Exosomes released by chronic lymphocytic leukemia cells induce the transition of stromal cells into cancer-associated fibroblasts

Tumor-associated stromal cells as key contributors to the tumor microenvironment

The tumor microenvironment is a heterogeneous population of cells consisting of the tumor bulk plus supporting cells. It is becoming increasingly evident that these supporting cells are recruited by cancer cells from nearby endogenous host stroma and promote events such as tumor angiogenesis, proliferation, invasion, and metastasis, as well as mediate mechanisms of therapeutic resistance. In addition, recruited stromal cells range in type and include vascular endothelial cells, pericytes, adipocytes, fibroblasts, and bone-marrow mesenchymal stromal cells. During normal wound healing and inflammatory processes, local stromal cells change their phenotype to become that of reactive stroma. Under certain conditions, however, tumor cells can co-opt these reactive stromal cells and further transition them into tumor-associated stromal cells (TASCs). These TASCs express higher levels of proteins, including alpha-smooth muscle actin, fibroblast activating protein, and matrix metalloproteinases, compared with their normal, non-reactive counterparts. TASCs are also known to secrete many pro-tumorigenic factors, including IL-6, IL-8, stromal-derived factor-1 alpha, vascular endothelial growth factor, tenascin-C, and matrix metalloproteinases, among others, which recruit additional tumor and pro-tumorigenic cells to the developing microenvironment. Here, we review the current literature pertaining to the origins of recruited host stroma, contributions toward tumor progression, tumor-associated stromal cells, and mechanisms of crosstalk between endogenous host stroma and tumor cells.

The roles of tumor- and metastasis-promoting carcinoma-associated fibroblasts in human carcinomas

Carcinoma-associated fibroblasts (CAFs) constitute a substantial proportion of the non-neoplastic mesenchymal cell compartment in various human tumors. These fibroblasts are phenotypically converted from their progenitors via interactions with nearby cancer cells during the course of tumor progression. The resulting CAFs, in turn, support the growth and progression of carcinoma cells. These fibroblasts have a major influence on the hallmarks of carcinoma and promote tumor malignancy through the secretion of tumor-promoting growth factors, cytokines and exosomes, as well as through the remodeling of the extracellular matrix. Coevolution of CAFs and carcinoma cells during tumorigenesis is therefore essential for progression into fully malignant tumors. Recent studies have revealed the molecular mechanisms underlying CAF functions, especially in tumor invasion, metastasis and drug resistance and have highlighted the significant heterogeneity among these cells. In this review, we summarize the impacts of recently identified roles of tumor-promoting CAFs and discuss the therapeutic implications of targeting the heterotypic interactions of these fibroblasts with carcinoma cells. Graphical Abstract ᅟ.

Exosomes in colorectal carcinoma formation: ALIX under the magnifying glass

Exosomes are small membrane vesicles that have important roles in transporting a great variety of bioactive molecules between epithelial compartment and their microenvironment during tumor formation including colorectal adenoma-carcinoma sequence. We tested the mRNA expression of the top 25 exosome-related markers based on ExoCharta database in healthy (n=49), adenoma (n=49) and colorectal carcinoma (n=49) patients using Affymetrix HGU133 Plus2.0 microarrays. Most related genes showed significantly elevated expression including PGK1, PKM, ANXA5, ENO1, HSP90AB1 and MSN during adenoma-carcinoma sequence. Surprisingly, the expression of ALIX (ALG 2-interacting protein X), involved in multivesicular body (MVB) and exosome formation, was significantly reduced in normal vs adenoma (P=5.02 × 10(-13)) and in normal vs colorectal carcinoma comparisons (P=1.51 × 10(-10)). ALIX also showed significant reduction (P<0.05) at the in situ protein level in the epithelial compartment of adenoma (n=35) and colorectal carcinoma (n=37) patients compared with 27 healthy individuals. Furthermore, significantly reduced ALIX protein levels were accompanied by their gradual transition from diffuse cytoplasmic expression to granular signals, which fell into the 0.6-2 μm diameter size range of MVBs. These ALIX-positive particles were seen in the tumor nests, including tumor-stroma border, which suggest their exosome function. MVB-like structures were also detected in tumor microenvironment including α-smooth muscle actin-positive stromal cells, budding off cancer cells in the tumor front as well as in cancer cells entrapped within lymphoid vessels. In conclusion, we determined the top aberrantly expressed exosome-associated markers and revealed the transition of diffuse ALIX protein signals into a MVB-like pattern during adenoma-carcinoma sequence. These tumor-associated particles seen both in the carcinoma and the surrounding microenvironment can potentially mediate epithelial-stromal interactions involved in the regulation of tumor growth, metastatic invasion and therapy response.

