Preparation of monoclonal antibodies to JC virus and their use in the diagnosis of progressive multifocal leucoencephalopathy

Polyomavirus T Antigen Induces APOBEC3B Expression Using an LXCXE-Dependent and TP53-Independent Mechanism

APOBEC3B is a single-stranded DNA cytosine deaminase with beneficial innate antiviral functions. However, misregulated APOBEC3B can also be detrimental by inflicting APOBEC signature C-to-T and C-to-G mutations in genomic DNA of multiple cancer types. Polyomavirus and papillomavirus oncoproteins induce APOBEC3B overexpression, perhaps to their own benefit, but little is known about the cellular mechanisms hijacked by these viruses to do so. Here we investigate the molecular mechanism of APOBEC3B upregulation by the polyomavirus large T antigen. First, we demonstrate that the upregulated APOBEC3B enzyme is strongly nuclear and partially localized to virus replication centers. Second, truncated T antigen (truncT) is sufficient for APOBEC3B upregulation, and the RB-interacting motif (LXCXE), but not the p53-binding domain, is required. Third, genetic knockdown of RB1 alone or in combination with RBL1 and/or RBL2 is insufficient to suppress truncT-mediated induction of APOBEC3B Fourth, CDK4/6 inhibition by palbociclib is also insufficient to suppress truncT-mediated induction of APOBEC3B Last, global gene expression analyses in a wide range of human cancers show significant associations between expression of APOBEC3B and other genes known to be regulated by the RB/E2F axis. These experiments combine to implicate the RB/E2F axis in promoting APOBEC3B transcription, yet they also suggest that the polyomavirus RB-binding motif has at least one additional function in addition to RB inactivation for triggering APOBEC3B upregulation in virus-infected cells.IMPORTANCE The APOBEC3B DNA cytosine deaminase is overexpressed in many different cancers and correlates with elevated frequencies of C-to-T and C-to-G mutations in 5'-TC motifs, oncogene activation, acquired drug resistance, and poor clinical outcomes. The mechanisms responsible for APOBEC3B overexpression are not fully understood. Here, we show that the polyomavirus truncated T antigen (truncT) triggers APOBEC3B overexpression through its RB-interacting motif, LXCXE, which in turn likely modulates the binding of E2F family transcription factors to promote APOBEC3B expression. This work strengthens the mechanistic linkage between active cell cycling, APOBEC3B overexpression, and cancer mutagenesis. Although this mutational mechanism damages cellular genomes, viruses may leverage it to promote evolution, immune escape, and pathogenesis. The cellular portion of the mechanism may also be relevant to nonviral cancers, where genetic mechanisms often activate the RB/E2F axis and APOBEC3B mutagenesis contributes to tumor evolution.

Archetype JC virus efficiently propagates in kidney-derived cells stably expressing HIV-1 Tat

Pathogenic JCV with rearranged regulatory regions (PML-type) causes PML, a demyelinating disease, in the brains of immunocompromised patients. On the other hand, archetype JCV persistently infecting the kidney is thought to be converted to PML-type virus during JCV replication in the infected host under immunosuppressed conditions. In addition, Tat protein, encoded by HIV-1, markedly enhances the expression of a reporter gene under control of the JCV late promoter. In order to examine the influence of Tat on JCV propagation, we used kidney-derived COS-7 cells, which only permit archetype JCV, and established COS-tat cells, which express HIV-1 Tat stably. We found that the extent of archetype JCV propagation in COS-tat cells is significantly greater than in COS-7 cells. On the other hand, COS-7 cells express SV40 T antigen, which is a strong stimulator of archetype JCV replication. The expression of SV40 T antigen was enhanced by HIV-1 Tat slightly according to real-time RT-PCR, this was not closely related to JCV replication in COS-tat cells. The efficiency of JCV propagation depended on the extent of expression of functional Tat. To our knowledge, this is the first report of increased production of archetype JCV in a culture system using cell lines stably expressing HIV-1 Tat. We propose here that COS-tat cells are a useful tool for studying the role of Tat in archetype JCV replication in the development of PML.

