Immune sensing of mouse polyomavirus DNA by p204 and cGAS DNA sensors

The mechanism by which DNA viruses interact with different DNA sensors and their connection with the activation of interferon (IFN) type I pathway are poorly understood. We investigated the roles of protein 204 (p204) and cyclic guanosine-adenosine synthetase (cGAS) sensors during infection with mouse polyomavirus (MPyV). The phosphorylation of IFN regulatory factor 3 (IRF3) and the stimulator of IFN genes (STING) proteins and the upregulation of IFN beta (IFN-β) and MX Dynamin Like GTPase 1 (MX-1) genes were detected at the time of replication of MPyV genomes in the nucleus. STING knockout abolished the IFN response. Infection with a mutant virus that exhibits defective nuclear entry via nucleopores and that accumulates in the cytoplasm confirmed that replication of viral genomes in the nucleus is required for IFN induction. The importance of both DNA sensors, p204 and cGAS, in MPyV-induced IFN response was demonstrated by downregulation of the IFN pathway observed in p204-knockdown and cGAS-knockout cells. Confocal microscopy revealed the colocalization of p204 with MPyV genomes in the nucleus. cGAS was found in the cytoplasm, colocalizing with viral DNA leaked from the nucleus and with DNA within micronucleus-like bodies, but also with the MPyV genomes in the nucleus. However, 2'3'-Cyclic guanosine monophosphate-adenosine monophosphate synthesized by cGAS was detected exclusively in the cytoplasm. Biochemical assays revealed no evidence of functional interaction between cGAS and p204 in the nucleus. Our results provide evidence for the complex interactions of MPyV and DNA sensors including the sensing of viral genomes in the nucleus by p204 and of leaked viral DNA and micronucleus-like bodies in the cytoplasm by cGAS.

Vaccination with Prion Peptide-Displaying Polyomavirus-Like Particles Prolongs Incubation Time in Scrapie-Infected Mice

Prion diseases like scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle or Creutzfeldt–Jakob disease (CJD) in humans are fatal neurodegenerative diseases characterized by the conformational conversion of the normal, mainly α-helical cellular prion protein (PrP^C) into the abnormal β-sheet rich infectious isoform PrP^Sc. Various therapeutic or prophylactic approaches have been conducted, but no approved therapeutic treatment is available so far. Immunisation against prions is hampered by the self-tolerance to PrP^C in mammalian species. One strategy to avoid this tolerance is presenting PrP variants in virus-like particles (VLPs). Therefore, we vaccinated C57/BL6 mice with nine prion peptide variants presented by hamster polyomavirus capsid protein VP1/VP2-derived VLPs. Mice were subsequently challenged intraperitoneally with the murine RML prion strain. Importantly, one group exhibited significantly increased mean survival time of 240 days post-inoculation compared with 202 days of the control group. These data show that immunisation with VLPs presenting PrP peptides may represent a promising strategy for an effective vaccination against transmissible spongiform encephalitis agents.

Antibody escape by polyomavirus capsid mutation facilitates neurovirulence

JCPyV polyomavirus, a member of the human virome, causes progressive multifocal leukoencephalopathy (PML), an oft-fatal demyelinating brain disease in individuals receiving immunomodulatory therapies. Mutations in the major viral capsid protein, VP1, are common in JCPyV from PML patients (JCPyV-PML) but whether they confer neurovirulence or escape from virus-neutralizing antibody (nAb) in vivo is unknown. A mouse polyomavirus (MuPyV) with a sequence-equivalent JCPyV-PML VP1 mutation replicated poorly in the kidney, a major reservoir for JCPyV persistence, but retained the CNS infectivity, cell tropism, and neuropathology of the parental virus. This mutation rendered MuPyV resistant to a monoclonal Ab (mAb), whose specificity overlapped the endogenous anti-VP1 response. Using cryo-EM and a custom sub-particle refinement approach, we resolved an MuPyV:Fab complex map to 3.2 Å resolution. The structure revealed the mechanism of mAb evasion. Our findings demonstrate convergence between nAb evasion and CNS neurovirulence in vivo by a frequent JCPyV-PML VP1 mutation.

