Decay-accelerating factor (CD55), a glycosylphosphatidylinositol-anchored complement regulatory protein, is a receptor for several echoviruses

Nanobody-based drug delivery systems for cancer therapy

Targeted delivery can elevate the local drug concentration within tumor tissues, while minimizing drug distribution to normal tissues, thus enhancing the effectiveness of anti-tumor medications and reducing adverse effects and systemic toxicities. Nanobodies, the novel molecular pattern of antibodies characterized by their small size, high stability, strong specificity, and low immunogenicity, have been extensively applied in targeted drug delivery for tumor therapy. This review discusses structural disparities and functional advantages of nanobodies compared to other antibody fragments and full-length antibody. It also highlights nanobody applications in targeted tumor therapy, focusing on their use in modifying delivery systems, e.g., liposomes, EVs, micelles, albumin nanoparticles, gold nanoparticles, polymeric nanoparticles, and as nanobody-drug conjugates. This review delves into the methods applied for integrating nanobodies into different drug delivery carriers, in order to provide useful information for researchers developing nanobody-based targeted drug delivery systems.

Current status and prospects of genetically modified porcine-to-human cardiac xenotransplantation

Cardiac xenotransplantation utilizing genetically modified pigs presents a promising avenue for treating end-stage heart failure, a leading cause of mortality worldwide. This paper delineates the current landscape of heart failure treatment in Japan, emphasizing the limitations of existing therapies such as heart transplantation and implantable left ventricular assist devices. It discusses the history and advancements in the development of genetically modified pigs for xenotransplantation, highlighting recent breakthroughs and challenges. The manuscript also addresses the specific challenges facing the implementation of xenotransplantation in Japan, including the selection of suitable genetically modified pigs, ensuring organ safety, patient selection criteria, transplantation protocols, and immunosuppression strategies. Drawing from international experiences and ongoing research efforts, the paper emphasizes the potential of xenotransplantation while acknowledging the hurdles that must be overcome for widespread clinical adoption.

Overview of the Trending Enteric Viruses and Their Pathogenesis in Intestinal Epithelial Cell Infection

Enteric virus infection is a major public health issue worldwide. Enteric viruses have become epidemic infectious diseases in several countries. Enteric viruses primarily infect the gastrointestinal tract and complete their life cycle in intestinal epithelial cells. These viruses are transmitted via the fecal-oral route through contaminated food, water, or person to person and cause similar common symptoms, including vomiting, abdominal pain, and diarrhea. Diarrheal disease is the third leading cause of death in children under five years of age, accounting for approximately 1.7 billion cases and 443,832 deaths annually in this age group. Additionally, some enteric viruses can invade other tissues, leading to severe conditions and even death. The pathogenic mechanisms of enteric viruses are also unclear. In this review, we organized the research on trending enteric virus infections, including rotavirus, norovirus, adenovirus, Enterovirus-A71, Coxsackievirus A6, and Echovirus 11. Furthermore, we discuss the gastrointestinal effects and pathogenic mechanisms of SARS-CoV-2 in intestinal epithelial cells, given the gastrointestinal symptoms observed during the COVID-19 pandemic. We conducted a literature review on their pathogenic mechanisms, which serves as a guide for formulating future treatment strategies for enteric virus infections.

The neonatal Fc receptor is a cellular receptor for human astrovirus

Human astroviruses (HAstV) are major causes of gastroenteritis, especially in children, and there are no vaccines or antivirals currently available. Little is known about host factors required for their cellular entry. Here we utilized complementary CRISPR-Cas9-based knockout and activation screens to identify neonatal Fc receptor (FcRn) and dipeptidyl-peptidase IV (DPP4) as entry factors for HAstV infection in vitro. Disruption of FcRn or DPP4 reduced HAstV infection in permissive cells and, reciprocally, overexpression of these factors in non-permissive cells was sufficient to promote infection. We observed direct binding of FcRn, but not DPP4, with HAstV virions and the purified spike protein. This suggests that FcRn is a receptor for HAstVs while DPP4 is a cofactor for entry. Inhibitors for DPP4 and FcRn currently in clinical use prevented HAstV infection in cell lines and human enteroids. Our results reveal mechanisms of HAstV entry as well as druggable targets to limit HAstV infection.

An Overview of the Characteristics, Pathogenesis, Epidemiology, and Detection of Human Enterovirus in the Arabian Gulf Region

Enteroviruses are RNA viruses that initiate infections through the gastrointestinal (GI) tract and are associated with enteric illness in individuals of all ages. Most serious infections of enteroviruses are in infants and young children where it is the common cause of aseptic meningitis and other systemic diseases, leading to a high mortality rate. Enteroviruses belong to the small non-enveloped family of the Picornaviridae family. The virus can spread mainly through fecal-oral and respiratory routes. In the Arabian Gulf countries, the incidence of enteroviral infections is only restricted to a few reports, and thus, knowledge of the epidemiology, characteristics, and pathogenesis of the virus in the gulf countries remains scarce. In this minireview, we sought to provide an overview of the characteristics of enterovirus and its pathogenesis, in addition to gathering the reports of enterovirus infection prevalence in Gulf Cooperation Council (GCC) countries. We also present a summary of the common methods used in its detection.

The neonatal Fc receptor and DPP4 are human astrovirus receptors

Human astroviruses (HAstV) are major global causes of gastroenteritis, but little is known about host factors required for their cellular entry. Here, we utilized complementary CRISPR-Cas9-based knockout and activation screening approaches and identified neonatal Fc receptor (FcRn) and dipeptidyl-peptidase IV (DPP4) as entry factors for HAstV infection of human intestinal epithelial cells. Disruption of FcRn or DPP4 reduced HAstV infection in permissive cells and, reciprocally, overexpression of these factors in non-permissive cells was sufficient to promote infection. We observed direct binding between FcRn and HAstV virions as well as purified spike protein. Finally, inhibitors for DPP4 and FcRn currently in clinical use prevent HAstV infection in cell lines and primary human enteroids. Thus, our results reveal mechanisms of HAstV entry as well as druggable targets.

One-Sentence Summary

Targeting FcRn or DPP4 using available therapies effectively prevents human astrovirus infection in human enteroid cultures.

The many ways in which alphaviruses bind to cells

Only a subset of viruses can productively infect many different host species. Some arthropod-transmitted viruses, such as alphaviruses, can infect invertebrate and vertebrate species including insects, reptiles, birds, and mammals. This broad tropism may be explained by their ability to engage receptors that are conserved across vertebrate and invertebrate classes. Through several genome-wide loss-of-function screens, new alphavirus receptors have been identified, some of which bind to multiple related viruses in different antigenic complexes. Structural analysis has revealed that distinct sites on the alphavirus glycoprotein can mediate receptor binding, which opposes the idea that a single receptor-binding site mediates viral entry. Here, we discuss how different paradigms of receptor engagement on cells might explain the promiscuity of alphaviruses for multiple hosts.

