Isolation and characterization of CD34+ blast-derived exosomes in acute myeloid leukemia

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.

Extracellular Vesicles: Evolving Factors in Stem Cell Biology

Stem cells are proposed to continuously secrete trophic factors that potentially serve as mediators of autocrine and paracrine activities, associated with reprogramming of the tumor microenvironment, tissue regeneration, and repair. Hitherto, significant efforts have been made to understand the level of underlying paracrine activities influenced by stem cell secreted trophic factors, as little is known about these interactions. Recent findings, however, elucidate this role by reporting the effects of stem cell derived extracellular vesicles (EVs) that mimic the phenotypes of the cells from which they originate. Exchange of genetic information utilizing persistent bidirectional communication mediated by stem cell-EVs could regulate stemness, self-renewal, and differentiation in stem cells and their subpopulations. This review therefore discusses stem cell-EVs as evolving communication factors in stem cell biology, focusing on how they regulate cell fates by inducing persistent and prolonged genetic reprogramming of resident cells in a paracrine fashion. In addition, we address the role of stem cell-secreted vesicles in shaping the tumor microenvironment and immunomodulation and in their ability to stimulate endogenous repair processes during tissue damage. Collectively, these functions ensure an enormous potential for future therapies.

Dendritic Cells as Pharmacological Tools for Cancer Immunotherapy

Although the earliest—rudimentary—attempts at exploiting the immune system for cancer therapy can be traced back to the late 18th Century, it was not until the past decade that cancer immunotherapeutics have truly entered mainstream clinical practice. Given their potential to stimulate both adaptive and innate antitumor immune responses, dendritic cells (DCs) have come under intense scrutiny in recent years as pharmacological tools for cancer immunotherapy. Conceptually, the clinical effectiveness of this form of active immunotherapy relies on the completion of three critical steps: 1) the DCs used as immunotherapeutic vehicles must properly activate the antitumor immune effector cells of the host, 2) these immune effector cells must be receptive to stimulation by the DCs and be competent to mediate their antitumor effects, which 3) requires overcoming the various immune-inhibitory mechanisms used by the tumor cells. In this review, following a brief overview of the pivotal milestones in the history of cancer immunotherapy, we will introduce the reader to the basic immunobiological and pharmacological principles of active cancer immunotherapy using DCs. We will then discuss how current research is trying to define the optimal parameters for each of the above steps to realize the full clinical potential of DC therapeutics. Given its high suitability for immune interventions, acute myeloid leukemia was chosen here to showcase the latest research trends driving the field of DC-based cancer immunotherapy.

Stem cell-derived exosomes: roles in stromal remodeling, tumor progression, and cancer immunotherapy

Stem cells are known to maintain stemness at least in part through secreted factors that promote stem-like phenotypes in resident cells. Accumulating evidence has clarified that stem cells release nano-vesicles, known as exosomes, which may serve as mediators of cell-to-cell communication and may potentially transmit stem cell phenotypes to recipient cells, facilitating stem cell maintenance, differentiation, self-renewal, and repair. It has become apparent that stem cell-derived exosomes mediate interactions among stromal elements, promote genetic instability in recipient cells, and induce malignant transformation. This review will therefore discuss the potential of stem cell-derived exosomes in the context of stromal remodeling and their ability to generate cancer-initiating cells in a tumor niche by inducing morphologic and functional differentiation of fibroblasts into tumor-initiating fibroblasts. In addition, the immunosuppressive potential of stem cell-derived exosomes in cancer immunotherapy and their prospective applications in cell-free therapies in future translational medicine is discussed.

The potential of tumor-derived exosomes for noninvasive cancer monitoring

Tumor-derived exosomes (TEX) are emerging as a new type of cancer biomarker. TEX are membrane-bound, virus-size vesicles of endocytic origin present in all body fluids of cancer patients. Based on the expanding albeit incomplete knowledge of their biogenesis, secretion by tumor cells and cancer cell-specific molecular and genetic contents, TEX are viewed as promising, clinically-relevant surrogates of cancer progression and response to therapy. Preliminary proteomic, genetic and functional profiling of tumor cell-derived or cancer plasma-derived exosomes confirms their unique characteristics. Alterations in protein or nucleic acid profiles of exosomes in plasma of cancer patients responding to therapies appear to correlate with clinical endpoints. However, methods for TEX isolation and separation from the bulk of human plasma-derived exosomes are not yet established and their role as biomarkers remains to be confirmed. Further development and validation of TEX as noninvasive, liquid equivalents of tumor biopsies are necessary to move this effort forward.

