Differential incorporation of CD45, CD80 (B7-1), CD86 (B7-2), and major histocompatibility complex class I and II molecules into human immunodeficiency virus type 1 virions and microvesicles: implications for viral pathogenesis and immune regulation

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.

Intrinsic factors behind long-COVID: II. SARS-CoV-2, extracellular vesicles, and neurological disorders

With the decline in the number of new Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infections, the World Health Organization announced the end of the SARS-CoV-2 pandemic. However, the repercussions of this viral pandemic may remain with us for a longer period of time, as it has remodeled the lives of humankind in many ways, including social and economic. Of course, its most important repercussions remain on the human health level. Long-coronavirus disease (COVID) or post-COVID is a state for which we do not have a concrete definition, a specific international classification of diseases Code, clear diagnostic tools, or well-known effective cures as of yet. In this second article from the Intrinsic Factors behind long-COVID Series, we try to link long-COVID symptoms with their causes, starting from the nervous system. Extracellular vesicles (ECVs) play very complex and ramified roles in the bodies of both healthy and not-healthy individuals. ECVs may facilitate the entry of many bioactive molecules and pathogens into the tissues and cells of the nervous system across the blood-brain barrier. Based on the size, quantity, and quality of their cargo, ECVs are directly proportional to the pathological condition and its severity through intertwined mechanisms that evoke inflammatory immune responses typically accompanied by pathological symptoms over variable time periods according to the type of these symptoms.

Nonenveloped Avian Reoviruses Released with Small Extracellular Vesicles Are Highly Infectious

Vesicle-encapsulated nonenveloped viruses are a recently recognized alternate form of nonenveloped viruses that can avoid immune detection and potentially increase systemic transmission. Avian orthoreoviruses (ARVs) are the leading cause of various disease conditions among birds and poultry. However, whether ARVs use cellular vesicle trafficking routes for egress and cell-to-cell transmission is still poorly understood. We demonstrated that fusogenic ARV-infected quail cells generated small (~100 nm diameter) extracellular vesicles (EVs) that contained electron-dense material when observed by transmission electron microscope. Cryo-EM tomography indicated that these vesicles did not contain ARV virions or core particles, but the EV fractions of OptiPrep gradients did contain a small percent of the ARV virions released from cells. Western blotting of detergent-treated EVs revealed that soluble virus proteins and the fusogenic p10 FAST protein were contained within the EVs. Notably, virus particles mixed with the EVs were up to 50 times more infectious than virions alone. These results suggest that EVs and perhaps fusogenic FAST-EVs could contribute to ARV virulence.

TDP-43 Controls HIV-1 Viral Production and Virus Infectiveness

The transactive response DNA-binding protein (TARDBP/TDP-43) is known to stabilize the anti-HIV-1 factor, histone deacetylase 6 (HDAC6). TDP-43 has been reported to determine cell permissivity to HIV-1 fusion and infection acting on tubulin-deacetylase HDAC6. Here, we studied the functional involvement of TDP-43 in the late stages of the HIV-1 viral cycle. The overexpression of TDP-43, in virus-producing cells, stabilized HDAC6 (i.e., mRNA and protein) and triggered the autophagic clearance of HIV-1 Pr55^Gag and Vif proteins. These events inhibited viral particle production and impaired virion infectiveness, observing a reduction in the amount of Pr55^Gag and Vif proteins incorporated into virions. A nuclear localization signal (NLS)-TDP-43 mutant was not able to control HIV-1 viral production and infection. Likewise, specific TDP-43-knockdown reduced HDAC6 expression (i.e., mRNA and protein) and increased the expression level of HIV-1 Vif and Pr55^Gag proteins and α-tubulin acetylation. Thus, TDP-43 silencing favored virion production and enhanced virus infectious capacity, thereby increasing the amount of Vif and Pr55^Gag proteins incorporated into virions. Noteworthy, there was a direct relationship between the content of Vif and Pr55^Gag proteins in virions and their infection capacity. Therefore, for TDP-43, the TDP-43/HDAC6 axis could be considered a key factor to control HIV-1 viral production and virus infectiveness.

Host Molecule Incorporation into HIV Virions, Potential Influences in HIV Pathogenesis

During the last phase of HIV viral production, nascent HIV virions acquire a fraction of the cellular lipid membrane to create the external lipid envelope, a process by which cellular proteins present on the surface of the infected cell can be incorporated along with Env trimers. Interestingly, several studies indicated that these incorporated host molecules could conserve their biological activity and consequently contribute to HIV pathogenesis either by enhancing the infectivity of HIV virions, their tissue tropism or by affecting immune cell functions. The following review will describe the main approaches used to characterize membrane bound host molecule incorporation into HIV virions, the proposed mechanisms involved, and the role of a non-exhaustive list of incorporated molecules.

The role of soluble CD80 in patients with soft tissue tumors

BACKGROUND

Immune checkpoint protein (ICP), which is a central factor group of the immune system, has been reported to have a correlation between the degree of its expression and the prognosis of patients with malignant tumors, and many inhibitors have appeared as therapeutic targets. On the other hand, a soluble form of ICP in circulating blood induced systemic immunosuppression. In this study, we investigated the relationship between the soluble form of CD80 (sCD80) which is a ligand for the inhibitory system CTLA-4, in blood, and clinicopathological parameters in patients with soft tissue tumors.

METHODS

A total of 119 patients with primary soft tissue tumors were enrolled in this study. The sCD80 levels were measured by enzyme immunoassay.

RESULTS

There were no significant differences in sCD80 levels between benign (34) and soft tissue sarcoma (STS) patients (85). In STS, the high-sCD80 group had significantly lower metastasis-free survival (MS) and lower overall survival (OS) than the low-sCD80 group at 5 years using the log-rank test (OS: high > 404 pg/mL, low ≤ 404 pg/mL, MS: high > 531 pg/ml, low ≤ 531 pg/ml). On multivariate Cox proportional hazard analysis, the high-sCD80 group had significant differences in 5MS and 5OS compared to the low-sCD80 group.

CONCLUSIONS

In conclusion, sCD80 may negatively affect systemic immune circumstances, in STS, and may have potential as a therapeutic target.

Alloimmunity to Class 2 Human Leucocyte Antigens May Reduce HIV-1 Acquisition – A Nested Case-Control Study in HIV-1 Serodiscordant Couples

Enveloped viruses, including the Human Immunodeficiency Virus-1 (HIV), incorporate host proteins such as human leucocyte antigens (HLA) into their envelope. Pre-existing antibodies against HLA, termed HLA antibodies, may bind to these surface proteins and reduce viral infectivity. Related evidence includes macaque studies which suggest that xenoimmunization with HLA antigens may protect against simian immunodeficiency virus infection. Since HIV gp120 shows homology with class 2 HLA, including shared affinity for binding to CD4, class 2 HLA antibodies may influence HIV acquisition via binding to gp120 on the viral envelope. We conducted a nested case-control study on HIV serodiscordant couples, comparing the frequency of HLA antibodies among highly exposed persistently seronegative controls with those who went on to acquire HIV (HIV-seroconverters). We first performed low resolution HLA typing on 143 individuals who were HIV-infected at enrollment (index partners) and their corresponding sexual partners (115 highly exposed persistently seronegative individuals and 28 HIV-seroconverters). We then measured HLA class 1 and 2 antibodies in the highly exposed persistently seronegative individuals and HIV-seroconverters at early and late timepoints. We analyzed whether such antibodies were directed at HLA specificities of their HIV-infected index partners, and whether autoantibodies or complement-fixing class 2 HLA antibodies were present. Seventy-nine percent of highly exposed persistently seronegative individuals had HLA antibodies; 56% against class 1 and 50% against class 2 alleles. Half of the group of highly exposed persistently seronegative individuals, prior to seroconversion, expressed class 2 HLA antibodies, compared with only 29% of controls (p=0.05). HIV infection was a sensitizing event leading to de novo development of antibodies against HLA-A and HLA-B loci, but not against class 2 loci. HLA autoantibodies were present in 27% of highly exposed persistently seronegative individuals. Complement-fixing class 2 HLA antibodies did not differ significantly between highly exposed persistently seronegative individuals and seroconverters. In multivariable regression, presence of class 2 HLA antibodies at early timepoints was associated with reduced odds of HIV acquisition (odds ratio 0.330, confidence interval 0.112-0.976, p=0.045). These epidemiological data suggest that pre-existing class 2 HLA antibodies were associated with reduced odds of HIV acquisition.

