Efficient production and enhanced tumor delivery of engineered extracellular vesicles

Extracellular vesicles for personalized medicine: The input of physically triggered production, loading and theranostic properties

Emerging advances in extracellular vesicle (EV) research brings along new promises for tailoring clinical treatments in order to meet specific disease features of each patient in a personalized medicine concept. EVs may act as regenerative effectors conveying endogenous therapeutic factors from parent cells or constitute a bio-camouflaged delivery system for exogenous therapeutic agents. Physical stimulation may be an important tool in the field of EVs for personalized therapy by powering EV production, loading and therapeutic properties. Physically-triggered EV production is inspired by naturally occurring EV release by shear stress in blood vessels. Bioinspired physically-triggered EV production technologies may bring along high yield advantages combined to scalability assets. Physical stimulation may also provide new prospects for high-efficient EV loading. Additionally, physically-triggered EV theranostic properties brings new hopes for spatio-temporal controlled therapy combined to tracking. Technological considerations related to EV-based personalized medicine and the input of physical stimulation on EV production, loading and theranostic properties will be overviewed herein.

Towards rationally designed biomanufacturing of therapeutic extracellular vesicles: impact of the bioproduction microenvironment

Extracellular vesicles (EVs), including exosomes, microvesicles, and others, have emerged as potential therapeutics for a variety of applications. Pre-clinical reports of EV efficacy in treatment of non-healing wounds, myocardial infarction, osteoarthritis, traumatic brain injury, spinal cord injury, and many other injuries and diseases demonstrate the versatility of this nascent therapeutic modality. EVs have also been demonstrated to be effective in humans, and clinical trials are underway to further explore their potential. However, for EVs to become a new class of clinical therapeutics, issues related to translation must be addressed. For example, approaches originally developed for cell biomanufacturing, such as hollow fiber bioreactor culture, have been adapted for EV production, but limited knowledge of how the cell culture microenvironment specifically impacts EVs restricts the possibility for rational design and optimization of EV production and potency. In this review, we discuss current knowledge of this issue and delineate potential focus areas for future research towards enabling translation and widespread application of EV-based therapeutics.

Therapeutic nanoplatforms and delivery strategies for neurological disorders

The major neurological disorders found in a central nervous system (CNS), such as brain tumors, Alzheimer's diseases, Parkinson's diseases, and Huntington's disease, have led to devastating outcomes on the human public health. Of these disorders, early diagnostics remains poor, and no treatment has been successfully discovered; therefore, they become the most life-threatening medical burdens worldwide compared to other major diseases. The major obstacles for the drug discovery are the presence of a restrictive blood-brain barrier (BBB), limiting drug entry into brains and undesired neuroimmune activities caused by untargeted drugs, leading to irreversible neuronal damages. Recent advances in nanotechnology have contributed to the development of novel nanoplatforms and effective delivering strategies to improve the CNS disorder treatment while less disturbing brain systems. The nanoscale drug carriers, including liposomes, dendrimers, viral capsids, polymeric nanoparticles, silicon nanoparticles, and magnetic/metallic nanoparticles, enable the effective drug delivery penetrating across the BBB, the aforementioned challenges in the CNS. Moreover, drugs encapsulated by the nanocarriers can reach further deeper into targeting regions while preventing the degradation. In this review, we classify novel disease hallmarks incorporated with emerging nanoplatforms, describe promising approaches for improving drug delivery to the disordered CNS, and discuss their implications for clinical practice.

Internalization of Exosomes through Receptor-Mediated Endocytosis

The tumor microenvironment is replete with factors secreted and internalized by surrounding cells. Exosomes are nano-sized, protein-embedded, membrane-bound vesicles that are released in greater quantities from cancer than normal cells and taken up by a variety of cell types. These vesicles contain proteins and genetic material from the cell of origin and in the case of tumor-derived exosomes, oncoproteins and oncogenes. With increasing understanding of the role exosomes play in basic biology, a more clear view of the potential exosomes are seen to have in cancer therapeutics emerges. However, certain essential aspects of exosome function, such as the uptake mechanisms, are still unknown. Various methods of cell-exosome interaction have been proposed, but this review focuses on the protein-protein interactions that facilitate receptor-mediated endocytosis, a broadly used mechanism by a variety of cells.

