Extracellular Vesicles Carry HIV Env and Facilitate Hiv Infection of Human Lymphoid Tissue

Extracellular vesicle isolation methods identify distinct HIV-1 particles released from chronically infected T-cells

The current study analyzed the intersecting biophysical, biochemical, and functional properties of extracellular particles (EPs) with the human immunodeficiency virus type-1 (HIV-1) beyond the currently accepted size range for HIV-1. We isolated five fractions (Frac-A through Frac-E) from HIV-infected cells by sequential differential ultracentrifugation (DUC). All fractions showed a heterogeneous size distribution with median particle sizes greater than 100 nm for Frac-A through Frac-D but not for Frac-E, which contained small EPs with an average size well below 50 nm. Synchronized and released cultures contained large infectious EPs in Frac-A, with markers of amphisomes and viral components. Additionally, Frac-E uniquely contained EPs positive for CD63, HSP70, and HIV-1 proteins. Despite its small average size, Frac-E contained membrane-protected viral integrase, detectable only after SDS treatment, indicating that it is enclosed in vesicles. Single particle analysis with dSTORM further supported these findings as CD63, HIV-1 integrase, and the viral surface envelope (Env) glycoprotein (gp) colocalized on the same Frac-E particles. Surprisingly, Frac-E EPs were infectious, and infectivity was significantly reduced by immunodepleting Frac-E with anti-CD63, indicating the presence of this protein on the surface of infectious small EPs in Frac-E. To our knowledge, this is the first time that extracellular vesicle (EV) isolation methods have identified infectious small HIV-1 particles (smHIV-1) that are under 50 nm. Collectively, our data indicate that the crossroads between EPs and HIV-1 potentially extend beyond the currently accepted biophysical properties of HIV-1, which may have further implications for viral pathogenesis.

Applying Flow Virometry to Study the HIV Envelope Glycoprotein and Differences Across HIV Model Systems

The HIV envelope glycoprotein (Env) is a trimeric protein that facilitates viral binding and fusion with target cells. As the sole viral protein on the HIV surface, Env is important both for immune responses to HIV and in vaccine designs. Targeting Env in clinical applications is challenging due to its heavy glycosylation, high genetic variability, conformational camouflage, and its low abundance on virions. Thus, there is a critical need to better understand this protein. Flow virometry (FV) is a useful methodology for phenotyping the virion surface in a high-throughput, single virion manner. To demonstrate the utility of FV to characterize Env, we stained HIV virions with a panel of 85 monoclonal antibodies targeting different regions of Env. A broad range of antibodies yielded robust staining of Env, with V3 antibodies showing the highest quantitative staining. A subset of antibodies tested in parallel on viruses produced in CD4+ T cell lines, HEK293T cells, and primary cells showed that the cellular model of virus production can impact Env detection. Finally, in addition to being able to highlight Env heterogeneity on virions, we show FV can sensitively detect differences in Env conformation when soluble CD4 is added to virions before staining.

Exploring the role of brain-derived extracellular vesicles in viral infections: from pathological insights to biomarker potential

Extracellular vesicles (EVs) are membrane-bound vesicles secreted by all cell types that play a central role in cell-to-cell communication. Since these vesicles serve as vehicles of cellular content (nucleic acids, proteins and lipids) with the potential to cross biological barriers, they represent a novel attractive window into an otherwise inaccessible organ, such as the brain. The composition of EVs is cell-type specific and mirrors the physiological condition of the cell-of-origin. Consequently, during viral infection, EVs undergo significant changes in their content and morphology, thereby reflecting alterations in the cellular state. Here, we briefly summarize the potential of brain-derived EVs as a lens into viral infection in the central nervous system, thereby: 1) uncovering underlying pathophysiological processes at play and 2) serving as liquid biopsies of the brain, representing a non-invasive source of biomarkers for monitoring disease activity. Although translating the potential of EVs from research to diagnosis poses complexities, characterizing brain-derived EVs in the context of viral infections holds promise to enhance diagnostic and therapeutic strategies, offering new avenues for managing infectious neurological diseases.

The Role of Extracellular Vesicles in Pandemic Viral Infections

Extracellular vesicles (EVs), of diverse origin and content, are membranous structures secreted by a broad range of cell types. Recent advances in molecular biology have highlighted the pivotal role of EVs in mediating intercellular communication, facilitated by their ability to transport a diverse range of biomolecules, including proteins, lipids, DNA, RNA and metabolites. A striking feature of EVs is their ability to exert dual effects during viral infections, involving both proviral and antiviral effects. This review explores the dual roles of EVs, particularly in the context of pandemic viruses such as HIV-1 and SARS-CoV-2. On the one hand, EVs can enhance viral replication and exacerbate pathogenesis by transferring viral components to susceptible cells. On the other hand, they have intrinsic antiviral properties, including activation of immune responses and direct inhibition of viral infection. By exploring these contrasting functions, our review emphasizes the complexity of EV-mediated interactions in viral pathogenesis and highlights their potential as targets for therapeutic intervention. The insights obtained from investigating EVs in the context of HIV-1 and SARS-CoV-2 provide a deeper understanding of viral mechanisms and pathologies, and offer a new perspective on managing and mitigating the impact of these global health challenges.

Dengue virus exploits autophagy vesicles and secretory pathways to promote transmission by human dendritic cells

Dengue virus (DENV), transmitted by infected mosquitoes, is a major public health concern, with approximately half the world's population at risk for infection. Recent decades have increasing incidence of dengue-associated disease alongside growing frequency of outbreaks. Although promising progress has been made in anti-DENV immunizations, post-infection treatment remains limited to non-specific supportive treatments. Development of antiviral therapeutics is thus required to limit DENV dissemination in humans and to help control the severity of outbreaks. Dendritic cells (DCs) are amongst the first cells to encounter DENV upon injection into the human skin mucosa, and thereafter promote systemic viral dissemination to additional human target cells. Autophagy is a vesicle trafficking pathway involving the formation of cytosolic autophagosomes, and recent reports have highlighted the extensive manipulation of autophagy by flaviviruses, including DENV, for viral replication. However, the temporal profiling and function of autophagy activity in DENV infection and transmission by human primary DCs remains poorly understood. Herein, we demonstrate that mechanisms of autophagosome formation and extracellular vesicle (EV) release have a pro-viral role in DC-mediated DENV transmission. We show that DENV exploits early-stage canonical autophagy to establish infection in primary human DCs. DENV replication enhanced autophagosome formation in primary human DCs, and intrinsically-heightened autophagosome biogenesis correlated with relatively higher rates of DC susceptibility to DENV. Furthermore, our data suggest that viral replication intermediates co-localize with autophagosomes, while productive DENV infection introduces a block at the late degradative stages of autophagy in infected DCs but not in uninfected bystander cells. Notably, we identify for the first time that approximately one-fourth of DC-derived CD9/CD81/CD63+ EVs co-express canonical autophagy marker LC3, and demonstrate that DC-derived EV populations are an alternative, cell-free mechanism by which DCs promote DENV transmission to additional target sites. Taken together, our study highlights intersections between autophagy and secretory pathways during viral infection, and puts forward autophagosome accumulation and viral RNA-laden EVs as host determinants of DC-mediated DENV infection in humans. Host-directed therapeutics targeting autophagy and exocytosis pathways thus have potential to enhance DC-driven resistance to DENV acquisition and thereby limit viral dissemination by initial human target cells following mosquito-to-human transmission of DENV.