Virus-Receptor Interactions and Receptor-Mediated Virus Entry into Host Cells

The virus particles described in the previous chapters of this book are vehicles that transmit the viral genome and the infection from cell to cell. To initiate the infective cycle, the viral genome must therefore translocate from the viral particle to the cell cytoplasm. Via distinct proteins or motifs in their outermost shell, the particles of animal viruses or bacteriophages attach initially to specific receptors on the host cell surface. These viral receptors thus mediate penetration of the viral genome inside the cell, where the intracellular infective cycle starts. The presence of these receptors on the cell surface is a principal determinant of virus-host tropism. Viruses can use diverse types of molecules to attach to and enter into cells. In addition, virus-receptor recognition can evolve over the course of an infection, and viral variants with distinct receptor-binding specificities and tropism can appear. The identification of viral receptors and the characterization of virus-receptor interactions have been major research goals in virology. In this chapter, we will describe, from a structural perspective, several virus-receptor interactions and the active role of receptor molecules in virus cell entry.

Observed Kinetics of Enterovirus Inactivation by Free Chlorine Are Host Cell-Dependent

Virucidal efficacies of disinfectants are typically assessed by infectivity assay utilizing a single type of host cell. Enteroviruses infect multiple host cells via various entry routes, and each entry route may be impaired differently by a given disinfectant. Yet, it is unknown how the choice of host cells affects the observed inactivation kinetics. Here, we evaluated the inactivation kinetics of echovirus 11 (E11) by free chlorine, ultraviolet (UV) irradiation, and heat, using three different host cells (BGMK, RD, and A549). Inactivation rates were independent of the host cell for treatment of E11 by UV or heat. Conversely, E11 inactivation by free chlorine occurred 2-fold faster when enumerated on BGMK cells compared with RD and A549 cells. Host cell-dependent inactivation kinetics by free chlorine were also observed for echovirus 7, 9, and 13, and coxsackievirus A9. E11 inactivation by free chlorine was partly caused by a loss in host cell attachment, which was most pronounced for BGMK cells. BGMK cells lack the attachment receptor CD55 and a key subunit of the uncoating receptor β2M, which may contribute to the differential inactivation kinetics for this cell type. Consequently, inactivation kinetics of enteroviruses should be assessed using host cells with different receptor profiles.

Entry receptors - the gateway to alphavirus infection

Alphaviruses are enveloped, insect-transmitted, positive-sense RNA viruses that infect humans and other animals and cause a range of clinical manifestations, including arthritis, musculoskeletal disease, meningitis, encephalitis, and death. Over the past four years, aided by CRISPR/Cas9-based genetic screening approaches, intensive research efforts have focused on identifying entry receptors for alphaviruses to better understand the basis for cellular and species tropism. Herein, we review approaches to alphavirus receptor identification and how these were used for discovery. The identification of new receptors advances our understanding of viral pathogenesis, tropism, and evolution and is expected to contribute to the development of novel strategies for prevention and treatment of alphavirus infection.

Morphogenesis of Hepatitis E Virus

Hepatitis E virus, a leading cause of acute hepatitis worldwide, has been recognized as non-enveloped virus since its discovery in the 1980s. However, the recent identification of lipid membrane-associated form termed as "quasi-enveloped" HEV has changed this long-held notion. Both naked HEV and quasi-enveloped HEV play important roles in the pathogenesis of hepatitis E. However, the biogenesis and the mechanisms underlying the composition, biogenesis regulation, and functions of the novel quasi-enveloped virions remain enigmatic. In this chapter, we highlight the most recent discoveries on the dual life cycle of these two different types of virions, and further discuss the implication of the quasi-envelopment in our understanding of the molecular biology of HEV.

CD55 in cancer: Complementing functions in a non-canonical manner

CD55, or decay accelerating factor, is a membrane lipid microdomain-associated, GPI-anchored protein implicated in the shielding of cells from complement-mediated attack via accelerating decay of C3 and C5. Loss of CD55 is associated with a number of pathologies due to hyperactivation of the complement system. CD55 is also implicated in cancer progression thought to be driven via its role in cell shielding mechanisms. We now appreciate that CD55 can signal intracellularly to promote malignant transformation, cancer progression, cell survival, angiogenesis, and inhibition of apoptosis. Outside-in signaling via CD55 is mediated by signaling pathways including JNK, JAK/STAT, MAPK/NF-κB, and LCK. Moreover, CD55 is enriched in the cancer stem cell (CSC) niche of multiple tumors including breast, ovarian, cervical, and can be induced by chemotherapeutics and hypoxic environments. CSCs are implicated in tumor recurrence and chemoresistance. Here, we review the unexpected roles of CD55 in cancer including the roles of canonical and noncanonical pathways that CD55 orchestrates. We will highlight opportunities for therapeutic targeting CD55 and gaps in the field that require more in-depth mechanistic insights.

Switching of Receptor Binding Poses between Closely Related Enteroviruses

Echoviruses, for which there are currently no approved vaccines or drugs, are responsible for a range of human diseases, for example echovirus 11 (E11) is a major cause of serious neonatal morbidity and mortality. Decay-accelerating factor (DAF, also known as CD55) is an attachment receptor for E11. Here, we report the structure of the complex of E11 and the full-length ectodomain of DAF (short consensus repeats, SCRs, 1-4) at 3.1 Å determined by cryo-electron microscopy (cryo-EM). SCRs 3 and 4 of DAF interact with E11 at the southern rim of the canyon via the VP2 EF and VP3 BC loops. We also observe an unexpected interaction between the N-linked glycan (residue 95 of DAF) and the VP2 BC loop of E11. DAF is a receptor for at least 20 enteroviruses and we classify its binding patterns from reported DAF/virus complexes into two distinct positions and orientations, named as E6 and E11 poses. Whilst 60 DAF molecules can attach to the virion in the E6 pose, no more than 30 can attach to E11 due to steric restrictions. Analysis of the distinct modes of interaction and structure and sequence-based phylogenies suggests that the two modes evolved independently, with the E6 mode likely found earlier.

An In Vivo Model of Echovirus-Induced Meningitis Defines the Differential Roles of Type I and Type III Interferon Signaling in Central Nervous System Infection

Echoviruses are among the most common worldwide causes of aseptic meningitis, which can cause long-term sequelae and death, particularly in neonates. However, the mechanisms by which these viruses induce meningeal inflammation are poorly understood, owing at least in part to the lack of in vivo models that recapitulate this aspect of echovirus pathogenesis. Here, we developed an in vivo neonatal mouse model that recapitulates key aspects of echovirus-induced meningitis. We show that expression of the human homologue of the primary echovirus receptor, the neonatal Fc receptor (FcRn), is not sufficient for infection of the brains of neonatal mice. However, ablation of type I, but not III, interferon (IFN) signaling in mice expressing human FcRn permitted high levels of echovirus replication in the brain, with corresponding clinical symptoms, including delayed motor skills and hind-limb weakness. Using this model, we defined the immunological response of the brain to echovirus infection and identified key cytokines, such as granulocyte colony-stimulating factor (G-CSF) and interleukin 6 (IL-6), that were induced by this infection. Lastly, we showed that echoviruses specifically replicate in the leptomeninges, where they induce profound inflammation and cell death. Together, this work establishes an in vivo model of aseptic meningitis associated with echovirus infections that delineates the differential roles of type I and type III IFNs in echovirus-associated neuronal disease and defines the specificity of echoviral infections within the meninges. IMPORTANCE Echoviruses are among the most common worldwide causes of aseptic meningitis, which can cause long-term sequelae or even death. The mechanisms by which echoviruses infect the brain are poorly understood, largely owing to the lack of robust in vivo models that recapitulate this aspect of echovirus pathogenesis. Here, we establish a neonatal mouse model of echovirus-induced aseptic meningitis and show that expression of the human homologue of the FcRn, the primary receptor for echoviruses, and ablation of type I IFN signaling are required to recapitulate echovirus-induced meningitis and clinical disease. These findings provide key insights into the host factors that control echovirus-induced meningitis and a model that could be used to test anti-echovirus therapeutics.

