The Parallel Lives of Angiogenesis and Immunosuppression

PERSPECTIVES

78. De Wilde, V. et al. Endotoxin-induced myeloid-derived suppressor cells inhibit alloimmune responses via heme OPINION oxygenase‑1. Am. J. Transplant. 9, 2034–2047 (2009). 79. Saraiva, M. & O’Garra, A. The regulation of IL‑10 production by immune cells. Nature Rev. Immunol. 10, The parallel lives of angiogenesis 170–181 (2010). 80. Kaiser, F. et al. TPL‑2 negatively regulates interferon-β production in macrophages and myeloid dendritic cells. J. Exp. Med. 206, 1863–1871 and immunosuppression: cancer and (2009). 81. Slack, E. C. et al. Syk-dependent ERK activation regulates IL‑2 and IL‑10 production by DC stimulated other tales with zymosan. Eur. J. Immunol. 37, 1600–1612 (2007). 82. Saraiva, M. et al. Interleukin‑10 production by Th1 Gregory T. Motz and George Coukos cells requires interleukin-12‑induced STAT4 transcription factor and ERK MAP kinase activation by high antigen dose. Immunity 31, 209–219 Abstract | Emerging evidence indicates that angiogenesis and immunosuppression (2009). 83. Shoemaker, J., Saraiva, M. & O’Garra, A. GATA‑3 frequently occur simultaneously in response to diverse stimuli. Here, we describe a directly remodels the IL‑10 locus independently of IL‑4 in CD4+ T cells. J. Immunol. 176, 3470–3479 fundamental biological programme that involves the activation of both angiogenesis (2006). and immunosuppressive responses, often through the same cell types or soluble 84. Xu, J. et al. c‑Maf regulates IL‑10 expression during Th17 polarization. J. Immunol. 182, 6226–6236 factors. We suggest that the initiation of these responses is part of a physiological (2009). 85. Pot, C. et al. Cutting edge: IL‑27 induces the and homeostatic tissue repair programme, which can be co-opted in pathological transcription factor c‑Maf, cytokine IL‑21, and the costimulatory receptor ICOS that coordinately act states, notably by tumours. This view can help to devise new cancer therapies and together to promote differentiation of IL‑10‑ may have implications for aseptic tissue injury, pathogen-mediated tissue producing Tr1 cells. J. Immunol. 183, 797–801 (2009). destruction, chronic inflammation and even reproduction. 86. Belkaid, Y. et al. CD4+CD25+ regulatory T cells control Leishmania major persistence and immunity. Nature 420, 502–507 (2002). 87. Anderson, C. F. et al. CD4+CD25–Foxp3– Th1 cells are The vascular system develops through the by diverse physiological stimuli, such as the source of IL‑10‑mediated immune suppression in chronic cutaneous leishmaniasis. J. Exp. Med. 204, coordinated actions of both vasculogenesis those that occur during aseptic tissue injury 285–297 (2007). and angiogenesis. Vasculogenesis gives rise resulting from ischaemia–reperfusion injury 88. Jankovic, D. et al. Conventional T‑bet+Foxp3– Th1 cells are the major source of host-protective regulatory to de novo blood vessels, whereas angio- or wounding, during infection and even IL‑10 during intracellular protozoan infection. genesis is the sprouting of new vessels from during pregnancy. We think that the benefit J. Exp. Med. 204, 273–283 (2007). 89. Redford, P. S., Murray, P. J. & O’Garra, A. pre-existing ones. Physiological angiogenesis of such an interconnected and reciprocal The role of IL‑10 in immune regulation during — which occurs during development and tissue repair programme is to ensure tissue M. tuberculosis infection. Mucosal Immunol. 4, 261–270 (2011). wound healing — proceeds through vessel homeostasis. Summoning cells that can 90. Maynard, C. L. et al. Regulatory T cells expressing destabilization, endothelial cell migration simultaneously mediate angiogenesis and interleukin 10 develop from Foxp3+ and Foxp3– precursor cells in the absence of interleukin 10. and proliferation, and sprouting. This is immunosuppression provides an efficient Nature Immunol. 8, 931–941 (2007). followed by the resolution phase, which is process that economizes resources at times 91. Chaudhry, A. et al. Interleukin‑10 signaling in regulatory T cells is required for suppression of Th17 characterized by reduced endothelial cell of homeostatic crisis. This hypothesis is sup- cell-mediated inflammation. Immunity 34, 566–578 proliferation and stabilization of the new ported by the ever-growing list of haemato (2011). 92. Huber, S. et al. Th17 cells express interleukin‑10 vessel. Pathological angiogenesis shares poietic cell types that, when appropriately receptor and are controlled by Foxp3– and Foxp3+ many of the same processes, but is charac- polarized, can promote both immuno regulatory CD4+ T cells in an interleukin-10‑ dependent manner. Immunity 34, 554–565 (2011). terized by a failure of the resolution phase suppression and angiogenesis. For example, and the generation of a highly disorganized myeloid-derived suppressor cells (MDSCs)2, Competing interests statement 3,4 The authors declare competing financial interests: see Web vascular network. Pathological angiogen- dendritic cell (DC) subsets , natural killer version for details. esis is a key feature of tumour biology, but (NK) cells5, neutrophils6, macrophages, 7,8 9 is also involved in a broad spectrum of B cells and regulatory T (TReg) cells , as FURTHER INFORMATION inflammatory diseases, such as rheumatoid well as the angiogenic endothelium itself 10, Medzhitov, R. Toll-like receptors and innate immunity. 1 Nature Rev. Immunol. 1, 135–145 (2001) | Shevach, E. arthritis and connective tissue disorders . have been shown to have this dual capacity. CD4+CD25+ suppressor T cells: more questions than answers. Although pathological angiogenesis is gener- Furthermore, mediators secreted by these Nature Rev. Immunol. 2, 389–400 (2002) | Trinchieri, G. Interleukin‑12 and the regulation of innate resistance and ally viewed as a process driven by resident cells — such as vascular endothelial growth adaptive immunity. Nature Rev. Immunol. 3, 133–146 (2003) | endothelial cells and mobilized endothelial factor A (VEGFA) and prostaglandin E2 Mellor, A. L. & Munn, D. H. IDO expression by dendritic cells: tolerance and tryptophan catabolism. Nature Rev. Immunol. progenitor cells, a complex tissue repair (PGE2) — have well-known functions in 4, 762–774 (2004) | Gordon, S. & Taylor, P. R. Monocyte and programme is responsible for regulating the both angiogenesis and immunosuppression. macrophage heterogeneity. Nature Rev. Immunol. 5, 953–964 (2005) | Hansson, G. K. & Libby, P. The immune response in process of remodelling and vessel formation. Tumour development, much like tissue atherosclerosis: a double-edged sword. Nature Rev. Immunol. It is our view that pathological angiogenesis is repair and wound healing, requires the devel- 6, 508–519 (2006) | Shortman, K. & Naik, S. H. Steady-state and inflammatory dendritic-cell development. Nature Rev. integrated with and co-regulated by immuno- opment of neovasculature and the suppres- Immunol. 7, 19–30 (2007) | Dong, C. T 17 cells in development: H suppressive processes in a homeostatic tissue sion of excessive inflammation. It is possible an updated view of their molecular identity and genetic programming. Nature Rev. Immunol. 8, 337–348 (2008) | repair programme. that tumour development proceeds by the Gabrilovich, D. I. & Nagaraj, S. Myeloid-derived suppressor There are numerous examples that co-option of the homeostatic tissue repair cells as regulators of the immune system. Nature Rev. Immunol. 9, 162–174 (2009) | Saraiva, M. & O’Garra, A. The regulation of demonstrate the existence of a biological programme, promoting concurrent angio- IL‑10 production by immune cells. Nature Rev. Immunol. 10, response characterized by the simultaneous genesis and immunosuppression, and that 170–181 (2010). activation of angiogenesis and immuno this becomes the overarching biological pro- ALL LINKS ARE ACTIVE IN THE ONLINE PDF suppression. This response can be initiated gramme that drives the polarization of the

tumour microenvironment. The dual regulation of angiogenesis and immunosuppression $NQQFXGUUGN is obviously complex, with often-overlapping and potentially redundant pathways, and this pro-angiogenic and immunosuppressive 'PFQVJGNKCNEGNN programme is initiated by the expression of 8')(# cellular functions and mediators in a context- D()(%%. 6WOQWT #0)26 specific manner. The stimuli responsible for OKETQGPXKTQPOGPV //2U 8')(# the initiation phase of this programme are //2 /&5% most likely to be chemical or physiological 6#/ +. in nature (for example, oxidative stress11 or hypoxia9). Under most circumstances, tissues would only encounter these stimuli briefly 64GIEGNN +OOCVWTG&% during a homeostatic crisis (such as that 4GIWNCVQT[ 8')(#! induced by wounding), but genetic mutation 0-EGNN 6)(β and transformation that drives tumour progression chronically activates these path- %%.%%. $4GIEGNN ways. Thus, tumours capitalize on existing %:%.%:%. tissue repair mechanisms to promote their #0)268')(# continued growth and dissemination. 2.)( 8')(#