Inhibitory effect of serotonin antagonists on JC virus propagation in a carrier culture of human neuroblastoma cells

Human polyomavirus, JCV, causes fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). It has been shown that 5HT(2A)R acts as a cellular receptor for JCV on human glial cells. In the current study, we examined the inhibitory effects of 5HT(2A)R antagonists, ketanserin and ritanserin, both on JCV infection and on propagation by using human neuroblastoma cells IMR-32 and JCI, which continuously produce JCV. Transcriptional analysis revealed that 5HT(2A)R was constitutively expressed in JCI cells. Treatments with 5HT(2A)R antagonists led to a significant reduction in the titers of progeny viruses and the population of infected JCI cells. In addition, the amount of JCV genomic DNA was decreased in JCI cells in the presence of 5HT(2A)R antagonists. These results indicate that 5HT(2A)R antagonists have an inhibitory effect on JCV infection and reproduction, and JCI cells are applicable to an experimental model for pharmacological evaluation of antiviral agents against JCV.

No excess risk for colorectal cancer among subjects seropositive for the JC polyomavirus

The human polyomaviruses JC virus (JCV) and BK virus (BKV) are oncogenic in experimental systems and commonly infect humans. JCV DNA has been reported to be present in human colon mucosa and in colorectal cancers. To investigate whether the risk for colorectal cancer is associated with JCV or BKV infection, we performed a case-control study nested in the Janus biobank, a cohort of 330,000 healthy Norwegian subjects. A 30-year prospective follow-up using registry linkages identified 386 men with colorectal cancer who had baseline serum samples taken >3 months before diagnosis. Control subjects were matched for sex, age and date of blood sampling and county of residence. Seropositivity for JCV or BKV had high (97-100%) sensitivity for detection of viral DNA-positive subjects and discriminated the different polyomaviruses. Seropositivity was mostly stable over time in serial samples. The relative risk for colorectal cancer among JCV seropositive subjects was 0.9 (95% CI: 0.7-1.3) and the BKV-associated relative risk was 1.1 (95% CI: 0.8-1.5). Determining seropositivity using alternative cutoffs also found no evidence of excess risk. In summary, this prospective study found no association between JCV or BKV infections and excess risk for colorectal cancer.

Maternal human polyomavirus infection and risk of neuroblastoma in the child

To investigate if polyomavirus infection during pregnancy is linked to development of neuroblastoma in the child, serum samples of 115 index mothers from the pregnancy where the child eventually developed neuroblastoma were identified and matched with serum samples from 8 control mothers per index mother. The samples were tested for specific IgG and IgM antibodies to BK and JC virus using enzyme immunoassays based on purified yeast-expressed virus-like particles (VLPs). The serum samples as well as 10 neuroblastoma cell lines were also analyzed using Real Time (TaqMan) PCR for detection and quantification of BK virus DNA. The BK virus IgG seroprevalence was similar among index mothers (80%) and control mothers (83%) [OR 0.8; 95% confidence interval (95% CI): 0.5-1.3]. BK virus IgM was also not associated with neuroblastoma risk (OR was OR = 0.6; 95% with CI, 0.2-1.9). Also JC virus had no association, neither for IgG (OR = 0.9; 95% CI, 0.6-1.4) nor for IgM (OR = 0.9; 95% CI, 0.4-1.9). All serum samples and all neuroblastoma cell lines were negative for BKV DNA. In summary, a comprehensive cohort using both serology and polyomavirus DNA detection found no evidence for association between BKV or JCV polyomaviruses and neuroblastoma.

Seroepidemiology of the human polyomaviruses

To assess the stability of polyomavirus antibodies in serial samples over time and the incidence and age-specific prevalence of polyomavirus infections, we established enzyme immunoassays (EIAs) using purified yeast-expressed virus-like particles (VLPs) containing the VP1 major capsid proteins of JC virus (JCV) and the AS and SB strains of BK virus (BKV). A random subsample of 150 Finnish women who had serum samples taken during the first trimester of pregnancy and had a second pregnancy during a 5 year follow-up period was selected, grouped by age of first pregnancy. The polyomavirus antibody levels were similar in samples taken during the first and second pregnancies (correlation coefficient 0.93 for BKV SB and 0.94 for JCV). Analysis of serum samples from 290 Swedish children aged 1-13 years, grouped by age in 2 year intervals, demonstrated that BKV seropositivity increased rapidly with increasing age of the children, reaching 98 % seroprevalence at 7-9 years of age, followed by a minor decrease. JCV seroprevalence increased only slowly with increasing age and reaching 72 % positivity among mothers >25 years of age. The age-specific seroprevalence of the human polyomaviruses measured using this VLP-based EIA was similar to previous serosurveys by other methods. The stability of the antibodies over time indicates that polyomavirus seropositivity is a valid marker of cumulative virus exposure, and polyoma VLP-based EIAs may therefore be useful for epidemiological studies of these viruses.