Human FcRn Is a Two-in-One Attachment-Uncoating Receptor for Echovirus 18

Virus-receptor interactions determine viral host range and tissue tropism. CD55 and human neonatal Fc receptor (FcRn) were found to be the binding and uncoating receptors for some of the echovirus-related enterovirus species B serotypes in our previous study. Echovirus 18 (E18), as a member of enterovirus species B, is a significant causative agent of aseptic meningitis and viral encephalitis in children. However, it does not use CD55 as a critical host factor. We conducted CRISPR/Cas9 knockout screening to determine the receptors and entry mechanisms and identified FcRn working as a dual-function receptor for E18. Knockout of FCGRT and B2M, which encode the two subunits of FcRn, prevented infection by E18 and other echoviruses in the same physiological cluster. We then elucidated the underlying molecular mechanism of receptor recognition by E18 using cryogenic electron microscopy. The binding of the FCGRT subunit to the canyon region rotates the residues around the pocket, triggering the release of the pocket factor as observed for other enterovirus species B members.

Enterovirus Replication and Dissemination Are Differentially Controlled by Type I and III Interferons in the Gastrointestinal Tract

Echovirus infections are associated with a broad spectrum of illness, particularly in neonates, and are primarily transmitted through the fecal-oral route. Little is known regarding how echoviruses infect the gastrointestinal tract and how the intestinal epithelium controls echoviral replication.

ICAM-1 induced rearrangements of capsid and genome prime rhinovirus 14 for activation and uncoating

Medical visits and missed days of school and work caused by rhinoviruses cost tens of billions of US dollars annually. Currently, there are no antivirals against rhinoviruses, and the available treatments only treat the symptoms. Here, we present the molecular structure of human rhinovirus 14 in complex with its cellular receptor intercellular adhesion molecule 1. The binding of the virus to its receptor initiates the infection. Knowledge of the structure of the human rhinovirus 14–intercellular adhesion molecule 1 interface and mechanism of interaction provides the basis for the design of compounds that may block the binding of rhinoviruses to receptors and thus prevent infection.

Most rhinoviruses, which are the leading cause of the common cold, utilize intercellular adhesion molecule-1 (ICAM-1) as a receptor to infect cells. To release their genomes, rhinoviruses convert to activated particles that contain pores in the capsid, lack minor capsid protein VP4, and have an altered genome organization. The binding of rhinoviruses to ICAM-1 promotes virus activation; however, the molecular details of the process remain unknown. Here, we present the structures of virion of rhinovirus 14 and its complex with ICAM-1 determined to resolutions of 2.6 and 2.4 Å, respectively. The cryo-electron microscopy reconstruction of rhinovirus 14 virions contains the resolved density of octanucleotide segments from the RNA genome that interact with VP2 subunits. We show that the binding of ICAM-1 to rhinovirus 14 is required to prime the virus for activation and genome release at acidic pH. Formation of the rhinovirus 14–ICAM-1 complex induces conformational changes to the rhinovirus 14 capsid, including translocation of the C termini of VP4 subunits, which become poised for release through pores that open in the capsids of activated particles. VP4 subunits with altered conformation block the RNA–VP2 interactions and expose patches of positively charged residues. The conformational changes to the capsid induce the redistribution of the virus genome by altering the capsid–RNA interactions. The restructuring of the rhinovirus 14 capsid and genome prepares the virions for conversion to activated particles. The high-resolution structure of rhinovirus 14 in complex with ICAM-1 explains how the binding of uncoating receptors enables enterovirus genome release.

Efficient delivery of oncolytic enterovirus by carrier cell line NK-92

Many members of the enterovirus family are considered as promising oncolytic agents; however, their systemic administration is largely inefficient due to the rapid neutralization of the virus in the circulation and the barrier functions of the endothelium. We aimed to evaluate natural killer cells as carriers for the delivery of oncolytic enteroviruses, which would combine the effects of cell immunotherapy with virotherapy. We tested four strains of nonpathogenic enteroviruses against the glioblastoma cell line panel and evaluated the produced infectious titers. Next, we explored whether these virus strains could be delivered to the tumor by natural killer cell line NK-92, which is being actively evaluated as a clinically acceptable therapeutic. Several strains of enteroviruses demonstrated oncolytic properties, but only coxsackievirus A7 (CVA7) could replicate in NK-92 cells efficiently. We compared the delivery efficiency of CVA7 in vivo, using NK-92 cells and direct intravenous administration, and found significant advantages of cell delivery even after a single injection. This suggests that the NK-92 cell line can be utilized as a vehicle for the delivery of the oncolytic strain of CVA7, which would improve the clinical potential of this viral oncolytic for the treatment of glioblastoma multiforme and other forms of cancer.

Cryo-EM structures reveal the molecular basis of receptor-initiated coxsackievirus uncoating

Enterovirus uncoating receptors bind at the surface depression ("canyon") that encircles each capsid vertex causing the release of a host-derived lipid called "pocket factor" that is buried in a hydrophobic pocket formed by the major viral capsid protein, VP1. Coxsackievirus and adenovirus receptor (CAR) is a universal uncoating receptor of group B coxsackieviruses (CVB). Here, we present five high-resolution cryoEM structures of CVB representing different stages of virus infection. Structural comparisons show that the CAR penetrates deeper into the canyon than other uncoating receptors, leading to a cascade of events: collapse of the VP1 hydrophobic pocket, high-efficiency release of the pocket factor and viral uncoating and genome release under neutral pH, as compared with low pH. Furthermore, we identified a potent therapeutic antibody that can neutralize viral infection by interfering with virion-CAR interactions, destabilizing the capsid and inducing virion disruption. Together, these results define the structural basis of CVB cell entry and antibody neutralization.

Return of the Neurotropic Enteroviruses: Co-Opting Cellular Pathways for Infection

Enteroviruses are among the most common human infectious agents. While infections are often mild, the severe neuropathogenesis associated with recent outbreaks of emerging non-polio enteroviruses, such as EV-A71 and EV-D68, highlights their continuing threat to public health. In recent years, our understanding of how non-polio enteroviruses co-opt cellular pathways has greatly increased, revealing intricate host-virus relationships. In this review, we focus on newly identified mechanisms by which enteroviruses hijack the cellular machinery to promote their replication and spread, and address their potential for the development of host-directed therapeutics. Specifically, we discuss newly identified cellular receptors and their contribution to neurotropism and spread, host factors required for viral entry and replication, and recent insights into lipid acquisition and replication organelle biogenesis. The comprehensive knowledge of common cellular pathways required by enteroviruses could expose vulnerabilities amenable for host-directed therapeutics against a broad spectrum of enteroviruses. Since this will likely include newly arising strains, it will better prepare us for future epidemics. Moreover, identifying host proteins specific to neurovirulent strains may allow us to better understand factors contributing to the neurotropism of these viruses.