Therapeutic application of extracellular vesicles in acute and chronic renal injury

A new cell-to-cell communication system was discovered in the 1990s, which involves the release of vesicles into the extracellular space. These vesicles shuttle bioactive particles, including proteins, mRNA, miRNA, metabolites, etc. This particular communication has been conserved throughout evolution, which explains why most cell types are capable of producing vesicles. Extracellular vesicles (EVs) are involved in the regulation of different physiological processes, as well as in the development and progression of several diseases. EVs have been widely studied over recent years, especially those produced by embryonic and adult stem cells, blood cells, immune system and nervous system cells, as well as tumour cells. EV analysis from bodily fluids has been used as a diagnostic tool for cancer and recently for different renal diseases. However, this review analyses the importance of EVs generated by stem cells, their function and possible clinical application in renal diseases and kidney transplantation.

Exosomes from the tumor microenvironment as reciprocal regulators that enhance prostate cancer progression

Distant organ metastasis of prostate cancer is a puzzle, and various theories have successively arisen to explain the mechanism of lethal cancer progression. While perhaps agreeable to many cancer biologists, the very statement of "seed and soil" proposed by Stephan Paget in 1881 is arguably still the major statement for organ-specific cancer metastasis. Since recent studies showed important correlations of regulation of cancer cells and the microenvironment, exosomes from cancer and stromal cells seem to create another important niche for metastasis. Stromal cells pretreated with exosomes from metastatic cancer cells increase the potential of change stromal cells. The poorly metastatic cancer cells could also enhance malignancy through transfer of proteins, microribonucleic acid and messenger ribonucleic acid to recipient cancer cells. Herein, we reviewed extracellular exosomes as a factor involved in cross-talk between stromal and prostate cancer epithelial cells.

Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders that have the capacity to progress to acute myeloid leukemia (AML). Accumulating evidence suggests that the altered bone marrow (BM) microenvironment in general, and in particular the components of the stem cell niche, including mesenchymal stem cells (MSCs) and their progeny, play a pivotal role in the evolution and propagation of MDS. We here present an overview of the role of MSCs in the pathogenesis of MDS, with emphasis on cellular interactions in the BM microenvironment and related stem cell niche concepts. MSCs have potent immunomodulatory capacities and communicate with diverse immune cells, but also interact with various other cellular components of the microenvironment as well as with normal and leukemic stem and progenitor cells. Moreover, compared to normal MSCs, MSCs in MDS and AML often exhibit altered gene expression profiles, an aberrant phenotype, and abnormal functional properties. These alterations supposedly contribute to the “reprogramming” of the stem cell niche into a disease-permissive microenvironment where an altered immune system, abnormal stem cell niche interactions, and an impaired growth control lead to disease progression. The current article also reviews molecular targets that play a role in such cellular interactions and possibilities to interfere with abnormal stem cell niche interactions by using specific targeted drugs.

Tumor-Stromal Cell Communication: Small Vesicles Signal Big Changes

Reciprocal interactions between malignant and stromal cells create a local microenvironment that fosters tumor growth. Extracellular vesicles (EVs) such as exosomes, microvesicles, and large oncosomes are involved in tumor-stroma communication by shuttling signaling cargo and other molecules. Here we discuss how EVs released by cancer or stromal cells impact the proliferation, differentiation, and metabolism of tumors.

