Review Article | Open Access
Wuzhen Chen, Jingxin Jiang, Wenjie Xia, Jian Huang, "Tumor-Related Exosomes Contribute to Tumor-Promoting Microenvironment: An Immunological Perspective", Journal of Immunology Research, vol. 2017, Article ID 1073947, 10 pages, 2017. https://doi.org/10.1155/2017/1073947
Tumor-Related Exosomes Contribute to Tumor-Promoting Microenvironment: An Immunological Perspective
Exosomes are a kind of cell-released membrane-form structures which contain proteins, lipids, and nucleic acids. These vesicular organelles play a key role in intercellular communication. Numerous experiments demonstrated that tumor-related exosomes (TEXs) can induce immune surveillance in the microenvironment in vivo and in vitro. They can interfere with the maturation of DC cells, impair NK cell activation, induce myeloid-derived suppressor cells, and educate macrophages into protumor phenotype. They can also selectively induce effector T cell apoptosis via Fas/FasL interaction and enhance regulatory T cell proliferation and function by releasing TGF-β. In this review, we focus on the TEX-induced immunosuppression and microenvironment change. Based on the truth that TEXs play crucial roles in suppressing the immune system, studies on modification of exosomes as immunotherapy strategies will also be discussed.
Traditionally, we always consider neoplasm as a disease driven by the alteration of the cellular genome, with overexpression of oncogenes, or deficiency of tumor suppressor genes . After decades of hypothesis and proof, now, it is widely accepted that tumor microenvironment and their interactions with the host immune system are important in tumor genesis and progression [2–4]. Although the host immune system mostly works well at eliminating tumor cells, defenses are sometimes blunted by the activation of suppressive pathways which degrade immune restraints on tumor spreading [5, 6]. Exosomes, a branch of extracellular vesicles, were termed by Trams in 1981 for exfoliated membrane vesicles with 5′-nucleotidase activity. Generally, exosomes are described as 30 to 100 nm size exfoliated vesicles originated from the endosome organelles, which are different from macrovesicles (>100 nm) in size . According to present studies, exosomes are accumulated in the multivesicular bodies and released to the extracellular environment through fusion of multivesicular bodies with the plasma membrane. Exosomes can be released by all types of cells including cancer cells, fibroblast cells, immune cells, and mesenchymal cells. The contents of exosomes, including a cargo of different genes, lipids, proteins, and miRNAs, are mostly defined by their parental cells. Being able to stably transfer their contents to distant sites, exosomes have been proved to be an effective mode of cross talk among cells far apart and are involved in multiple physiological and pathological processes.
Cancer cells have built such a subtle and sophisticated intercellular communication with the host environment and facilitate tumor progression through secreting exosomes, including the process of tumorigenesis, tumor growth, invasion, and metastasis. Tumor-derived exosomes (TEXs) were initially discovered from peripheral circulation and malignant effusions in ovarian cancer patients [8–10]. After then, exosomes were found in many other malignancies such as breast cancer and colon cancer [1, 11, 12]. TEXs emerged as a new pattern of intercellular communication and play a crucial role in the tumor microenvironment. Previous studies have demonstrated that TEXs play an essential role in tumor angiogenesis, matrix remodeling, tumor migration, and metastasis . Stress, microenvironment hypoxia, and activation of wild-type p53 would lead to more releases of tumor-related exosomes [14, 15]. Apart from tumor cells, exosomes can be released by a variety of activated immune cells, including dendritic cells (DCs), macrophages, B cells, T cells, and natural killer (NK) cells [16–18]. These organelles make available for strategic function in intercellular communication and regulation of immune responses. The immunosuppression role of TEXs have been widely indicated and furtherly result in the tumor progression outcome. TEXs can participate in multiple immune mechanisms, such as mast cell degranulation, germinal center reaction, and cell apoptosis, with a consequent downstream blockade in the natural antitumor immune responses . Western blots of TEXs isolated from tumor cell supernatants and exosome fractions obtained from cancer patients’ plasma confirm the expression of various immunosuppressive molecules, including death receptor ligands such as FasL and TRAIL, checkpoint receptor ligands such as PD-L1, and inhibitory cytokines such as IL-10 and TGF-β, as well as prostaglandin E2 (PGE2) and ectoenzymes engaged in the adenosine pathway (CD39 and D73) . A large amount of TEX-derived noncoding RNAs are also regarded as immunosuppressive agents. Obviously, it is a complex network involving TEXs and the host immune system, together with the mechanisms of exosome, which mediate phenotypical and functional defects. In the following paragraphs, this review will discuss the moderating role of TEXs on multiple immune cells such as DCs, NKs, macrophages, effector T cells, regulatory T/B cells, and myeloid-derived suppressor cells (MDSCs). For practical applications, the new immunotherapy strategy based on DC-derived exosomes and bioengineering of exosomes will also be illustrated in this work.
2. Dendritic Cells
Generally considering, dendritic cells (DCs) are professional antigen-presenting cells (APCs) that process and present tumor antigens and initiate T cell responses to cancer cells. As studies reported, TEXs can impair DC proliferation and maturation as well as their functions. TEXs can interfere with monocytes differentiating into DC cells (Figure 1, (a)). In melanoma and colon cancer, TEXs could curb peripheral CD14+ monocytes differentiating into DC cells, while inducing them into myeloid-derived suppressor cells (MDSCs) . Furthermore, TEXs could directly inhibit DCs’ bioactivity and induce immune tolerance (Figure 1, (a)). TEXs force CD14+ monocyte to express HLA-DR at a low level . In the presence of TEXs in culture medium, costimulatory molecule expression in human DCs were attenuated while inhibitory cytokines (e.g., TGF-β and PGE2) were elicited, with a dose-dependent suppression of T cell proliferation and antitumor cytotoxicity [22, 23]. What is more, TEXs of pancreatic cancers were indicated to downregulate the toll-like receptor 4 (TLR4) expression in DCs via miRNA-203, thus reducing downstream cytokines TNF-α and interleukin-12 (IL-12) .