The notion that angiogenesis and 6+' OQPQE[VG D()(%%. #0)26 immunosuppression work hand-in-hand //2U can be used to study the tumour micro 5RTQWVKPI DNQQFXGUUGN environment under a new light, in order to derive novel cancer therapies. This para- 0GWVTQRJKN digm is becoming increasingly relevant to cutting-edge immunotherapy strategies #FGPQUKPG2)' for cancer. For example, we and others 8')(#+.6)(β have demonstrated that disruption of 415QZKFK\GFNKRKFU angiogenesis substantially enhances the 6WOQWTEGNNU efficacy of immune-based cancer therapies Figure 1 | Promotion of angiogenesis by immunosuppressive cells. Within the tumour micro such as tumour vaccines and adoptive cell environment, multiple cell types with established roles in immunosuppression0CVWTG4G XKGYUhave been^+OOWPQNQI[ shown to therapy10,12,13 . Furthermore, this view of promote angiogenesis through the production of various growth factors. Tumour cells, either in the the tumour microenvironment could steady state or in response to hypoxia, secrete soluble factors that recruit immunosuppressive cells to also be used to enhance anti-angiogenesis the tumour site. These factors include CC-chemokine ligand 2 (CCL2), CCL28, CXC-chemokine therapy. For example, combining canoni- ligand 8 (CXCL8), CXCL12, angiopoietin 2 (ANGPT2), vascular endothelial growth factor A (VEGFA) cal anti-angiogenesis therapeutics with and placenta growth factor (PLGF). Recruited immunosuppressive cells include tumour-associated immunomodulatory drugs that promote macrophages (TAMs), TIE2+ monocytes, neutrophils, myeloid-derived suppressor cells (MDSCs), immature dendritic cells (DCs), regulatory T (T ) cells, regulatory B (B ) cells and regulatory natural pro-inflammatory T helper 1 (TH1) cells or Reg Reg deplete pro-angiogenic leukocyte subsets killer (NK) cells. The immunosuppressive cells secrete factors — such as VEGFA, basic fibroblast may provide a superior tumour therapy. growth factor (bFGF), CCL2 and ANGPT2 — that directly promote endothelial cell proliferation and migration, and/or induce the production of matrix metalloproteinases (MMPs) that act on the extra Ultimately, we envision that future integrative cellular matrix, allowing for the development of new blood vessels. Pro-angiogenic growth factors biological treatment of tumours will capital- derived from these cells probably promote angiogenesis in an additive or synergistic manner, together ize on this view to deliver combined therapies with tumour-derived VEGFA, transforming growth factor-β (TGFβ), adenosine, prostaglandin E2 that target immune and angiogenesis mecha- (PGE2), interleukin‑6 (IL‑6), reactive oxygen species (ROS) and oxidized lipids. nisms12,13. Lessons that have been learnt from cancer biology could then be applied to basic investigation in diverse areas of immunology, but lymphocytes also have key roles (see phenotype of these myeloid cells may including infection, tissue regeneration, below). It is possible that tumour-derived reflect a reversible functional state, rather autoimmunity, tolerance, transplantation factors recruit immature myeloid cells and than terminal and irreversible differentia- biology and reproduction. myeloid cell precursors from the periphery, tion, opens the door to designing pharma- and that in the tumour microenvironment cological manipulation strategies to reverse Cellular players these cells differentiate into cells committed this phenotype, and this could have a pro- Various haematopoietic cells that pos- to suppressive and pro-angiogenic func- found impact on both tumour suppression sess both immunosuppressive and pro- tions. However, it may be equally plausible and angiogenesis. angiogenic abilities have been identified in that mature, differentiated myeloid cells tumours, including both myeloid and lym- are ‘edited’ by the tumour to acquire a sup- Myeloid cells. Myeloid cells are perhaps phocyte populations (FIG. 1). Myeloid cells pressive and pro-angiogenic phenotype, as the best-studied cell types in terms of their have received much attention given their most of these cell types exhibit at least some ability to promote immunosuppression and prominent roles in the processes of both degree of plasticity. The notion that the angiogenesis in tumours. Principal among immunosuppression and angiogenesis, immunosuppressive and pro-angiogenic them are MDSCs (reviewed extensively

in REF. 14). MDSC numbers are markedly implicating MDSCs in this process17. These receptor CC‑chemokine receptor 10 increased in the spleens of tumour-bearing cells have been shown to secrete the pro- (CCR10) on TReg cells. Overexpression of mice and in the blood of patients with can- angiogenic factors VEGFA and matrix CCL28 correlated with shorter survival in cer, with reports that up to 40% of spleno- metalloproteinase 9 (MMP9)2. Importantly, patients with ovarian cancer, and resulted cytes of tumour-bearing mice are MDSCs14. the pro-angiogenic function of MDSCs can in rapid ovarian tumour growth in mice. Their functional characterization is ulti- render tumours refractory to angiogenic This was due to increased recruitment of mately based on their ability to suppress T blockade by VEGFA-specific antibodies TReg cells to tumour sites, which established and NK cell activation15, probably through through the secretion of alternative pro- an immunosuppressive microenviron- several mechanisms, including the produc- angiogenic factors, such as BV8 (also ment rich in VEGFA and with increased tion of nitric oxide (NO), reactive oxygen known as prokineticin 2), which is upregu- angiogenesis. species (ROS), arginase, interleukin‑10 lated by granulocyte colony-stimulating Although the pro-angiogenic effects 17 (IL‑10) and transforming growth factor‑β factor . of TReg cells might be indirect, we found + + (TGFβ). There are also reports that MDSCs Several other myeloid cell subsets pos- that human and mouse CD4 CD25 TReg may specifically induce the expansion of sess the capacity to promote angiogenesis, cells secrete higher amounts of VEGFA in 16 TReg cell populations . including myeloid and plasmacytoid DCs, the steady state and under hypoxic condi- MDSCs have also been demonstrated tumour-associated macrophages (TAMs), tions than CD4+CD25– T cells and promote to directly promote angiogenesis2. Indeed, monocytes that express the angiopoietin endothelial cell proliferation in vitro and tumour-bearing mice treated with a neu- receptor TIE2, mast cells and neutrophils in vivo. Importantly, depletion of CD25+ REF. 18 (FIG. 1) + tralizing BV8‑specific antibody (which (reviewed in ) . For example, cells or CCR10 cells eliminated TReg cells reduces the number of MDSCs) had myeloid cells such as immature DCs and from the tumour microenvironment and markedly reduced angiogenesis, strongly TAMs can alter their phenotype following substantially suppressed VEGFA expression their recruitment to the tumour micro and angiogenesis at these sites9. environment in response to tumour-derived These observations are supported by 19 Glossary chemokines or antimicrobial peptides . the demonstration that T cells exposed to These cells acquire a pro-angiogenic profile hypoxia express VEGFA, and T cells within Adoptive cell therapy characterized by the secretion or expres- tumours may express VEGFA26. Moreover, Very simply, the transfusion of lymphocytes into patients for the treatment of cancer. Strategies that have enjoyed sion of VEGFA, basic fibroblast growth CD4‑deficient mice have an impaired success include the rapid ex vivo expansion of tumour- factor (bFGF; also known as FGF2), CXC- angiogenesis response to hypoxia during infiltrating lymphocytes followed by autologous chemokine ligand 8 (CXCL8) and cyclo ischaemia, suggesting that T cells may also reinjection. Engineering of patient peripheral blood T cells oxygenase 2 (COX2; also known as PTGS2). participate in homeostatic tissue repair fol- to express artificial T cell receptors or chimeric antigen Moreover, they downregulate their immuno lowing ischaemia27. However, it remains receptors that recognize tumour antigens is a recently + developed strategy that has proved successful. stimulatory functions (for example, by to be determined whether CD4 T cells

downregulating IL‑12 expression owing to (particularly TReg cells), make significant Diapedesis autocrine IL‑10 production)18,20–22. contributions to angiogenesis, given that Leukocyte migration through the endothelium that is most tumours autonomously produce large mediated by leukocyte-secreted proteases that disrupt the endothelial cell barrier. Lymphocyte populations. Given the cru- amounts of VEGFA. Furthermore, the cial role of lymphocyte populations in capacity of TReg cells to contribute to angio- Extravasation immunosuppression and tolerance, it is not genesis may depend entirely on the context, The multistep process of leukocyte infiltration through surprising that emerging evidence suggests as TReg cells have been implicated in the the endothelium. This process proceeds through the that these cells play key parts in the homeo- prevention of angiogenesis in a mouse stages of leukocyte rolling, adhesion, diapedesis and 28 finally migration to the surrounding tissues. static tissue repair programme that is co- model of airway inflammation . opted by tumours. CD4+CD25+FOXP3+ Recently, it has been demonstrated Ischaemia–reperfusion injury TReg cells (which can suppress effector T cell that, during interaction with DCs, acti- Disruption of proper blood flow, either experimentally or functions) accumulate at tumour sites vated CD4+ T cells can acquire mature otherwise, followed by restoration of normal blood flow results in significant hypoxia, tissue damage and inflammation and are correlated with a poor prognostic DC-expressed neuropilin 1 (NRP1; a 23 followed by angiogenesis and immunosuppression. outcome . Although the accumulation co-receptor that binds VEGFA) through trogocytosis29 of TReg cells at tumour sites has been cor- a process known as . NRP1 Mural cells related with angiogenesis in endometrial24 expressed in the plasma membrane of DCs Cells that physically surround the endothelial cells of blood and breast25 cancer, no direct role for T is transferred and becomes incorporated vessels. This population is comprised of vascular smooth Reg muscle cells (associated with veins and arteries) and cells in tumour angiogenesis had been into the membrane of recipient T cells, pericytes (associated with capillaries and developing vessels). demonstrated until we recently uncovered and this was shown to enable T cells to

a role for TReg cells in hypoxia-induced bind DC‑secreted VEGFA, potentially Pericyte angiogenesis in ovarian cancer9. Hypoxia converting CD4+ T cells into VEGFA- A mural cell that is thought to have significant roles in 29 + supporting the growth and survival of endothelial cells is recognized as a major contributor to shuttling cells . Although activated CD4 during angiogenesis, particularly in tumours. cancer progression and treatment failures. T cells can capture NRP1 from DCs, + + + We found that hypoxic ovarian tumour CD4 CD25 FOXP3 TReg cells constitutively Trogocytosis cells specifically upregulate expression of express NRP1, allowing for the possibil- Following the formation of the immunological synapse, CC‑chemokine ligand 28 (CCL28), and ity that they could transport additional membrane fragments from the antigen-presenting cell are physically transferred to, and transiently incorporated in, this chemokine preferentially recruits VEGFA to the tumour site following + + + the membrane of the interacting T cell (or B or NK cell). CD4 CD25 FOXP3 TReg cells from periph- their recruitment by CCL22 and CCL28 The biological significance remains wholly unknown. eral blood through ligation of the cognate (REFS 9,23,30).

