Epidemiology : first isolated in 1971 from the brain of a patient with progressive mulifocal leukoencephalopathy (PML)^ref; prevalence of serum antibodies = 35% (rises gradually from 11% among children < 5 years to 50% at 60-69 years). Significantly more males than females have antibody to JCV. In individuals under 40 years of age there was a significant negative association between the presence of antibody to BKV and JCV. There was a significant positive association between the presence of antibody to SV40 and antibody to both BKV and JCV^ref; infecting > 80% of the human population early in life^ref. Lower seroprevalence in NHL patients (49% vs. 59%)^ref, but not associated with NHL^ref. JCV is often transmitted from parents to children. There are at least 14 subtypes of the virus associated with different human populations. Because of its presumed codivergence with humans, JCV has been used as a genetic marker for human evolution and migration^ref.
Genomics : JCV may evolve nearly 2 orders of magnitude faster than predicted under the codivergence hypothesis^ref.

• type 1 is the most common genotype in Europe, occasionally reported in Asia^ref
• type 2 is the most common genotype in Asia

In healthy Irish individuals genotype 1 was the predominant genotype in 62.5%, followed by genotype 4 in 16.7% and genotype 2 in 12.5%. In contrast, genotype 2 was significantly more often isolated from the urine of both HIV-positive patients (60%) and rheumatoid arthritis patients (54.4%; P < .01). The pattern of genotype distribution among healthy Irish individuals is in agreement with data reported from other European countries, whereas the overall level of JCV urinary excretion is lower. Previous studies have found genotype 2 significantly more often in CSF samples of patients with PML. An increased frequency of genotype 2 has also been reported in urine samples of immunocompromised non-PML patients. This finding further underlines the hypothesis that there could be biologic differences between JCV genotypes^ref. JCV has a hyper-variable non-coding transcriptional control region (TCR), which contains the origin of replication and the promoters of viral transcription and replication. The archetype form of TCR-JCV is frequently found in the urine and kidneys of healthy and immunocompromised subjects. However, the rearranged forms, possibly generated by deletion and duplication of segments of the archetype sequence, are found in the peripheral blood, CSF, and brain of PML patients. Most experience on this setting has come from the HIV pandemic. Little has been described on the JCV-TCR sequences from PML-HIV^- patients affected by other immunosuppressive disorders. The aim of this study was to analyze the JCV-TCR detected in CSF samples from 12 HIV^- immunosuppressed patients suffering from PML and to investigate the possible role of genomic organization in the different incidences of PML in HIV⁺ and HIV^- patients. The results confirm that the JCV-TCR rearrangements play a crucial role in the development of PML, although they do not account for the higher frequency of the disease in HIV infection. These data support the hypothesis that, independently of the rearrangement patterns of JCV-TCR, the direct action of HIV together with other as yet unidentified cellular determinants can be a key to explaining the high rate of PML in HIV infection with respect to other underlying immunosuppressive conditions^ref. An NF-1 class member, NF-1X, as a critical transcription factor affecting JCV cellular host range. Within variant JCV promoters, as well as other viral and cellular promoters, adjacently located NF-1 and AP-1 consensus sites are often found. The close proximity of these two binding sites suggests the opportunity for interaction between NF-1 and AP-1 proteins. EMSA showed temporal and dose-dependent interference by an AP-1 family member, c-Jun, upon NF-1 proteins binding an NF-1 consensus site derived from JCV promoter sequence. Moreover, as demonstrated by protein-protein interaction assays, we identify specific binding affinity independent of DNA binding between NF-1X and c-Jun. Finally, to compare the binding profiles of NF-1X and c-Jun on JCV promoter sequence in parallel with in-vivo detection of viral activity levels, an anchored transcriptional promoter (ATP) assay was developed. By using extracts from JCV infected cells transfected to over express either NF-1X or c-Jun, ATP assays showed concurrent increases in NF-1X binding and viral protein expression. Conversely, increased c-Jun binding accompanied decreases in both NF-1X binding and viral protein expression. Therefore, inhibition of NF-1X binding by c-Jun appears to play a role in regulating levels of JCV activity^ref. A new biochemical approach for studying relevant JCV promoter-binding proteins, anchored-JCV transcriptional promoter (ATP) assay, utilizes the product of PCR-amplified JCV promoter sequences coupled with Sepharose beads in order to capture and isolate cellular nuclear proteins with specific promoter-binding affinity for analysis. Proteins that bind to JCV-ATPs can be eluted and subjected to proteomic analysis. Insights from this approach may improve the understanding of viral and cellular parameters that control JCV tropism^ref.