Exosome-Mediated Metastasis: From Epithelial-Mesenchymal Transition to Escape from Immunosurveillance

Exosomes are extracellular signalosomes that facilitate eukaryotic intercellular communication under a wide range of normal physiological contexts. In malignancies, this regulatory circuit is co-opted to promote cancer cell survival and outgrowth. Tumour-derived exosomes (TDEs) carry a pro-EMT (epithelial-mesenchymal transition) programme including transforming growth factor beta (TGFβ), caveolin-1, hypoxia-inducible factor 1 alpha (HIF1α), and β-catenin that enhances the invasive and migratory capabilities of recipient cells, and contributes to stromal remodelling and premetastatic niche formation. The integrin expression patterns on TDEs appear to dictate their preferential uptake by organ-specific cells, implying a crucial role of this pathway in organotropic metastasis. Through the expression of immunomodulatory molecules such as CD39 and CD73, TDEs modify the immune contexture of the tumour microenvironment, which could have implications for immunotherapy. Hence, targeting TDE dysregulation pathways, such as the heparanase/syndecan-1 axis, could represent novel therapeutic strategies in the quest to conquer cancer.

Extracellular vesicles released by CD40/IL-4-stimulated CLL cells confer altered functional properties to CD4+ T cells

The complex interplay between cancer cells, stromal cells, and immune cells in the tumor microenvironment (TME) regulates tumorigenesis and provides emerging targets for immunotherapies. Crosstalk between CD4(+) T cells and proliferating chronic lymphocytic leukemia (CLL) tumor B cells occurs within lymphoid tissue pseudofollicles, and investigating these interactions is essential to understand both disease pathogenesis and the effects of immunotherapy. Tumor-derived extracellular vesicle (EV) shedding is emerging as an important mode of intercellular communication in the TME. In order to characterize tumor EVs released in response to T-cell-derived TME signals, we performed microRNA (miRNA [miR]) profiling of EVs released from CLL cells stimulated with CD40 and interleukin-4 (IL-4). Our results reveal an enrichment of specific cellular miRNAs including miR-363 within EVs derived from CD40/IL-4-stimulated CLL cells compared with parental cell miRNA content and control EVs from unstimulated CLL cells. We demonstrate that autologous patient CD4(+) T cells internalize CLL-EVs containing miR-363 that targets the immunomodulatory molecule CD69. We further reveal that autologous CD4(+) T cells that are exposed to EVs from CD40/IL-4-stimulated CLL cells exhibit enhanced migration, immunological synapse signaling, and interactions with tumor cells. Knockdown of miR-363 in CLL cells prior to CD40/IL-4 stimulation prevented the ability of CLL-EVs to induce increased synapse signaling and confer altered functional properties to CD4(+) T cells. Taken together, these data reveal a novel role for CLL-EVs in modifying T-cell function that highlights unanticipated complexity of intercellular communication that may have implications for bidirectional CD4(+) T-cell:tumor interactions within the TME.

Lung tumor exosomes induce a pro-inflammatory phenotype in mesenchymal stem cells via NFκB-TLR signaling pathway

Background

In tumor microenvironment, a continuous cross-talk between cancer cells and other cellular components is required to sustain tumor progression. Accumulating evidence suggests that exosomes, a novel way of cell communication, play an important role in such cross-talk. Exosomes could facilitate the direct intercellular transfer of proteins, lipids, and miRNA/mRNA/DNAs between cells. Since mesenchymal stem cells (MSCs) can be attracted to tumor sites and become an important component of the tumor microenvironment, there is an urgent need to reveal the effect of tumor exosomes on MSCs and to further explore the underlying molecular mechanisms.

Methods

Exosomes were harvested from lung cancer cell line A549 and added to MSCs. Secretion of inflammation-associated cytokines in exosome-treated MSCs were analyzed by RT-PCR and ELISA. The growth-promoting effect of exosome-treated MSCs on lung tumor cells was evaluated by in vivo mouse xenograft model. Signaling pathway involved in exosomes-treated MSCs was detected by PCR array of human toll-like receptor signaling pathway, RT-PCR, and Western blot.

