Surface functionalization strategies of extracellular vesicles

Label-Free Isolation of Exosomes Using Microfluidic Technologies

Exosomes are cell-derived structures packaged with lipids, proteins, and nucleic acids. They exist in diverse bodily fluids and are involved in physiological and pathological processes. Although their potential for clinical application as diagnostic and therapeutic tools has been revealed, a huge bottleneck impeding the development of applications in the rapidly burgeoning field of exosome research is an inability to efficiently isolate pure exosomes from other unwanted components present in bodily fluids. To date, several approaches have been proposed and investigated for exosome separation, with the leading candidate being microfluidic technology due to its relative simplicity, cost-effectiveness, precise and fast processing at the microscale, and amenability to automation. Notably, avoiding the need for exosome labeling represents a significant advance in terms of process simplicity, time, and cost as well as protecting the biological activities of exosomes. Despite the exciting progress in microfluidic strategies for exosome isolation and the countless benefits of label-free approaches for clinical applications, current microfluidic platforms for isolation of exosomes are still facing a series of problems and challenges that prevent their use for clinical sample processing. This review focuses on the recent microfluidic platforms developed for label-free isolation of exosomes including those based on sieving, deterministic lateral displacement, field flow, and pinched flow fractionation as well as viscoelastic, acoustic, inertial, electrical, and centrifugal forces. Further, we discuss advantages and disadvantages of these strategies with highlights of current challenges and outlook of label-free microfluidics toward the clinical utility of exosomes.

Extracellular Vesicles Tropism: A Comparative Study between Passive Innate Tropism and the Active Engineered Targeting Capability of Lymphocyte-Derived EVs

Cellular communications take place thanks to a well-connected network of chemical–physical signals, biomolecules, growth factors, and vesicular messengers that travel inside or between cells. A deep knowledge of the extracellular vesicle (EV) system allows for a better understanding of the whole series of phenomena responsible for cell proliferation and death. To this purpose, here, a thorough immuno-phenotypic characterization of B-cell EV membranes is presented. Furthermore, the cellular membrane of B lymphocytes, Burkitt lymphoma, and human myeloid leukemic cells were characterized through cytofluorimetry assays and fluorescent microscopy analysis. Through cytotoxicity and internalization tests, the tropism of B lymphocyte-derived EVs was investigated toward the parental cell line and two different cancer cell lines. In this study, an innate capability of passive targeting of the native EVs was distinguished from the active targeting capability of monoclonal antibody-engineered EVs, able to selectively drive the vesicles, enhancing their internalization into the target cancer cells. In particular, the specific targeting ability of anti-CD20 engineered EVs towards Daudi cells, highly expressing CD20 marker on their cell membrane, was proved, while almost no internalization events were observed in HL60 cells, since they did not express an appreciable amount of the CD20 marker on their plasma membranes.

Biomembrane-based nanostructures for cancer targeting and therapy: From synthetic liposomes to natural biomembranes and membrane-vesicles

The translational success of liposomes in chemotherapeutics has already demonstrated the great potential of biomembrane-based nanostructure in effective drug delivery. Meanwhile, increasing efforts are being dedicated to the application of naturally derived lipid membranes, including cellular membranes and extracellular vesicles in anti-cancer therapies. While synthetic liposomes support superior multifunctional flexibility, natural biomembrane materials possess interesting biomimetic properties and can also be further engineered for intelligent design. Despite being remarkably different from each other in production and composition, the phospholipid bilayer structure in common allows liposomes, cell membrane-derived nanomaterials, and extracellular vesicles to be modified, functionalized, and exploited in many similar manners against challenges posed by tumor-targeted drug delivery. This review will summarize the recent advancements in engineering the membrane-derived nanostructures with "intelligent" modules to respond, regulate, and target tumor cells and the microenvironment to fight against malignancy. We will also discuss perspectives of combining engineered functionalities with naturally occurring activity for enhanced cancer therapy.

