Human polyomavirus JC (JCV) infection of human B lymphocytes: a possible mechanism for JCV transmigration across the blood-brain barrier

Understanding the link between neurotropic viruses, BBB permeability, and MS pathogenesis

Neurotropic viruses can infiltrate the CNS by crossing the blood-brain barrier (BBB) through various mechanisms including paracellular, transcellular, and "Trojan horse" mechanisms during leukocyte diapedesis. These viruses belong to several families, including retroviruses; human immunodeficiency virus type 1 (HIV-1), flaviviruses; Japanese encephalitis (JEV); and herpesviruses; herpes simplex virus type 1 (HSV-1), Epstein-Barr virus (EBV), and mouse adenovirus 1 (MAV-1). For entering the brain, viral proteins act upon the tight junctions (TJs) between the brain microvascular endothelial cells (BMECs). For instance, HIV-1 proteins, such as glycoprotein 120, Nef, Vpr, and Tat, disrupt the BBB and generate a neurotoxic effect. Recombinant-Tat triggers amendments in the BBB by decreasing expression of the TJ proteins such as claudin-1, claudin-5, and zona occludens-1 (ZO-1). Thus, the breaching of BBB has been reported in myriad of neurological diseases including multiple sclerosis (MS). Neurotropic viruses also exhibit molecular mimicry with several myelin sheath proteins, i.e., antibodies against EBV nuclear antigen 1 (EBNA1) aa411-426 cross-react with MBP and EBNA1 aa385-420 was found to be associated with MS risk haplotype HLA-DRB1*150. Notably, myelin protein epitopes (PLP139-151, MOG35-55, and MBP87-99) are being used to generate model systems for MS such as experimental autoimmune encephalomyelitis (EAE) to understand the disease mechanism and therapeutics. Viruses like Theiler's murine encephalomyelitis virus (TMEV) are also commonly used to generate EAE. Altogether, this review provide insights into the viruses' association with BBB leakiness and MS along with possible mechanistic details which could potentially use for therapeutics.

Progressive multifocal leukoencephalopathy triggered by COVID-19 in a previously asymptomatic person living with undiagnosed HIV infection

This report presents the case of a 47-year-old male patient who worked as a mathematics teacher and experienced the sudden onset of disorientation, aphasia, and acalculia during an online class. The current study reveals the first documented case of HIV and progressive multifocal leukoencephalopathy with the detection of SARS-CoV-2 and human polyomavirus 2 (previously known as John Cunningham virus) in the cerebrospinal fluid. Furthermore, serum analysis revealed elevated concentrations of interleukin (IL)-6, IL-17, and IL-8, which are potential factors known to reduce the expression of tight junctions and adhesion molecules in the extracellular matrix, thereby affecting the permeability of the blood-brain barrier. Finally, the study discusses whether SARS-CoV-2 triggers or exacerbates progressive multifocal leukoencephalopathy.

Polyomavirus Wakes Up and Chooses Neurovirulence

JC polyomavirus (JCPyV) is a human-specific polyomavirus that establishes a silent lifelong infection in multiple peripheral organs, predominantly those of the urinary tract, of immunocompetent individuals. In immunocompromised settings, however, JCPyV can infiltrate the central nervous system (CNS), where it causes several encephalopathies of high morbidity and mortality. JCPyV-induced progressive multifocal leukoencephalopathy (PML), a devastating demyelinating brain disease, was an AIDS-defining illness before antiretroviral therapy that has "reemerged" as a complication of immunomodulating and chemotherapeutic agents. No effective anti-polyomavirus therapeutics are currently available. How depressed immune status sets the stage for JCPyV resurgence in the urinary tract, how the virus evades pre-existing antiviral antibodies to become viremic, and where/how it enters the CNS are incompletely understood. Addressing these questions requires a tractable animal model of JCPyV CNS infection. Although no animal model can replicate all aspects of any human disease, mouse polyomavirus (MuPyV) in mice and JCPyV in humans share key features of peripheral and CNS infection and antiviral immunity. In this review, we discuss the evidence suggesting how JCPyV migrates from the periphery to the CNS, innate and adaptive immune responses to polyomavirus infection, and how the MuPyV-mouse model provides insights into the pathogenesis of JCPyV CNS disease.

Co-Detection of EBV and Human Polyomavirus JCPyV in a Case of AIDS-Related Multifocal Primary Central Nervous System Diffuse Large B-Cell Lymphoma

The human neurotropic Polyomavirus JCPyV is the widespread opportunistic causative pathogen of the fatal demyelinating disease progressive multifocal leukoencephalopathy; however, it has also been implicated in the oncogenesis of several types of cancers. It causes brain tumors when intracerebrally inoculated into rodents, and genomic sequences of different strains and expression of the viral protein large T-Antigen have been detected in a wide variety of glial brain tumors and CNS lymphomas. Here, we present a case of an AIDS-related multifocal primary CNS lymphoma in which JCPyV genomic sequences of the three regions of JCPyV and expression of T-Antigen were detected by PCR and immunohistochemistry, respectively. No capsid proteins were detected, ruling out active JCPyV replication. Sequencing of the control region revealed that Mad-4 was the strain of JCPyV present in tumor cells. In addition, expression of viral proteins LMP and EBNA-1 from another ubiquitous oncogenic virus, Epstein-Barr, was also detected in the same lymphocytic neoplastic cells, co-localizing with JCPyV T-Antigen, suggesting a potential collaboration between these two viruses in the process of malignant transformation of B-lymphocytes, which are the site of latency and reactivation for both viruses.

JC polyomavirus: a short review of its biology, its association with progressive multifocal leukoencephalopathy, and the diagnostic value of different methods to manifest its activity or presence

INTRODUCTION

JC polyomavirus is the causative agent of progressive multifocal leukoencephalopathy (PML), a demyelinating disease resulting from the lytic infection of oligodendrocytes that may develop in immunosuppressed individuals: HIV1 infected or individuals under immunosuppressive therapies. Understanding the biology of JCPyV is necessary for a proper patient management, the development of diagnostic tests, and risk stratification.

AREAS COVERED

The review covers different areas of expertise including the genomic characterization of JCPyV strains detected in different body compartments (urine, plasma, and cerebrospinal fluid) of PML patients, viral mutations, molecular diagnostics, viral miRNAs, and disease.

EXPERT OPINION

The implementation of molecular biology techniques improved our understanding of JCPyV biology. Deep sequencing analysis of viral genomes revealed the presence of viral quasispecies in the cerebrospinal fluid of PML patients characterized by noncoding control region rearrangements and VP1 mutations. These neurotropic JCPyV variants present enhanced replication and an altered cell tropism that contribute to PML development. Monitoring these variants may be relevant for the identification of patients at risk of PML. Multiplex realtime PCR targeting both the LTAg and the archetype NCCR could be used to identify them. Failure to amplify NCCR should indicate the presence of a JCPyV prototype speeding up the diagnostic process.

The choroid plexus and its role in the pathogenesis of neurological infections

The choroid plexus is situated at an anatomically and functionally important interface within the ventricles of the brain, forming the blood-cerebrospinal fluid barrier that separates the periphery from the central nervous system. In contrast to the blood-brain barrier, the choroid plexus and its epithelial barrier have received considerably less attention. As the main producer of cerebrospinal fluid, the secretory functions of the epithelial cells aid in the maintenance of CNS homeostasis and are capable of relaying inflammatory signals to the brain. The choroid plexus acts as an immunological niche where several types of peripheral immune cells can be found within the stroma including dendritic cells, macrophages, and T cells. Including the epithelia cells, these cells perform immunosurveillance, detecting pathogens and changes in the cytokine milieu. As such, their activation leads to the release of homing molecules to induce chemotaxis of circulating immune cells, driving an immune response at the choroid plexus. Research into the barrier properties have shown how inflammation can alter the structural junctions and promote increased bidirectional transmigration of cells and pathogens. The goal of this review is to highlight our foundational knowledge of the choroid plexus and discuss how recent research has shifted our understanding towards viewing the choroid plexus as a highly dynamic and important contributor to the pathogenesis of neurological infections. With the emergence of several high-profile diseases, including ZIKA and SARS-CoV-2, this review provides a pertinent update on the cellular response of the choroid plexus to these diseases. Historically, pharmacological interventions of CNS disorders have proven difficult to develop, however, a greater focus on the role of the choroid plexus in driving these disorders would provide for novel targets and routes for therapeutics.

