Immune capture and protein profiling of small extracellular vesicles from human plasma.

Extracellular vesicles (EVs), the key players in inter-cellular communication, are produced by all cell types and are present in all body fluids. Analysis of the proteome content is an important approach in structural and functional studies of these vesicles. EVs circulating in human plasma are heterogeneous in size, cellular origin, and functions. This heterogeneity and the potential presence of contamination with plasma components such as lipoprotein particles and soluble plasma proteins represent a challenge in profiling the proteome of EV subsets by mass spectrometry. An immunocapture strategy prior to mass spectrometry may be used to isolate a homogeneous subpopulation of small EVs (sEV) with a specific endocytic origin from plasma or other biofluids. Immunocapture selectively separates EV subpopulations in biofluids based on the presence of a unique protein carried on the vesicle surface. The advantages and disadvantages of EV immune capture as a preparative step for mass spectrometry are discussed.

TGFß carrying exosomes in plasma: potential biomarkers of cancer progression in patients with head and neck squamous cell carcinoma.

OBJECTIVES: Contributions of TGFß to cancer progression are well documented. However, plasma TGFß levels often do not correlate with clinicopathological data. We examine the role of TGFß carried in exosomes isolated from murine and human plasma as a contributor to disease progression in head and neck squamous cell carcinoma (HNSCC). MATERIALS AND METHODS: The 4-nitroquinoline-1-oxide (4-NQO) mouse model was used to study changes in TGFß expression levels during oral carcinogenesis. In human HNSCC, TGFß and Smad3 protein expression levels and TGFB1 gene expression were determined. Soluble TGFß levels were evaluated by ELISA and TGFß bioassays. Exosomes were isolated from plasma using size exclusion chromatography, and TGFß content was quantified using bioassays and bioprinted microarrays. RESULTS: During 4-NQO carcinogenesis, TGFß levels in tumour tissues and in serum increased as the tumour progressed. The TGFß content of circulating exosomes also increased. In HNSCC patients, TGFß, Smad3 and TGFB1 were overexpressed in tumour tissues and correlated with increased soluble TGFß levels. Neither TGFß expression in tumours nor levels of soluble TGFß correlated with clinicopathological data or survival. Only exosome-associated TGFß reflected tumour progression and correlated with tumour size. CONCLUSIONS: Circulating TGFß+ exosomes in the plasma of patients with HNSCC emerge as potential non-invasive biomarkers of disease progression in HNSCC.

Tumor gene signatures that correlate with release of extracellular vesicles shape the immune landscape in head and neck squamous cell carcinoma.

Head and neck squamous cell carcinomas (HNSCCs) evade immune responses through multiple resistance mechanisms. Extracellular vesicles (EVs) released by the tumor and interacting with immune cells induce immune dysfunction and contribute to tumor progression. This study evaluates the clinical relevance and impact on anti-tumor immune responses of gene signatures expressed in HNSCC and associated with EV production/release. Expression levels of two recently described gene sets were determined in The Cancer Genome Atlas Head and Neck Cancer cohort (n = 522) and validated in the GSE65858 dataset (n = 250) as well as a recently published single-cell RNA sequencing dataset (n = 18). Clustering into HPV(+) and HPV(-) patients was performed in all cohorts for further analysis. Potential associations between gene expression levels, immune cell infiltration, and patient overall survival were analyzed using GEPIA2, TISIDB, TIMER, and the UCSC Xena browser. Compared to normal control tissues, vesiculation-related genes were upregulated in HNSCC cells. Elevated gene expression levels positively correlated (P < 0.01) with increased abundance of CD4(+) T cells, macrophages, neutrophils, and dendritic cells infiltrating tumor tissues but were negatively associated (P < 0.01) with the presence of B cells and CD8(+) T cells in the tumor. Expression levels of immunosuppressive factors NT5E and TGFB1 correlated with the vesiculation-related genes and might explain the alterations of the anti-tumor immune response. Enhanced expression levels of vesiculation-related genes in tumor tissues associates with the immunosuppressive tumor milieu and the reduced infiltration of B cells and CD8(+) T cells into the tumor.