Virion-incorporated CD14 enables HIV-1 to bind LPS and initiate TLR4 signaling in immune cells

HIV-1 has a broad range of nuanced interactions with the immune system, and the incorporation of cellular proteins by nascent virions continues to redefine our understanding of the virus-host relationship. Proteins located at the sites of viral egress can be selectively incorporated into the HIV-1 envelope, imparting new functions and phenotypes onto virions, and impacting viral spread and disease. Using virion capture assays and western blot, we show that HIV-1 can incorporate the myeloid antigen CD14 into its viral envelope. Virion-incorporated CD14 remained biologically active and able to bind its natural ligand, bacterial lipopolysaccharide (LPS), as demonstrated by flow virometry and immunoprecipitation assays. Using a Toll-like receptor 4 (TLR4) reporter cell line, we also demonstrated that virions with bound LPS can trigger TLR4 signaling to activate transcription factors that regulate inflammatory gene expression. Complementary assays with THP-1 monocytes demonstrated enhanced secretion of inflammatory cytokines like tumor necrosis factor alpha (TNF-α) and the C-C chemokine ligand 5 (CCL5), when exposed to LPS-loaded virus. These data highlight a new type of interplay between HIV-1 and the myeloid cell compartment, a previously well-established cellular contributor to HIV-1 pathogenesis and inflammation. Persistent gut inflammation is a hallmark of chronic HIV-1 infection, and contributing to this effect is the translocation of microbes across the gut epithelium. Our data herein provide proof of principle that virion-incorporated CD14 could be a novel mechanism through which HIV-1 can drive chronic inflammation, facilitated by HIV-1 particles binding bacterial LPS and initiating inflammatory signaling in TLR4-expressing cells.IMPORTANCEHIV-1 establishes a lifelong infection accompanied by numerous immunological changes. Inflammation of the gut epithelia, exacerbated by the loss of mucosal T cells and cytokine dysregulation, persists during HIV-1 infection. Feeding back into this loop of inflammation is the translocation of intestinal microbes across the gut epithelia, resulting in the systemic dissemination of bacterial antigens, like lipopolysaccharide (LPS). Our group previously demonstrated that the LPS receptor, CD14, can be readily incorporated by HIV-1 particles, supporting previous clinical observations of viruses derived from patient plasma. We now show that CD14 can be incorporated by several primary HIV-1 isolates and that this virion-incorporated CD14 can remain functional, enabling HIV-1 to bind to LPS. This subsequently allowed CD14+ virions to transfer LPS to monocytic cells, eliciting pro-inflammatory signaling and cytokine secretion. We posit here that virion-incorporated CD14 is a potential contributor to the dysregulated immune responses present in the setting of HIV-1 infection.

Identification of extracellular vesicles from their Raman spectra via self-supervised learning

Extracellular vesicles (EVs) released from cells attract interest for their possible role in health and diseases. The detection and characterization of EVs is challenging due to the lack of specialized methodologies. Raman spectroscopy, however, has been suggested as a novel approach for biochemical analysis of EVs. To extract information from the spectra, a novel deep learning architecture is explored as a versatile variant of autoencoders. The proposed architecture considers the frequency range separately from the intensity of the spectra. This enables the model to adapt to the frequency range, rather than requiring that all spectra be pre-processed to the same frequency range as it was trained on. It is demonstrated that the proposed architecture accepts Raman spectra of EVs and lipoproteins from 13 biological sources and from two laboratories. High reconstruction accuracy is maintained despite large variances in frequency range and noise level. It is also shown that the architecture is able to cluster the biological nanoparticles by their Raman spectra and differentiate them by their origin without pre-processing of the spectra or supervision during learning. The model performs label-free differentiation, including separating EVs from activated vs. non-activated blood platelets and EVs/lipoproteins from prostate cancer patients versus non-cancer controls. The differentiation is evaluated by creating a neural network classifier that observes the features extracted by the model to classify the spectra according to their sample origin. The classification reveals a test sensitivity of 92.2 % and selectivity of 92.3 % over 769 measurements from two labs that have different measurement configurations.

Cell Type-Specific Extracellular Vesicles and Their Impact on Health and Disease

Extracellular vesicles (EVs), a diverse group of cell-derived exocytosed particles, are pivotal in mediating intercellular communication due to their ability to selectively transfer biomolecules to specific cell types. EVs, composed of proteins, nucleic acids, and lipids, are taken up by cells to affect a variety of signaling cascades. Research in the field has primarily focused on stem cell-derived EVs, with a particular focus on mesenchymal stem cells, for their potential therapeutic benefits. Recently, tissue-specific EVs or cell type-specific extracellular vesicles (CTS-EVs), have garnered attention for their unique biogenesis and molecular composition because they enable highly targeted cell-specific communication. Various studies have outlined the roles that CTS-EVs play in the signaling for physiological function and the maintenance of homeostasis, including immune modulation, tissue regeneration, and organ development. These properties are also exploited for disease propagation, such as in cancer, neurological disorders, infectious diseases, autoimmune conditions, and more. The insights gained from analyzing CTS-EVs in different biological roles not only enhance our understanding of intercellular signaling and disease pathogenesis but also open new avenues for innovative diagnostic biomarkers and therapeutic targets for a wide spectrum of medical conditions. This review comprehensively outlines the current understanding of CTS-EV origins, function within normal physiology, and implications in diseased states.

Extracellular vesicles as tools and targets in therapy for diseases

Extracellular vesicles (EVs) are nano-sized, membranous structures secreted into the extracellular space. They exhibit diverse sizes, contents, and surface markers and are ubiquitously released from cells under normal and pathological conditions. Human serum is a rich source of these EVs, though their isolation from serum proteins and non-EV lipid particles poses challenges. These vesicles transport various cellular components such as proteins, mRNAs, miRNAs, DNA, and lipids across distances, influencing numerous physiological and pathological events, including those within the tumor microenvironment (TME). Their pivotal roles in cellular communication make EVs promising candidates for therapeutic agents, drug delivery systems, and disease biomarkers. Especially in cancer diagnostics, EV detection can pave the way for early identification and offers potential as diagnostic biomarkers. Moreover, various EV subtypes are emerging as targeted drug delivery tools, highlighting their potential clinical significance. The need for non-invasive biomarkers to monitor biological processes for diagnostic and therapeutic purposes remains unfulfilled. Tapping into the unique composition of EVs could unlock advanced diagnostic and therapeutic avenues in the future. In this review, we discuss in detail the roles of EVs across various conditions, including cancers (encompassing head and neck, lung, gastric, breast, and hepatocellular carcinoma), neurodegenerative disorders, diabetes, viral infections, autoimmune and renal diseases, emphasizing the potential advancements in molecular diagnostics and drug delivery.

Identification of CD38, CD97, and CD278 on the HIV surface using a novel flow virometry screening assay

While numerous cellular proteins in the HIV envelope are known to alter virus infection, methodology to rapidly phenotype the virion surface in a high throughput, single virion manner is lacking. Thus, many human proteins may exist on the virion surface that remain undescribed. Herein, we developed a novel flow virometry screening assay to discover new proteins on the surface of HIV particles. By screening a CD4+ T cell line and its progeny virions, along with four HIV isolates produced in primary cells, we discovered 59 new candidate proteins in the HIV envelope that were consistently detected across diverse HIV isolates. Among these discoveries, CD38, CD97, and CD278 were consistently present at high levels on virions when using orthogonal techniques to corroborate flow virometry results. This study yields new discoveries about virus biology and demonstrates the utility and feasibility of a novel flow virometry assay to phenotype individual virions.

Viral Components Trafficking with(in) Extracellular Vesicles

The global public health burden exerted by viruses partially stems from viruses' ability to subdue host cells into creating an environment that promotes their multiplication (i.e., pro-viral). It has been discovered that viruses alter cell physiology by transferring viral material through extracellular vesicles (EVs), which serve as vehicles for intercellular communication. Here, we aim to provide a conceptual framework of all possible EV-virus associations and their resulting functions in infection output. First, we describe the different viral materials potentially associated with EVs by reporting that EVs can harbor entire virions, viral proteins and viral nucleic acids. We also delineate the different mechanisms underlying the internalization of these viral components into EVs. Second, we describe the potential fate of EV-associated viral material cargo by detailing how EV can circulate and target a naive cell once secreted. Finally, we itemize the different pro-viral strategies resulting from EV associations as the Trojan horse strategy, an alternative mode of viral transmission, an expansion of viral cellular tropism, a pre-emptive alteration of host cell physiology and an immunity decoy. With this conceptual overview, we aim to stimulate research on EV-virus interactions.

Mechanisms underlying HIV-associated cognitive impairment and emerging therapies for its management

People living with HIV are affected by the chronic consequences of neurocognitive impairment (NCI) despite antiretroviral therapies that suppress viral replication, improve health and extend life. Furthermore, viral suppression does not eliminate the virus, and remaining infected cells may continue to produce viral proteins that trigger neurodegeneration. Comorbidities such as diabetes mellitus are likely to contribute substantially to CNS injury in people living with HIV, and some components of antiretroviral therapy exert undesirable side effects on the nervous system. No treatment for HIV-associated NCI has been approved by the European Medicines Agency or the US Food and Drug Administration. Historically, roadblocks to developing effective treatments have included a limited understanding of the pathophysiology of HIV-associated NCI and heterogeneity in its clinical manifestations. This heterogeneity might reflect multiple underlying causes that differ among individuals, rather than a single unifying neuropathogenesis. Despite these complexities, accelerating discoveries in HIV neuropathogenesis are yielding potentially druggable targets, including excessive immune activation, metabolic alterations culminating in mitochondrial dysfunction, dysregulation of metal ion homeostasis and lysosomal function, and microbiome alterations. In addition to drug treatments, we also highlight the importance of non-pharmacological interventions. By revisiting mechanisms implicated in NCI and potential interventions addressing these mechanisms, we hope to supply reasons for optimism in people living with HIV affected by NCI and their care providers.