The Inhibition of DNA Viruses by the Amphibian Antimicrobial Peptide Temporin G: A Virological Study Addressing HSV-1 and JPCyV

Herpes simplex virus type-1 (HSV-1) and John Cunningham polyomavirus (JCPyV) are widely distributed DNA viruses causing mainly asymptomatic infection, but also mild to very severe diseases, especially when these viruses reach the brain. Some drugs have been developed to inhibit HSV-1 replication in host cells, but their prolonged use may induce resistance phenomena. In contrast, to date, there is no cure for JCPyV. The search for alternative drugs that can reduce viral infections without undermining the host cell is moving toward antimicrobial peptides (AMPs) of natural occurrence. These include amphibian AMPs belonging to the temporin family. Herein, we focus on temporin G (TG), showing that it strongly affects HSV-1 replication by acting either during the earliest stages of its life cycle or directly on the virion. Computational studies have revealed the ability of TG to interact with HSV-1 glycoprotein B. We also found that TG reduced JCPyV infection, probably affecting both the earliest phases of its life cycle and the viral particle, likely through an interaction with the viral capsid protein VP1. Overall, our results are promising for the development of short naturally occurring peptides as antiviral agents used to counteract diseases related to HSV-1 and JCPyV.

Breaching Brain Barriers: B Cell Migration in Multiple Sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) known for the manifestation of demyelinated lesions throughout the CNS, leading to neurodegeneration. To date, not all pathological mechanisms that drive disease progression are known, but the clinical benefits of anti-CD20 therapies have put B cells in the spotlight of MS research. Besides their pathological effects in the periphery in MS, B cells gain access to the CNS where they can contribute to disease pathogenesis. Specifically, B cells accumulate in perivascular infiltrates in the brain parenchyma and the subarachnoid spaces of the meninges, but are virtually absent from the choroid plexus. Hence, the possible migration of B cells over the blood-brain-, blood-meningeal-, and blood-cerebrospinal fluid (CSF) barriers appears to be a crucial step to understanding B cell-mediated pathology. To gain more insight into the molecular mechanisms that regulate B cell trafficking into the brain, we here provide a comprehensive overview of the different CNS barriers in health and in MS and how they translate into different routes for B cell migration. In addition, we review the mechanisms of action of diverse therapies that deplete peripheral B cells and/or block B cell migration into the CNS. Importantly, this review shows that studying the different routes of how B cells enter the inflamed CNS should be the next step to understanding this disease.

Rearrangement in the Hypervariable Region of JC Polyomavirus Genomes Isolated from Patient Samples and Impact on Transcription Factor-Binding Sites and Disease Outcomes

JC polyomavirus (JCPyV) is the causative agent of the fatal, incurable, neurological disease, progressive multifocal leukoencephalopathy (PML). The virus is present in most of the adult population as a persistent, asymptotic infection in the kidneys. During immunosuppression, JCPyV reactivates and invades the central nervous system. A main predictor of disease outcome is determined by mutations within the hypervariable region of the viral genome. In patients with PML, JCPyV undergoes genetic rearrangements in the noncoding control region (NCCR). The outcome of these rearrangements influences transcription factor binding to the NCCR, orchestrating viral gene transcription. This study examines 989 NCCR sequences from patient isolates deposited in GenBank to determine the frequency of mutations based on patient isolation site and disease status. The transcription factor binding sites (TFBS) were also analyzed to understand how these rearrangements could influence viral transcription. It was determined that the number of TFBS was significantly higher in PML samples compared to non-PML samples. Additionally, TFBS that could promote JCPyV infection were more prevalent in samples isolated from the cerebrospinal fluid compared to other locations. Collectively, this research describes the extent of mutations in the NCCR that alter TFBS and how they correlate with disease outcome.

Progressive multifocal leukoencephalopathy in the context of newer therapies in hematology and review of new treatment strategies

Progressive multifocal leukoencephalopathy (PML) is a rare, often fatal demyelinating disease of the central nervous system (CNS) caused by the reactivation of JC polyomavirus in the CNS. We present a case of a 54-year-old man with follicular lymphoma diagnosed with PML after being treated with anti-CD20 monoclonal antibody-based regimens for several years. Due to the lack of effective treatment choices for PML, the patient was treated with nivolumab, based on recent reports, but succumbed to his disease a few months after diagnosis. In this paper, we focus on reviewing the literature of PML cases correlated with newer agents used in hematology, possible factors affecting disease prognosis, as well as the available data on upcoming therapeutic options for patients with PML. Though newer promising treatments such as anti-PD1 monoclonal antibodies arise, a definitive treatment option is yet to be found. Vigilance, early detection, and prompt intervention play a crucial role in the prognosis of PML in patients with hematological malignancies.

Role of Dendritic Cells in Viral Brain Infections

To gain access to the brain, a so-called immune-privileged organ due to its physical separation from the blood stream, pathogens and particularly viruses have been selected throughout evolution for their use of specific mechanisms. They can enter the central nervous system through direct infection of nerves or cerebral barriers or through cell-mediated transport. Indeed, peripheral lymphoid and myeloid immune cells can interact with the blood-brain and the blood-cerebrospinal fluid barriers and allow viral brain access using the "Trojan horse" mechanism. Among immune cells, at the frontier between innate and adaptive immune responses, dendritic cells (DCs) can be pathogen carriers, regulate or exacerbate antiviral responses and neuroinflammation, and therefore be involved in viral transmission and spread. In this review, we highlight an important contribution of DCs in the development and the consequences of viral brain infections.

PI3K/AKT/mTOR Signaling Pathway Is Required for JCPyV Infection in Primary Astrocytes

Astrocytes are a main target of JC polyomavirus (JCPyV) in the central nervous system (CNS), where the destruction of these cells, along with oligodendrocytes, leads to the fatal disease progressive multifocal leukoencephalopathy (PML). There is no cure currently available for PML, so it is essential to discover antivirals for this aggressive disease. Additionally, the lack of a tractable in vivo models for studying JCPyV infection makes primary cells an accurate alternative for elucidating mechanisms of viral infection in the CNS. This research to better understand the signaling pathways activated in response to JCPyV infection reveals and establishes the importance of the PI3K/AKT/mTOR signaling pathway in JCPyV infection in primary human astrocytes compared to transformed cell lines. Using RNA sequencing and chemical inhibitors to target PI3K, AKT, and mTOR, we have demonstrated the importance of this signaling pathway in JCPyV infection of primary astrocytes not observed in transformed cells. Collectively, these findings illuminate the potential for repurposing drugs that are involved with inhibition of the PI3K/AKT/mTOR signaling pathway and cancer treatment as potential therapeutics for PML, caused by this neuroinvasive virus.