Results

Data showed that lung tumor cell A549-derived exosomes could induce a pro-inflammatory phenotype in MSCs named P-MSCs, which have significantly elevated secretion of IL-6, IL-8, and MCP-1. P-MSCs possess a greatly enhanced ability in promoting lung tumor growth in mouse xenograft model. Analysis of the signaling pathways in P-MSCs revealed a fast triggering of NF-κB. Genetic ablation of Toll-like receptor 2 (TLR2) by siRNA and TLR2-neutralizing antibody could block NF-κB activation by exosomes. We further found that Hsp70 present on the surface of lung tumor exosomes contributed to the induction of P-MSCs by A549 exosomes.

Conclusions

Our studies suggest a novel mechanism by which lung tumor cell-derived exosomes induce pro-inflammatory activity of MSCs which in turn get tumor supportive characteristics.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0269-y) contains supplementary material, which is available to authorized users.

Extensive surface protein profiles of extracellular vesicles from cancer cells may provide diagnostic signatures from blood samples

Extracellular vesicles (EV) are membranous particles (30–1,000 nm in diameter) secreted by cells. Important biological functions have been attributed to 2 subsets of EV, the exosomes (bud from endosomal membranes) and the microvesicles (MV; bud from plasma membranes). Since both types of particles contain surface proteins derived from their cell of origin, their detection in blood may enable diagnosis and prognosis of disease. We have used an antibody microarray (DotScan) to compare the surface protein profiles of live cancer cells with those of their EV, based on their binding patterns to immobilized antibodies. Initially, EV derived from the cancer cell lines, LIM1215 (colorectal cancer) and MEC1 (B-cell chronic lymphocytic leukaemia; CLL), were used for assay optimization. Biotinylated antibodies specific for EpCAM (CD326) and CD19, respectively, were used to detect captured particles by enhanced chemiluminescence. Subsequently, this approach was used to profile CD19⁺ EV from the plasma of CLL patients. These EV expressed a subset (~40%) of the proteins detected on CLL cells from the same patients: moderate or high levels of CD5, CD19, CD31, CD44, CD55, CD62L, CD82, HLA-A,B,C, HLA-DR; low levels of CD21, CD49c, CD63. None of these proteins was detected on EV from the plasma of age- and gender-matched healthy individuals.

Multiple myeloma exosomes establish a favourable bone marrow microenvironment with enhanced angiogenesis and immunosuppression

Multiple myeloma (MM) pathogenesis and progression largely rely on the cells and extracellular factors in the bone marrow (BM) microenvironment. Compelling studies have identified tumour exosomes as key regulators in the maintenance and education of the BM microenvironment by targeting stromal cells, immune cells, and vascular cells. However, the role of MM exosomes in the modification of the BM microenvironment and MM progression remains unclear. Here, we explored the functions of MM exosomes in angiogenesis and immunosuppression in vitro and in vivo. Murine MM exosomes carrying multiple angiogenesis-related proteins enhanced angiogenesis and directly promoted endothelial cell growth. Several pathways such as signal transducer and activator of transcription 3 (STAT3), c-Jun N-terminal kinase, and p53 were modulated by the exosomes in endothelial and BM stromal cells. These exosomes promoted the growth of myeloid-derived suppressor cells (MDSCs) in naive mice through activation of the STAT3 pathway and changed their subsets to similar phenotypes to those seen in MM-bearing mice. Moreover, MM exosomes up-regulated inducible nitric oxide synthase and enhanced the immunosuppressive capacity of BM MDSCs in vivo. Our data show that MM exosomes modulate the BM microenvironment through enhancement of angiogenesis and immunosuppression, which will further facilitate MM progression. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Delivery of Therapeutic Proteins via Extracellular Vesicles: Review and Potential Treatments for Parkinson's Disease, Glioma, and Schwannoma

Extracellular vesicles present an attractive delivery vehicle for therapeutic proteins. They intrinsically contain many proteins which can provide information to other cells. Advantages include reduced immune reactivity, especially if derived from the same host, stability in biologic fluids, and ability to target uptake. Those from mesenchymal stem cells appear to be intrinsically therapeutic, while those from cancer cells promote tumor progression. Therapeutic proteins can be loaded into vesicles by overexpression in the donor cell, with oligomerization and membrane sequences increasing their loading. Examples of protein delivery for therapeutic benefit in pre-clinical models include delivery of: catalase for Parkinson's disease to reduce oxidative stress and thus help neurons to survive; prodrug activating enzymes which can convert a prodrug which crosses the blood-brain barrier into a toxic chemotherapeutic drug for schwannomas and gliomas; and the apoptosis-inducing enzyme, caspase-1 under a Schwann cell specific promoter for schwannoma. This therapeutic delivery strategy is novel and being explored for a number of diseases.

