Human fetal Schwann cells support JC virus multiplication

Polyomaviruses

Over the last 10 years, the number of identified polyomaviruses has grown to more than 35 subtypes, including 13 in humans. The polyomaviruses have similar genetic makeup, including genes that encode viral capsid proteins VP1, 2, and 3 and large and small T region proteins. The T proteins play a role in viral replication and have been implicated in viral chromosomal integration and possible dysregulation of growth factor genes. In humans, the Merkel cell polyomavirus has been shown to be highly associated with integration and the development of Merkel cell cancers. The first two human polyomaviruses discovered, BKPyV and JCPyV, are the causative agents for transplant-related kidney disease, BK commonly and JC rarely. JC has also been strongly associated with the development of progressive multifocal leukoencephalopathy (PML), a rare but serious infection in untreated HIV-1-infected individuals and in other immunosuppressed patients including those treated with monoclonal antibody therapies for autoimmune diseases systemic lupus erythematosus, rheumatoid arthritis, or multiple sclerosis. The trichodysplasia spinulosa-associated polyomavirus (TSAPyV) may be the causative agent of the rare skin disease trichodysplasia spinulosa. The remaining nine polyomaviruses have not been strongly associated with clinical disease to date. Antiviral therapies for these infections are under development. Antibodies specific for each of the 13 human polyomaviruses have been identified in a high percentage of normal individuals, indicating a high rate of exposure to each of the polyomaviruses in the human population. PCR methods are now available for detection of these viruses in a variety of clinical samples.

The role of primary infection of Schwann cells in the aetiology of infective inflammatory neuropathies

Numerous different pathogens are responsible for infective peripheral neuropathies and this is generally the result of the indirect effects of pathogen infection, namely anti pathogen antibodies cross reacting with epitopes on peripheral nerve, auto reactive T cells attacking myelin, circulating immune complexes and complement fixation. Primary infection of Schwann cells (SC) associated with peripheral nerve inflammation is rare requiring pathogens to cross the Blood Peripheral Nerve Barrier (BPNB) evade anti-pathogen innate immune pathways and invade the SC. Spirochetes Borrelia bourgdorferi and Trepomema pallidum are highly invasive, express surface lipo proteins, but despite this SC are rarely infected. However, Trypanosoma cruzi (Chaga's disease) and Mycobacterium leprae. Leprosy are two important causes of peripheral nerve infection and both demonstrate primary infection of SC. This is due to two novel strategies; T. cruzi express a trans-silalidase that mimics host neurotrophic factors and infects SC via tyrosine kinase receptors. M. leprae demonstrates multi receptor SC tropism and subsequent infection promotes nuclear reprogramming and dedifferentiation of host SC into progenitor stem like cells (pSLC) that are vulnerable to M. leprae infection. These two novel pathogen evasion strategies, involving stem cells and receptor mimicry, provide potential therapeutic targets relevant to the prevention of peripheral nerve inflammation by inhibiting primary SC infection.

The human JC polyomavirus (JCPyV): virological background and clinical implications

JC polyomavirus (JCPyV) was the first of now 12 PyVs detected in humans, when in 1964, PyV particles were revealed by electron microscopy in progressive multifocal leukoencephalopathy (PML) tissues. JCPyV infection is common in 35-70% of the general population, and the virus thereafter persists in the renourinary tract. One third of healthy adults asymptomatically shed JCPyV at approximately 50,000 copies/mL urine. PML is rare having an incidence of <0.3 per 100,000 person years in the general population. This increased to 2.4 per 1000 person years in HIV-AIDS patients without combination antiretroviral therapy (cART). Recently, PML emerged in multiple sclerosis patients treated with natalizumab to 2.13 cases per 1000 patients. Natalizumab blocks α4-integrin-dependent lymphocyte homing to the brain suggesting that not the overall cellular immunodeficiency but local failure of brain immune surveillance is a pivotal factor for PML. Recovering JCPyV-specific immune control, e.g., by starting cART or discontinuing natalizumab, significantly improves PML survival, but is challenged by the immune reconstitution inflammatory syndrome. Important steps of PML pathogenesis are undefined, and antiviral therapies are lacking. New clues might come from molecular and functional profiling of JCPyV and PML pathology and comparison with other replicative pathologies such as granule cell neuronopathy and (meningo-)encephalitis, and non-replicative JCPyV pathology possibly contributing to some malignancies. Given the increasing number of immunologically vulnerable patients, a critical reappraisal of JCPyV infection, replication and disease seems warranted.