Development of Three-Dimensional Human Intestinal Organoids as a Physiologically Relevant Model for Characterizing the Viral Replication Kinetics and Antiviral Susceptibility of Enteroviruses

Enteroviruses are important causes of hand, foot, and mouth disease, respiratory infections, and neurological infections in human. A major hurdle for the development of anti-enterovirus agents is the lack of physiologically relevant evaluation platforms that closely correlate with the in vivo state. We established the human small intestinal organoids as a novel platform for characterizing the viral replication kinetics and evaluating candidate antivirals for enteroviruses. The organoids supported productive replication of enterovirus (EV)-A71, coxsackievirus B2, and poliovirus type 3, as evidenced by increasing viral loads, infectious virus titers, and the presence of cytopathic effects. In contrast, EV-D68, which mainly causes respiratory tract infection in humans, did not replicate significantly in the organoids. The differential expression profiles of the receptors for these enteroviruses correlated with their replication kinetics. Using itraconazole as control, we showed that the results of various antiviral assays, including viral load reduction, plaque reduction, and cytopathic effect inhibition assays, were highly reproducible in the organoids. Moreover, itraconazole attenuated virus-induced inflammatory response in the organoids, which helped to explain its antiviral effects and mechanism. Collectively, these data showed that the human small intestinal organoids may serve as a robust platform for investigating the pathogenesis and evaluating antivirals for enteroviruses.

In the Crosshairs: RNA Viruses OR Complement?

Complement, a part of the innate arm of the immune system, is integral to the frontline defense of the host against innumerable pathogens, which includes RNA viruses. Among the major groups of viruses, RNA viruses contribute significantly to the global mortality and morbidity index associated with viral infection. Despite multiple routes of entry adopted by these viruses, facing complement is inevitable. The initial interaction with complement and the nature of this interaction play an important role in determining host resistance versus susceptibility to the viral infection. Many RNA viruses are potent activators of complement, often resulting in virus neutralization. Yet, another facet of virus-induced activation is the exacerbation in pathogenesis contributing to the overall morbidity. The severity in disease and death associated with RNA virus infections shows a tip in the scale favoring viruses. Growing evidence suggest that like their DNA counterparts, RNA viruses have co-evolved to master ingenious strategies to remarkably restrict complement. Modulation of host genes involved in antiviral responses contributed prominently to the adoption of unique strategies to keep complement at bay, which included either down regulation of activation components (C3, C4) or up regulation of complement regulatory proteins. All this hints at a possible “hijacking” of the cross-talk mechanism of the host immune system. Enveloped RNA viruses have a selective advantage of not only modulating the host responses but also recruiting membrane-associated regulators of complement activation (RCAs). This review aims to highlight the significant progress in the understanding of RNA virus–complement interactions.

Structures of Echovirus 30 in complex with its receptors inform a rational prediction for enterovirus receptor usage

Receptor usage that determines cell tropism and drives viral classification closely correlates with the virus structure. Enterovirus B (EV-B) consists of several subgroups according to receptor usage, among which echovirus 30 (E30), a leading causative agent for human aseptic meningitis, utilizes FcRn as an uncoating receptor. However, receptors for many EVs remain unknown. Here we analyzed the atomic structures of E30 mature virion, empty- and A-particles, which reveals serotype-specific epitopes and striking conformational differences between the subgroups within EV-Bs. Of these, the VP1 BC loop markedly distinguishes E30 from other EV-Bs, indicative of a role as a structural marker for EV-B. By obtaining cryo-electron microscopy structures of E30 in complex with its receptor FcRn and CD55 and comparing its homologs, we deciphered the underlying molecular basis for receptor recognition. Together with experimentally derived viral receptor identifications, we developed a structure-based in silico algorithm to inform a rational prediction for EV receptor usage.

Echovirus 30 (E30) belongs to the Enterovirus-B group and causes aseptic meningitis in humans. Here, the authors present the cryo-EM structures of the E30 E-particle, A-particle and the mature virion, as well as structures of E30 in complex with its receptor FcRn and CD55, and furthermore they describe a structure-based algorithm that allows the prediction of EV receptor usage.

Exosomes and GPI-anchored proteins: Judicious pairs for investigating biomarkers from body fluids

Exosomes are 50-100 nm membranous vesicles actively released by cells which can be indicative of a diseased cell status. They contain various kinds of molecule - proteins, mRNA, miRNA, lipids - that are actively being studied as potential biomarkers. Hereafter I put forward several arguments in favor of the potential use of glycosylphosphatidylinositol-anchored proteins (GPI-APs) as biomarkers especially of cancerous diseases. I will briefly update readers on the exosome field and review various features of GPI-APs, before further discussing the advantages of this class of proteins as potential exosomal biomarkers. I will finish with a few examples of exosomal GPI-APs that have already been demonstrated to be good prognostic markers, as well as innovative approaches developed to quantify these exosomal biomarkers.

Early Entry Events in Echovirus 30 Infection

Echovirus 30 (E30), a member of the enterovirus B species, is a major cause of viral meningitis, targeting children and adults alike. While it is a frequently isolated enterovirus and the cause of several outbreaks all over the world, surprisingly little is known regarding its entry and replication strategy within cells. In this study, we used E30 strain Bastianni (E30B) generated from an infectious cDNA clone in order to study early entry events during infection in human RD cells. E30B required the newly discovered Fc echovirus receptor (FcRn) for successful infection, but not the coxsackievirus and adenovirus receptor (CAR) or decay-accelerating factor (DAF), although an interaction with DAF was observed. Double-stranded RNA replication intermediate was generated between 2 and 3 h postinfection (p.i.), and viral capsid production was initiated between 4 and 5 h p.i. The drugs affecting Rac1 (NSC 23766) and cholesterol (filipin III) compromised infection, whereas bafilomycin A1, dyngo, U-73122, wortmannin, and nocodazole did not, suggesting the virus follows an enterovirus-triggered macropinocytic pathway rather than the clathrin pathway. Colocalization with early endosomes and increased infection due to constitutively active Rab5 expression suggests some overlap and entry to classical early endosomes. Taken together, these results suggest that E30B induces an enterovirus entry pathway, leading to uncoating in early endosomes.IMPORTANCE Echovirus 30 (E30) is a prevalent enterovirus causing regular outbreaks in both children and adults in different parts of the world. It is therefore surprising that relatively little is known of its infectious entry pathway. We set out to generate a cDNA clone and gradient purified the virus in order to study the early entry events in human cells. We have recently studied other enterovirus B group viruses, like echovirus 1 (EV1) and coxsackievirus A9 (CVA9), and found many similarities between those viruses, allowing us to define a so-called "enterovirus entry pathway." Here, E30 is reminiscent of these viruses, for example, by not relying on acidification for infectious entry. However, despite not using the clathrin entry pathway, E30 accumulates in classical early endosomes.