Proteomics :

• receptor : JCV infection of SVG astroglial cells in culture can be mediated in part by serotonergic receptors, in particular 5HT_2a^ref. Anyway SVG-A cells have been previously characterized as astrocyte-derived rather than oligodendrocyte-derived^{ref1, ref2}, and IHC analysis of human and rat CNS tissue reported in the literature has shown that astrocytes express 5HT_2a^{ref1, ref2}; there is as of yet no clear report that oligodendrocytes also express 5HT_2a. Although JCV can infect both astrocytes and oligodendroglia in human patients^ref, productive infection is established in oligodendrocytes, and it is these cells that are predominantly destroyed by the virus. It clearly remains possible and even likely that JCV infection of astrocytes and other 5HT_2a-expressing cells such as vascular endothelial and choroid plexus cells play an important role in the pathogenesis of PML. Primary cultures of oligodendrocytes isolated from adult brain are rare and difficult to obtain. A human oligodendrocyte cell line has not been established^ref.
• the JC virus early mRNA is alternatively spliced to yield 5 transcripts that encode :
• large T antigen : major early regulatory that translocates to the nucleus IRS-1 and interacts with c-Fos and c-Jun. Binding of T-antigen to pRb promotes the activation of the E2F family of transcription factors, which induce the expression of cellular genes required for S phase. In the context of lytic infection, this cell cycle progression is necessary for viral replication because polyomaviruses rely on S phase-specific host factors for their DNA synthesis. In the context of cellular transformation and tumorigenesis, T-antigen/pRB interaction is an indispensable event^ref. It may induce apoptosis in rodent cells, an activity that may be blocked by other JC virus early proteins. T-antigen and agnoprotein, whose expression is detected in 50% of colon carcinomas, interact with b-catenin and may have a role in carcinogenesis. Analyses of JCV TAg phosphorylation mutants indicated that the amino-terminal phosphorylation site at threonine 125 (T125) is critical to TAg replication function. This site is also conserved in the TAg splice variants T'(135), T'(136), and T'(165). By constructing stable cell lines expressing JCV T125A and T125D mutants, it was shown that mutation of this phosphorylation site to alanine generates an unstable TAg; however, the stability of the 3 T' proteins is unaffected. JCV T125A mutant proteins bind the retinoblastoma protein (RB) family members p107 and p130 with slightly reduced efficiencies and fail to induce the release of transcriptionally active E2F from RB-E2F complexes. On the other hand, cell lines expressing JCV T125D mutant proteins produce stable TAg and T' proteins which bind p107 and p130 more efficiently than do the wild-type proteins. In addition, T125D mutant proteins efficiently induce the release of E2F from RB-E2F complexes. T125D mutant cell lines, unlike the T125A mutant lines, continue to grow under conditions of low serum concentration and anchorage independence. Finally, both T125A and T125D mutant viruses are replication defective. Phosphorylation of the T125 site is likely mediated by a cyclin-CDK, suggesting that JCV TAg and T' protein functions that mediate viral replication and oncogenic transformation events are regulated in a cell cycle-dependent manner^ref. Despite much stronger tumorigenic potential, JCV T-antigen positive medulloblastoma cells are more sensitive to genotoxic agents (cisplatin and g-irradiation). Subsequent analysis of DNA repair of DSBs indicated that homologous recombination-directed DNA repair (HRR) was selectively attenuated in JCV T-antigen positive medulloblastoma cells. JCV T-antigen did not affect HRR directly. In the presence of JCV T-antigen, IRS-1 translocated to the nucleus where it co-localized with Rad51, possibly attenuating HRR^ref.
• small t antigen
• T'(135)
• T'(136)
• T'(165)
The splicing process is regulated differentially in transformed versus lytically infected cells and temporally during the course of a productive infection.