Other lymphocyte subsets with Molecular mediators haematopoiesis and by increasing the immunosuppressive functions include In addition to its well-established func- sensitivity of thymocytes to apoptosis52,53. regulatory B cells8,31, type II natural killer T tions as the master regulator of the tumour Furthermore, VEGFA treatment of mouse (NKT) cells32, NK cells33 and γδ T cells34. In angiogenic switch46, VEGFA regulates a splenocytes during T cell stimulation was addition, B cells35, γδ T cells34, NK cells5,36 diverse array of immune functions and thus found to induce IL‑10 production by T cells and invariant (type I) NKT cells37 have been serves as the prototypical molecule that can and to suppress interferon-γ (IFNγ) produc- reported to produce VEGFA. The precise mediate both angiogenesis and immuno- tion through an undefined mechanism54. role of these cells in tumour angiogenesis suppression (FIG. 2). VEGFA impairs DC It has also been shown that overexpres- is unknown, but some of these lymphocyte function and maturation, and this effect is sion of VEGFA in tumour cells can lead to subsets can be quite abundant in various thought to be responsible for the defects in increased numbers of intratumoural TReg tumours, raising the possibility that they antigen presentation and DC maturation cells55, demonstrating its significant role in make a crucial contribution to tumour observed in patients with cancer47–49. Ishida the establishment of a tolerogenic tumour development through the acquisition of a and colleagues demonstrated that tumour- microenvironment. Lastly, expression of dual pro-angiogenic and immunosuppres- bearing mice have decreased DC numbers NRP1 — a receptor that interacts with VEGF sive phenotype. However, the exact role and impaired DC function compared with receptor 1 (VEGFR1) and VEGFR2 — has + + 30 of these lymphocytes in tumours requires control mice, and that these defects could be been detected on CD4 CD25 TReg cells . further investigation. reversed by VEGFA blockade50. In addition, Neutralizing antibodies specific for NRP1

programmed cell death ligand 1 (PDL1) diminished the interactions of DCs with TReg Stromal cells. Typically associated with — a major negative-regulatory ligand that cells, and ectopic overexpression of NRP1 wound healing through the deposition suppresses T cell activation through its in T cells enhanced their interactions with of extracellular matrix, fibroblasts have receptor programmed cell death protein 1 DCs30. Although not directly tested, VEGFA- important roles in both immune modula- (PD1) — is highly expressed by tumour- expressing DCs could potentially stabilize 38 tion and angiogenesis . In the tumour associated myeloid DCs in response to their interaction with TReg cells via NRP1 (or microenvironment, cancer-associated tumour-derived VEGFA51. even VEGFR2 (REF. 56)), leading to enhanced fibroblasts (CAFs) can be activated by In addition to its effects on DCs, TReg cell activation. This would create a TGFβ, fibroblast growth factor (FGF) and VEGFA can suppress T cell development tolerogenic environment and thus promote platelet-derived growth factor (PDGF)38. In and function through the disruption of tumour evasion. turn, CAFs may secrete angiogenic growth factors such as bFGF and VEGFA38,39, while promoting the recruitment and function of immunosuppressive cells (particularly those of the myeloid lineage, such as TAMs and MDSCs) through the secretion of +OOCVWTG&% CCL2 and CXCL12 (REFS 18,40). In addi- /CVWTG&% #EVKXCVKQP tion, CAFs may suppress effector T cells 2&. through the secretion of TGFβ41. 8')(# 6EGNN Another adherent stromal cell popu- 8')(# lation is the mesenchymal stem cells (MSCs), which are derived from the bone marrow. Myeloid-derived MSCs secrete 6WOQWT VEGFA and promote tumour angio- 2TQNQPIGF 042 genesis by differentiating into CAFs or KPVGTCEVKQP YKVJ&% perivascular mural cells, which express 8')(# α-smooth muscle actin, TIE2 and other 'PJCPEGFCEVKXCVKQP 42 pericyte markers . Importantly, MSCs QHVWOQWTURGEKȮE 64GIEGNN exert important immunosuppressive func- 64GIEGNNU! tions by blocking the proliferation and function of effector T cells43,44. MSCs may be part of a homeostatic programme that &KȭGTGPVKCVKQP responds to tissue injury, and the robust capacity of their immunosuppressive *CGOCVQRQKGVKE RTGEWTUQTEGNN capabilities has been demonstrated from /WNVKRNGEGNNV[RGU 44,45 their roles in transplantation tolerance . 8')(# The full extent of the contributions of fibroblasts and myeloid-derived MSCs of the tumour stroma is unknown, but it is Figure 2 | The role of VEGFA in immune suppression. Vascular endothelial growth factor A (VEGFA) becoming apparent that these cells proba- has a multitude of suppressive effects on the immune response. For example, VEGFA can inhibit the 0CVWTG4GXKGYU^+OOWPQNQI[ bly have integral roles in the establishment maturation of dendritic cells (DCs) and disrupt the normal differentiation of haematopoietic precursor of a tumour-promoting microenvironment, cells. VEGFA can also induce the expression of inhibitory molecules such as programmed cell death supporting both immunosuppression and ligand 1 (PDL1) on DCs, and VEGFA may activate antigen-specific regulatory T (TReg) cells by signalling angiogenesis. through neuropilin 1 (NRP1) on TReg cells.

We have chosen to focus on VEGFA Additional factors — such as adenosine57, maturation and antigen presentation, or owing to the abundance of data regard- PGE2 (REF. 58) and TGFβ59 — have key directly suppress T cell activation while (TABLE 1) ing its function in the above processes, roles in endothelial cell proliferation, sur- promoting TReg cell functions . but numerous mediators that are found vival, migration and vessel formation11. It is important to note that, although in the tumour microenvironment have Furthermore, many of these mediators the mediators listed in TABLE 1 possess the the capacity to promote both immuno have known functions in the suppression capacity for immunosuppression and angio- suppression and angiogenesis (see TABLE 1). of antigen-presenting cell activation, genesis, their contribution to these processes

Table 1 | Factors with the capacity to promote both immunosuppression and angiogenesis Mediator Roles in immunosuppression Roles in angiogenesis Refs PGE2 • Decreases DC maturation, co-stimulatory molecule • Induces VEGFA production 58, expression, IL‑12 production and CD8+ T cell • Activates the RAC and nitric oxide–cGMP pathways 117–120 cross-priming by tumours • Stimulates migration and survival of endothelial cells

• Increases tolerogenic DC and TReg cells numbers, arginase 1 • Directly promotes tube formation and proliferation expression and the suppressive activity of MDSCs Adenosine • Induces an immunosuppressive DC phenotype • Has a mitogenic effect on endothelium 57, • Increases IL‑10 and IL‑6 production by APCs • Promotes VEGFA, IL‑8, bFGF and angiopoetin 1 121–123 • Suppresses T cell effector functions production by numerous cell types

• Induces T cell anergy and TReg cell development TGFβ • Decreases T cell and macrophage functions • Stabilizes angiogenic endothelium 59,124 • Drives the proliferation of TReg cells • Can promote the proliferation and migration of endothelial cells

IL‑6 • Decreases TH1 cell differentiation • Increases VEGFA production 98 VEGFA • Impairs DC maturation • Increases the proliferation, migration, activation, 47–49 • Increases PDL1 expression by DCs recruitment and survival of endothelial cells • Blocks T cell activation IDO • Inhibits T cell activation through tryptophan depletion • Kynurenine (a tryptophan metabolite produced by IDO) 125 may promote endothelial tube formation and angiogenesis FASL • Induces caspase-mediated cell death of immune cells • FAS ligation with agonist antibody stimulates matrigel 126 neoangiogenesis

CCL2 • Recruits TAMs and TReg cells • Increases VEGFA production and angiogenesis 127 • Promotes the recruitment of endothelial cell precursors IL‑4 • Promotes alternatively activated macrophages • Promotes VEGFA production during hypoxia 128–130

• Inhibits TH1 cell differentiation • A low dose promotes angiogenesis M-CSF • Promotes the recruitment and/or activation of • Induces VEGFA production by monocytes 131 immunosuppressive myeloid cells G-CSF • Promotes myeloid cell recruitment • Promotes angiogenesis through effects on myeloid cells 132,133 • May increase the numbers of endothelial precursor cells ROS and RNS • Inhibit T cell activation • Promote endothelial migration through the production of 11, oxidized lipids 134,135 Endothelin 1 • Decreases ICAM1 expression on activated endothelial • Increases VEGFA and PGE2 production 10,136 cells, preventing leukocyte diapedesis CXCL12 • Can be involved in the recruitment of TAMs, MDSCs and • Induces VEGFA production 137 pDCs that induce IL‑10 production by CD8+ T cells • Promotes the production of MMP9 Angiopoietin 1 • Has roles in the recruitment of TAMs and MDSCs • Has direct effects on endothelial cells 17 PDGF • Has roles in the recruitment of TAMs and MDSCs • Has direct effects on endothelial cells 38 PLGF • Can impair DC functions • Has indirect and direct effects on angiogenesis 138,139 • Recruits immunosuppressive cells