Clinical Application of Mesenchymal Stem Cell-Derived Extracellular Vesicle-Based Therapeutics for Inflammatory Lung Diseases

It is currently thought that extracellular vesicles (EVs), such as exosomes and microvesicles, play an important autocrine/paracrine role in intercellular communication. EVs package proteins, mRNA and microRNA (miRNA), which have the ability to transfer biological information to recipient cells in the lungs. Depending on their origin, EVs fulfil different functions. EVs derived from mesenchymal stem cells (MSCs) have been found to promote therapeutic activities that are comparable to MSCs themselves. Recent animal model-based studies suggest that MSC-derived EVs have significant potential as a novel alternative to whole-cell therapies. Compared to their parent cells, EVs may have a superior safety profile and can be stored without losing function. It has been observed that MSC-derived EVs suppress pro-inflammatory processes and reduce oxidative stress, pulmonary fibrosis and remodeling in a variety of in vivo inflammatory lung disease models by transferring their components. However, there remain significant challenges to translate this therapy to the clinic. From this view point, we will summarize recent studies on EVs produced by MSCs in preclinical experimental models of inflammatory lung diseases. We will also discuss the most relevant issues in bringing MSC-derived EV-based therapeutics to the clinic for the treatment of inflammatory lung diseases.

Possibility of Exosome-Based Therapeutics and Challenges in Production of Exosomes Eligible for Therapeutic Application

Exosomes are cell-derived vesicles with a diameter 30-120 nm. Exosomes contain endogenous proteins and nucleic acids; delivery of these molecules to exosome-recipient cells causes biological effects. Exosomes derived from some types of cells such as mesenchymal stem cells and dendritic cells have therapeutic potential and may be biocompatible and efficient agents against various disorders such as organ injury. However, there are many challenges for the development of exosome-based therapeutics. In particular, producing exosomal formulations is the major barrier for therapeutic application because of their heterogeneity and low productivity. Development and optimization of producing methods, including methods for isolation and storage of exosome formulations, are required for realizing exosome-based therapeutics. In addition, improvement of therapeutic potential and delivery efficiency of exosomes are important for their therapeutic application. In this review, we summarize current knowledge about therapeutic application of exosomes and discuss some challenges in their successful use.

Novel alternatives to extracellular vesicle-based immunotherapy - exosome mimetics derived from natural killer cells

Exosomes are endogenous nanocarriers that can deliver biological information between cells. They are secreted by all cell types, including immune cells such as natural killer (NK) cells. However, mammalian cells release low quantities of exosomes, and the purification of exosomes is difficult. Here, nanovesicles were developed by extrusion of NK cells through filters with progressively smaller pore sizes to obtain exosome mimetics (NK-EM). The anti-tumour effect of the NK-EM was confirmed in vitro and in vivo. The morphological features of the NK-EM were revealed by transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA) and Western blot. In vitro, the cytotoxicity of the NK-EM to cancer cells (glioblastoma, breast carcinoma, anaplastic thyroid cancer and hepatic carcinoma) was assessed using bioluminescence imaging (BLI) and CCK-8 assay. For in vivo study, a xenograft glioblastoma mouse model was established. The anti-tumour activity of NK-EM was confirmed in vivo by the significant decreases of BLI, size and weight (all p < .001) of the tumour compared with the control group. Moreover, NK-EM cytotoxicity for glioblastoma cells that related with decreased levels of the cell survival markers p-ERK and p-AKT, and increased levels of apoptosis protein markers cleaved-caspase 3, cytochrome-c and cleaved-PARP was confirmed. All those results suggest that NK-EM exert stronger killing effects to cancer cells compared with the traditional NK-Exo, at the same time, the tumour targeting ability of the NK-EM was obtained in vivo. Therefore, NK-EM might be a promising immunotherapeutic agent for treatment of cancer.