Molecular biology, epidemiology, and pathogenesis of progressive multifocal leukoencephalopathy, the JC virus-induced demyelinating disease of the human brain

Progressive multifocal leukoencephalopathy (PML) is a debilitating and frequently fatal central nervous system (CNS) demyelinating disease caused by JC virus (JCV), for which there is currently no effective treatment. Lytic infection of oligodendrocytes in the brain leads to their eventual destruction and progressive demyelination, resulting in multiple foci of lesions in the white matter of the brain. Before the mid-1980s, PML was a relatively rare disease, reported to occur primarily in those with underlying neoplastic conditions affecting immune function and, more rarely, in allograft recipients receiving immunosuppressive drugs. However, with the onset of the AIDS pandemic, the incidence of PML has increased dramatically. Approximately 3 to 5% of HIV-infected individuals will develop PML, which is classified as an AIDS-defining illness. In addition, the recent advent of humanized monoclonal antibody therapy for the treatment of autoimmune inflammatory diseases such as multiple sclerosis (MS) and Crohn's disease has also led to an increased risk of PML as a side effect of immunotherapy. Thus, the study of JCV and the elucidation of the underlying causes of PML are important and active areas of research that may lead to new insights into immune function and host antiviral defense, as well as to potential new therapies.

The influence of Epstein-Barr virus reactivation in patients with Graves' disease

In Graves' disease, the IgG class autoantibody against thyrotropin receptor (TRAb) is produced excessively and induces hyperthyroidism. Epstein-Barr virus (EBV) is one of the human herpesviruses that persists for life, mainly in B lymphocytes, and is occasionally reactivated. Therefore, EBV may affect the antibody production of B lymphocytes that would normally produce TRAb. The purpose of the present study was to evaluate the association of EBV reactivation with the etiology of Graves' disease. Serum levels of EBV antibodies and IgE were determined by ELISA. TRAb levels were determined by radioreceptor assay. We performed in-situ hybridization (ISH) of EBV-encoded small RNA (EBER)1 on the thyroid tissue of one of our patients. In Graves' disease patients with TRAb levels ≥ 10%, EA antibody levels, which indicate EBV reactivation, were moderately but significantly correlated with the levels of TRAb, and weakly but significantly correlated with IgE. EBER1-ISH revealed that one of our patients had EBV-infected lymphocytes infiltrating the thyroid gland. EBV reactivation may stimulate antibody-producing B lymphocytes predisposed to make TRAb, and this may contribute to or exacerbate the disease.

Hexadecyloxypropyl-cidofovir (CMX001) suppresses JC virus replication in human fetal brain SVG cell cultures

JC virus (JCV) is a polyomavirus that infects human oligodendrocytes, leading to development of progressive multifocal leukoencephalopathy (PML), an often fatal demyelinating disease occurring in immunocompromised individuals. Currently there are no effective therapies for the treatment of PML that result in clearance of JCV from the brain. Cidofovir (CDV) is an acyclic nucleoside phosphonate that inhibits DNA polymerases and has been used for the treatment of PML. However, CDV demonstrated little efficacy as a treatment for PML and causes substantial side effects to patients. To improve efficacy and reduce the toxicity of CDV, a lipid-ester derivative, CMX001, was generated by Chimerix and is currently in multicenter phase II clinical trials for the prevention or control of cytomegalovirus infection in hematopoietic stem cell transplant recipients and of BK virus in the urine of stem cell or renal allograft recipients. CMX001 caused minimal cytotoxic effects in human fetal brain SVG cells when used at concentrations between 0.01 μM and 0.1 μM. CMX001 resulted in a dose-dependent decrease in the number of JCV-infected cells during initial infection and nearly eliminated JCV-infected cells during an established infection. In addition, CMX001 treatment resulted in a 60% reduction in JCV DNA copy number during initial infection, which suggests that suppression of JCV infection by CMX001 is likely due to inhibition of virus DNA replication. This study demonstrates that CMX001 suppresses JCV infection at concentrations that have limited toxicity to human brain cells, indicating its potential use to limit JCV replication in infected patients.