A Comprehensive Insight into the Role of Exosomes in Viral Infection: Dual Faces Bearing Different Functions

Extracellular vesicles (EVs) subtype, exosome is an extracellular nano-vesicle that sheds from cells’ surface and originates as intraluminal vesicles during endocytosis. Firstly, it was thought to be a way for the cell to get rid of unwanted materials as it loaded selectively with a variety of cellular molecules, including RNAs, proteins, and lipids. However, it has been found to play a crucial role in several biological processes such as immune modulation, cellular communication, and their role as vehicles to transport biologically active molecules. The latest discoveries have revealed that many viruses export their viral elements within cellular factors using exosomes. Hijacking the exosomal pathway by viruses influences downstream processes such as viral propagation and cellular immunity and modulates the cellular microenvironment. In this manuscript, we reviewed exosomes biogenesis and their role in the immune response to viral infection. In addition, we provided a summary of how some pathogenic viruses hijacked this normal physiological process. Viral components are harbored in exosomes and the role of these exosomes in viral infection is discussed. Understanding the nature of exosomes and their role in viral infections is fundamental for future development for them to be used as a vaccine or as a non-classical therapeutic strategy to control several viral infections.

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.

Immunogenicity of HIV-1-Based Virus-Like Particles with Increased Incorporation and Stability of Membrane-Bound Env

An optimal prophylactic vaccine to prevent human immunodeficiency virus (HIV-1) transmission should elicit protective antibody responses against the HIV-1 envelope glycoprotein (Env). Replication-incompetent HIV-1 virus-like particles (VLPs) offer the opportunity to present virion-associated Env with a native-like structure during vaccination that closely resembles that encountered on infectious virus. Here, we optimized the incorporation of Env into previously designed mature-form VLPs (mVLPs) and assessed their immunogenicity in mice. The incorporation of Env into mVLPs was increased by replacing the Env transmembrane and cytoplasmic tail domains with those of influenza haemagglutinin (HA-TMCT). Furthermore, Env was stabilized on the VLP surface by introducing an interchain disulfide and proline substitution (SOSIP) mutations typically employed to stabilize soluble Env trimers. The resulting mVLPs efficiently presented neutralizing antibody epitopes while minimizing exposure of non-neutralizing antibody sites. Vaccination of mice with mVLPs elicited a broader range of Env-specific antibody isotypes than Env presented on immature VLPs or extracellular vesicles. The mVLPs bearing HA-TMCT-modified Env consistently induced anti-Env antibody responses that mediated modest neutralization activity. These mVLPs are potentially useful immunogens for eliciting neutralizing antibody responses that target native Env epitopes on infectious HIV-1 virions.

Recent Progress on Exosomes in RNA Virus Infection

Recent research indicates that most tissue and cell types can secrete and release membrane-enclosed small vesicles, known as exosomes, whose content reflects the physiological/pathological state of the cells from which they originate. These exosomes participate in the communication and cell-to-cell transfer of biologically active proteins, lipids, and nucleic acids. Studies of RNA viruses have demonstrated that exosomes release regulatory factors from infected cells and deliver other functional host genetic elements to neighboring cells, and these functions are involved in the infection process and modulate the cellular responses. This review provides an overview of the biogenesis, composition, and some of the most striking functions of exosome secretion and identifies physiological/pathological areas in need of further research. While initial indications suggest that exosome-mediated pathways operate in vivo, the exosome mechanisms involved in the related effects still need to be clarified. The current review focuses on the role of exosomes in RNA virus infections, with an emphasis on the potential contributions of exosomes to pathogenesis.

Effects of Cell-Derived Microparticles on Immune Cells and Potential Implications in Clinical Medicine

In the past few years, interest has increased in cell-derived microparticles (MPs), which are defined by their size of from 0.1 to 1 μm, and can be derived from various cell types, including endothelial cells, leukocytes, red blood cells (RBCs), and platelets. These MPs carry negatively charged phosphatidylserine (PS) on their surfaces and proteins packaged from numerous cellular components. MPs that have been shed by the body can play important roles in the pathophysiology of diseases and can affect various biological systems. Among these systems, the immune components have been shown to be modulated by MPs. Therefore, understanding the roles of MPs in the immune system is crucial to developing alternative therapeutic treatments for diseases. This review describes the effects of MPs on various immune cells and provides plausible potential applications of the immune-modulating properties of MPs in clinical medicine.

Revisiting Membrane Microdomains and Phase Separation: A Viral Perspective

Retroviruses selectively incorporate a specific subset of host cell proteins and lipids into their outer membrane when they bud out from the host plasma membrane. This specialized viral membrane composition is critical for both viral survivability and infectivity. Here, we review recent findings from live cell imaging of single virus assembly demonstrating that proteins and lipids sort into the HIV retroviral membrane by a mechanism of lipid-based phase partitioning. The findings showed that multimerizing HIV Gag at the assembly site creates a liquid-ordered lipid phase enriched in cholesterol and sphingolipids. Proteins with affinity for this specialized lipid environment partition into it, resulting in the selective incorporation of proteins into the nascent viral membrane. Building on this and other work in the field, we propose a model describing how HIV Gag induces phase separation of the viral assembly site through a mechanism involving transbilayer coupling of lipid acyl chains and membrane curvature changes. Similar phase-partitioning pathways in response to multimerizing structural proteins likely help sort proteins into the membranes of other budding structures within cells.

Lipid rafts and pathogens: the art of deception and exploitation

Lipid rafts, solid regions of the plasma membrane enriched in cholesterol and glycosphingolipids, are essential parts of a cell. Functionally, lipid rafts present a platform that facilitates interaction of cells with the outside world. However, the unique properties of lipid rafts required to fulfill this function at the same time make them susceptible to exploitation by pathogens. Many steps of pathogen interaction with host cells, and sometimes all steps within the entire lifecycle of various pathogens, rely on host lipid rafts. Such steps as binding of pathogens to the host cells, invasion of intracellular parasites into the cell, the intracellular dwelling of parasites, microbial assembly and exit from the host cell, and microbe transfer from one cell to another all involve lipid rafts. Interaction also includes modification of lipid rafts in host cells, inflicted by pathogens from both inside and outside the cell, through contact or remotely, to advance pathogen replication, to utilize cellular resources, and/or to mitigate immune response. Here, we provide a systematic overview of how and why pathogens interact with and exploit host lipid rafts, as well as the consequences of this interaction for the host, locally and systemically, and for the microbe. We also raise the possibility of modulation of lipid rafts as a therapeutic approach against a variety of infectious agents.

