A granule cell neuron-associated JC virus variant has a unique deletion in the VP1 gene

Hemorrhagic cystitis induced by JC polyomavirus infection following COVID-19: a case report

JC polyomavirus (JCPyV) is a human polyomavirus that can establish lifelong persistent infection in the majority of adults. It is typically asymptomatic in immunocompetent individuals. However, there is a risk of developing progressive multifocal leukoencephalopathy (PML) in immunocompromised or immunosuppressed patients. Though JCPyV commonly resides in the kidney-urinary tract, its involvement in urinary system diseases is extremely rare. Here, we reported a case of a 60-year-old male patient with coronavirus disease 2019 (COVID-19) infection who developed hemorrhagic cystitis after receiving treatment with nirmatrelvir 300 mg/ritonavir 100 mg quaque die (QD). Subsequent metagenomic next-generation sequencing (mNGS) confirmed the infection to be caused by JCPyV type 2. Then, human immunoglobulin (PH4) for intravenous injection at a dose of 25 g QD was administered to the patient. Three days later, the hematuria resolved. This case illustrates that in the setting of compromised host immune function, JCPyV is not limited to causing central nervous system diseases but can also exhibit pathogenicity in the urinary system. Moreover, mNGS technology facilitates rapid diagnosis of infectious etiology by clinical practitioners, contributing to precise treatment for patients.

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.

Long-term outcome of progressive multifocal leukoencephalopathy with recombinant interleukin-2 treatment and an associated increase in the number of HPyV-2-specific T-cells: a case report

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease caused by reactivation of the human polyomavirus 2 (HPyV-2). PML is associated with a high morbidity and mortality rate and there is currently no standard curative therapy. We report short-term immunologic response and long-term clinical outcomes in a patient diagnosed with follicular lymphoma (FL) who developed PML. Diagnosis of PML was established conclusively based on findings from a brain biopsy. The patient was treated with recombinant interleukin 2 (IL-2) and showed rapid clinical improvement. HPyV-2-specific T-cells were tracked longitudinally and correlation with clinical status, viral load, and radiographic imaging was documented. After the progression of the patient's FL, which required an allogeneic bone marrow transplant, the patient prophylactically received human leukocyte antigen-matched donor-derived HPyV-2 T-cells to prevent the recurrence of the PML as part of a clinical trial. Twelve years after the initial diagnosis of PML, he did not develop a relapse of his PML, supporting data that therapies that increase HPyV-2-specific T-cells, including IL-2, may be effective in the management of PML.

A multivalent polyomavirus vaccine elicits durable neutralizing antibody responses in macaques

In 2019, there were about 100,000 kidney transplants globally, with more than a quarter of them performed in the United States. Unfortunately, some engrafted organs are lost to polyomavirus-associated nephropathy (PyVAN) caused by BK and JC viruses (BKPyV and JCPyV). Both viruses cause brain disease and possibly bladder cancer in immunosuppressed individuals. Transplant patients are routinely monitored for BKPyV viremia, which is an accepted hallmark of nascent nephropathy. If viremia is detected, a reduction in immunosuppressive therapy is standard care, but the intervention comes with increased risk of immune rejection of the engrafted organ. Recent reports have suggested that transplant recipients with high levels of polyomavirus-neutralizing antibodies are protected against PyVAN. Virus-like particle (VLP) vaccines, similar to approved human papillomavirus vaccines, have an excellent safety record and are known to induce high levels of neutralizing antibodies and long-lasting protection from infection. In this study, we demonstrate that VLPs representing BKPyV genotypes I, II, and IV, as well as JCPyV genotype 2 produced in insect cells elicit robust antibody titers. In rhesus macaques, all monkeys developed neutralizing antibody titers above a previously proposed protective threshold of 10,000. A second inoculation, administered 19 weeks after priming, boosted titers to a plateau of ≥ 25,000 that was maintained for almost two years. No vaccine-related adverse events were observed in any macaques. A multivalent BK/JC VLP immunogen did not show inferiority compared to the single-genotype VLP immunogens. Considering these encouraging results, we believe a clinical trial administering the multivalent VLP vaccine in patients waiting to receive a kidney transplant is warranted to evaluate its ability to reduce or eliminate PyVAN.

A Case of John Cunningham Virus Induced Rhombencephalitis after Rituximab Therapy for Idiopathic Thrombocytopenic Purpura

Background

John Cunningham virus (JCV) is known to cause progressive multifocal leukoencephalopathy (PML) in immuno-compromised patients due to lytic infection of oligodendrocytes and astrocytes. Rarely, it may also present as granule cell neuronopathy (GCN), leading to degeneration of cerebellar granule cell neurons. It is described in patients with underlying conditions or medication contributing to immune compromise. Case Presentation. A 73-year-old man presented with ataxia and difficulty in speech which began 3 months after initiation of treatment for idiopathic thrombocytopenic purpura with rituximab. Neurological examination was significant for torsional nystagmus, motor aphasia, right-sided dysmetria, and dysdiadochokinesia with gait ataxia. Magnetic resonance imaging (MRI) showed right cerebellar lesion and cerebrospinal fluid (CSF) polymerase chain reaction (PCR) was positive for JC virus.

Conclusion

The diagnosis of JC virus-related cerebellar disease can be missed, due to the subacute to chronic onset and challenges in detection. Clinicians should have a high degree of suspicion for development of these symptoms, even a few months after initiation of immune-modulatory therapy because the progression and outcomes can be disastrous.

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.