Impact of contracted manufacturing organization protocols on operations in an aca demically based Current Good Manufacturing Practice facility.

Immunotherapy of cancer and other diseases is often dependent on adoptive transfer to patients of cellular products generated in Current Good Manufacturing Practice (cGMP) facilities. With the availability and approval of various cellular products for therapy, cell production facilities are experiencing unprecedented growth in demand for services. Increasingly, these services involve processing of externally generated cells for transfer to the bedside. The arrival of cells from external manufacturing facilities for processing and eventual infusion of cell therapy products into patients creates a new layer of responsibility and adds to an already demanding list of the existing procedures in academic cGMP facilities. Sponsors introduce their own requirements for the handling of cells that the laboratory must incorporate and follow. The challenges of creating additional access to cleanrooms, writing new standard operating procedures, expanding personnel training, altering pre-existing schedules and incorporating additional monitoring for safety of external products alter the balance of laboratory operations. Adjustments for accommodating externally manufactured products are numerous and varied, as each sponsor has requests that are product-specific. If cells produced by several different external manufacturers are handled by the same facility, the negative impact on the regular activities in this facility may be considerable. Here the authors provide a review of operational challenges that an academic-based laboratory faces and discuss solutions that could ameliorate the difficulties related to an increasing volume of industry-sponsored trials. The solution may be the development under the auspices of the Foundation for Accreditation of Cellular Therapy or the Food and Drug Administration of regulations that will guide the processing of products manufactured by external companies and make these regulations broadly applicable in all cGMP facilities.

Exosome and mesenchymal stem cell cross-talk in the tumor microenvironment.

Mesenchymal stem cells (MSCs) are a major component of the tumor microenvironment (TME) and play a key role in promoting tumor progression. The tumor uses exosomes to co-opt MSCs and re-program their functional profile from normally trophic to pro-tumorigenic. These tumor-derived small vesicles called "TEX" carry and deliver a cargo rich in proteins and nucleic acids to MSCs. Upon interactions with surface receptors on MSCs and uptake of the exosome cargo by MSCs, molecular, transcriptional and translational changes occur that convert MSCs into producers of factors that are necessary for tumor growth and that also alter functions of non-tumor cells in the TME. The MSCs re-programmed by TEX become avid producers of their own exosomes that carry and deliver mRNA and miRNA species as well as molecular signals not only back to tumor cells, directly enhancing their growth, but also horizontally to fibroblasts, endothelial cells and immune cells in the TME, indirectly enhancing their pro-tumor functions. TEX-driven cross-talk of MSCs with immune cells blocks their anti-tumor activity and/or converts them into suppressor cells. MSCs re-programmed by TEX mediate pro-angiogenic activity and convert stromal cells into cancer-associated fibroblasts (CAFs). Although MSCs have a potential to exert anti-tumor activities, they largely provide service to the tumor using the multidirectional communication system established by exosomes in the TME. Future therapeutic options consider disruption of this complex vicious cycle by either molecular or gene-regulated silencing of pro-tumor effects mediated by MSCs in the TME.

Characteristics of Exosomes and the Vascular Landscape Regulate Exosome Sequestration by Peripheral Tissues and Brain.

Exosomes mediate intercellular communication, shuttling messages between cells and tissues. We explored whether exosome tissue sequestration is determined by the exosomes or the tissues using ten radiolabeled exosomes from human or murine, cancerous or noncancerous cell lines. We measured sequestration of these exosomes by the liver, kidney, spleen, and lung after intravenous injection into male CD-1 mice. Except for kidney sequestration of three exosomes, all exosomes were incorporated by all tissues, but sequestration levels varied greatly among exosomes and tissues. Species of origin (mouse vs. human) or source (cancerous vs. noncancerous cells) did not influence tissue sequestration. Sequestration of J774A.1 exosomes by liver involved the mannose-6 phosphate (M6P) receptor. Wheatgerm agglutinin (WGA) or lipopolysaccharide (LPS) treatments enhanced sequestration of exosomes by brain and lung but inhibited sequestration by liver and spleen. Response to LPS was not predictive of response to WGA. Path and heat map analyses included our published results for brain and found distinct clusters among the exosomes and the tissues. In conclusion, we found no evidence for a universal binding site controlling exosome-tissue interactions. Instead, sequestration of exosomes by tissues is differentially regulated by both exosomes and tissues and may be stimulated or inhibited by WGA and inflammation.