Elucidating the role of extracellular vesicles in liver injury induced by HIV

INTRODUCTION

Liver disease is known as one of the leading co-morbidities in HIV infection, with 18% of non-AIDS-related mortality. There is constant crosstalk between liver parenchymal (hepatocytes) and non-parenchymal cells (macrophages, hepatic stellate cells, endothelial cells), and extracellular vesicles (EVs) are one of the most important ways of cell-to-cell communication.

AREAS COVERED

We briefly cover the role of EVs in liver disease as well as what is known about the role of small EVs, exosomes, in HIV-induced liver disease potentiated by alcohol as one of the second hits. We also touch large EVs, apoptotic bodies (ABs), in HIV-induced liver injury, the mechanisms of their formation and potentiation by second hits, and their role in the progression of liver disease.

EXPERT OPINION/COMMENTARY

Liver cells are an important source of EVs, which may provide the connection between different organs via secretion into the circulating blood (exosomes) or serve for the communication between the cells within the organ (ABs). Understanding the role of liver EVs in HIV infection and the involvement of second hits in EV generation would provide a new angle for the analysis of HIV-related liver disease pathogenesis and progression to end-stage liver disease.

Exosomes as Novel Diagnostic Biomarkers and Therapeutic Tools in Gliomas

Exosomes constitute small extracellular vesicles that contain lipids, proteins, nucleic acids, and glycoconjugates from the secreted cells and are capable of transmitting signals between cells and coordinating cellular communication. By this means, they are ultimately involved in physiology and disease, including development, homeostasis, and immune system regulation, as well as contributing to tumor progression and neurodegenerative diseases pathology. Recent studies have shown that gliomas secrete a panel of exosomes which have been associated with cell invasion and migration, tumor immune tolerance, potential for malignant transformation, neovascularization, and resistance to treatment. Exosomes have therefore emerged as intercellular communicators, which mediate the tumor-microenvironment interactions and exosome-regulated glioma cell stemness and angiogenesis. They may induce tumor proliferation and malignancy in normal cells by carrying pro-migratory modulators from cancer cells as well as many different molecular cancer modifiers, such as oncogenic transcripts, miRNAs, mutant oncoproteins, etc., which promote the communication of cancer cells with the surrounding stromal cells and provide valuable information on the molecular profile of the existing tumor. Moreover, engineered exosomes can provide an alternative system for drug delivery and enable efficient treatment. In the present review, we discuss the latest findings regarding the role of exosomes in glioma pathogenesis, their utility in non-invasive diagnosis, and potential applications to treatment.

The complex role of extracellular vesicles in HIV infection

During normal physiological and abnormal pathophysiological conditions, all cells release membrane vesicles, termed extracellular vesicles (EVs). Growing evidence has revealed that EVs act as important messengers in intercellular communication. EVs play emerging roles in cellular responses and the modulation of immune responses during virus infection. EVs contribute to triggering antiviral responses to restrict virus infection and replication. Conversely, the role of EVs in the facilitation of virus spread and pathogenesis has been widely documented. Depending on the cell of origin, EVs carry effector functions from one cell to the other by horizontal transfer of their bioactive cargoes, including DNA, RNA, proteins, lipids, and metabolites. The diverse constituents of EVs can reflect the altered states of cells or tissues during virus infection, thereby offering a diagnostic readout. The exchanges of cellular and/or viral components by EVs can inform the therapeutic potential of EVs for infectious diseases. This review discusses recent advances of EVs to explore the complex roles of EVs during virus infection and their therapeutic potential, focusing on HIV-1. [BMB Reports 2023; 56(6): 335-340].

Circulating Plasma Exosomal Proteins of Either SHIV-Infected Rhesus Macaque or HIV-Infected Patient Indicates a Link to Neuropathogenesis

Despite the suppression of human immunodeficiency virus (HIV) replication by combined antiretroviral therapy (cART), 50-60% of HIV-infected patients suffer from HIV-associated neurocognitive disorders (HAND). Studies are uncovering the role of extracellular vesicles (EVs), especially exosomes, in the central nervous system (CNS) due to HIV infection. We investigated links among circulating plasma exosomal (crExo) proteins and neuropathogenesis in simian/human immunodeficiency virus (SHIV)-infected rhesus macaques (RM) and HIV-infected and cART treated patients (Patient-Exo). Isolated EVs from SHIV-infected (SHIV-Exo) and uninfected (CTL-Exo) RM were predominantly exosomes (particle size < 150 nm). Proteomic analysis quantified 5654 proteins, of which 236 proteins (~4%) were significantly, differentially expressed (DE) between SHIV-/CTL-Exo. Interestingly, different CNS cell specific markers were abundantly expressed in crExo. Proteins involved in latent viral reactivation, neuroinflammation, neuropathology-associated interactive as well as signaling molecules were expressed at significantly higher levels in SHIV-Exo than CTL-Exo. However, proteins involved in mitochondrial biogenesis, ATP production, autophagy, endocytosis, exocytosis, and cytoskeleton organization were significantly less expressed in SHIV-Exo than CTL-Exo. Interestingly, proteins involved in oxidative stress, mitochondrial biogenesis, ATP production, and autophagy were significantly downregulated in primary human brain microvascular endothelial cells exposed with HIV+/cART+ Patient-Exo. We showed that Patient-Exo significantly increased blood-brain barrier permeability, possibly due to loss of platelet endothelial cell adhesion molecule-1 protein and actin cytoskeleton structure. Our novel findings suggest that circulating exosomal proteins expressed CNS cell markers-possibly associated with viral reactivation and neuropathogenesis-that may elucidate the etiology of HAND.

Immune Cells Release MicroRNA-155 Enriched Extracellular Vesicles That Promote HIV-1 Infection

The hallmark of HIV-1 infection is the rapid dysregulation of immune functions. Recent investigations for biomarkers of such dysregulation in people living with HIV (PLWH) reveal a strong correlation between viral rebound and immune activation with an increased abundance of extracellular vesicles (EVs) enriched with microRNA-155. We propose that the activation of peripheral blood mononuclear cells (PBMCs) leads to an increased miR-155 expression and production of miR-155-rich extracellular vesicles (miR-155-rich EVs), which can exacerbate HIV-1 infection by promoting viral replication. PBMCs were incubated with either HIV-1 (NL4.3Balenv), a TLR-7/8 agonist, or TNF. EVs were harvested from the cell culture supernatant by differential centrifugation, and RT-qPCR quantified miR-155 in cells and derived EVs. The effect of miR-155-rich EVs on replication of HIV-1 in incubated PBMCs was then measured by viral RNA and DNA quantification. HIV-1, TLR7/8 agonist, and TNF each induced the release of miR-155-rich EVs by PBMCs. These miR-155-rich EVs increased viral replication in PBMCs infected in vitro. Infection with HIV-1 and inflammation promote the production of miR-155-rich EVs, enhancing viral replication. Such autocrine loops, therefore, could influence the course of HIV-1 infection by promoting viral replication.

The Role of Platelet-Derived Extracellular Vesicles in Immune-Mediated Thrombosis

Platelet-derived extracellular vesicles (PEVs) play important roles in hemostasis and thrombosis. There are three major types of PEVs described based on their size and characteristics, but newer types may continue to emerge owing to the ongoing improvement in the methodologies and terms used to define various types of EVs. As the literature on EVs is growing, there are continuing attempts to standardize protocols for EV isolation and reach consensus in the field. This review provides information on mechanisms of PEV production, characteristics, cellular interaction, and their pathological role, especially in autoimmune and infectious diseases. We also highlight the mechanisms through which PEVs can activate parent cells in a feedback loop.

Trained Immunity and HIV Infection

Findings that certain infections induce immunity not only against the causing agent, but also against an unrelated pathogen have intrigued investigators for many years. Recently, underlying mechanisms of this phenomenon have started to come to light. It was found that the key cells responsible for heterologous protection are innate immune cells such as natural killer cells (NKs), dendritic cells, and monocytes/macrophages. These cells are 'primed' by initial infection, allowing them to provide enhanced response to subsequent infection by the same or unrelated agent. This phenomenon of innate immune memory was termed 'trained immunity'. The proposed mechanism for trained immunity involves activation by the first stimulus of metabolic pathways that lead to epigenetic changes, which maintain the cell in a "trained" state, allowing enhanced responses to a subsequent stimulus. Innate immune memory can lead either to enhanced responses or to suppression of subsequent responses ('tolerance'), depending on the strength and length of the initial stimulation of the immune cells. In the context of HIV infection, innate memory induced by infection is not well understood. In this Hypothesis and Theory article, we discuss evidence for HIV-induced trained immunity in human monocytes, its possible mechanisms, and implications for HIV-associated co-morbidities.