3. Myeloid-Derived Suppressor Cells
Myeloid-derived suppressor cells (MDSC) is a well-known immune suppression factor that consists of immature myeloid cells including the precursors of DCs. Intravenous injected TEXs also showed marked accumulation of MDSCs in tumor, spleen, peripheral blood, and lung in vivo . The accumulation of MDSCs could negatively affect the antigen processing and presentation and produce numerous immunosuppressive inhibitory factors, including NO and ROS, which cause TCRs nitration or T cell apoptosis . Valenti et al. found that exosomes released by melanoma prohibit myeloid cells differentiating into DCs, while inducing them into TGF-β-secreting CD14+HLA-DR− phenotype which was associated with suppressing T cell proliferation and cytotoxic functions . CD14+HLA-DR− MDSCs can also be found in patient’s peripheral blood in many other malignancies, including hepatocellular carcinoma, bladder carcinoma, glioblastoma, and multiple myeloma [25–27]. An in vitro study indicated that TEX-driven MDSCs were capable to polarize normal monocytes to M2 phenotypes with higher expression of CD163, along with Th2 immune response and a tumor-promoting environment. Comparing to those in normal control, higher CD11b+CD14+HLA-DR− TGF-β secreting cells could be found in the peripheral blood of stages II-III melanoma patients, but minor boost in stage IV patients [28–30]. This indicated that systematic MDSCs proliferation occurred in the early stage of neoplasm and melanoma released TEXs not only influenced the amount of MDSCs but also exerted impact on the differentiation of bone marrow to produce more immunosuppressive cell subsets . Taylor and Gercel-Taylor confirmed that TEXs could activate the STAT1 and STAT3 pathways and increase antiapoptotic proteins Bcl-xL and Mcl-1 to prolong the survival of MDSCs . TEXs could also boost NO releasing from MDSCs and enhance their suppressive activity in myeloma models. In TS/A mammary tumor murine model, TEXs injected into the bone marrow interacted with CD11b+ myeloid precursors, inducing IL-6 producing, Stat3 phosphorylation, and skewing bone marrow-derived cells (BMDCs) differentiation to MDSCs . In breast cancer models, TEXs adopt TGF-β and IL-6 pathway to differentiate BMDCs towards MDSCs phenotype . Chalmin et al. discovered that colon cancer TEXs with Hsp72-induced IL-6 toll-like receptor could accumulate MDSCs in mice and human beings [33–35]. Recent data also showed that MyD88 served as an important role in murine TEX-mediated MDSCs proliferation and contributed to lung metastasis through CCL2 in the C57BL/6J mice model . Membrane-associated Hsp72 of TEXs can also trigger STAT3 activation in MDSCs through IL-6 via TLR2/MyD88 signal [33, 37]. But more functions of these TEX-related receptors needs to be further explored [33, 34, 38].
Macrophages are among the most abundant of innate immune cells that function as antitumor responses. In addition to phagocytes, macrophages can serve as cytokines and chemokines resource to recruit and induce other immune cells. Classically, macrophage can be activated by a range of environmental stimuli such as bacterial LPS and IFN-γ, can be transformed into M1-phenotype, and can enhance both innate and adaptive immunity. Studies have proved that M2 cytokine profile macrophages, also called tumor-associated macrophages, help enhance tumor metastasis and invasion. Cytokines such as CCL2, MIP2, IL-8, and IL-1Rα that support tumor metastasis, angiogenesis, and protumor inflammation are upregulated, while the expression of antitumor cytokines such as TIMP-1, IFN-γ, IL-Ra, IL-13, and IL-16 are attenuated. As for the mechanism involved, proteins such as and Hsp72 and RNAs from TEXs have been shown to play a role through pattern recognition receptors (PRRs). Chow et al. demonstrated that palmitoylated proteins on TEXs can play as the ligand and bind to TLR2 on macrophages, stimulate NF-κB signals in macrophages, and promote secretion of proinflammatory cytokines, such as IL-6, TNF-α, and CCL2  (Figure 1, (b)). Fabbri et al. proved that TEX-derived miRNAs such as miR-21 and miR-29 served as the ligands of murines TLR7 and TLR8, leading to TLR-mediated NF-κB activation in macrophage . Another novel mechanism for the intercellular communication between cancer cells and tumor-associated macrophages is recently proposed by Menck et al. . TEXs could induce the upregulation of Wnt 5α in macrophages and Wnt 5α could be delivered into tumor cells via macrophage-derived exosomes, thus leading to the activation of β-catenin-independent Wnt signaling in tumor cells and enhancing tumor invasion in breast cancer . Recently, evidences proved that TEXs could also prolong tumor-associated macrophages survival in the inflammatory niche .
5. NK Cells
NK cells are the first-line defensive immune cells with cytotoxicity that directly kill tumor cells. TEXs contribute to immune escape via interfering the amount and function of NK cells. Whiteside showed that the percentage of NK cells in the spleen and lung decreased when treated with TEXs in mice models . NK cells in tumor patients have a lower activity with less activation receptors such as NKp30, NKp46, NKG2C, and NKG2D [43, 44]. Among these receptors, NKG2D is the most critical one that binds to human MHC class I chain-related MICA and MICB to stimulate T cells’ immune response. As the literature reported, TEXs can downregulate NKG2D expression, induce Smad phosphorylation, and reducing the cytolytic activity in NK cells  (Figure 1, (c)). In breast cancer and mesothelioma, tumor cells excreted NKG2D ligand containing TEXs to downregulate NKG2D expression, resulting in lower activity of NK cells [38, 46–48]. Apart from the NK receptors, other impaired signaling pathways contribute to less NK activation as well. In syngeneic BALB/c and nude mice models, TEXs released by TS/A or 4T.1 murine mammary tumor cell lines could intercept IL-2-mediated pathway to prevent NK cell activation and promote implanted tumor progression and metastasis . In vitro and in vivo experiments demonstrate TEXs can also directly attenuate NK cell perforin and cyclin D3 expression, as well as the activation of JAK-3, furtherly inhibiting NK cell-mediated cytolysis . In acute myeloid leukemia (AML), the serum soluble TGF-β also plays a role in TEX-associated NK cell dysfunction, which is consistent with the report that neutralizing antibodies against TGF-β could remove the TEX-induced inhibition .
