Chemokine-containing exosomes are released from heat-stressed tumor cells via lipid raft-dependent pathway and act as efficient tumor vaccine

Exosomes derived from dendritic cells or tumor cells are a population of nanometer-sized membrane vesicles that can induce specific antitumor immunity. During investigation of the effects of hyperthermia on antitumor immune response, we found that exosomes derived from heat-stressed tumor cells (HS-TEX) could chemoattract and activate dendritic cells (DC) and T cells more potently than that by conventional tumor-derived exosomes. We show that HS-TEX contain chemokines, such as CCL2, CCL3, CCL4, CCL5, and CCL20, and the chemokine-containing HS-TEX are functionally competent in chemoattracting CD11c(+) DC and CD4(+)/CD8(+) T cells both in vitro and in vivo. Moreover, the production of chemokine-containing HS-TEX could be inhibited by ATP inhibitor, calcium chelator, and cholesterol scavenger, indicating that the mobilization of chemokines into exosomes was ATP- and calcium-dependent and via a lipid raft-dependent pathway. We consistently found that the intracellular chemokines could be enriched in lipid rafts after heat stress. Accordingly, intratumoral injection of HS-TEX could induce specific antitumor immune response more efficiently than that by tumor-derived exosomes, thus inhibiting tumor growth and prolonging survival of tumor-bearing mice more significantly. Therefore, our results demonstrate that exosomes derived from HS-TEX represent a kind of efficient tumor vaccine and can chemoattract and activate DC and T cells, inducing more potent antitumor immune response. Release of chemokines through exosomes via lipid raft-dependent pathway may be a new method of chemokine exocytosis.     

Murine mammary carcinoma exosomes promote tumor growth by suppression of NK cell function

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.     

Therapeutic effects of autologous tumor-derived nanovesicles on melanoma growth and metastasis

Cancer vaccines with optimal tumor-associated antigens show promise for anti-tumor immunotherapy. Recently, nano-sized vesicles, such as exosomes derived from tumors, were suggested as potential antigen candidates, although the total yield of exosomes is not sufficient for clinical applications. In the present study, we developed a new vaccine strategy based on nano-sized vesicles derived from primary autologous tumors. Through homogenization and sonication of tumor tissues, we achieved high yields of vesicle-bound antigens. These nanovesicles were enriched with antigenic membrane targets but lacked nuclear autoantigens. Furthermore, these nanovesicles together with adjuvant activated dendritic cells in vitro, and induced effective anti-tumor immune responses in both primary and metastatic melanoma mouse models. Therefore, autologous tumor-derived nanovesicles may represent a novel source of antigens with high-level immunogenicity for use in acellular vaccines without compromising safety. Our strategy is cost-effective and can be applied to patient-specific cancer therapeutic vaccination.     

Dendritic cells loaded with exogenous antigen by electroporation can enhance MHC class I–mediated antitumor immunity

To develop an efficient antitumor immunotherapy, we have examined if dendritic cells (DCs) loaded with soluble antigens by electroporation present more antigens via the MHC (major histocompatibility complex) class I pathway, which mediate a cytotoxic T-cell response. DCs loaded with ovalbumin (OVA) by electroporation presented more MHC class I–restricted determinants compared with DCs pulsed with OVA. When electroporated DCs were pulsed with OVA for additional times, both MHC class I– and II–restricted presentation of OVA were increased compared with each single procedure, including electroporation or simple pulse. Immunization with DCs loaded with OVA by electroporation induced higher cytotoxicity of splenocytes to E.G7 cells, a clone of EL4 cells transfected with an OVA cDNA, than immunization with DCs pulsed with OVA. In the animal study, immunization with DCs loaded with OVA or tumor cell lysates by electroporation induced an effective antitumor immunity against tumor of E.G7 cells or Lewis lung carcinoma cells, respectively. In addition, immunization with DCs loaded with antigen by combination of electroporation and pulse, completely protected mice from tumor formation, and prolonged survival, in both tumor models. These results demonstrated that electroporation would be a useful way to enhance MHC class I–mediated antitumor immunity without functional deterioration, and that the combination of electroporation and pulse could be a simple and efficient antigen-loading method and consequently lead to induction of strong antitumor immunity.Abbreviations DCs dendritic cells - MHC major histocompatibility complex - OVA ovalbumin - TAA tumor-associated antigen - CTL cytotoxic T lymphocyte - LDH lactate dehydrogenase     