In vivo Non-invasive Imaging of Radio-Labeled Exosome-Mimetics Derived From Red Blood Cells in Mice

Exosomes are natural nano-sized membrane vesicles that have garnered recent interest owing to their potential as drug delivery vehicles. Though exosomes are effective drug carriers, their production and in vivo biodistribution are still not completely elucidated. We analyzed the production of exosome mimetics (EMs) from red blood cells (RBCs) and the radio-labeling of the RBC-EMs for in vivo imaging. Engineered EMs from RBCs were produced in large-scale by a one-step extrusion method, and further purified by density-gradient centrifugation. RBC-EMs were labeled with technetium-99m (99mTc). For non-invasive imaging, 99mTc (free) or 99mTc-RBC-EMs were injected in mice, and their biodistribution was analyzed by gamma camera imaging. Animals were sacrificed, and organs were collected for further biodistribution analysis. RBC-EMs have similar characteristics as the RBC exosomes but have a 130-fold higher production yield in terms of particle numbers. Radiochemical purity of 99mTc-RBC-EMs was almost 100% till 2 h reduced to 97% at 3 h. Radio-labeling did not affect the size and morphology of RBC-EMs. In contrast to free 99mTc, in vivo imaging of 99mTc-RBC-EMs in mice showed higher uptake in the liver and spleen, and no uptake in the thyroid. Ex vivo imaging confirmed the in vivo findings. Furthermore, fluorescent imaging confirmed the nuclear imaging findings. Immunofluorescent imaging revealed that the hepatic uptake of RBC-EMs was significantly mediated by kupffer cells (resident hepatic macrophages). Our results demonstrate a simple yet large-scale production method for a novel type of RBC-EMs, which can be effectively labeled with 99mTc, and feasibly monitored in vivo by nuclear imaging. The RBC-EMs may be used as in vivo drug delivery vehicles.

An improvised one-step sucrose cushion ultracentrifugation method for exosome isolation from culture supernatants of mesenchymal stem cells

BACKGROUND

Exosomes are nanovesicles (30-120 nm) of endosomal origin. These exosomes contain various functional proteins and RNAs that could be used for therapeutic purposes. Currently, having a standard method for exosome isolation retaining its biological properties with increased yield and purity is a major challenge. The most commonly used method is differential ultracentrifugation but it has its own disadvantages, which include high time consumption, low yield due to disruption of exosome integrity, and high protein contaminants. In this study, we have identified an improved method addressing these problems for exosome isolation using ultracentrifugation since it is cost-effective and used worldwide.

METHOD

We have compared differential ultracentrifugation with the modified method called one-step sucrose cushion ultracentrifugation for exosome isolation. The conditioned serum-free media from human mesenchymal stem cells cultured for 48 h was collected for exosome isolation. The cellular debris was removed by centrifugation at 300g for 10 min, followed by centrifugation at 10,000g for 30 min to remove microvesicles. Equal volumes of pre-processed conditioned media were used for exosome isolation by direct ultracentrifugation and one-step sucrose cushion ultracentrifugation. The exosomes isolated using these methods were characterized for their size, morphology, concentration, and surface marker protein expression.

RESULT

It was observed that the recovery of exosomes with cup-shaped morphology from one-step sucrose cushion ultracentrifugation was comparatively high as estimated by nanoparticle tracking analysis and electron microscopy. These results were confirmed by Western blotting and flow cytometry.

CONCLUSION

We conclude that this one-step sucrose cushion ultracentrifugation method provides an effective and reproducible potential standard method which could be used for various starting materials for isolating exosomes. We believe that this method will have a wide application in the field of extracellular vesicle research where exosome isolation with high yield and purity is an imperative step. Schematic representation of comparison of UC and SUC exosome isolation methods for tissue-specific human mesenchymal stem cells. The SUC isolation method yields a greater number of cup-shaped exosomes with a relatively homogenous population for mass-scale production of exosomes for downstream analysis.

ABBREVIATIONS

SUC One-step sucrose cushion ultracentrifugation, UC Direct ultracentrifugation.

Targeting and Therapy of Glioblastoma in a Mouse Model Using Exosomes Derived From Natural Killer Cells

OBJECTIVE

Glioblastoma is a highly aggressive primary brain tumor that is resistant to radiotherapy and chemotherapy. Natural killer (NK) cells have been used to treat incurable cancers. Recent studies have investigated the effectiveness of NK-cell-derived exosomes (NK-Exo) for treating incurable cancers such as melanoma, leukemia, and neuroblastoma; however, NK-Exo have not been used to treat glioblastoma. In the present study, we investigated the antitumor effects of NK-Exo against aggressive glioblastoma both in vitro and in vivo and determined the tumor-targeting ability of NK-Exo by performing fluorescence imaging.