Different Sourced Extracellular Vesicles and Their Potential Applications in Clinical Treatments

Extracellular vesicles (EVs) include a heterogeneous group of natural cell-derived nanostructures that are increasingly regarded as promising biotherapeutic agents and drug delivery vehicles in human medicine. Desirable intrinsic properties of EVs including the ability to bypass natural membranous barriers and to deliver their unique biomolecular cargo to specific cell populations position them as fiercely competitive alternatives for currently available cell therapies and artificial drug delivery platforms. EVs with distinct characteristics can be released from various cell types into the extracellular environment as a means of transmitting bioactive components and altering the status of the target cell. Despite the existence of a large number of preclinical studies confirming the therapeutic efficacy of different originated EVs for treating several pathological conditions, in this review, we first provide a brief overview of EV biophysical properties with an emphasis on their intrinsic therapeutic benefits over cell-based therapies and synthetic delivery systems. Next, we describe in detail different EVs derived from distinct cell sources, compare their advantages and disadvantages, and recapitulate their therapeutic effects on various human disorders to highlight the progress made in harnessing EVs for clinical applications. Finally, knowledge gaps and concrete hurdles that currently hinder the clinical translation of EV therapies are debated with a futuristic perspective.

P-selectin glycoprotein ligand-1 (PSGL-1/CD162) is incorporated into clinical HIV-1 isolates and can mediate virus capture and subsequent transfer to permissive cells

Background

P-selectin glycoprotein ligand-1 (PSGL-1/CD162) has been studied extensively for its role in mediating leukocyte rolling through interactions with its cognate receptor, P-selectin. Recently, PSGL-1 was identified as a novel HIV-1 host restriction factor, particularly when expressed at high levels in the HIV envelope. Importantly, while the potent antiviral activity of PSGL-1 has been clearly demonstrated in various complementary model systems, the breadth of PSGL-1 incorporation across genetically diverse viral isolates and clinical isolates has yet to be described. Additionally, the biological activity of virion-incorporated PSGL-1 has also yet to be shown.

Results

Herein we assessed the levels of PSGL-1 on viruses produced through transfection with various amounts of PSGL-1 plasmid DNA (0–250 ng), compared to levels of PSGL-1 on viruses produced through infection of T cell lines and primary PBMC. We found that very low levels of PSGL-1 plasmid DNA (< 2.5 ng/well) were necessary to generate virus models that could closely mirror the phenotype of viruses produced via infection of T cells and PBMC. Unique to this study, we show that PSGL-1 is incorporated in a broad range of HIV-1 and SIV isolates and that virions with incorporated PSGL-1 are detectable in plasma from viremic HIV-1-infected individuals, corroborating the relevance of PSGL-1 in natural infection. Additionally, we show that PSGL-1 on viruses can bind its cognate selectin receptors, P-, E-, and L-selectins. Finally, we show viruses with endogenous levels of PSGL-1 can be captured by P-selectin and transferred to HIV-permissive bystander cells, highlighting a novel role for PSGL-1 in HIV-1 infection. Notably, viruses which contained high levels of PSGL-1 were noninfectious in our hands, in line with previous findings reporting the potent antiviral activity of PSGL-1.

Conclusions

Our results indicate that levels of PSGL-1 incorporation into virions can vary widely among model systems tested, and that careful tailoring of plasmid levels is required to recapitulate physiological systems when using pseudovirus models. Taken together, our data suggest that PSGL-1 may play diverse roles in the physiology of HIV-1 infection, particularly due to the functionally active state of PSGL-1 on virion surfaces and the breadth of PSGL-1 incorporation among a wide range of viral isolates.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12977-022-00593-5.

Methamphetamine Induces the Release of Proadhesive Extracellular Vesicles and Promotes Syncytia Formation: A Potential Role in HIV-1 Neuropathogenesis

Despite the success of combinational antiretroviral therapy (cART), the high pervasiveness of human immunodeficiency virus-1 (HIV)-associated neurocognitive disorders (HAND) poses a significant challenge for society. Methamphetamine (meth) and related amphetamine compounds, which are potent psychostimulants, are among the most commonly used illicit drugs. Intriguingly, HIV-infected individuals who are meth users have a comparatively higher rate of neuropsychological impairment and exhibit a higher viral load in the brain than infected individuals who do not abuse meth. Effectively, all cell types secrete nano-sized lipid membrane vesicles, referred to as extracellular vesicles (EVs) that can function as intercellular communication to modulate the physiology and pathology of the cells. This study shows that meth treatments on chronically HIV-infected promonocytic U1 cells induce the release of EVs that promote cellular clustering and syncytia formation, a phenomenon that facilitates HIV pathogenesis. Our analysis also revealed that meth exposure increased intercellular adhesion molecule-1 (ICAM-1) and HIV-Nef protein expression in both large (10 K) and small (100 K) EVs. Further, when meth EVs are applied to uninfected naïve monocyte-derived macrophages (MDMs), we saw a significant increase in cell clustering and syncytia formation. Furthermore, treatment of MDMs with antibodies against ICAM-1 and its receptor, lymphocyte function-associated antigen 1 (LFA1), substantially blocked syncytia formation, and consequently reduced the number of multinucleated cells. In summary, our findings reveal that meth exacerbates HIV pathogenesis in the brain through release of proadhesive EVs, promoting syncytia formation and thereby aiding in the progression of HIV infection in uninfected cells.

Virus-like Particles: Measures and Biological Functions

Virus-like particles resemble infectious virus particles in size, shape, and molecular composition; however, they fail to productively infect host cells. Historically, the presence of virus-like particles has been inferred from total particle counts by microscopy, and infectious particle counts or plaque-forming-units (PFUs) by plaque assay; the resulting ratio of particles-to-PFUs is often greater than one, easily 10 or 100, indicating that most particles are non-infectious. Despite their inability to hijack cells for their reproduction, virus-like particles and the defective genomes they carry can exhibit a broad range of behaviors: interference with normal virus growth during co-infections, cell killing, and activation or inhibition of innate immune signaling. In addition, some virus-like particles become productive as their multiplicities of infection increase, a sign of cooperation between particles. Here, we review established and emerging methods to count virus-like particles and characterize their biological functions. We take a critical look at evidence for defective interfering virus genomes in natural and clinical isolates, and we review their potential as antiviral therapeutics. In short, we highlight an urgent need to better understand how virus-like genomes and particles interact with intact functional viruses during co-infection of their hosts, and their impacts on the transmission, severity, and persistence of virus-associated diseases.

Extracellular Vesicles as a New Promising Therapy in HIV Infection

Combination antiretroviral therapy (cART) effectively blocks HIV replication but cannot completely eliminate HIV from the body mainly due to establishment of a viral reservoir. To date, clinical strategies designed to replace cART for life and alternatively to eliminate the HIV reservoir have failed. The reduced expression of viral antigens in the latently infected cells is one of the main reasons behind the failure of the strategies to purge the HIV reservoir. This situation has forced the scientific community to search alternative therapeutic strategies to control HIV infection. In this regard, recent findings have pointed out extracellular vesicles as therapeutic agents with enormous potential to control HIV infection. This review focuses on their role as pro-viral and anti-viral factors, as well as their potential therapeutic applications.

Extracellular Vesicles Regulated by Viruses and Antiviral Strategies

Extracellular vesicles (EVs), consisting of exosomes, micro-vesicles, and other vesicles, mainly originate from the multi-vesicular body (MVB) pathway or plasma membrane. EVs are increasingly recognized as a tool to mediate the intercellular communication and are closely related to human health. Viral infection is associated with various diseases, including respiratory diseases, neurological diseases, and cancers. Accumulating studies have shown that viruses could modulate their infection ability and pathogenicity through regulating the component and function of EVs. Non-coding RNA (ncRNA) molecules are often targets of viruses and also serve as the main functional cargo of virus-related EVs, which have an important role in the epigenetic regulation of target cells. In this review, we summarize the research progress of EVs under the regulation of viruses, highlighting the content alteration and function of virus-regulated EVs, emphasizing their isolation methods in the context of virus infection, and potential antiviral strategies based on their use. This review would promote the understanding of the viral pathogenesis and the development of antiviral research.