6. Effector T Cells
It is believed that TEXs can both impair the activation of effector T cells and induce apoptosis of activated T cells in kinds of ways. Researchers found numerous malignant cells could release TEXs to induce T cell apoptosis, including nose pharynx cancer, pancreatic carcinoma, colon cancer, and gastric carcinoma [49–51]. Galectin-9, as the agonist of Tim-3, has been reported to be abundant in human nose pharynx cancer and served as a death-inducing receptor . In Epstein-Barr virus-infected nose pharynx cancer, galectin-9 containing TEXs circulated to T cells and bind to Tim-3, thus inducing massive EBV-specific CD4+ lymphocyte apoptosis and inhibiting the function of Th1 cells . Research findings suggest that TEXs could also express bioactive membrane-bound form of FasL and selectively induce T cell apoptosis via Fas/FasL interaction  (Figure 1, (d)). In vitro studies also showed that TEXs separated from malignant effusions such as ascites could also inhibit effector T cell activity through Fas/FasL interaction [49, 54, 55]. Besides, in ovarian carcinoma, TEXs utilize membrane-formed FasL to inhibit expression of CD3-ζ and further suppress the follow-up TCR signaling . Andreola et al. discovered that melanoma TEXs not only expressed bioactive FasL but also specifically expressed CD63 and exosomal proteins, such as TRAIL, gp100, and MART-1 . Both galectin-9 and Fas/FasL mechanisms are originally designed for T cell homeostasis control and self-limitation of immune response [58–61]. These research give us hints to understand that TEXs could circulate in the body and exert harmful effects on immune effector cells through some specific pathways, which might be the potential target of immunological therapy [49, 57, 62].
TEXs can impair the activation of T cell responses as well. TEXs could selectively inactivate CD8+ T cells by interfering with TCR- and IL-2R-mediated signaling  (Figure 1, (d)). In glioblastoma mice models, TEXs from glioblastoma GL26 cell line reduced the percentages of CD8+ T cells and inhibited the activation of CD8+ T cells, inducing decreased release of IFN-γ and granzyme B . TCR signaling would be uncoupled by TEX-driven ROS burst, which would disrupt both CD4+ and CD8+ T cell signals and in turn downregulate T cell numbers .
Several studies have also demonstrated that exosomes can transport antigens from tumor cells to antigen-presenting dendritic cells [64–66]. Via MHC-I molecules, dendritic cells’ prime cytotoxic T lymphocytes evoke an antitumor response and suppress tumor growth in vivo [65, 67]. Moreover, a potential direct presentation to T cells via HLA/peptide complex exosomal expression is also under investigation. Using these characteristics, modified TEXs could be designed as a tumor vaccine which would be discussed in Section 8.
Adenosine is another pathway that is related to T cell suppression. As one of the well-known immunosuppressive factors, adenosine has a role in T cell suppression by binding to its receptors (A1, A2A, A2B, and A3) [42, 68]. TEXs could increase the level of extracellular adenosine and thus decrease the local immunity. With the existence of both CD39 (ATP hydrolase) and CD73 (5′-nucleotidase) in cell surface, Treg cell could produce adenosine [69, 70]. TEXs could not only have activated CD39 and CD73 on the membrane surface but also directly deliver membrane-tethered CD73 to CD39+ cells, inducing the hydrolysis of ATP to adenosine and forming a T cell suppression environment [42, 71, 72].
7. Treg and Breg Cells
Most studies concentrated on the immunosuppressive effect of MDSC, lacking of research on regulatory T (Treg) cells and regulatory B (Breg) cells. TEXs could regulate other critical parts of the immune system, especially the impact on the immunosuppressive cells and cytokines. In addition to MDSCs, TEXs could enhance Treg and Breg proliferation and function [22, 23]. In vivo studies represented a crucial step for proving a true involvement of this pathway in immune suppression and tumor progression . Myeloma patients’ peripheral blood contains more CD4+CD25+FOXP3+ Treg cells than that of healthy donors, and high-concentrate TEXs could be found in the serum [27, 73]. Szajnik et al. reported TEXs separated from serum and ascites of cancer patients can phosphorylate Smad2/3 and Stat3, inducing CD4+CD25− T cell transformed into CD4+CD25+Foxp3+ Treg cell [6, 73]. Clayton et al. found that TEXs could promote Treg cells and inhibit cytotoxicity cells via skewing IL-2 responsiveness . TEXs with TGF-β upregulate Treg-related genes through TGF-β/Smad signaling activation and SAPK signaling devitalization in colorectal cancer . Furthermore, TEXs can utilize the IL-10-dependent mechanism to promote the amount and function of Tregs and enhance the immunosuppression function [73, 75] (Figure 1, (e)). In vitro culture medium, TEXs could not only expand Tregs’ amount and enhance Tregs’ function but also help them be resistant to cell apoptosis . Furthermore, Tregs showed a higher expression in FasL, IL-10, TGF-β, CTLA-4, and granzyme B and perforin in coculture with TEXs, as well as enhanced Smad2/3 and STAT3 phosphorylation [42, 73] (Figure 1, (e)). These TEX-mediated effects mainly rely on TGF-β and IL-10, while other molecules in TEXs such as miRNA-214-PTEN and EGFR might also be participated in the signaling pathway . Antibodies designed for these cytokines can prevent TEXs from proliferating Treg cells .
Bregs are a unique subset of B cells which produce inhibitory cytokines and play suppressive roles in antitumor immune responses. High percentage and density of Bregs have been proved to be accumulated in the tissues and peripheral blood of invasive carcinoma of breast compared with that in patients with benign breast tumor or healthy women [76, 77]. Bregs expressing suppressive molecules such as IL-10, TGF-β, IL-35, IL-21, and PD-L1 can induce the generation of Tregs, upregulate MDSC function, and suppress CD4+ T cell-protective immune responses in both animal models and in vitro studies [77–81]. Recent research indicates that in murine splenocyte culture, exosomes from mycoplasma-infected tumor cells induce B cell-dependent IL-10 and suppress T cell activity . Extracellular vesicles derived from esophageal cancer cells were also found to induce naive B cells to differentiate into TGF-β-producing Bregs which showed immune suppressor functions on CD8+ T cell proliferation . Yang et al. discovered that mycoplasma-infected tumor cells could produce TEXs containing a component from mycoplasma, and these TEX-accumulated Breg cells in turn inhibit the activation of effector T cells  (Figure 1, (e)). These findings open a window to illustrate the mechanism of interaction between Breg cells and TEXs.
