JC virus: Current concepts and controversies in the molecular virology and pathogenesis of progressive multifocal leucoencephalopathy

Neuroimaging of Natalizumab Complications in Multiple Sclerosis: PML and Other Associated Entities

Natalizumab (Tysabri) is a monoclonal antibody (α4 integrin antagonist) approved for treatment of multiple sclerosis, both for patients who fail therapy with other disease modifying agents and for patients with aggressive disease. Natalizumab is highly effective, resulting in significant decreases in rates of both relapse and disability accumulation, as well as marked decrease in MRI evidence of disease activity. As such, utilization of natalizumab is increasing, and the presentation of its associated complications is increasing accordingly. This review focuses on the clinical and neuroimaging features of the major complications associated with natalizumab therapy, focusing on the rare but devastating progressive multifocal leukoencephalopathy (PML). Associated entities including PML associated immune reconstitution inflammatory syndrome (PML-IRIS) and the emerging phenomenon of rebound of MS disease activity after natalizumab discontinuation are also discussed. Early recognition of neuroimaging features associated with these processes is critical in order to facilitate prompt diagnosis, treatment, and/or modification of therapies to improve patient outcomes.

Progressive multifocal leukoencephalopathy in an AIDS patient

Progressive multifocal leukoencephalopathy (PML) is a demyelinating brain disease caused by Jamestown Canyon virus (JCV). This disease is an important cause of morbidity and mortality in acquired immunodeficiency syndrome (AIDS) patients. We report a 34-year-old man infected with HIV-1 who presented with frequent general tonic clonic seizure and left side weakness for 2 months. Clinical features and magnetic resonance imaging (MRI) findings with hyperintensity on T2-weighted imaging and low density on T2 fluid attenuated inversion recovery involving multiple white matter were compatible with PML. He died of sepsis 2 months after diagnosis. Autopsy demonstrated progressive multifocal leukoencephalopathy according to characteristic histopathologic picture with multifocal demyelination, bizarre astrocytes formation and basophilic intranuclear inclusion bodies in the oligodendrocytes. JCV genome was demonstrated in the nucleus of oligodendrocytes using in situ hybridization. In conclusion, in AIDS patients with neurologic signs and typical MRI findings who present with multifocal demyelination lesions, PML should be diagnosed clinically.

Derivation of a JC virus-resistant human glial cell line: implications for the identification of host cell factors that determine viral tropism

JC virus (JCV) is a common human polyomavirus that infects 70-80% of the population worldwide. In immunosuppressed individuals, JCV infects oligodendrocytes and causes a fatal demyelinating disease known as progressive multifocal leukoencephalopathy (PML). The tropism of JCV is restricted to oligodendrocytes, astrocytes, and B lymphocytes. Several mechanisms may contribute to the restricted tropism of JCV, including the presence or absence of cell-type-specific transcription and replication factors and the presence or absence of cell-type-specific receptors. We have established a system to investigate cellular factors that influence viral tropism by selecting JCV-resistant cells from a susceptible glial cell line (SVG-A). SVG-A cells were subjected to several rounds of viral infection using JC virus (M1/SVE Delta). A population of resistant cells emerged (SVGR2) that were refractory to infection with the Mad-4 strain of JCV, the hybrid virus M1/SVE Delta, as well as to the related polyomavirus SV40. SVGR2 cells were as susceptible as the SVG-A cells to infection with an unrelated amphotropic retrovirus. The stage at which these cells are resistant to infection was investigated and the block appears to be at early viral gene transcription. This system should ultimately allow us to identify glial specific factors that influence the tropism of JCV.

Traffic of JC virus from sites of initial infection to the brain: the path to progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disorder of the human brain caused by infection with the human polyomavirus, JC. Up to 80% of humans express serum antibodies to JC virus (JCV), yet considerably fewer people develop PML-predominantly those under immunosuppressive conditions. Recent research showed JCV infection in multiple tissues throughout the body, suggesting sites for viral latency. These observations allow the proposal of pathways that JCV may use from sites of initial infection to the brain. Results from investigations into cell-surface receptors, intracellular DNA-binding proteins, and variant viral regulatory regions also suggest mechanisms that may regulate cellular susceptibility to JCV infection. Together, these data elucidate how JCV may establish infection in various cell types, persist latently or become reactivated, and ultimately reach the brain to cause PML.