Truncation of the Cytoplasmic Tail of Equine Infectious Anemia Virus Increases Virion Production by Improving Env Cleavage and Plasma Membrane Localization

Envelope glycoproteins (Envs) of lentiviruses harbor unusually long cytoplasmic tails (CTs). Natural CT truncations always occur in vitro and are accompanied by attenuated virulence, but their effects on viral replication have not been fully elucidated. The Env in equine infectious anemia virus (EIAV) harbors the longest CT in the lentiviral family, and a truncated CT was observed in a live attenuated vaccine. This study demonstrates that CT truncation significantly increased EIAV production, as determined by comparing the virion yields from EIAV infectious clones in the presence and absence of the CT. A significant increase in a cleaved product from the CT-truncated Env precursor, but not the full-length Env, was observed. We further confirmed that the presence of the CT inhibited the cleavage of the Env precursor and found that a functional domain located at the C terminus was responsible for this function. Moreover, CT-truncated Env was mainly localized at the plasma membrane (PM), while full-length Env was mainly localized in the cytoplasm. The CT truncation caused a dramatic reduction in the endocytosis of Env. These results suggest that the CT can modulate the processing and trafficking of EIAV Env and thus regulate EIAV replication.

IMPORTANCE The mature lentivirus envelope glycoprotein (Env) is composed of a surface unit (SU) and a transmembrane unit (TM), which are cleaved products of the Env precursor. After mature Env is heterodimerically formed from the cleavage of the Env precursor, it is trafficked to the plasma membrane (PM) for incorporation and virion assembly. Env harbors a long cytoplasmic tail (CT), which has been increasingly found to play multiple roles in the Env biological cycle. Here, we revealed for the first time that the CT of equine infectious anemia virus (EIAV) Env inhibits cleavage of the Env precursor. Simultaneously, the CT promoted Env endocytosis, resulting in weakened Env localization at the PM. We also validated that the CT could significantly decrease EIAV production. These findings suggest that the CT regulates the processing and trafficking of EIAV Env to balance virion production.

Increased IL-6 expression precedes reliable viral detection in the rhesus macaque brain during acute SIV infection

Knowledge of immune activation in the brain during acute HIV infection is crucial for the prevention and treatment of HIV-associated neurological disorders. We determined regional brain (basal ganglia, thalamus, and frontal cortex) immune and virological profiles at 7 and 14 days post infection (dpi) with SIVmac239 in rhesus macaques. The basal ganglia and thalamus had detectable viruses earlier (7 dpi) than the frontal cortex (14 dpi) and contained higher quantities of viruses than the latter. Increased immune activation of astrocytes and significant infiltration of macrophages in the thalamus at 14 dpi coincided with elevated plasma viral load, and SIV colocalized only within macrophages. RNA signatures of proinflammatory responses, including IL-6, were detected at 7 dpi in microglia and interestingly, preceded reliable detection of virus in tissues and were maintained in the chronically infected macaques. Countering the proinflammatory response, the antiinflammatory response was not detected until increased TGF-β expression was found in perivascular macrophages at 14 dpi. But this response was not detected in chronic infection. Our data provide evidence that the interplay of acute proinflammatory and antiinflammatory responses in the brain likely contributed to the overt neuroinflammation, where the immune activation preceded reliable viral detection.

Exosomes in HIV infection

PURPOSE OF REVIEW

The exosomes play a critical role in HIV infection, which constitute a pathway to release intracellular material and exchange material and information between cells. Exosomes have become a hotspot in the field of AIDS research. This review introduces the formation process of HIV particles and exosomes, and summarizes the role of exosomes in the progression of HIV disease from multiple aspects.

RECENT FINDINGS

Many components of the exosomes involved in HIV transfer and replication affect the occurrence, development, and outcome of AIDS, and are closely related to HIV infection. Exosomes can have a dual impact on HIV infection, and play an important role in activating the latent reservoir of HIV and affecting the chronic inflammation of HIV. The biological information carried by exosomes is also of great significance for the prediction of HIV disease.

SUMMARY

The present review summarizes the role of exosomes in HIV disease progression in various aspects in order to further understand the underlying mechanism affecting the infection and providing a new idea for the clinical diagnosis and treatment of AIDS.

Endocytic Motif on a Biotin-Tagged HIV-1 Env Modulates the Co-Transfer of Env and Gag during Cell-to-Cell Transmission

During HIV-1 transmission through T cell virological synapses, the recruitment of the envelope (Env) glycoprotein to the site of cell-cell contact is important for adhesion and for packaging onto nascent virus particles which assemble at the site. Live imaging studies in CD4 T cells have captured the rapid recruitment of the viral structural protein Gag to VSs. We explored the role of endocytic trafficking of Env initiated by a membrane proximal tyrosine motif during HIV transfer into target cells and examined the factors that allow Gag and Env to be transferred together across the synapse. To facilitate tracking of Env in live cells, we adapted an Env tagging method and introduced a biotin acceptor peptide (BAP) into the V4 loop of Env gp120, enabling sensitive fluorescent tracking of V4-biotinylated Env. The BAP-tagged and biotinylated HIVs were replication-competent in cell-free and cell-to-cell infection assays. Live cell fluorescent imaging experiments showed rapid internalized cell surface Env on infected cells. Cell-cell transfer experiments conducted with the Env endocytosis mutant (Y712A) showed increased transfer of Env. Paradoxically, this increase in Env transfer was associated with significantly reduced Gag transfer into target cells, when compared to viral transfer associated with WT Env. This Y712A Env mutant also exhibited an altered Gag/biotin Env fluorescence ratio during transfer that correlated with decreased productive cell-to-cell infection. These results may suggest that the internalization of Env into recycling pools plays an important role in the coordinated transfer of Gag and Env across the VS, which optimizes productive infection in target cells.

Mechanisms of residual immune activation in HIV-1-infected human lymphoid tissue ex vivo

OBJECTIVE

HIV-1 infection triggers immune activation, as reflected by the upregulation of various cytokines. This immune activation remains elevated despite antiretroviral therapy (ART) and leads to early age-related diseases. Here, we addressed the mechanisms of sustained immune activation in HIV-1-infected human lymphoid tissues ex vivo.

DESIGN/METHOD

We investigated several potential causes of immunoactivation, including: a proinflammatory effect of ART drugs themselves; an early HIV-1-triggered cytokine storm, which could in turn trigger a sustained cytokine dysregulation; herpesvirus reactivation; HIV-1 protein release; and production of defective virions and extracellular vesicles. Tissue immune activation was evaluated from measurements of cytokines in culture medium using multiplexed immunoassays.

RESULTS

Neither ART itself nor simulated cytokine storms nor exogenously added HIV-1 proteins triggered a sustained cytokine upregulation. In contrast, defective (replicative-incompetent) virions and extracellular vesicles induced sustained cytokine upregulation, as did infectious virus. Tissue immune activation was accompanied by reactivation of cytomegalovirus.

CONCLUSION

The system of ex-vivo human lymphoid tissue allowed investigation, under laboratory-controlled conditions, of possible mechanisms involved in persistent immune activation in HIV-1 patients under ART. Mechanisms of this immunoactivation identified in ex-vivo tissues may indicate potential therapeutic targets for restoration of immune system homeostasis in HIV-1-infected patients.

Luminal microvesicles uniquely influence translocating bacteria after SIV infection

Microbial translocation contributes to persistent inflammation in both treated and untreated HIV infection. Although translocation is due in part to a disintegration of the intestinal epithelial barrier, there is a bias towards the translocation of Proteobacteria. We hypothesized that intestinal epithelial microvesicle cargo differs after HIV infection and contributes to biased translocation. We isolated gastrointestinal luminal microvesicles before and after progressive simian immunodeficiency virus (SIV) infection in rhesus macaques and measured miRNA and antimicrobial peptide content. We demonstrate that these microvesicles display decreased miR-28-5p, -484, -584-3p, and -584-5p, and let-7b-3p, as well as increased beta-defensin 1 after SIV infection. We further observed dose-dependent growth sensitivity of commensal Lactobacillus salivarius upon co-culture with isolated microvesicles. Infection-associated microvesicle differences were not mirrored in non-progressively SIV-infected sooty mangabeys. Our findings describe novel alterations of antimicrobial control after progressive SIV infection that influence the growth of translocating bacterial taxa. These studies may lead to the development of novel therapeutics for treating chronic HIV infection, microbial translocation, and inflammation.