Exosomal miRNAs: novel players in viral infection

Exosomes are secreted nanovesicles that are able to transfer their cargo (such as miRNAs) between cells. To determine to what extent exosomes and exosomal miRNAs are involved in the pathogenesis, progression and diagnosis of viral infections. The scientific literature (PubMed and Google Scholar) was searched from 1970 to 2019. The complex biogenesis of exosomes and miRNAs was reviewed. Exosomes contain both viral and host miRNAs that can be used as diagnostic biomarkers for viral diseases. Viral proteins can alter miRNAs, and conversely miRNAs can alter the host response to viral infections in a positive or negative manner. It is expected that exosomal miRNAs will be increasingly used for diagnosis, monitoring and even treatment of viral infections.

HIV-1-based Virus-like Particles that Morphologically Resemble Mature, Infectious HIV-1 Virions

A prophylactic vaccine eliciting both broad neutralizing antibodies (bNAbs) to the HIV-1 envelope glycoprotein (Env) and strong T cell responses would be optimal for preventing HIV-1 transmissions. Replication incompetent HIV-1 virus-like particles (VLPs) offer the opportunity to present authentic-structured, virion-associated Env to elicit bNAbs, and also stimulate T cell responses. Here, we optimize our DNA vaccine plasmids as VLP expression vectors for efficient Env incorporation and budding. The original vector that was used in human trials inefficiently produced VLPs, but maximized safety by inactivating RNA genome packaging, enzyme functions that are required for integration into the host genome, and deleting accessory proteins Vif, Vpr, and Nef. These original DNA vaccine vectors generated VLPs with incomplete protease-mediated cleavage of Gag and were irregularly sized. Mutations to restore function within the defective genes revealed that several of the reverse transcriptase (RT) deletions mediated this immature phenotype. Here, we made efficient budding, protease-processed, and mature-form VLPs that resembled infectious virions by introducing alternative mutations that completely removed the RT domain, but preserved most other safety mutations. These VLPs, either expressed from DNA vectors in vivo or purified after expression in vitro, are potentially useful immunogens that can be used to elicit antibody responses that target Env on fully infectious HIV-1 virions.

Combination of metformin with sodium selenite induces a functional phenotypic switch of human GM-CSF monocyte-derived macrophages

OBJECTIVES

We evaluated the effects of metformin (Met, 1,1‑dimethylbiguanide hydrochloride) combined or not with sodium selenite (Ss, Na₂SeO₃) on the functional activities of LPS-activated GM-CSF monocyte-derived macrophages (GM-MDM).

MATERIALS AND METHODS

Human GM-MDMs from three healthy donors were treated with Met or Ss alone, or with the combination of Met and Ss, and assayed for various biological activities and cytokines expression.

RESULTS

Met alone and Ss alone had significantly different effects on phagocytosis and killing capacities and IL-β production, but had similar effects on the downregulation of inducible nitric oxide synthase (iNOS) activity, relative nicotinamide adenine dinucleotide reduced (NADH) dehydrogenase (Complex I), intracellular free calcium ions (_ifCa²⁺), and on the upregulation of arginase activity. Additionally, iNOS activity-to-arginase activity ratio was downregulated in Met or Ss treated-GM-MDMs, and, conversely, upregulated in GM-MDMs treated with Met + Ss in combination, indicating that arginase activity dominates that of iNOS when the two treatments are associated. Moreover, combination of Met with Ss significantly upregulated hydrogen peroxide (H₂O₂) production and phagocytic capacity, but significantly downregulated the production of IL-1β, iNOS activity and killing capacity. On the contrary, we show that Met alone induced significant downregulation of phagocytic capacity and slight upregulation of killing capacity. Nevertheless, Ss seems to accentuate the effect of Met on the downregulation of NO production, as well as to reverse its effect on both phagocytic and killing capacities. On the other hand, all treatments induced a sharp decrease in relative levels of NADH dehydrogenase, and a marked decrease in the levels of _ifCa²⁺. Finally, we found that GM-MDMs treated with Met or Ss, or Met combined with Ss exhibited different functional activation phenotypes, as indicated by the surface expression of co-stimulatory and cell activation and presentation molecules CD14, CD80, CD86 and HLA-DR.

CONCLUSIONS

Our results demonstrated that Met/Ss combination can play an important role in the modulation of functional activities of human LPS-activated GM-MDMs. Additionally, the overall effects of Met and the induction of "M2" GM-MDMs-associated arginase could be influenced by its combination with Ss.

A lipid-based partitioning mechanism for selective incorporation of proteins into membranes of HIV particles

Particles that bud off from the cell surface, including viruses and microvesicles, typically have a unique membrane protein composition distinct from that of the originating plasma membrane. This selective protein composition enables viruses to evade the immune response and infect other cells. But how membrane proteins sort into budding viruses such as human immunodeficiency virus (HIV) remains unclear. Proteins could passively distribute into HIV-assembly-site membranes producing compositions resembling pre-existing plasma-membrane domains. Here, we demonstrate that proteins instead sort actively into HIV-assembly-site membranes, generating compositions enriched in cholesterol and sphingolipids that undergo continuous remodelling. Proteins are recruited into and removed from the HIV assembly site through lipid-based partitioning, initiated by oligomerization of the HIV structural protein Gag. Changes in membrane curvature at the assembly site further amplify this sorting process. Thus, a lipid-based sorting mechanism, aided by increasing membrane curvature, generates the unique membrane composition of the HIV surface.

Vehicles of intercellular communication: exosomes and HIV-1

The terms extracellular vesicles, microvesicles, oncosomes, or exosomes are often used interchangeably as descriptors of particles that are released from cells and comprise a lipid membrane that encapsulates nucleic acids and proteins. Although these entities are defined based on a specific size range and/or mechanism of release, the terminology is often ambiguous. Nevertheless, these vesicles are increasingly recognized as important modulators of intercellular communication. The generic characterization of extracellular vesicles could also be used as a descriptor of enveloped viruses, highlighting the fact that extracellular vesicles and enveloped viruses are similar in both composition and function. Their high degree of similarity makes differentiating between vesicles and enveloped viruses in biological specimens particularly difficult. Because viral particles and extracellular vesicles are produced simultaneously in infected cells, it is necessary to separate these populations to understand their independent functions. We summarize current understanding of the similarities and differences of extracellular vesicles, which henceforth we will refer to as exosomes, and the enveloped retrovirus, HIV-1. Here, we focus on the presence of these particles in semen, as these are of particular importance during HIV-1 sexual transmission. While there is overlap in the terminology and physical qualities between HIV-1 virions and exosomes, these two types of intercellular vehicles may differ depending on the bio-fluid source. Recent data have demonstrated that exosomes from human semen serve as regulators of HIV-1 infection that may contribute to the remarkably low risk of infection per sexual exposure.

The Incorporation of Host Proteins into the External HIV-1 Envelope

The incorporation of biologically active host proteins into HIV-1 is a well-established phenomenon, particularly due to the budding mechanism of viral egress in which viruses acquire their external lipid membrane directly from the host cell. While this mechanism might seemingly imply that host protein incorporation is a passive uptake of all cellular antigens associated with the plasma membrane at the site of budding, this is not the case. Herein, we review the evidence indicating that host protein incorporation can be a selective and conserved process. We discuss how HIV-1 virions displaying host proteins on their surface can exhibit a myriad of altered phenotypes, with notable impacts on infectivity, homing, neutralization, and pathogenesis. This review describes the canonical and emerging methods to detect host protein incorporation, highlights the well-established host proteins that have been identified on HIV-1 virions, and reflects on the role of these incorporated proteins in viral pathogenesis and therapeutic targeting. Despite many advances in HIV treatment and prevention, there remains a global effort to develop increasingly effective anti-HIV therapies. Given the broad range of biologically active host proteins acquired on the surface of HIV-1, additional studies on the mechanisms and impacts of these incorporated host proteins may inform the development of novel treatments and vaccine designs.