8. Immunotherapy Strategy
TEXs have been proved to play crucial roles in suppressing the immune system by attenuating the differentiation, proliferation, or functions of various immune cells. Thus, modulating the processes and reprogramming immune cells towards the opposite direction have great promises and might be effective. Relieving the suppression of TEXs on host immune system might be the key points for exosome-based immunotherapy.
Bioengineered exosomes mean load antitumor antigen into exosomes to produce a potent and antigen-specific immunostimulatory function. Now, there are 3 confirmed ways to import exogenous proteins into exosomes [84–88]. The first way is to use the transfection technique to load the exogenous proteins into exosomes directly [85, 86]. The second way is to bind onto the exosome membrane surface protein LAMP-2b . The third way is to fuse the exogenous proteins with lipid-binding C1C2 domains of the human lactadherin protein (MFGE8) noncovalently [85, 87, 88] (Figure 2(a)). In vitro tests have been proved that importing immunostimulatory molecules into exosomes could yield immunogenicity of exosomes . Immunostimulatory exosomes could be used as an immunogen for potent cancer vaccines in the future clinical use. But no successful data have been reported so far.
(a) Bioengineered exosomes
(b) DC-derived exosomes
Alternatively, TEX can be used as a drug delivery system. Biological therapeutics, including short-interfering RNA and recombinant proteins, which are easy to degradation, have limitation in crossing the biological membranes and avoiding host immune responses [90, 91]. Exosomes as carriers for biological therapeutics could be served as a promising strategy to overcome these issues and to achieve efficient delivery to target cells . However, the considerable complexity and the related high chance of off-target effects of these carriers are major barriers for clinical use . Considering that not all components of exosomes are required for their proper function, artificial exosomes could be an alternative strategy [84, 93, 94]. But the necessary exosomal components required for the assembly of functional artificial exosomes remain to be identified [90, 94].
DC-derived exosomes work in totally different ways. This strategy focuses more on the host system and aims to reverse the tumor-induced immunosuppression. DC-derived exosomes are produced by mature DCs and can express MHC-I, MHC-II, and costimulatory molecules (CD40, CD80, and CD86) which could induce normal DCs’ maturation and active cytotoxic T cells and natural killer (NK) cells [95–99] (Figure 2(b)). Besides, DC-derived exosomes could alter tumor-induced immunosuppression and activate innate and adaptive immune cells to induce antigen-specific responses against tumor cells [89, 99–101]. DC-derived exosomes could yield a Th1-polarized immune response to inhibit tumor antigen specifically in vivo, with IFN-γ accumulation and cytotoxic T cells proliferation [99–101] (Figure 2(b)). Following the promising preclinical animal studies, two phase I human clinical trials in melanoma and non-small-cell lung cancer using DC-derived exosome therapy have been completed. Only modest efficacy has been observed with no obvious toxicity [101, 102]. The authors suggest that these positive effects might be attributable to a small amount of NK cell activation [101, 102].
TEXs are rapidly emerging as a critical component which is designed to facilitate tumor immune escape and promote tumor growth. These TEXs could promote the differentiation of monocytes to MDSCs, educate macrophages into TAMs, inhibit NK cells activation, induce activated cytotoxic T cells apoptosis, and increase Tregs and Bregs, so as to suppress the host immune response. Due to these exosomal effects, they represent a central mediator of the tumor-supportive microenvironment. A large amount of research is emerging on the interaction between TEXs and host cells, which is still not fully clarified at present. Based on the known results, researchers have proposed some novel antitumor strategies including DC-derived exosomes and bioengineering of exosomes. In vitro and preclinical animal studies of these immunotherapy strategies have shown promising results, but there is still a long way to gain effective therapeutic effect in cancer patients. Actually, the responsible molecules including proteins and RNAs for TEXs-specific responses are still poorly understood, which leads to no systematic approach to generate TEXs with specified immune functions. Meanwhile, tumor microenvironment is essential for TEXs’ contents and functions. Whether there is a batch of TEXs that could produce some immune stimulation effects is still doubtful. Additionally, the heterogeneous molecules within TEXs are involved in varieties of immunosuppressive or immune-stimulative signaling pathways, respectively. Thus, it is unclear whether changes in TEXs’ contents or functions would occur when a specific molecule is loaded into or dissociated from TEXs, which directly influence the balance between tumor-promoting effects and antitumor effects of TEXs. Based on the above evidence and analysis, TEXs should not be thought as simple extracellular vesicles, but as bioactive vesicles with critical biological functions, which have great potential in cancer research and targeted therapy. Nevertheless, further researches are needed to illuminate the molecular mechanisms on TEX-specific effects and put forward more potent antitumor immunotherapy based on TEXs.
Conflicts of Interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
Wuzhen Chen and Jingxin Jiang contributed equally to this work.
The authors give special thanks to Dr. Fuming Qiu, Dr. Jun Ye, Dr. Ke Wang, and Dr. Pin Wu for their great help in editing this essay and providing a lot of useful information.
- M. Iero, R. Valenti, V. Huber et al., “Tumour-released exosomes and their implications in cancer immunity,” Cell Death and Differentiation, vol. 15, no. 1, pp. 80–88, 2008.
- F. Balkwill, K. A. Charles, and A. Mantovani, “Smoldering and polarized inflammation in the initiation and promotion of malignant disease,” Cancer Cell, vol. 7, no. 3, pp. 211–217, 2005.
- W. W. Lin and M. Karin, “A cytokine-mediated link between innate immunity, inflammation, and cancer,” Journal of Clinical Investigation, vol. 117, no. 5, pp. 1175–1183, 2007.
- C. Yang and P. D. Robbins, “The roles of tumor-derived exosomes in cancer pathogenesis,” Clinical and Developmental Immunology, vol. 2011, Article ID 842849, p. 11, 2011.
- L. Rivoltini, P. Canese, V. Huber et al., “Escape strategies and reasons for failure in the interaction between tumour cells and the immune system: how can we tilt the balance towards immune-mediated cancer control?” Expert Opinion on Biological Therapy, vol. 5, no. 4, pp. 463–476, 2005.
- P. Filipazzi, M. Bürdek, A. Villa, L. Rivoltini, and V. Huber, “Recent advances on the role of tumor exosomes in immunosuppression and disease progression,” Seminars in Cancer Biology, vol. 22, no. 4, pp. 342–349, 2012.