Infratentorial onset of progressive multifocal leukoencephalopathy in a patient with systematic lupus erythematosus complicated with lymphoma: a case report

Progressive multifocal leukoencephalopathy (PML) is a rare opportunistic infection of the central nervous system caused by reactivation of JC virus (JCV). Typical PML shows confluent, bilateral but asymmetric, subcortical lesions in the supratentorial white matter on magnetic resonance imaging (MRI). We report here a 50-year-old woman with systemic lupus erythematosus complicated with lymphoma who developed PML with atypical brain MRI findings limited to the infratentorial area at presentation. She presented with numbness on the right side of the face, including her tongue, clumsiness of the right hand, and gait disturbance, after completion of remission induction therapy for lymphoma, including rituximab. Brain MRI demonstrated a solitary lesion limited to the cerebellum and brainstem, but a definitive diagnosis could not be made from cerebrospinal fluid study or tentative histologic evaluation of brain biopsy specimens. Despite methylprednisolone pulse therapy, her neurological deficits progressively worsened. One month later, in-depth analysis of her cerebrospinal fluid and brain biopsy specimens confirmed the presence of JCV. Eventually, the localised unilateral crescent-shaped cerebellar lesions on MRI expanded to the contralateral cerebellum, middle cerebellar hemisphere, pons, and midbrain and finally developed multifocal invasion into the white matter of the cerebral hemispheres. Our case suggests that PML could first present with a solitary infratentorial lesion in immunocompromised patients.

Progressive multifocal leukoencephalopathy and the spectrum of JC virus-related disease

Progressive multifocal leukoencephalopathy (PML) is a devastating CNS infection caused by JC virus (JCV), a polyomavirus that commonly establishes persistent, asymptomatic infection in the general population. Emerging evidence that PML can be ameliorated with novel immunotherapeutic approaches calls for reassessment of PML pathophysiology and clinical course. PML results from JCV reactivation in the setting of impaired cellular immunity, and no antiviral therapies are available, so survival depends on reversal of the underlying immunosuppression. Antiretroviral therapies greatly reduce the risk of HIV-related PML, but many modern treatments for cancers, organ transplantation and chronic inflammatory disease cause immunosuppression that can be difficult to reverse. These treatments — most notably natalizumab for multiple sclerosis — have led to a surge of iatrogenic PML. The spectrum of presentations of JCV-related disease has evolved over time and may challenge current diagnostic criteria. Immunotherapeutic interventions, such as use of checkpoint inhibitors and adoptive T cell transfer, have shown promise but caution is needed in the management of immune reconstitution inflammatory syndrome, an exuberant immune response that can contribute to morbidity and death. Many people who survive PML are left with neurological sequelae and some with persistent, low-level viral replication in the CNS. As the number of people who survive PML increases, this lack of viral clearance could create challenges in the subsequent management of some underlying diseases.

In this Review, Cortese et al. provide an overview of the pathobiology and evolving presentations of progressive multifocal leukoencephalopathy and other diseases caused by JC virus, and discuss emerging immunotherapeutic approaches that could increase survival.

Progressive multifocal leukoencephalopathy (PML) is a rare, debilitating and often fatal disease of the CNS caused by JC virus (JCV).

JCV establishes asymptomatic, lifelong persistent or latent infection in immune competent hosts, but impairment of cellular immunity can lead to reactivation of JCV and PML.

PML most commonly occurs in patients with HIV infection or lymphoproliferative disease and in patients who are receiving natalizumab for treatment of multiple sclerosis.

The clinical phenotype of PML varies and is shaped primarily by the host immune response; changes in the treatment of underlying diseases associated with PML have changed phenotypes over time.

Other clinical manifestations of JCV infection have been described, including granule cell neuronopathy.

Survival of PML depends on reversal of the underlying immunosuppression; emerging immunotherapeutic strategies include use of checkpoint inhibitors and adoptive T cell transfer.

Structural Analysis of Merkel Cell Polyomavirus (MCPyV) Viral Capsid Protein 1 (VP1) in HIV-1 Infected Individuals

Merkel cell polyomavirus (MCPyV) viral protein 1 (VP1) is the capsid protein that mediates virus attachment to host cell receptors and is the major immune target. Given the limited data on MCPyV VP1 mutations, the VP1 genetic variability was examined in 100 plasma and 100 urine samples from 100 HIV+ individuals. Sequencing of VP1 DNA in 17 urine and 17 plasma specimens, simultaneously MCPyV DNA positive, revealed that 27 samples displayed sequences identical to VP1 of MCC350 strain. VP1 from two urine specimens had either Thr47Ser or Ile115Phe substitution, whereas VP1 of one plasma contained Asp69Val and Ser251Phe substitutions plus deletion (∆) of Tyr79. VP1 DNA in the remaining samples had mutations encoding truncated protein. Three-dimensional prediction models revealed that Asp69Val, Ser251Phe, and Ile115Phe caused neutral effects while Thr47Ser and Tyr79∆ produced a deleterious effect reducing VP1 stability. A549 cells infected with urine or plasma samples containing full-length VP1 variants with substitutions, sustained viral DNA replication and VP1 expression. Moreover, medium harvested from these cells was able to infect new A549 cells. In cells infected by samples with truncated VP1, MCPyV replication was hampered. In conclusion, MCPyV strains with unique mutations in the VP1 gene are circulating in HIV+ patients. These strains display altered replication efficiency compared to the MCC350 prototype strain in A549 cells.

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.

JC Virus Infects Neurons and Glial Cells in the Hippocampus

The human polyomavirus JC (JCV) infects glial cells and is the etiologic agent of the CNS demyelinating disease progressive multifocal leukoencephalopathy. JCV can infect granule cell neurons of the cerebellum, causing JCV granule cell neuronopathy and cortical pyramidal neurons in JCV encephalopathy. Whether JCV also infects neurons in other areas of the CNS is unclear. We determined the prevalence and pattern of JCV infection of the hippocampus in archival samples from 28 patients with known JCV infection of the CNS and 66 control subjects. Among 28 patients, 11 (39.3%) had JCV infection of hippocampus structures demonstrated by immunohistochemistry. Those included gray matter (dentate gyrus and cornu ammonis, subiculum) in 11/11 and afferent or efferent white matter tracts (perforant path, alveus, fimbria) in 10/11. In the hippocampus, JCV infected granule cell and pyramidal neurons, astrocytes, and oligodendrocytes. Although glial cells expressed either JCV regulatory T Antigen or JCV VP1 capsid protein, infected neurons expressed JCV T Antigen only, suggesting an abortive/restrictive infection. None of the 66 control subjects had evidence of hippocampal JCV protein expression by immunohistochemistry or JCV DNA by in situ hybridization. These results greatly expand our understanding of JCV pathogenesis in the CNS.