• at the late stage of the lytic cycle : structural capsid proteins
• VP1
• VP2
• VP3
• agnoprotein : a small nonstructural protein encoded by the late gene and expressed in the cytoplasmic processes of oligodendrocytes and partly in the astrocytes. It may play a role in the stability of microtubules and the preservation of JCV infected cells via an interaction with tubulin^ref. The late leader peptide region, which encodes agnoprotein, contains important regulatory elements to which transcription factors bind and contribute to the JCV gene regulation and replication^ref. Agnoprotein contains several potential phosphorylation sites, including Ser7, Ser11, and Thr21, which are phosphorylated by PKC : mutation to Ala singly and in combination impairs propagation, while an agnoprotein start codon point (Pt) mutant where agnoprotein expression was completely inhibited is viable but replicates less efficiently than the wild type (WT). Moreover, conservative substitutions at PKC phosphorylation sites (Ser7, Ser11, and Thr21 to Asp) resulted in a viable virus, which further demonstrate the importance of these sites on agnoprotein function. Further analysis of the mutants by viral release assay and electron microscopy studies revealed that viral particles were efficiently released from infected cells and morphologically indistinguishable from those of WT but were deficient in DNA content. This may account for the defective propagation of the mutants. These results imply that phosphorylated forms of agnoprotein may have essential functions in the viral life cycle and serve as potential targets for therapeutic interventions to limit JCV propagation and JCV-induced diseases^ref. Agnoprotein through its N-terminal domain associates with HIV-1 Tat and the interaction causes the suppression of Tat-mediated enhancement of HIV-1 promoter activity in these cells. Results from RNA and protein binding assays showed that agnoprotein can inhibit the association of Tat with its target RNA sequence, TAR, and with cyclin T1. Furthermore, agnoprotein is able to interfere with cross-interaction of Tat with the p65 subunit of NF-kB and Sp1, whose functions are critical for Tat activation of the long terminal repeat. These observations unravel a new pathway for the molecular interaction of these two viruses in biologically relevant cells in the brains of AIDS/PML patients^ref.
• nuclease sensitive element binding protein 1 (NSEP1) interacts with JCV agnoprotein to modulate transcriptional activity of JCV promoters

T' proteins enhance viral DNA replication and bind differentially to the pRB family of cellular tumor suppressor proteins in vitro^ref. DEAD box protein 1 (DDX1), an RNA helicase, and the cleavage stimulation factor (CstF) form a complex that binds to the JC virus transcriptional control region (JCV-TCR)^ref : overexpression of DDX1 significantly increased transactivation of the JCV promoter. Furthermore, DDX1 enhanced the expression of JCV proteins in JCV infected cells^ref.
Transmission : inhalational or oral routes
Pathogenesis : JCV enters cells by clathrin-dependent endocytosis, is transported immediately to early endosomes, and is then sorted to a caveolin-1-positive endosomal compartment. This latter step is dependent on Rab5-GTPase, cholesterol, caveolin-1, and pH^ref. JCV DNA can be detected by PCR amplification from monocytes, granulocytes, and T and B lymphocytes from HIV-1-infected individuals and uninfected controls^ref. In PML patients, JCV can be detected in glial cells in the CNS; in B-lymphocytes in the peripheral blood, bone marrow, spleen, tonsi and CNSl; and in tonsillar stromal cells. In vitro, JCV infects glial cells, tonsillar stromal cells, and to a limited extent B-lymphocytes. The presence or absence of as yet unidentified cell type specific transcription factors^{ref1, ref2} contributes to the restricted tropism of JCV for these cell types^ref. Only 1 or 2 copies of JCV genome exist in a cell based on the time course analysis of PCR. The result that B lymphocytes contained a copy number of JCV genome similar to T lymphocytes suggests that there is some barrier to viral growth in susceptible B lymphocytes, and that the growth of JCV is different from that of other virulent viruses^ref. However, several studies indicate that cell surface receptors may also contribute to the limited host range of JCV : JCV does not bind to primary T cells but binds to the Jurkat T cell line : the majority of infectious JCV virions remain cell surface associated and do not efficiently establish infection of B cells. This may explain the in vivo observation that JCV DNA is frequently detected