The MAPK/ERK Pathway and the Role of DUSP1 in JCPyV Infection of Primary Astrocytes

JC polyomavirus (JCPyV) is a neuroinvasive pathogen causing a fatal, demyelinating disease of the central nervous system (CNS) known as progressive multifocal leukoencephalopathy (PML). Within the CNS, JCPyV predominately targets two cell types: oligodendrocytes and astrocytes. The underlying mechanisms of astrocytic infection are poorly understood, yet recent findings suggest critical differences in JCPyV infection of primary astrocytes compared to a widely studied immortalized cell model. RNA sequencing was performed in primary normal human astrocytes (NHAs) to analyze the transcriptomic profile that emerges during JCPyV infection. Through a comparative analysis, it was validated that JCPyV requires the mitogen-activated protein kinase, extracellular signal-regulated kinase (MAPK/ERK) pathway, and additionally requires the expression of dual-specificity phosphatases (DUSPs). Specifically, the expression of DUSP1 is needed to establish a successful infection in NHAs, yet this was not observed in an immortalized cell model of JCPyV infection. Additional analyses demonstrated immune activation uniquely observed in NHAs. These results support the hypothesis that DUSPs within the MAPK/ERK pathway impact viral infection and influence potential downstream targets and cellular pathways. Collectively, this research implicates DUSP1 in JCPyV infection of primary human astrocytes, and most importantly, further resolves the signaling events that lead to successful JCPyV infection in the CNS.

Understanding progressive multifocal leukoencephalopathy: links between milky-way appearance and mismatch T2/FLAIR

BACKGROUND

Magnetic resonance imaging is essential to diagnose progressive multifocal leukoencephalopathy. The broad radiological spectrum may partially be explained by genetic viral mutations and their differential neurotropism. Recent pharmacovigilance-magnetic resonance imaging studies have provided new insight into pathophysiology and radiological markers of early stages. However, how lesions evolve and why certain anatomical locations are more frequently affected remains unknown. We aim to describe a new sign - T2/fluid-attenutated inversion recovery mismatch - as a complementary marker of cavitated lesions and propose a link with the milky-way appearance, a key early sign. Furthermore, we hypothesise viral dissemination routes.

METHODS

We conducted a retrospective longitudinal study from January 2010 to January 2020, to analyse clinical and magnetic resonance imaging features of 13 progressive multifocal leukoencephalopathy individuals at the symptomatic stage (mean age 58.3 years (SD ± 16.8) - 61.5% were women).

RESULTS

The most prevalent pathology was HIV (61.5%) and motor deficit prevailed regarding other symptoms (76.9%). Frontal lobes (76.9%), middle cerebellar peduncle (61.5%), cerebellum (61.5%), and pons (53.8%) were most commonly affected, and the cortico-ponto-cerebellar pathway seemed involved in these patients. Five patients had a pure radiological pattern. Milky-way appearance was the most frequent radiological sign (58.3%). Five patients with milky-way appearance had concomitantly T2/fluid-attenuated inversion recovery mismatch (P = 0.02). This sign showed high sensitivity and specificity (100-71%, P = 0.02) to assess evolved lesions besides diffusion.

CONCLUSION

The possible tract-dependent spread, as well as clinical and genetic, have implications on the MRI variability of progressive multifocal leukoencephalopathy. The milky-way appearance could reflect a transitional phase towards evolved lesions, the latter demonstrated by T2/fluid-attenuated inversion recovery mismatch. Both could be key magnetic resonance imaging signs to diagnose progressive multifocal leukoencephalopathy at the symptomatic stage.

JC Virus Seroprevalence and JCVAb Index in Polish Multiple Sclerosis Patients Treated with Immunomodulating or Immunosuppressive Therapies

The use of a highly-effective treatment for multiple sclerosis (MS) is associated with a severe risk of developing complications, such as progressive multifocal leukoencephalopathy (PML) caused by the John Cunningham virus (JCV). The aim of this study was to evaluate the correlation between anti-JCV Ab seroprevalence, anti-JCV AI, demographic and clinical factors as well as the type of therapy used in the Polish MS population. This is a multicentre, prospective and cross-sectional study involving 1405 MS patients. The seroprevalence of anti-JCV Ab and anti-JCV AI levels as well as AI categories were analysed with the use of a second-generation two-step ELISA test (STRATIFY JCV DxSelect). The overall prevalence of anti-JCV Ab was 65.8%. It was shown that seroprevalence increases with the patient's age. The seroprevalence was significantly associated with the treatment type, and the highest values (76%) were obtained from immunosuppressant-treated patients. Overall, 63.3% of seropositive patients had an antibody index (AI) level of >1.5. In the seropositive patient group, the mean AI level amounted to 2.09. Similarly to the seroprevalence, AI levels correlated with the patient's age; AI level for patients above 40 years old and from subsequent age quintiles plateaued, amounting to at least 1.55. Patients treated with immunosuppressants and immunomodulatory drugs obtained the highest (1.67) and lowest (1.35) AI levels, respectively. Of the immunosuppressants used, the highest mean AI levels were observed in mitoxantrone and cladribine groups, amounting to 1.75 and 1.69, respectively. In patients treated with immunomodulatory drugs, the lowest AI levels were observed in the dimethyl fumarate (DMF) group (1.11). The seroprevalence rate in the Polish MS population is one of the highest in Europe. The majority of seropositive patients had an anti-JCV Ab level qualifying them for a high-risk category. The highest mean AI levels are observed in patients receiving immunosuppressants, especially mitoxantrone and cladribine. Patients receiving immunomodulatory drugs have lower AI levels compared to treatment-naïve subjects, especially when treated with DMF. Further studies, especially longitudinal studies, are required to determine the impact of MS drugs on the seroprevalence of anti-JCV Ab and AI levels.

Trafficking of JC virus-like particles across the blood-brain barrier

Hollow viral vectors, such as John Cunningham virus-like particles (JC VLPs), provide a unique opportunity to deliver drug cargo into targeted cells and tissue. Current understanding of the entry of JC virus in brain cells has remained insufficient. In particular, interaction of JC VLPs with the blood-brain barrier (BBB) has not been analyzed in detail. Thus, JC VLPs were produced in this study for investigating the trafficking across the BBB. We performed a carotid artery injection procedure for mouse brain to qualitatively study JC VLPs' in vivo binding and distribution and used in vitro approaches to analyze their uptake and export kinetics in brain endothelial cells. Our results show that clathrin-dependent mechanisms contributed to the entry of VLPs into brain endothelial cells, and exocytosis or transcytosis of VLPs across the BBB was observed in vitro. VLPs were found to interact with sialic acid glycans in mouse brain endothelia. The ability of JC VLPs to cross the BBB can be useful in developing a delivery system for transport of genes and small molecule cargoes to the brain.

JC Polyomavirus Infection Potentiated by Biologics

The risk of JC polyomavirus encephalopathy varies among biologic classes and among agents within the same class. Of currently used biologics, the highest risk is seen with natalizumab followed by rituximab. Multiple other agents have also been implicated. Drug-specific causality is difficult to establish because many patients receive multiple immunomodulatory medications concomitantly or sequentially, and have other immunocompromising factors related to their underlying disease. As use of biologic therapies continues to expand, further research is needed into pathogenesis, treatment, and prevention of JC polyomavirus encephalopathy such that risk for its development is better understood and mitigated, if not eliminated altogether.

JC Polyomavirus and Transplantation: Implications for Virus Reactivation after Immunosuppression in Transplant Patients and the Occurrence of PML Disease

The JC polyomavirus (JCPyV/JCV) is a member of the Polyomaviridae family and is ubiquitious in the general population, infecting 50–80% of individuals globally. A primary infection with JCV usally results in an asymptomatic, persistent infection that establishes latency in the renourinary tract. Reactivation from latency via iatrogenic immununosuppression for allograft transplantation may result in organ pathology and a potential life-threatening neuropathological disease in the form of progressive multifocal leukoencephalopathy (PML). Currently, no treatment exists for PML, a rare complication that occurs after transplantation, with an incidence of 1.24 per 1000 persons a year among solid organ transplant patients. PML is also observed in HIV patients who are immununosuppressed and are not receiving antiretroviral therapy, as well as individuals treated with biologics to suppress chronic inflammatory responses due to multiple sclerosis, Crohn’s disease, non-Hodgkin’s lymphoma, rheumatoid arthritis, and other autoimmune-mediated hematological disorders. Here, we describe the proposed mechanisms of JCV reactivation as it relates to iatrogenic immunosuppression for graft survival and the treatment of proinflammatory disease, such as biologics, proposed trafficking of JCV from the renourinary tract, JCV central nervous system dissemination and the pathology of PML in immunosuppressed patients, and potential novel therapeutics for PML disease.