Lymphoma Microenvironment and Immunotherapy

Understanding of the lymphoma tumor microenvironment is poised to expand in the era of next-generation sequencing studies of the tumor cells themselves. Successful therapies of the future will rely on deeper appreciation of the interactions between elements of the microenvironment. Although the phenotypic, cytogenetic, and molecular characterization of tumor cells in lymphomas has progressed faster than most other solid organ tumors, concrete advancements in understanding the lymphoma microenvironment have been fewer. This article explores the composition of the lymphoma tumor microenvironment; its role in immune surveillance, evasion, and drug resistance; and its potential role in the development of targeted therapies.

Novel mechanisms of regulation of miRNAs in CLL

B-cell chronic lymphocytic leukemia (CLL) is the most common adult human leukemia. Although, the molecular alterations leading to CLL onset and progression are still under investigation (specifically, the interplay and exact role of oncogenes and tumor suppressors in CLL pathogenesis). MicroRNAs are small non-coding RNAs that regulate gene expression and are expressed in a tissue specific manner. Deregulation of microRNAs can alter expression levels of genes involved in the development and/or progression of tumors. In CLL, microRNAs can function as oncogenes or tumor suppressors. Here, we review the most recent findings on the role of microRNAs in the onset/progression of CLL, and how this knowledge can be used to identify new biomarkers and targets to treat this leukemia.

The chronic lymphocytic leukemia microenvironment: Beyond the B-cell receptor

Malignant B cells accumulate in the peripheral blood, bone marrow, and lymphoid organs of patients with chronic lymphocytic leukemia (CLL). In the tissue compartments, CLL shape a protective microenvironment by coopting normal elements. The efficacy of drugs that target these interactions further underscores their importance in the pathogenesis of CLL. While the B cell receptor (BCR) pathway clearly plays a central role in the CLL microenvironment, there is also rationale to evaluate agents that inhibit other aspects or modulate the immune cells in the microenvironment. Here we review the main cellular components, soluble factors, and signaling pathways of the CLL microenvironment, and highlight recent clinical advances. As the BCR pathway is reviewed elsewhere, we focus on other aspects of the microenvironment.

Integrated Magneto-Electrochemical Sensor for Exosome Analysis

Extracellular vesicles, including exosomes, are nanoscale membrane particles that carry molecular information on parental cells. They are being pursued as biomarkers of cancers that are difficult to detect or serially follow. Here we present a compact sensor technology for rapid, on-site exosome screening. The sensor is based on an integrated magneto-electrochemical assay: exosomes are immunomagnetically captured from patient samples and profiled through electrochemical reaction. By combining magnetic enrichment and enzymatic amplification, the approach enables (i) highly sensitive, cell-specific exosome detection and (ii) sensor miniaturization and scale-up for high-throughput measurements. As a proof-of-concept, we implemented a portable, eight-channel device and applied it to screen extracellular vesicles in plasma samples from ovarian cancer patients. The sensor allowed for the simultaneous profiling of multiple protein markers within an hour, outperforming conventional methods in assay sensitivity and speed.

Exosomes derived from endometriotic stromal cells have enhanced angiogenic effects in vitro

Our objective has been to establish a pro-angiogenic role for exosomes in endometriosis and to determine whether a differential expression profile of cellular and exosomal microRNAs (miRNAs) exists in endometriosis. We performed an in vitro study of human primary endometrial stromal cells (ESCs) and human umbilical vein endothelial cells (HUVECs). We isolated and characterized exosomes from ESCs from five endometriosis patients and five phase-matched controls. Exosomes were characterized by transmission electron microscopy and NanoSight technology. MiRNA was assessed by deep sequencing and reverse transcription with quantitative polymerase chain reaction. Exosome uptake studies were achieved by means of confocal microscopy. The pro-angiogenic experiments were executed by treating HUVECs with ESC-derived exosomes. We observed differential profiles of exosomal miRNA expression between exosomes derived from endometriosis lesion cells and diseased eutopic stromal cells compared with exosomes derived from control ESCs. We also demonstrated autocrine cellular uptake of exosomes and paracrine functional angiogenic effects of exosomes on HUVECs. The results of this study support the hypothesis that exosomes derived from ESCs play autocrine/paracrine roles in the development of endometriosis, potentially modulating angiogenesis. The broader clinical implications are that Sampson’s theory of retrograde menstruation possibly encompasses the finding that exosomes work as intercellular communication modulators in endometriosis.