Human adenovirus binding to host cell receptors: a structural view

Human Adenoviruses (HAdVs) are a family of clinically and therapeutically relevant viruses. A precise understanding of their host cell attachment and entry mechanisms can be applied in inhibitor design and the construction of targeted gene delivery vectors. In this article, structural data on adenovirus attachment and entry are reviewed. HAdVs engage two types of receptors: first, an attachment receptor that is bound by the fibre knob protein protruding from the icosahedral capsid, and next, an integrin entry receptor bound by the pentameric penton base at the capsid vertices. Adenoviruses use remarkably diverse attachment receptors, five of which have been studied structurally in the context of HAdV binding: Coxsackie and Adenovirus Receptor, CD46, the glycans GD1a and polysialic acid, and desmoglein-2. Together with the integrin entry receptors, they display both symmetrical and asymmetrical modes of binding to the virus as demonstrated by the structural analyses reviewed here. The diversity of HAdV receptors contributes to the broad tropism of these viruses, and structural studies are thus an important source of information on HAdV-host cell interactions. The imbalance in structural data between the more and less extensively studied receptors remains to be addressed by future research.

The life cycle of non-polio enteroviruses and how to target it

The genus Enterovirus (EV) of the family Picornaviridae includes poliovirus, coxsackieviruses, echoviruses, numbered enteroviruses and rhinoviruses. These diverse viruses cause a variety of diseases, including non-specific febrile illness, hand-foot-and-mouth disease, neonatal sepsis-like disease, encephalitis, paralysis and respiratory diseases. In recent years, several non-polio enteroviruses (NPEVs) have emerged as serious public health concerns. These include EV-A71, which has caused epidemics of hand-foot-and-mouth disease in Southeast Asia, and EV-D68, which recently caused a large outbreak of severe lower respiratory tract disease in North America. Infections with these viruses are associated with severe neurological complications. For decades, most research has focused on poliovirus, but in recent years, our knowledge of NPEVs has increased considerably. In this Review, we summarize recent insights from enterovirus research with a special emphasis on NPEVs. We discuss virion structures, host-receptor interactions, viral uncoating and the recent discovery of a universal enterovirus host factor that is involved in viral genome release. Moreover, we briefly explain the mechanisms of viral genome replication, virion assembly and virion release, and describe potential targets for antiviral therapy. We reflect on how these recent discoveries may help the development of antiviral therapies and vaccines.

EXTL3-interacting endometriosis-specific serum factors induce colony formation of endometrial stromal cells

Endometriosis is a benign chronic condition characterized by the existence of endometrial-like stroma and glandular tissue in extrauterine locations. The molecular mechanisms of its pathogenesis have not been elucidated. We have studied the role of EXTL3 (exostosin-like 3) in endometriosis and found that it is expressed in endometrial tissue as well as endometriosis lesions. We have found that serum from endometriosis patients contains a factor or factors, which interact with EXTL3 resulting in strongly increased colony formation in regenerating cell culture. We also found increased anti-EXTL3 antibodies in endometriosis patients’ sera. EXTL3 is an N-acetyl glucosamine (GlcNAc) transferase, performing a key step in heparan sulfate (HS) glucosaminoglycan synthesis. Many viruses replicate in regenerating epithelial cells and use HS as a receptor for cell entry. We measured antibody titres to viruses, which use HS as a receptor for cell entry, and found rarely increased titres for these viruses in endometriosis sera, whereas titres to viruses using other receptors were equally distributed in study groups. The data indicate that perturbation of HS metabolism is associated with endometriosis.

Evolutionary and Structural Overview of Human Picornavirus Capsid Antibody Evasion

Picornaviruses constitute one of the most relevant viral groups according to their impact on human and animal health. Etiologic agents of a broad spectrum of illnesses with a clinical presentation that ranges from asymptomatic to fatal disease, they have been the cause of uncountable epidemics throughout history. Picornaviruses are small naked RNA-positive single-stranded viruses that include some of the most important pillars in the development of virology, comprising poliovirus, rhinovirus, and hepatitis A virus. Picornavirus infectious particles use the fecal-oral or respiratory routes as primary modes of transmission. In this regard, successful viral spread relies on the capability of viral capsids to (i) shelter the viral genome, (ii) display molecular determinants for cell receptor recognition, (iii) facilitate efficient genome delivery, and (iv) escape from the immune system. Importantly, picornaviruses display a substantial amount of genetic variability driven by both mutation and recombination. Therefore, the outcome of their replication results in the emergence of a genetically diverse cloud of individuals presenting phenotypic variance. The host humoral response against the capsid protein represents the most active immune pressure and primary weapon to control the infection. Since the preservation of the capsid function is deeply rooted in the virus evolutionary dynamics, here we review the current structural evidence focused on capsid antibody evasion mechanisms from that perspective.

Hantavirus entry: Perspectives and recent advances

Hantaviruses are important zoonotic pathogens of public health importance that are found on all continents except Antarctica and are associated with hemorrhagic fever with renal syndrome (HFRS) in the Old World and hantavirus pulmonary syndrome (HPS) in the New World. Despite the significant disease burden they cause, no FDA-approved specific therapeutics or vaccines exist against these lethal viruses. The lack of available interventions is largely due to an incomplete understanding of hantavirus pathogenesis and molecular mechanisms of virus replication, including cellular entry. Hantavirus Gn/Gc glycoproteins are the only viral proteins exposed on the surface of virions and are necessary and sufficient to orchestrate virus attachment and entry. In vitro studies have implicated integrins (β_1-3), DAF/CD55, and gC1qR as candidate receptors that mediate viral attachment for both Old World and New World hantaviruses. Recently, protocadherin-1 (PCDH1) was demonstrated as a requirement for cellular attachment and entry of New World hantaviruses in vitro and lethal HPS in vivo, making it the first clade-specific host factor to be identified. Attachment of hantavirus particles to cellular receptors induces their internalization by clathrin-mediated, dynamin-independent, or macropinocytosis-like mechanisms, followed by particle trafficking to an endosomal compartment where the fusion of viral and endosomal membranes can occur. Following membrane fusion, which requires cholesterol and acid pH, viral nucleocapsids escape into the cytoplasm and launch genome replication. In this review, we discuss the current mechanistic understanding of hantavirus entry, highlight gaps in our existing knowledge, and suggest areas for future inquiry.