Pharmacovigilance during treatment of multiple sclerosis: early recognition of CNS complications

An increasing number of highly effective disease-modifying therapies for people with multiple sclerosis (MS) have recently gained marketing approval. While the beneficial effects of these drugs in terms of clinical and imaging outcome measures is welcomed, these therapeutics are associated with substance-specific or group-specific adverse events that include severe and fatal complications. These adverse events comprise both infectious and non-infectious complications that can occur within, or outside of the central nervous system (CNS). Awareness and risk assessment strategies thus require interdisciplinary management, and robust clinical and paraclinical surveillance strategies. In this review, we discuss the current role of MRI in safety monitoring during pharmacovigilance of patients treated with (selective) immune suppressive therapies for MS. MRI, particularly brain MRI, has a pivotal role in the early diagnosis of CNS complications that potentially are severely debilitating and may even be lethal. Early recognition of such CNS complications may improve functional outcome and survival, and thus knowledge on MRI features of treatment-associated complications is of paramount importance to MS clinicians, but also of relevance to general neurologists and radiologists.

Natalizumab in Multiple Sclerosis Treatment: From Biological Effects to Immune Monitoring

Multiple sclerosis is a chronic demyelinating disease of the central nervous system (CNS) with an autoimmune component. Among the recent disease-modifying treatments available, Natalizumab, a monoclonal antibody directed against the alpha chain of the VLA-4 integrin (CD49d), is a potent inhibitor of cell migration toward the tissues including CNS. It potently reduces relapses and active brain lesions in the relapsing remitting form of the disease. However, it has also been associated with a severe infectious complication, the progressive multifocal leukoencephalitis (PML). Using the standard protocol with an injection every 4 weeks it has been shown by a close monitoring of the drug that trough levels soon reach a plateau with an almost saturation of the target cell receptor as well as a down modulation of this receptor. In this review, mechanisms of action involved in therapeutic efficacy as well as in PML risk will be discussed. Furthermore the interest of a biological monitoring that may be helpful to rapidly adapt treatment is presented. Indeed, development of anti-NAT antibodies, although sometimes unapparent, can be detected indirectly by normalization of CD49d expression on circulating mononuclear cells and might require to switch to another drug. On the other hand a stable modulation of CD49d expression might be useful to follow the circulating NAT levels and apply an extended interval dose scheme that could contribute to limiting the risk of PML.

Fifty Years of JC Polyomavirus: A Brief Overview and Remaining Questions

In the fifty years since the discovery of JC polyomavirus (JCPyV), the body of research representing our collective knowledge on this virus has grown substantially. As the causative agent of progressive multifocal leukoencephalopathy (PML), an often fatal central nervous system disease, JCPyV remains enigmatic in its ability to live a dual lifestyle. In most individuals, JCPyV reproduces benignly in renal tissues, but in a subset of immunocompromised individuals, JCPyV undergoes rearrangement and begins lytic infection of the central nervous system, subsequently becoming highly debilitating-and in many cases, deadly. Understanding the mechanisms allowing this process to occur is vital to the development of new and more effective diagnosis and treatment options for those at risk of developing PML. Here, we discuss the current state of affairs with regards to JCPyV and PML; first summarizing the history of PML as a disease and then discussing current treatment options and the viral biology of JCPyV as we understand it. We highlight the foundational research published in recent years on PML and JCPyV and attempt to outline which next steps are most necessary to reduce the disease burden of PML in populations at risk.

The Role of the JC Virus in Central Nervous System Tumorigenesis

Cancer is the second leading cause of mortality worldwide. The study of DNA tumor-inducing viruses and their oncoproteins as a causative agent in cancer initiation and tumor progression has greatly enhanced our understanding of cancer cell biology. The initiation of oncogenesis is a complex process. Specific gene mutations cause functional changes in the cell that ultimately result in the inability to regulate cell differentiation and proliferation effectively. The human neurotropic Polyomavirus JC (JCV) belongs to the family Polyomaviridae and it is the causative agent of progressive multifocal leukoencephalopathy (PML), which is a fatal neurodegenerative disease in an immunosuppressed state. Sero-epidemiological studies have indicated JCV infection is prevalent in the population (85%) and that initial infection usually occurs during childhood. The JC virus has small circular, double-stranded DNA that includes coding sequences for viral early and late proteins. Persistence of the virus in the brain and other tissues, as well as its potential to transform cells, has made it a subject of study for its role in brain tumor development. Earlier observation of malignant astrocytes and oligodendrocytes in PML, as well as glioblastoma formation in non-human primates inoculated with JCV, led to the hypothesis that JCV plays a role in central nervous system (CNS) tumorigenesis. Some studies have reported the presence of both JC viral DNA and its proteins in several primary brain tumor specimens. The discovery of new Polyomaviruses such as the Merkel cell Polyomavirus, which is associated with Merkel cell carcinomas in humans, ignited our interest in the role of the JC virus in CNS tumors. The current evidence known about JCV and its effects, which are sufficient to produce tumors in animal models, suggest it can be a causative factor in central nervous system tumorigenesis. However, there is no clear association between JCV presence in CNS and its ability to initiate CNS cancer and tumor formation in humans. In this review, we will discuss the correlation between JCV and tumorigenesis of CNS in animal models, and we will give an overview of the current evidence for the JC virus’s role in brain tumor formation.

Progressive multifocal leukoencephalopathy presenting with acute sensorineural hearing loss in an intestinal transplant recipient

A 20-year-old male presented 3.5 years after intestinal transplantation with rapidly progressive sensorineural hearing loss. Initial brain imaging was consistent with inflammation and/or demyelination. Lumbar puncture was initially non-diagnostic and a broad infectious workup was unrevealing. Three months after presentation, a repeat LP detected JC virus for which tests had not earlier been conducted. He continued to deteriorate despite withdrawal of prior immunosuppression and addition of mirtazapine, maraviroc, and steroids. He died of progressive neurologic decompensation 5 months after his initial presentation. This case highlights progressive multifocal leukoencephalopathy (PML) as a rare complication after solid organ transplantation and acute sensorineural hearing loss as an unusual first presenting symptom of PML. JC virus should be considered in the differential diagnosis of acute sensorineural hearing loss in any immunocompromised patient.