Do cell-autonomous and non-cell-autonomous effects drive the structure of tumor ecosystems?

By definition, a driver mutation confers a growth advantage to the cancer cell in which it occurs, while a passenger mutation does not: the former is usually considered as the engine of cancer progression, while the latter is not. Actually, the effects of a given mutation depend on the genetic background of the cell in which it appears, thus can differ in the subclones that form a tumor. In addition to cell-autonomous effects generated by the mutations, non-cell-autonomous effects shape the phenotype of a cancer cell. Here, we review the evidence that a network of biological interactions between subclones drives cancer cell adaptation and amplifies intra-tumor heterogeneity. Integrating the role of mutations in tumor ecosystems generates innovative strategies targeting the tumor ecosystem's weaknesses to improve cancer treatment.

MicroRNAs in cholangiopathies: Potential diagnostic and therapeutic tools

Cholangiopathies are the group of diseases targeting the bile duct epithelial cells (i.e. cholangiocytes). These disorders arise from different etiologies and represent a current diagnostic, prognostic and therapeutic challenge. Different molecular mechanisms participate in the development and progression of each type of biliary disease. However, microRNA deregulation is a common central event occurring in all of them that plays a key role in their pathogenesis. MicroRNAs are highly stable small non-coding RNAs present in cells, extracellular microvesicles and biofluids, representing valuable diagnostic tools and potential targets for therapy. In the following sections, the most novel and significant discoveries in this field are summarized and their potential clinical value is highlighted.

Chromatography and its hyphenation to mass spectrometry for extracellular vesicle analysis

Extracellular vesicles (EVs), such as exosomes, microvesicles and apoptotic bodies are released by cells, both under physiological and pathological conditions. EVs can participate in a novel type of intercellular communication and deliver cargo of nucleic acids, proteins and lipids near or to distant host cells. EV research is proceeding at a fast pace; now they start to appear as promising therapeutic targets, diagnostic tools and drug delivery systems. Isolation and analysis of EVs are prerequisites for understanding their biological roles and for their clinical exploitation. In this process chromatography and mass spectrometry (MS)-based strategies are rapidly gaining importance; and are reviewed in the present communication. Isolation and purification of EVs is mostly performed by ultracentrifugation at present. Chromatography-based strategies are gaining ground, among which affinity and size exclusion chromatography (SEC) are particularly strong contenders. Their major advantages are the relative simplicity, robustness and throughput. Affinity chromatography has the added advantage of separating EV subtypes based on molecular recognition of EV surface motifs. SEC has the advantage that isolated EVs may retain their biological activity. EVs are typically isolated in small amounts, therefore high sensitivity is required for their analysis. Study of the molecular content of EVs (all compounds beside nucleic acids) is predominantly based on liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. The chromatographic separation is mostly performed by reverse phase, nanoscale, ultra high performance LC technique. The MS analysis relying typically on nano-electrospray ionization MS/MS provides high sensitivity, selectivity and resolution, so that thousand(s) of proteins can be detected/identified/quantified in a EV sample. Beside protein identification, quantitation and characterization of protein post-translational modifications (PTMs), like glycosylation and phosphorylation are becoming feasible and increasingly important. Along with conventional LC-MS/MS, other chromatographic approaches hyphenated to MS are gaining importance for EV characterization. Hydrophilic interaction LC is used to characterize PTMs; LC-inductively coupled plasma/MS to identify metal containing molecules; while gas chromatography-MS to analyze some lipids and metabolites.