JC virus granule cell neuronopathy in the setting of chronic lymphopenia treated with recombinant interleukin-7

JC virus (JCV) is a human polyomavirus that infects the central nervous system (CNS) of immunocompromised patients. JCV granule cell neuronopathy (JCV-GCN) is caused by infection of cerebellar granule cells, causing ataxia. A 77-year-old man with iatrogenic lymphopenia presented with severe ataxia and was diagnosed with JCV-GCN. His ataxia and cerebrospinal fluid (CSF) improved with intravenous immunoglobulin, high-dose intravenous methylprednisolone, mirtazapine, and mefloquine. Interleukin-7 (IL-7) therapy reconstituted his lymphocytes and reduced his CSF JCV load. One month after IL-7 therapy, he developed worsening ataxia and CSF inflammation, which raised suspicion for immune reconstitution inflammatory syndrome. Steroids were restarted and his ataxia stabilized.

Concomitant granule cell neuronopathy in patients with natalizumab-associated PML

Granule cell neuronopathy (GCN) is a rare JC virus infection of the cerebellar granule cell neurons in immunocompromised patients. On brain imaging, GCN is characterized by cerebellar atrophy which can be accompanied by infratentorial white matter lesions. The objective of this study is to investigate the prevalence of MRI findings suggestive of GCN in a large natalizumab-associated progressive multifocal leukoencephalopathy (PML) cohort. MRI scans from before, at the time of, and during follow-up after diagnosis of PML in 44 natalizumab-treated MS patients, and a control group of 25 natalizumab-treated non-PML MS patients were retrospectively reviewed for imaging findings suggestive of GCN. To assess and quantify the degree of cerebellar atrophy, we used a 4 grade rating scale. Three patients in the PML group showed imaging findings suggestive of GCN and none in the control group. In two of these PML patients, cerebellar atrophy progressed from grade 0 at the time of diagnosis of isolated supratentorial PML to grade 1 and 2 after 2.5 and 3 months, respectively, in the absence of infratentorial white mater lesions. The third patient had grade 1 cerebellar atrophy before diagnosis of infra- and supratentorial PML, and showed progression of cerebellar atrophy to grade 2 in the 3 months following PML diagnosis. None of the other eight patients with infratentorial PML lesions developed cerebellar atrophy suggestive of GCN. Three cases with imaging findings suggestive of GCN were detected among 44 natalizumab-associated PML patients. GCN may, therefore, be more common than previously considered in natalizumab-associated PML patients.

Novel syndromes associated with JC virus infection of neurons and meningeal cells: no longer a gray area

PURPOSE OF REVIEW

The availability of a growing number of immunomodulatory medications over the past few years has been associated with various JC virus (JCV)-associated brain syndromes in patients with autoimmune diseases, including multiple sclerosis, Crohn's disease, and psoriasis that had not been previously recognized as predisposing factors for progressive multifocal leukoencephalopathy. This review covers the three novel syndromes discovered in the last decade that are caused by JCV infection of neurons and meningeal cells.

RECENT FINDINGS

For more than 30 years, JCV was thought to exclusively infect oligodendrocytes and astrocytes in the white matter of the brain of immunosuppressed individuals. We now recognize that JCV-infected glial cells are frequently located at the gray-white matter junction or exclusively within the gray matter causing demyelination in the cortex. Mutations in JCV can trigger a change in tropism leading to involvement of other cell types, such as neurons and meningeal cells, causing clinically distinct entities. These new features of JCV infection provide challenges for clinicians taking care of affected patients and investigators studying the biology of this polyomavirus, its pathogenesis, and tropism.

SUMMARY

We hope that increasing awareness of these syndromes will lead to early diagnosis, and pave the way for new avenues of research to better understand all aspects of JCV pathogenesis and develop efficient therapies for our patients. However, we need to remain vigilant and open to the possibility that additional JC variants or yet unknown polyomaviruses may also be associated with neurological diseases.

Simian Virus 40 Infection in the Spinal Cord of Simian Immunodeficiency Virus-Immunosuppressed Rhesus Macaques

Progressive multifocal leukoencephalopathy (PML) is an often-fatal demyelinating disease of the CNS that usually develops in immunocompromised individuals because of reactivation of quiescent JC virus (JCV). There are only a few reports of JCV infection in the human spinal cord. Progressive multifocal leukoencephalopathy-like demyelinating lesions have been documented in the brains of simian immunodeficiency virus-infected macaques. To determine whether simian virus 40 (SV40) can infect and cause PML lesions in spinal cords of immunosuppressed macaques, we examined archival spinal cord samples from 15 simian immunodeficiency virus-infected rhesus monkeys with acquired immunodeficiency syndrome and SV40 infection of the brain. Among those, 6 (40%) had SV40-infected cells in the spinal cord, including 1 with PML-like lesions, 1 with PML-like lesions and meningoencephalitis, 2 with meningoencephalitis, 1 with gray matter gliosis, and 1 with no lesions. One animal with a large PML-like lesion had extensive demyelination and SV40 infection of astrocytes, oligodendrocytes, and meningeal cells. None of the 6 animals had SV40-infected spinal cord neurons. These observations indicate that, like JCV in immunosuppressed humans, SV40 can infect glial cells and cause PML-like lesions in the spinal cord of immunosuppressed rhesus macaques. Rhesus macaques could serve as an animal model to study polyomavirus infection and pathogenesis in the spinal cord.