Recent advances on the role of host factors during non-poliovirus enteroviral infections

Non-polio enteroviruses are emerging viruses known to cause outbreaks of polio-like infections in different parts of the world with several cases already reported in Asia Pacific, Europe and in United States of America. These outbreaks normally result in overstretching of health facilities as well as death in children under the age of five. Most of these infections are usually self-limiting except for the neurological complications associated with human enterovirus A 71 (EV-A71). The infection dynamics of these viruses have not been fully understood, with most inferences made from previous studies conducted with poliovirus.Non-poliovirus enteroviral infections are responsible for major outbreaks of hand, foot and mouth disease (HFMD) often associated with neurological complications and severe respiratory diseases. The myriad of disease presentations observed so far in children calls for an urgent need to fully elucidate the replication processes of these viruses. There are concerted efforts from different research groups to fully map out the role of human host factors in the replication cycle of these viral infections. Understanding the interaction between viral proteins and human host factors will unravel important insights on the lifecycle of this groups of viruses.This review provides the latest update on the interplay between human host factors/processes and non-polio enteroviruses (NPEV). We focus on the interactions involved in viral attachment, entry, internalization, uncoating, replication, virion assembly and eventual egress of the NPEV from the infected cells. We emphasize on the virus- human host interplay and highlight existing knowledge gaps that needs further studies. Understanding the NPEV-human host factors interactions will be key in the design and development of vaccines as well as antivirals against enteroviral infections. Dissecting the role of human host factors during NPEV infection cycle will provide a clear picture of how NPEVs usurp the human cellular processes to establish an efficient infection. This will be a boost to the drug and vaccine development against enteroviruses which will be key in control and eventual elimination of the viral infections.

Human Neonatal Fc Receptor Is the Cellular Uncoating Receptor for Enterovirus B

Enterovirus B (EV-B), a major proportion of the genus Enterovirus in the family Picornaviridae, is the causative agent of severe human infectious diseases. Although cellular receptors for coxsackievirus B in EV-B have been identified, receptors mediating virus entry, especially the uncoating process of echovirus and other EV-B remain obscure. Here, we found that human neonatal Fc receptor (FcRn) is the uncoating receptor for major EV-B. FcRn binds to the virus particles in the "canyon" through its FCGRT subunit. By obtaining multiple cryo-electron microscopy structures at different stages of virus entry at atomic or near-atomic resolution, we deciphered the underlying mechanisms of enterovirus attachment and uncoating. These structures revealed that different from the attachment receptor CD55, binding of FcRn to the virions induces efficient release of "pocket factor" under acidic conditions and initiates the conformational changes in viral particle, providing a structural basis for understanding the mechanisms of enterovirus entry.

Enteroviruses: A Gut-Wrenching Game of Entry, Detection, and Evasion

Enteroviruses are a major source of human disease, particularly in neonates and young children where infections can range from acute, self-limited febrile illness to meningitis, endocarditis, hepatitis, and acute flaccid myelitis. The enterovirus genus includes poliovirus, coxsackieviruses, echoviruses, enterovirus 71, and enterovirus D68. Enteroviruses primarily infect by the fecal-oral route and target the gastrointestinal epithelium early during their life cycles. In addition, spread via the respiratory tract is possible and some enteroviruses such as enterovirus D68 are preferentially spread via this route. Once internalized, enteroviruses are detected by intracellular proteins that recognize common viral features and trigger antiviral innate immune signaling. However, co-evolution of enteroviruses with humans has allowed them to develop strategies to evade detection or disrupt signaling. In this review, we will discuss how enteroviruses infect the gastrointestinal tract, the mechanisms by which cells detect enterovirus infections, and the strategies enteroviruses use to escape this detection.

The neonatal Fc receptor is a pan-echovirus receptor

Echoviruses are amongst the most common causative agents of aseptic meningitis worldwide and are particularly devastating in the neonatal population, where they are associated with severe hepatitis, neurological disease, including meningitis and encephalitis, and even death. Here, we identify the neonatal Fc receptor (FcRn) as a pan-echovirus receptor. We show that loss of expression of FcRn or its binding partner beta 2 microglobulin (β2M) renders cells resistant to infection by a panel of echoviruses at the stage of virus attachment, and that a blocking antibody to β2M inhibits echovirus infection in cell lines and in primary human intestinal epithelial cells. We also show that expression of human, but not mouse, FcRn renders nonpermissive human and mouse cells sensitive to echovirus infection and that the extracellular domain of human FcRn directly binds echovirus particles and neutralizes infection. Lastly, we show that neonatal mice expressing human FcRn are more susceptible to echovirus infection by the enteral route. Our findings thus identify FcRn as a pan-echovirus receptor, which may explain the enhanced susceptibility of neonates to echovirus infections.

The advent of oncolytic virotherapy in oncology: The Rigvir® story

Oncolytic viruses are a fast-developing cancer treatment field. Numerous viruses have been tested in clinical trials and three are approved. The first, Rigvir, is an immunomodulator with anti-tumour effect for treatment of melanoma, local treatment of skin and subcutaneous metastases of melanoma, for prevention of relapse and metastasis after radical surgery registered in Latvia, Georgia, Armenia and Uzbekistan. The aim of the present review is to summarize the development of Rigvir. Approximately 60 viruses were screened preclinically. Clinical safety and efficacy trials were with 5 oncolytic enteroviruses. Safety of the selected and melanoma-adapted ECHO-7 virus Rigvir was tested in over 180 patients with no severe adverse events observed. Pre-registration efficacy studies involved over 700 cancer patients: over 540 melanoma patients, and patients with late stage stomach (ca. 90), colorectal cancer (ca. 60), and other cancers. Patients were treated with Rigvir for 3 years after surgery and compared to immunotherapy: 3- and 5-year overall survival appeared to be increased in Rigvir treated patients. In post-marketing retrospective studies, Rigvir-treated stage II melanoma patients showed a 6.67-fold decreased risk for disease progression in comparison to those that had been observed according to guidelines, and stage IB and stage II melanoma patients that had received Rigvir therapy had 4.39-6.57-fold lower mortality. The results are confirmed and extended by case reports. Several immunological markers have been measured. In conclusion, Rigvir is an oncotropic and oncolytic virus for treatment of melanoma; the results will be confirmed and updated by modern clinical studies.

Effect of the oncolytic ECHO-7 virus Rigvir® on the viability of cell lines of human origin in vitro

Background: The role of oncolytic viruses in cancer treatment is increasingly studied. The first oncolytic virus (Rigvir®, ECHO-7) was registered in Latvia over a decade ago. In a recent retrospective study Rigvir® decreased mortality 4.39-6.57-fold in stage IB-IIC melanoma patients. The aims of the present study are to test the effect of Rigvir® on cell line viability in vitro and to visualize the cellular presence of Rigvir® by immunocytochemistry.

Methods: The cytolytic effect of Rigvir® on the viability of FM-9, RD, AGS, A549, HDFa, HPAF‑II, MSC, MCF7, HaCaT, and Sk-Mel-28 cell lines was measured using live cell imaging. PBMC viability was measured using flow cytometry. The presence of ECHO-7 virus was visualized using immunocytochemistry. Statistical difference between treatment groups was calculated using two-way ANOVA.

Results: Rigvir® (10%, volume/volume) reduced cell viability in FM-9, RD, AGS, A549, HDFa, HPAF‑II and MSC cell lines by 67-100%. HaCaT cell viability was partly affected while Rigvir® had no effect on MCF7, Sk-Mel-28 and PBMC viability. Detection of ECHO-7 by immunocytochemistry in FM-9, RD, AGS, A549, HDFa, HPAF-II and Sk-Mel-28 cell lines suggests that the presence of Rigvir® in the cells preceded or coincided with the time of reduction of cell viability. Rigvir® (10%) had no effect on live PBMC count.