Evaluation of Exosome Proteins by on-Bead Flow Cytometry.

Exosomes, recently re-named "small extracellular vesicles" or "sEV," are emerging as an intercellular communication system. Quantification of the molecular cargo exosomes carry by on-bead flow cytometry is needed for defining their role in information transfer and in human disease. Exosomes (sEV) isolated from cell supernatants or plasma of cancer patients by size-exclusion chromatography were captured by biotinylated antibodies specific for antigens in the exosome cargo (e.g., tetraspanins) and placed on streptavidin-labeled beads. Detection was performed with pretitered fluorochrome-labeled antibodies of desired specificity. The data were acquired in a conventional cytometer, and molecules of equivalent soluble fluorochrome (MESF) beads were used to quantify the number of fluorescent molecules bound per bead. Isotype antibody controls were obligatory. The mean fluorescence intensity (MFI) value of each sample was converted into MESF units, and the separation index (SI), which quantifies separation of stained and isotype control beads, was determined. Various proteins identified by labeled antibodies were quantified on the surface of tumor cell-derived exosomes. To identify intravesicular cargo, such as cytokines or chemokines, exosomes were lysed with 0.3% Triton-100, and the proteins in lysates were loaded on aldehyde/sulfate latex beads for flow cytometry. Examples of quantitative surface and/or intravesicular on-bead flow cytometry for exosomes produced by various cells or present in body fluids of cancer patients are provided. On-bead flow cytometry standardized for use with conventional cytometers is a useful method for protein detection and quantitation in exosomes isolated from supernatants of cell lines or plasma of patients with cancer. © 2020 International Society for Advancement of Cytometry.

Tumor-Derived Exosomes (TEX) and Their Role in Immuno-Oncology.

Extracellular vesicles (EVs) play a key role in health and disease, including cancer. Tumors produce a mix of EVs differing in size, cellular origin, biogenesis and molecular content. Small EVs (sEV) or exosomes are a subset of 30-150 nm (virus-size) vesicles originating from the multivesicular bodies (MVBs) and carrying a cargo that in its content and topography approximates that of a parent cell. Tumor-derived exosomes (TEX) present in all body fluids of cancer patients, are considered promising candidates for a liquid tumor biopsy. TEX also mediate immunoregulatory activities: they maintain a crosstalk between the tumor and various non-malignant cells, including immunocytes. Effects that EVs exert on immune cells may be immunosuppressive or immunostimulatory. Here, we review the available data for TEX interactions with immunocytes, focusing on strategies that allow isolation from plasma and separation of TEX from sEV produced by non-malignant cells. Immune effects mediated by either of the subsets can now be distinguished and measured. The approach has allowed for the comparison of molecular and functional profiles of the two sEV fractions in plasma of cancer patients. While TEX carried an excess of immunosuppressive proteins and inhibited immune cell functions in vitro and in vivo, the sEV derived from non-malignant cells, including CD3(+)T cells, were variably enriched in immunostimulatory proteins and could promote functions of immunocytes. Thus, sEV in plasma of cancer patients are heterogenous, representing a complex molecular network which is not evident in healthy donors' plasma. Importantly, TEX appear to be able to reprogram functions of non-malignant CD3(+)T cells inducing them to produce CD3(+)sEV enriched in immunosuppressive proteins. Ratios of stimulatory/inhibitory proteins carried by TEX and by CD3(+)sEV derived from reprogrammed non-malignant cells vary broadly in patients and appear to negatively correlate with disease progression. Simultaneous capture from plasma and functional/molecular profiling of TEX and the CD3(+)sEV fractions allows for defining their role as cancer biomarkers and as monitors of cancer patients' immune competence, respectively.