- E. G. Trams, C. J. Lauter, J. N. Salem, and U. Heine, “Exfoliation of membrane ecto-enzymes in the form of micro-vesicles,” Biochimica et Biophysica Acta, vol. 645, no. 1, pp. 63–70, 1981.
- D. D. Taylor and G. J. Doellgast, “Quantitation of peroxidase-antibody binding to membrane-fragments using column chromatography,” Analytical Biochemistry, vol. 98, no. 1, pp. 53–59, 1979.
- D. D. Taylor, H. D. Homesley, and G. J. Doellgast, “Binding of specific peroxidase-labeled antibody to placental-type phosphatase on tumor-derived membrane-fragments,” Cancer Research, vol. 40, no. 11, pp. 4064–4069, 1980.
- D. D. Taylor, H. D. Homesley, and G. J. Doellgast, “Membrane-associated immunoglobulins in cyst and ascites fluids of ovarian-cancer patients,” American Journal of Reproductive Immunology, vol. 3, no. 1, pp. 7–11, 1983.
- F. Andre, N. E. Schartz, N. Chaput et al., “Tumor-derived exosomes: a new source of tumor rejection antigens,” Vaccine, vol. 20, Supplement 4, pp. A28–A31, 2002.
- T. L. Whiteside and R. B. Herberman, “The role of natural killer cells in immune surveillance of cancer,” Current Opinion in Immunology, vol. 7, no. 5, pp. 704–710, 1995.
- D. D. Taylor and C. Gercel-Taylor, “Exosomes/microvesicles: mediators of cancer-associated immunosuppressive microenvironments,” Seminars in Immunopathology, vol. 33, no. 5, pp. 441–454, 2011.
- W. Stoorvogel, M. J. Kleijmeer, H. J. Geuze, and G. Raposo, “The biogenesis and functions of exosomes,” Traffic, vol. 3, no. 5, pp. 321–330, 2002.
- X. Yu, S. L. Harris, and A. J. Levine, “The regulation of exosome secretion: a novel function of the p53 protein,” Cancer Research, vol. 66, no. 9, pp. 4795–4801, 2006.
- Y. Xie, H. Zhang, W. Li et al., “Dendritic cells recruit T cell exosomes via exosomal LFA-1 leading to inhibition of CD8(+) CTL responses through downregulation of peptide/MHC class I and Fas ligand-mediated cytotoxicity,” Journal of Immunology, vol. 185, no. 9, pp. 5268–5278, 2010.
- E. Zumaquero, P. Muñoz, M. Cobo et al., “Exosomes from human lymphoblastoid B cells express enzymatically active CD38 that is associated with signaling complexes containing CD81, Hsc-70 and Lyn,” Experimental Cell Research, vol. 316, no. 16, pp. 2692–2706, 2010.
- P. K. Anand, “Exosomal membrane molecules are potent immune response modulators,” Communicative & Integrative Biology, vol. 3, no. 5, pp. 405–408, 2010.
- T. L. Whiteside, “Exosomes and tumor-mediated immune suppression,” Journal of Clinical Investigation, vol. 126, no. 4, p. 1216, 2016.
- D. I. Gabrilovich and S. Nagaraj, “Myeloid-derived suppressor cells as regulators of the immune system,” Nature Reviews Immunology, vol. 9, no. 3, pp. 162–174, 2009.
- S. Temme, A. M. Eis-Hübinger, M. L. AD, and N. Koch, “The herpes simplex virus-1 encoded glycoprotein B diverts HLA-DR into the exosome pathway,” Journal of Immunology, vol. 184, no. 1, pp. 236–243, 2010.
- R. Valenti, V. Huber, P. Filipazzi et al., “Human tumor-released microvesicles promote the differentiation of myeloid cells with transforming growth factor-β-mediated suppressive activity on T lymphocytes,” Cancer Research, vol. 66, no. 18, pp. 9290–9298, 2006.
- R. Valenti, V. Huber, M. Iero, P. Filipazzi, G. Parmiani, and L. Rivoltini, “Tumor-released microvesicles as vehicles of immunosuppression,” Cancer Research, vol. 67, no. 7, pp. 2912–2915, 2007.
- Y. Liu, Y. Gu, and X. Cao, “The exosomes in tumor immunity,” Oncoimmunology, vol. 4, no. 9, article e1027472, 2015.
- B. Hoechst, L. A. Ormandy, M. Ballmaier et al., “A new population of myeloid-derived suppressor cells in hepatocellular carcinoma patients induces CD4+CD25+Foxp3+ T cells,” Gastroenterology, vol. 135, no. 1, pp. 234–243, 2008.
- X. K. Yuan, X. K. Zhao, Y. C. Xia, X. Zhu, and P. Xiao, “Increased circulating immunosuppressive CD14 +HLA-DR −/low cells correlate with clinical cancer stage and pathological grade in patients with bladder carcinoma,” Journal of International Medical Research, vol. 39, no. 4, pp. 1381–1391, 2011.
- M. K. Brimnes, A. J. Vangsted, L. M. Knudsen et al., “Increased level of both CD4+FOXP3+ regulatory t cells and CD14+HLA-DR−/low myeloid-derived suppressor cells and decreased level of dendritic cells in patients with multiple myeloma,” Scandinavian Journal of Immunology, vol. 72, no. 6, pp. 540–547, 2010.
- P. Filipazzi, R. Valenti, V. Huber et al., “Identification of a new subset of myeloid suppressor cells in peripheral blood of melanoma patients with modulation by a granulocyte-macrophage colony-stimulation factor-based antitumor vaccine,” Journal of Clinical Oncology, vol. 25, no. 18, pp. 2546–2553, 2007.
- X. Song, Y. Ding, G. Liu et al., “Cancer cell-derived exosomes induce mitogen-activated protein kinase-dependent monocyte survival by transport of functional receptor tyrosine kinases,” Journal of Biological Chemistry, vol. 291, no. 16, pp. 8453–8464, 2016.
- P. Filipazzi, V. Huber, and L. Rivoltini, “Phenotype, function and clinical implications of myeloid-derived suppressor cells in cancer patients,” Cancer Immunology, Immunotherapy, vol. 61, no. 2, pp. 255–263, 2012.