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

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

Expression and antigenic characterization of the major capsid proteins of human polyomaviruses BK and JC in Saccharomyces cerevisiae

BK and JC viruses are ubiquitous human polyomaviruses that are associated with post-transplant interstitial nephritis (BK virus) and progressive multifocal leucoencephalopathy (JC virus). The use of a yeast system to express the major capsid protein (VP1) of two antigenic variants of BKV (strains SB and AS) and JCV is described. VP1s of AS and JCV expressed in Saccharomyces cerevisiae produced proteins of expected molecular weight as determined by gel electrophoresis whereas that of SB appeared to be lower than anticipated. However, all VP1s self-assembled into virus-like particles (VLP) retaining sialic acid-binding and antigenic properties of native virions. This method is highly efficient for producing recombinant proteins and therefore provides an alternative to the baculovirus system.

Human anti-JC virus serum reacts with native but not denatured JC virus major capsid protein VP1

The immunoreactivity of human anti-JC virus (JCV) serum against the major capsid protein VP1 of JCV was analyzed by Western blot, dot blot, and hemagglutination inhibition (HAI) assays. JCV-positive human serum reacted with native but not denatured JCV major capsid protein VP1, as demonstrated by dot blot and Western blot. Rabbit antiserum raised against native JCV capsid had immunoreactivities similar to those of human anti-JCV serum. These results indicate that the antigenecity of native and denatured JCV VP1 is different. In addition, both JCV-positive human serum and rabbit antiserum raised against native JCV capsid protein inhibited the hemagglutination activity of JCV capsid particles. In contrast, rabbit antiserum raised against denatured JCV VP1 did not inhibit hemagglutination. These findings reveal that denaturation may alter the antigenic epitopes of JCV VP1. Therefore, keeping the JCV capsid protein native appears to be essential for serological or other immunological analyses of the virus.

Antibody against synthetic multiple antigen peptides (MAP) of JC virus capsid protein (VP1) without cross reaction to BK virus: a diagnostic tool for progressive multifocal leukoencephalopathy

Antibody against JC virus (JCV) was raised in rabbits with the use of synthetic multiple antigen peptides. The peptide sequences were derived from three regions of JCV VP1 protein, which showed less similarity with BK virus (BKV) counterpart. The antibodies raised with these peptides were designated as JCAb1, 2 and 3. JCAb1 specifically reacted with JCV and not with BKV, while JCAb2 and 3 reacted both with JCV and BKV. All of these antibodies reacted with JCV antigen of formalin-fixed paraffin sections of progressive multifocal leukoencephalopathy (PML) brain tissue. As JCAb1 is JCV-specific and reacted with JCV in formalin-fixed paraffin sections, it will contribute not only to rapid and accurate immunohistochemical diagnoses of PML but also to clarification of the pathogenesis of JCV infection.

The JC virus antibody response in serum and cerebrospinal fluid in progressive multifocal leucoencephalopathy

BACKGROUND

A clinical diagnosis of progressive multifocal leucoencephalopathy (PML) can be confirmed by histological or virological examination of brain material. Whilst a less invasive method is provided by the detection of JC DNA in cerebrospinal fluid (CSF), very few studies have been done to assess the value of JC virus (JCV) serology in PML diagnosis.

OBJECTIVES

To study the JCV antibody response in the serum and CSF of PML patients.

STUDY DESIGN

A retrospective study was done using haemagglutination inhibition (HI), M-antibody capture radioimmunoassay (MACRIA) and JC-specific oligoclonal IgG banding on one or more sera and/or CSFs from 28 confirmed PML patients. Seventy-one serum and CSF samples were tested from patients with memory loss or dementia as a control group.