Tumor-derived exosomes promote carcinogenesis of murine oral squamous cell carcinoma.

Circulating tumor-derived exosomes (TEX) interact with a variety of cells in cancer-bearing hosts, leading to cellular reprogramming which promotes disease progression. To study TEX effects on the development of solid tumors, immunosuppressive exosomes carrying PD-L1 and FasL were isolated from supernatants of murine or human HNSCC cell lines. TEX were delivered (IV) to immunocompetent C57BL/6 mice bearing premalignant oral/esophageal lesions induced by the carcinogen, 4-nitroquinoline 1-oxide (4NQO). Progression of the premalignant oropharyngeal lesions to malignant tumors was monitored. A single TEX injection increased the number of developing tumors (6.2 versus 3.2 in control mice injected with phosphate-buffered saline; P < 0.0002) and overall tumor burden per mouse (P < 0.037). The numbers of CD4+ and CD8+ T lymphocytes infiltrating the developing tumors were coordinately reduced (P < 0.01) in mice injected with SCCVII-derived TEX relative to controls. Notably, TEX isolated from mouse or human tumors had similar effects on tumor development and immune cells. A single IV injection of TEX was sufficient to condition mice harboring premalignant OSCC lesions for accelerated tumor progression in concert with reduced immune cell migration to the tumor.

Tumor-derived exosomes promote angiogenesis via adenosine A2B receptor signaling.

RATIONALE: One hallmark of tumor-derived exosomes (TEX) is the promotion of cancer progression by stimulating angiogenesis. This study was performed to evaluate the role of adenosine receptors in TEX-induced angiogenesis. METHODS: TEX produced by UMSCC47 head and neck cancer cell line were isolated by mini size exclusion chromatography (mini-SEC). Enzymatic activity of ectonucleotidases CD39/CD73 carried by TEX was measured by HPLC. Adenosine content of TEX was measured by UPLC-MS/MS. Primary human macrophages were co-incubated with TEX or exosomes derived from the plasma of head and neck cancer patients and their marker expression profile was analyzed by flow cytometry. The macrophage secretome was analyzed by angiogenesis arrays. The in vitro angiogenic potential of TEX was evaluated in endothelial growth studies. Results were validated in vivo using basement membrane extract plug assays in A1R-/-, A2AR-/- and A2BR-/- rats. Vascularization was analyzed by hemoglobin quantification and immunohistology with vessel and macrophage markers. RESULTS: TEX carried enzymatically active CD39/CD73 and adenosine. TEX promoted A2BR-mediated polarization of macrophages toward an M2-like phenotype (p < 0.05) and enhanced their secretion of angiogenic factors. Growth of endothelial cells was stimulated directly by TEX and indirectly via macrophage-reprogramming dependent on A2BR signaling (p < 0.01). In vivo, TEX stimulated the formation of defined vascular structures and macrophage infiltration. This response was absent in A2BR-/- rats (p < 0.05). CONCLUSION: This report provides the first evidence for adenosine production by TEX to promote angiogenesis via A2BR. A2BR antagonism emerges as a potential strategy to block TEX-induced angiogenesis.

Incorporation of extracorporeal photopheresis into a reduced intensity conditioning regimen in myelodysplastic syndrome and aggressive lymphoma: results from ECOG 1402 and 1902.

BACKGROUND: Extracorporeal photopheresis (ECP) is an immunomodulatory cellular therapy which has been shown to induce a tolerogenic state in patients with acute and chronic graft-vs-host disease. ECOG-ACRIN explored the activity of ECP as a part of a reduced intensity conditioning regimen in two multicenter trials in patients with MDS (E1902) and lymphomas (E1402). While both studies closed before completing accrual, we report results in 23 patients (17 MDS and 6 lymphoma). STUDY DESIGN AND METHODS: Patients received 2 days of ECP followed by pentostatin 4 mg/m2 /day for two consecutive days, followed by 600 cGy of total body irradiation prior to stem cell infusion. Immunosuppression for aGVHD was infusional cyclosporine A or tacrolimus and methotrexate on day +1, +3, with mycophenolate mofetil starting on day 100 for chronic GVHD prophylaxis. RESULTS: All patients engrafted, with median time to neutrophil and platelet engraftment of 15-18 days and 10-18 days respectively. Grade 3 or 4 aGVHD occurred in 13% and chronic extensive GVHD in 30%. CONCLUSIONS: These studies demonstrate that ECP/pentostatin/TBI is well tolerated and associated with adequate engraftment of neutrophils and platelets in patients with lymphomas and MDS.