TLR2 ligands • Expand TReg cell populations • Promote angiogenesis 11, • Induce IL‑10 production by DCs • MYD88-deficient mice have impaired angiogenesis and 140–142 wound healing IL‑17 • Can increase IL‑6 production and promote tumour • Increases angiogenesis by acting on endothelial cells 143 growth under certain circumstances • IL‑6–STAT3-mediated activation of tumour cells generates a pro-angiogenic phenotype APC, antigen-presenting cell; bFGF, basic fibroblast growth factor; CCL2, CC-chemokine ligand 2; cGMP, cyclic GMP; CXCL12, CXC-chemokine ligand 12; DC, dendritic cell; FASL, FAS ligand; G‑CSF, granulocyte colony-stimulating factor; ICAM1, intercellular adhesion molecule 1; IDO, indoleamine 2,3-dioxygenase; IL, interleukin; M‑CSF, macrophage colony-stimulating factor; MDSC, myeloid-derived suppressor cell; MMP9, matrix metalloproteinase 9; MYD88, myeloid differentiation primary response protein 88; pDC, plasmacytoid DC; PDGF, platelet-derived growth factor; PDL1, programmed cell death ligand 1; PGE2, prostaglandin E2; PLGF, placenta growth factor; PTGER2, PGE2 receptor EP2 subtype; RNS, reactive nitrogen species; ROS, reactive oxygen species;

STAT3, signal transducer and activator of transcription 3; TAM, tumour-associated macrophage; TGFβ, transforming growth factor-β; TH1, T helper 1; TLR2, Toll-like receptor 2; TReg, regulatory T; VEGFA, vascular endothelial growth factor A.

may be entirely context dependent. For exam- adhesion molecules such as intercellular infiltration to tumours that involves activa- ple, ligands for Toll-like receptor 2 (TLR2) adhesion molecule 1 (ICAM1) and vas- tion of the endothelin B receptor (ETBR)10. have recently been implicated in the regula- cular cell adhesion molecule 1 (VCAM1) Endothelial-expressed ETBR was found tion of both physiological and pathological (reviewed extensively in REF. 66). Although to be upregulated in ovarian tumours angiogenesis11. West and colleagues demon- the tumour vasculature is considered to be that lacked tumour-infiltrating lympho- strated that end products of lipid oxidation ‘leaky’, a pro-angiogenic tumour micro- cytes10 and, similarly to the absence of that are generated during inflammation are environment typically lacks infiltrating tumour-infiltrating lymphocytes68, ETBR present in high concentrations in both mouse immune cells67,68 and, mechanistically, most overexpression was associated with poor and human tumours, and that these end of the in vitro and in vivo data indicate that survival. Signalling by endothelin 1 through products are endogenous ligands for TLR2 angiogenic factors reduce the adhesion and ETBR was found to block T cell adhesion to that promote angiogenesis in a manner migration of leukocytes69–74 (FIG. 3). the endothelium through the suppression of dependent on TLR2–MYD88 (myeloid dif- The potent angiogenic growth factors ICAM1 clustering on endothelial cell mem- ferentiation primary response protein 88) VEGFA and bFGF attenuate the adhesion branes, an effect mediated by nitric oxide10. signalling11. In addition, the endogenous of T cells to either quiescent or tumour Importantly, endothelin 1 has been shown TLR2 ligand heat shock protein 60 (HSP60) necrosis factor (TNF)-activated endothelial to be overexpressed in human ovarian has been shown to enhance the functions cells70–72. Depending on the experimental cancer75, suggesting that tumours can sup- of TReg cells in a cell-autonomous manner conditions, these angiogenic factors can press T cell adhesion to the endothelium in by increasing IL‑10 and TGFβ production by suppress the expression of VCAM1 and an endothelin 1–ETBR-dependent manner, 60 10 HSP60‑treated TReg cells . Furthermore, ICAM1 on endothelial cells or can abro- even in the presence of TNF . This would TLR2 signalling in DCs was found to pro- gate the clustering of surface adhesion explain the coexistence of inflammation mote TReg cell differentiation through IL‑10 molecules via caveolin 1 (a process that is (TNF is commonly overexpressed in the and retinoic acid production following important for adhesive interactions with tumour microenvironment, particularly in TLR2 stimulation61. Injection of mice T cells)72. We have recently demonstrated ovarian cancer68) and a quiescent tumour with TLR2 agonists increased TReg cell an additional endothelial cell-associated endothelium phenotype that does not numbers and promoted tumour development mechanism for the regulation of T cell support the homing of T cells68. 62 in a TReg cell‑dependent manner . Despite these observations, TLR2‑ mediated activation of mast cells was CD shown to promote antitumour immunity 63 and to inhibit angiogenesis . Moreover, 6EGNN TLR2 ligands have an established role in the 6EGNN activation of DCs to promote antimicrobial immunity, and they possess the capacity &KCRGFGUKU 0QKPȮNVTCVKQP &KCRGFGUKU .(# 8.# to directly enhance the functions of TH1 64 7PMPQYP cells . Therefore, it is likely that the context +%#/ 8%#/ TGEGRVQT under which stimulation occurs, or how a $NQQF particular mediator interacts with a par- 65 ticular cellular target , determines how the 'PFQVJGNKCN %.'8'4 mediator is integrated into a programme of EGNN 6EGNN '6$4 6 EGNN immunosuppression and angiogenesis. 8')(4 ()(4 4GI 60( Immune regulation by tumour vasculature 8')(# Much of the information presented above is D()( GPFQVJGNKP focused on cells and mediators that have the +PȯCOOCVQT[TGURQPUG QYKPIVQKPHGEVKQP ability to influence endothelial cell activa- HQTGZCORNG tion, resulting in angiogenesis, and to sup- 6WOQWT press the immune response. However, the EGNNU angiogenic endothelium can also regulate leukocyte trafficking and can directly Figure 3 | Modulation of immune cell recruitment and diapedesis through the endothelial suppress and regulate an immune response. barrier by the tumour microenvironment. a | The endothelium acts as a physical barrier to leukocyte traffic to sites of inflammation or tumour growth. In the initial inflammatory0CVWTG4G response,XKGYU^+OOWPQNQI[ factors such Adhesion and transmigration of leuko- as tumour necrosis factor (TNF) upregulate the expression of chemotactic factors and adhesion mol- cytes. The endothelium stands as a physical ecules, including intercellular adhesion molecule 1 (ICAM1) and vascular cell adhesion molecule 1 barrier to leukocytes and regulates their (VCAM1). These molecules recruit leukocytes to the site of inflammation and mediate diapedesis through LFA1–ICAM1 and VLA1–VCAM1 interactions. b | In the context of a tumour microenvironment extravasation from the circulation into the (as well as during the resolution phase of infection), growth factors such as endothelin 1, basic fibro- surrounding tissue. Leukocytes extravasate blast growth factor (bFGF) and vascular endothelial growth factor A (VEGFA) block the expression of to tumours by crossing the endothelial ICAM1 and VCAM1, thus reducing leukocyte trafficking. The tumour endothelium probably also cell layer through a multistep process that functions as a selective barrier, preventing effector cell infiltration while promoting regulatory T (TReg) involves binding to adhesion molecules cell infiltration through molecules such as common lymphatic endothelial and vascular endothe- expressed by endothelial cells followed lial receptor 1 (CLEVER1). ETBR, endothelin B receptor; FGFR, FGF receptor; LFA1, lymphocyte by diapedesis. The process is mediated by function-associated antigen 1; VEGFR, VEGF receptor; VLA1, very late antigen 1.

An open question that remains is trafficking may also exist for suppressive Additional vascular cells. Surrounding the whether the endothelium can distinguish myeloid populations, and may be medi- endothelial cells, but integral to the vascu- between leukocyte subsets, selectively ated by adhesion molecules such as CD31 lature, are mural cells, which are endowed allowing trafficking of only certain immune or CD99 (REF. 78). Thus, it is likely that the with plasticity and can acquire phenotypes of subsets according to their polarization tumour endothelium is an active participant pericytes or vascular smooth muscle cells42.