Conclusions: The results suggest that Rigvir® in vitro reduces the viability of cells of human melanoma, rhabdomyosarcoma, gastric adenocarcinoma, lung carcinoma, pancreas adenocarcinoma but not in PBMC. The presence of Rigvir® in the sensitive cells was confirmed using anti-ECHO-7 antibodies. The present results suggest that a mechanism of action for the clinical benefit of Rigvir® is its cytolytic properties. The present results suggest that the effect of Rigvir® could be tested in other cancers besides melanoma. Further studies of possible Rigvir® entry receptors are needed.

Beyond the Role of CD55 as a Complement Component

The complement is a part of the immune system that plays several roles in removing pathogens. Despite the importance of the complement system, the exact role of each component has been overlooked because the complement system was thought to be a nonspecific humoral immune mechanism that worked against pathogens. Decay-accelerating factor (DAF or CD55) is a known inhibitor of the complement system and has recently attracted substantial attention due to its role in various diseases, such as cancer, protein-losing enteropathy, and malaria. Some protein-losing enteropathy cases are caused by CD55 deficiency, which leads to complement hyperactivation, malabsorption, and angiopathic thrombosis. In addition, CD55 has been reported to be an essential host receptor for infection by the malaria parasite. Moreover, CD55 is a ligand of the seven-span transmembrane receptor CD97. Since CD55 is present in various cells, the functional role of CD55 has been expanded by showing that CD55 is associated with a variety of diseases, including cancer, malaria, protein-losing enteropathy, paroxysmal nocturnal hemoglobinuria, and autoimmune diseases. This review summarizes the current understanding of CD55 and the role of CD55 in these diseases. It also provides insight into the development of novel drugs for the diagnosis and treatment of diseases associated with CD55.

Resistance of Echovirus 11 to ClO2 Is Associated with Enhanced Host Receptor Use, Altered Entry Routes, and High Fitness

Waterborne viruses can exhibit resistance to common water disinfectants, yet the mechanisms that allow them to tolerate disinfection are poorly understood. Here, we generated echovirus 11 (E11) with resistance to chlorine dioxide (ClO₂) by experimental evolution, and we assessed the associated genotypic and phenotypic traits. ClO₂ resistance emerged after E11 populations were repeatedly reduced (either by ClO₂-exposure or by dilution) and then regrown in cell culture. The resistance was linked to an improved capacity of E11 to bind to its host cells, which was further attributed to two potential causes: first, the resistant E11 populations possessed mutations that caused amino acid substitutions from ClO₂-labile to ClO₂-stable residues in the viral proteins, which likely increased the chemical stability of the capsid toward ClO₂. Second, resistant E11 mutants exhibited the capacity to utilize alternative cell receptors for host binding. Interestingly, the emergence of ClO₂ resistance resulted in an enhanced replicative fitness compared to the less resistant starting population. Overall this study contributes to a better understanding of the mechanism underlying disinfection resistance in waterborne viruses, and processes that drive resistance development.

Complement Evasion Strategies of Viruses: An Overview

Being a major first line of immune defense, the complement system keeps a constant vigil against viruses. Its ability to recognize large panoply of viruses and virus-infected cells, and trigger the effector pathways, results in neutralization of viruses and killing of the infected cells. This selection pressure exerted by complement on viruses has made them evolve a multitude of countermeasures. These include targeting the recognition molecules for the avoidance of detection, targeting key enzymes and complexes of the complement pathways like C3 convertases and C5b-9 formation - either by encoding complement regulators or by recruiting membrane-bound and soluble host complement regulators, cleaving complement proteins by encoding protease, and inhibiting the synthesis of complement proteins. Additionally, viruses also exploit the complement system for their own benefit. For example, they use complement receptors as well as membrane regulators for cellular entry as well as their spread. Here, we provide an overview on the complement subversion mechanisms adopted by the members of various viral families including Poxviridae, Herpesviridae, Adenoviridae, Flaviviridae, Retroviridae, Picornaviridae, Astroviridae, Togaviridae, Orthomyxoviridae and Paramyxoviridae.

PLA2G16 represents a switch between entry and clearance of Picornaviridae

Picornaviruses are a leading cause of human and veterinary infections that result in various diseases, including polio and the common cold. As archetypical non-enveloped viruses, their biology has been extensively studied. Although a range of different cell-surface receptors are bound by different picornaviruses, it is unclear whether common host factors are needed for them to reach the cytoplasm. Using genome-wide haploid genetic screens, here we identify the lipid-modifying enzyme PLA2G16 (refs 8, 9, 10, 11) as a picornavirus host factor that is required for a previously unknown event in the viral life cycle. We find that PLA2G16 functions early during infection, enabling virion-mediated genome delivery into the cytoplasm, but not in any virion-assigned step, such as cell binding, endosomal trafficking or pore formation. To resolve this paradox, we screened for suppressors of the ΔPLA2G16 phenotype and identified a mechanism previously implicated in the clearance of intracellular bacteria. The sensor of this mechanism, galectin-8 (encoded by LGALS8), detects permeated endosomes and marks them for autophagic degradation, whereas PLA2G16 facilitates viral genome translocation and prevents clearance. This study uncovers two competing processes triggered by virus entry: activation of a pore-activated clearance pathway and recruitment of a phospholipase to enable genome release.

Rhinoviruses and Respiratory Enteroviruses: Not as Simple as ABC

Rhinoviruses (RVs) and respiratory enteroviruses (EVs) are leading causes of upper respiratory tract infections and among the most frequent infectious agents in humans worldwide. Both are classified in the Enterovirus genus within the Picornaviridae family and they have been assigned to seven distinct species, RV-A, B, C and EV-A, B, C, D. As viral infections of public health significance, they represent an important financial burden on health systems worldwide. However, the lack of efficient antiviral treatment or vaccines against these highly prevalent pathogens prevents an effective management of RV-related diseases. Current advances in molecular diagnostic techniques have revealed the presence of RV in the lower respiratory tract and its role in lower airway diseases is increasingly reported. In addition to an established etiological role in the common cold, these viruses demonstrate an unexpected capacity to spread to other body sites under certain conditions. Some of these viruses have received particular attention recently, such as EV-D68 that caused a large outbreak of respiratory illness in 2014, respiratory EVs from species C, or viruses within the newly-discovered RV-C species. This review provides an update of the latest findings on clinical and fundamental aspects of RV and respiratory EV, including a summary of basic knowledge of their biology.

Virus-Induced Demyelination: The Case for Virus(es) in Multiple Sclerosis

Multiple Sclerosis (MS) is the most common demyelinating disease of man with over 400,000 cases in the United States and over 2.5 million cases worldwide. There are over 64,000 citations in Pubmed dating back as far as 1887. Much has been learned over the past 129 years with a recent burst in therapeutic options (mostly anti-inflammatory) with newer medications in development that are neuroprotective and/or neuroreparative. However, with all these advancements the cause of MS remains elusive. There is a clear interplay of genetic, immunologic, and environmental factors that influences both the development and progression of this disorder. This chapter will give a brief overview of the history and pathogenesis of MS with attention to how host immune responses in genetically susceptible individuals contribute to the MS disease process. In addition, we will explore the role of infectious agents in MS as potential “triggers” of disease. Models of virus-induced demyelination will be discussed, with an emphasis on the recent interest in human herpesviruses and the role they may play in MS disease pathogenesis. Although we remain circumspect as to the role of any microbial pathogen in MS, we suggest that only through well-controlled serological, cellular immune, molecular, and animal studies we will be able to identify candidate agents. Ultimately, clinical interventional trials that either target a specific pathogen or class of pathogens will be required to make definitive links between the suspected agent and MS.