METHODS

U87/MG cells were transfected with the enhanced firefly luciferase (effluc) and thy1.1 genes; thy1.1-positive cells were selected using microbeads. U87/MG/F cells were assessed by reverse transcription polymerase chain reaction (RT-PCR), western blotting, and luciferase-activity assays. NK-Exo were isolated by ultracentrifugation, purified by density gradient centrifugation, and characterized by transmission electron microscopy, dynamic light scattering (DLS), nanoparticle-tracking analysis (NTA), and western blotting. Cytokine levels in NK-Exo were compared to those in NK cells and NK-cell medium by performing an enzyme-linked immunosorbent assay (ELISA). NK-Exo-induced apoptosis of cancer cells was confirmed by flow cytometry and western blotting. In vivo therapeutic effects and specificity of NK-Exo against glioblastoma were assessed in a xenograft mouse model by fluorescence imaging. Xenograft mice were treated with NK-Exo, which was administered seven times through the tail vein. Tumor growth was monitored by bioluminescence imaging (BLI), and tumor volume was measured by ultrasound imaging. The mice were intraperitoneally injected with dextran sulfate 2 h before NK-Exo injection to decrease the liver uptake and increase the tumor specificity of NK-Exo.

RESULTS

RT-PCR and western blotting confirmed the gene and protein expression of effluc in U87/MG/F cells, with the bioluminescence activity of U87/MG/F cells increasing with an increase in cell number. NTA and DLS results indicated that the size of NK-Exo was ~100 nm, and the western blot results confirmed that NK-Exo expressed exosome markers CD63 and Alix. We confirmed the in vitro cytotoxic effects of NK-Exo on U87/MG/F cells by performing BLI, and the killing effect on U87/MG and U87MG/F cells was measured by CCK-8 and MTT assays (p < 0.001). ELISA results indicated that NK-Exo contained tumor necrosis factor-α and granzyme B. In vivo NK-Exo treatment inhibited tumor growth compared to in control mice (p < 0.001), and pretreatment of xenograft mice with dextran sulfate 2 h before NK-Exo treatment increased the antitumor effect of NK-Exo (p < 0.01) compared to in control and NK-Exo-alone-treated mice.

CONCLUSION

NK-Exo targeted and exerted antitumor effects on glioblastoma cells both in vitro and in vivo, suggesting their utility in treating incurable glioblastoma.

An Update on in Vivo Imaging of Extracellular Vesicles as Drug Delivery Vehicles

Extracellular vesicles (EVs) are currently being considered as promising drug delivery vehicles. EVs are naturally occurring vesicles that exhibit many characteristics favorable to serve as drug delivery vehicles. In addition, EVs have inherent properties for treatment of cancers and other diseases. For research and clinical translation of use of EVs as drug delivery vehicles, in vivo tracking of EVs is essential. The latest molecular imaging techniques enable the tracking of EVs in living animals. However, each molecular imaging technique has its certain advantages and limitations for the in vivo imaging of EVs; therefore, understanding the molecular imaging techniques is essential to select the most appropriate imaging technology to achieve the desired imaging goal. In this review, we summarize the characteristics of EVs as drug delivery vehicles and the molecular imaging techniques used in visualizing and monitoring EVs in in vivo environments. Furthermore, we provide a perceptual vision of EVs as drug delivery vehicles and in vivo monitoring of EVs using molecular imaging technologies.