Evaluation of In Vivo Toxicity of Biological Nanoparticles

Biologically derived nanoparticles such as extracellular vesicles are promising candidates for therapeutic applications. In vivo toxicity of biological nanoparticles can result in tissue or organ damage, immunological perturbations, or developmental effects but cannot be readily predicted from in vitro studies. Therefore, an essential component of the preclinical assessment of these particles for their use as therapeutics requires screening for adverse effects and detailed characterization of their toxicity in vivo. However, there are no standardized, comprehensive methods to evaluate the toxicity profile of nanoparticle treatment in a preclinical model. Here, we first describe a method to prepare bovine milk-derived nanovesicles (MNVs). These MNVs are inexpensive to isolate, have a scalable production platform, and can be modified to achieve a desired biological effect. We also describe two vertebrate animal models, mice and zebrafish, that can be employed to evaluate the toxicity profile of biologically derived nanoparticles, using MNVs as an example. Treatment-induced organ toxicity and immunological effects can be assessed in mice receiving systemic injections of MNVs, and developmental toxicity can be assessed in zebrafish embryos exposed to MNVs in embryo water. Utilizing these animal models provides opportunities to analyze the toxicity profiles of therapeutic extracellular vesicles in vivo. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Preparation of milk-derived nanovesicles Basic Protocol 2: In vivo screening for organ toxicity and immune cell profiling using mice Basic Protocol 3: In vivo developmental toxicity screening using zebrafish.

Development of Extracellular Vesicle Therapeutics: Challenges, Considerations, and Opportunities

Extracellular vesicles (EVs) hold great promise as therapeutic modalities due to their endogenous characteristics, however, further bioengineering refinement is required to address clinical and commercial limitations. Clinical applications of EV-based therapeutics are being trialed in immunomodulation, tissue regeneration and recovery, and as delivery vectors for combination therapies. Native/biological EVs possess diverse endogenous properties that offer stability and facilitate crossing of biological barriers for delivery of molecular cargo to cells, acting as a form of intercellular communication to regulate function and phenotype. Moreover, EVs are important components of paracrine signaling in stem/progenitor cell-based therapies, are employed as standalone therapies, and can be used as a drug delivery system. Despite remarkable utility of native/biological EVs, they can be improved using bio/engineering approaches to further therapeutic potential. EVs can be engineered to harbor specific pharmaceutical content, enhance their stability, and modify surface epitopes for improved tropism and targeting to cells and tissues in vivo. Limitations currently challenging the full realization of their therapeutic utility include scalability and standardization of generation, molecular characterization for design and regulation, therapeutic potency assessment, and targeted delivery. The fields' utilization of advanced technologies (imaging, quantitative analyses, multi-omics, labeling/live-cell reporters), and utility of biocompatible natural sources for producing EVs (plants, bacteria, milk) will play an important role in overcoming these limitations. Advancements in EV engineering methodologies and design will facilitate the development of EV-based therapeutics, revolutionizing the current pharmaceutical landscape.

Amelioration of systemic inflammation via the display of two different decoy protein receptors on extracellular vesicles

Extracellular vesicles (EVs) can be functionalized to display specific protein receptors on their surface. However, surface-display technology typically labels only a small fraction of the EV population. Here, we show that the joint display of two different therapeutically relevant protein receptors on EVs can be optimized by systematically screening EV-loading protein moieties. We used cytokine-binding domains derived from tumour necrosis factor receptor 1 (TNFR1) and interleukin-6 signal transducer (IL-6ST), which can act as decoy receptors for the pro-inflammatory cytokines tumour necrosis factor alpha (TNF-α) and IL-6, respectively. We found that the genetic engineering of EV-producing cells to express oligomerized exosomal sorting domains and the N-terminal fragment of syntenin (a cytosolic adaptor of the single transmembrane domain protein syndecan) increased the display efficiency and inhibitory activity of TNFR1 and IL-6ST and facilitated their joint display on EVs. In mouse models of systemic inflammation, neuroinflammation and intestinal inflammation, EVs displaying the cytokine decoys ameliorated the disease phenotypes with higher efficacy as compared with clinically approved biopharmaceutical agents targeting the TNF-α and IL-6 pathways.

A Comprehensive Review on the Applications of Exosomes and Liposomes in Regenerative Medicine and Tissue Engineering

Tissue engineering and regenerative medicine are generally concerned with reconstructing cells, tissues, or organs to restore typical biological characteristics. Liposomes are round vesicles with a hydrophilic center and bilayers of amphiphiles which are the most influential family of nanomedicine. Liposomes have extensive research, engineering, and medicine uses, particularly in a drug delivery system, genes, and vaccines for treatments. Exosomes are extracellular vesicles (EVs) that carry various biomolecular cargos such as miRNA, mRNA, DNA, and proteins. As exosomal cargo changes with adjustments in parent cells and position, research of exosomal cargo constituents provides a rare chance for sicknesses prognosis and care. Exosomes have a more substantial degree of bioactivity and immunogenicity than liposomes as they are distinctly chiefly formed by cells, which improves their steadiness in the bloodstream, and enhances their absorption potential and medicinal effectiveness in vitro and in vivo. In this review, the crucial challenges of exosome and liposome science and their functions in disease improvement and therapeutic applications in tissue engineering and regenerative medicine strategies are prominently highlighted.