Generation and characterization of JCV permissive hybrid cell lines

JC virus (JCV) is a human neurotropic polyomavirus whose replication in the central nervous system induces the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). JCV particles have been detected primarily in oligodendrocytes and astrocytes of the brains of patients with PML and in the laboratory its propagation is limited to primary cultures of human fetal glial cells. In this short communication, the development of a new cell culture system is described through the fusion of primary human fetal astrocytes with the human glioblastoma cell line, U-87MG. The new hybrid cell line obtained from this fusion has the capacity to support efficiently expression of JCV and replication of viral DNA in vitro up to 16 passages. This cell line can serve as a reliable culture system to study the biology of JCV host-cell interaction, determine the mechanisms involved in cell type specific replication of JCV, and provide a convenient cell culture system for high throughput screening of anti-viral agents.

SV40 vectors carrying minimal sequence of viral origin with exchangeable capsids

Polyomaviral vectors are generated by transfecting 293T cells with three sets of DNAs: DNA for the expression of simian virus 40 (SV40) T antigen; DNA for the expression of SV40 capsid proteins, and vector DNA harboring a reporter gene expression cassette carrying a SV40 origin. The vector DNA harbors a minimal sequence originating from SV40, and thus can carry a longer transgene. Moreover, the viable recombinants are not detectable in the vector preparation, and the vectors can transduce the DNA with efficiency similar to that of virions. Vector particles bearing capsid proteins of BK virus, JC virus, and B-lymphotropic papovavirus instead of SV40 were prepared, and they exhibited differential efficiency of gene transduction to the target cells. This method can be used to develop a surrogate system to study the functions of capsid proteins of polyomaviruses and to generate a set of polyomaviral vectors targeted at specific cell types.

Polyomaviruses and human diseases

Polyomaviruses are small, nonenveloped DNA viruses, which are widespread in nature. In immunocompetent hosts, the viruses remain latent after primary infection. With few exceptions, illnesses associated with these viruses occur in times of immune compromise, especially in conditions that bring about T cell deficiency. The human polyomaviruses BKV and JCV are known to cause, respectively, hemorrhagic cystitis in recipients of bone marrow transplantation and progressive multifocal leukoencephalopathy in immunocompromised patients, for example, by HIV infection. Recently, transplant nephropathy due to BKV infection has been increasingly recognized as the cause for renal allograft failure. Quantitation of polyomavirus DNA in the blood, cerebrospinal fluid, and urine, identification of virus laden "decoy cells" in urine, and histopathologic demonstration of viral inclusions in the brain parenchyma and renal tubules are the applicable diagnostic methods. Genomic sequences of polyomaviruses have been reported to be associated with various neoplastic disorders and autoimmune conditions. While various antiviral agents have been tried to treat polyomavirus-related illnesses, current management aims at the modification and/or improvement in the hosts' immune status. In this chapter, we provide an overview of polyomaviruses and briefly introduce its association with human diseases, which will be covered extensively in other chapters by experts in the field.