Construction of a novel JCV/SV40 hybrid virus (JCSV) reveals a role for the JCV capsid in viral tropism

JC virus (JCV) is a common human polyomavirus that infects greater than 70% of the general population worldwide. JCV is also the causative agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the CNS. Currently, little is known about the mechanisms that restrict JCV tropism to a few human cell types and tissues. In vivo, JCV can be detected in oligodendrocytes and astrocytes in the CNS of patients with PML. The virus can also be detected in kidney, tonsil, and B lymphocytes of patients both with and without PML. In vitro, JCV can only be propagated in cultures of human fetal glial cells or in cell lines derived from this tissue. In contrast, the closely related monkey polyomavirus, SV40, has a broad tropism for primate cells, including those cells that are also susceptible to infection by JCV. We hypothesized that one potential block to infection is at the level of virus entry. To examine this, we constructed a JCV-SV40 chimeric viral genome that contains the regulatory region and the early genes of SV40 and the late structural genes of JCV. The hybrid virus (JCSV) induced SV40-like cytopathic effect in human glial cells and hemagglutinated human type O red blood cells similar to JCV. More importantly, the hybrid virus maintained the host range of JCV, suggesting that interactions between the virus capsid and host cell receptors contribute to JCV tropism.

Chorea in patients with AIDS

OBJECTIVE

To describe differing etiologies and possible anatomoclinical correlates of choreic movements in a series of AIDS patients.

METHODS

We analyzed the clinical records and neuroimaging data of 5 consecutive AIDS patients who developed choreic movements at our center from January, 1994 to December, 1996.

RESULTS

There were 2 cases of focal choreic dyskinesias, 1 of right hemichorea, and 2 of generalized chorea. Onset was acute and febrile in 1 case, and subacute in the other 4. In 1 patient the chorea was the AIDS onset symptom; in another choreic movements were the first neurological symptom following AIDS diagnosis; in 2 patients AIDS had a neurological onset other than chorea; and in the fifth patient buccofacial dyskinesias appeared following the development of bacterial encephalitis.

CONCLUSION

Chorea was associated with cerebral toxoplasmosis in 2 patients, progressive multifocal leukoencephalopathy in 1, subacute HIV encephalopathy in another, and was probably iatrogenic in the last. Chorea is not unusual in AIDS, however the causes are variable and careful neuroradiological and clinical evaluation is required to identify them. AIDS-related disease should be considered in young patients presenting with chorea without a family history of movement disorders.

[Progressive multifocal leukoencephalopathy]

PATHOGENESIS

Progressive multifocal leukoencephalopathy is a demyelinating disease of the central nervous system caused by infection and reactivation of JC-virus. About 5% of all HIV-infected patients develop this fatal disease. Although pathogenesis is not completely understood, progressive multifocal leukoencephalopathy is thought to be a persistent infection. The kidneys, bone marrow, peripheral blood lymphocytes and the brain itself are candidates for latency sites of JC-virus. Loss of T-helper-cells in the course of HIV-infection or other immunosuppressive states result in reactivation of JC-virus.

DIAGNOSIS

Progressive multifocal leukoencephalopathy can be diagnosed by focal neurological symptoms, radiographic signs in magnetic resonance imaging and detection of JC-virus in brain tissue or cerebrospinal fluid.

TREATMENT

A specific therapy is not yet available or established. Highly active antiretroviral therapy (HAART) and cidofovir are promising and may prove useful in the near future.

Regulation of DNA virus transcription by cellular POU family transcription factors

In the same way as other viral functions, the transcription of viral genes is frequently controlled by cellular regulatory proteins either acting alone or together with virally encoded factors. In this review, I discuss three examples of such regulation in different types of DNA viruses by different members of the POU family of transcription factors, all of which involve viruses which play a role in the aetiology of specific human diseases. These are the glial cell-specific transcription of JC virus which is controlled by the glial cell specific POU factor Tst-1; the regulation of human papillomavirus gene expression in the cervix by positively and negatively acting POU factors and the manner in which the balance between lytic or latent infection with HSV is controlled by positively and negatively acting POU factors which differ in their ability to interact with the virally encoded transactivator VP16. As well as being of interest in themselves, these processes may offer a therapeutic target for controlling the diseases caused by these very different viruses.