Lack of Major Histocompatibility Complex Class I Upregulation and Restrictive Infection by JC Virus Hamper Detection of Neurons by T Lymphocytes in the Central Nervous System

The human polyomavirus JC (JCV) infects glial cells in immunosuppressed individuals, leading to progressive multifocal leukoencephalopathy. Polyomavirus JC can also infect neurons in patients with JCV granule cell neuronopathy and JCV encephalopathy. CD8-positive T cells play a crucial role in viral containment and outcome in progressive multifocal leukoencephalopathy, but whether CD8-positive T cells can also recognize JCV-infected neurons is unclear. We used immunohistochemistry to determine the prevalence of T cells in neuron-rich areas of archival brain samples from 77 patients with JCV CNS infections and 94 control subjects. Neurons predominantly sustained a restrictive infection with expression of JCV regulatory protein T antigen (T Ag), whereas glial cells were productively infected and expressed both T Ag and the capsid protein VP1. T cells were more prevalent near JCV-infected cells with intact nuclei expressing both T Ag and VP1 compared with those expressing either protein alone. CD8-positive T cells also colocalized more with JCV-infected glial cells than with JCV-infected neurons. Major histocompatibility complex class I expression was upregulated in JCV-infected areas but could only be detected in rare neurons interspersed with infected glial cells. These results suggest that isolated neurons harboring restrictive JCV infection do not upregulate major histocompatibility complex class I and thus may escape recognition by CD8-positive T cells.

JC polyomavirus mutants escape antibody-mediated neutralization

JC polyomavirus (JCV) persistently infects the urinary tract of most adults. Under conditions of immune impairment, JCV causes an opportunistic brain disease, progressive multifocal leukoencephalopathy (PML). JCV strains found in the cerebrospinal fluid of PML patients contain distinctive mutations in surface loops of the major capsid protein, VP1. We hypothesized that VP1 mutations might allow the virus to evade antibody-mediated neutralization. Consistent with this hypothesis, neutralization serology revealed that plasma samples from PML patients neutralized wild-type JCV strains but failed to neutralize patient-cognate PML-mutant JCV strains. This contrasted with serological results for healthy individuals, most of whom robustly cross-neutralized all tested JCV variants. Mice administered a JCV virus-like particle (VLP) vaccine initially showed neutralizing "blind spots" (akin to those observed in PML patients) that closed after booster immunization. A PML patient administered an experimental JCV VLP vaccine likewise showed markedly increased neutralizing titer against her cognate PML-mutant JCV. The results indicate that deficient humoral immunity is a common aspect of PML pathogenesis and that vaccination may overcome this humoral deficiency. Thus, vaccination with JCV VLPs might prevent the development of PML.

JC virus granule cell neuronopathy: A cause of infectious cerebellar degeneration

JC virus (JCV) infection of glial cells can lead to progressive multifocal leukoencephalopathy (PML) in immunocompromised patients. A newly described phenotype of the infection is infection of neurons. This distinct clinical and radiological syndrome is named JCV granule cell neuronopathy, characterized by exclusive or predominant cerebellar atrophy. We report the clinical and radiological longitudinal findings of 5 HIV-infected patients referred to us between September 2004 and November 2011 who exhibited JCV granule cell neuronopathy (4 probable cases and 1 possible). The association of immunocompromised status, progressive cerebellar syndrome, MRI abnormalities with cortical cerebellar atrophy and cerebrospinal fluid positive for JCV on PCR allowed for a highly probable diagnosis. The reversal of the immunocompromised status is the only way to stop the disease evolution. Motor functioning can remain impaired, but the illness itself, unlike progressive multifocal leukoencephalopathy, does not seem to threaten life.

Naturally arising strains of polyomaviruses with severely attenuated microRNA expression

Several different polyomaviruses (PyVs) encode microRNAs (miRNAs) that regulate viral as well as host gene expression. However, the functions of polyomaviral miRNAs, particularly during in vivo infection, remain poorly understood. Here we identify rare naturally arising PyVs that are severely attenuated or null for miRNA expression. We identify hypomorphic or null strains for miRNA expression from rhesus macaque simian virus 40 (SV40) and human JC virus. These strains were isolated from immunocompromised hosts and derive from insertions or deletions in the viral DNA that preserve the amino acid reading frame of opposing-strand large T antigen gene. Characterization of the SV40 miRNA hypomorph, K661, shows that it is inhibited at the early miRNA biogenesis step of Drosha-mediated processing. Despite having a nonrearranged enhancer, which a previous study has shown renders some PyVs more susceptible to the autoregulatory activities of the miRNA, restoring miRNA expression to K661 has little effect on virus growth in either immortalized or primary monkey kidney cells. Thus, in addition to any effect of accompanying genomic elements, these results suggest that the cellular context also determines susceptibility to PyV miRNA-mediated effects. Combined, these results demonstrate that polyomaviruses lacking miRNAs can arise infrequently and that the functional importance of polyomaviral miRNAs is context dependent, consistent with an activity connected to the immune status of the host.

IMPORTANCE

Diverse virus families encode miRNAs, yet much remains unknown about viral miRNA function and contribution to the infectious cycle. Polyomaviruses (PyVs) are small DNA viruses, long known to be important as etiological agents of rare diseases and valuable models of DNA virus infection. Here, in immunosuppressed hosts, we uncover rare naturally arising variants of different PyVs that have lost the ability to express miRNAs. This represents some of the only known natural viruses to have lost miRNA expression. By probing the biogenesis pathways of these variants, we uncover that miRNA expression is lost via small insertions or deletions that render the transcripts resistant to early steps of miRNA biogenesis while preserving the reading frame of the opposing T antigen transcripts. Overall, our study informs how miRNA genes evolve/devolve in viruses and suggests that miRNA function is exquisitely dependent not only on viral genomic context but also on the cellular and host environment.