Scalable, cGMP-compatible purification of extracellular vesicles carrying bioactive human heterodimeric IL-15/lactadherin complexes

The development of extracellular vesicles (EV) for therapeutic applications is contingent upon the establishment of reproducible, scalable, and high-throughput methods for the production and purification of clinical grade EV. Methods including ultracentrifugation (U/C), ultrafiltration, immunoprecipitation, and size-exclusion chromatography (SEC) have been employed to isolate EV, each facing limitations such as efficiency, particle purity, lengthy processing time, and/or sample volume. We developed a cGMP-compatible method for the scalable production, concentration, and isolation of EV through a strategy involving bioreactor culture, tangential flow filtration (TFF), and preparative SEC. We applied this purification method for the isolation of engineered EV carrying multiple complexes of a novel human immunostimulatory cytokine-fusion protein, heterodimeric IL-15 (hetIL-15)/lactadherin. HEK293 cells stably expressing the fusion cytokine were cultured in a hollow-fibre bioreactor. Conditioned medium was collected and EV were isolated comparing three procedures: U/C, SEC, or TFF + SEC. SEC demonstrated comparable particle recovery, size distribution, and hetIL-15 density as U/C purification. Relative to U/C, SEC preparations achieved a 100-fold reduction in ferritin concentration, a major protein-complex contaminant. Comparative proteomics suggested that SEC additionally decreased the abundance of cytoplasmic proteins not associated with EV. Combination of TFF and SEC allowed for bulk processing of large starting volumes, and resulted in bioactive EV, without significant loss in particle yield or changes in size, morphology, and hetIL-15/lactadherin density. Taken together, the combination of bioreactor culture with TFF + SEC comprises a scalable, efficient method for the production of highly purified, bioactive EV carrying hetIL-15/lactadherin, which may be useful in targeted cancer immunotherapy approaches.

Biocompatibility of highly purified bovine milk-derived extracellular vesicles

Extracellular vesicles (EVs) deliver biologically active cargos from donor cells to recipient cells for intercellular communication. Since the existence of RNA cargo was discovered, EVs have been considered to be useful drug-delivery systems. Specifically, EVs from bovine milk (mEV) are one of the most promising platforms, since bovine milk is a scalable source of EVs for mass production. However, it is still difficult to isolate pure EVs from bovine milk owing to the complexity of raw materials. Furthermore, the biocompatibility and immunotoxicity of mEVs are still unclear. In this study, we developed a new method for isolating bovine milk-derived EVs by employing acid treatment and ultracentrifugation. Isolated mEVs are spherical in shape, measure 120 nm in diameter and contain typical EV marker proteins, such as tetraspanins. Compared with the previously reported method, our method can isolate purer mEVs. When mEVs are contacted with the mouse macrophage cell line Raw264.7, mEVs are readily taken up by the cells without a cytotoxic effect, suggesting that mEVs can deliver the cargo molecules into cells. While systemic administration of mEVs into mice resulted in the absence of systemic toxicity, certain types of cytokines were slightly induced. No anaphylaxis effect was observed after serial administration of mEVs in mice. Thus, mEVs isolated using our method are well tolerated in vivo and may be useful for the drug-delivery application.

Extracellular vesicle therapeutics for liver disease

Extracellular vesicles (EVs) are endogenous nanoparticles that play important roles in intercellular communication. Unmodified and engineered EVs can be utilized for therapeutic purposes. For instance, mesenchymal stem cell (MSC)-derived EVs have shown promise for tissue repair, while drug-loaded EVs have the potential to be used for cancer treatment. The liver is an ideal target for EV therapy due to the intrinsic regenerative capacity of hepatic tissue and the tropism of systemically injected nanovesicles for this organ. This review will give an overview of the potential of EV therapeutics in liver disease. Specifically, the mechanisms by which MSC-EVs induce liver repair will be covered. Moreover, the use of drug-loaded EVs for the treatment of hepatocellular carcinoma will also be discussed. Although there are several challenges associated with the clinical translation of EVs, these biological nanoparticles represent a promising new therapeutic modality for liver disease.

Use of a Hollow Fiber Bioreactor to Collect Extracellular Vesicles from Cells in Culture

Current approaches for collection of extracellular vesicles (EV) are based on classical cell culture media production. This involves collection from cells grown in flasks, and can require multiple rounds of centrifugation or filtration, followed by ultracentrifugation or density gradient centrifugation. There are several limitations of these approaches, for example, they require a large input volume, the yield and concentration is low, and the process is time consuming. Most cell cultures require the use of fetal bovine serum which contains a large amount of endogenous EV that can contaminate isolations of cell-derived EVs. The use of cell cultures within a hollow fiber bioreactor could address many of these limitations and produce a continuous source of highly concentrated EVs without contamination from serum EVs, and that are suitable for downstream applications.