The Ambiguous Roles of Extracellular Vesicles in HIV Replication and Pathogenesis

Cells from all kingdoms of life can release membrane-enclosed vesicles to the extracellular milieu. These extracellular vesicles (EVs) may function as mediators of intercellular communication, allowing the transfer of biologically active molecules between cells and organisms. It has become clear that HIV particles and certain types of EVs, such as exosomes, share many similarities regarding morphology, composition, and biogenesis. This review presents a summary of the literature describing the intricate relationship between HIV and EVs biogenesis. Also, we discuss the latest progress toward understanding the mechanisms by which EVs influence HIV pathogenesis, as well as, how HIV modulates EVs composition in infected cells to facilitate viral spread.

Exosome markers associated with immune activation and oxidative stress in HIV patients on antiretroviral therapy

Exosomes are nanovesicles released from most cell types including immune cells. Prior studies suggest exosomes play a role in HIV pathogenesis, but little is known about exosome cargo in relation to immune responses and oxidative stress. Here, we characterize plasma exosomes in HIV patients and their relationship to immunological and oxidative stress markers. Plasma exosome fractions were isolated from HIV-positive subjects on ART with suppressed viral load and HIV-negative controls. Exosomes were characterized by electron microscopy, nanoparticle tracking, immunoblotting, and LC-MS/MS proteomics. Plasma exosomes were increased in HIV-positive subjects compared to controls, and correlated with increased oxidative stress markers (cystine, oxidized cys-gly) and decreased PUFA (DHA, EPA, DPA). Untargeted proteomics detected markers of exosomes (CD9, CD63, CD81), immune activation (CD14, CRP, HLA-A, HLA-B), oxidative stress (CAT, PRDX1, PRDX2, TXN), and Notch4 in plasma exosomes. Exosomal Notch4 was increased in HIV-positive subjects versus controls and correlated with immune activation markers. Treatment of THP-1 monocytic cells with patient-derived exosomes induced expression of genes related to interferon responses and immune activation. These results suggest that exosomes in ART-treated HIV patients carry proteins related to immune activation and oxidative stress, have immunomodulatory effects on myeloid cells, and may have pro-inflammatory and redox effects during pathogenesis.

Discrimination Between Human Leukocyte Antigen Class I-Bound and Co-Purified HIV-Derived Peptides in Immunopeptidomics Workflows

Elucidation of novel peptides presented by human leukocyte antigen (HLA) class I alleles by immunopeptidomics constitutes a powerful approach that can inform the rational design of CD8⁺ T cell inducing vaccines to control infection with pathogens such as human immunodeficiency virus type 1 (HIV-1) or to combat tumors. Recent advances in the sensitivity of liquid chromatography tandem mass spectrometry instrumentation have facilitated the discovery of thousands of natural HLA-restricted peptides in a single measurement. However, the extent of contamination of class I-bound peptides identified using HLA immunoprecipitation (IP)-based immunopeptidomics approaches with peptides from other sources has not previously been evaluated in depth. Here, we investigated the specificity of the IP-based immunopeptidomics methodology using HLA class I- or II-deficient cell lines and membrane protein-specific antibody IPs. We demonstrate that the 721.221 B lymphoblastoid cell line, widely regarded to be HLA class Ia-deficient, actually expresses and presents peptides on HLA-C*01:02. Using this cell line and the C8166 (HLA class I- and II-expressing) cell line, we show that some HLA class II-bound peptides were co-purified non-specifically during HLA class I and membrane protein IPs. Furthermore, IPs of "irrelevant" membrane proteins from HIV-1-infected HLA class I- and/or II-expressing cells revealed that unusually long HIV-1-derived peptides previously reported by us and other immunopeptidomics studies as potentially novel CD8⁺ T cell epitopes were non-specifically co-isolated, and so constitute a source of contamination in HLA class I IPs. For example, a 16-mer (FLGKIWPSYKGRPGNF), which was detected in all samples studied represents the full p1 segment of the abundant intracellular or virion-associated proteolytically-processed HIV-1 Gag protein. This result is of importance, as these long co-purified HIV-1 Gag peptides may not elicit CD8⁺ T cell responses when incorporated into candidate vaccines. These results have wider implications for HLA epitope discovery from abundant or membrane-associated antigens by immunopeptidomics in the context of infectious diseases, cancer, and autoimmunity.

Role of Microvesicles in the Spread of Herpes Simplex Virus 1 in Oligodendrocytic Cells

Herpes simplex virus 1 (HSV-1) is a neurotropic pathogen that can infect many types of cells and establishes latent infections in the neurons of sensory ganglia. In some cases, the virus spreads into the central nervous system, causing encephalitis or meningitis. Cells infected with several different types of viruses may secrete microvesicles (MVs) containing viral proteins and RNAs. In some instances, extracellular microvesicles harboring infectious virus have been found. Here we describe the features of shedding microvesicles released by the human oligodendroglial HOG cell line infected with HSV-1 and their participation in the viral cycle. Using transmission electron microscopy, we detected for the first time microvesicles containing HSV-1 virions. Interestingly, the Chinese hamster ovary (CHO) cell line, which is resistant to infection by free HSV-1 virions, was susceptible to HSV-1 infection after being exposed to virus-containing microvesicles. Therefore, our results indicate for the first time that MVs released by infected cells contain virions, are endocytosed by naive cells, and lead to a productive infection. Furthermore, infection of CHO cells was not completely neutralized when virus-containing microvesicles were preincubated with neutralizing anti-HSV-1 antibodies. The lack of complete neutralization and the ability of MVs to infect nectin-1/HVEM-negative CHO-K1 cells suggest a novel way for HSV-1 to spread to and enter target cells. Taken together, our results suggest that HSV-1 could spread through microvesicles to expand its tropism and that microvesicles could shield the virus from neutralizing antibodies as a possible mechanism to escape the host immune response.IMPORTANCE Herpes simplex virus 1 (HSV-1) is a neurotropic pathogen that can infect many types of cells and establishes latent infections in neurons. Extracellular vesicles are a heterogeneous group of membrane vesicles secreted by most cell types. Microvesicles, which are extracellular vesicles which derive from the shedding of the plasma membrane, isolated from the supernatant of HSV-1-infected HOG cells were analyzed to find out whether they were involved in the viral cycle. The importance of our investigation lies in the detection, for the first time, of microvesicles containing HSV-1 virions. In addition, virus-containing microvesicles were endocytosed into CHO-K1 cells and were able to actively infect these otherwise nonpermissive cells. Finally, the infection of CHO cells with these virus-containing microvesicles was not completely neutralized by anti-HSV-1 antibodies, suggesting that these extracellular vesicles might shield the virus from neutralizing antibodies as a possible mechanism of immune evasion.