JC Polyomavirus Infection Reveals Delayed Progression of the Infectious Cycle in Normal Human Astrocytes

JC polyomavirus (JCPyV) infects 50 to 80% of the population and is the causative agent of a fatal demyelinating disease of the central nervous system (CNS). JCPyV presents initially as a persistent infection in the kidneys of healthy people, but during immunosuppression, the virus can reactivate and cause progressive multifocal leukoencephalopathy (PML). Within the CNS, JCPyV predominately targets two cell types, oligodendrocytes and astrocytes. Until recently, the role of astrocytes has been masked by the pathology in the myelin-producing oligodendrocytes, which are lytically destroyed by the virus. To better understand how astrocytes are impacted during JCPyV infection, the temporal regulation and infectious cycle of JCPyV were analyzed in primary normal human astrocytes (NHAs). Previous research to define the molecular mechanisms underlying JCPyV infection has mostly relied on the use of cell culture models, such as SVG-A cells (SVGAs), an immortalized, mixed population of glial cells transformed with simian virus 40 (SV40) T antigen. However, SVGAs present several limitations due to their immortalized characteristics, and NHAs represent an innovative approach to study JCPyV infection in vitro Using infectivity assays, quantitative PCR, and immunofluorescence assay approaches, we have further characterized JCPyV infectivity in NHAs. The JCPyV infectious cycle is significantly delayed in NHAs, and the expression of SV40 T antigen alters the cellular environment, which impacts viral infection in immortalized cells. This research establishes a foundation for the use of primary NHAs in future studies and will help unravel the role of astrocytes in PML pathogenesis.IMPORTANCE Animal models are crucial in advancing biomedical research and defining the pathogenesis of human disease. Unfortunately, not all diseases can be easily modeled in a nonhuman host or such models are cost prohibitive to generate, including models for the human-specific virus JC polyomavirus (JCPyV). JCPyV infects most of the population but can cause a rare, fatal disease, progressive multifocal leukoencephalopathy (PML). There have been considerable advancements in understanding the molecular mechanisms of JCPyV infection, but this has mostly been limited to immortalized cell culture models. In contrast, PML pathogenesis research has been greatly hindered because of the lack of an animal model. We have further characterized JCPyV infection in primary human astrocytes to better define the infectious process in a primary cell type. Albeit a cell culture model, primary astrocytes may better recapitulate human disease, are easier to maintain than other primary cells, and are less expensive than using an animal model.

Human BK and JC polyomaviruses: Molecular insights and prevalence in Asia

Polyomaviridae family consists of small circular dsDNA viruses. Out of the 14 human polyomaviruses described so far, BKPyV and JCPyV have been studied extensively since their discovery in 1971. Reportedly, both BKPyV and JCPyV are widely distributed across the globe with the frequency of 80-90 % in different populations. The primary infection of these viruses is usually asymptomatic and latent which is activated as a consequence of immunosuppression. Activated BKPyV and JCPyV viruses lead to the development of BK Virus Associated Nephropathy and Progressive Multifocal Leukoencephalopathy, respectively. Immense progress has been made during the last few decades regarding the molecular understanding of polyomaviruses. Epidemiology of polyomaviruses has also been studied extensively. However, most of the epidemiological studies have focused on European and American populations. Therefore, limited data is available regarding the geographical distribution of these potentially oncogenic viruses in Asian countries. In this article, we have presented a compendium of latest advances in the molecular understanding of polyomaviruses and their pathobiology. We also present a comprehensive review of published literature regarding the epidemiology and prevalence of BKPyV and JCPyV in Asian regions. For this purpose, a thorough search of available online resources was performed. As a result, we retrieved 24 studies for BKPyV and 22 studies for JCPyV, that describe their prevalence in Asia. These studies unanimously report high occurrence of both BKPyV and JCPyV in Asian populations. The available data from these studies was categorized into two groups: on the basis of prevalence (low, medium and high) and disease development (healthy and diseased). Altogether, Korean population hasbeen evidenced to possess highest frequency of BKPyV (66.7 %), while JCPyV was found to be most prevalent in Taiwan (88 %). Due to high and ubiquitous distribution of these viruses, frequent studies are required to develop a better understanding regarding the epidemiology and pathobiology of these viruses in Asia.

The case for BK polyomavirus as a cause of bladder cancer

In 2014, the International Agency for Research on Cancer judged Merkel cell polyomavirus (MCPyV) to be a probable human carcinogen. BK polyomavirus (BKPyV, a distant cousin of MCPyV) was ruled a possible carcinogen. In this review, we argue that it has recently become reasonable to view both of these viruses as known human carcinogens. In particular, several complementary lines of evidence support a causal role for BKPyV in the development of bladder carcinomas affecting organ transplant patients. The expansion of inexpensive deep sequencing has opened new approaches to investigating the important question of whether BKPyV causes urinary tract cancers in the general population.

Regulation of expansion of CD11c+ B cells and anti-viral immunity by epithelial V-like antigen

Prior work demonstrated that epithelial V-like antigen (EVA), a cell surface adhesion molecule, is expressed in B lymphocytes and is necessary for the efficacy of anti-alpha₄ integrin treatment of experimental autoimmune encephalomyelitis (EAE), the mouse model of human multiple sclerosis. EVA deficiency is associated with a severe clinical phenotype of EAE in the presence or absence of treatment. Histological analysis revealed enhanced B cell-mediated autoimmunity and deposition of antibody and complement within the brain and spinal cord. Here our goal was to determine the molecular mechanism of EVA regulation of B lymphocyte function. Analysis of bone marrow from MOG-immunized mice revealed increased expansion of CD11c⁺ B cells in EVA-deficient mice as compared to wild type controls. In vitro studies of mouse bone marrow B lymphocytes revealed enhanced proliferation of the CD11c⁺ population in response to the Tlr7/8 agonist R848. An increase in R848-induced proliferation of CD11c⁺ B cells was also seen in vitro in Daudi cells, a human B cell line, following knockdown of the mpzl2 gene that encodes EVA. These mechanisms were characterized further by global expression analysis of bone marrow from immunized EVA-deficient and wild type control mice. These data revealed increased expression of B cell associated genes and decreased expression of the anti-viral oligoadenylate synthase genes, Oas1 and Oas2, in the knockout condition. In Daudi cells, R848 treatment induced an increase in Oas2 expression in control cells that was not observed in EVA-deficient cells. EVA deficiency also was associated with increased transcription of an Epstein-Barr virus gene during lytic replication. These results suggest EVA expression and signaling prevent expansion of CD11c⁺ B lymphocytes, a cellular phenotype associated with autoimmunity, increase expression of anti-viral oligoadenylate synthase genes, and reduce replication of a DNA virus.

Human Polyomavirus JCPyV and Its Role in Progressive Multifocal Leukoencephalopathy and Oncogenesis

The human neurotropic virus JCPyV, a member of the Polyomaviridiae family, is the opportunistic infectious agent of Progressive Multifocal Leukoencephalopathy (PML), a fatal disease seen in severe immunosuppressive conditions and, during the last decade, in patients undergoing immunotherapy. JCPyV is a ubiquitous pathogen with up to 85% of the adult population word-wide exhibiting antibodies against it. Early experiments demonstrated that direct inoculation of JCPyV into the brain of different species resulted in the development of brain tumors and other neuroectodermal-derived neoplasias. Later, several reports showed the detection of viral sequences in medulloblastomas and glial tumors, as well as expression of the viral protein T-Antigen. Few oncogenic viruses, however, have caused so much controversy regarding their role in the pathogenesis of brain tumors, but the discovery of new Polyomaviruses that cause Merkel cell carcinomas in humans and brain tumors in racoons, in addition to the role of JCPyV in colon cancer and multiple mechanistic studies have shed much needed light on the role of JCPyV in cancer. The pathways affected by the viral protein T-Antigen include cell cycle regulators, like p53 and pRb, and transcription factors that activate pro-proliferative genes, like c-Myc. In addition, infection with JCPyV causes chromosomal damage and T-Antigen inhibits homologous recombination, and activates anti-apoptotic proteins, such as Survivin. Here we review the different aspects of the biology and physiopathology of JCPyV.

Diffuse large B cell lymphoma secondary to JC virus in progressive multifocal leukoencephalopathy

We present the case of a 43-year-old-man with a past medical history of HIV with recently initiated HAART and existing PML that presented with altered mental status. The initial diagnosis was deemed to be PML-IRIS; however, neuroimaging brought into question this diagnosis. Flow cytometry performed from the cerebrospinal fluid revealed diffuse large B cell lymphoma. JC virus may act in an oncogenic role similarly to EBV and predispose to CNS lymphomas. Patients with PML caused by JC virus may develop secondary malignancies.