Heterogeneous imaging characteristics of JC virus granule cell neuronopathy (GCN): a case series and review of the literature

Granule cell neuronopathy (GCN) is a rare JC virus (JCV)-related disease in immunocompromised patients, characterized by lytic infection of the cerebellar granule cell layer. To enable early diagnosis and intervention, we identify features of GCN and describe possible aspects of disease heterogeneity. We report on two new cases of GCN in HIV-infected patients of whom we retrospectively assessed clinical and radiologic data. In addition, we carried out a literature search and review of clinical, radiologic and histopathologic findings of all published GCN cases. Including the two new cases reported here, a total of 18 GCN cases were included in this study. HIV infection, present in 12 of the cases, was the most common underlying condition, followed by monoclonal antibody treatment which was present in three cases. Cerebellar atrophy was detected in all except two cases. In 12 patients a heterogeneous distribution pattern of white matter changes in the cerebellum and brainstem was observed. Imaging findings in GCN are remarkably heterogeneous; exhibiting cerebellar atrophy, as well as white matter pathology, particularly in the adjacent infratentorial white matter. This suggests an overlap of GCN with other JCV-related diseases, such as progressive multifocal leukoencephalopathy.

JCV GCN in a natalizumab-treated MS patient is associated with mutations of the VP1 capsid gene

OBJECTIVE

To describe the clinical, neuroimaging, immunologic, and virologic characteristics of JC virus-associated granule cell neuronopathy (JCV GCN) in a natalizumab-treated patient with multiple sclerosis (MS) who developed immune reconstitution inflammatory syndrome (IRIS) after natalizumab withdrawal.

METHODS

We obtained longitudinal clinical data as well as MRI and proton magnetic resonance spectroscopy from this patient with MS. We measured JCV-specific cellular immune response in his peripheral blood by intracellular cytokine staining and sequenced a fragment of JCV VP1 capsid gene detected in his CSF. We contrast our findings with the first recently reported case.

RESULTS

This patient presented with worsening cerebellar symptoms and progressive cerebellar atrophy without new MS lesions on MRI after 63 months of natalizumab monotherapy. JCV DNA was detected in his CSF by PCR and harbored novel GCN-type mutations in the VP1 gene. He developed IRIS upon discontinuation of natalizumab and plasma exchange, which manifested itself by a worsening of clinical symptoms and contrast enhancement in the cerebellum on MRI. Treatment with corticosteroids resulted in resolution of IRIS, as demonstrated by proton magnetic resonance spectroscopy. The patient had a strong JCV-specific T-cell response in his peripheral blood and remains alive after 15 months from onset of symptoms, although with significant disability. He did not have MS relapse on glatiramer acetate.

CONCLUSIONS

JCV GCN should be considered in patients on natalizumab presenting with progressive cerebellar symptoms and cerebellar atrophy, and is associated with mutations in the JCV VP1 gene. Natalizumab withdrawal may be complicated by JCV GCN IRIS, and require treatment with corticosteroids.

A fatal case of JC virus meningitis presenting with hydrocephalus in a human immunodeficiency virus-seronegative patient

JC virus (JCV) is the etiologic agent of progressive multifocal leukoencephalopathy, JCV granule cell neuronopathy, and JCV encephalopathy. Whether JCV can also cause meningitis has not yet been demonstrated. We report a case of aseptic meningitis resulting in symptomatic hydrocephalus in a human immunodeficiency virus-seronegative patient. Brain imaging showed enlargement of ventricles but no parenchymal lesion. She had a very high JC viral load in the cerebrospinal fluid (CSF) and developed progressive cognitive dysfunction despite ventricular drainage. She was diagnosed with pancytopenia and passed away after 5.5 months. Postmortem examination revealed productive JCV infection of leptomeningeal and choroid plexus cells, and limited parenchymal involvement. Sequencing of JCV CSF strain showed an archetype-like regulatory region. Further studies of the role of JCV in aseptic meningitis and in idiopathic hydrocephalus are warranted.

JC polyomavirus granule cell neuronopathy in a patient treated with rituximab

IMPORTANCE

Progressive multifocal leukoencephalopathy results from lytic infection of the glia by the JC polyomavirus (JCV); JCV granule cell neuronopathy is caused by infection with a mutated form of JCV, leading to a shift in viral tropism from the glia to cerebellar granule cells. This shift results in a clinical syndrome dominated by progressive cerebellar dysfunction that might elude standard diagnostic workup strategies for ataxia.

OBSERVATIONS

We present the case report of a patient receiving long-term rituximab therapy who developed progressive cerebellar ataxia and marked isolated cerebellar degeneration. This syndrome resulted from JCV granule cell neuronopathy associated with a novel JCV mutation.

CONCLUSIONS AND RELEVANCE

New onset or worsening of isolated cerebellar ataxia in patients being treated with rituximab or natalizumab warrants early assessment for JCV infection.

