Cellular & Molecular Immunology (2015) 12, 1–4 ß 2015 CSI and USTC. All rights reserved 1672-7681/15 $32.00 www.nature.com/cmi

RESEARCH HIGHLIGHT

The origin and function of tumor-associated

Yang Liu and Xuetao Cao

Cellular & Molecular Immunology (2015) 12, 1–4; doi:10.1038/cmi.2014.83; published online 15 September 2014

dentifying the cellular and molecular remain to be further investigated. Another on the Notch signaling pathway via the I suppressors of the key question in this field surrounds the dif- transcription factor RBPJ (Figure 1). against tumors is a popular topic in the ference and functional relationship between These new findings not only enrich our field of tumor immunology that will pro- the migrating or recruited immune cells understanding of the origin and function vide new targets for the immu- and the tissue-resident immune cells in of TAMs, but also propose new pathways notherapy. Suppressing the suppressor the tumor microenvironment. for the differentiation of TAMs, thus is a very attractive approach to enhan- Macrophages are a population of providing new clues for developing strat- cing the anti-tumor immune response immune cells with a high degree of egies for . by reversing the immunosuppression or phenotypic and functional heterogen- As an important type of immune cells blocking immune escape in the late eity. Macrophages, which are widely dis- in the tumor microenvironment, macro- stages of cancer progression. It is well tributed in all tissues, play a major role in phages have been demonstrated to be known that tumors, especially at the late the host innate immune response against important in tumor progression, depend- stage of development, can actively drive infections; additionally, macrophages ing on the stage of tumor development and the generation of immunosuppressive or are well recognized for their roles in the tumor type.7 Generally, TAMs are regulatory immune cell subtypes and can homeostasis, tissue repair and develop- accepted to promote tumor progression also induce the massive accumulation of ment.2 In the last decade, there have been via different mechanisms. Macrophages tumor-promoting myeloid immune cells numerous reports about the relation- are a heterogeneous cell population that in the tumor microenvironment. For ship between macrophages and tumors. can be conventionally divided into two sub- example, myeloid-derived suppressor cells, One of the major concerns in this field groups:M1andM2.M1-typemacro- tumor-associated macrophages (TAMs) is the origin and function of TAMs. phages, which are classically activated, play and regulatory T cells have been found to TAMs can enhance tumor cell prolifera- important roles in the innate response be the major tumor-promoting immune tion, invasion and metastasis; stimulate against invading pathogens. M2-type cells in the tumor microenvironment.1 ; and inhibit the - macrophages, which are alternatively acti- Although much work has been con mediated anti-tumor immune response, vated, play important roles in tissue repair ducted to identify the molecular mechan- thus promoting tumor progression.3,4 and tumor progression. Previous studies isms of the generation and accumulation Much clinical data show that more accu- have shown that Notch signaling plays a of these types of tumor-promoting cells lo- mulation of TAMs in the tumor tissue decisive role in the polarization of M2 cally in the tumor microenvironment and indicates a poor prognosis for cancer macrophages.8,9 A recent study shows that systemically in the draining lymph nodes patients.5 However, there are contradict- mouse peritoneal macrophages can speci- and other organs, the precise molecular ing reports about the cellular origin of fically express the transcription factor Gata6, mechanisms for their mobilization, dif- TAMs accumulated in the tumor micro- which can affect the phenotype of macro- ferentiation, accumulation and function environment and the identification of phages by altering their transcriptome, thus National Key Laboratory of Medical Molecular the master molecule responsible for contributing to the inflammatory response Biology & Department of Immunology, Institute TAM differentiation from their precur- and the renewal of macrophages in the of Basic Medical Sciences, Chinese Academy of sors. In a recent issue of Science, Franklin inflammatory response.10 Furthermore, the Medical Sciences, Beijing, China et al.6 reported that TAMs are phenoty- localization of tissue-specific macrophages Correspondence: Dr XT Cao, National Key Laboratory of Medical Molecular Biology & pically and functionally different from and the polarization of func- Department of Immunology, Institute of Basic the traditional M2 TAMs in the mouse tion can be determined, at least partially, Medical Sciences, Chinese Academy of Medical model of mammary cancer; the group by this pathway.11 Several cytokines, such Sciences, Beijing 100005, China. reported that TAMs are differentiated as IL-6, have been found to be important E-mail: [email protected] 1 Received: 9 August 2014; Accepted: 9 August from CCR2 inflammatory monocytes in the development and maintenance of 2014 and that their differentiation depends the macrophage subsets and their functions Research Highlight 2

Ly6C+ Ly6C– CD11c– CD11c+ MHCII– MHCII+ hi Io CD11b CD11c CD11b – + Vcam1 Ly6C MHCII CD11b Vcam 1 Vcam1

RBPJ RBPJ RBPJ

TAM

CCR2+ CD11b monocyte F4/80 CD11c Proliferation CD206 HSC Recruitment Differentiation CCL2, M-CSF, IL-3, IL-4, M-CSF, IL-10, TGF-β, PGE2, VEGF VEGF TAM