Application of a Persistent Heparin Treatment Inhibits the Malignant Potential of Oral Squamous Carcinoma Cells Induced by Tumor Cell-Derived Exosomes

Exosomes are 30–100 nm-sized membranous vesicles, secreted from a variety of cell types into their surrounding extracellular space. Various exosome components including lipids, proteins, and nucleic acids are transferred to recipient cells and affect their function and activity. Numerous studies have showed that tumor cell-derived exosomes play important roles in tumor growth and progression. However, the effect of exosomes released from oral squamous cell carcinoma (OSCC) into the tumor microenvironment remains unclear. In the present study, we isolated exosomes from OSCC cells and investigated the influence of OSCC cell-derived exosomes on the tumor cell behavior associated with tumor development. We demonstrated that OSCC cell-derived exosomes were taken up by OSCC cells themselves and significantly promoted proliferation, migration, and invasion through the activation of the PI3K/Akt, MAPK/ERK, and JNK-1/2 pathways in vitro. These effects of OSCC cell-derived exosomes were obviously attenuated by treatment with PI3K, ERK-1/2, and JNK-1/2 pharmacological inhibitors. Furthermore, the growth rate of tumor xenografts implanted into nude mice was promoted by treatment with OSCC cell-derived exosomes. The uptake of exosomes by OSCC cells and subsequent tumor progression was abrogated in the presence of heparin. Taken together, these data suggest that OSCC cell-derived exosomes might be a novel therapeutic target and the use of heparin to inhibit the uptake of OSCC-derived exosomes by OSCC cells may be useful for treatment.     

Immunotherapy of cancer with dendritic-cell-based vaccines

 Animal studies have shown that vaccination with genetically modified tumor cells or with dendritic cells (DC) pulsed with tumor antigens are potent strategies to elicit protective immunity in tumor-bearing animals, more potent than “conventional” strategies that have been tested in clinical settings with limited success. While both vaccination strategies are forms of cell therapy requiring complex and costly ex vivo manipulations of the patient’s cells, current protocols using dendritic cells are considerably simpler and would be more widely available. Vaccination with defined tumor antigens presented by DC has obvious appeal. However, in view of the expected emergence of antigen-loss variants as well as natural immunovariation, effective vaccine formulations must contain mixtures of commonly, if not universally, expressed tumor antigens. When, or even if, such common tumor antigens will be identified cannot be, predicted, however. Thus, for the foreseeable future, vaccination with total-tumor-derived material as source of tumor antigens may be preferable to using defined tumor antigens. Vaccination with undefined tumor-derived antigens will be limited, however, by the availability of sufficient tumor tissue for antigen preparation. Because the mRNA content of single cells can be amplified, tumor mRNA, or corresponding cDNA libraries, offer an unlimited source of tumor antigens. DC transfected with tumor RNA were shown to engender potent antitumor immunity in animal studies. Thus, immunotherapy using autologous DC loaded with unfractionated tumor-derived antigens in the form of RNA emerges as a potentially powerful and broadly useful vaccination strategy for cancer patients. Received: 10 October 1997 / Accepted: 12 January 1998     

The avidity of tumor‐specific T cells amplified by a plasmacytoid dendritic cell‐based assay can predict the clinical evolution of melanoma patients

The advent of immune checkpoint blockers and targeted therapies has changed the outcome of melanoma. However, many patients experience relapses, emphasizing the need for predictive and prognostic biomarkers. We developed a strategy based on plasmacytoid dendritic cells (pDCs) loaded with melanoma tumor antigens that allows eliciting highly efficient antitumor T‐cell responses. We used it to investigate antitumor T‐cell functionality in peripheral blood mononuclear cells and tumor‐infiltrating lymphocytes from melanoma patients. The pDCs elicited tumor‐specific T cells in different proportions and displaying diverse functional features, dependent upon the stage of the disease, but independent of the histological parameters at diagnosis. Strikingly, the avidity of the MelA‐specific T cells triggered by the pDCs was found to predict patient relapse time and overall survival. Our findings highlighted unexplored aspects of antitumor T‐cell responsiveness in melanoma, and revealed for the first time the structural avidity of tumor‐specific T cells as a crucial feature for predicting clinical evolution.     