(TH1 versus TH2, TH17 or TReg cell), pheno- in the control of immunosuppression Mural cells have significant roles in angio- type and/or activation status. One could during tumour angiogenesis. genesis, and have also been shown to have an hypothesize that, under the influence of immunosuppressive function42. In addition, the local angiogenic milieu, the tumour Suppression of T cell activation by the monocyte populations have been described endothelium could allow immunosuppres- endothelium. In addition to regulating the to participate in the process of blood vessel sive cells to pass, while blocking access to adhesion and extravasation of leukocytes, formation in tissues undergoing post- tumour-reactive effector T cells or NK cells. endothelial cells can express mediators that infarction repair94. Similar participation of This notion is supported by the observation suppress the actions of effector lymphocytes myeloid cells in rapidly forming vessels could (FIG. 4) 2,95,96 that TReg cells selectively traffic through the . These mediators include PDL1 and also occur in tumours , and incorporation tumour endothelium by virtue of enhanced PDL2 (REFS 79,80), FAS ligand (FASL; also of myeloid cells into the developing vascula- interaction with addressins in human pan- known as CD95L)81, TNF-related apoptosis- ture has been suggested by several groups2,95, creatic cancer76. Furthermore, VEGFA and inducing ligand (TRAIL)82 and possibly but remains controversial. hepatocyte growth factor (HGF) may pro- the endothelial cell marker CD31 (REF. 83). Context is key mote selective migration of TReg cells across Endothelial cells also express numerous the endothelium in hepatic cell carcinoma soluble mediators that suppress immune Although many of the cells and mediators through common lymphatic endothelial and responses, such as IL‑6, IL‑10, TGFβ and discussed have the capacity to promote vascular endothelial receptor 1 (CLEVER1; PGE2 (REFS 84,85). immunosuppression and angiogenesis, it is also known as stabilin 1)77. Selective Very recently, the endothelium within important to emphasize that their functions lymphomas was shown to express T cell in these processes are likely to be entirely immunoglobulin domain and mucin domain context dependent. Therefore, these cells +PJKDKV6EGNN protein 3 (TIM3; also known as HAVCR2). and mediators may require the correct CEVKXCVKQP This protein contributes to immuno microenvironmental conditions to exert 6EGNN suppression through the activation of the their full potential in this pro-angiogenic– STAT3 (signal transducer and activator of immunosuppressive programme. IL‑6 +. 2)' transcription 3) pathway for IL‑6 produc- is a particularly relevant example, as 6T[RVQRJCP +. 86 6)(β tion in endothelial cells . TIM3‑expressing it is a pleiotropic cytokine that may have FGRNGVKQP endothelial cells promoted the onset, growth pro-inflammatory or anti-inflammatory 2&. 2&. and dissemination of lymphomas by inhibit- (immunosuppressive) effects depending %& 6+/ + ing the activation of CD4 T cells and TH1 cell on the context of expression and the cellu ↑+&1 polarization, thus revealing a novel role for lar target. For example, within the hypoxic the endothelium in immune suppression86. In tumour microenvironment, IL‑6 expression addition, indoleamine 2,3‑dioxygenase (IDO) is inducible97, and IL‑6 could synergize with 'PFQVJGNKCN /WTCNEGNN can be expressed by tumour endothelium87,88. other factors to induce the expression of EGNN 6WOQWTOKETQGPXKTQPOGPV Endothelial IDO is known to be upregulated VEGFA by multiple cell types98,99 and/or to FGTKXGFCPIKQIGPKECPF KOOWPQUWRRTGUUKXGHCEVQTU! by infection and may be required for the regu- promote immunosuppression through the lation of blood pressure through kynurenine89, induction of immunosuppressive molecules but it can also suppress T cell activation such as B7H4 (also known as VTCN1)100. through the depletion of tryptophan90. However, IL‑6 can also promote the differen- 101 6WOQWT Endothelial cells can also express several tiation of TH17 cells over TReg cells , thereby molecules that may be involved in the direct driving a pro-inflammatory microenviron- Figure 4 | Direct immune regulation by the endothelium. In addition to the well-established stimulation of T cells — such as ICOS ligand ment, as is seen in rheumatoid arthritis. role for the endothelium0CVWTG4G in trafficking,XKGYU^+OOWPQNQI[ the tumour (ICOSL), CD40, CD58, CD80, CD86, CD137 Thus, it is important to emphasize that the endothelium can express several inhibitory mol- and MHC class I and class II molecules — context of mediator expression is crucial to ecules that could limit the antitumour immune and many of these molecules are upregulated its contribution to functional outcomes. 91 response. Programmed cell death ligand 1 (PDL1) by angiostatic, TH1 cell-associated cytokines . and PDL2 can be expressed by endothelial cells, Whether the expression and/or function Conclusions and implications and indoleamine 2,3‑dioxygenase (IDO) and T cell of these immunostimulatory molecules are Implications of this paradigm for cancer immunoglobulin domain and mucin domain pro- influenced by angiogenic mechanisms is immunotherapy. Solid tumours grow and tein 3 (TIM3) have been shown to be expressed by largely unknown, but it is possible that down- evolve through a constant crosstalk with the tumour endothelium. The adhesion molecule regulation or inhibition of the expression of the surrounding microenvironment. The CD31 is used as a marker of endothelial cells and has been demonstrated to inhibit T cell activation. these molecules on endothelial cells occurs evidence discussed here suggests that the Furthermore, soluble mediators released from the during tumour angiogenesis. Support for tumour stroma and microenvironment tumour endothelium — such as prostaglandin E2 this hypothesis comes from the observation activate homeostatic tissue repair mecha- (PGE2), interleukin‑10 (IL‑10) and transforming that tumour cell supernatants can induce nisms that include cellular and molecular growth factor-β (TGFβ) — would further impair an endothelial suppressor phenotype that is events traditionally considered to pertain to immune responses. partly dependent on VEGFA92,93. either angiogenesis or immunosuppressive

mechanisms. The growing understanding of could be more successful at tipping the responses and avert autoreactivity while pro- these complex networks has revealed that the balance of the tumour microenvironment. moting the regeneration of damaged, stressed same cell populations or soluble factors can However, key questions remain. For example, or infected tissues through increased blood simultaneously promote angiogenesis and what are the most important mediators or supply and tissue rebuilding. As such, many mediate immunosuppression. The daunting cells in the establishment of this tissue repair of the processes described above also occur in complexity of these overlapping mechanisms programme in tumours, and how, exactly, do the context of aseptic tissue injury, ischaemia– could in part explain therapeutic failures, as tumours orchestrate this programme? Gene reperfusion injury and infection11. Perhaps the the field has traditionally targeted only one signatures and studies that investigate tissue best example of this hypothesis in action was (but rarely both) of these mechanisms. repair networks could provide hints as to the the demonstration that oxidative stress gener- 40 years of dedicated research following most relevant interactions106. ates oxidized lipids that act as endogenous Judah Folkman’s anti-angiogenesis hypoth- According to the proposed view that ligands for the TLR2–MYD88 pathway — a esis102 has yielded only a handful of US Food integrates tumour angiogenesis and immuno- pathway known for its role during infection. and Drug Administration (FDA)-approved suppression in the homeostatic tissue repair This pathway was shown to control angiogen- drugs available to disrupt angiogenesis, all programme co-opted by tumours, strategies esis by directly stimulating endothelial cells of which interfere with the VEGF pathway for the elimination of tumours might be in different inflammatory contexts, such as in (although more than 40 new drugs are more successful if they include complemen- wound healing, ischaemia and tumour angio in development103). The first such drug tary approaches to block mediators of both genesis11. Furthermore, following instances of to be approved, bevacizumab (Avastin; angiogenesis and immunosuppression while extreme tissue damage and inflammation (as Genentech/Roche), is a neutralizing anti- simultaneously inducing a strong antitumour is the case with sepsis), high levels of VEGFA body that specifically inhibits VEGFA, and immune response. For example, in preclini- are expressed114 and, following the resolution despite overwhelming preclinical efficacy it cal models, greater success has been achieved of sepsis, a large expansion occurs in the 115 does not provide benefit as a monotherapy with combinatorial approaches using a TReg cell population , indicating that this in patients (except in a few types of tumour, tumour lysate vaccine and ETBR blockade10, a pro-angiogenic and immunosuppressive such as glioblastoma multiforme and recur- tumour lysate-pulsed DC vaccine with COX2 programme is also active during the most rent ovarian carcinoma). It is possible that inhibitors107, or a VEGFA-specific neutral- severe infections. blocking VEGFA alone is not sufficient to izing antibody and adoptive T cell therapy12 This paradigm could be extended even disable key tissue repair pathways in the than with any monotherapy. This strategy is to pregnancy, during which immuno tumour stroma, with ensuing therapeutic further strengthened by some success with suppression and angiogenesis are required failure. Indeed, TReg cells recruited by tumour combining IFNα therapy and bevacizumab for proper development of the fetal– hypoxia and tumour-infiltrating MDSCs for the treatment of metastatic renal cell carci- maternal interface. For example, it was have been shown to promote angiogenesis noma108,109. In addition, strategies to eliminate demonstrated that NK cells can promote and resistance to VEGFA blockade, respec- the tumour endothelium itself have shown angiogenesis through the secretion of tively9,17. Interestingly, bevacizumab has some success110. An alternative approach is VEGFA at the fetal–maternal interface, proved to be quite effective when used aimed at eliminating immunosuppressive while remaining tolerant5. The relationship in combination with traditional chemo cells, such as TReg cells, in combination with between immunosuppression and angiogen- therapeutics, extending both progression- VEGFA blockade, and this is also currently esis may also be present during fetal develop- free and overall survival (reviewed in being investigated13. It is important to note ment, as embryonic macrophages have been REF. 104 ). Given the emerging off-target that strong TH1‑type cytokines that are shown to express many of the same genes effects of chemotherapy drugs on the known for their roles in tumour elimination as TIE2+ monocytes and TAMs116. Thus, an tumour microenvironment, it is possible that — including IL‑12, IFNγ and IFN-inducible understanding of the paradigm presented chemotherapy drugs could also help to abro- chemokines such as CXCL9 (also known as here should aid new treatment possibilities gate some of the tissue repair mechanisms in MIG) and CXCL10 (also known as IP10) — that perhaps would otherwise be overlooked. the tumour microenvironment that account can exert potent angiostatic effects through Here, we have presented parallels between for resistance to bevacizumab. Similarly, direct action on endothelial cells111–113. Thus, cancer and other biological processes that cancer immunotherapies that have relied complete tumour eradication will ultimately support the hypothesis that angiogenesis and solely on promoting antitumour immune require regulation in favour of an immuno immunosuppression cooperate in the same responses without addressing the tumour stimulatory and angiostatic microenviron- tissue repair programme. This programme microenvironment are often met with lim- ment. The open question remains as to operates normally to ensure homeostasis, ited success in the clinic, perhaps owing in whether there exists a central regulatory cell but is also co-opted by pathological pro- part to a lack of immune cell recruitment type or central mediator that, when blocked, cesses such as cancer. The open challenges through the tumour endothelial barrier105 or can relieve both the immunosuppression and are to discover therapeutic approaches to other local immunosuppressive factors. angiogenesis programmes, thereby promoting to target this tissue repair programme to The notion that the pro-angiogenic and an antitumour immune response and leading eliminate cancer, expedite wound healing, immunosuppressive phenotype is likely to be to the elimination of the tumour. promote transplant tolerance and relieve dynamic and responsive to local conditions symptoms of autoimmunity. has particular relevance for the develop- Implications for other biological processes. Gregory T. Motz and George Coukos are at the Ovarian ment of new therapies. Given the degree of It is our belief that the fact that so many media- Cancer Research Center, University of Pennsylvania, cooperation and functional overlap between tors and cellular players have the capacity Philadelphia, Pennsylvania 19104, USA. angiogenesis and immunosuppressive mech- to promote both immunosuppression and Correspondence to G.C. anisms, strategies that use anti-angiogenic angiogenesis is a result of an evolutionary e‑mail: [email protected] therapy along with immune modulation pressure to temper excessive inflammatory doi:10.1038/nri3064