High-Throughput Characterization of Viral and Cellular Protein Expression Patterns During JC Polyomavirus Infection

JC polyomavirus (JCPyV) is a ubiquitous human pathogen and the causative agent of a fatal demyelinating disease in severely immunocompromised individuals. Due to the lack of successful pharmacological interventions, the study of JCPyV infection strategies in a rapid and highly sensitive manner is critical for the characterization of potential antiviral therapeutics. Conventional methodologies for studying viral infectivity often utilize the detection of viral proteins through immunofluorescence microscopy-based techniques. While these methodologies are well established in the field, they require significant time investments and lack a high-throughput modality. Scanning imager-based detection methods like the In-cell Western (ICW)^TM have been previously utilized to overcome these challenges incurred by traditional microscopy-based infectivity assays. This automated technique provides not only rapid detection of viral infection status, but can also be optimized to detect changes in host-cell protein expression during JCPyV challenge. Compared to traditional manual determinations of infectivity through microscopy-based techniques, the ICW provides an expeditious and robust determination of JCPyV infection. The optimization of the ICW for the detection of viral and cellular proteins during JCPyV infection provides significant time and cost savings by diminishing sample preparation time and increasing resource utilization. While the ICW cannot provide single-cell analysis information and is limited in the detection of quantitation of low-expressing proteins, this assay provides a high-throughput system to study JCPyV, previously unavailable to the field. Thus, the high-throughput nature and dynamic experimental range of the ICW can be applied to the study of JCPyV infection.

JC Polyomavirus Entry by Clathrin-Mediated Endocytosis Is Driven by β-Arrestin

JC polyomavirus (JCPyV) establishes a persistent, lifelong, asymptomatic infection within the kidney of the majority of the human population. Under conditions of severe immunosuppression or immune modulation, JCPyV can reactivate in the central nervous system (CNS) and cause progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease. Initiation of infection is mediated through viral attachment to α2,6-sialic acid-containing lactoseries tetrasaccharide c (LSTc) on the surface of host cells. JCPyV internalization is dependent on serotonin 5-hydroxytryptamine subfamily 2 receptors (5-HT₂Rs), and entry is thought to occur by clathrin-mediated endocytosis (CME). However, the JCPyV entry process and the cellular factors involved in viral internalization remain poorly understood. Treatment of cells with small-molecule chemical inhibitors and RNA interference of 5-HT₂R endocytic machinery, including β-arrestin, clathrin, AP2, and dynamin, significantly reduced JCPyV infection. However, infectivity of the polyomavirus simian virus 40 (SV40) was not affected by CME-specific treatments. Inhibition of clathrin or β-arrestin specifically reduced JCPyV internalization but did not affect viral attachment. Furthermore, mutagenesis of a β-arrestin binding domain (Ala-Ser-Lys) within the intracellular C terminus of 5-HT_2AR severely diminished internalization and infection, suggesting that β-arrestin interactions with 5-HT_2AR are critical for JCPyV infection and entry. These conclusions illuminate key host factors that regulate clathrin-mediated endocytosis of JCPyV, which is necessary for viral internalization and productive infection.IMPORTANCE Viruses usurp cellular factors to invade host cells. Activation and utilization of these proteins upon initiation of viral infection are therefore required for productive infection and resultant viral disease. The majority of healthy individuals are asymptomatically infected by JC polyomavirus (JCPyV), but if the host immune system is compromised, JCPyV can cause progressive multifocal leukoencephalopathy (PML), a rare, fatal, demyelinating disease. Individuals infected with HIV or taking prolonged immunomodulatory therapies have a heightened risk for developing PML. The cellular proteins and pathways utilized by JCPyV to mediate viral entry are poorly understood. Our findings further characterize how JCPyV utilizes the clathrin-mediated endocytosis pathway to invade host cells. We have identified specific components of this pathway that are necessary for the viral entry process and infection. Collectively, the conclusions increase our understanding of JCPyV infection and pathogenesis and may contribute to the future development of novel therapeutic strategies for PML.

Favorable Response to Mirtazapine in John Cunningham Virus-related Gray Matter Lesion in a Patient with Human Immunodeficiency Virus

Mirtazapine has recently emerged as a promising agent for the treatment of progressive multifocal leukoencephalopathy (PML). While there is no Class I evidence for its use, numerous case reports have illustrated mirtazapine’s efficacy. True to its name, PML is known to occur mostly in the white matter of the brain as its causative agent, John Cunningham virus (JC virus), has a predilection for infecting glial cells. The virus replicates vigorously in oligodendrocytes and causes lysis of the glial cell culminating in demyelination. Therefore, gray matter involvement is rare. Mirtazapine’s 5HT2A receptor blocking capacity is presumed to hinder JC virus’ entry into glial cells. We report a case of a patient with human immunodeficiency virus (HIV) with predominantly gray matter lesions from JC virus reactivation. This case is the first reported case of gray matter PML in an Arabic patient who responded favorably to mirtazapine therapy.

JC polyomavirus replication and associated disease in pediatric renal transplantation: an international CERTAIN Registry study

BACKGROUND

JC polyomavirus (JCPyV)-associated nephropathy (JCPyVAN) is a severe, but rare complication in adult renal transplant (RTx) recipients. Related data in pediatric patients are scarce.

METHODS

Based on the CERTAIN Registry, we therefore performed a multi-center, retrospective study on the JCPyV antibody status, prevalence of JCPyV replication, and its associated disease in 139 pediatric RTx recipients (mean age, 8.5 ± 5.3 years). JCPyV DNA in plasma and/or urine was measured by quantitative PCR at a median time of 3.2 (IQR, 0.3-8.1) years post-transplant.

RESULTS

53.2% of patients were JCPyV-seronegative prior to transplantation; younger age was associated with JCPyV seronegativity. 34/139 (24.5%) patients post-transplant showed active JCPyV replication in either urine (22.0%), plasma (13.4%), or both (7.6%). JCPyV viremia occurred significantly (p < 0.001) more often in patients with viruria (34.6%) than in those without (7.6%), but 7/118 (5.9%) had isolated viremia. High-level viruria (> 10⁷ copies/mL) was found in 29.6% of viruric patients. A higher net state of immunosuppression constituted an independent risk factor for JCPyV replication both in urine and plasma (OR 1.2, p < 0.02). Male patients tended to have a higher risk of JCPyV viremia than females (OR 4.3, p = 0.057). There was one male patient (0.7%) with JCPyVAN 7 years post-transplant, which resolved after reduction of immunosuppressive therapy. No patient exhibited progressive multifocal leukoencephalopathy.

CONCLUSIONS

This first multi-center study on JCPyV in pediatric renal transplant recipients shows that JCPyV replication is common (24.5%), with strong immunosuppression being a significant risk factor, but associated nephropathy is rare.

Viral microRNA effects on persistent infection of human lymphoid cells by polyomavirus SV40

BACKGROUND

Polyomaviruses, including simian virus 40 (SV40), display evidence of lymphotropic properties. This study analyzed the nature of SV40-human lymphocyte interactions in established cell lines and in primary lymphocytes. The effects of viral microRNA and the structure of the viral regulatory region on SV40 persistence were examined.