Extracellular vesicles carry SARS-CoV-2 spike protein and serve as decoys for neutralizing antibodies

In late 2019, a novel coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in Wuhan, China. SARS-CoV-2 and the disease it causes, coronavirus disease 2019 (COVID-19), spread rapidly and became a global pandemic in early 2020. SARS-CoV-2 spike protein is responsible for viral entry and binds to angiotensin converting enzyme 2 (ACE2) on host cells, making it a major target of the immune system - particularly neutralizing antibodies (nAbs) that are induced by infection or vaccines. Extracellular vesicles (EVs) are small membraned particles constitutively released by cells, including virally-infected cells. EVs and viruses enclosed within lipid membranes share some characteristics: they are small, sub-micron particles and they overlap in cellular biogenesis and egress routes. Given their shared characteristics, we hypothesized that EVs released from spike-expressing cells could carry spike and serve as decoys for anti-spike nAbs, promoting viral infection. Here, using mass spectrometry and nanoscale flow cytometry (NFC) approaches, we demonstrate that SARS-CoV-2 spike protein can be incorporated into EVs. Furthermore, we show that spike-carrying EVs act as decoy targets for convalescent patient serum-derived nAbs, reducing their effectiveness in blocking viral entry. These findings have important implications for the pathogenesis of SARS-CoV-2 infection in vivo and highlight the complex interplay between viruses, extracellular vesicles, and the immune system that occurs during viral infections.

Emerging Role of Nef in the Development of HIV Associated Neurological Disorders

Despite adherence to treatment, individuals living with HIV have an increased risk for developing cognitive impairments, referred to as HIV-associated neurological disorders (HAND). Due to continued growth in the HIV population, particularly amongst the aging cohort, the neurobiological mechanisms of HAND are increasingly relevant. Similar to other viral proteins (e.g. Tat, Gp120, Vpr), the Negative Factor (Nef) is associated with numerous adverse effects in the CNS as well as cognitive impairments. In particular, emerging data indicate the consequences of Nef may be facilitated by the modulation of cellular autophagy as well as its inclusion into extracellular vesicles (EVs). The present review examines evidence for the molecular mechanisms by which Nef might contribute to neuronal dysfunction underlying HAND, with a specific focus on autophagy and EVs. Based on the these data, we propose an integrated model by which Nef may contribute to underlying neuronal dysfunction in HAND and highlight potentially novel therapeutic targets for HAND. Graphical abstract.

Unbiased proteomic profiling of host cell extracellular vesicle composition and dynamics upon HIV-1 infection

Cells release diverse types of extracellular vesicles (EVs), which transfer complex signals to surrounding cells. Specific markers to distinguish different EVs (e.g. exosomes, ectosomes, enveloped viruses like HIV) are still lacking. We have developed a proteomic profiling approach for characterizing EV subtype composition and applied it to human Jurkat T cells. We generated an interactive database to define groups of proteins with similar profiles, suggesting release in similar EVs. Biochemical validation confirmed the presence of preferred partners of commonly used exosome markers in EVs: CD81/ADAM10/ITGB1, and CD63/syntenin. We then compared EVs from control and HIV-1-infected cells. HIV infection altered EV profiles of several cellular proteins, including MOV10 and SPN, which became incorporated into HIV virions, and SERINC3, which was re-routed to non-viral EVs in a Nef-dependent manner. Furthermore, we found that SERINC3 controls the surface composition of EVs. Our workflow provides an unbiased approach for identifying candidate markers and potential regulators of EV subtypes. It can be widely applied to in vitro experimental systems for investigating physiological or pathological modifications of EV release.

Latent HIV-Exosomes Induce Mitochondrial Hyperfusion Due to Loss of Phosphorylated Dynamin-Related Protein 1 in Brain Endothelium

Damage to the cerebral vascular endothelium is a critical initiating event in the development of HIV-1-associated neurocognitive disorders. To study the role of mitochondria in cerebral endothelial dysfunction, we investigated how exosomes, isolated from both cell lines with integrated provirus and HIV-1 infected primary cells (HIV-exosomes), accelerate the dysfunction of primary human brain microvascular endothelial cells (HBMVECs) by inducing mitochondrial hyperfusion, and reducing the expression of phosphorylated endothelial nitric oxide synthase (p-eNOS). The quantitative analysis of the extracellular vesicles (EVs) indicates that the isolated EVs were predominantly exosomes. It was further supported by the detection of exosomal markers, and the absence of large EV-related protein in the isolated EVs. The exosomes were readily taken up by primary HBMVECs. HIV-exosomes induce cellular and mitochondrial superoxide production but reduce mitochondrial membrane potential in HBMVECs. HIV-exosomes increase mitochondrial hyperfusion, possibly due to loss of phosphorylated dynamin-related protein 1 (p-DRP1). HIV-exosomes, containing the HIV-Tat protein, and viral Tat protein reduce the expression of p-DRP1 and p-eNOS, and accelerate brain endothelial dysfunction. Finally, exosomes isolated from HIV-1 infected primary human peripheral blood mononuclear cells (hPBMCs) produce more exosomes than uninfected controls and reduce both p-DRP1 and p-eNOS expressions in primary HBMVECs. Our novel findings reveal the significant role of HIV-exosomes on dysregulation of mitochondrial function, which induces adverse changes in the function of the brain microvascular endothelium.

Plasma Extracellular Vesicle Subtypes May be Useful as Potential Biomarkers of Immune Activation in People With HIV

Background

Extracellular vesicles (EVs) are intercellular messengers with epigenetic potential since they can shuttle microRNA (miRNA). EVs and miRNA play a role in human immunodeficiency virus (HIV) infection immunopathogenesis. Chronic immune activation and systemic inflammation during HIV infection despite effective antiretroviral therapy (ART) are associated with non-acquired immunodeficiency syndrome (AIDS) comorbidities in people living with HIV (PLWH). Analysis of plasma EVs and their miRNA content may be useful as immune activation or inflammatory biomarkers in PLWH receiving ART. In this study, we hypothesized that the number, size, and miRNA of large and small EVs could reflect immune activation associated with an elevated CD8 T-cell count or a low CD4/CD8 ratio in PLWH.

Methods

Plasma EVs subtype purified from PLWH and uninfected controls were sized using dynamic light scattering and quantified using flow cytometry and acetylcholine esterase (AChE) activity. Expression of mature miRNAs miR-92, miR-155, miR-223 was measured by quantitative reverse-transcriptase polymerase chain reaction in EVs and leucocytes.

Results

HIV infection induces increased production of small EVs in plasma. EV subtypes were differentially enriched in miR-92, miR-155, and miR-223. Positive correlations between CD8 T-cell count and large EVs abundance and small EVs AChE activity were observed. CD4/CD8 ratio was negatively correlated with small EV AChE activity, and miRNA-155 level per small EV was negatively correlated with CD8 T-cell count.

Conclusions

These findings suggest that quantifying large or small EVs and profiling miRNA content per EV might provide new functional biomarkers of immune activation and inflammation.

Extracellular Vesicles in Viral Pathogenesis: A Case of Dr. Jekyll and Mr. Hyde

Secretion of extracellular vesicles (EVs) is a fundamental property of living cells. EVs are known to transfer biological signals between cells and thus regulate the functional state of recipient cells. Such vesicles mediate the intercellular transport of many biologically active molecules (proteins, nucleic acids, specific lipids) and participate in regulation of key physiological processes. In addition, EVs are involved in the pathogenesis of multiple diseases: infectious, neurodegenerative, and oncological. The current EV classification into microvesicles, apoptotic bodies, and exosomes is based on their size, pathways of cellular biogenesis, and molecular composition. This review is focused on analysis of the role of EVs (mainly exosomes) in the pathogenesis of viral infection. We briefly characterize the biogenesis and molecular composition of various EV types. Then, we consider EV-mediated pro- and anti-viral mechanisms. EV secretion by infected cells can be an important factor of virus spread in target cell populations, or a protective factor limiting viral invasion. The data discussed in this review, on the effect of EV secretion by infected cells on processes in neighboring cells and on immune cells, are of high significance in the search for new therapeutic approaches and for design of new generations of vaccines.