1. Szekanecz, Z. & Koch, A. E. Mechanisms of disease: T cells in angiogenesis. Cancer Res. 55, 4140–4145 53. Huang, Y. et al. Distinct roles of VEGFR‑1 and angiogenesis in inflammatory diseases. Nature Clin. (1995). VEGFR‑2 in the aberrant hematopoiesis associated Pract. Rheumatol. 3, 635–643 (2007). 27. Stabile, E. et al. Impaired arteriogenic response to with elevated levels of VEGF. Blood 110, 624–631 2. Yang, L. et al. Expansion of myeloid immune acute hindlimb ischemia in CD4‑knockout mice. (2007). suppressor Gr+CD11b+ cells in tumor-bearing host Circulation 108, 205–210 (2003). 54. Shin, J. Y., Yoon, I. H., Kim, J. S., Kim, B. & Park, C. G. directly promotes tumor angiogenesis. Cancer Cell 6, 28. Huang, M. T. et al. Regulatory T cells negatively regulate Vascular endothelial growth factor-induced chemotaxis 409–421 (2004). neovasculature of airway remodeling via DLL4–Notch and IL‑10 from T cells. Cell. Immunol. 256, 72–78 3. Zou, W. Immunosuppressive networks in the tumour signaling. J. Immunol. 183, 4745–4754 (2009). (2009). environment and their therapeutic relevance. 29. Bourbie-Vaudaine, S., Blanchard, N., Hivroz, C. & 55. Li, B. et al. Vascular endothelial growth factor Nature Rev. Cancer 5, 263–274 (2005). Romeo, P. H. Dendritic cells can turn CD4+ T blockade reduces intratumoral regulatory T cells and 4. Riboldi, E. et al. Cutting edge: proangiogenic lymphocytes into vascular endothelial growth factor- enhances the efficacy of a GM‑CSF‑secreting cancer properties of alternatively activated dendritic cells. carrying cells by intercellular neuropilin‑1 transfer. immunotherapy. Clin. Cancer Res. 12, 6808–6816 J. Immunol. 175, 2788–2792 (2005). J. Immunol. 177, 1460–1469 (2006). (2006). 5. Hanna, J. et al. Decidual NK cells regulate key 30. Sarris, M., Andersen, K. G., Randow, F., Mayr, L. & 56. Suzuki, H. et al. VEGFR2 is selectively expressed by developmental processes at the human fetal–maternal Betz, A. G. Neuropilin‑1 expression on regulatory T cells FOXP3high CD4+ Treg. Eur. J. Immunol. 40, 197–203 interface. Nature Med. 12, 1065–1074 (2006). enhances their interactions with dendritic cells during (2010). 6. Jablonska, J., Leschner, S., Westphal, K., Lienenklaus, S. antigen recognition. Immunity 28, 402–413 (2008). 57. Montesinos, M. C., Shaw, J. P., Yee, H., Shamamian, P.

& Weiss, S. Neutrophils responsive to endogenous 31. Inoue, S., Leitner, W. W., Golding, B. & Scott, D. & Cronstein, B. N. Adenosine A2A receptor activation IFN-β regulate tumor angiogenesis and growth in a Inhibitory effects of B cells on antitumor immunity. promotes wound neovascularization by stimulating mouse tumor model. J. Clin. Invest. 120, 1151–1164 Cancer Res. 66, 7741–7747 (2006). angiogenesis and vasculogenesis. Am. J. Pathol. 164, (2010). 32. Halder, R. C., Aguilera, C., Maricic, I. & Kumar, V. 1887–1892 (2004). 7. Shrestha, B. et al. B cell-derived vascular endothelial Type II NKT cell-mediated anergy induction in type I 58. Alfranca, A. et al. PGE2 induces angiogenesis via growth factor A promotes lymphangiogenesis and NKT cells prevents inflammatory liver disease. MT1‑MMP‑mediated activation of the TGFβ/Alk5 high endothelial venule expansion in lymph nodes. J. Clin. Invest. 117, 2302–2312 (2007). signaling pathway. Blood 112, 1120–1128 (2008). J. Immunol. 184, 4819–4826 (2010). 33. Lu, L. et al. Regulation of activated CD4+ T cells by 59. Lebrin, F., Deckers, M., Bertolino, P. & Ten Dijke, P. 8. Qin, Z. et al. B cells inhibit induction of T cell-dependent NK cells via the Qa‑1–NKG2A inhibitory pathway. TGF-β receptor function in the endothelium. tumor immunity. Nature Med. 4, 627–630 (1998). Immunity 26, 593–604 (2007). Cardiovasc. Res. 65, 599–608 (2005). 9. Facciabene, A. et al. Tumour hypoxia promotes 34. Wakita, D. et al. Tumor-infiltrating IL‑17‑producing γδ 60. Zanin-Zhorov, A. et al. Heat shock protein 60 tolerance and angiogenesis via Ccl28 and Treg cells. T cells support the progression of tumor by promoting enhances CD4+ CD25+ regulatory T cell function Nature 475, 226–230 (2011). angiogenesis. Eur. J. Immunol. 40, 1927–1937 (2010). via innate TLR2 signaling. J. Clin. Invest. 116, 10. Buckanovich, R. J. et al. Endothelin B receptor 35. Angeli, V. et al. B cell-driven lymphangiogenesis in 2022–2032 (2006). mediates the endothelial barrier to T cell homing to inflamed lymph nodes enhances dendritic cell 61. Manicassamy, S. et al. Toll-like receptor 2‑dependent tumors and disables immune therapy. Nature Med. mobilization. Immunity 24, 203–215 (2006). induction of vitamin A-metabolizing enzymes in 14, 28–36 (2008). 36. Kalkunte, S. S. et al. Vascular endothelial growth dendritic cells promotes T regulatory responses and 11. West, X. Z. et al. Oxidative stress induces factor C facilitates immune tolerance and endovascular inhibits autoimmunity. Nature Med. 15, 401–409 angiogenesis by activating TLR2 with novel activity of human uterine NK cells at the maternal– (2009). endogenous ligands. Nature 467, 972–976 (2010). fetal interface. J. Immunol. 182, 4085–4092 (2009). 62. Yamazaki, S. et al. TLR2‑dependent induction of 12. Shrimali, R. K. et al. Antiangiogenic agents can 37. Kyriakakis, E. et al. Invariant natural killer T cells: IL‑10 and Foxp3+CD25+CD4+ regulatory T cells increase lymphocyte infiltration into tumor and linking inflammation and neovascularization in human prevents effective anti-tumor immunity induced by enhance the effectiveness of adoptive immunotherapy atherosclerosis. Eur. J. Immunol. 40, 3268–3279 Pam2 lipopeptides in vivo. PLoS ONE 6, e18833 of cancer. Cancer Res. 70, 6171–6180 (2010). (2010). (2011). 13. Kandalaft, L. E., Powell, D. J. Jr, Singh, N. & Coukos, G. 38. Kalluri, R. & Zeisberg, M. Fibroblasts in cancer. 63. Oldford, S. A. et al. A critical role for mast cells and Immunotherapy for ovarian cancer: what’s next? Nature Rev. Cancer 6, 392–401 (2006). mast cell-derived IL‑6 in TLR2‑mediated inhibition of J. Clin. Oncol. 29, 925–933 (2010). 39. Fukumura, D. et al. Tumor induction of VEGF promoter tumor growth. J. Immunol. 185, 7067–7076 14. Gabrilovich, D. I. & Nagaraj, S. Myeloid-derived activity in stromal cells. Cell 94, 715–725 (1998). (2010). suppressor cells as regulators of the immune system. 40. Bottazzi, B., Walter, S., Govoni, D., Colotta, F. & 64. Imanishi, T. et al. Cutting edge: TLR2 directly triggers Nature Rev. Immunol. 