Adenosine receptors regulate exosome production.

Exosomes, small-sized extracellular vesicles, carry components of the purinergic pathway. The production by cells of exosomes carrying this pathway remains poorly understood. Here, we asked whether type 1, 2A, or 2B adenosine receptors (A1Rs, A2ARs, and A2BRs, respectively) expressed by producer cells are involved in regulating exosome production. Preglomerular vascular smooth muscle cells (PGVSMCs) were isolated from wildtype, A1R-/-, A2AR-/-, and A2BR-/- rats, and exosome production was quantified under normal or metabolic stress conditions. Exosome production was also measured in various cancer cells treated with pharmacologic agonists/antagonists of A1Rs, A2ARs, and A2BRs in the presence or absence of metabolic stress or cisplatin. Functional activity of exosomes was determined in Jurkat cell apoptosis assays. In PGVSMCs, A1R and A2AR constrained exosome production under normal conditions (p = 0.0297; p = 0.0409, respectively), and A1R, A2AR, and A2BR constrained exosome production under metabolic stress conditions. Exosome production from cancer cells was reduced (p = 0.0028) by the selective A2AR agonist CGS 21680. These exosomes induced higher levels of Jurkat apoptosis than exosomes from untreated cells or cells treated with A1R and A2BR agonists (p = 0.0474). The selective A2AR antagonist SCH 442416 stimulated exosome production under metabolic stress or cisplatin treatment, whereas the selective A2BR antagonist MRS 1754 reduced exosome production. Our findings indicate that A2ARs suppress exosome release in all cell types examined, whereas effects of A1Rs and A2BRs are dependent on cell type and conditions. Pharmacologic targeting of cancer with A2AR antagonists may inadvertently increase exosome production from tumor cells.

Optimization of cell culture conditions for exosome isolation using mini-size exclusion chromatography (mini-SEC).

Extracellular vesicles (EVs) are emerging as a major intercellular communication system engaged in a variety of physiological and pathophysiological processes. Tumor-derived exosomes (TEX) are a subset of EVs of special interest as potential cancer biomarkers. Supernatants of tumor cell lines are widely used as the source of pure TEX for molecular/genetic studies. To optimize TEX isolation and characterization for these studies, we evaluated culture conditions for different tumor cell lines and used mini size exclusion chromatography (mini-SEC) for TEX isolation. Each tumor cell line showed unique culture requirements that determined the recovery, purity and total yield of TEX. Culture conditions for optimal TEX purity and recovery by mini-SEC could be modified by altering the media composition and numbers of seeded cells. TEX recovered from mini-SEC fraction #4 under optimized conditions were biologically active, were sized from 30 to 150 nm in diameter, had a typical vesicular morphology and carried endocytic markers. The most critical requirement for reproducible exosome recovery was re-seeding of tumor cells in numbers adjusted to reflect the optimized culture conditions for each tumor cell line. This study provides insights into a cell culture technique, which can be optimized for exosome production by various human or mouse tumor cell lines for isolation by mini-SEC.

Arginase-1+ Exosomes from Reprogrammed Macrophages Promote Glioblastoma Progression.