Bone Marrow Blood Tumor

Figure 1 Origin and differentiation of TAMs. TAMs originate from the circulating Ly6C1CCR21 monocytes, which are derived from bone marrow hematopoietic stem cells. The inflammatory monocytes are recruited to the tumor tissues and then differentiate into TAMs. At the early stage of differentiation, the inflammatory monocytes exhibit an increase in CD11c and a decrease in Ly6C; this process involves RBPJ-mediated Notch signaling. However, at a relatively late stage of differentiation, RBPJ induces the upregulation of MHC-II and downregulation of CD11b, then the significant upregulation of Vcam1 on the inflammatory monocytes, finally driving the differentiation of the CCR21 inflammatory monocytes to Ly6C2CD11c1MHCII1CD11bloVcam11 TAMs that can further proliferate in the tumor tissue and mediate the suppression of T-cell immunity against cancer. TAM, tumor-associated macrophage.

in and tissue homeostasis.12 breast tumor growth can actively recruit expressed low levels of the protein Much work has been performed to identify CCR21 inflammatory monocytes to the CD11b but high levels of Vcam1 following the soluble factors, such as and tumor tissue and expand the number of tumor progression. Unexpectedly, TAMs growth factors, in polarizing macrophage macrophages in the tumor microenviron- did not express the markers of alternatively function in tumor progression. For example, ment. Unexpectedly, they distinguished activated macrophages, including Mrc1 the CCL2 and macrophage col- the TAMs from the ‘breast tissue macro- (CD206), Ym1 and Fizz1, while MTMs ony-stimulating factor can recruit monocytes phages’ (mammary tissue macrophages, did. This observation further shows that to the tumor tissue, and then IL-4, IL-10, IL- MTMs) using a series of experiments the TAMs that the authors discovered in 13 and other cytokines in the tumor micro- including morphology, flow cytometry this study are not generated by conversion environment can induce the monocytes to and transcriptional analysis. Additionally, from MTMs. By analyzing the molecular differentiate into TAMs.13 TAMs have a very they showed that TAMs express the mechanism for TAM differentiation, the weak ability to present but exhibit a macrophage transcription factor Mafb authors revealed that transcription factor very potent ability to promote tumor pro- and the macrophage markers CD64 and RBPJ-mediated Notch signaling pathway gression through a variety of mechanisms. MerTK, but not the dendritic cell-specific is responsible for the TAM differentiation However, the detailed mechanisms for the transcription factors Zbtb46 and Flt3, c- from CCR21 inflammatory monocytes recruitment and tumor-promoting function Kit and other markers. Furthermore, using (Figure 1). Finally, the team demonstrated of TAMs are not fully understood; thus, fur- many mouse models that were deficient in that the in vivo depletion of TAMs, but not ther investigation is required to identify new different molecules involved in cell migra- MTMs, can efficiently restore the tumor- targets for cancer immunotherapy. tion and differentiation, the authors con- infiltrating cytotoxic T-cell response by In this article, Franklin and colleagues vincingly showed that TAMs were derived decreasing the number of immunosup- utilized the MMTV-PyMT (PyMT) mouse from bone marrow cells and originated pressive PD-11GzmB2CD81 T cells. mammary tumor model to investigate the from CCR21 inflammatory monocytes, TAMs have been verified to promote cellular components in CD451 tumor- but independent of pre-dendritic cell. tumor progression via different mechan- infiltrating leukocytes and to attempt to Thus, the authors proposed a new origin isms (Figure 2). TAMs can suppress the elucidate the three subsets of myeloid cells of conventional TAMs. Notably, using CD81 T-cell immune response against the roles they play in tumor progression. gene profiling to distinguish TAMs from cancer by directly interacting with T The authors found that MMTV-PyMT MTMs, the investigators found that TAMs cells or by secreting immunosuppressive

Cellular & Molecular Immunology Research Highlight 3

Tumor growth Immunosuppression

PD-1+GzmB-CD8+T cell

Naive T cell anergy β VEGFs, PDGF, EGF, IL-10, TGF- , CCL17, FGF, TNF-α, IFN-β CCL18, CCL22, PGE2, ROS, Inhibition of Th1 cell Tumor cell IDO, B7-H1 Recruitment of Th2 cell

Induction of Treg cell

MMPs, TGF-β, uPA, uPAR, VEGFs, PDGF, EGF, FGF, TGF-β, VEGFs, PDGF, Cathepsins, MMP9, CXCL8, ELR+chemokine, TNF-α, MCP-1, M-CSF, TAM cyclooxygenase SR-A, HIF1

Lymphatic vessel Tumor cell

Matrix remodeling, tumor Angiogenesis and invasion and metastasis lymphangiogenesis