- S. Yu, C. Liu, K. Su et al., “Tumor exosomes inhibit differentiation of bone marrow dendritic cells,” Journal of Immunology, vol. 178, no. 11, pp. 6867–6875, 2007.
- X. Xiang, A. Poliakov, C. Liu et al., “Induction of myeloid-derived suppressor cells by tumor exosomes,” International Journal of Cancer, vol. 124, no. 11, pp. 2621–2633, 2009.
- X. Xiang, Y. Liu, X. Zhuang et al., “TLR2-mediated expansion of MDSCs is dependent on the source of tumor exosomes,” American Journal of Pathology, vol. 177, no. 4, pp. 1606–1610, 2010.
- G. Mignot, F. Chalmin, S. Ladoire et al., “Tumor exosome-mediated MDSC activation,” American Journal of Pathology, vol. 178, no. 3, pp. 1403-1404, 2011.
- F. Chalmin, S. Ladoire, G. Mignot et al., “Membrane-associated Hsp72 from tumor-derived exosomes mediates STAT3-dependent immunosuppressive function of mouse and human myeloid-derived suppressor cells,” Journal of Clinical Investigation, vol. 120, no. 2, pp. 457–471, 2010.
- Y. Liu, X. Xiang, X. Zhuang et al., “Contribution of MyD88 to the tumor exosome-mediated induction of myeloid derived suppressor cells,” American Journal of Pathology, vol. 176, no. 5, pp. 2490–2499, 2010.
- G. Mignot, F. Chalmin, S. Ladoire et al., “Tumor exosome-mediated MDSC activation,” The American Journal of Pathology, vol. 178, no. 3, pp. 1403–1405, 2011.
- A. Clayton and Z. Tabi, “Exosomes and the MICA-NKG2D system in cancer,” Blood Cells, Molecules, and Diseases, vol. 34, no. 3, pp. 206–213, 2005.
- A. Chow, W. Zhou, L. Liu et al., “Macrophage immunomodulation by breast cancer-derived exosomes requires toll-like receptor 2-mediated activation of NF-κB,” Scientific Reports, vol. 4, p. 5750, 2014.
- M. Fabbri, A. Paone, F. Calore et al., “MicroRNAs bind to toll-like receptors to induce prometastatic inflammatory response,” Proceedings of the National Academy of Sciences, vol. 109, no. 31, pp. E2110–E2116, 2012.
- K. Menck, F. Klemm, J. C. Gross, T. Pukrop, D. Wenzel, and C. Binder, “Induction and transport of Wnt 5a during macrophage-induced malignant invasion is mediated by two types of extracellular vesicles,” Oncotarget, vol. 4, no. 11, pp. 2057–2066, 2013.
- T. L. Whiteside, “Immune modulation of T-cell and NK (natural killer) cell activities by TEXs (tumour-derived exosomes),” Biochemical Society Transactions, vol. 41, no. 1, pp. 245–251, 2013.
- T. Bauernhofer, I. Kuss, B. Henderson, A. S. Baum, and T. L. Whiteside, “Preferential apoptosis of CD56dim natural killer cell subset in patients with cancer,” European Journal of Immunology, vol. 33, no. 1, pp. 119–124, 2003.
- M. J. Szczepanski, M. Szajnik, A. Welsh, K. A. Foon, T. L. Whiteside, and M. Boyiadzis, “Interleukin-15 enhances natural killer cell cytotoxicity in patients with acute myeloid leukemia by upregulating the activating NK cell receptors,” Cancer Immunology, Immunotherapy, vol. 59, no. 1, pp. 73–79, 2010.
- M. J. Szczepanski, M. Szajnik, A. Welsh, T. L. Whiteside, and M. Boyiadzis, “Blast-derived microvesicles in sera from patients with acute myeloid leukemia suppress natural killer cell function via membrane-associated transforming growth factor-β1,” Haematologica, vol. 96, no. 9, pp. 1302–1309, 2011.
- M. Hedlund, O. Nagaeva, D. Kargl, V. Baranov, and L. Mincheva-Nilsson, “Thermal- and oxidative stress causes enhanced release of NKG2D ligand-bearing immunosuppressive exosomes in leukemia/lymphoma T and B cells,” PloS One, vol. 6, no. 2, article e16899, 2011.
- A. Clayton, J. P. Mitchell, S. Linnane, M. D. Mason, and Z. Tabi, “Human tumor-derived exosomes down-modulate NKG2D expression,” Journal of Immunology, vol. 180, no. 11, pp. 7249–7258, 2008.
- O. Ashiru, P. Boutet, L. Fernández-Messina et al., “Natural killer cell cytotoxicity is suppressed by exposure to the human NKG2D ligand MICA*008 that is shed by tumor cells in exosomes,” Cancer Research, vol. 70, no. 2, pp. 481–489, 2010.
- V. Huber, S. Fais, M. Iero et al., “Human colorectal cancer cells induce T-cell death through release of proapoptotic microvesicles: role in immune escape,” Gastroenterology, vol. 128, no. 7, pp. 1796–1804, 2005.
- A. J. Abusamra, Z. Zhong, X. Zheng et al., “Tumor exosomes expressing Fas ligand mediate CD8+ T-cell apoptosis,” Blood Cells, Molecules, and Diseases, vol. 35, no. 2, pp. 169–173, 2005.
- J. L. Qu, X. J. Qu, J. L. Qu et al., “The role of cbl family of ubiquitin ligases in gastric cancer exosome-induced apoptosis of Jurkat T cells,” Acta Oncologica, vol. 48, no. 8, pp. 1173–1180, 2009.
- V. C. Liu, L. Y. Wong, T. Jang et al., “Tumor evasion of the immune system by converting CD4+ CD25− T cells into CD4+ CD25+ T regulatory cells: role of tumor-derived TGF-β,” The Journal of Immunology, vol. 178, no. 5, pp. 2883–2892, 2007.
- J. Klibi, T. Niki, A. Riedel et al., “Blood diffusion and Th1-suppressive effects of galectin-9-containing exosomes released by Epstein-Barr virus-infected nasopharyngeal carcinoma cells,” Blood, vol. 113, no. 9, pp. 1957–1966, 2009.