Therapeutic application of extracellular vesicles in kidney disease: promises and challenges

Extracellular vesicles (EVs) are nanosized, membrane‐bound vesicles released from different cells. Recent studies have revealed that EVs may participate in renal tissue damage and regeneration through mediating inter‐nephron communication. Thus, the potential use of EVs as therapeutic vector has gained considerable interest. In this review, we will discuss the basic characteristics of EVs and its role in nephron cellular communication. Then, the application of EVs as therapeutic vector based on its natural content or as carriers of drug, in acute and chronic kidney injury, was discussed. Finally, perspectives and challenges of EVs in therapy of kidney disease were described.

Toward Exosome-Based Therapeutics: Isolation, Heterogeneity, and Fit-for-Purpose Potency

Exosomes are defined as submicron (30-150 nm), lipid bilayer-enclosed extracellular vesicles (EVs), specifically generated by the late endosomal compartment through fusion of multivesicular bodies with the plasma membrane. Produced by almost all cells, exosomes were originally considered to represent just a mechanism for jettisoning unwanted cellular moieties. Although this may be a major function in most cells, evolution has recruited the endosomal membrane-sorting pathway to duties beyond mere garbage disposal, one of the most notable examples being its cooption by retroviruses for the generation of Trojan virions. It is, therefore, tempting to speculate that certain cell types have evolved an exosome subclass active in intracellular communication. We term this EV subclass "signalosomes" and define them as exosomes that are produced by the "signaling" cells upon specific physiological or environmental cues and harbor cargo capable of modulating the programming of recipient cells. Our recent studies have established that signalosomes released by mesenchymal stem/stromal cells (MSCs) represent the main vector of MSC immunomodulation and therapeutic action in animal models of lung disease. The efficacy of MSC-exosome treatments in a number of preclinical models of cardiovascular and pulmonary disease supports the promise of application of exosome-based therapeutics across a wide range of pathologies within the near future. However, the full realization of exosome therapeutic potential has been hampered by the absence of standardization in EV isolation, and procedures for purification of signalosomes from the main exosome population. This is mainly due to immature methodologies for exosome isolation and characterization and our incomplete understanding of the specific characteristics and molecular composition of signalosomes. In addition, difficulties in defining metrics for potency of exosome preparations and the challenges of industrial scale-up and good manufacturing practice compliance have complicated smooth and timely transition to clinical development. In this manuscript, we focus on cell culture conditions, exosome harvesting, dosage, and exosome potency, providing some empirical guidance and perspectives on the challenges in bringing exosome-based therapies to clinic.

The potential and promise of IL-15 in immuno-oncogenic therapies

This review provides an in-depth description of the preclinical and clinical studies demonstrating the effectiveness and limitations of IL-15 and IL-15 analogs given as an exogenous immuno-oncology agent. IL-15 is a cytokine that primarily stimulates the proliferation and cytotoxic functions of CD8T cells and NK cells leading to enhanced anti-tumor responses. While initially showing promise as a cancer therapeutic, the efficacy of IL-15 was limited by its short in vivo half-life. More recently, various approaches have been developed to improve the in vivo half-life and efficacy of IL-15, largely by generating IL-15/IL-15Rα conjugates. These new IL-15 based agents renew the prospect of IL-15 as a cancer immunotherapeutic agent. While having some efficacy in inducing tumor regression as a monotherapy, IL-15 agents also show great potential in being used in combination with other immuno-oncological therapies. Indeed, IL-15 used in combination therapy yields even better anti-tumor responses and prolongs survival than IL-15 treatment alone in numerous murine cancer models. The promising results from these preclinical studies have led to the implementation of several clinical trials to test the safety and efficacy of IL-15-based agents as a stand-alone treatment or in conjunction with other therapies to treat both advanced solid tumors and hematological malignancies.