9, 162–174 (2009). Mantovani, A. Monocyte chemotactic cytokine gene Th1 effector functions. J. Immunol. 178, 6715–6719 15. Gallina, G. et al. Tumors induce a subset of transfer modulates macrophage infiltration, growth, (2007). inflammatory monocytes with immunosuppressive and susceptibility to IL‑2 therapy of a murine 65. Chamorro, S. et al. TLR triggering on tolerogenic activity on CD8+ T cells. J. Clin. Invest. 116, melanoma. J. Immunol. 148, 1280–1285 (1992). dendritic cells results in TLR2 up-regulation and a 2777–2790 (2006). 41. Bhowmick, N. A., Neilson, E. G. & Moses, H. L. reduced proinflammatory immune program. 16. Huang, B. et al. Gr‑1+CD115+ immature myeloid Stromal fibroblasts in cancer initiation and J. Immunol. 183, 2984–2994 (2009). suppressor cells mediate the development of tumor- progression. Nature 432, 332–337 (2004). 66. Muller, W. A. Mechanisms of leukocyte transendothelial induced T regulatory cells and T‑cell anergy in tumor- 42. da Silva Meirelles, L., Caplan, A. I. & Nardi, N. B. In migration. Annu. Rev. Pathol. 28, 323–344 (2011). bearing host. Cancer Res. 66, 1123–1131 (2006). search of the in vivo identity of mesenchymal stem 67. Bouma-ter Steege, J. C. et al. Angiogenic profile of 17. Shojaei, F. et al. Bv8 regulates cells. Stem Cells 26, 2287–2299 (2008). breast carcinoma determines leukocyte infiltration. myeloid‑cell‑dependent tumour angiogenesis. Nature 43. Krampera, M. et al. Bone marrow mesenchymal Clin. Cancer Res. 10, 7171–7178 (2004). 450, 825–831 (2007). stem cells inhibit the response of naive and memory 68. Zhang, L. et al. Intratumoral T cells, recurrence, and 18. Murdoch, C., Muthana, M., Coffelt, S. B. & Lewis, C. E. antigen-specific T cells to their cognate peptide. survival in epithelial ovarian cancer. N. Engl. J. Med. The role of myeloid cells in the promotion of tumour Blood 101, 3722–3729 (2003). 348, 203–213 (2003). angiogenesis. Nature Rev. Cancer 8, 618–631 (2008). 44. Aggarwal, S. & Pittenger, M. F. Human mesenchymal 69. Detmar, M. et al. Increased microvascular density and 19. Conejo-Garcia, J. R. et al. Tumor-infiltrating dendritic stem cells modulate allogeneic immune cell responses. enhanced leukocyte rolling and adhesion in the skin of cell precursors recruited by a β-defensin contribute to Blood 105, 1815–1822 (2005). VEGF transgenic mice. J. Invest. Dermatol. 111, 1–6 vasculogenesis under the influence of Vegf‑A. 45. Ringden, O. et al. Mesenchymal stem cells for (1998). Nature Med. 10, 950–958 (2004). treatment of therapy-resistant graft‑versus‑host 70. Griffioen, A. W., Damen, C. A., Blijham, G. H. & 20. Sica, A. et al. Autocrine production of IL‑10 mediates disease. Transplantation 81, 1390–1397 (2006). Groenewegen, G. Tumor angiogenesis is accompanied defective IL‑12 production and NF‑κB activation in 46. Ellis, L. M. & Hicklin, D. J. VEGF-targeted therapy: by a decreased inflammatory response of tumor- tumor-associated macrophages. J. Immunol. 164, mechanisms of anti-tumour activity. Nature Rev. associated endothelium. Blood 88, 667–673 (1996). 762–767 (2000). Cancer 8, 579–591 (2008). 71. Griffioen, A. W., Damen, C. A., Martinotti, S., 21. Burke, B. et al. Hypoxia-induced gene expression in 47. Della Porta, M. et al. Dendritic cells and vascular Blijham, G. H. & Groenewegen, G. Endothelial human macrophages: implications for ischemic tissues endothelial growth factor in colorectal cancer: intercellular adhesion molecule‑1 expression is and hypoxia-regulated gene therapy. Am. J. Pathol. correlations with clinicobiological findings. Oncology suppressed in human malignancies: the role of 163, 1233–1243 (2003). 68, 276–284 (2005). angiogenic factors. Cancer Res. 56, 1111–1117 22. Dirkx, A. E., Oude Egbrink, M. G., Wagstaff, J. & 48. Takahashi, A. et al. Vascular endothelial growth (1996). Griffioen, A. W. Monocyte/macrophage infiltration in factor inhibits maturation of dendritic cells induced 72. Bouzin, C., Brouet, A., De Vriese, J., Dewever, J. & tumors: modulators of angiogenesis. J. Leukoc. Biol. by lipopolysaccharide, but not by proinflammatory Feron, O. Effects of vascular endothelial growth factor 80, 1183–1196 (2006). cytokines. Cancer Immunol. Immunother. 53, on the lymphocyte–endothelium interactions: 23. Curiel, T. J. et al. Specific recruitment of regulatory 543–550 (2004). identification of caveolin‑1 and nitric oxide as control T cells in ovarian carcinoma fosters immune privilege 49. Gabrilovich, D. I. et al. Production of vascular points of endothelial cell anergy. J. Immunol. 178, and predicts reduced survival. Nature Med. 10, endothelial growth factor by human tumors inhibits 1505–1511 (2007). 942–949 (2004). the functional maturation of dendritic cells. 73. Min, J. K. et al. Hepatocyte growth factor suppresses 24. Giatromanolaki, A. et al. The presence of tumor- Nature Med. 2, 1096–1103 (1996). vascular endothelial growth factor-induced expression infiltrating FOXP3+ lymphocytes correlates with 50. Ishida, T., Oyama, T., Carbone, D. P. & Gabrilovich, D. I. of endothelial ICAM‑1 and VCAM‑1 by inhibiting the intratumoral angiogenesis in endometrial cancer. Defective function of Langerhans cells in tumor- nuclear factor-κB pathway. Circ. Res. 96, 300–307 Gynecol. Oncol. 110, 216–221 (2008). bearing animals is the result of defective maturation (2005). 25. Gupta, S., Joshi, K., Wig, J. D. & Arora, S. K. from hemopoietic progenitors. J. Immunol. 161, 74. Dirkx, A. E. et al. Tumor angiogenesis modulates Intratumoral FOXP3 expression in infiltrating breast 4842–4851 (1998). leukocyte–vessel wall interactions in vivo by reducing carcinoma: its association with clinicopathologic 51. Curiel, T. J. et al. Blockade of B7‑H1 improves endothelial adhesion molecule expression. parameters and angiogenesis. Acta Oncol. 46, myeloid dendritic cell-mediated antitumor immunity. Cancer Res. 63, 2322–2329 (2003). 792–797 (2007). Nature Med. 9, 562–567 (2003). 75. Bagnato, A. et al. Expression of endothelin 1 and 26. Freeman, M. R. et al. Peripheral blood T lymphocytes 52. Ohm, J. E. et al. VEGF inhibits T‑cell development endothelin A receptor in ovarian carcinoma: evidence and lymphocytes infiltrating human cancers express and may contribute to tumor-induced immune for an autocrine role in tumor growth. Cancer Res. 59, vascular endothelial growth factor: a potential role for suppression. Blood 101, 4878–4886 (2003). 720–727 (1999).