- E. U. Wieckowski, C. Visus, M. Szajnik, M. J. Szczepanski, W. J. Storkus, and T. L. Whiteside, “Tumor-derived microvesicles promote regulatory T cell expansion and induce apoptosis in tumor-reactive activated CD8+ T lymphocytes,” Journal of Immunology, vol. 183, no. 6, pp. 3720–3730, 2009.
- P. Peng, Y. Yan, and S. Keng, “Exosomes in the ascites of ovarian cancer patients: origin and effects on anti-tumor immunity,” Oncology Reports, vol. 25, no. 3, pp. 749–762, 2011.
- D. D. Taylor, Ç. Gerçel-Taylor, K. S. Lyons, J. Stanson, and T. L. Whiteside, “T-cell apoptosis and suppression of T-cell receptor/CD3-xi by fas ligand-containing membrane vesicles shed from ovarian tumors,” Clinical Cancer Research, vol. 9, no. 14, pp. 5113–5119, 2003.
- G. Andreola, L. Rivoltini, C. Castelli et al., “Induction of lymphocyte apoptosis by tumor cell secretion of FasL-bearing microvesicles,” Journal of Experimental Medicine, vol. 195, no. 10, pp. 1303–1316, 2002.
- L. Van Parijs and A. K. Abbas, “Role of Fas-mediated cell death in the regulation of immune responses,” Current Opinion in Immunology, vol. 8, no. 3, pp. 355–361, 1996.
- B. A. Osborne, “Apoptosis and the maintenance of homoeostasis in the immune system,” Current Opinion in Immunology, vol. 8, no. 2, pp. 245–254, 1996.
- M. R. Alderson, T. W. Tough, T. Davis-Smith et al., “Fas ligand mediates activation-induced cell death in human T lymphocytes,” Journal of Experimental Medicine, vol. 181, no. 1, pp. 71–77, 1995.
- T. Suda, T. Okazaki, Y. Naito et al., “Expression of the fas ligand in cells of T cell lineage,” Journal of Immunology, vol. 154, no. 8, pp. 3814–3820, 1995.
- D. D. Taylor and C. Gercel-Taylor, “Tumour-derived exosomes and their role in cancer-associated T-cell signalling defects,” British Journal of Cancer, vol. 92, no. 2, pp. 305–311, 2005.
- M. Tafani, L. Sansone, F. Limana et al., “The interplay of reactive oxygen species, hypoxia, inflammation, and sirtuins in cancer initiation and progression,” Oxidative Medicine and Cellular Longevity, vol. 2016, Article ID 3907147, p. 18, 2016.
- F. Andre, N. E. Schartz, M. Movassagh et al., “Malignant effusions and immunogenic tumour-derived exosomes,” The Lancet, vol. 360, no. 9329, pp. 295–305, 2002.
- J. Wolfers, A. Lozier, G. Raposo et al., “Tumor-derived exosomes are a source of shared tumor rejection antigens for CTL cross-priming,” Nature Medicine, vol. 7, no. 3, pp. 297–303, 2001.
- S. Dai, X. Zhou, B. Wang et al., “Enhanced induction of dendritic cell maturation and HLA-A* 0201-restricted CEA-specific CD8+ CTL response by exosomes derived from IL-18 gene-modified CEA-positive tumor cells,” Journal of Molecular Medicine, vol. 84, no. 12, pp. 1067–1076, 2006.
- C. Kahlert and R. Kalluri, “Exosomes in tumor microenvironment influence cancer progression and metastasis,” Journal of Molecular Medicine, vol. 91, no. 4, pp. 431–437, 2013.
- H. Zhang, D. M. Conrad, J. J. Butler, C. Zhao, J. Blay, and D. W. Hoskin, “Adenosine acts through A2 receptors to inhibit IL-2-induced tyrosine phosphorylation of STAT5 in T lymphocytes: role of cyclic adenosine 3′,5′-monophosphate and phosphatases,” Journal of Immunology, vol. 173, no. 2, pp. 932–944, 2004.
- S. Deaglio, K. M. Dwyer, W. Gao et al., “Adenosine generation catalyzed by CD39 and CD73 expressed on regulatory T cells mediates immune suppression,” Journal of Experimental Medicine, vol. 204, no. 6, pp. 1257–1265, 2007.
- G. Borsellino, M. Kleinewietfeld, D. Di Mitri et al., “Expression of ectonucleotidase CD39 by Foxp3+ Treg cells: hydrolysis of extracellular ATP and immune suppression,” Blood, vol. 110, no. 4, pp. 1225–1232, 2007.
- B. Zhang, “CD73: a novel target for cancer immunotherapy,” Cancer Research, vol. 70, no. 16, pp. 6407–6411, 2010.
- A. Clayton, S. Al-Taei, J. Webber, M. D. Mason, and Z. Tabi, “Cancer exosomes express CD39 and CD73, which suppress T cells through adenosine production,” Journal of Immunology, vol. 187, no. 2, pp. 676–683, 2011.
- M. Szajnik, M. Czystowska, M. J. Szczepanski, M. Mandapathil, and T. L. Whiteside, “Tumor-derived microvesicles induce, expand and up-regulate biological activities of human regulatory T cells (Treg),” PloS One, vol. 5, no. 7, 2010.
- A. Clayton, J. P. Mitchell, M. D. Mason, and Z. Tabi, “Human tumor-derived exosomes selectively impair lymphocyte responses to interleukin-2,” Cancer Research, vol. 67, no. 15, pp. 7458–7466, 2007.
- J. Wada, H. Onishi, H. Suzuki et al., “Surface-bound TGF-β1 on effusion-derived exosomes participates in maintenance of number and suppressive function of regulatory T-cells in malignant effusions,” Anticancer Research, vol. 30, no. 9, pp. 3747–3757, 2010.
- H. Guan, Y. Lan, Y. Wan et al., “PD-L1 mediated the differentiation of tumor-infiltrating CD19+ B lymphocytes and T cells in invasive breast cancer,” Oncoimmunology, vol. 5, no. 2, article e1075112, 2016.
- H. Guan, Y. Wan, J. Lan et al., “PD-L1 is a critical mediator of regulatory B cells and T cells in invasive breast cancer,” Scientific Reports, vol. 6, p. 35651, 2016.