Interactions between tumor cells and tumor-associated macrophages (TAMs) are critical for glioblastoma progression. The TAMs represent up to 30% of the glioblastoma mass. The role of TAMs in tumor progression and in the mechanisms underlying tumor growth remain unclear. Using an in vitro model resembling the crosstalk between macrophages and glioblastoma cells, we show that glioblastoma-derived exosomes (GBex) reprogram M1 (mediate pro-inflammatory function) and M2 (mediate anti-inflammatory function) macrophages, converting M1 into TAMs and augmenting pro-tumor functions of M2 macrophages. In turn, these GBex-reprogrammed TAMs, produce exosomes decorated by immunosuppressive and tumor-growth promoting proteins. TAM-derived exosomes disseminate these proteins in the tumor microenvironment (TME) promoting tumor cell migration and proliferation. Mechanisms underlying the promotion of glioblastoma growth involved Arginase-1+ exosomes produced by the reprogrammed TAMs. A selective Arginase-1 inhibitor, nor-NOHA reversed growth-promoting effects of Arginase-1 carried by TAM-derived exosomes. The data suggest that GBex-reprogrammed Arginase-1+ TAMs emerge as a major source of exosomes promoting tumor growth and as a potential therapeutic target in glioblastoma.

Transport of Extracellular Vesicles across the Blood-Brain Barrier: Brain Pharmacokinetics and Effects of Inflammation.

Extracellular vesicles can cross the blood-brain barrier (BBB), but little is known about passage. Here, we used multiple-time regression analysis to examine the ability of 10 exosome populations derived from mouse, human, cancerous, and non-cancerous cell lines to cross the BBB. All crossed the BBB, but rates varied over 10-fold. Lipopolysaccharide (LPS), an activator of the innate immune system, enhanced uptake independently of BBB disruption for six exosomes and decreased uptake for one. Wheatgerm agglutinin (WGA) modulated transport of five exosome populations, suggesting passage by adsorptive transcytosis. Mannose 6-phosphate inhibited uptake of J774A.1, demonstrating that its BBB transporter is the mannose 6-phosphate receptor. Uptake rates, patterns, and effects of LPS or WGA were not predicted by exosome source (mouse vs. human) or cancer status of the cell lines. The cell surface proteins CD46, AVß6, AVß3, and ICAM-1 were variably expressed but not predictive of transport rate nor responses to LPS or WGA. A brain-to-blood efflux mechanism variably affected CNS retention and explains how CNS-derived exosomes enter blood. In summary, all exosomes tested here readily crossed the BBB, but at varying rates and by a variety of vesicular-mediated mechanisms involving specific transporters, adsorptive transcytosis, and a brain-to-blood efflux system.

mRNA and miRNA Profiles of Exosomes from Cultured Tumor Cells Reveal Biomarkers Specific for HPV16-Positive and HPV16-Negative Head and Neck Cancer.

Human papillomavirus (HPV)(+) and HPV(-) head and neck cancer (HNC) cells' interactions with the host immune system are poorly understood. Recently, we identified molecular and functional differences in exosomes produced by HPV(+) vs. HPV(-) cells, suggesting that genetic cargos of exosomes might identify novel biomarkers in HPV-related HNCs. Exosomes were isolated by size exclusion chromatography from supernatants of three HPV(+) and two HPV(-) HNC cell lines. Paired cell lysates and exosomes were analyzed for messenger RNA (mRNA) by qRT-PCR and microRNA (miR) contents by nanostring analysis. The mRNA profiles of HPV(+) vs. HPV(-) cells were distinct, with EGFR, TP53 and HSPA1A/B overexpressed in HPV(+) cells and IL6, FAS and DPP4 in HPV(-) cells. The mRNA profiles of HPV(+) or HPV(-) exosomes resembled the cargo of their parent cells. miR expression profiles in cell lysates identified 8 miRs expressed in HPV(-) cells vs. 14 miRs in HPV(+) cells. miR-205-5p was exclusively expressed in HPV(+) exosomes, and miR-1972 was only detected in HPV(-) exosomes. We showed that HPV(+) and HPV(-) exosomes recapitulated the mRNA expression profiles of their parent cells. Expression of miRs was dependent on the HPV status, and miR-205-5p in HPV(+) and miR-1972 in HPV(-) exosomes emerge as potential discriminating HPV-associated biomarkers.

Impact of combination immunochemotherapies on progression of 4NQO-induced murine oral squamous cell carcinoma.