Current strategies in tailoring methods for engineered exosomes and future avenues in biomedical applications

Exosomes are naturally occurring nanovesicles of endosomal origin, responsible for cellular communication. Depending on the cell type, exosomes display disparity in the cargo and are involved in up/down regulation of different biological pathways. Naturally secreted exosomes, owing to their inherent delivery potential, non-immunogenic nature and limited structural resemblance to the cells have emerged as ideal candidates for various drug delivery and therapeutic applications. Moreover, the structural versatility of exosomes provides greater flexibility for surface modifications to be made in the native configuration, by different methods, like genetic-engineering, chemical procedures, physical methods and microfluidic-technology, to enhance the cargo quality for expanded biomedical applications. Post isolation and prior to engineering exosomes for various applications, the internal and external structural compositions of exosomes are studied via different techniques. Efficiency and scalability of the exosome modification methods are pivotal in determining the scope of the technique for clinical applications. This review majorly focuses on different methods employed for engineering exosomes, and advantages/disadvantages associated with different tailoring approaches, along with the efficacy of engineered exosomes in biomedical applications. Further, the review highlights the importance of a relatively recent avenue for delivery of exosomes via scaffold-based delivery of naïve/engineered exosomes for regenerative medicine and tissue engineering. This review is based on the recent knowledge generated in this field and our comprehension in this domain.

Biodistribution of Exosomes and Engineering Strategies for Targeted Delivery of Therapeutic Exosomes

Exosomes are cell-secreted nano-sized vesicles which deliver diverse biological molecules for intercellular communication. Due to their therapeutic potential, exosomes have been engineered in numerous ways for efficient delivery of active pharmaceutical ingredients to various target organs, tissues, and cells. In vivo administered exosomes are normally delivered to the liver, spleen, kidney, lung, and gastrointestinal tract and show rapid clearance from the blood circulation after systemic injection. The biodistribution and pharmacokinetics (PK) of exosomes can be modulated by engineering various factors such as cellular origin and membrane protein composition of exosomes. Recent advances accentuate the potential of targeted delivery of engineered exosomes even to the most challenging organs including the central nervous system. Major breakthroughs have been made related to various imaging techniques for monitoring in vivo biodistribution and PK of exosomes, as well as exosomal surface engineering technologies for inducing targetability. For inducing targeted delivery, therapeutic exosomes can be engineered to express various targeting moieties via direct modification methods such as chemically modifying exosomal surfaces with covalent/non-covalent bonds, or via indirect modification methods by genetically engineering exosome-producing cells. In this review, we describe the current knowledge of biodistribution and PK of exosomes, factors determining the targetability and organotropism of exosomes, and imaging technologies to monitor in vivo administered exosomes. In addition, we highlight recent advances in strategies for inducing targeted delivery of exosomes to specific organs and cells.

Drug Delivery to the Bone Microenvironment Mediated by Exosomes: An Axiom or Enigma

The increasing incidence of bone-related disorders is causing a burden on the clinical scenario. Even though bone is one of the tissues that possess tremendous regenerative potential, certain bone anomalies need therapeutic intervention through appropriate delivery of a drug. Among several nanosystems and biologics that offer the potential to contribute towards bone healing, the exosomes from the class of extracellular vesicles are outstanding. Exosomes are extracellular nanovesicles that, apart from the various advantages, are standing out of the crowd for their ability to conduct cellular communication. The internal cargo of the exosomes is leading to its potential use in therapeutics. Exosomes are being unraveled in terms of the mechanism as well as application in targeting various diseases and tissues. Through this review, we have tried to understand and review all that is already established and the gap areas that still exist in utilizing them as drug delivery vehicles targeting the bone. The review highlights the potential of the exosomes towards their contribution to the drug delivery scenario in the bone microenvironment. A comparison of the pros and cons of exosomes with other prevalent drug delivery systems is also done. A section on the patents that have been generated so far from this field is included.