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.

Natural isolates of simian virus 40 from immunocompromised monkeys display extensive genetic heterogeneity: new implications for polyomavirus disease

Simian virus 40 (SV40) DNAs in brain tissue and peripheral blood mononuclear cells (PBMCs) of eight simian immunodeficiency virus-infected rhesus monkeys with SV40 brain disease were analyzed. We report the detection, cloning, and identification of five new SV40 strains following a quadruple testing-verification strategy. SV40 genomes with archetypal regulatory regions (containing a duplication within the G/C-rich regulatory region segment and a single 72-bp enhancer element) were recovered from seven animal brains, two tissues of which also contained viral genomes with nonarchetypal regulatory regions (containing a duplication within the G/C-rich regulatory region segment as well as a variable duplication within the enhancer region). In contrast, PBMC DNAs from five of six animals had viral genomes with both regulatory region types. It appeared, based on T-antigen variable-region sequences, that nonarchetypal virus variants arose de novo within each animal. The eighth animal exclusively yielded a new type of SV40 strain (SV40-K661), containing a protoarchetypal regulatory region (lacking a duplication within the G/C-rich segment of the regulatory region and containing one 72-bp element in the enhancer region), from both brain tissue and PBMCs. The presence of SV40 in PBMCs suggests that hematogenous spread of viral infection may occur. An archetypal version of a virus similar to SV40 reference strain 776 (a kidney isolate) was recovered from one brain, substantiating the idea that SV40 is neurotropic as well as kidney-tropic. Indirect evidence suggests that maternal-infant transmission of SV40 may have occurred in one animal. These findings provide new insights for human polyomavirus disease.

Detection of archetype and rearranged variants of JC virus in multiple tissues from a pediatric PML patient

JC virus (JCV) establishes persistent infections in its human host, and in some immunocompromised individuals, the virus causes the fatal brain disease progressive multifocal leukoencephalopathy (PML). Two forms of the virus, archetype and rearranged, have been isolated, with the latter being derived from the archetype form by deletion and duplication of sequences within the viral transcriptional control region (TCR). We have used the PCR technique to amplify JCV TCR sequences present within multiple tissues of a pediatric PML patient and have cloned and sequenced the PCR products. Archetype JCV was readily detected in kidney tissue; this form of JCV was also identified for the first time in brain and lymph node tissue by employing archetype-specific PCR primers. In addition, several archetype-like variants containing small deletions within their regulatory regions were isolated from cardiac muscle and lung. Different, but related rearranged forms were detected in most of the tissue examined. Each of the rearranged TCRs lacked portions of a 66 base pair (bp) region found within the archetype promoter-enhancer but retained a 23 bp region that is deleted in the prototype (Mad 1) rearranged form of JCV. Although several rearranged forms of JCV were identified in this patient, the TCRs could be assigned to one of two groups based upon the deletion boundaries generated during the adaptation from archetype to rearranged JCV. This study is the first to characterize multiple JCV variants present in different tissues from a patient likely to have succumbed to PML during a primary infection.

Expression of tyrosine hydroxylase in an immortalized human fetal astrocyte cell line; in vitro characterization and engraftment into the rodent striatum