Impact of cell culture parameters on production and vascularization bioactivity of mesenchymal stem cell-derived extracellular vesicles

Mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs) have emerged as potential therapeutic agents for numerous applications. EVs offer potential advantages over cell-based therapies with regard to safety, stability and clearance profiles, however production and potency limitations must be addressed to enable eventual translation of EV-based approaches. Thus, we sought to examine the role of specific cell culture parameters on MSC EV production and bioactivity toward informing rational design parameters for scalable EV biomanufacturing. We report significantly reduced MSC EV vascularization bioactivity, as measured by an endothelial cell gap closure assay, with increasing passage in culture by trypsinization, especially beyond passage 4. We further show that increased frequency of EV collection yielded higher numbers of EVs from the same initial number of MSCs over a 24 hr period. Finally, we demonstrate that decreased cell seeding density in culture flasks resulted in increased production of EVs per cell in MSCs and other cell types. Overall, these studies highlight the need for careful consideration of the parameters of cell passage number and cell seeding density in the production of therapeutic EVs at laboratory scale and for rational design of large-scale EV biomanufacturing schemes.

Labeling Extracellular Vesicles for Nanoscale Flow Cytometry

Extracellular vesicles (EVs), including exosomes and microvesicles, are 30-800 nm vesicles that are released by most cell types, as biological packages for intercellular communication. Their importance in cancer and inflammation makes EVs and their cargo promising biomarkers of disease and cell-free therapeutic agents. Emerging high-resolution cytometric methods have created a pressing need for efficient fluorescent labeling procedures to visualize and detect EVs. Suitable labels must be bright enough for one EV to be detected without the generation of label-associated artifacts. To identify a strategy that robustly labels individual EVs, we used nanoFACS, a high-resolution flow cytometric method that utilizes light scattering and fluorescence parameters along with sample enumeration, to evaluate various labels. Specifically, we compared lipid-, protein-, and RNA-based staining methods and developed a robust EV staining strategy, with the amine-reactive fluorescent label, 5-(and-6)-Carboxyfluorescein Diacetate Succinimidyl Ester, and size exclusion chromatography to remove unconjugated label. By combining nanoFACS measurements of light scattering and fluorescence, we evaluated the sensitivity and specificity of EV labeling assays in a manner that has not been described for other EV detection methods. Efficient characterization of EVs by nanoFACS paves the way towards further study of EVs and their roles in health and disease.

Higher functionality of extracellular vesicles isolated using size-exclusion chromatography compared to ultracentrifugation

Extracellular vesicles (EVs) are nano-sized, lipid bilayer-enclosed particles involved in intercellular communication. EVs are increasingly being considered as drug delivery vehicles or as cell-free approach to regenerative medicine. However, one of the major challenges for their clinical application is finding a scalable EV isolation method that yields functional EVs. Although the golden standard for EV isolation is ultracentrifugation (UC), a recent study suggested that isolation using size-exclusion chromatography (SEC) yielded EVs with more intact biophysical properties. Whether this also leads to differences in functionality remained to be investigated. Therefore, we investigated possible differences in functionality of cardiomyocyte progenitor cell-derived EVs isolated using UC and SEC. Western blot analysis showed higher pERK/ERK ratios in endothelial cells after stimulation with SEC-EVs compared to UC-EVs, indicating that SEC-EVs bear higher functionality. Therefore, we propose to use SEC-EVs for further investigation of EVs' therapeutic potential. Further optimization of isolation protocols may accelerate clinical adoption of therapeutic EVs.

Exosomes in Cancer Nanomedicine and Immunotherapy: Prospects and Challenges

Exosomes (versatile, cell-derived nanovesicles naturally endowed with exquisite target-homing specificity and the ability to surmount in vivo biological barriers) hold substantial promise for developing exciting approaches in drug delivery and cancer immunotherapy. Specifically, bioengineered exosomes are being successfully deployed to deliver potent tumoricidal drugs (siRNAs and chemotherapeutic compounds) preferentially to cancer cells, while a new generation of exosome-based therapeutic cancer vaccines has produced enticing results in early-phase clinical trials. Here, we review the state-of-the-art technologies and protocols, and discuss the prospects and challenges for the clinical development of this emerging class of therapeutics.