Agnogene deletion in a novel pathogenic JC virus isolate impairs VP1 expression and virion production

Infection of glial cells by the human polyomavirus JC (JCV) causes progressive multifocal leukoencephalopathy (PML). JCV Encephalopathy (JCVE) is a newly identified disease characterized by JCV infection of cortical pyramidal neurons. The virus JCV_CPN associated with JCVE contains a unique 143 base pair deletion in the agnogene. Contrary to most JCV brain isolates, JCV_CPN has an archetype-like regulatory region (RR) usually found in kidney strains. This provided us with the unique opportunity to determine for the first time how each of these regions contributed to the phenotype of JCV_CPN. We characterized the replication of JCV_CPN compared to the prototype virus JCV_Mad-1 in kidney, glial and neuronal cell lines. We found that JCV_CPN is capable of replicating viral DNA in all cell lines tested, but is unable to establish persistent infection seen with JCV_Mad-1. JCV_CPN does not have an increased ability to replicate in the neuronal cell line tested. To determine whether this phenotype results from the archetype-like RR or the agnogene deletion, we generated chimeric viruses between JCV_CPN of JCV_Mad-1. We found that the deletion in the agnogene is the predominant cause of the inability of the virus to maintain a persistent infection, with the introduction of a full length agnogene, either with or without agnoprotein expression, rescues the replication of JCV_CPN. Studying this naturally occurring pathogenic variant of JCV provides a valuable tool for understanding the functions of the agnogene and RR form in JCV replication.

Frequent infection of neurons by SV40 virus in SIV-infected macaque monkeys with progressive multifocal leukoencephalopathy and meningoencephalitis

Simian virus 40 (SV40), family Polyomaviridae, in immunocompromised macaques can cause fatal demyelinating central nervous system disease analogous to progressive multifocal leukoencephalopathy caused by John Cunningham (JC) virus in immunocompromised humans. Recently, we have demonstrated that JC virus can infect cerebellar granule cell neurons and cortical pyramidal neurons in immunosuppressed people. To examine whether SV40 neuronal infection occurs spontaneously in immunosuppressed macaques, we analyzed archival brain specimens from 20 simian immunodeficiency virus-infected rhesus with AIDS and 1 cynomolgus post-transplant selected with SV40 brain infection from archival records from 1991 to 2012. In addition to white matter SV40 distribution in classic demyelinating progressive multifocal leukoencephalopathy, some of the 21 monkeys exhibited meningeal, subpial neocortical, and periventricular virus. This distribution pattern corresponded to broader viral tropism with neuronal infection in 14 (66.7%) of 21 cases. In all 14 cases, identified neurons were positive for early SV40 transcript large T antigen, but only 4 of the 14 cases exhibited late viral transcript viral protein 1-positive neurons. SV40-infected neurons were detected in frontal, parietal, occipital, and temporal cortices, hippocampus, thalamus, and brain stem. These observations confirm that spontaneous SV40 neuronal infection occurs in immunosuppressed macaques, which parallels JC virus-neuronal infection in immunosuppressed patients. Neuronal infection may be an important aspect of both SV40 and JC virus neuropathogenesis in their respective hosts.

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.

PML diagnostic criteria: consensus statement from the AAN Neuroinfectious Disease Section

OBJECTIVE

To establish criteria for the diagnosis of progressive multifocal leukoencephalopathy (PML).

METHODS

We reviewed available literature to identify various diagnostic criteria employed. Several search strategies employing the terms "progressive multifocal leukoencephalopathy" with or without "JC virus" were performed with PubMed, SCOPUS, and EMBASE search engines. The articles were reviewed by a committee of individuals with expertise in the disorder in order to determine the most useful applicable criteria.

RESULTS

A consensus statement was developed employing clinical, imaging, pathologic, and virologic evidence in support of the diagnosis of PML. Two separate pathways, histopathologic and clinical, for PML diagnosis are proposed. Diagnostic classification includes certain, probable, possible, and not PML.

CONCLUSION

Definitive diagnosis of PML requires neuropathologic demonstration of the typical histopathologic triad (demyelination, bizarre astrocytes, and enlarged oligodendroglial nuclei) coupled with the techniques to show the presence of JC virus. The presence of clinical and imaging manifestations consistent with the diagnosis and not better explained by other disorders coupled with the demonstration of JC virus by PCR in CSF is also considered diagnostic. Algorithms for establishing the diagnosis have been recommended.

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.

Progressive multifocal leukoencephalopathy: why gray and white matter

Since it was first described in 1958, progressive multifocal leukoencephalopathy (PML), a demyelinating disease of the brain caused by the polyomavirus JC (JCV), has evolved tremendously. It was once considered a noninflammatory disease that affected exclusively oligodendrocytes and astrocytes in the white matter of immunosuppressed individuals and was almost always fatal. Today, we understand that PML can present during the course of an immune reconstitution inflammatory syndrome and that it affects a broader range of individuals, including patients with minimal immunosuppression and those who are treated with novel immunomodulatory medications. Furthermore, JCV-infected glial cells are frequently located at the gray matter-white matter junction or within the gray matter, causing demyelinating lesions within cortical areas. Finally, JCV variants can also infect neurons, leading to the recognition of two distinct clinical entities: JCV granule cell neuronopathy and JCV encephalopathy.

JC virus encephalopathy is associated with a novel agnoprotein-deletion JCV variant

JC virus encephalopathy (JCVE) is a newly described gray matter disease of the brain caused by productive infection of cortical pyramidal neurons. We characterized the full length sequence of JCV isolated from the brain of a JCVE patient, analyzed its distribution in various compartments by PCR, and determined viral gene expression in the brain by immunohistochemistry(IHC). We identified a novel JCV variant, JCV_CPN1, with a unique 143 bp deletion in the Agno gene encoding a truncated 10 amino acid peptide, and harboring an archetype-like regulatory region. This variant lacked one of three nuclear protein binding regions in the Agno gene. It was predominant in the brain, where it coexisted with an Agno-intact wild-type strain. Double immunostaining with anti-Agno and anti- VP1 antibodies demonstrated that the truncated JCV_CPN1 Agno peptide was present in the majority of cortical cells productively infected with JCV. We then screened 68 DNA samples from 8 brain, 30 CSF and 30 PBMC samples of PML patients, HIV+ and HIV- control subjects. Another JCV_CPN strain with a different pattern of Agno-deletion was found in the CSF of an HIV+/PML patient, where it also coexisted with wild-type, Agno-intact JCV. These findings suggest that the novel tropism for cortical pyramidal neurons of JCV_CPN1, may be associated with the Agno deletion. Productive and lytic infection of these cells, resulting in fulminant JCV encephalopathy and death may have been facilitated by the co-infection with a wild- type strain of JCV.