76. Nummer, D. et al. Role of tumor endothelium in 101. Bettelli, E. et al. Reciprocal developmental pathways 125. Li, Y. et al. Local expression of indoleamine + + CD4 CD25 regulatory T cell infiltration of human for the generation of pathogenic effector TH17 and 2,3‑dioxygenase protects engraftment of xenogeneic pancreatic carcinoma. J. Natl Cancer Inst. 99, regulatory T cells. Nature 441, 235–238 (2006). skin substitute. J. Invest. Dermatol. 126, 128–136 1188–1199 (2007). 102. Folkman, J. Tumor angiogenesis: therapeutic (2006). 77. Shetty, S. et al. Common lymphatic endothelial and implications. N. Engl. J. Med. 285, 1182–1186 126. Biancone, L. et al. Development of inflammatory vascular endothelial receptor‑1 mediates the (1971). angiogenesis by local stimulation of Fas in vivo. transmigration of regulatory T cells across human 103. Ivy, S. P., Wick, J. Y. & Kaufman, B. M. An overview J. Exp. Med. 186, 147–152 (1997). hepatic sinusoidal endothelium. J. Immunol. 186, of small-molecule inhibitors of VEGFR signaling. 127. Li, X. et al. A destructive cascade mediated by CCL2 4147–4155 (2011). Nature Rev. Clin. Oncol. 6, 569–579 (2009). facilitates prostate cancer growth in bone. Cancer Res. 78. Schenkel, A. R., Mamdouh, Z., Chen, X., Liebman, R. M. 104. Ebos, J. M. & Kerbel, R. S. Antiangiogenic therapy: 69, 1685–1692 (2009). & Muller, W. A. CD99 plays a major role in the impact on invasion, disease progression, and 128. Volpert, O. V. et al. Inhibition of angiogenesis by migration of monocytes through endothelial junctions. metastasis. Nature Rev. Clin. Oncol. 8, 210–221 interleukin 4. J. Exp. Med. 188, 1039–1046 Nature Immunol. 3, 143–150 (2002). (2011). (1998). 79. Mazanet, M. M. & Hughes, C. C. B7‑H1 is expressed 105. Quezada, S. A. et al. Limited tumor infiltration by 129. Fukushi, J., Ono, M., Morikawa, W., Iwamoto, Y. & by human endothelial cells and suppresses T cell activated T effector cells restricts the therapeutic Kuwano, M. The activity of soluble VCAM‑1 in cytokine synthesis. J. Immunol. 169, 3581–3588 activity of regulatory T cell depletion against angiogenesis stimulated by IL‑4 and IL‑13. (2002). established melanoma. J. Exp. Med. 205, 2125–2138 J. Immunol. 165, 2818–2823 (2000). 80. Rodig, N. et al. Endothelial expression of PD‑L1 and (2008). 130. Yamaji-Kegan, K., Su, Q., Angelini, D. J. & Johns, R. A. PD‑L2 down-regulates CD8+ T cell activation and 106. Chang, H. Y. et al. Robustness, scalability, and IL‑4 is proangiogenic in the lung under hypoxic cytolysis. Eur. J. Immunol. 33, 3117–3126 (2003). integration of a wound-response gene expression conditions. J. Immunol. 182, 5469–5476 (2009). 81. Sata, M. & Walsh, K. TNFα regulation of Fas ligand signature in predicting breast cancer survival. 131. Eubank, T. D., Galloway, M., Montague, C. M., expression on the vascular endothelium modulates Proc. Natl Acad. Sci. USA 102, 3738–3743 (2005). Waldman, W. J. & Marsh, C. B. M‑CSF induces leukocyte extravasation. Nature Med. 4, 415–420 107. Basu, G. D. et al. Cyclooxygenase‑2 inhibitor vascular endothelial growth factor production and (1998). enhances the efficacy of a breast cancer vaccine: angiogenic activity from human monocytes. 82. Secchiero, P. & Zauli, G. The puzzling role of TRAIL in role of IDO. J. Immunol. 177, 2391–2402 (2006). J. Immunol. 171, 2637–2643 (2003). endothelial cell biology. Arterioscler. Thromb. Vasc. 108. Escudier, B. et al. Phase III trial of bevacizumab plus 132. Shojaei, F. et al. G‑CSF‑initiated myeloid cell Biol. 28, e4; author reply e5–e6 (2008). interferon alfa‑2a in patients with metastatic renal cell mobilization and angiogenesis mediate tumor 83. Ma, L. et al. Ig gene-like molecule CD31 plays a carcinoma (AVOREN): final analysis of overall survival. refractoriness to anti-VEGF therapy in mouse nonredundant role in the regulation of T‑cell immunity J. Clin. Oncol. 28, 2144–2150 (2010). models. Proc. Natl Acad. Sci. USA 106, 6742–6747 and tolerance. Proc. Natl Acad. Sci. USA 107, 109. Rini, B. I. et al. Phase III trial of bevacizumab plus (2009). 19461–19466 (2010). interferon alfa versus interferon alfa monotherapy in 133. Okazaki, T. et al. Granulocyte colony-stimulating factor 84. Hernandez, G. L. et al. Selective inhibition of vascular patients with metastatic renal cell carcinoma: final promotes tumor angiogenesis via increasing endothelial growth factor-mediated angiogenesis by results of CALGB 90206. J. Clin. Oncol. 28, circulating endothelial progenitor cells and cyclosporin A: roles of the nuclear factor of activated 2137–2143 (2010). Gr1+CD11b+ cells in cancer animal models. T cells and cyclooxygenase 2. J. Exp. Med. 193, 110. Chinnasamy, D. et al. Gene therapy using genetically Int. Immunol. 18, 1–9 (2006). 607–620 (2001). modified lymphocytes targeting VEGFR‑2 inhibits the 134. Bronte, V. & Zanovello, P. Regulation of immune 85. Pirtskhalaishvili, G. & Nelson, J. B. Endothelium- growth of vascularized syngenic tumors in mice. responses by l‑arginine metabolism. Nature Rev. derived factors as paracrine mediators of prostate J. Clin. Invest. 120, 3953–3968 (2010). Immunol. 5, 641–654 (2005). cancer progression. Prostate 44, 77–87 (2000). 111. Arenberg, D. A. et al. Interferon-γ‑inducible protein 10 135. Otsuji, M., Kimura, Y., Aoe, T., Okamoto, Y. & Saito, T. 86. Huang, X. et al. Lymphoma endothelium preferentially (IP‑10) is an angiostatic factor that inhibits human Oxidative stress by tumor-derived macrophages expresses Tim‑3 and facilitates the progression of non-small cell lung cancer (NSCLC) tumorigenesis and suppresses the expression of CD3 ζ chain of T‑cell lymphoma by mediating immune evasion. J. Exp. Med. spontaneous metastases. J. Exp. Med. 184, 981–992 receptor complex and antigen-specific T‑cell 207, 505–520 (2010). (1996). responses. Proc. Natl Acad. Sci. USA 93, 87. Batista, C. E. et al. Imaging correlates of differential 112. Sgadari, C. et al. Mig, the monokine induced by 13119–13124 (1996). expression of indoleamine 2,3‑dioxygenase in human interferon-γ, promotes tumor necrosis in vivo. 136. Spinella, F., Rosano, L., Di Castro, V., Natali, P. G. & brain tumors. Mol. Imaging Biol. 11, 460–466 (2009). Blood 89, 2635–2643 (1997). Bagnato, A. Endothelin-1‑induced prostaglandin 88. Riesenberg, R. et al. Expression of indoleamine 113. Lasagni, L. et al. An alternatively spliced variant of E2‑EP2, EP4 signaling regulates vascular endothelial 2,3‑dioxygenase in tumor endothelial cells correlates CXCR3 mediates the inhibition of endothelial cell growth factor production and ovarian carcinoma cell with long-term survival of patients with renal cell growth induced by IP‑10, Mig, and I‑TAC, and acts as invasion. J. Biol. Chem. 279, 46700–46705 (2004). carcinoma. Clin. Cancer Res. 13, 6993–7002 (2007). functional receptor for platelet factor 4. J. Exp. Med. 137. Zou, W. et al. Stromal-derived factor‑1 in human 89. Wang, Y. et al. Kynurenine is an endothelium-derived 197, 1537–1549 (2003). tumors recruits and alters the function of plasmacytoid relaxing factor produced during inflammation. 114. Yano, K. et al. Vascular endothelial growth factor is an precursor dendritic cells. Nature Med. 7, 1339–1346 Nature Med. 16, 279–285 (2010). important determinant of sepsis morbidity and (2001). 90. Munn, D. H. et al. Inhibition of T cell proliferation by mortality. J. Exp. Med. 203, 1447–1458 (2006). 138. Lin, Y. L., Liang, Y. C. & Chiang, B. L. Placental growth macrophage tryptophan catabolism. J. Exp. Med. 115. Cavassani, K. A. et al. The post sepsis-induced factor down-regulates type 1 T helper immune 189, 1363–1372 (1999). expansion and enhanced function of regulatory T cells response by modulating the function of dendritic cells. 91. Choi, J., Enis, D. R., Koh, K. P., Shiao, S. L. & Pober, J. S. create an environment to potentiate tumor growth. J. Leukoc. Biol. 82, 1473–1480 (2007). T lymphocyte–endothelial cell interactions. Annu. Rev. Blood 115, 4403–4411 (2010). 139. Fischer, C., Mazzone, M., Jonckx, B. & Carmeliet, P. Immunol. 22, 683–709 (2004). 116. Pucci, F. et al. A distinguishing gene signature shared FLT1 and its ligands VEGFB and PlGF: drug targets 92. Mulligan, J. K., Day, T. A., Gillespie, M. B., by tumor-infiltrating Tie2‑expressing monocytes, blood for anti-angiogenic therapy? Nature Rev. Cancer 8, Rosenzweig, S. A. & Young, M. R. Secretion of “resident” monocytes, and embryonic macrophages 942–956 (2008). vascular endothelial growth factor by oral squamous suggests common functions and developmental 140. Sutmuller, R. P. et al. Toll-like receptor 2 controls cell carcinoma cells skews endothelial cells to relationships. Blood 114, 901–914 (2009). expansion and function of regulatory T cells. suppress T‑cell functions. Hum. Immunol. 70, 117. Muthuswamy, R. et al. Ability of mature dendritic J. Clin. Invest. 116, 485–494 (2006). 375–382 (2009). cells to interact with regulatory T cells is imprinted 141. Jarnicki, A. G. et al. Attenuating regulatory T cell 93. Mulligan, J. K. & Young, M. R. Tumors induce the during maturation. Cancer Res. 68, 5972–5978 induction by TLR agonists through inhibition of p38 formation of suppressor endothelial cells in vivo. (2008). MAPK signaling in dendritic cells enhances their Cancer Immunol. Immunother. 59, 267–277 (2009). 118. Baratelli, F. et al. Prostaglandin E2 induces FOXP3 efficacy as vaccine adjuvants and cancer 94. Nahrendorf, M., Pittet, M. J. & Swirski, F. K. gene expression and T regulatory cell function in immunotherapeutics. J. Immunol. 180, 3797–3806 Monocytes: protagonists of infarct inflammation and human CD4+ T cells. J. Immunol. 175, 1483–1490 (2008). repair after myocardial infarction. Circulation 121, (2005). 142. Macedo, L. et al. Wound healing is impaired in 2437–2445 (2010). 119. Ahmadi, M., Emery, D. C. & Morgan, D. J. Prevention MyD88‑deficient mice: a role for MyD88 in the 95. Conejo-Garcia, J. R. et al. Vascular leukocytes of both direct and cross-priming of antitumor CD8+ regulation of wound healing by adenosine A2A contribute to tumor vascularization. Blood 105, T‑cell responses following overproduction of receptors. Am. J. Pathol. 171, 1774–1788 (2007). 679–681 (2005). prostaglandin E2 by tumor cells in vivo. Cancer Res. 143. Wang, L. et al. IL‑17 can promote tumor growth 96. De Palma, M., Venneri, M. A., Roca, C. & Naldini, L. 68, 7520–7529 (2008). through an IL‑6–Stat3 signaling pathway. J. Exp. Med. Targeting exogenous genes to tumor angiogenesis by 120. Rodriguez, P. C. et al. Arginase I in myeloid suppressor 206, 1457–1464 (2009). transplantation of genetically modified hematopoietic cells is induced by COX‑2 in lung carcinoma. J. Exp. stem cells. Nature Med. 9, 789–795 (2003). Med. 202, 931–939 (2005). Acknowledgements 97. Yan, S. F. et al. Induction of interleukin 6 (IL‑6) by 121. Ohta, A. et al. A2A adenosine receptor may allow The authors are supported by US National Institutes of hypoxia in vascular cells. Central role of the binding expansion of T cells lacking effector functions in Health grant R01‑CA116779, US National Cancer Institute site for nuclear factor-IL‑6. J. Biol. Chem. 270, extracellular adenosine-rich microenvironments. ovarian cancer SPORE grant P01‑CA83638 and the Ovarian 11463–11471 (1995). J. Immunol. 183, 5487–5493 (2009). Cancer Research Fund. 98. Cohen, T., Nahari, D., Cerem, L. W., Neufeld, G. & 122. Zarek, P. E. et al. A2A receptor signaling promotes Levi, B. Z. Interleukin 6 induces the expression of peripheral tolerance by inducing T‑cell anergy and the Competing interests statement vascular endothelial growth factor. J. Biol. Chem. 271, generation of adaptive regulatory T cells. Blood 111, The authors declare no competing financial interests. 736–741 (1996). 251–259 (2008). 99. Wei, L. H. et al. Interleukin‑6 promotes cervical tumor 123. Hasko, G., Linden, J., Cronstein, B. & Pacher, P. growth by VEGF-dependent angiogenesis via a STAT3 Adenosine receptors: therapeutic aspects for FURTHER INFORMATION pathway. Oncogene 22, 1517–1527 (2003). inflammatory and immune diseases. Nature Rev. Drug Authors’ homepage: http://www.uphs.upenn.edu/obgyn/ 100. Kryczek, I. et al. B7‑H4 expression identifies a novel Discov. 7, 759–770 (2008). research/ovarian.htm 124. suppressive macrophage population in human ovarian Taylor, A. W. Review of the activation of TGF-β in ALL LINKS ARE ACTIVE IN THE ONLINE PDF carcinoma. J. Exp. Med. 203, 871–881 (2006). immunity. J. Leukoc. Biol. 85, 29–33 (2009).