Exosomes in cancer: small particle, big player

Exosomes have emerged as a novel mode of intercellular communication. Exosomes can shuttle bioactive molecules including proteins, DNA, mRNA, as well as non-coding RNAs from one cell to another, leading to the exchange of genetic information and reprogramming of the recipient cells. Increasing evidence suggests that tumor cells release excessive amount of exosomes, which may influence tumor initiation, growth, progression, metastasis, and drug resistance. In addition, exosomes transfer message from tumor cells to immune cells and stromal cells, contributing to the escape from immune surveillance and the formation of tumor niche. In this review, we highlight the recent advances in the biology of exosomes as cancer communicasomes. We review the multifaceted roles of exosomes, the small secreted particles, in communicating with other cells within tumor microenvironment. Given that exosomes are cell type specific, stable, and accessible from body fluids, exosomes may provide promising biomarkers for cancer diagnosis and represent new targets for cancer therapy.

Tumour-derived exosomes: Tiny envelopes for big stories

The discovery of exosomes, which are small, 30-100 nm sized extracellular vesicles that are released by virtual all cells, has initiated a rapidly expanding and vibrant research field. Current investigations are mainly directed toward the role of exosomes in intercellular communication and their potential value as biomarkers for a broad set of diseases. By horizontal transfer of molecular information such as micro RNAs, messenger RNAs or proteins, as well as by receptor-cell interactions, exosomes are capable to mediate the reprogramming of surrounding cells. Herein, we review how especially cancer cells take advantage of this mechanism to influence their microenvironment in favour of immune escape, therapy resistance, tumour growth and metastasis. Moreover, we provide a comprehensive microarray analysis (n > 1970) to study the expression patterns of genes known to be intimately involved in exosome biogenesis across 26 different cancer entities and a normal tissue atlas. Consistent with the elevated production of exosomes observed in cancer patient plasma, we found a significant overexpression especially of RAB27A, CHMP4C and SYTL4 in the corresponding cancer entities as compared to matched normal tissues. Finally, we discuss the immune-modulatory and anti-tumorigenic functions of exosomes as well as innovative approaches to specifically target the exosomal circuits in experimental cancer therapy.

Mass spectrometry in leukemia research and treatment

Mass spectrometry (MS) is a complex analytical chemistry tool that allows qualitative and quantitative assessments of the components of complex chemical compounds. Applications of MS in medicine include the identification and quantification of drugs and metabolites; identification of proteins, biopolymers and disease markers and investigation of differential protein expression and proteins altered by mutations and/or post-translational changes. A variety of MS methods and technologies now play valuable and expanding roles in the diagnosis and monitoring of acute leukemia, as well as in identification of therapeutic targets and biomarkers, drug discovery, and other important areas of leukemia research. The objective of this review is to present a clinically oriented review of the roles of MS in the research, diagnosis and therapy of acute leukemia.

Information transfer by exosomes: A new frontier in hematologic malignancies

Exosomes are small (30-150 mm) vesicles secreted by all cell types and present in all body fluids. They are emerging as vehicles for delivery of membrane-tethered signaling molecules and membrane enclosed genes to target cells. Exosome-mediated information transfer allows for crosstalk of cells within the hematopoietic system and for interactions between hematopoietic cells and local or distant tissue cells. Exosomes carry physiological signals essential for health and participate in pathological processes, including malignant transformation. In hematologic malignancies, exosomes reprogram the bone marrow microenvironment, creating a niche for abnormal cells and favoring their expansion. The molecular and genetic mechanisms exosomes utilize to shuttle information between cells are currently being examined as are the potential roles exosomes play as biomarkers of disease or future therapeutic targets.

Exosomes Derived from Breast Cancer Cells, Small Trojan Horses?

Exosomes are small extracellular vesicles secreted to the extracellular environment by several cell types, including tumor cells. It has been demonstrated that exosomes have an important role in intercellular communication, but they have recently been implicated in various tumor processes, including the oncogenic transformation of cells in the tumor microenvironment, tumor drug resistance, and the transport of tumor factors. Tumors appear to use exosomes to dialogue with and transform neighboring cells to create an ideal environment for their growth and expansion. On the other hand, the structure and function of exosomes may make them useful in cancer diagnosis and prognosis, because they contain molecules that could serve as biomarkers, including oncogenes, miRNAs, and certain proteins. They have the ability to travel via body fluids, from which they could be isolated and used to transport drugs to specific targets. This review aims to provide an update on the role of exosomes derived from breast cancer cells.