Effect of the Large and Small T-Antigens of Human Polyomaviruses on Signaling Pathways

Viruses are intracellular parasites that require a permissive host cell to express the viral genome and to produce new progeny virus particles. However, not all viral infections are productive and some viruses can induce carcinogenesis. Irrespective of the type of infection (productive or neoplastic), viruses hijack the host cell machinery to permit optimal viral replication or to transform the infected cell into a tumor cell. One mechanism viruses employ to reprogram the host cell is through interference with signaling pathways. Polyomaviruses are naked, double-stranded DNA viruses whose genome encodes the regulatory proteins large T-antigen and small t-antigen, and structural proteins that form the capsid. The large T-antigens and small t-antigens can interfere with several host signaling pathways. In this case, we review the interplay between the large T-antigens and small t-antigens with host signaling pathways and the biological consequences of these interactions.

Loss of amphiregulin reduces myoepithelial cell coverage of mammary ducts and alters breast tumor growth

BACKGROUND

Amphiregulin (AREG), a ligand of the epidermal growth factor receptor, is not only essential for proper mammary ductal development, but also associated with breast cancer proliferation and growth. In the absence of AREG, mammary ductal growth is stunted and fails to expand. Furthermore, suppression of AREG expression in estrogen receptor-positive breast tumor cells inhibits in-vitro and in-vivo growth.

METHODS

We crossed AREG-null (AREG-/-) mice with the murine luminal B breast cancer model, MMTV-PyMT (PyMT), to generate spontaneous breast tumors that lack AREG (AREG-/- PyMT). We evaluated tumor growth, cytokeratin-8 (K8)-positive luminal cells, cytokeratin-14 (K14)-positive myoepithelial cells, and expression of AREG, Ki67, and PyMT. Primary myoepithelial cells from nontumor-bearing AREG+/+ mice underwent fluorescence-activated cell sorting and were adapted to culture for in-vitro coculture studies with AT-3 cells, a cell line derived from C57Bl/6 PyMT mammary tumors.

RESULTS

Intriguingly, PyMT-induced lesions progress more rapidly in AREG-/- mice than in AREG+/+ mice. Quantification of K8+ luminal and K14+ myoepithelial cells in non-PyMT AREG-/- mammary glands showed fewer K14+ cells and a thinner myoepithelial layer. Study of AT-3 cells indicated that coculture with myoepithelial cells or exposure to AREG, epidermal growth factor, or basic fibroblast growth factor can suppress PyMT expression. Late-stage AREG-/- PyMT tumors are significantly less solid in structure, with more areas of papillary and cystic growth. Papillary areas appear to be both less proliferative and less necrotic. In The Cancer Genome Atlas database, luminal-B invasive papillary carcinomas have lower AREG expression than luminal B invasive ductal carcinomas.

CONCLUSIONS

Our study has revealed a previously unknown role of AREG in myoepithelial cell development and PyMT expression. AREG expression is essential for proper myoepithelial coverage of mammary ducts. Both AREG and myoepithelial cells can suppress PyMT expression. We find that lower AREG expression is associated with invasive papillary breast cancer in both the MMTV-PyMT model and human breast cancer.

