets for therapeutic intervention aimed at depriving tumor cells of important growth support and enhancing the antitumor immune response.

Development of TLR9 agonists for cancer therapy

In vertebrates, the TLRs are a family of specialized immune receptors that induce protective immune responses when they detect highly conserved pathogen-expressed molecules. Synthetic agonists for several TLRs, including TLR3, TLR4, TLR7, TLR8, and TLR9, have been or are being developed for the treatment of cancer. TLR9 detects the unmethylated CpG dinucleotides prevalent in bacterial and viral DNA but not in vertebrate genomes. As discussed in this Review, short synthetic oligodeoxynucleotides containing these immune stimulatory CpG motifs activate TLR9 in vitro and in vivo, inducing innate and adaptive immunity, and are currently being tested in multiple phase II and phase III human clinical trials as adjuvants to cancer vaccines and in combination with conventional chemotherapy and other therapies.