- S. Lindner, K. Dahlke, K. Sontheimer et al., “Interleukin 21-induced granzyme B-expressing B cells infiltrate tumors and regulate T cells,” Cancer Research, vol. 73, no. 8, pp. 2468–2479, 2013.
- P. B. Olkhanud, B. Damdinsuren, M. Bodogai et al., “Tumor-evoked regulatory B cells promote breast cancer metastasis by converting resting CD4(+) T cells to T-regulatory cells,” Cancer Research, vol. 71, no. 10, pp. 3505–3515, 2011.
- M. J. Townsend, J. G. Monroe, and A. C. Chan, “B-cell targeted therapies in human autoimmune diseases: an updated perspective,” Immunological Reviews, vol. 237, no. 1, pp. 264–283, 2010.
- Y. Zhang, R. Morgan, C. Chen et al., “Mammary-tumor-educated B cells acquire LAP/TGF-beta and PD-L1 expression and suppress anti-tumor immune responses,” International Immunology, vol. 28, no. 9, pp. 423–433, 2016.
- C. Yang, G. Chalasani, Y. H. Ng, and P. D. Robbins, “Exosomes released from mycoplasma infected tumor cells activate inhibitory B cells,” PloS One, vol. 7, no. 4, article e36138, 2012.
- Y. Li, J. An, S. Huang, J. He, and J. Zhang, “Esophageal cancer-derived microvesicles induce regulatory B cells,” Cell Biochemistry and Function, vol. 33, no. 5, pp. 308–313, 2015.
- L. Alvarez-Erviti, Y. Seow, H. Yin, C. Betts, S. Lakhal, and M. J. Wood, “Delivery of siRNA to the mouse brain by systemic injection of targeted exosomes,” Nature Biotechnology, vol. 29, no. 4, pp. 341–345, 2011.
- A. Delcayre, A. Estelles, J. Sperinde et al., “Exosome display technology: applications to the development of new diagnostics and therapeutics,” Blood Cells, Molecules, and Diseases, vol. 35, no. 2, pp. 158–168, 2005.
- A. Estelles, J. Sperinde, T. Roulon et al., “Exosome nanovesicles displaying G protein-coupled receptors for drug discovery,” International Journal of Nanomedicine, vol. 2, no. 4, p. 751, 2007.
- B. Shen, N. Wu, J. M. Yang, and S. J. Gould, “Protein targeting to exosomes/microvesicles by plasma membrane anchors,” Journal of Biological Chemistry, vol. 286, no. 16, pp. 14383–14395, 2011.
- A. Ghosh, M. Davey, I. C. Chute et al., “Rapid isolation of extracellular vesicles from cell culture and biological fluids using a synthetic peptide with specific affinity for heat shock proteins,” PloS One, vol. 9, no. 10, article e110443, 2014.
- B. M. Bell, I. D. Kirk, S. Hiltbrunner, S. Gabrielsson, and J. J. Bultema, “Designer exosomes as next-generation cancer immunotherapy,” Nanomedicine: Nanotechnology, Biology and Medicine, vol. 12, no. 1, pp. 163–169, 2016.
- S. A. Kooijmans, P. Vader, S. M. van Dommelen, W. W. van Solinge, and R. M. Schiffelers, “Exosome mimetics: a novel class of drug delivery systems,” International Journal of Nanomedicine, vol. 7, no. 1525, article e41, 2012.
- C. D. Gregory and J. D. Pound, “Microenvironmental influences of apoptosis in vivo and in vitro,” Apoptosis, vol. 15, no. 9, pp. 1029–1049, 2010.
- D. H. Kim and J. J. Rossi, “Strategies for silencing human disease using RNA interference,” Nature Reviews Genetics, vol. 8, no. 3, pp. 173–184, 2007.
- Y. Malam, M. Loizidou, and A. M. Seifalian, “Liposomes and nanoparticles: nanosized vehicles for drug delivery in cancer,” Trends in Pharmacological Sciences, vol. 30, no. 11, pp. 592–599, 2009.
- Y. Tarahovsky, “Smart liposomal nanocontainers in biology and medicine,” Biochemistry (Moscow), vol. 75, no. 7, pp. 811–824, 2010.
- J. Colino and C. M. Snapper, “Exosomes from bone marrow dendritic cells pulsed with diphtheria toxoid preferentially induce type 1 antigen-specific IgG responses in naive recipients in the absence of free antigen,” The Journal of Immunology, vol. 177, no. 6, pp. 3757–3762, 2006.
- C. Théry, A. Regnault, J. Garin et al., “Molecular characterization of dendritic cell-derived exosomes selective accumulation of the heat shock protein hsc73,” The Journal of Cell Biology, vol. 147, no. 3, pp. 599–610, 1999.
- G. Raposo, H. W. Nijman, W. Stoorvogel et al., “B lymphocytes secrete antigen-presenting vesicles,” The Journal of Experimental Medicine, vol. 183, no. 3, pp. 1161–1172, 1996.
- S. Viaud, M. Terme, C. Flament et al., “Dendritic cell-derived exosomes promote natural killer cell activation and proliferation: a role for NKG2D ligands and IL-15Rα,” PloS One, vol. 4, no. 3, article e4942, 2009.
- L. Zitvogel, A. Regnault, A. Lozier et al., “Eradication of established murine tumors using a novel cell-free vaccine: dendritic cell derived exosomes,” Nature Medicine, vol. 4, no. 5, pp. 594–600, 1998.
- T. I. Näslund, U. Gehrmann, K. R. Qazi, M. C. Karlsson, and S. Gabrielsson, “Dendritic cell–derived exosomes need to activate both T and B cells to induce antitumor immunity,” The Journal of Immunology, vol. 190, no. 6, pp. 2712–2719, 2013.
- B. Escudier, T. Dorval, N. Chaput et al., “Vaccination of metastatic melanoma patients with autologous dendritic cell (DC) derived-exosomes: results of thefirst phase I clinical trial,” Journal of Translational Medicine, vol. 3, no. 1, p. 1, 2005.
- M. A. Morse, J. Garst, T. Osada et al., “A phase I study of dexosome immunotherapy in patients with advanced non-small cell lung cancer,” Journal of Translational Medicine, vol. 3, no. 1, p. 9, 2005.
Copyright © 2017 Wuzhen Chen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.