JC Virus Can Infect Human Immune and Nervous System Progenitor Cells

Recent advances in stem cell biology have called attention to the role these cells may play in the pathogenesis of systemic and nervous system diseases. Although not capable of indefinite self renewal and pluripotentiality as stem cells are, progenitor cells can give rise to cells of different lineages. It is infection of these differentiated cells that has traditionally been associated with the pathology and symptoms of viral-induced disease. However, neural progenitor cells have been shown, in vitro, to be susceptible to infection by neurotropic viruses such as the human polyomavirus, JCV, and the lentivirus, HIV-1. These progenitor cells, which exist during development as well as in the fully developed adult brain, could therefore be involved in neuropathogenesis. Morever, JCV can also infect progenitor cells of the hematopoietic system, derivatives of which have been implicated in the trafficking of virus from the periphery to the brain. Interestingly, susceptibility to and molecular regulation of JCV infection in hematopoietic cells closely parallels what has been observed in glial cells. The biological interaction between the immune and nervous systems that exists in the dissemination of virus from periphery to nervous system and the susceptibility of both systems to JCV infection provide potential for hematopoietic and neural progenitor cell involvement in JCV pathogenesis.

Human neurotropic polyomavirus, JCV, and its role in carcinogenesis

A number of recent studies have reported the detection of the ubiquitous human polyomavirus, JC virus (JCV), in samples derived from several types of neural as well as non-neural human tumors. The human neurotropic JCV was first identified as the etiologic agent of the fatal demyelinating disease, progressive multifocal leukoencephalopathy, which usually occurs in individuals with defects in cell-mediated immunity, including AIDS. However, upon mounting evidence of the oncogenic potential of the viral regulatory protein, T-antigen, and JCV's oncogenecity in a broad range of animal models, studies were initiated to determine its potential involvement in human carcinogenesis. Initially, the most frequently observed tumors in rodent models, including medulloblastoma, astrocytoma, glioblastoma, and other neural-origin tumors were analysed. These studies were followed by analysis of non-neural tumors such as colorectal carcinomas. In a subset of each tumor type examined, JC viral genomic DNA sequences could be detected by PCR and confirmed by Southern blot hybridization or direct sequencing. In a smaller subset of the tumors, the expression of T-antigen was observed by immunohistochemical analysis. Owing to the established functions of T-antigen including its ability to interact with tumor suppressor proteins such as Rb and p53, and its ability to influence chromosomal stability, potential mechanisms of JCV T-antigen-mediated cellular dysregulation are discussed. Further, as increasing evidence suggests that T-antigen is not required for maintenance of a transformed phenotype, a hit-and-run model for T-antigen-induced transformation is proposed.

Comparison of cell culture-grown JC virus (primary human fetal glial cells and the JCI cell line) and recombinant JCV VP1 as antigen for the detection of anti-JCV antibody by haemagglutination inhibition

JC virus (JCV) is the causative agent of the demyelinating disease progressive multifocal leucoencephalopathy (PML), which can be diagnosed by detection in the cerebrospinal fluid (CSF) of both JCV DNA and intrathecally-produced anti-JCV antibody. However, the restricted in-vitro species and cell tropism shown by JCV has made antigen production difficult and limited serological investigations both in PML diagnosis and for JCV epidemiology. In this study antigen prepared as a crude cell lysate of JCV-infected primary human fetal glial (PHFG) cells was compared in a haemagglutination inhibition (HI) assay with antigen produced from the JCV carrier cell line, JCI, and yeast-expressed JCV VP1. Forty-two sera were tested with each antigen and there was a high level of correlation between the assays: 96.5% between the HI assays with PHFG and JCI antigens and 98.1% between the HI assays with PHFG and recombinant VP1 (rVP1) antigens. The JCI antigen gave HI titres 19% lower than the PHFG antigen (P=0.022). Titres with the rVP1 antigen were 2% higher than with the PHFG antigen (P=0.83). When serum/CSF pairs from 11 PML patients were tested, the antibody index calculated in each case confirmed the production of intrathecal anti-JCV antibody. Antibody testing for JCV is no longer reliant on PHFG cells and JCV serological tests should be available more widely.