The anti-caspase inhibitor Q-VD-OPH prevents AIDS disease progression in SIV-infected rhesus macaques

Apoptosis has been proposed as a key mechanism responsible for CD4+ T cell depletion and immune dysfunction during HIV infection. We demonstrated that Q-VD-OPH, a caspase inhibitor, inhibits spontaneous and activation-induced death of T cells from SIV-infected rhesus macaques (RMs). When administered during the acute phase of infection, Q-VD-OPH was associated with (a) reduced levels of T cell death, (b) preservation of CD4+/CD8+ T cell ratio in lymphoid organs and in the gut, (c) maintenance of memory CD4+ T cells, and (d) increased specific CD4+ T cell response associated with the expression of cytotoxic molecules. Although therapy was limited to the acute phase of infection, Q-VD-OPH-treated RMs showed lower levels of both viral load and cell-associated SIV DNA as compared with control SIV-infected RMs throughout the chronic phase of infection, and prevented the development of AIDS. Overall, our data demonstrate that Q-VD-OPH injection in SIV-infected RMs may represent an adjunctive therapeutic agent to control HIV infection and delaying disease progression to AIDS.

Polymorphic Nature of Human T-Cell Leukemia Virus Type 1 Particle Cores as Revealed through Characterization of a Chronically Infected Cell Line

Human T-cell leukemia virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-1 cell-to-cell transmission is dependent on the release of infectious virus particles into the virological synapse. The HTLV-1 particle structure is still poorly understood, and previous studies analyzed viruses produced by transformed lymphocytic cell lines chronically infected with HTLV-1, particularly the MT-2 cell line, which harbors truncated proviruses and expresses aberrant forms of the Gag protein. In this study, we demonstrate that the chronically infected SP cell line harbors a relatively low number of proviruses, making it a more promising experimental system for the study of the HTLV-1 particle structure. We first identified the genomic sites of integration and characterized the genetic structure of the gag region in each provirus. We also determined that despite encoding a truncated Gag protein, only the full-length Gag protein was incorporated into virus particles. Cryo-transmission electron microscopy analyses of the purified virus particles revealed three classes of particles based upon capsid core morphology: complete cores, incomplete cores, and particles without distinct electron densities that would correlate with the capsid region of a core structure. Observed cores were generally polygonal, and virus particles were on average 115 nm in diameter. These data corroborate particle morphologies previously observed for MT-2 cells and provide evidence that the known poor infectivity of HTLV-1 particles may correlate with HTLV-1 particle populations containing few virus particles possessing a complete capsid core structure.IMPORTANCE Studies of retroviral particle core morphology have demonstrated a correlation between capsid core stability and the relative infectivity of the virus. In this study, we used cryo-transmission electron microscopy to demonstrate that HTLV-1 particles produced from a distinct chronically infected cell line are polymorphic in nature, with many particles lacking organized electron densities that would correlate with a complete core structure. These findings have important implications for infectious HTLV-1 spread, particularly in the context of cell-to-cell transmission, a critical step in HTLV-1 transmission and pathogenesis.

Role of TIM-4 in exosome-dependent entry of HIV-1 into human immune cells

Exosomes, 30–200 nm nanostructures secreted from donor cells and internalized by recipient cells, can play an important role in the cellular entry of some viruses. These microvesicles are actively secreted into various body fluids, including blood, urine, saliva, cerebrospinal fluid, and breast milk. We successfully isolated exosomes from human breast milk and plasma. The size and concentration of purified exosomes were measured by nanoparticle tracking, while Western blotting confirmed the presence of the exosomal-associated proteins CD9 and CD63, clathrin, and T cell immunoglobulin and mucin proteins (TIMs). Through viral infection assays, we determined that HIV-1 utilizes an exosome-dependent mechanism for entry into human immune cells. The virus contains high amounts of phosphatidylserine (PtdSer) and may bind PtdSer receptors, such as TIMs. This mechanism is supported by our findings that exosomes from multiple sources increased HIV-1 entry into T cells and macrophages, and viral entry was potently blocked with anti-TIM-4 antibodies.

Virion incorporation of integrin α4β7 facilitates HIV-1 infection and intestinal homing

The intestinal mucosa is a key anatomical site for HIV-1 replication and CD4⁺ T cell depletion. Accordingly, in vivo treatment with an antibody to the gut-homing integrin α4β7 was shown to reduce viral transmission, delay disease progression, and induce persistent virus control in macaques challenged with simian immunodeficiency virus (SIV). We show that integrin α4β7 is efficiently incorporated into the envelope of HIV-1 virions. Incorporated α4β7 is functionally active as it binds mucosal addressin cell adhesion molecule-1 (MAdCAM-1), promoting HIV-1 capture by and infection of MAdCAM-expressing cells, which in turn mediate trans-infection of bystander cells. Functional α4β7 is present in circulating virions from HIV-infected patients and SIV-infected macaques, with peak levels during the early stages of infection. In vivo homing experiments documented selective and specific uptake of α4β7⁺ HIV-1 virions by high endothelial venules in the intestinal mucosa. These results extend the paradigm of tissue homing to a retrovirus and are relevant for the pathogenesis, treatment, and prevention of HIV-1 infection.

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

Cells productively infected with HIV-1 release virions along with extracellular vesicles (EVs) whose biogenesis, size, and physical properties resemble those of retroviruses. Here, we found that a significant number of EVs (exosomes) released by HIV-1 infected cells carry gp120 (Env), a viral protein that mediates virus attachment and fusion to target cells, and also facilitates HIV infection in various indirect ways. Depletion of viral preparations of EVs, in particular of those that carry gp120, decreases viral infection of human lymphoid tissue ex vivo. Thus, EVs that carry Env identified in our work seem to facilitate HIV infection and therefore may constitute a new therapeutic target for antiviral strategy.

High sensitivity detection and sorting of infectious human immunodeficiency virus (HIV-1) particles by flow virometry

Detection of viruses by flow cytometry is complicated by their small size. Here, we characterized the ability of a standard (FACSAria II) and a sub-micron flow cytometer (A50 Micro) to resolve HIV-1 viruses. The A50 was superior at resolving small particles but did not reliably distinguish HIV-1, extracellular vesicles, and laser noise by light scatter properties alone. However, single fluorescent HIV-1 particles could readily be detected by both cytometers. Fluorescent particles were sorted and retained infectivity, permitting further exploration of the functional consequences of HIV-1 heterogeneity. Finally, flow cytometry had a limit of detection of 80 viruses/ml, nearly equal to PCR assays. These studies demonstrate the power of flow cytometry to detect and sort viral particles and provide a critical toolkit to validate methods to label wild-type HIV-1; quantitatively assess integrity and aggregation of viruses and virus-based therapeutics; and efficiently screen drugs inhibiting viral assembly and release.

Isolation and Characterization of Microvesicles from Peripheral Blood

The release of extracellular vesicles (EVs) including small endosomal-derived exosomes (Exos, diameter < 100 nm) and large plasma membrane-derived microvesicles (MVs, diameter > 100 nm) is a fundamental cellular process that occurs in all living cells. These vesicles transport proteins, lipids and nucleic acids specific for their cell of origin and in vitro studies have highlighted their importance as mediators of intercellular communication. EVs have been successfully isolated from various body fluids and especially EVs in blood have been identified as promising biomarkers for cancer or infectious diseases. In order to allow the study of MV subpopulations in blood, we present a protocol for the standardized isolation and characterization of MVs from peripheral blood samples. MVs are pelleted from EDTA-anticoagulated plasma samples by differential centrifugation and typically possess a diameter of 100 - 600 nm. Due to their larger size, they can easily be studied by flow cytometry, a technique that is routinely used in clinical diagnostics and available in most laboratories. Several examples for quality control assays of the isolated MVs will be given and markers that can be used for the discrimination of different MV subpopulations in blood will be presented.