Pharmacokinetics of Exosomes-An Important Factor for Elucidating the Biological Roles of Exosomes and for the Development of Exosome-Based Therapeutics

Exosomes are small membrane vesicles containing lipids, proteins, and nucleic acids. Recently, researchers have uncovered that exosomes are involved in various biological events, such as tumor growth, metastasis, and the immune response, by delivering their cargos to exosome-receiving cells. Moreover, exosomes are expected to be used in therapeutic treatments, such as tissue regeneration therapy and antitumor immunotherapy, because exosomes are effective delivery vehicles for proteins, nucleic acids, and other bioactive compounds. To elucidate the biological functions of exosomes, and for the development of exosome-based therapeutics, the pharmacokinetics of exosomes is important. In this review, we aim to summarize current knowledge about the pharmacokinetics and biodistribution of exosomes. The pharmacokinetics of exogenously administered exosomes is discussed based on the tissue distribution, types of cells taking up exosomes, and key molecules in the pharmacokinetics of exosomes. In addition, recent progress in the methods to control the pharmacokinetics of exosomes is reviewed.

Functional Roles and Therapeutic Applications of Exosomes in Hepatocellular Carcinoma

Exosomes are important in intercellular communication. They assure the horizontal transfer of specific functional contents (i.e., proteins, lipids, RNA molecules, and circulating DNA) from donor to recipient cells. Notably, tumor-derived exosomes (TDEs) appear to be an important vehicle of specific signals in cancer, impacting on tumor growth and metastasis. Recent researches point to the characterization of exosomes in Hepatocellular Carcinoma (HCC), the major adult liver malignancy. In this review, we summarize current findings on HCC exosomes, focusing on the identification of noncoding RNAs as exosome-enriched functional regulators and new potential biomarkers. The great potential of exosomes in future HCC diagnostic and therapeutic approaches is underlined.

Exosome-Based Cancer Therapy: Implication for Targeting Cancer Stem Cells

Drug resistance, difficulty in specific targeting and self-renewal properties of cancer stem cells (CSCs) all contribute to cancer treatment failure and relapse. CSCs have been suggested as both the seeds of the primary cancer, and the roots of chemo- and radio-therapy resistance. The ability to precisely deliver drugs to target CSCs is an urgent need for cancer therapy, with nanotechnology-based drug delivery system being one of the most promising tools to achieve this in the clinic. Exosomes are cell-derived natural nanometric vesicles that are widely distributed in body fluids and involved in multiple disease processes, including tumorigenesis. Exosome-based nanometric vehicles have a number of advantages: they are non-toxic, non-immunogenic, and can be engineered to have robust delivery capacity and targeting specificity. This enables exosomes as a powerful nanocarrier to deliver anti-cancer drugs and genes for CSC targeting therapy. Here, we will introduce the current explorations of exosome-based delivery system in cancer therapy, with particular focus on several exosomal engineering approaches that have improved their efficiency and specificity for CSC targeting.

Supramolecular hydrogel based on high-solid-content mPECT nanoparticles and cyclodextrins for local and sustained drug delivery

A novel injectable and high-solid-content drug-loaded supramolecular hydrogel (PTX-mPECT NP/α-CD^gel) was prepared by self-assembly of inclusion complexes based on PTX-loaded mPECT nanoparticles and α-cyclodextrin.

Cell type-specific and common characteristics of exosomes derived from mouse cell lines: Yield, physicochemical properties, and pharmacokinetics

Exosomes are small membrane vesicles secreted from cells and are expected to be used as drug delivery systems. Important characteristics of exosomes, such as yield, physicochemical properties, and pharmacokinetics, may be different among different cell types. However, there is limited information about the effect of cell type on these characteristics. In the present study, we evaluated these characteristics of exosomes derived from five different types of mouse cell lines: B16BL6 murine melanoma cells, C2C12 murine myoblast cells, NIH3T3 murine fibroblasts cells, MAEC murine aortic endothelial cells, and RAW264.7 murine macrophage-like cells. Exosomes were collected using a differential ultracentrifugation method. The exosomes collected from all the cell types were negatively charged globular vesicles with a diameter of approximately 100nm. C2C12 and RAW264.7 cells produced more exosomes than the other types of cells. The exosomes were labeled with a fusion protein of Gaussia luciferase and lactadherin to evaluate their pharmacokinetics. After intravenous injection into mice, all the exosomes rapidly disappeared from the systemic circulation and mainly distributed to the liver. In conclusion, the exosome yield was significantly different among the cell types, and all the exosomes evaluated in this study showed comparable physicochemical and pharmacokinetic properties.