Advanced oral squamous cell carcinomas (OSCC) have limited therapeutic options. Although immune therapies are emerging as a potentially effective alternative or adjunct to chemotherapies, the therapeutic efficacy of combination immune chemotherapies has yet to be determined. Using a 4-nitroquinolone-N-oxide (4NQO) orthotopic model of OSCC in immunocompetent mice, we evaluated the therapeutic efficacy of single- and combined-agent treatment with a poly-epitope tumor peptide vaccine, cisplatin and/or an A2AR inhibitor, ZM241385. The monotherapies or their combinations resulted in a partial inhibition of tumor growth and, in some cases, a significant but transient upregulation of systemic anti-tumor CD8+ T cell responses. These responses eroded in the face of expanding immunoregulatory cell populations at later stages of tumor progression. Our findings support the need for the further development of combinatorial therapeutic approaches that could more effectively silence dominant immune inhibitory pathways operating in OSCC and provide novel, more beneficial treatment options for this tumor.

Challenges in Exosome Isolation and Analysis in Health and Disease.

A growing body of evidence emphasizes the important role exosomes in different physiological and pathological conditions. Exosomes, virus-size extracellular vesicles (EVs), carry a complex molecular cargo, which is actively processed in the endocytic compartment of parental cells. Exosomes carry and deliver this cargo to recipient cells, serving as an intercellular communication system. The methods for recovery of exosomes from supernatants of cell lines or body fluids are not uniformly established. Yet, studies of the quality and quantity of exosome cargos underlie the concept of "liquid biopsy." Exosomes are emerging as a potentially useful diagnostic tool and a predictor of disease progression, response to therapy and overall survival. Although many novel approaches to exosome isolation and analysis of their cargos have been introduced, the role of exosomes as diagnostic or prognostic biomarkers of disease remains unconfirmed. This review considers existing challenges to exosome validation as disease biomarkers. Focusing on advantages and limitations of methods for exosome isolation and characterization, approaches are proposed to facilitate further progress in the development of exosomes as biomarkers in human disease.

Inhibition of the Adenosinergic Pathway in Cancer Rejuvenates Innate and Adaptive Immunity.

The adenosine pathway plays a key role in modulating immune responses in physiological and pathological conditions. Physiologically, anti-inflammatory effects of adenosine balance pro-inflammatory adenosine 5'-triphosphate (ATP), protecting tissues from damage caused by activated immune cells. Pathologically, increased adenosine monophosphatase (AMPase) activity in tumors leads to increased adenosine production, generating a deeply immunosuppressed microenvironment and promoting cancer progression. Adenosine emerges as a promising target for cancer therapy. It mediates protumor activities by inducing tumor cell proliferation, angiogenesis, chemoresistance, and migration/invasion by tumor cells. It also inhibits the functions of immune cells, promoting the formation of a tumor-permissive immune microenvironment and favoriting tumor escape from the host immune system. Pharmacologic inhibitors, siRNA or antibodies specific for the components of the adenosine pathway, or antagonists of adenosine receptors have shown efficacy in pre-clinical studies in various in vitro and in vivo tumor models and are entering the clinical arena. Inhibition of the adenosine pathway alone or in combination with classic immunotherapies offers a potentially effective therapeutic strategy in cancer.

Exosomes in acute myeloid leukemia inhibit hematopoiesis.

PURPOSE OF REVIEW: Exosomes are cell-derived, biologically active membrane-bound vesicles, and are emerging as key modulators of hematopoiesis. Recent studies have provided a clearer understanding of the mechanisms whereby blast-derived exosomes act to suppress hematopoiesis in acute myeloid leukemia (AML). RECENT FINDINGS: Exosomes released from leukemia blasts have been shown to suppress hematopoietic progenitor cell (HPC) functions indirectly through stromal reprogramming of niche-retention factors and also as a consequence of AML exosome-directed microRNA delivery to HPC. Furthermore, exosomes secreted by AML blasts remodel the bone marrow niche into a leukemia growth-permissive microenvironment. SUMMARY: Exosomes suppress hematopoiesis in AML. Strategies to block the production, secretion and reprogramming that exosomes induce may be a novel therapeutic approach in AML and other leukemias.