Tumor-derived exosomes confer antigen-specific immunosuppression in a murine delayed-type hypersensitivity model

Exosomes are endosome-derived small membrane vesicles that are secreted by most cell types including tumor cells. Tumor-derived exosomes usually contain tumor antigens and have been used as a source of tumor antigens to stimulate anti-tumor immune responses. However, many reports also suggest that tumor-derived exosomes can facilitate tumor immune evasion through different mechanisms, most of which are antigen-independent. In the present study we used a mouse model of delayed-type hypersensitivity (DTH) and demonstrated that local administration of tumor-derived exosomes carrying the model antigen chicken ovalbumin (OVA) resulted in the suppression of DTH response in an antigen-specific manner. Analysis of exosome trafficking demonstrated that following local injection, tumor-derived exosomes were internalized by CD11c+ cells and transported to the draining LN. Exosome-mediated DTH suppression is associated with increased mRNA levels of TGF-β1 and IL-4 in the draining LN. The tumor-derived exosomes examined were also found to inhibit DC maturation. Taken together, our results suggest a role for tumor-derived exosomes in inducing tumor antigen-specific immunosuppression, possibly by modulating the function of APCs.     

T-cell responses to multiple antigens presented by RNA-transfected APCs: a possible immunomonitoring tool

The increasingly deeper understanding of how the immune system recognizes and destroys tumors promises to enable the development of new approaches for gene therapy and immunotherapy. However, a treatment that induces safe and potentially beneficial antitumor responses is expected to require stepwise refinements. As part of this challenge, assays are needed to measure specific antitumor immune responses in patients. This becomes problematic because most tumors express unknown tumor antigens and it is often difficult to obtain sufficient amounts of viable tumor material for in vitro assays. Recently it was demonstrated that RNA derived from tumor cells stimulated T cells in an antigen-specific manner. These studies have formed the basis for the development of dendritic cell vaccines that express tumor antigens following translation of tumor RNA. Therefore, it occurred to us that antigen-presenting cells transfected with total tumor RNA might also be valuable in monitoring the antitumor responses induced in patients who participate in clinical trials. To test this hypothesis, we developed a model in which Epstein-Barr virus (EBV)–transformed lymphoblastoid cell lines were used as a source of RNA. Since this RNA encodes for known EBV antigens, it was possible to determine whether the expected responses were observed. Our results show for the first time that T cells primed to APC transfected with RNA isolated from EBV-infected lymphocytes exhibited a fine specificity that enabled them to recognize individual EBV antigens.This work was supported by a Developmental Research Grant from the Derald H. Ruttenberg Cancer Center, Mount Sinai School of Medicine.     

Exosomes derived from tumor cells genetically modified to express <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> antigen: a novel vaccine for cancer therapy

Objectives

To examine the potential of exosomes derived from the tumor cells, which had been genetically modified to express a Mycobacterium tuberculosis antigen, as a cancer vaccine aimed at overcoming the weak immunogenicity of tumor antigens.

Results

We transfected B16 melanoma cells with a plasmid encoding the M. tuberculosis antigen, early secretory antigenic target-6 (ESAT-6). The secreted exosomes bearing both tumor-associated antigens and the pathogenic antigen (or their epitopes) were collected. When the exosomes were injected into foot pads of mice, they significantly (p < 0.05) evoked cellular immunity against both ESAT-6, and B16 tumor cells. Intra-tumoral injection of the exosomes significantly suppressed (p < 0.001) tumor growth in syngeneic B16 tumor-bearing mice, while the exosomes derived from the non-transfected B16 cells showed no effect on tumor growth, although both exosomes should have similar tumor antigens.

Conclusions

Exosomes bearing both tumor antigens and the M. tuberculosis antigen (or their epitopes) have a high potential as a candidate for cancer vaccine to overcome the immune escape by tumor cells.

     

Microenvironmental pH Is a Key Factor for Exosome Traffic in Tumor Cells

Exosomes secreted by normal and cancer cells carry and deliver a variety of molecules. To date, mechanisms referring to tumor exosome trafficking, including release and cell-cell transmission, have not been described. To gain insight into this, exosomes purified from metastatic melanoma cell medium were labeled with a lipid fluorescent probe, R18, and analyzed by spectrofluorometry and confocal microscopy. A low pH condition is a hallmark of tumor malignancy, potentially influencing exosome release and uptake by cancer cells. Using different pH conditions as a modifier of exosome traffic, we showed (i) an increased exosome release and uptake at low pH when compared with a buffered condition and (ii) exosome uptake by melanoma cells occurred by fusion. Membrane biophysical analysis, such as fluidity and lipid composition, indicated a high rigidity and sphingomyelin/ganglioside GM3 (N-acetylneuraminylgalactosylglucosylceramide) content in exosomes released at low pH. This was likely responsible for the increased fusion efficiency. Consistent with these results, pretreatment with proton pump inhibitors led to an inhibition of exosome uptake by melanoma cells. Fusion efficiency of tumor exosomes resulted in being higher in cells of metastatic origin than in those derived from primary tumors or normal cells. Furthermore, we found that caveolin-1, a protein involved in melanoma progression, is highly delivered through exosomes released in an acidic condition. The results of our study provide the evidence that exosomes may be used as a delivery system for paracrine diffusion of tumor malignancy, in turn supporting the importance of both exosomes and tumor pH as key targets for future anti-cancer strategies.     