Frequent infection of cortical neurons by JC virus in patients with progressive multifocal leukoencephalopathy

The human polyomavirus JC (JCV) infects glial cells and causes progressive multifocal leukoencephalopathy (PML), a demyelinating disease of the brain, in immunosuppressed individuals. The extent of JCV infection of neurons is unclear. We determined the prevalence and pattern of JCV infection in gray matter (GM) by immunostaining in archival brain samples of 49 PML patients and 109 control subjects. Among PML patients, 96% had demyelinating lesions in white matter and at the gray-white junction (GWJ); 57% had them in the GM. Most JCV-infected cells in GWJ and GM were glia, but JCV also infected neurons in PML lesions at the GWJ of 54% and GM of 50% patients and in GM outside areas of demyelination in 11% of patients. The JCV regulatory T antigen (Ag) was expressed more frequently in cortical neurons than the VP1 capsid protein. None of the control subjects without PML had any cells expressing JCV proteins. Thus, the cerebral cortex often harbors demyelinating lesions of PML, and JCV infection of cortical neurons is frequent in PML patients. The predominance of T Ag over VP1 expression suggests a restrictive infection in neurons. These results indicate that JCV infection of cerebral cortical neurons is a previously under appreciated component of PML pathogenesis.

JC virus granule cell neuronopathy is associated with VP1 C terminus mutants

The polyomavirus JC (JCV) infects glial cells and causes progressive multifocal leukoencephalopathy (PML). We described a novel JCV-variant with a 10 bp deletion in the C terminus of the VP1 capsid protein, JCV(GCN1). This mutant was associated with lytic infection of cerebellar granule cell neurons and cerebellar atrophy in an human immunodeficiency virus/PML patient. This condition, also observed independently from PML, was named JCV granule cell neuronopathy (JCV GCN). We characterized JCV mutations in cerebrospinal fluid (CSF) of four other JCV GCN patients, and reviewed the literature on 10 reported cases. The strain from one patient harboured the identical GCN1-deletion, while the other patients had novel mutations in the same area, named JCV(GCN2-4), causing variable changes in VP1 structure. One patient also had wild-type JCV in the CSF. To study the mechanisms leading to JCV GCN, we compared viral replication kinetics from JCV(GCN1) with the prototype JCV(Mad1), the PML isolate JCV(HWM) and the prototype JCV(Mad1D) engineered with the GCN1-deletion. While all strains replicated at low levels in the medulloblastoma cell line DAOY from a cerebellar neuronal tumour, JCV(Mad1) replicated better in astroglial SVG cells than JCV(Mad1D) or JCV(GCN1) and all strains replicated at higher levels in COS-7 kidney cells, suggesting that the GCN1-deletion confers a disadvantage for viral growth in central nervous system white matter. The GCN1-deletion remained stable after 100 days in culture and VP1 protein was produced in all cell lines, indicating that JCV(GCN1) is replication-competent in vitro. These data highlight an important and previously overlooked aspect of JCV-pathogenesis. Detection of GCN-type JCV strains in CSF may help clinicians diagnose JCV GCN.

Progressive multifocal leukoencephalopathy and natalizumab

Natalizumab (TYSABRI(®)), a specific α4-integrin antagonist, is approved as a second-line treatment of relapsing-remitting MS (RRMS) patients who fail therapy with interferons or as first-line treatment of patients with highly active relapsing-remitting disease. Since the market introduction of natalizumab as a monotherapy in July of 2006, 111 cases of PML have been reported in natalizumab-treated MS patients as of April 2011. This review focuses on the available data regarding risk stratification for PML under long-term natalizumab therapy, and summarizes the current approach for PML management, as a natalizumab treatment complication is not necessarily associated with a fatal outcome. There is a need for development of surrogate markers that would help to better define the risk of PML in individual patients.

JC virus variant associated with cerebellar atrophy in a patient with AIDS

The human polyomavirus JC virus (JCV) is the agent of progressive multifocal leukoencephalopathy (PML). It has also recently been involved in cerebellar atrophy. Factors involved in this entity are elusive. We present a case of a human immunodeficiency virus (HIV)-infected patient with PML and cerebellar atrophy. In addition to a compartmentalization of JCV strains between urine, cerebrospinal fluid, and cerebellum, specific rearrangements in the JCV regulatory region were observed in the cerebellum, resulting in alterations of transcription factor binding sites. Our data underline the importance of searching for JCV in HIV-infected patients with cerebellar disorders and suggest that mutations in the regulatory region may be involved in cerebellar degeneration.

JC virus infection of the brain

Since its initial description, there have been significant changes in the epidemiology, pathogenesis, and clinical and imaging manifestations of JCV infection of brain. The most common clinical manifestation is PML. Other recently described CNS manifestations are JCE, JCVGCN, and JCM. Although AIDS is the most common predisposing factor for JCV reactivation, there is increasing incidence of brain manifestations of JCV reactivation in non-HIV settings, including different rheumatologic, hematologic, and oncologic conditions; monoclonal antibody therapy; transplant recipients; primary immunodeficiency syndromes; and even in patients without any recognizable immune deficiency. IRIS may develop secondary to restoration of immunity in HIV-positive patients with PML receiving antiretroviral therapy. This is of profound clinical significance and needs to be diagnosed promptly. Imaging plays a crucial role in the diagnosis of the disease, monitoring of treatment response, identifying disease progression, and predicting prognosis. In this article, current understanding of the epidemiology, pathogenesis, clinical presentations, and all aspects of imaging of JCV infection of the brain have been comprehensively reviewed.