RESULTS

SV40 DNA was maintained in infected B cell and myeloid cell lines during cell growth for at least 28 days. Limiting dilution analysis showed that low amounts of SV40 DNA (~2 copies per cell) were retained over time. Infected B cells remained viable and able to proliferate. Genome copies of the SV40 microRNA-null mutant persisted at higher levels than the DNA of wild-type viruses. Complex viral regulatory regions produced modestly higher DNA levels than simple regulatory regions. Viral large T-antigen protein was detected at low frequency and at low levels in infected B cells. Following infection of primary lymphocytes, SV40 DNA was detected in CD19+ B cells and CD14+ monocytes, but not in CD3+ T cells. Rescue attempts using either lysates of SV40-infected B lymphocytes, coculture of live cells, or infectious center assays all showed that replication-competent SV40 could be recovered on rare occasions. SV40 infections altered the expression of several B cell surface markers, with more pronounced changes following infections with the microRNA-null mutant.

CONCLUSION

These findings indicate that SV40 can establish persistent infections in human B lymphocytes. The cells retain low copy numbers of viral DNA; the infections are nonproductive and noncytolytic but can occasionally produce infectious virus. SV40 microRNA negatively regulates the degree of viral effects on B cells.

SIGNIFICANCE

Lymphocytes may serve as viral reservoirs and may function to disseminate polyomaviruses to different tissues in a host. To our knowledge, this report is the first extensive analysis of viral microRNA effects on SV40 infection of human lymphocytes.

COS-7-based model: methodological approach to study John Cunningham virus replication cycle

John Cunningham virus (JCV) is a human neurotropic polyomavirus whose replication in the Central Nervous System (SNC) induces the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). JCV propagation and PML investigation have been severely hampered by the lack of an animal model and cell culture systems to propagate JCV have been very limited in their availability and robustness. We previously confirmed that JCV CY strain efficiently replicated in COS-7 cells as demonstrated by the progressive increase of viral load by quantitative PCR (Q-PCR) during the time of transfection and that archetypal regulatory structure was maintained, although two characteristic point mutations were detected during the viral cycle. This short report is an important extension of our previous efforts in defining our reliable model culture system able to support a productive JCV infection.

Supernatants collected from transfected cells have been used to infect freshly seeded COS-7 cell line. An infectious viral progeny was obtained as confirmed by Western blot and immunofluorescence assay. During infection, the archetype regulatory region was conserved.

Importantly, in this study we developed an improved culture system to obtain a large scale production of JC virus in order to study the genetic features, the biology and the pathogenic mechanisms of JC virus that induce PML.

T cell deficiencies as a common risk factor for drug associated progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a disease of the central nervous system caused by neuropathogenic prototypes of ubiquitous community-acquired JC virus (JCV). The disease became of particular concern following its association with certain therapies that modulate immune system function without heavy immunosuppression. Due to lack of prophylactic/treatment options and poor outcomes, which often include severe disability or death, PML is a considerable concern for development of new drugs that interfere with immune system functions. In this review of clinical and research findings, we discuss the evidence that deficiencies in CD4⁺ T helper cells, cytotoxic CD8⁺ T cells, and interferon gamma are of crucial importance for development of PML under a variety of circumstances, including those associated with use of various drugs, regardless of differences in their mechanisms of action. These deficiencies apparently enable transformation of the harmless JCV archetype into neuropathogenic prototypes, but the site(s), and the mechanisms, of this transformation are yet to be elucidated. Here we discuss the evidence for brain as one of the sites of this transformation, and propose a model of PML pathogenesis that emphasizes the central role of T cell deficiencies in the two life cycles of the JCV, one non-pathogenic and one neuropathogenic. Finally, we conclude that the development of clinical grade T cell functional tests and more consistent use of already available laboratory tests for T cell subset analysis would greatly aid the effort to more accurately predict and assess the magnitude of PML risk for concerned therapeutic interventions.

Understanding Progressive Multifocal Leukoencephalopathy Risk in Multiple Sclerosis Patients Treated with Immunomodulatory Therapies: A Bird's Eye View

The increased use of newer potent immunomodulatory therapies for multiple sclerosis (MS), including natalizumab, fingolimod, and dimethyl fumarate, has expanded the patient population at risk for developing progressive multifocal leukoencephalopathy (PML). These MS therapies shift the profile of lymphocytes within the central nervous system (CNS) leading to increased anti-inflammatory subsets and decreased immunosurveillance. Similar to MS, PML is a demyelinating disease of the CNS, but it is caused by the JC virus. The manifestation of PML requires the presence of an active, genetically rearranged form of the JC virus within CNS glial cells, coupled with the loss of appropriate JC virus-specific immune responses. The reliability of metrics used to predict risk for PML could be improved if all three components, i.e., viral genetic strain, localization, and host immune function, were taken into account. Advances in our understanding of the critical lymphocyte subpopulation changes induced by these MS therapies and ability to detect viral mutation and reactivation will facilitate efforts to develop these metrics.

Progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a relatively common complication of HIV disease. In this chapter changes to the epidemiology are discussed along with an update in its pathogenesis and treatment. Immune reconstitution inflammatory syndrome is increasingly frequent in PML; accordingly management strategies and prognosis are detailed.

Diagnosis and Treatment of Progressive Multifocal Leukoencephalopathy Associated with Multiple Sclerosis Therapies

Progressive multifocal leukoencephalopathy (PML) is a rare, but serious, complication encountered in patients treated with a select number of disease-modifying therapies (DMTs) utilized in treating multiple sclerosis (MS). PML results from a viral infection in the brain for which the only demonstrated effective therapy is restoring the perturbed immune system-typically achieved in the patient with MS by removing the offending therapeutic agent or, in the case of HIV-associated PML, treatment with highly active antiretroviral therapies. Other therapies for PML remain either ineffective or experimental. Significant work to understand the virus and host interaction has been undertaken, but lack of an animal model for the disorder has significantly hindered progress, especially with respect to development of treatments. Strategies to limit risk of PML with natalizumab, a drug that carries a uniquely high risk for the development of the disorder, have been developed. Identifying factors such as positive JC virus antibody status that increase PML risk, at least in theory, should decrease the incidence rate of the disease. Whether other risk factors for PML can be identified and validated or unique strategies should be employed in association with other DMTs that predispose to PML and whether this has a salutary effect on outcome remains to be demonstrated. Identifying PML early, then promptly eliminating drug in the case of natalizumab-associated PML has demonstrated better outcomes, but the complication of PML continues to carry significant morbidity and mortality. While the scientific community has yet to identify targeted therapy with proven efficacy against JCV or PML there are several candidates being studied.

Efficient propagation of archetype JC polyomavirus in COS-7 cells: evaluation of rearrangements within the NCCR structural organization after transfection

John Cunningham virus (JCPyV) is an ubiquitous human pathogen that causes disease in immunocompromised patients. The JCPyV genome is composed of an early region and a late region, which are physically separated by the non-coding control region (NCCR). The DNA sequence of the NCCR distinguishes two forms of JCPyV, the designated archetype and the prototype, which resulted from a rearrangement of the archetype sequence. To date, the cell culture systems for propagating JCPyV archetype have been very limited in their availability and robustness. Prior to this study, it was demonstrated that JCPyV archetype DNA replicates in COS-7 simian kidney cells expressing SV40 TAg and COS-7 cells expressing HIV-1 Tat. Based on these observations, the present study was conducted to reproduce an in vitro model in COS-7 cells transfected with the JCPyV archetype strain in order to study JCPyV DNA replication and analyze NCCR rearrangements during the viral life cycle. The efficiency of JCPyV replication was evaluated by quantitative PCR (Q-PCR) and by hemagglutination (HA) assay after transfection. In parallel, sequence analysis of JCPyV NCCR was performed. JCPyV efficiently replicated in kidney-derived COS-7 cells, as demonstrated by a progressive increase in viral load and virion particle production after transfection. The archetypal structure of NCCR was maintained during the viral cycle, but two characteristic point mutations were detected 28 days after transfection. This model is a useful tool for analyzing NCCR rearrangements during in vitro replication in cells that are sites of viral persistence, such as tubular epithelial cells of the kidney.