Challenges in Biomaterial-Based Drug Delivery Approach for the Treatment of Neurodegenerative Diseases: Opportunities for Extracellular Vesicles

Biomaterials have been the subject of numerous studies to pursue potential therapeutic interventions for a wide variety of disorders and diseases. The physical and chemical properties of various materials have been explored to develop natural, synthetic, or semi-synthetic materials with distinct advantages for use as drug delivery systems for the central nervous system (CNS) and non-CNS diseases. In this review, an overview of popular biomaterials as drug delivery systems for neurogenerative diseases is provided, balancing the potential and challenges associated with the CNS drug delivery. As an effective drug delivery system, desired properties of biomaterials are discussed, addressing the persistent challenges such as targeted drug delivery, stimuli responsiveness, and controlled drug release in vivo. Finally, we discuss the prospects and limitations of incorporating extracellular vesicles (EVs) as a drug delivery system and their use for biocompatible, stable, and targeted delivery with limited immunogenicity, as well as their ability to be delivered via a non-invasive approach for the treatment of neurodegenerative diseases.

Extracellular Vesicles: Roles in Human Viral Infections, Immune-Diagnostic, and Therapeutic Applications

Membrane-bound vesicles that are released from cells are increasingly being studied as a medium of intercellular communication, as these act to shuttle functional proteins, such as lipids, DNA, rRNA, and miRNA, between cells during essential physiological processes. Extracellular vesicles (EVs), most commonly exosomes, are consistently produced by virus-infected cells, and they play crucial roles in mediating communication between infected and uninfected cells. Notably, pathophysiological roles for EVs have been established in various viral infections, including human immune deficiency virus (HIV), coronavirus (CoV), and human adenovirus (HAdv). Retroviruses, such as HIV, modulate the production and composition of EVs, and critically, these viruses can exploit EV formation, secretion, and release pathways to promote infection, transmission, and intercellular spread. Consequently, EV production has been investigated as a potential tool for the development of improved viral infection diagnostics and therapeutics. This review will summarize our present knowledge of EV–virus relationships, focusing on their known roles in pathophysiological pathways, immunomodulatory mechanisms, and utility for biomarker discovery. This review will also discuss the potential for EVs to be exploited as diagnostic and treatment tools for viral infection.

Extracellular Vesicles Orchestrate Immune and Tumor Interaction Networks

Simple Summary

Significant strides have been made to describe the pervasive role of extracellular vesicles (EVs) in health and disease. This work provides an insightful and unifying mechanistic understanding of EVs in immunity and tumorigenesis. This is achieved by dissecting the role of EVs within the continuum of immune cell physiology, immune–infection responses, and the immune–tumor microenvironment. Our work synthesizes important topical findings on immune EV signaling in mediating immune–tumor interaction networks.

Abstract

Extracellular vesicles (EVs) are emerging as potent and intricate intercellular communication networks. From their first discovery almost forty years ago, several studies have bolstered our understanding of these nano-vesicular structures. EV subpopulations are now characterized by differences in size, surface markers, cargo, and biological effects. Studies have highlighted the importance of EVs in biology and intercellular communication, particularly during immune and tumor interactions. These responses can be equally mediated at the proteomic and epigenomic levels through surface markers or nucleic acid cargo signaling, respectively. Following the exponential growth of EV studies in recent years, we herein synthesize new aspects of the emerging immune–tumor EV-based intercellular communications. We also discuss the potential role of EVs in fundamental immunological processes under physiological conditions, viral infections, and tumorigenic conditions. Finally, we provide insights on the future prospects of immune–tumor EVs and suggest potential avenues for the use of EVs in diagnostics and therapeutics.

Persistent Immune Activation in HIV-1-Infected Ex Vivo Model Tissues Subjected to Antiretroviral Therapy: Soluble and Extracellular Vesicle-Associated Cytokines

BACKGROUND

Residual immune activation after successful antiretroviral therapy (ART) in HIV-1-infected patients is associated with the increased risk of complications. Cytokines, both soluble and extracellular vesicle (EV)-associated, may play an important role in this immune activation.

SETTING

Ex vivo tissues were infected with X4LAI04 or R5SF162 HIV-1. Virus replicated for 16 days, or tissues were treated with the anti-retroviral drug ritonavir.

METHODS

Viral replication and production of 33 cytokines in soluble and EV-associated forms were measured with multiplexed bead-based assays.

RESULTS

Both variants of HIV-1 efficiently replicated in tissues and triggered upregulation of soluble cytokines, including IL-1β, IL-7, IL-18, IFN-γ, MIP-1α, MIP-1β, and RANTES. A similar pattern was observed in EV-associated cytokine release by HIV-infected tissues. In addition, TNF-α and RANTES demonstrated a significant shift to a more soluble form compared with EV-associated cytokines. Ritonavir treatment efficiently suppressed viral replication; however, both soluble and EV-associated cytokines remained largely upregulated after 13 days of treatment. EV-associated cytokines were more likely to remain elevated after ART. Treatment of uninfected tissues with ritonavir itself did not affect cytokine release.

CONCLUSIONS

We demonstrated that HIV-1 infection of ex vivo lymphoid tissues resulted in their immune activation as evaluated by upregulation of various cytokines, both soluble and EV-associated. This upregulation persisted despite inhibition of viral replication by ART. Thus, similar to in vivo, HIV-1-infected human tissues ex vivo continue to be immune-activated after viral suppression, providing a new laboratory model to study this phenomenon.

Extracellular Vesicles in the Pathogenesis of Viral Infections in Humans

Most cells can release extracellular vesicles (EVs), membrane vesicles containing various proteins, nucleic acids, enzymes, and signaling molecules. The exchange of EVs between cells facilitates intercellular communication, amplification of cellular responses, immune response modulation, and perhaps alterations in viral pathogenicity. EVs serve a dual role in inhibiting or enhancing viral infection and pathogenesis. This review examines the current literature on EVs to explore the complex role of EVs in the enhancement, inhibition, and potential use as a nanotherapeutic against clinically relevant viruses, focusing on neurotropic viruses: Zika virus (ZIKV) and human immunodeficiency virus (HIV). Overall, this review's scope will elaborate on EV-based mechanisms, which impact viral pathogenicity, facilitate viral spread, and modulate antiviral immune responses.

Extracellular Vesicles in Viral Replication and Pathogenesis and Their Potential Role in Therapeutic Intervention

Extracellular vesicles (EVs) have shown their potential as a carrier of molecular information, and they have been involved in physiological functions and diseases caused by viral infections. Virus-infected cells secrete various lipid-bound vesicles, including endosome pathway-derived exosomes and microvesicles/microparticles that are released from the plasma membrane. They are released via a direct outward budding and fission of plasma membrane blebs into the extracellular space to either facilitate virus propagation or regulate the immune responses. Moreover, EVs generated by virus-infected cells can incorporate virulence factors including viral protein and viral genetic material, and thus can resemble noninfectious viruses. Interactions of EVs with recipient cells have been shown to activate signaling pathways that may contribute to a sustained cellular response towards viral infections. EVs, by utilizing a complex set of cargos, can play a regulatory role in viral infection, both by facilitating and suppressing the infection. EV-based antiviral and antiretroviral drug delivery approaches provide an opportunity for targeted drug delivery. In this review, we summarize the literature on EVs, their associated involvement in transmission in viral infections, and potential therapeutic implications.

Characterizing Extracellular Vesicles and Their Diverse RNA Contents

Cells release nanometer-scale, lipid bilayer-enclosed biomolecular packages (extracellular vesicles; EVs) into their surrounding environment. EVs are hypothesized to be intercellular communication agents that regulate physiological states by transporting biomolecules between near and distant cells. The research community has consistently advocated for the importance of RNA contents in EVs by demonstrating that: (1) EV-related RNA contents can be detected in a liquid biopsy, (2) disease states significantly alter EV-related RNA contents, and (3) sensitive and specific liquid biopsies can be implemented in precision medicine settings by measuring EV-derived RNA contents. Furthermore, EVs have medical potential beyond diagnostics. Both natural and engineered EVs are being investigated for therapeutic applications such as regenerative medicine and as drug delivery agents. This review focuses specifically on EV characterization, analysis of their RNA content, and their functional implications. The NIH extracellular RNA communication (ERC) program has catapulted human EV research from an RNA profiling standpoint by standardizing the pipeline for working with EV transcriptomics data, and creating a centralized database for the scientific community. There are currently thousands of RNA-sequencing profiles hosted on the Extracellular RNA Atlas alone (Murillo et al., 2019), encompassing a variety of human biofluid types and health conditions. While a number of significant discoveries have been made through these studies individually, integrative analyses of these data have thus far been limited. A primary focus of the ERC program over the next five years is to bring higher resolution tools to the EV research community so that investigators can isolate and analyze EV sub-populations, and ultimately single EVs sourced from discrete cell types, tissues, and complex biofluids. Higher resolution techniques will be essential for evaluating the roles of circulating EVs at a level which impacts clinical decision making. We expect that advances in microfluidic technologies will drive near-term innovation and discoveries about the diverse RNA contents of EVs. Long-term translation of EV-based RNA profiling into a mainstay medical diagnostic tool will depend upon identifying robust patterns of circulating genetic material that correlate with a change in health status.