The use of primary human fetal tissue in the treatment of neurodegenerative disorders, while promising, faces several difficult technical and ethical issues. An alternative approach that would obviate these problems would be to use immortalized cell lines of human fetal central nervous system origin. An immortalized human fetal astrocyte cell line (SVG) has been established (45) and herein we describe the in vitro and in vivo characteristics of this cell line which suggest that it may be a useful vehicle for neural transplantation. The SVG cell line is vimentin, GFAP, Thy 1.1 and MHC class I positive, and negative for neurofilament and neuron specific enolase, consistent with its glial origin. To determine whether the cell line could be used as a drug delivery system, a cDNA expression vector for tyrosine hydroxylase was constructed (phTH/Neo) and stably expressed in the SVG cells for over 18 months as demonstrated by immunohistochemistry and Western blotting of the stable transfectants. HPLC analysis of the supernatant from these cells, termed SVG-TH, consistently found 4-6 pmol/ml/min of l-dopa produced with the addition of BH4 to the media. Furthermore, in cocultivation experiments with hNT neurons, PC-12 cells and primary rat fetal mesencephalic tissue, both the SVG and SVG-TH cells demonstrated neurotrophic potential, suggesting that they constituitively express factors with neuroregenerative potential. To determine the viability of these cells in vivo, SVG-TH cells were grafted into the striatum of Sprague-Dawley rats and followed over time. A panel of antibodies was used to unequivocally differentiate the engrafted cells from the host parenchyma, including antibodies to: SV40 large T antigen (expressed in the SVG-TH cells), human and rat MHC class 1, vimentin, GFAP, and tyrosine hydroxylase. While the graft was easily identified with the first week, over the course of a four week period of time the engrafted cells decreased in number. Concomittantly, rat CD4 and CD8 expression in the vicinity of the graft increased, consistent with xenograft rejection. When the SVG-TH cells were grafted to the lesioned striatum of a 6-hydroxydopamine lesioned rats, rotational behavior of the rat decreased as much as 80% initially, then slowly returned to baseline over the next four weeks, parallelling graft rejection. Thus, the SVG-TH cells can induce a functional recovery in an animal model of Parkinson's disease, however as a xenograft, the SVG cells are recognized by the immune system.

Expression of Tyrosine Hydroxylase in an Immortalized Human Fetal Astrocyte Cell Line; in Vitro Characterization and Engraftment into the Rodent Striatum

The use of primary human fetal tissue in the treatment of neurodegenerative disorders, while promising, faces several difficult technical and ethical issues. An alternative approach that would obviate these problems would be to use immortalized cell lines of human fetal central nervous system origin. An immortalized human fetal astrocyte cell line (SVG) has been established (45) and herein we describe the in vitro and in vivo characteristics of this cell line which suggest that it may be a useful vehicle for neural transplantation. The SVG cell line is vimentin, GFAP, Thy 1.1 and MHC class I positive, and negative for neurofilament and neuron specific enolase, consistent with its glial origin. To determine whether the cell line could be used as a drug delivery system, a cDNA expression vector for tyrosine hydroxylase was constructed (phTH/Neo) and stably expressed in the SVG cells for over 18 months as demonstrated by immunohistochemistry and Western blotting of the stable transfectants. HPLC analysis of the supernatant from these cells, termed SVG-TH, consistently found 4-6 pmol/ml/min of 1-dopa produced with the addition of BH4to the media. Furthermore, in cocultivation experiments with hNT neurons, PC-12 cells and primary rat fetal mesencephalic tissue, both the SVG and SVG-TH cells demonstrated neurotrophic potential, suggesting that they constituitively express factors with neuroregenerative potential. To determine the viability of these cells in vivo, SVG-TH cells were grafted into the striatum of Sprague-Dawley rats and followed over time. A panel of antibodies was used to unequivocally differentiate the engrafted cells from the host parenchyma, including antibodies to: SV40 large T antigen (expressed in the SVG-TH cells), human and rat MHC class 1, vimentin, GFAP, and tyrosine hydroxylase. While the graft was easily identified with the first week, over the course of a four week period of time the engrafted cells decreased in number. Concomittantly, rat CD4 and CD8 expression in the vicinity of the graft increased, consistent with xenograft rejection. When the SVG-TH cells were grafted to the lesioned striatum of a 6-hydroxydopamine lesioned rats, rotational behavior of the rat decreased as much as 80% initially, then slowly returned to baseline over the next four weeks, parallelling graft rejection. Thus, the SVG-TH cells can induce a functional recovery in an animal model of Parkinson's disease, however as a xenograft, the SVG cells are recognized by the immune system.