HIV-1 Env associates with HLA-C free-chains at the cell membrane modulating viral infectivity

HLA-C has been demonstrated to associate with HIV-1 envelope glycoprotein (Env). Virions lacking HLA-C have reduced infectivity and increased susceptibility to neutralizing antibodies. Like all others MHC-I molecules, HLA-C requires β₂-microglobulin (β₂m) for appropriate folding and expression on the cell membrane but this association is weaker, thus generating HLA-C free-chains on the cell surface. In this study, we deepen the understanding of HLA-C and Env association by showing that HIV-1 specifically increases the amount of HLA-C free chains, not bound to β₂m, on the membrane of infected cells. The association between Env and HLA-C takes place at the cell membrane requiring β₂m to occur. We report that the enhanced infectivity conferred to HIV-1 by HLA-C specifically involves HLA-C free chain molecules that have been correctly assembled with β₂m. HIV-1 Env-pseudotyped viruses produced in the absence of β₂m are less infectious than those produced in the presence of β₂m. We hypothesize that the conformation and surface expression of HLA-C molecules could be a discriminant for the association with Env. Binding stability to β₂m may confer to HLA-C the ability to preferentially act either as a conventional immune-competent molecule or as an accessory molecule involved in HIV-1 infectivity.

Characterization and Role of Lentivirus-Associated Host Proteins

Enveloped viruses obtain their envelopes during the process of budding from infected cells. During this process, however, these viruses acquire parts of the host cell membranes and host cell-derived proteins as integral parts of their mature envelopes. These host-derived components of viral envelopes may subsequently exhibit various effects on the life cycle of the virus; virus cell interactions, especially host response to virus-incorporated self-proteins; and the pathogenesis of the disease induced by these viruses. Although it was known for some time that various viruses incorporate host cell-derived proteins, the issue of the role of these proteins has received increased attention, specifically in connection with human immunodeficiency virus (HIV) infection and development of acquired immunodeficiency syndrome (AIDS) in humans. The aim of this review is to summarize our current knowledge of the analysis and role of host-derived proteins associated with enveloped viruses, with emphasis on the potential role of these proteins in the pathogenesis of AIDS. Clearly, differences in the clinical outcome of those nonhuman primates infected with simian immunodeficiency virus (SIV) that are disease resistant compared with SIV-infected species that are disease susceptible provide a unique opportunity to determine whether differences in the incorporation of distinct sets of host proteins play a role with distinct clinical outcomes.

Glycosylphosphatidylinositol Anchor Deficiency Attenuates the Production of Infectious HIV-1 and Renders Virions Sensitive to Complement Attack

Human immunodeficiency virus type 1 (HIV-1) escapes complement-mediated lysis (CML) by incorporating host regulators of complement activation (RCA) into its envelope. CD59, a key member of RCA, is incorporated into HIV-1 virions at levels that protect against CML. Since CD59 is a glycosylphosphatidylinositol-anchored protein (GPI-AP), we used GPI anchor-deficient Jurkat cells (Jurkat-7) that express intracellular CD59, but not surface CD59, to study the molecular mechanisms underlying CD59 incorporation into HIV-1 virions and the role of host proteins in virus replication. Compared to Jurkat cells, Jurkat-7 cells were less supportive to HIV-1 replication and more sensitive to CML. Jurkat-7 cells exhibited similar capacities of HIV-1 binding and entry to Jurkat cells, but were less supportive to viral RNA and DNA biosynthesis as infected Jurkat-7 cells produced reduced amounts of HIV-1 RNA and DNA. HIV-1 virions produced from Jurkat-7 cells were CD59 negative, suggesting that viral particles acquire CD59, and probably other host proteins, from the cell membrane rather than intracellular compartments. As a result, CD59-negative virions were sensitive to CML. Strikingly, these virions exhibited reduced activity of virus binding and were less infectious, implicating that GPI-APs may be also important in ensuring the integrity of HIV-1 particles. Transient expression of the PIG-A gene restored CD59 expression on the surface of Jurkat-7 cells. After HIV-1 infection, the restored CD59 was colocalized with viral envelope glycoprotein gp120/gp41 within lipid rafts, which is identical to that on infected Jurkat cells. Thus, HIV-1 virions acquire RCA from the cell surface, likely lipid rafts, to escape CML and ensure viral infectivity.

Mammalian Lipopolysaccharide Receptors Incorporated into the Retroviral Envelope Augment Virus Transmission

The orally transmitted retrovirus mouse mammary tumor virus (MMTV) requires the intestinal microbiota for persistence. Virion-associated lipopolysaccharide (LPS) activates Toll-like receptor 4 (TLR4), stimulating production of the immunosuppressive cytokine IL-10 and MMTV evasion of host immunity. However, the mechanisms by which MMTV associates with LPS remain unknown. We find that the viral envelope contains the mammalian LPS-binding factors CD14, TLR4, and MD-2, which, in conjunction with LPS-binding protein (LBP), bind LPS to the virus and augment transmission. MMTV isolated from infected mice lacking these LBPs cannot engage LPS or stimulate TLR4 and have a transmission defect. Furthermore, MMTV incorporation of a weak agonist LPS from Bacteroides, a prevalent LPS source in the gut, significantly enhances the ability of this LPS to stimulate TLR4, suggesting that MMTV intensifies these immunostimulatory properties. Thus, an orally transmitted retrovirus can capture, modify, and exploit mammalian receptors for bacterial ligands to ensure successful transmission.

Extracellular vesicles and viruses: Are they close relatives?

Extracellular vesicles (EVs) released by various cells are small phospholipid membrane-enclosed entities that can carry miRNA. They are now central to research in many fields of biology because they seem to constitute a new system of cell-cell communication. Physical and chemical characteristics of many EVs, as well as their biogenesis pathways, resemble those of retroviruses. Moreover, EVs generated by virus-infected cells can incorporate viral proteins and fragments of viral RNA, being thus indistinguishable from defective (noninfectious) retroviruses. EVs, depending on the proteins and genetic material incorporated in them, play a significant role in viral infection, both facilitating and suppressing it. Deciphering the mechanisms of EV-cell interactions may facilitate the design of EVs that inhibit viral infection and can be used as vehicles for targeted drug delivery.

Extracellular vesicles during Herpes Simplex Virus type 1 infection: an inquire

Extracellular vesicles are defined as a heterogeneous group of vesicles that are released by prokaryotic to higher eukaryotic cells and by plant cells in an evolutionary conserved manner. The significance of these vesicles lies in their capacity to transfer selected cargo composed of proteins, lipids and nucleic acids to both recipient and parent cells and to influence various physiological and pathological functions. Microorganisms such as parasites, fungi and protozoa and even single cell organisms such as bacteria generate extracellular vesicles. In addition, several viruses have evolved strategies to hijack the extracellular vesicles for egress or to alter the surrounding environment. The thesis of this article is that: a) during HSV-1 infection vesicles are delivered from infected to uninfected cells that influence the infection; b) the cargo of these vesicles consists of viral and host transcripts (mRNAs, miRNAs and non-coding RNAs) and proteins including innate immune components, such as STING; and c) the viral vesicles carry the tetraspanins CD9, CD63 and CD81, which are considered as markers of exosomes. Therefore, we assume that the STING-carrying vesicles, produced during HSV-1 infection, are reminiscent to exosomes. The presumed functions of the exosomes released from HSV-1 infected cells include priming the recipient cells and accelerating antiviral responses to control the dissemination of the virus. This may be one strategy used by the virus to prevent the elimination by the host and establish persistent infection. In conclusion, the modification of the cargo of exosomes appears to be part of the strategy that HSV-1 has evolved to establish lifelong persistent infections into the human body to ensure successful dissemination between individuals.