The Role of Exosomes in Pancreatic Cancer Microenvironment

Exosomes are nanovesicles shed by cells as a means of communication with other cells. Exosomes contain mRNAs, microRNAs (miRs) and functional proteins. In the present paper, we develop a mathematical model of tumor–immune interaction by means of exosomes shed by pancreatic cancer cells and dendritic cells. Cancer cells’ exosomes contain miRs that promote their proliferation and that inhibit immune response by dendritic cells, and by CD4+ and CD8+ T cells. Dendritic cells release exosomes with proteins that induce apoptosis of cancer cells and that block regulatory T cells. Simulations of the model show how the size of the pancreatic cancer can be determined by measurement of specific miRs (miR-21 and miR-203 in the case of pancreatic cancer), suggesting these miRs as biomarkers for cancer.     

光免疫治疗的抗肿瘤研究进展

光免疫治疗是一种新兴的肿瘤靶向光疗手段,它将单克隆抗体的肿瘤特异性与光吸收剂的光毒性相结合,可以快速且极具免疫原选择性地诱导靶肿瘤细胞的死亡。由于靶向性强,光免疫治疗的副作用小。而且因为该疗法诱导的免疫原性死亡会引起垂死肿瘤细胞周围未成熟树突状细胞的快速成熟,继而将肿瘤抗原提呈给CD8+T细胞,导致治疗后CD8+T细胞的激活和增殖,增强宿主抗肿瘤免疫反应。不仅如此,光免疫治疗还能通过增强纳米药物的肿瘤组织穿透性而提高疗效。鉴于光免疫治疗的优良应用前景,文中从其免疫激活机制、超级高渗透长滞留效应、新进展与联合治疗等方面进行综述,旨在为其深入研究和临床转化提供参考。     

Shikonin induces immunogenic cell death in tumor cells and enhances dendritic cell-based cancer vaccine

Immunogenic cell death is characterized by damage-associated molecular patterns, which can enhance the maturation and antigen uptake of dendritic cells. Shikonin, an anti-inflammatory and antitumor phytochemical, was exploited here as an adjuvant for dendritic cell-based cancer vaccines via induction of immunogenic cell death. Shikonin can effectively activate both receptor- and mitochondria-mediated apoptosis and increase the expression of all five tested damage-associated molecular patterns in the resultant tumor cell lysates. The combination treatment with damage-associated molecular patterns and LPS activates dendritic cells to a high maturation status and enhances the priming of Th1/Th17 effector cells. Shikonin-tumor cell lysate-loaded mature dendritic cells exhibit a high level of CD86 and MHC class II and activate Th1 cells. The shikonin-tumor cell lysate-loaded dendritic cell vaccines result in a strong induction of cytotoxic activity of splenocytes against target tumor cells, a retardation in tumor growth, and an increase in the survival of test mice. The much enhanced immunogenicity and efficacy of the current cancer vaccine formulation, that is, the use of shikonin-treated tumor cells as cell lysates for the pulse of dendritic cells in culture, may suggest a new ex vivo approach for developing individualized, dendritic cells-based anticancer vaccines.     

外体（exosome）在肿瘤免疫治疗中的应用

外体（exosome）是由细胞分泌至细胞外的膜性小囊泡。研究发现,来源于树突状细胞和来源于肿瘤细胞的外体富集MHCⅠ/Ⅱ类分子、协同刺激分子、热激蛋白70和90等多种活性分子和肿瘤抗原,在体内外免疫调节中起关键作用,以外体为基础的肿瘤免疫治疗已成为热点。我们简要介绍外体的特征、分离制备和临床应用研究。     