The biology of JC polyomavirus

JC polyomavirus (JCPyV) is the causative agent of a fatal central nervous system demyelinating disease known as progressive multifocal leukoencephalopathy (PML). PML occurs in people with underlying immunodeficiency or in individuals being treated with potent immunomodulatory therapies. JCPyV is a DNA tumor virus with a double-stranded DNA genome and encodes a well-studied oncogene, large T antigen. Its host range is highly restricted to humans and only a few cell types support lytic infection in vivo or in vitro. Its oncogenic potential in humans has not been firmly established and the international committee on oncogenic viruses lists JCPyV as possibly carcinogenic. Significant progress has been made in understanding the biology of JCPyV and here we present an overview of the field and discuss some important questions that remain unanswered.

The Enigmatic Role of Viruses in Multiple Sclerosis: Molecular Mimicry or Disturbed Immune Surveillance?

Multiple sclerosis (MS) is a T cell driven autoimmune disease of the central nervous system (CNS). Despite its association with Epstein-Barr Virus (EBV), how viral infections promote MS remains unclear. However, there is increasing evidence that the CNS is continuously surveyed by virus-specific T cells, which protect against reactivating neurotropic viruses. Here, we discuss how viral infections could lead to the breakdown of self-tolerance in genetically predisposed individuals, and how the reactivations of viruses in the CNS could induce the recruitment of both autoaggressive and virus-specific T cell subsets, causing relapses and progressive disability. A disturbed immune surveillance in MS would explain several experimental findings, and has important implications for prognosis and therapy.

A huge body of evidence suggests that viral infections promote MS; however, no single causal virus has been identified. Multiple viruses could promote MS via bystander effects.

Molecular mimicry is an established pathogenic mechanism in selected autoimmune diseases. It is also well documented in MS, but its contribution to MS pathogenesis is still unclear.

Bystander activation upon viral infection could be involved in the generation of the autoreactive and potentially encephalitogenic T helper (Th)-1/17 central memory (Th1/17_CM) cells found in the circulation of patients with MS.

Autoreactive Th1/17_CM cells could expand at the cost of antiviral Th1_CM cells in patients with MS, in particular in those undergoing natalizumab therapy, because these cells are expected to compete for the same homeostatic niche.

Autoreactive Th1/17 cells and antiviral Th1 cells are recruited to the CSF of patients with MS following attacks, suggesting that viral reactivations in the CNS induce the recruitment of pathogenic Th1/17 cells. Autoreactive Th1/17 cells in the CNS might also induce de novo viral reactivations in a circuit of self-induced inflammation.

T cell responses in the central nervous system

T cells are required for immune surveillance of the central nervous system (CNS); however, they can also induce severe immunopathology in the context of both viral infections and autoimmunity. The mechanisms that are involved in the priming and recruitment of T cells to the CNS are only partially understood, but there has been renewed interest in this topic since the 'rediscovery' of lymphatic drainage from the CNS. Moreover, tissue-resident memory T cells have been detected in the CNS and are increasingly recognized as an autonomous line of host defence. In this Review, we highlight the main mechanisms that are involved in the priming and CNS recruitment of CD4⁺ T cells, CD8⁺ T cells and regulatory T cells. We also consider the plasticity of T cell responses in the CNS, with a focus on viral infection and autoimmunity.

Antimicrobial Nanostructures for Neurodegenerative Infections

Nanostructures have been widely involved in changes in the drug delivery system. Nanoparticles have unique physicochemical properties, e.g., ultrasmall size, large surface area, and the ability to target specific actions. Various nanomaterials, like Ag, ZnO, Cu/CuO, and Al₂O₃, have antimicrobial activity. Basically, six mechanisms are involved in the production of antimicrobial activity, i.e., (1) destruction of the peptidoglycan layer, (2) release of toxic metal ions, (3) alteration of cellular pH via proton efflux pumps, (4) generation of reactive oxygen species, (5) damage of nuclear materials, and (6) loss of ATP production. Nanomedicine contributes to various pharmaceutical applications, like diagnosis and treatment of various ailments including microbial diseases. Furthermore, nanostructured antimicrobial agents are also involved in the treatment of the neuroinfections associated with neurodegenerative disorders. This chapter focuses on the nanostructure and nanomedicine of antimicrobial agents and their prospects for the possible management of infections associated with neurodegenerative disorders.

JC polyomavirus expression and bell-shaped regulation of its SF2/ASF suppressor during the follow-up of multiple sclerosis patients treated with natalizumab

Natalizumab is effective against multiple sclerosis (MS), but is associated with progressive multifocal leukoencephalopathy (PML), fatal disease caused by the JCV polyomavirus. The SF2/ASF (splicing factor2/alternative splicing factor) inhibits JCV in glial cells. We wondered about SF2/ASF modulation in the blood of natalizumab-treated patients and if this could influence JCV reactivation. Therefore, we performed a longitudinal study of MS patients under natalizumab, in comparison to patients under fingolimod and to healthy blood donors. Blood samples were collected at time intervals. The expression of SF2/ASF and the presence and expression of JCV in PBMC were analyzed. A bell-shaped regulation of SF2/ASF was observed in patients treated with natalizumab, increased in the first year of therapy, and reduced in the second one, while slightly changed, if any, in patients under fingolimod. Notably, SF2/ASF was up-regulated, during the first year, only in JCV DNA-positive patients, or with high anti-JCV antibody response; the expression of the JCV T-Ag protein in circulating B cells was inversely related to SF2/ASF protein expression. The SF2/ASF reduction, parallel to JCV activation, during the second year of therapy with natalizumab, but not with fingolimod, may help explain the increased risk of PML after the second year of treatment with natalizumab, but not with fingolimod. We propose that SF2/ASF has a protective role against JCV reactivation in MS patients. This study suggests new markers of disease behavior and, possibly, help in re-evaluations of therapy protocols.

JC polyomavirus viremia and progressive multifocal leukoencephalopathy in human leukocyte antigen-sensitized kidney transplant recipients desensitized with intravenous immunoglobulin and rituximab

BACKGROUND

Desensitization (DES) with intravenous immunoglobulin (IVIG) + rituximab is effective, safe, and increases the transplantation rate in human leukocyte antigen-sensitized patients. However, reports of progressive multifocal leukoencephalopathy (PML) caused by JC polyomavirus (JCPyV) in autoimmune patients treated with rituximab is concerning. Here, we report on the JCPyV viremia and PML status in kidney transplant patients with/without DES (non-DES).

METHODS

In total 1195 and 699 DNA samples from plasma in 117 DES (78% lymphocyte-depleting [LyD] induction) and 100 non-DES patients (45% LyD), respectively, were submitted for JCPyV-polymerase chain reaction. Results were compared in both groups.

RESULTS

No patients in either DES or non-DES developed PML or presented with any neurological symptoms. The JCPyV viremia rate was similar in DES and non-DES patients (3/117 vs. 9/100, P = 0.07). The JCPyV levels were low (median peak levels, 1025 copies/mL) and JCPyV viremia was observed only once during the study period in most patients. All 3 DES patients with JCPyV(+) received 1 dose rituximab and no DES patients with >1 dose rituximab showed JCPyV(+). All 3 JCPyV(+) DES patients received LyD induction, while only 2 of 9 JCPyV(+) non-DES patients did so, and the remaining 7 received non-LyD or no induction. JCPyV in leukocyte was mostly negative in DES and non-DES patients. Immunosuppression in patients with or without JCPyV(+) was similar. BK polyomavirus viremia was observed more commonly in patients with JCPyV(+) than in those without (P < 0.02).

CONCLUSIONS

Patients with IVIG + rituximab DES followed by transplantation with LyD induction and additional rituximab rarely show JCPyV viremia and appear at low risk for PML.