Exosomes in Human Immunodeficiency Virus Type I Pathogenesis: Threat or Opportunity?

Nanometre-sized vesicles, also known as exosomes, are derived from endosomes of diverse cell types and present in multiple biological fluids. Depending on their cellular origins, the membrane-bound exosomes packed a variety of functional proteins and RNA species. These microvesicles are secreted into the extracellular space to facilitate intercellular communication. Collective findings demonstrated that exosomes from HIV-infected subjects share many commonalities with Human Immunodeficiency Virus Type I (HIV-1) particles in terms of proteomics and lipid profiles. These observations postulated that HIV-resembled exosomes may contribute to HIV pathogenesis. Interestingly, recent reports illustrated that exosomes from body fluids could inhibit HIV infection, which then bring up a new paradigm for HIV/AIDS therapy. Accumulative findings suggested that the cellular origin of exosomes may define their effects towards HIV-1. This review summarizes the two distinctive roles of exosomes in regulating HIV pathogenesis. We also highlighted several additional factors that govern the exosomal functions. Deeper understanding on how exosomes promote or abate HIV infection can significantly contribute to the development of new and potent antiviral therapeutic strategy and vaccine designs.

Exosomes and Their Role in the Life Cycle and Pathogenesis of RNA Viruses

Exosomes are membrane-enclosed vesicles actively released into the extracellular space, whose content reflect the physiological/pathological state of the cells they originate from. These vesicles participate in cell-to-cell communication and transfer of biologically active proteins, lipids, and RNAs. Their role in viral infections is just beginning to be appreciated. RNA viruses are an important class of pathogens and affect millions of people worldwide. Recent studies on Human Immunodeficiency Virus (HIV), Hepatitis C Virus (HCV), human T-cell lymphotropic virus (HTLV), and Dengue Virus (DENV) have demonstrated that exosomes released from infected cells harbor and deliver many regulatory factors including viral RNA and proteins, viral and cellular miRNA, and other host functional genetic elements to neighboring cells, helping to establish productive infections and modulating cellular responses. Exosomes can either spread or limit an infection depending on the type of pathogen and target cells, and can be exploited as candidates for development of antiviral or vaccine treatments. This review summarizes recent progress made in understanding the role of exosomes in RNA virus infections with an emphasis on their potential contribution to pathogenesis.

Immunogenic Display of Purified Chemically Cross-Linked HIV-1 Spikes

HIV-1 envelope glycoprotein (Env) spikes are prime vaccine candidates, at least in principle, but suffer from instability, molecular heterogeneity and a low copy number on virions. We anticipated that chemical cross-linking of HIV-1 would allow purification and molecular characterization of trimeric Env spikes, as well as high copy number immunization. Broadly neutralizing antibodies bound tightly to all major quaternary epitopes on cross-linked spikes. Covalent cross-linking of the trimer also stabilized broadly neutralizing epitopes, although surprisingly some individual epitopes were still somewhat sensitive to heat or reducing agent. Immunodepletion using non-neutralizing antibodies to gp120 and gp41 was an effective method for removing non-native-like Env. Cross-linked spikes, purified via an engineered C-terminal tag, were shown by negative stain EM to have well-ordered, trilobed structure. An immunization was performed comparing a boost with Env spikes on virions to spikes cross-linked and captured onto nanoparticles, each following a gp160 DNA prime. Although differences in neutralization did not reach statistical significance, cross-linked Env spikes elicited a more diverse and sporadically neutralizing antibody response against Tier 1b and 2 isolates when displayed on nanoparticles, despite attenuated binding titers to gp120 and V3 crown peptides. Our study demonstrates display of cross-linked trimeric Env spikes on nanoparticles, while showing a level of control over antigenicity, purity and density of virion-associated Env, which may have relevance for Env based vaccine strategies for HIV-1.

IMPORTANCE

The envelope spike (Env) is the target of HIV-1 neutralizing antibodies, which a successful vaccine will need to elicit. However, native Env on virions is innately labile, as well as heterogeneously and sparsely displayed. We therefore stabilized Env spikes using a chemical cross-linker and removed non-native Env by immunodepletion with non-neutralizing antibodies. Fixed native spikes were recognized by all classes of known broadly neutralizing antibodies but not by non-neutralizing antibodies and displayed on nanoparticles in high copy number. An immunization experiment in rabbits revealed that cross-linking Env reduced its overall immunogenicity; however, high-copy display on nanoparticles enabled boosting of antibodies that sporadically neutralized some relatively resistant HIV-1 isolates, albeit at a low titer. This study describes the purification of stable and antigenically correct Env spikes from virions that can be used as immunogens.

Immune Activation: Contribution to AIDS-Associated Non-Hodgkin Lymphoma

HIV infection is associated with a greatly elevated risk for the development of non-Hodgkin lymphoma (NHL), which while diminished, remains elevated in the highly active antiretroviral therapy (HAART) era. Chronic B cell activation, driven by contact with HIV virions, B cell-stimulatory cytokines, viruses (EBV, HPV, HCV), and by high levels of antigenic stimulation occurs in HIV infected persons, and it is seen at even higher levels in those who go on to develop AIDS-NHL. Evidence from multiple studies indicates that elevated serum levels of several B cell-stimulatory cytokines and biomarkers are seen preceding AIDS-NHL, as well as in immunocompetent persons that develop NHL. Phenotypic changes in circulating B cells also are seen preceding AIDS-NHL, including the expression of AICDA, and of cell-surface molecules and miRNA that are associated with activated B cells. HAART only partially normalizes the immune system of treated HIV⁺ persons as they still show clear evidence for ongoing inflammation and immune activation in, even those who show complete suppression of HIV viremia. Together, this provides ample evidence to support the notion that chronic activation of B cells contributes to the genesis of B cell lymphomas.

Molecular determinants of the ratio of inert to infectious virus particles

The ratio of virus particles to infectious units is a classic measurement in virology and ranges widely from several million to below 10 for different viruses. Much evidence suggests a distinction be made between infectious and infecting particles or virions: out of many potentially infectious virions, few infect under regular experimental conditions, largely because of diffusion barriers. Still, some virions are inert from the start; others become defective through decay. And with increasing cell- and molecular-biological knowledge of each step in the replicative cycle for different viruses, it emerges that many processes entail considerable losses of potential viral infectivity. Furthermore, all-or-nothing assumptions about virion infectivity are flawed and should be replaced by descriptions that allow for spectra of infectious propensities. A more realistic understanding of the infectivity of individual virions has both practical and theoretical implications for virus neutralization, vaccine research, antiviral therapy, and the use of viral vectors.