Progressive multifocal leukoencephalopathy and other disorders caused by JC virus: clinical features and pathogenesis

Progressive multifocal leukoencephalopathy (PML) is a rare but often fatal brain disease caused by reactivation of the polyomavirus JC. Knowledge of the characteristics of PML has substantially expanded since the introduction of combination antiretroviral therapy during the HIV epidemic and the development of immune reconstitution inflammatory syndrome (IRIS) in patients with PML. Recently, the monoclonal antibodies natalizumab, efalizumab, and rituximab--used for the treatment of multiple sclerosis, psoriasis, haematological malignancies, Crohn's disease, and rheumatic diseases--have been associated with PML. Additionally, the JC virus can also lead to novel neurological disorders such as JC virus granule cell neuronopathy and JC virus encephalopathy, and might also cause meningitis. The increasingly diverse populations at risk and the recent discovery of the presence of the JC virus in the grey matter invite us to reappraise the pathogenesis of this virus in the CNS.

Fulminant JC virus encephalopathy with productive infection of cortical pyramidal neurons

The polyomavirus JC (JCV) is the causative agent of progressive multifocal leukoencephalopathy and of JCV granule cell neuronopathy. We present a human immunodeficiency virus-negative patient who experienced development of multiple cortical lesions, aphasia, and progressive cognitive decline after chemotherapy for non-small-cell lung cancer. Brain biopsy and cerebrospinal fluid polymerase chain reaction demonstrated JCV, and she had a rapidly fatal outcome. Postmortem analysis showed diffuse cortical lesions and areas of necrosis at the gray-white junction. Immunostaining showed a productive JCV infection of cortical pyramidal neurons, confirmed by electron microscopy, with limited demyelination. This novel gray matter syndrome expands the scope of JCV clinical presentation and pathogenesis.

Frequent infection of cerebellar granule cell neurons by polyomavirus JC in progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) occurs most often in immunosuppressed individuals. The lesions of PML result from astrocyte and oligodendrocyte infection by the polyomavirus JC (JCV); JCV has also been shown to infect and destroy cerebellar granule cell neurons (GCNs) in 2 human immunodeficiency virus (HIV)-positive patients. To determine the prevalence and pattern of JCV infection in GCNs, we immunostained formalin-fixed paraffin-embedded cerebellar samples from 40 HIV-positive and 3 HIV-negative PML patients for JCV, and glial and neuronal markers. The JCV infection was detected in 30 patients (70%); 28 (93%) of them had JCV-infected cells in the GC layer; JCV-infected GCNs were demonstrated in 15 (79%) of 19 tested cases. The JCV regulatory T antigen was expressed more frequently and abundantly in GCNs than JCV VP1 capsid protein. None of 37 HIV-negative controls but 1 (3%) of 35 HIV-positive subjects without PML had distinct foci of JCV-infected GCNs. Thus, JCV infection of GCNs is frequent in PML patients and may occur in the absence of cerebellar white matter demyelinating lesions. The predominance of Tantigen over VP1 expression in GCNs suggests that they may be the site of early or latent central nervous system JCV infection. These results indicate that infection of GCNs is an important, previously overlooked, aspect of JCV pathogenesis in immunosuppressed individuals.

Frequent detection of Merkel cell polyomavirus in human Merkel cell carcinomas and identification of a unique deletion in the VP1 gene

Merkel cell carcinoma (MCC) is a rare but very aggressive human malignancy of the elderly or immunosuppressed patients. Recently, the clonal integration of a new human polyoma virus, which was termed Merkel cell polyomavirus (MCPyV), has been reported in 8 of 10 MCC patients. In the present study, we studied the formalin-fixed and paraffin-embedded tissue specimens of 39 MCC for the presence of MCPyV by PCR. We applied four different primer sets directed against the large T antigen and the VP1 gene of MCPyV. We were able to detect MCPyV in 77% (n = 30) of MCC as confirmed by sequence analyses of the PCR products. Sequence analyses showed only minor nucleotide changes compared with the previously published MCC sequences. In addition, one patient revealed the amplification of two PCR products using PCR primers directed against the VP1 gene. Sequence analyses confirmed the presence of the expected 351-bp PCR product and in addition a second PCR product of 261 bp containing a unique 90-bp deletion in the VP1 gene, which will lead to a predicted loss of 28 amino acids. The unique 90-bp deletion within the VP1 gene possibly is a result of incomplete viral integration of MCPyV in the MCC. The presence of MCPyV in the majority of MCC tissue specimens in our study strongly underlines a possible role for MCPyV as an etiologic agent in the carcinogenesis of MCC.

Progressive multifocal leukoencephalopathy revisited: Has the disease outgrown its name?

Nothing is more disappointing for patients than when a promising new treatment hits a roadblock because of unexpected side effects. This is what happened when natalizumab (Tysabri) was associated with a few cases of progressive multifocal leukoencephalopathy (PML) in multiple sclerosis and Crohn's disease patients, caused by the reactivation of the polyomavirus JC. These dramatic events drew PML squarely into the spotlight and generated considerable interest from the medical community, the pharmaceutical industry, financial markets, and regulatory agencies alike. This scrutiny, in turn, helped crystallize areas of consensus and expose gaps in our understanding of PML pathogenesis. Indeed, since its initial description, there has been a considerable evolution in both the epidemiology and clinical presentations of this disease, and new manifestations of central nervous system infection by polyomavirus JC have been characterized. To keep pace with this opportunistic pathogen, we are therefore forced to reexamine the foundations of our knowledge of virus-host interactions, reappraise our investigational approaches, and in short, rethink PML down to its very name. Hopefully, this crisis will be instrumental in helping us define novel avenues of research, develop predictive tests for PML in populations at risk, and challenge us to find a treatment for this deadly disease.