in association with lymphocytes by PCR but that JCV mRNA is rarely detected in association with lymphocytes by RT-PCR. So B cells may just be involved in trafficking of JCV to the CNS^ref. However other groups reported that both CD34⁺ HSCs and B lymphocytes are susceptible to JCV infection and, moreover, that JCV can infect only those cells that differentiate into lymphocytic lineage^ref : furthermore JCV is able to multiply in either EBV-transformed or EBV negative human B cell lines resulting in production of infectious, progeny virions. In addition, nuclear proteins extracted from these B cells bind to similar nucleotides within the JCV regulatory region that are bound by nuclear proteins extracted from human fetal glial cells, the most susceptible host and principal target cell for JCV infection in vitro. It is not known, however, whether these DNA binding proteins from susceptible B cells and glial cells are similar^ref. Macrophages not only may phagocytize JCV particles but may also be actively infected. Rarely, JCV DNA signals were noted in vascular endothelium^ref. Blood harbored JCV DNA in 31.8% of AIDS patients (vs. 2.3% of healthy blood donors) and urine in 56%. VP1 mRNAs were detected in blood of 1 AIDS patient. Notably, 38% of DNA-positive urine samples and 10 CSF from AIDS patients with PML contained JCV mRNAs. Thus, JCV was significantly more frequent in blood from AIDS patients than from controls, but, in most instances, it was latent, whereas active replication was detected in urine and CSF^ref. The JCV genome was detected in the lymphocytes of 89% of the patients with PML (only 30% of them had JCV detected in CSF), 38% of the HIV-1-seropositive patients without PML, and none of the patients with Parkinson's disease^ref. High titers of antibodies to JCV and BKV,correlate with increased frequency of chromosome aberrations in human lymphocytes, including rogue cell (cells with multiple chromosome-type aberrations)^ref. JCV sequences amplified from urine samples showed a restriction pattern similar to the archetype one, whereas sequences obtained from lymphocytes showed rearranged pattern as well as archetype pattern. Finally all JCV sequences from cerebrospinal fluid seemed to be rearranged. These observations suggest that peripheral blood lymphocytes have a fundamental role in the persistence of polyomaviruses infection and in the dissemination at least of JCV within the organism allowing that rearranged variants, better adapted to grow in brain tissue, emerge^ref. 2 HLA-A*02-restricted epitopes have been identified within the VP1 polypeptide of a human polyomavirus, BK virus, which is associated with polyomavirus-associated nephropathy in kidney transplant patients. Immunization of transgenic mice with recombinant modified vaccinia Ankara expressing BKV VP1 (rMVA-BKV VP1) elicited functional CTL populations recognizing the sequences LLMWEAVTV (amino acids residues 108-116, BKV VP1p108) and AITEVECFL (residues 44-52, BKV VP1p44) and cross-reactive to the previously described JC virus VP1 homologs. Flow-based analyses of PBMC from a panel of thirty healthy HLA-A*02 human volunteers indicated that the majority of these subjects harbored functional CTL populations recognizing the BKV epitopes and cross-reactive with the JCV homologs. CTL recognizing the JCV VP1p100 and JCV VP1p36 epitopes have previously been associated with prolonged survival in progressive multifocal leukoencephalopathy patients. These findings suggest that infection with BKV or JCV could potentially induce cross-protective T-cell immunity against diseases associated with these viruses^ref. In multiple sclerosis patients, CTL response against VP1, the major capsid protein of the polyomavirus JC (JCV), was significantly higher than the one against epitopes of MBP and PLP. The JCV-specific CTL response was also significantly stronger in MS patients than healthy control subjects. These findings may shed a new light on the recent events related to the development of PML in 3 multiple sclerosis patients treated with natalizumab^ref. Since the antibodies to a₄b₁ integrin are known to block cell receptors for murine polyomaviruses at the postattachment level^ref, it is quite possible that natalizumab induces an overwhelming JC viremia in patients by similar mechanisms^ref. Infection with BK virus (BKV) induces both humoral and cellular immunity, but the viral antigens of T-antigen (T-ag) stimulating T-cell responses are largely unknown. To identify BKV-specific T cells in healthy individuals, PBLs were cultured with autologous DCs loaded with BKV lysate and T cells were screened for intracellular IFN-g production after stimulation with an overlapping 15mer peptide library of the BKV T-ag. Among many immunogenic peptides identified, 4 T-ag peptides were identified as candidate MHC class I and II T-cell epitopes, restricted to HLA-B*0702, -B*08, -DRB1*0301 and -DRB1*0901. Further, a candidate 9mer peptide, LPLMRKAYL, was confirmed to be restricted to HLA-B*0702 and -B*08. Because the polyomaviruses BKV, JCV and SV40 share extensive sequence similarity in the immunogenic proteins T-ag and VP1, it was hypothesized that, in humans, these proteins contain conserved CTL target epitopes. 