RESULTS

Twenty-seven PML patients (96%) had detectable JCV HI antibody in the serum, with titres ranging from 1 : 10 to > 1 : 20480, compared to 48 (68%) of the controls (P = <0.005). JCV IgM antibody was detected in the serum of 12/22 (55%) PML patients. JCV HI antibody was detected in the CSF in 12 of 18 (67%) PML patients, antibody index measurements being used to control for a possible breakdown of the blood-brain barrier. Intrathecal JCV antibody was not found in any control patient. Locally produced JCV-specific IgG bands were detected in the CSF of 7 PML patients tested, confirming the intrathecal origin and specificity of the HI antibody.

CONCLUSIONS

The presence of intrathecal JCV antibody indicates active central nervous system infection with JC virus, and provides a useful diagnostic test for PML, with a sensitivity of 67% and a specificity of 100%. The absence of serum JCV antibody nearly always excludes a diagnosis of PML, but the titre of antibody, IgG or IgM, correlates with the underlying condition rather than the development of neurological symptoms.

Re-evaluation of a case of progressive multifocal leukoencephalopathy previously diagnosed as simian virus 40 (SV40) etiology

A case of progressive multifocal leukoencephalopathy (PML) reported previously to be of simian virus (SV40) etiology was re-evaluated. The supernatant from a 10% homogenate of brain material was inoculated into African green monkey kidney cells and BSC-1 cells which are permissive for SV40. However no cytopathic effect (CPE) developed and no virus was isolated. The brain supernatant agglutinated human group O erythrocytes and contained 5120 units/mL. The Hirt supernatant from the brain contained three DNA bands corresponding to forms I, II and III of circular double-stranded viral DNA. Restriction endonuclease cleavage analysis revealed that this viral DNA was different from SV40 DNA, but similar to JC virus DNA. After cloning of this viral DNA into pBR322 at the BamHI site, DNA homology of this virus and of SV40 was investigated. Cloned DNA from the brain hybridized with all the HpaI/EcoRI fragments of the SV40 genome at the effective temperature of Tm -50 degrees C [corrected]. At Tm -28 degrees C, however, the cloned DNA hybridized with only HpaI/EcoRI fragment B of the SV40 genome. In contrast to this, JC virus DNA hybridized with all five EcoRI/BamHI/HindIII fragments of cloned DNA even at Tm -28 degrees C. Therefore, the causative agent of this PML case was not SV40 but JC virus.

An M-antibody capture radioimmunoassay (MACRIA) for detection of JC virus-specific IgM

A solid-phase M-antibody capture radioimmunoassay (MACRIA) for detecting JC-specific IgM is described. The assay is based on a JC-specific monoclonal antibody (17.7.6) and Nonidet P40-treated, glycine-extracted antigen. MACRIA is more sensitive for JC IgM detection than haemagglutination inhibition (HI) following serum fractionation on a sucrose density gradient, and can be applied to large numbers of sera. The specificity of the assay was confirmed by examining sera from several acute virus infections and also those containing rheumatoid factor. Sera collected from renal transplant recipients with known active JC virus infection were found to contain more than 5 units of JC IgM. In this group of patients JC IgM represents either primary or reactivated JC infection. JC IgM was detected by MACRIA in 15 of 100 unselected blood donors, indicating that JC IgM is frequently produced in healthy seropositive individuals. Thirteen of the 15 sera positive from blood donors contained only low levels of JC IgM (< 5 units), but the specificity of all these results was confirmed in a blocking assay. It is suggested that these low levels of JC IgM may occur in up to 28% of seropositive individuals and result from active JC antigenic stimulation in healthy immunocompetent adults.

PAb 2000 specifically recognizes the large T and small t proteins of JC virus

A monoclonal antibody, PAb 2000, has been derived which recognizes the large T protein of JC virus (JCV), but not the corresponding proteins of the related polyomaviruses BK virus (BKV) and SV40. The epitope bound by PAb 2000 was localized to the amino-terminal 81 amino acids of this multifunctional protein. As observed previously with several monoclonal antibodies that bind a similar region of SV40 large T antigen, PAb 2000 was found to interact with the small t antigen and the denatured form of large T antigen. This monoclonal antibody recognized a subpopulation of T protein, the abundance of which varied in different species of cells transformed by JCV. The availability of PAb 2000, the first JCV T antigen-specific monoclonal antibody, will facilitate the purification and biochemical characterization of the JCV oncoproteins.