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

OBJECTIVEWe sought to determine whether exosome-like vesicles (ELVs) released from adipose tissue play a role in activation of macrophages and subsequent development of insulin resistance in a mouse model.RESEARCH DESIGN AND METHODSELVs released from adipose tissue were purified by sucrose gradient centrifugation and labeled with green fluorescent dye and then intravenously injected into B6 ob/ob mice (obese model) or B6 mice fed a high-fat diet. The effects of injected ELVs on the activation of macrophages were determined through analysis of activation markers by fluorescence-activated cell sorter and induction of inflammatory cytokines using an ELISA. Glucose tolerance and insulin tolerance were also evaluated. Similarly, B6 mice with different gene knockouts including TLR2, TLR4, MyD88, and Toll-interleukin-1 receptor (TIR) domain–containing adaptor protein inducing interferon-β (TRIF) were also used for testing their responses to the injected ELVs.RESULTSELVs are taken up by peripheral blood monocytes, which then differentiate into activated macrophages with increased secretion of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Injection of obELVs into wild-type C57BL/6 mice results in the development of insulin resistance. When the obELVs were intravenously injected into TLR4 knockout B6 mice, the levels of glucose intolerance and insulin resistance were much lower. RBP4 is enriched in the obELVs. Bone marrow–derived macrophages preincubated with recombinant RBP4 led to attenuation of obELV-mediated induction of IL-6 and TNF-α.CONCLUSIONSELVs released by adipose tissue can act as a mode of communication between adipose tissues and macrophages. The obELV-mediated induction of TNF-α and IL-6 in macrophages and insulin resistance requires the TLR4/TRIF pathway.

Myeloid‐derived suppressor cells (MDSCs) promote tumor progression. The mechanisms of MDSC development during tumor growth remain unknown. Tumor exosomes (T‐exosomes) have been implicated to play a role in immune regulation, however the role of exosomes in the induction of MDSCs is unclear. Our previous work demonstrated that exosomes isolated from tumor cells are taken up by bone marrow myeloid cells. Here, we extend those findings showing that exosomes isolated from T‐exosomes switch the differentiation pathway of these myeloid cells to the MDSC pathway (CD11b+Gr‐1+). The resulting cells exhibit MDSC phenotypic and functional characteristics including promotion of tumor growth. Furthermore, we demonstrated that in vivo MDSC mediated promotion of tumor progression is dependent on T‐exosome prostaglandin E2 (PGE2) and TGF‐β molecules. T‐exosomes can induce the accumulation of MDSCs expressing Cox2, IL‐6, VEGF, and arginase‐1. Antibodies against exosomal PGE2 and TGF‐β block the activity of these exosomes on MDSC induction and therefore attenuate MDSC‐mediated tumor‐promoting ability. Exosomal PGE2 and TGF‐β are enriched in T‐exosomes when compared with exosomes isolated from the supernatants of cultured tumor cells (C‐exosomes). The tumor microenvironment has an effect on the potency of T‐exosome mediated induction of MDSCs by regulating the sorting and the amount of exosomal PGE2 and TGF‐β available. Together, these findings lend themselves to developing specific targetable therapeutic strategies to reduce or eliminate MDSC‐induced immunosuppression and hence enhance host antitumor immunotherapy efficacy. © 2008 Wiley‐Liss, Inc.

Many tumor cells shed specialized membrane vesicles known as exosomes. In this study, we show that pretreatment of mice with exosomes produced by TS/A or 4T.1 murine mammary tumor cells resulted in accelerated growth of implanted tumor cells in both syngeneic BALB/c mice and nude mice. As implanted TS/A tumor cells grew more rapidly in mice that had been depleted of NK cells, we analyzed the effects of the tumor-derived exosomes on NK cells. The tumor-derived exosomes inhibit NK cell cytotoxic activity ex vivo and in vitro as demonstrated by chromium release assays. The treatment of mice with TS/A tumor exosomes also led to a reduction in the percentages of NK cells, as determined by FACS analysis, in the lungs and spleens. Key features of NK cell activity were inhibited, including release of perforin but not granzyme B, as well as the expression of cyclin D3 and activation of the Jak3-mediated pathways. Human tumor cell lines also were found to produce exosomes that were capable of inhibiting IL-2-stimulated NK cell proliferation. Exosomes produced by dendritic cells or B cells did not. The presentation of tumor Ags by exosomes is under consideration as a cancer vaccine strategy; however, we found that pretreatment of mice with tumor exosomes blunted the protective effect of syngeneic dendritic cells pulsed ex vivo with tumor exosomes. We propose that tumor exosomes contribute to the growth of tumors by blocking IL-2-mediated activation of NK cells and their cytotoxic response to tumor cells.

The production of exosomes by tumor cells has been implicated in tumor-associated immune suppression. In this study, we show that, in mice, exosomes produced by TS/A murine mammary tumor cells target CD11b+ myeloid precursors in the bone marrow (BM) in vivo, and that this is associated with an accumulation of myeloid precursors in the spleen. Moreover, we demonstrate that TS/A exosomes block the differentiation of murine myeloid precursor cells into dendritic cells (DC) in vitro. Addition of tumor exosomes at day 0 led to a significant block of differentiation into DC, whereas addition at later time points was less effective. Similarly, exosomes produced by human breast tumor cells inhibited the differentiation of human monocytes in vitro. The levels of IL-6 and phosphorylated Stat3 were elevated 12 h after the tumor exosome stimulation of murine myeloid precursors, and tumor exosomes were less effective in inhibiting differentiation of BM cells isolated from IL-6 knockout mice. Addition of a rIL-6 to the IL-6 knockout BM cell culture restored the tumor exosome-mediated inhibition of DC differentiation. These data suggest that tumor exosome-mediated induction of IL-6 plays a role in blocking BM DC differentiation.