Transcriptional control in myelinating glia: flavors and spices

Transcriptional control in myelinating glia is often described in terms of a handful of trans-acting proteins with preferential expression in these cells. An equally valid approach is the identification of cis-acting elements in genes, which are specifically transcribed in myelinating glia. Regulatory regions of several myelin genes have been analyzed in transgenic animals, transient transfections and in vitro. In some cases, these studies have identified regions responsible for glial expression within the promoters or immediate upstream regions. Other myelin genes possess promoters, which simply secure basal levels of transcription, but do not contain glia-specific cis-acting elements. Promoters of myelin genes also differ strongly in other respects. They either contain a TATA-box or are TATA-less and GC-rich. They exhibit multiple transcription initiation sites or a single strong one. Binding sites for general transcription factors, such as NF-I, Sp1, and CAAT-box binding proteins, and for downstream effectors of major signaling pathways are found in them in abundance. In agreement, members of the AP-1, CREB, STAT, and NF-kappaB families are well-described components of the transcription machinery in myelinating glia. Together with several members of the nuclear receptor family, they are an intrinsic part of the transcriptional control in myelinating glia.

Infection of glial cells by the human polyomavirus JC is mediated by an N-linked glycoprotein containing terminal alpha(2-6)-linked sialic acids

The human JC polyomavirus (JCV) is the etiologic agent of the fatal central nervous system (CNS) demyelinating disease progressive multifocal leukoencephalopathy (PML). PML typically occurs in immunosuppressed patients and is the direct result of JCV infection of oligodendrocytes. The initial event in infection of cells by JCV is attachment of the virus to receptors present on the surface of a susceptible cell. Our laboratory has been studying this critical event in the life cycle of JCV, and we have found that JCV binds to a limited number of cell surface receptors on human glial cells that are not shared by the related polyomavirus simian virus 40 (C. K. Liu, A. P. Hope, and W. J. Atwood, J. Neurovirol. 4:49-58, 1998). To further characterize specific JCV receptors on human glial cells, we tested specific neuraminidases, proteases, and phospholipases for the ability to inhibit JCV binding to and infection of glial cells. Several of the enzymes tested were capable of inhibiting virus binding to cells, but only neuraminidase was capable of inhibiting infection. The ability of neuraminidase to inhibit infection correlated with its ability to remove both alpha(2-3)- and alpha(2-6)-linked sialic acids from glial cells. A recombinant neuraminidase that specifically removes the alpha(2-3) linkage of sialic acid had no effect on virus binding or infection. A competition assay between virus and sialic acid-specific lectins that recognize either the alpha(2-3) or the alpha(2-6) linkage revealed that JCV preferentially interacts with alpha(2-6)-linked sialic acids on glial cells. Treatment of glial cells with tunicamycin, but not with benzyl N-acetyl-alpha-D-galactosaminide, inhibited infection by JCV, indicating that the sialylated JCV receptor is an N-linked glycoprotein. As sialic acid containing glycoproteins play a fundamental role in mediating many virus-cell and cell-cell recognition processes, it will be of interest to determine what role these receptors play in the pathogenesis of PML.

Propagation of JC virus in human neuroblastoma cell line IMR-32

JC virus (JCV), the causative agent of a human demyelinating disease, progressive multifocal leukoencephalopathy, has a very narrow host range. Cells permissive for infection by JCV have been essentially limited to primary human fetal glial cells, which are difficult to obtain and maintain. In pilot studies, it was found that JCV can multiply in an established cell line of human neuroblastoma. JCV strains Mad-1 and Tokyo-1 were inoculated, respectively, into two cell lines, IMR-32 (neuroblastoma) and A-172 (glioblastoma). Viral infection with cytopathic effect was observed only in IMR-32 cells, and the most efficient viral proliferation was obtained in cells cultured in medium containing 2% fetal calf serum (FCS). Both Mad-1 and Tokyo-1 strains propagated well, with the former being more efficient than the latter. Viral replication was confirmed by immunofluorescence, electron microscopy, and a hemagglutination assay. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and Western blot analysis of the purified virus revealed the characteristic JCV protein profile. Thus, IMR-32 cells have been found to be permissive for JCV, which should provide a useful system for further studies of virus proliferation and viral tissue tropism.