Exosomes as Tools to Suppress Primary Brain Tumor

Exosomes are small microvesicles released by cells that efficiently transfer their molecular cargo to other cells, including tumor. Exosomes may pass the blood–brain barrier and have been demonstrated to deliver RNAs contained within to brain. As they are non-viable, the risk profile of exosomes is thought to be less than that of cellular therapies. Exosomes can be manufactured at scale in culture, and exosomes can be engineered to incorporate therapeutic miRNAs, siRNAs, or chemotherapeutic molecules. As natural biological delivery vehicles, interest in the use of exosomes as therapeutic delivery agents is growing. We previously demonstrated a novel treatment whereby mesenchymal stromal cells were employed to package tumor-suppressing miR-146b into exosomes, which were then used to reduce malignant glioma growth in rat. The use of exosomes to raise the immune system against tumor is also drawing interest. Exosomes from dendritic cells which are antigen-presenting, and have been used for treatment of brain tumor may be divided into three categories: (1) exosomes for immunomodulation-based therapy, (2) exosomes as delivery vehicles for anti-tumor nucleotides, and (3) exosomes as drug delivery vehicles. Here, we will provide an overview of these three applications of exosomes to treat brain tumor, and examine their prospects on the long road to clinical use.     

Leukemia cancer cells and immune cells derived-exosomes: Possible roles in leukemia progression and therapy

Exosomes have a significant impact on tumor survival, proliferation, metastasis, and recurrence. They also open up new therapeutic options and aid in the pathological identification and diagnosis of cancers. Exosomes have been shown in numerous studies to be essential for facilitating cell-to-cell communication. In B-cell hematological malignancies, the proteins and RNAs that are encased by circulating exosomes are thought to represent prospective sources for therapeutic drugs as well as biomarkers for diagnosis and prognosis. Additionally, exosomes can offer a “snapshot” of the tumor and the metastatic environment at any given point in time. In this review study, we concluded that leukemia-derived exosomes could be utilized as prognostic, diagnostic, and therapeutic biomarkers for individuals suffering from leukemia. Moreover, clinical studies have demonstrated that immune cells like dendritic cells create exosomes, which have the ability to activate the immune system against leukemia.     

Clinical trials of antitumor vaccination with an autologous tumor cell vaccine modified by virus infection: improvement of patient survival based on improved antitumor immune memory

For active specific immunotherapy of cancer patients, we designed the autologous virus–modified tumor cell vaccine ATV-NDV. The rationale of this vaccine is to link multiple tumor-associated antigens (TAAs) from individual patient-derived tumor cells with multiple danger signals (DS) derived from virus infection (dsRNA, HN, IFN-). This allows activation of multiple innate immune responses (monocytes, dendritic cells, and NK cells) as well as adaptive immune responses (CD4 and CD8 memory T cells). Preexisting antitumor memory T cells from cancer patients could be activated by antitumor vaccination with ATV-NDV as seen by augmentation of antitumor memory delayed-type hypersensitivity (DTH) responses. In a variety of phase II vaccination studies, an optimal formulation of this vaccine could improve long-term survival beyond what is seen in conventional standard therapies. A new concept is presented which proposes that a certain threshold of antitumor immune memory plays an important role (1) in the control of residual tumor cells which remain after most therapies and (2) for long-term survival of treated cancer patients. This immune memory is T-cell based and most likely maintained by persisting TAAs from residual dormant tumor cells. Such immune memory was prominent in the bone marrow in animal tumor models as well as in cancer patients. Immunization with a tumor vaccine in which individual TAAs are combined with DS from virus infection appears to have a positive effect on antitumor immune memory and on patient survival.     

Preparation of dendritic cells for cancer immunotherapy

Development of new effective method for cancer therapy is one of the most important trends in the modern medicine. Along with surgery, chemotherapy and radiotherapy, induction of an immune response against the tumor cells is a promising approach for therapy of cancer, particularly metastatic, slowly dividing tumors and cancer stem cells. Induction of the antitumor T-cell immune response involves activation of antigen-presenting cells, which can efficiently present the cancer antigens and activate T-lymphocytes. The immune response may be activated by dendritic cells (DC) loaded with tumor antigens, such as tumor-specific proteins, tumor cell lysates, apoptotic or necrotic tumor cells, as well as nucleic acids encoding tumor antigens. Regardless of the selected source of the tumor antigen, preparation of mature DC is a principal step in the development of anticancer vaccines aimed at the induction of the cytotoxic T-cell immune response. Recently, various research groups have proposed several strategies for producing mature DC, differed by the set of agents used. It has been shown that the maturation strategy influences both their phenotype and the ability to induce the immune response. In this review we have analyzed the results of studies on the various strategies of preparation of mature DCs.