IntroductionIncreased numbers of myeloid cells expressing the Gr-1 and CD11b markers have been detected in the spleen and bone marrow of mice bearing transplantable tumors and in many conditions associated with impaired immune activity. 1-10 The CD11b ϩ Gr-1 ϩ cell population is phenotypically heterogeneous, consisting primarily of immature myeloid cells and cells expressing immature dendritic cell (DC) markers, both of which play a role in suppression of the T-cell immune response. In healthy subjects, a small number of CD11b ϩ Gr-1 ϩ cells (less than 4%) can be found in the blood and spleen. Immature myeloid cells isolated from human or murine bone marrow or peripheral blood can be induced to differentiate in vitro into mature antigen-presenting cells (APCs)/ DCs by means of various cytokine combinations. Disturbances in cytokine homeostasis induced by tumor-derived factors result in the expansion of myeloid suppressor cells ([MSCs] CD11b ϩ Gr-1 ϩ ) in vivo. 1,8,11,12 The accumulation of MSCs in the spleen and blood of tumor-bearing individuals has been observed in many different types of cancers and is associated with increased tumor burden and predicts poor survival rates. 4,8,13,14 As MSCs in the spleen of tumor-bearing subjects dramatically increase, the MSCs suppress the activation of CD4 ϩ and CD8 ϩ T lymphocytes and thereby inhibit immune surveillance.Natural killer (NK) cell tumor cytotoxicity in cancer patients and tumor-bearing animal models is suppressed. [15][16][17][18][19][20][21][22] It is unclear whether accumulation of MSCs is responsible for immunosuppression of NK cell tumor cytotoxicity. NK cells participate in the innate immune response to malignant cells. Unlike T lymphocytes, NK cells do not depend on recognition of tumor-specific antigens for antitumor cytotoxicity. In addition to their ability to recognize and eliminate altered cells by cytotoxic mechanisms, activated NK cells are potent sources of immune modulatory cytokines that directly aid in the elimination of tumor cells and also indirectly augment a developing adaptive immune response against tumor growth.In this study, evidence is provided that in murine systems, MSCs potently suppress NK cell cytotoxicity in vitro and in vivo. The inhibitory effect requires NK-MSC direct contact, which inhibits IL-2-mediated activation of NK cells and perforin production. Materials and methods MiceAdult female BALB/c mice (The Jackson Laboratory, Bar Harbor, ME) were 6 to 8 weeks old when used and were housed in the Animal Care Facility at University of Alabama at Birmingham. Cell linesThe TS/A cell line, a major histocompatibility complex (MHC) class I-positive (H-2D d , H-2K d ) moderately differentiated and immunogenic mammary adenocarcinoma of spontaneous origin in BALB/c mice, was maintained in vitro at 37°C in a humidified 5% CO 2 atmosphere in complete medium. YAC-1 cells (American Type Culture Collection, [ATCC] Manassas, VA) were maintained in RPMI 1640 medium supplemented with 10% fetal bovine serum, 2 mM glutamine, 10 mM HEPES (pH ...

In common with many other cell types, synovial fibroblasts produce exosomes. In this study, we show that the exosomes produced by synovial fibroblasts obtained from individuals with rheumatoid arthritis (RASF), but not exosomes produced by synovial fibroblasts obtained from individuals with osteoarthritis, contain a membrane bound form of TNF-α as demonstrated by colloidal gold immunostaining of TNF-α and confirmed by both Western blot and mass spectrometry. The RASF-derived exosomes, but not exosomes derived from fibroblasts obtained from individuals with osteoarthritis, are cytotoxic for the L929 cell, a TNF-α-sensitive cell line, and stimulate activation of NF-κB and induction of collagenase-1 in RASF. These effects are blocked by addition of soluble TNFR1 (sTNFbp), suggesting that a TNF-α-signaling pathway mediates these biological activities. sTNFbp also reduced the production of exosomes by RASF, suggesting the interruption of a positive amplification loop. Exosomes can transmit signals between cells, and RASF exosomes, effectively taken up by anti-CD3-activated T cells, activated AKT and NF-κB and rendered these activated T cells resistant to apoptosis. Neutralization of exosomal membrane TNF-α by sTNFbp partially reversed this resistance, suggesting that not only TNF-α but also additional exosomal proteins may contribute to the development of apoptosis resistance.

In this study we observed that mice pretreated with tumor exosomes had a significant acceleration of tumor metastasis in the lung. Tumor metastasis correlated significantly with an increase in recruitment of more Myeloid-derived suppressor cells (MDSCs) in the lung of C57BL/6j (B6) mice pretreated with tumor exosomes. These effects were blunted when MyD88 knockout (KO) mice were pretreated with tumor exosomes. MDSCs induced by tumor exosomes and isolated from wild-type B6 mice also more potently inhibited T cell activation and induction of interleukin-6 and tumor necrosis factor-alpha than MDSCs isolated from the lung of MyD88 KO mice. In vitro, addition of tumor exosomes to bone marrow-derived CD11b(+)Gr-1(+) cells isolated from wild-type B6 mice resulted in more cytokine production, including tumor necrosis factor-alpha, interleukin-6, and the chemokine CCL2, than CD11b(+)Gr-1(+) cells isolated from MyD88 KO mice. Moreover, lower levels of CCL2 were observed in the lungs in MyD88 KO mice pretreated with tumor exosomes than that in wild-type mice. Together these data demonstrate a pivotal role for MyD88 in tumor exosome-mediated expansion of MDSCs and tumor metastasis.