HIV-1 Intersection with CD4 T Cell Vesicle Exocytosis: Intercellular Communication Goes Viral

In cells of the immune system, the secretion of extracellular vesicles is modulated through cellular activation. In particular, T cell activation is achieved through cell-cell contacts with antigen presenting cells and the consequent formation of a specialized signaling junction called the immunological synapse. Recent works on CD4 T cells have elucidated that cognate antigen recognition by the T cell receptor (TCR) engages two distinct exocytic events. The first involves the exocytic targeting of signaling molecules at the synaptic membrane and drives the functional architecture of the immunological synapse. The second enlists the extracellular secretion of the TCR itself, once the functional architecture of the immunological synapse is accomplished. HIV-1, a human lymphotropic virus, has evolved sophisticated mechanisms to co-opt CD4 T cell physiology. Notably, it has become apparent that HIV-1 intersects the regulated secretory system of CD4 T cells in order to bud from the plasma membrane of the infected cell and to promote bystander cell death. Here, I review the relevance of CD4 vesicle exocytosis to immune regulation and to HIV-1 pathogenesis and discuss their potential therapeutic applications.

The microvesicle component of HIV-1 inocula modulates dendritic cell infection and maturation and enhances adhesion to and activation of T lymphocytes

HIV-1 is taken up by immature monocyte derived dendritic cells (iMDDCs) into tetraspanin rich caves from which the virus can either be transferred to T lymphocytes or enter into endosomes resulting in degradation. HIV-1 binding and fusion with the DC membrane results in low level de novo infection that can also be transferred to T lymphocytes at a later stage. We have previously reported that HIV-1 can induce partial maturation of iMDDCs at both stages of trafficking. Here we show that CD45⁺ microvesicles (MV) which contaminate purified HIV-1 inocula due to similar size and density, affect DC maturation, de novo HIV-1 infection and transfer to T lymphocytes. Comparing iMDDCs infected with CD45-depleted HIV-1BaL or matched non-depleted preparations, the presence of CD45⁺ MVs was shown to enhance DC maturation and ICAM-1 (CD54) expression, which is involved in DC∶T lymphocyte interactions, while restricting HIV-1 infection of MDDCs. Furthermore, in the DC culture HIV-1 infected (p24⁺) MDDCs were more mature than bystander cells. Depletion of MVs from the HIV-1 inoculum markedly inhibited DC∶T lymphocyte clustering and the induction of alloproliferation as well as limiting HIV-1 transfer from DCs to T lymphocytes. The effects of MV depletion on these functions were reversed by the re-addition of purified MVs from activated but not non-activated SUPT1.CCR5-CL.30 or primary T cells. Analysis of the protein complement of these MVs and of these HIV-1 inocula before and after MV depletion showed that Heat Shock Proteins (HSPs) and nef were the likely DC maturation candidates. Recombinant HSP90α and β and nef all induced DC maturation and ICAM-1 expression, greater when combined. These results suggest that MVs contaminating HIV-1 released from infected T lymphocytes may be biologically important, especially in enhancing T cell activation, during uptake by DCs in vitro and in vivo, particularly as MVs have been detected in the circulation of HIV-1 infected subjects.

Blood/plasma secretome and microvesicles

A major but hitherto overseen component of the blood/plasma secretome is that of extracellular vesicles (EVs) which are shed from all blood cell types. These EVs are made up of microvesicles (MVs) and exosomes. MVs, 100nm-1μm in diameter, are released from the cell surface, and are a rich source of non-conventionally secreted proteins lacking a conventional signal peptide, and thus not secreted by the classical secretory pathways. Exosomes are smaller vesicles (≤100nm) having an endocytic origin and released upon multivesicular body fusion with the plasma membrane. Both vesicle types play major roles in intercellular cross talk and constitute an important component of the secretome especially in the area of biomarkers for cancer. The release of EVs, which are found in all the bodily fluids, is enhanced in cancer and a major focus of cancer proteomics is therefore targeted at EVs. The blood/plasma secretome is also a source of EVs, potentially diagnostic of infectious disease, whether from EVs released from infected cells or from the pathogens themselves. Despite the great excitement in this field, as is stated here and in other parts of this Special issue entitled: An Updated Secretome, much of the EV research, whether proteomic or functional in nature, urgently needs standardisation both in terms of nomenclature and isolation protocols. This article is part of a Special Issue entitled: An Updated Secretome.

The conserved set of host proteins incorporated into HIV-1 virions suggests a common egress pathway in multiple cell types

HIV-1 incorporates a large array of host proteins into virions. Determining the host protein composition in HIV virions has technical difficulties, including copurification of microvesicles. We developed an alternative purification technique using cholesterol that differentially modulates the density of virions and microvesicles (density modification, DM) allowing for high-yield virion purification that is essential for tandem mass spectrometric and quantitative proteomic (iTRAQ) analysis. DM purified virions were analyzed using iTRAQ and validated against Optiprep (60% iodixanol) purified virions. We were able to characterize host protein incorporation in DM-purified HIV particles derived from CD4+ T-cell lines; we compared this data set to a reprocessed data set of monocyte-derived macrophages (MDM) derived HIV-1 using the same bioinformatics pipeline. Seventy-nine clustered proteins were shared between the MDM derived and T-cell derived data set. These clusters included an extensive collection of actin isoforms, HLA proteins, chaperones, and a handful of other proteins, many of which have previously been documented to interact with viral proteins. Other proteins of note were ERM proteins, the dynamin domain containing protein EH4, a phosphodiesterase, and cyclophilin A. As these proteins are incorporated in virions produced in both cell types, we hypothesize that these proteins may have direct interactions with viral proteins or may be important in the viral life cycle. Additionally, identified common set proteins are predicted to interact with >1000 related human proteins. Many of these secondary interacting proteins are reported to be incorporated into virions, including ERM proteins and adhesion molecules. Thus, only a few direct interactions between host and viral proteins may dictate the host protein composition in virions. Ultimately, interaction and expression differences in host proteins between cell types may drive virion phenotypic diversity, despite conserved viral protein-host protein interactions between cell types.

Immune regulation and evasion of Mammalian host cell immunity during viral infection

The mammalian host immune system has wide array of defence mechanisms against viral infections. Depending on host immunity and the extent of viral persistence, either the host immune cells might clear/restrict the viral load and disease progression or the virus might evade host immunity by down regulating host immune effector response(s). Viral antigen processing and presentation in the host cells through major histocompatibility complex (MHC) elicit subsequent anti-viral effector T cell response(s). However, modulation of such response(s) might generate one of the important viral immune evasion strategies. Viral peptides are mostly generated by proteolytic cleavage in the cytosol of the infected host cells. CD8(+) T lymphocytes play critical role in the detection of viral infection by recognizing these peptides displayed at the plasma membrane by MHC-I molecules. The present review summarises the current knowledge on the regulation of mammalian host innate and adaptive immune components, which are operative in defence mechanisms against viral infections and the variety of strategies that viruses have evolved to escape host cell immunity. The understanding of viral immune evasion strategies is important for designing anti-viral immunotherapies.

Human cervicovaginal mucus contains an activity that hinders HIV-1 movement

Cervical and vaginal epithelia are primary barriers against HIV type I (HIV-1) entry during male-to-female transmission. Cervical mucus (CM) is produced by the endocervix and forms a layer locally as well as in the vaginal compartment in the form of cervicovaginal mucus (CVM). To study the potential barrier function of each mucus type during HIV-1 transmission, we quantified HIV-1 mobility in CM and CVM ex vivo using fluorescent microscopy. Virions and 200-nm PEGylated beads were digitally tracked and mean-squared displacement was calculated. The mobility of beads increased significantly in CVM compared with CM, consistent with the known decreased mucin concentration of CVM. Unexpectedly, HIV-1 diffusion was significantly hindered in the same CVM samples in which bead diffusion was unhindered. Inhibition of virus transport was envelope-independent. Our results reveal a previously unknown activity in CVM that is capable of impeding HIV-1 mobility to enhance mucosal barrier function.