Coxsackie-adenovirus receptor expression is enhanced in pancreas from patients with type 1 diabetes

OBJECTIVES

One of the theories connecting enterovirus (EV) infection of human islets with type 1 diabetes (T1D) is the development of a fertile field in the islets. This implies induction of appropriate proteins for the viral replication such as the coxsackie-adenovirus receptor (CAR). The aim of this study was to investigate to what extent CAR is expressed in human islets of Langerhans, and what conditions that would change the expression.

DESIGN

Immunohistochemistry for CAR was performed on paraffin-embedded pancreatic tissue from patients with T1D (n=9 recent onset T1D, n=4 long-standing T1D), islet autoantibody-positive individuals (n=14) and non-diabetic controls (n=24) individuals. The expression of CAR was also examined by reverse transcription PCR on microdissected islets (n=5), exocrine tissue (n=5) and on explanted islets infected with EV or exposed to chemokines produced by EV-infected islet cells.

RESULTS

An increased frequency of patients with T1D and autoantibody-positive individuals expressed CAR in the pancreas (p<0.039). CAR staining was detected more frequently in pancreatic islets from patients with T1D and autoantibody-positive subjects (15/27) compared with (6/24) non-diabetic controls (p<0.033). Also in explanted islets cultured in UV-treated culture medium from coxsackievirus B (CBV)-1-infected islets, the expression of the CAR gene was increased compared with controls. Laser microdissection of pancreatic tissue revealed that CAR expression was 10-fold higher in endocrine compared with exocrine cells of the pancreas. CAR was also expressed in explanted islets and the expression level decreased with time in culture. CBV-1 infection of explanted islets clearly decreased the expression of CAR (p<0.05). In contrast, infection with echovirus 6 did not affect the expression of CAR.

CONCLUSIONS

CAR is expressed in pancreatic islets of patients with T1D and the expression level of CAR is increased in explanted islets exposed to proinflammatory cytokines/chemokines produced by infected islets. T1D is associated with increased levels of certain chemokines/cytokines in the islets and this might be the mechanism behind the increased expression of CAR in TID islets.

The Suramin Derivative NF449 Interacts with the 5-fold Vertex of the Enterovirus A71 Capsid to Prevent Virus Attachment to PSGL-1 and Heparan Sulfate

NF449, a sulfated compound derived from the antiparasitic drug suramin, was previously reported to inhibit infection by enterovirus A71 (EV-A71). In the current work, we found that NF449 inhibits virus attachment to target cells, and specifically blocks virus interaction with two identified receptors—the P-selectin ligand, PSGL-1, and heparan sulfate glycosaminoglycan—with no effect on virus binding to a third receptor, the scavenger receptor SCARB2. We also examined a number of commercially available suramin analogues, and newly synthesized derivatives of NF449; among these, NF110 and NM16, like NF449, inhibited virus attachment at submicromolar concentrations. PSGL-1 and heparan sulfate, but not SCARB2, are both sulfated molecules, and their interaction with EV-A71 is thought to involve positively charged capsid residues, including a conserved lysine at VP1-244, near the icosahedral 5-fold vertex. We found that mutation of VP1-244 resulted in resistance to NF449, suggesting that this residue is involved in NF449 interaction with the virus capsid. Consistent with this idea, NF449 and NF110 prevented virus interaction with monoclonal antibody MA28-7, which specifically recognizes an epitope overlapping VP1-244 at the 5-fold vertex. Based on these observations we propose that NF449 and related compounds compete with sulfated receptor molecules for a binding site at the 5-fold vertex of the EV-A71 capsid.

Enterovirus A71 is epidemic in the Asia-Pacific region, and has been responsible for thousands of cases of fatal neurological disease in young children. There are no specific therapies available. We previously identified NF449 as a compound with anti-EV-A71 activity, although its mechanism of action was uncertain. In the current work we found that NF449 and related molecules prevent virus attachment both to PSGL-1, a receptor molecule important for virus interaction with white blood cells, and to heparan sulfate, a receptor that may be important for virus interaction with a variety of other cell types. In contrast, we found that NF449 had no effect on virus attachment to another proposed receptor, SCARB2. We also found that NF449 and related compounds interact with a specific site on the viral capsid, remote from the binding site for another major receptor, SCARB2. Our work provides information that may facilitate development of improved antiviral compounds that block the attachment of EV-A71 to cellular receptors.

Anti-infective immunoadhesins from plants

Immunoadhesins are recombinant proteins that combine the ligand-binding region of a receptor or adhesion molecule with immunoglobulin constant domains. All FDA-approved immunoadhesins are designed to modulate the interaction of a human receptor with its normal ligand, such as Etanercept (Enbrel(®) ), which interferes with the binding of tumour necrosis factor (TNF) to the TNF-alpha receptor and is used to treat inflammatory diseases such as rheumatoid arthritis. Like antibodies, immunoadhesins have long circulating half-lives, are readily purified by affinity-based methods and have the avidity advantages conferred by bivalency. Immunoadhesins that incorporate normal cellular receptors for viruses or bacterial toxins hold great, but as yet unrealized, potential for treating infectious disease. As decoy receptors, immunoadhesins have potential advantages over pathogen-targeted monoclonal antibodies. Planet Biotechnology has specialized in developing anti-infective immunoadhesins using plant expression systems. An immunoadhesin incorporating the cellular receptor for anthrax toxin, CMG2, potently blocks toxin activity in vitro and protects animals against inhalational anthrax. An immunoadhesin based on the receptor for human rhinovirus, ICAM-1, potently blocks infection of human cells by one of the major causes of the common cold. An immunoadhesin targeting the MERS coronavirus is in an early stage of development. We describe here the unique challenges involved in designing and developing immunoadhesins targeting infectious diseases in the hope of inspiring further research into this promising class of drugs.

Hunting Viral Receptors Using Haploid Cells

Viruses have evolved intricate mechanisms to gain entry into the host cell. Identification of host proteins that serve as viral receptors has enabled insights into virus particle internalization, host and tissue tropism, and viral pathogenesis. In this review we discuss the most commonly employed methods for virus receptor discovery, specifically highlighting the use of forward genetic screens in human haploid cells. The ability to generate true knockout alleles at high saturation provides a sensitive means to study virus-host interactions. To illustrate the power of such haploid genetic screens, we highlight the discovery of the lysosomal proteins NPC1 and LAMP1 as intracellular receptors for Ebola virus and Lassa virus, respectively. From these studies emerges the notion that receptor usage by these viruses is highly dynamic, involving a programmed switch from cell surface receptor to intracellular receptor. Broad application of genetic knockout approaches will chart functional landscapes of receptors and endocytic pathways hijacked by viruses.