4 HLA-restricted conserved epitopes of BKV, JCV and SV40 were identified: HLA-B*07, -B*08 and -DRB1*0901 for T-ag and -A*0201 for VP1. T cells cultured in vitro that were specific for one viral antigen recognized other conserved epitopes. CTLs generated from BKV T-ag and VP1 peptide were cytotoxic to DC targets pulsed with either BKV or JCV. Therefore, infection by one of the 2 viruses (BKV and JCV) could establish cross-immunity against the other. Although cross-cytotoxicity experiments were not performed with SV40, cross-recognition data from conserved antigen epitopes of polyomaviruses suggest strongly that cross-immunity might also exist among the 3 viruses^ref. Cyclosporin A inhibited JCV infection by preventing the activation of the transcription factor NFAT4. Luciferase reporter assays and ChIP assays revealed that NFAT4 directly bound the JCV promoter during infection, and was important for the activation of both early and late transcription. In addition, expression of the JCV early viral gene products increased NFAT activity to further aid viral transcription. The necessity of NFAT for JCV infection suggests that calcium signalling and the activation of NFAT in glial cells are required for JCV infection of the CNS^ref. The viruses form intranuclear viral inclusions in infected oligodendrocytes. The outer capsid of JCV is thought to be composed of 360 molecules of major capsid protein VP1, and minor capsid proteins VP2 and VP3 in an appropriate ratio. However, the regulatory mechanisms of gene expression for the capsid proteins, their nuclear transport, and formation of viral inclusions are not well understood. Major and minor capsid proteins are synthesized from messenger RNAs, the expression ratio of which is determined by alternative splicing; mRNAs for the major and minor capsid proteins are polycistronic, and their translation occurs downstream of the regulatory protein, agnoprotein; major and minor capsid proteins are translocated to the nucleus in a cooperative manner and accumulate at the dot-shaped intranuclear structures called promyelocytic leukemia nuclear bodies (PML-NBs). Efficient viral replication can occur at the PML-NBs, where capsid assembly is likely to be associated with viral DNA replication. PML-NBs are the sites for expression of important nuclear functions for the host cells. The finding that the target of JCV infection is the PML-NB may contribute greatly to our understanding of the mechanism underlying cellular degeneration, which occurs after the formation of intranuclear viral inclusions^ref.

=> tubulointerstitial nephritis. JCV 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^ref. Reactivation results in ...
=> progressive multifocal leukoencephalopathy (PML)
=> JCV granule cell neuronopathy (JCV GCN) : infection restricted to granule cell neurons of the cerebellum => cerebellar atrophy without white matter lesions^ref. A unique deletion was found in the C terminus of the VP1 gene of JCV(GCN1), which encodes the major capsid protein, resulting in a frame shift and a total change of the C-terminal amino acid sequence of this protein. This deletion was not present in the JCV isolate from the classic PML lesions present in the hemispheric white matter of the same individual, suggesting that this mutation may be instrumental in facilitating entry or replication of JCV into granule cell neurons^ref
=> colon carcinomas (?) : T antigen might be integrated in cancer cells in approximately 25% of Japanese colon cancer cases without clear and diffuse expression of the protein, suggesting a possible role in oncogenesis which might involve a hit-and-run mechanism^ref. Wnt pathway signaling proteins and T-antigen interact to regulate JCV in colonic epithelial cells^ref. JCV can induce chromosomal instability (CIN) in CRC cells. The association between T-Ag expression and promoter methylation in CRC suggests that this viral oncogene may induce methylator phenotype and that JCV may be involved in CRC through multiple mechanisms of genetic and epigenetic instability^ref.