Omics Approaches for Understanding Biogenesis, Composition and Functions of Fungal Extracellular Vesicles

Extracellular vesicles (EVs) are lipid bilayer structures released by organisms from all kingdoms of life. The diverse biogenesis pathways of EVs result in a wide variety of physical properties and functions across different organisms. Fungal EVs were first described in 2007 and different omics approaches have been fundamental to understand their composition, biogenesis, and function. In this review, we discuss the role of omics in elucidating fungal EVs biology. Transcriptomics, proteomics, metabolomics, and lipidomics have each enabled the molecular characterization of fungal EVs, providing evidence that these structures serve a wide array of functions, ranging from key carriers of cell wall biosynthetic machinery to virulence factors. Omics in combination with genetic approaches have been instrumental in determining both biogenesis and cargo loading into EVs. We also discuss how omics technologies are being employed to elucidate the role of EVs in antifungal resistance, disease biomarkers, and their potential use as vaccines. Finally, we review recent advances in analytical technology and multi-omic integration tools, which will help to address key knowledge gaps in EVs biology and translate basic research information into urgently needed clinical applications such as diagnostics, and immuno- and chemotherapies to fungal infections.

M. de Rosales R. Radiolabelling of Extracellular Vesicles for PET and SPECT imaging

Extracellular vesicles (EVs) such as exosomes and microvesicles have gained recent attention as potential biomarkers of disease as well as nanomedicinal tools, but their behaviour in vivo remains mostly unexplored. In order to gain knowledge of their in vivo biodistribution it is important to develop imaging tools that allow us to track EVs over time and at the whole-body level. Radionuclide-based imaging (PET and SPECT) have properties that allow us to do so efficiently, mostly due to their high sensitivity, imaging signal tissue penetration, and accurate quantification. Furthermore, they can be easily translated from animals to humans. In this review, we summarise and discuss the different studies that have used PET or SPECT to study the behaviour of EVs in vivo. With a focus on the different radiolabelling methods used, we also discuss the advantages and disadvantages of each one, and the challenges of imaging EVs due to their variable stability and heterogeneity.

General and mild modification of food-derived extracellular vesicles for enhanced cell targeting

Food-derived extracellular vesicles (FDEVs) have attracted increasing attention as potential delivery vehicles for therapeutic agents due to their desirable features such as excellent biocompatibility, easy accessibility and cost effectiveness. However, the intrinsic targeting capability of FDEVs is unsatisfactory compared to artificial nanoparticles or other source-derived EVs, which calls for efficient surface engineering strategies to equip them with specific ligands. Here we report a general and mild modification method via reduction of disulfide groups to maleimide reactive thiols. Taking milk-derived EVs (mEVs) as a model system, we demonstrated the feasibility for tethering various ligands on the surface without compromising the vesicular structures. Building an ultra-sensitive nano-flow cytometer (nFCM), the heterogeneous nature of the functionalized samples was revealed, and a magnetic separation approach was proposed accordingly to remove the as-observed non-EV particles. The cellular uptake and cytotoxicity experiments provided direct evidence showing an enhanced cell targeting and cargo delivery capability of the ligand conjugated mEVs. In addition, the in vivo imaging further proved the applicability of transferrin conjugation for increased tumor enrichment of mEVs. Collectively, this general and mild ligand conjugation method enables an efficient surface functionalization of FDEVs, which is of vital importance for enhanced targeting delivery.

Camouflage strategies for therapeutic exosomes evasion from phagocytosis

Background

Even though exosome-based therapy has been shown to be able to control the progression of different pathologies, the data revealed by pharmacokinetic studies warn of the low residence time of exogenous exosomes in circulation that can hinder the clinical translation of therapeutic exosomes. The macrophages related to the organs of the mononuclear phagocytic system are responsible primarily for the rapid clearance and retention of exosomes, which strongly limits the amount of exosomal particles available to reach the target tissue, accumulate in it and release with high efficiency its therapeutic cargo in acceptor target cells to exert the desired biological effect.

Aim of review

Endowing exosomes with surface modifications to evade the immune system is a plausible strategy to contribute to the suppression of exosomal clearance and increase the efficiency of their targeted content delivery. Here, we summarize the current evidence about the mechanisms underlying the recognition and sequestration of therapeutic exosomes by phagocytic cells. Also, we propose different strategies to generate 'invisible' exosomes for the immune system, through the incorporation of different anti-phagocytic molecules on the exosomes’ surface that allow increasing the circulating half-life of therapeutic exosomes with the purpose to increase their bioavailability to reach the target tissue, transfer their therapeutic molecular cargo and improve their efficacy profile.