Figure 2 Multiple functions of TAMs in tumor progression. TAMs can promote tumor progression in a variety of ways. Monocyte-derived, RBPJ- dependent TAMs can induce the expansion of PD-11GzmB2CD81 T cells in the tumor tissue to mediate immunosuppression; TAMs can inhibit the proliferation of effector T cells or recruit more Th2 or regulatory T cells to the tumor tissue to suppress the anti-tumor immune response. TAMs can release a large number of angiogenic factors, such as VEGF and PDGF, which can promote tumor angiogenesis. In addition, TAMs can secrete numerous growth factors, MMPs, which can work jointly to promote tumor cell proliferation, invasion and metastasis. MMP, matrix metallopro- teinase; PDGF, platelet-derived growth factor; TAM, tumor-associated macrophage; VEGF, vascular endothelial growth factor. factors to inhibit T-cell effector func- mechanism for the generation of TAMs may homeostasis and disease. Nature 2013; tion.5,14 This study showed the role of 496: 445–455. be more complicated than we expected. 3 Qian BZ, Pollard JW. Macrophage diversity Notch-dependent, monocyte-derived TAMs The identification of new origins and enhances tumor progression and in tumor progression by disrupting anti- the molecular profiling of TAMs is of great metastasis. Cell 2010; 141: 39–51. tumor T-cell immunity, adding new insight interest. It remains to be determined how 4 Grivennikov SI, Greten FR, Karin M. to the and escape of Immunity, inflammation, and cancer. Cell broadly applicable the findings obtained 2010; 140: 883–899. tumors. However, some concerns still exist from the mouse mammary cancer model 5 Noy R, Pollard JW. Tumor-associated regarding the roles of these TAMs in tumor the authors used are. Future questions will macrophages: from mechanisms to metastasis. Whether these TAMs can pro- surround the phenotypic and functional therapy. Immunity 2014; 41: 49–61. mote tumor angiogenesis, or induce the 6 Franklin RA, Liao W, Sarkar A, Kim MV, identification of these TAMs in other Bivona MR, Liu K et al. The cellular and apoptotic resistance of tumor cells, remains non-mammary mouse cancer models. molecular origin of tumor-associated to be determined. One important question How to translate the basic results from macrophages. Science 2014; 344: 921– surrounds the relationship of these TAMs the mouse model to clinical practice and 925. with M2 macrophages or other regulatory 7 Perdiguero EG, Geissmann F. Cancer how to link these TAM results to clinical immunology. Identifying the infiltrators. immune cells, such as regulatory T cells studieswillbecriticaltocancerimmu- Science 2014; 344: 801–802. and myeloid-derived suppressor cells, in notherapy. These questions require further 8 Palaga T, Ratanabunyong S, Pattarakankul tumor immune escape. It remains to be investigation in the future, and any pro- T, Sangphech N, Wongchana W, Hadae Y determined what mechanisms TAM deletion et al. Notch signaling regulates expression gress in addressing these questions will of Mcl-1 and in PPD-treated drives the restoration of the immuno- benefit the design of powerful cancer macrophages. Cell Mol Immunol 2013; suppression in the tumor microenvironment immunotherapy. 10: 444–452. by affecting the tumor-promoting functions 9 Wang YC, He F, Feng F, Liu XW, Dong GY, of other types of immunosuppressive cell Qin HY et al. Notch signaling determines the M1 versus M2 polarization of macrophages subsets. Hypoxia and cell death in the tumor in antitumor immune responses. Cancer microenvironment may contribute to the 1 Gajewski TF, Schreiber H, Fu YX. Innate and Res 2010; 70: 4840–4849. induction of tumor immunosuppression.15 adaptive immune cells in the tumor 10RosasM,DaviesLC,GilesPJ,LiaoCT, microenvironment. Nat Immunol 2013; Furthermore, many new immunosuppres- Kharfan B, Stone TC et al. The transcription 14: 1014–1022. factor Gata6 links tissue macrophage sive cell subsets have been identified in cancer 2 Wynn TA, Chawla A, Pollard JW. phenotype and proliferative renewal. patients.16 Thus, the cellular and molecular Macrophage biology in development, Science 2014; 344: 645–648.

Cellular & Molecular Immunology Research Highlight 4

11 Okabe Y, Medzhitov R. Tissue-specific 13 van Dyken SJ, Locksley RM. Interleukin-4- induction of regulatory T cells and signals control reversible program of and interleukin-13-mediated alternatively tolerogenic dendritic cells. Cell Mol localization and functional polarization activated macrophages: roles in Immunol 2013; 10: 393–402. of macrophages. Cell 2014; 157: 832– homeostasis and disease. Annu Rev 16 Han Y, Chen Z, Yang Y, Jiang Z, Gu Y, Liu Y 844. Immunol 2013; 31: 317–343. et al. Human CD141 CTLA-41 regulatory 12 Mauer J, Chaurasia B, Goldau J, Vogt MC, 14 Alderton GK. Tumour immunology: turning dendritic cells suppress T-cell response by Ruud J, Nguyen KD et al. Signaling by IL-6 macrophages on, off and on again. Nat Rev cytotoxic T-lymphocyte -4- promotes alternative activation of Immunol 2014; 14: 136–137. dependent IL-10 and indoleamine-2,3- macrophages to limit endotoxemia and 15 Wu C, Zhang Y, Jiang Y, Wang Q, Long Y, dioxygenase production in hepatocellular obesity-associated resistance to insulin. Wang C et al. Apoptotic cell administration . Hepatology 2014; 59:567– Nat Immunol 2014; 15: 423–430. enhances pancreatic islet engraftment by 579.

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