=> gastric carcinoma : 57% of 37 gastric cancers harbored JCV T-Ag sequences, and 13 of 37 gastric cancers (30%) contained VP-1 sequences. T-Ag sequences also were found in adjacent nonneoplastic mucosa. In addition, JCV regulatory region sequences were present frequently in gastric cancers and adjacent nonneoplastic mucosa. T-Ag protein expression was found in 9 of 23 gastric cancers (39%), whereas no expression was observed in any of the nonneoplastic tissues^ref. 22 sample pairs of fresh tumor and adjacent non-cancerous tissue (ANCT) as well as 10 normal gastric mucosa specimens were investigated on the basis of nested PCR followed by Southern blotting, DNA direct sequencing, real-time PCR, in situ PCR and immunohistochemistry. The T antigen sequence was detected in 86.4% of gastric cancers and ANCT, and in 100% of the normal mucosa samples, as for virus capsid protein, 54.1%, 68.1% and 70%, respectively. A generally low incidence was noted for agnoprotein. The JCV DNA load was approximately 10-fold higher in both gastric cancers and paired ANCT (4784 +/- 759 and 5394 +/- 1466 copies/microg DNA, respectively) than in normal gastric tissue (542.4 +/- 476.0 copies/microg DNA, P < 0.0001). In situ PCR revealed sporadic JCV genome-positive cancer cells and foveolar epithelial cells. T antigen protein expression assessed by immunohistochemistry was detected only in one case (1/22; 4.5%), probably because the half life of T antigen might be short. It was concluded that the gastric epithelium in most Japanese people is infected with JCV at a low rate but levels of infection are increased markedly in both cancer cells and ANCT, indicating that multiplication of JCV copies might be a risk factor and a background for gastric carcinogenesis^ref
=> a variety of brain tumors, including medulloblastoma. Paraffin-embedded brain biopsy tissue from 60 neoplasms (55 gliomas and five medulloblastomas) and 15 reactive gliosis cases for the presence of JCV DNA sequences and proteins. 4 post mortem cases of HIV-associated PML were used as positive controls. Samples were assessed by PCR amplification of early (large T antigen) and late (virion protein 3) sequences and immunohistochemistry (IHC) with both PAb 2024 and anti-SV40 large T antigen monoclonal antibodies. 5 cases (3 neoplasms and 2 reactive gliosis instances) showed low viral DNA levels when PCR-tested for VP3 or large T, while no case was immunoreactive for any of the 2 antibodies used. The 4 PML cases yielded positive results with both PCR and IHC. Additionally, IHC with both antibodies was applied to a tissue micro-array including 109 CNS tumours and 21 reactive gliosis samples. No immunoreactivity was detected in any of these tissue micro-array samples. The rarity of JCV DNA sequences and early proteins in our brain tumours enriches the controversy over the role of JCV in human neurooncogenesis, whose clarification is in need of further molecular and epidemiologic studies^ref
Laboratory examinations :

• on MRI, PML lesions typically appear as hyperintense signal on T2-weighted and FLAIR images located in the subcortical white matter, which are devoid of contrast enhancement or mass effect. The prognosis is poor, but unusual inflammatory forms of PML characterized by contrast enhancement have been associated with a cellular immune response against JCV and a better prognosis. An atypical presentation of PML with contrast-enhancing lesions and mass effect on the MRI in a liver transplant recipient, who had a progressive course and fatal outcome, has been reported^ref
• stereotactic cerebral biopsy
• JCV DNA in CSF may be negative in PML patients^ref
• shedding in urine of viral DNA : the rate of BK viruria was relatively low in subjects aged <30 years old, but gradually increased with age in subjects >/=30 years old. However, BK viruria was less frequent than JC viruria in adults. The detected BKV isolates were classified into subtypes and detection rates for individual subtypes were compared among age groups; this analysis showed that viruria of subtypes I (the most prevalent subtype) and IV (the second most prevalent subtype) occurred more frequently in older subjects^ref.