Massive release of CD9+ microvesicles in HIV infection, regardless of virologic control

Background

The role of extracellular vesicles (EVs) in human immunodeficiency virus (HIV) pathogenesis is unknown. We examine the cellular origin of plasma microvesicles (MVs), a type of ectocytosis-derived EV, the presence of mitochondria in MVs, and their relationship to circulating cell-free mitochondrial deoxyribonucleic acid (ccf-mtDNA) in HIV-infected patients and controls.

Methods

Five participant groups were defined: 30 antiretroviral therapy (ART)-naive; 30 ART-treated with nondetectable viremia; 30 elite controllers; 30 viremic controllers; and 30 HIV-uninfected controls. Microvesicles were quantified and characterized from plasma samples by flow cytometry. MitoTrackerDeepRed identified MVs containing mitochondria and ccf-mtDNA was quantified by real-time polymerase chain reaction.

Results

Microvesicle numbers were expanded at least 10-fold in all HIV-infected groups compared with controls. More than 79% were platelet-derived MVs. Proportions of MVs containing mitochondria (22.3% vs 41.6%) and MV mitochondrial density (706 vs 1346) were significantly lower among HIV-infected subjects than controls, lowest levels for those on ART. Microvesicle numbers correlated with ccf-mtDNA levels that were higher among HIV-infected patients.

Conclusions

A massive release of platelet-derived MVs occurs during HIV infection. Some MVs contain mitochondria, but their proportion and mitochondrial densities were lower in HIV infection than in controls. Platelet-derived MVs may be biomarkers of platelet activation, possibly reflecting pathogenesis even in absence of HIV replication.

Exosomes

Exosomes are small, single-membrane, secreted organelles of ∼30 to ∼200 nm in diameter that have the same topology as the cell and are enriched in selected proteins, lipids, nucleic acids, and glycoconjugates. Exosomes contain an array of membrane-associated, high-order oligomeric protein complexes, display pronounced molecular heterogeneity, and are created by budding at both plasma and endosome membranes. Exosome biogenesis is a mechanism of protein quality control, and once released, exosomes have activities as diverse as remodeling the extracellular matrix and transmitting signals and molecules to other cells. This pathway of intercellular vesicle traffic plays important roles in many aspects of human health and disease, including development, immunity, tissue homeostasis, cancer, and neurodegenerative diseases. In addition, viruses co-opt exosome biogenesis pathways both for assembling infectious particles and for establishing host permissiveness. On the basis of these and other properties, exosomes are being developed as therapeutic agents in multiple disease models.

Extracellular Vesicles in Viral Infections of the Nervous System

Almost all types of cells release extracellular vesicles (EVs) into the extracellular space. EVs such as exosomes and microvesicles are membrane-bound vesicles ranging in size from 30 to 1000 nm in diameter. Under normal conditions, EVs mediate cell to cell as well as inter-organ communication via the shuttling of their cargoes which include RNA, DNA and proteins. Under pathological conditions, however, the number, size and content of EVs are found to be altered and have been shown to play crucial roles in disease progression. Emerging studies have demonstrated that EVs are involved in many aspects of viral infection-mediated neurodegenerative diseases. In the current review, we will describe the interactions between EV biogenesis and the release of virus particles while also reviewing the role of EVs in various viral infections, such as HIV-1, HTLV, Zika, CMV, EBV, Hepatitis B and C, JCV, and HSV-1. We will also discuss the potential uses of EVs and their cargoes as biomarkers and therapeutic vehicles for viral infections.

The Role of Extracellular Vesicles as Allies of HIV, HCV and SARS Viruses

Extracellular vesicles (EVs) are lipid bilayer-enclosed entities containing proteins and nucleic acids that mediate intercellular communication, in both physiological and pathological conditions. EVs resemble enveloped viruses in both structural and functional aspects. In full analogy with viral biogenesis, some of these vesicles are generated inside cells and, once released into the extracellular milieu, are called “exosomes”. Others bud from the plasma membrane and are generally referred to as “microvesicles”. In this review, we will discuss the state of the art of the current studies on the relationship between EVs and viruses and their involvement in three important viral infections caused by HIV, HCV and Severe Acute Respiratory Syndrome (SARS) viruses. HIV and HCV are two well-known pathogens that hijack EVs content and release to create a suitable environment for viral infection. SARS viruses are a new entry in the world of EVs studies, but are equally important in this historical framework. A thorough knowledge of the involvement of the EVs in viral infections could be helpful for the development of new therapeutic strategies to counteract different pathogens.

The Messenger Apps of the cell: Extracellular Vesicles as Regulatory Messengers of Microglial Function in the CNS

The intense effort of investigators, in particular during the past decade, has highlighted the importance of extracellular vesicles (EVs) such as exosomes in regulating both innate and adaptive immunity in the course of a variety of infections, with clear implications for development of novel vaccines, therapeutics, and diagnostics. Current and future efforts now need to focus strongly on teasing apart the intricate and complex molecular mechanisms that operate during EV regulation of immunity. In this review, we discuss recent advances that bear on our current understanding of how EVs, including exosomes, can contribute to the innate immune functions of microglia within the central nervous system (CNS), and we also highlight future important mechanistic questions that need to be addressed. In particular, recent findings that highlight the crosstalk between autophagy and exosome pathways and their implications for innate immune functions of microglia will be presented. Microglial activation has been shown to play a key role in neuroAIDS, a neuro-infectious disease for which the importance of exosome functions, including exosome-autophagy interplay, has been reported. The importance of exosomes and exosome-autophagy crosstalk involving microglia has also been shown for the Parkinson's disease (PD), a neurodegenerative disease that is thought to be linked with immune dysfunction and involve infectious agents as trigger. Considering the accumulation of recent findings and the vibrancy of the EV field, we anticipate that future studies will continue to have a deep impact on our understanding of the CNS pathologies that are influenced by the functions of microglia and of the infectious disease mechanisms in general. Graphical Abstract.

Inhibition of HIV Replication by Apolipoprotein A-I Binding Protein Targeting the Lipid Rafts

Apolipoprotein A-I binding protein (AIBP) is a recently identified innate anti-inflammatory factor. Here, we show that AIBP inhibited HIV replication by targeting lipid rafts and reducing virus-cell fusion. Importantly, AIBP selectively reduced levels of rafts on cells stimulated by an inflammatory stimulus or treated with extracellular vesicles containing HIV-1 protein Nef without affecting rafts on nonactivated cells. Accordingly, fusion of monocyte-derived macrophages with HIV was sensitive to AIBP only in the presence of Nef. Silencing of endogenous AIBP significantly upregulated HIV-1 replication. Interestingly, HIV-1 replication in cells from donors with the HLA-B*35 genotype, associated with rapid progression of HIV disease, was not inhibited by AIBP. These results suggest that AIBP is an innate anti-HIV factor that targets virus-cell fusion.

Apolipoprotein A-I binding protein (AIBP) is a protein involved in regulation of lipid rafts and cholesterol efflux. AIBP has been suggested to function as a protective factor under several sets of pathological conditions associated with increased abundance of lipid rafts, such as atherosclerosis and acute lung injury. Here, we show that exogenously added AIBP reduced the abundance of lipid rafts and inhibited HIV replication in vitro as well as in HIV-infected humanized mice, whereas knockdown of endogenous AIBP increased HIV replication. Endogenous AIBP was much more abundant in activated T cells than in monocyte-derived macrophages (MDMs), and exogenous AIBP was much less effective in T cells than in MDMs. AIBP inhibited virus-cell fusion, specifically targeting cells with lipid rafts mobilized by cell activation or Nef-containing exosomes. MDM-HIV fusion was sensitive to AIBP only in the presence of Nef provided by the virus or exosomes. Peripheral blood mononuclear cells from donors with the HLA-B*35 genotype, associated with rapid progression of HIV disease, bound less AIBP than cells from donors with other HLA genotypes and were not protected by AIBP from rapid HIV-1 replication. These results provide the first evidence for the role of Nef exosomes in regulating HIV-cell fusion by modifying lipid rafts and suggest that AIBP is an innate factor that restricts HIV replication by targeting lipid rafts.