The ability of multipotent mesenchymal stromal cells from the bone marrow of patients with leukemia to maintain normal hematopoietic progenitor cells

BACKGROUND

The development of leukemia impairs normal hematopoiesis and marrow stromal microenvironment. The aim of the investigation was to study the ability of multipotent mesenchymal stromal cells (MSCs) derived from the bone marrow of patients with leukemia to maintain normal hematopoietic progenitor cells.

METHODS

MSCs were obtained from the bone marrow of 14 patients with acute lymphoblastic (ALL), 25 with myeloid (AML), and 15 with chronic myeloid (CML) leukemia. As a control, MSCs from 22 healthy donors were used. The incidence of cobblestone area forming cells (CAFC 7-8 d) in the bone marrow of healthy donor cultivated on the supportive layer of patients MSCs was measured.

RESULTS

The ability of MSCs from AML and ALL patients at the moment of diagnosis to maintain normal CAFC was significantly decreased when compared to donors. After chemotherapy, the restoration of ALL patients' MSCs functions was slower than that of AML. CML MSCs maintained CAFC better than donors' at the moment of diagnosis and this ability increased with treatment.

CONCLUSIONS

The ability of patients' MSCs to maintain normal hematopoietic progenitor cells was shown to change in comparison with MSCs from healthy donors and depended on nosology. During treatment, the functional capacity of patients' MSCs had been partially restored.

Exosomes and CAFs: partners in crime

In this issue of Blood, Paggetti et al present novel findings that chronic lymphocytic leukemia (CLL)-derived exosomes and their molecular cargo are actively transferred to stromal cells that reside in the lymphoid tumor microenvironment (TME), promoting the reprogramming of these cells into cancer-associated fibroblasts (CAFs).

Circulating MicroRNAs as Biomarkers and Mediators of Cell-Cell Communication in Cancer

The realization of personalized medicine for cancer will rely not only on the development of new therapies, but on biomarkers that direct these therapies to the right patient. MicroRNA expression profiles in the primary tumor have been shown to differ between cancer patients and healthy individuals, suggesting they might make useful biomarkers. However, examination of microRNA expression in the primary tumor requires an invasive biopsy procedure. More recently, microRNAs have been shown to be released from the primary tumor into the circulation where they can be utilized as non-invasive biomarkers to diagnose patients, predict prognosis, or indicate therapeutic response. This review provides an overview of the current use of circulating microRNAs as biomarkers as well as recent findings on their role in regulating cell signaling interactions in the tumor microenvironment.

Exosome-mediated microenvironment dysregulation in leukemia

The hematopoietic stem cell (HSC) niche is composed of a complex set of stromal support cells that maintain HSCs and promote normal hematopoiesis. We now know that molecular changes within the hematopoietic niche contribute to leukemia development. Leukemia cells often reorganize the hematopoietic niche to promote and support their own survival and growth. Here we will summarize recent works that decipher the normal hematopoietic niche cellular components and describe how the leukemia-transformed niche contributes to hematological malignances. Finally, we will discuss recent publications that highlight a possible role for exosomes in the leukemia-induced niche reorganization. This article is part of a Special Issue entitled: Tumor Microenvironment Regulation of Cancer Cell Survival, Metastasis, Inflammation, and Immune Surveillance edited by Peter Ruvolo and Gregg L. Semenza.

Complexity in the tumour microenvironment: Cancer associated fibroblast gene expression patterns identify both common and unique features of tumour-stroma crosstalk across cancer types

Cancer is a complex disease, driven by the accumulation of several somatic aberrations but fostered by a two-way interaction between tumour cells and the surrounding microenvironment. Cancer associated fibroblasts (CAFs) represent one of the major players in tumour-stroma crosstalk. Recent in vitro and in vivo studies, often conducted by employing high throughput approaches, have started unravelling the key pathways involved in their functional effects. This review focus on open challenges in the study of CAF properties and function, highlighting at the same time the existence of common mechanisms as well as peculiarities in different cancer types (breast, prostate and lung cancer). Although still limited by current experimental models, which are unable to deal with the full level of complexity of the tumour microenvironment, a better understanding of these mechanisms may enable the identification of new biomarkers and therapeutic targets, to improve current strategies for cancer diagnosis and treatment.