Key scientific concepts of review

Macrophage-mediated phagocytosis are the main responsible behind the short half-life in circulation of systemically injected exosomes, hindering their therapeutic effect. Exosomes ‘Camouflage Cloak’ strategy using antiphagocytic molecules can contribute to the inhibition of exosomal clearance, hence, increasing the on-target effect. Some candidate molecules that could exert an antiphagocytic role are CD47, CD24, CD44, CD31, β2M, PD-L1, App1, and DHMEQ. Pre- and post-isolation methods for exosome engineering are compatible with the loading of therapeutic cargo and the expression of antiphagocytic surface molecules.

Hydrophobic insertion-based engineering of tumor cell-derived exosomes for SPECT/NIRF imaging of colon cancer

Background

Tumor cell-derived exosomes (TEx) have emerged as promising nanocarriers for drug delivery. Noninvasive multimodality imaging for tracing the in vivo trafficking of TEx may accelerate their clinical translation. In this study, we developed a TEx-based nanoprobe via hydrophobic insertion mechanism and evaluated its performance in dual single-photon emission computed tomography (SPECT) and near-infrared fluorescence (NIRF) imaging of colon cancer.

Results

TEx were successfully isolated from HCT116 supernatants, and their membrane vesicle structure was confirmed by TEM. The average hydrodynamic diameter and zeta potential of TEx were 110.87 ± 4.61 nm and –9.20 ± 0.41 mV, respectively. Confocal microscopy and flow cytometry findings confirmed the high tumor binding ability of TEx. The uptake rate of ^99mTc-TEx-Cy7 by HCT116 cells increased over time, reaching 14.07 ± 1.31% at 6 h of co-incubation. NIRF and SPECT imaging indicated that the most appropriate imaging time was 18 h after the injection of ^99mTc-TEx-Cy7 when the tumor uptake (1.46% ± 0.06% ID/g) and tumor-to-muscle ratio (8.22 ± 0.65) peaked. Compared with radiolabeled adipose stem cell derived exosomes (^99mTc-AEx-Cy7), ^99mTc-TEx-Cy7 exhibited a significantly higher tumor accumulation in tumor-bearing mice.

Conclusion

Hydrophobic insertion-based engineering of TEx may represent a promising approach to develop and label exosomes for use as nanoprobes in dual SPECT/NIRF imaging. Our findings confirmed that TEx has a higher tumor-targeting ability than AEx and highlight the potential usefulness of exosomes in biomedical applications.

Extracellular Vesicles as Nanotherapeutics for Parkinson's Disease

Extracellular vesicles (EVs) are naturally occurring membranous structures secreted by normal and diseased cells, and carrying a wide range of bioactive molecules. In the central nervous system (CNS), EVs are important in both homeostasis and pathology. Through receptor-ligand interactions, direct fusion, or endocytosis, EVs interact with their target cells. Accumulating evidence indicates that EVs play crucial roles in the pathogenesis of many neurodegenerative disorders (NDs), including Parkinson's disease (PD). PD is the second most common ND, characterized by the progressive loss of dopaminergic (DAergic) neurons within the Substantia Nigra pars compacta (SNpc). In PD, EVs are secreted by both neurons and glial cells, with either beneficial or detrimental effects, via a complex program of cell-to-cell communication. The functions of EVs in PD range from their etiopathogenetic relevance to their use as diagnostic tools and innovative carriers of therapeutics. Because they can cross the blood-brain barrier, EVs can be engineered to deliver bioactive molecules (e.g., small interfering RNAs, catalase) within the CNS. This review summarizes the latest findings regarding the role played by EVs in PD etiology, diagnosis, prognosis, and therapy, with a particular focus on their use as novel PD nanotherapeutics.

Mastering the Tools: Natural versus Artificial Vesicles in Nanomedicine

Naturally occurring extracellular vesicles and artificially made vesicles represent important tools in nanomedicine for the efficient delivery of biomolecules and drugs. Since its first appearance in the literature 50 years ago, the research on vesicles is progressing at a fast pace, with the main goal of developing carriers able to protect cargoes from degradation, as well as to deliver them in a time- and space-controlled fashion. While natural occurring vesicles have the advantage of being fully compatible with their host, artificial vesicles can be easily synthetized and functionalized according to the target to reach. Research is striving to merge the advantages of natural and artificial vesicles, in order to provide a new generation of highly performing vesicles, which would improve the therapeutic index of transported molecules. This progress report summarizes current manufacturing techniques used to produce both natural and artificial vesicles, exploring the promises and pitfalls of the different production processes. Finally, pros and cons of natural versus artificial vesicles are discussed and compared, with special regard toward the current applications of both kinds of vesicles in the healthcare field.