Regulation of JC virus by the POU-domain transcription factor Tst-1: implications for progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy results from an opportunistic infection of myelin-producing oligodendrocytes by the glia-specific human papovavirus JC. In this report, evidence is presented that the glial transcription factor Tst-1, a member of the POU-domain family, stimulates transcription of both early and late viral genes. Stimulation was dependent on site-specific binding of Tst-1 to the JC viral regulatory region and on the presence of an intact amino-terminal transactivation domain within Tst-1. Because of its ability to increase the expression of viral large tumor antigen, Tst-1 stimulated viral DNA replication, without participating directly in the replication event. Our results suggest that Tst-1 is one of the determining factors in the glia specificity of JC virus.

JC virus and simian virus 40 enhancers and transforming proteins: role in determining tissue specificity and pathogenicity in transgenic mice

When introduced into the germ line of mice, the simian virus 40 (SV40) T antigen under the control of its own transcriptional enhancer and promoter selectively induced tumors in the choroid plexus as well as thymic hyperplasia and kidney pathology. In contrast, the JC virus (JCV) T antigen under the control of its own regulatory sequences induced hypomyelination of the central nervous system and tumors of neural origin. Since SV40 and JCV have extensive sequence homology, except for their transcriptional control regions, these observations suggest but do not prove that, although the diseases induced by the two viruses, are consequences of the transforming gene, they are determined predominantly by the respective viral enhancers and promoters. To test this hypothesis, the regulatory regions of the two viruses were exchanged, and transgenic mice were derived with either chimeric construct. Like wild-type JCV, the construct containing the SV40 T antigen under the control of the JCV regulatory region induced hypomyelination of the central nervous system and neural tumors. Surprisingly, mice with this construct also developed choroid plexus carcinomas. Like the wild-type SV40 transgenic mice, mice with the JCV T antigen under the control of the SV40 enhancer and promoter developed choroid plexus tumors and renal pathology. Unexpectedly, they also had hyperplasia of the thyroid follicular cells. These findings not only provide direct evidence for the specificity of the respective viral regulatory region but also, more importantly, show that the transforming genes play a critical role in determining viral pathogenesis.

Pathogenesis and molecular biology of progressive multifocal leukoencephalopathy, the JC virus-induced demyelinating disease of the human brain

Studies of the pathogenesis and molecular biology of JC virus infection over the last two decades have significantly changed our understanding of progressive multifocal leukoencephalopathy, which can be described as a subacute viral infection of neuroglial cells that probably follows reactivation of latent infection rather than being the consequence of prolonged JC virus replication in the brain. There is now sufficient evidence to suggest that JC virus latency occurs in kidney and B cells. However, JC virus isolates from brain or kidney differ in the regulatory regions of their viral genomes which are controlled by host cell factors for viral gene expression and replication. DNA sequences of noncoding regions of the viral genome display a certain heterogeneity among isolates from brain and kidney. These data suggest that an archetypal strain of JC virus exists whose sequence is altered during replication in different cell types. The JC virus regulatory region likely plays a significant role in establishing viral latency and must be acted upon for reactivation of the virus. A developing hypothesis is that reactivation takes place from latently infected B lymphocytes that are activated as a result of immune suppression. JC virus enters the brain in the activated B cell. Evidence for this mechanism is the detection of JC virus DNA in peripheral blood lymphocytes and infected B cells in the brains of patients with progressive multifocal leukoencephalopathy. Once virus enters the brain, astrocytes as well as oligodendrocytes support JC virus multiplication. Therefore, JC virus infection of neuroglial cells may impair other neuroglial functions besides the production and maintenance of myelin. Consequently our increased understanding of the pathogenesis of progressive multifocal leukoencephalopathy suggests new ways to intervene in JC virus infection with immunomodulation therapies. Perhaps along with trials of nucleoside analogs or interferon administration, this fatal disease, for which no consensus of antiviral therapy exists, may yield to innovative treatment protocols.