• JC/BK Consensus test : a new commercially available PCR and microplate colorimetric hybridization assay for the standardized differential detection of JCV and BKV genomes in clinical samples. This test was first evaluated by testing serial dilutions of JCV or BKV plasmid DNA standards and was then compared with an in-house reference PCR assay for the detection of JC and BK virus genomes in 70 CSF samples of patients with neurological disorders and in 75 serum or plasma samples and 125 urine samples of renal graft recipients. This new test allowed a limit of detection of 10 copies and 1 copy of JC and BK virus genomes, respectively, and was able to differentiate various levels of JCV, BKV, and mixed JCV and BKV DNA genomes in a single reaction tube. Our results showed 100% specificity and sensitivity for the JC/BK Consensus test with CSF samples. With serum or plasma samples, this test had a sensitivity and a specificity of 100% for both JCV and mixed JCV and BKV DNA detection and a sensitivity and a specificity of 100 and 97.8% for BKV DNA detection, respectively. With urine samples, the sensitivity and specificity were 100 and 96.6%, respectively, for JCV DNA detection; 100 and 89.4%, respectively, for BKV DNA detection; and 44.4 and 100%, respectively, for mixed JCV and BKV DNA detection. This new test, the JC/BK Consensus test, is valuable for the sensitive and specific differential detection of single JCV and BKV infections in CSF, serum or plasma, and urine samples. The use of this reliable PCR assay would improve the routine virological diagnosis as well as the clinical care of immunocompromised patients with polyomavirus-related pathologies^ref. Nested PCR whose amplicons should be confirmed by Southern blot and sequencing was a comparatively sensitive approach to detect JCV genomic DNA in human non-neural tissues. Real-time PCR might be employed to quantify copy number of JCV. In situ PCR was a good method to observe the JCV location in cells, given appropriate modulation of amplification cycles^ref.
• an antibody to SV40 TAg (PAb416), which cross-reacts with TAgs of both JCV and BKV, has been used widely for the detection of JCV and BKV TAgs. As a consequence, it is difficult to discriminate between the TAgs of SV40, BKV and JCV by immunohistochemical analyses. JCV TAg-specific polyclonal antibodies (JCT629 and JCT652) have been generated by immunization of New Zealand white rabbits with synthetic peptides reproducing the JCV TAg carboxyl-terminal region as immunogens. Immunoblotting analyses indicated that the new antibodies bind specifically to JCV TAg, and not to those of SV40 or BKV. We also demonstrated that these antibodies can be used for immunoprecipitation, immunocytochemical analyses and immunohistochemical staining of routinely processed specimens^ref

Therapy :

• discontinuation of iatrogenic immunosuppression (not always feasible)^ref
• HAART remains the only partially effective treatment option : mortality has decreased from 90% to approximately 50% during the first 3 months as a result of recovery of the immune system^ref. However, in rare instances, an immune-reconstitution inflammatory syndrome (IRIS) may cause paradoxical clinical deterioration despite raising CD4⁺ counts and decreasing HIV load, due to an imbalance of CD8⁺/CD4⁺ T cells, with massive infiltration of the cerebral parenchyma by CD8⁺ CTLs in the absence of sufficient CD4⁺ response^ref.
• cytosine arabinoside has been shown to have in vitro activity against JCV^ref. 19 patients with PML proven by brain biopsy or spinal fluid PCR were treated with i.v. araC 2 mg/kg per day for 5 days and followed for neurologic outcome by neurologic examination and MRI scanning. 7 of 19 PML patients treated with cytosine arabinoside intravenously improved neurologically. The range of follow-up for these patients was 2.0 to 4.5 years. All were left with neurologic deficits but were functionally improved, and 6 of 7 were able to independently carry out the activities of daily living. 12 PML patients showed no evidence of response and died rapidly of their disease after treatment (range, 8 days to 6 months). All who survived their neurologic disease recovered from treatment-induced pancytopenia. Cytosine arabinoside given i.v. to non-AIDS PML patients in this small study was associated with a 36% chance of developing stabilization at 1 year. Treatment was associated with significant bone marrow toxicity. The improvement in MRI scan changes in those patients who responded took 6 weeks or longer^ref.
• the finding of 5HT_2a as a a receptor is potentially of great clinical importance, as it suggests that serotonin receptor antagonists may be useful in the treatment of PML. In vitro they used the older antipsychotic medications chlorpromazine and clozapine to block the serotonin 5HT_2a receptor and block JC virus cell entry. Unfortunately, however, chlorpromazine and clozapine have such significant side effects and toxicities, e.g., extrapyramidal symptoms and the possibility of bone marrow dyscrasias - that they may be problematic to use clinically. Some newer atypical antipsychotics such as ziprasidone, risperidone and olanzapine--medicines with much better side effect and toxicity profiles than the older antipsychotics--in vitro are significantly more potent 5HT_2a antagonists than chlorpromazine or clozapine by in some cases more than a factor of 10, and thus may be useful as treatment for or prophylaxis against PML^ref
• IFN-b treatment in monotherapy has not any effect on JCV active replication^ref
• several anticonvulsants, amantadine, acyclovir, and ganciclovir^ref