Seroprevalence of fourteen human polyomaviruses determined in blood donors

The polyomavirus family currently includes thirteen human polyomavirus (HPyV) species. In immunocompromised and elderly persons HPyVs are known to cause disease, such as progressive multifocal leukoencephalopathy (JCPyV), haemorrhagic cystitis and nephropathy (BKPyV), Merkel cell carcinoma (MCPyV), and trichodysplasia spinulosa (TSPyV). Some recently discovered polyomaviruses are of still unknown prevalence and pathogenic potential. Because HPyVs infections persist and might be transferred by blood components to immunocompromised patients, we studied the seroprevalence of fourteen polyomaviruses in adult Dutch blood donors. For most polyomaviruses the observed seroprevalence was high (60–100%), sometimes slightly increasing or decreasing with age. Seroreactivity increased with age for JCPyV, HPyV6 and HPyV7 and decreased for BKPyV and TSPyV. The most recently identified polyomaviruses HPyV12, NJPyV and LIPyV showed low overall seroprevalence (~5%) and low seroreactivity, questioning their human tropism. Altogether, HPyV infections are common in Dutch blood donors, with an average of nine polyomaviruses per subject.

Exploitation of stable nanostructures based on the mouse polyomavirus for development of a recombinant vaccine against porcine circovirus 2

The aim of this study was to develop a suitable vaccine antigen against porcine circovirus 2 (PCV2), the causative agent of post-weaning multi-systemic wasting syndrome, which causes significant economic losses in swine breeding. Chimeric antigens containing PCV2b Cap protein sequences based on the mouse polyomavirus (MPyV) nanostructures were developed. First, universal vectors for baculovirus-directed production of chimeric MPyV VLPs or pentamers of the major capsid protein, VP1, were designed for their exploitation as vaccines against other pathogens. Various strategies were employed based on: A) exposure of selected immunogenic epitopes on the surface of MPyV VLPs by insertion into a surface loop of the VP1 protein, B) insertion of foreign protein molecules inside the VLPs, or C) fusion of a foreign protein or its part with the C-terminus of VP1 protein, to form giant pentamers of a chimeric protein. We evaluated these strategies by developing a recombinant vaccine against porcine circovirus 2. All candidate vaccines induced the production of antibodies against the capsid protein of porcine circovirus after immunization of mice. The candidate vaccine, Var C, based on fusion of mouse polyomavirus and porcine circovirus capsid proteins, could induce the production of antibodies with the highest PCV2 neutralizing capacity. Its ability to induce the production of neutralization antibodies was verified after immunization of pigs. The advantage of this vaccine, apart from its efficient production in insect cells and easy purification, is that it represents a DIVA (differentiating infected from vaccinated animals) vaccine, which also induces an immune response against the mouse polyoma VP1 protein and is thus able to distinguish between vaccinated and naturally infected animals.

In Vitro and In Vivo Models for the Study of Human Polyomavirus Infection

Developments of genome amplification techniques have rapidly expanded the family of human polyomaviruses (PyV). Following infection early in life, PyV persist in their hosts and are generally of no clinical consequence. High-level replication of PyV can occur in patients under immunosuppressive or immunomodulatory therapy and causes severe clinical entities, such as progressive multifocal leukoencephalopathy, polyomavirus-associated nephropathy or Merkel cell carcinoma. The characterization of known and newly-discovered human PyV, their relationship to human health, and the mechanisms underlying pathogenesis remain to be elucidated. Here, we summarize the most widely-used in vitro and in vivo models to study the PyV-host interaction, pathogenesis and anti-viral drug screening. We discuss the strengths and limitations of the different models and the lessons learned.

Seroepidemiology of Human Polyomaviruses in a US Population

Polyomaviruses (PyV) are potentially tumorigenic in humans. However, limited data exist on the population seroprevalence of PyVs and individual characteristics that relate to seropositivity. Using multiplex serology, we determined the seroprevalence of 10 human PyVs (BK, JC, KI, WU, MCV, HPyV6, HPyV7, TSV, HPyV9, and HPyV10) among controls from a population-based skin cancer case-control study (n = 460) conducted in New Hampshire between 1993 and 1995. On a subset of participants (n = 194), methylation at CpG dinucleotides across the genome was measured in peripheral blood using the Illumina Infinium HumanMethylation27 BeadChip array (Illumina Inc., San Diego, California), from which lymphocyte subtype proportions were inferred. All participants were seropositive for at least 1 PyV, with seroprevalences ranging from 17.6% (HPyV9) to 99.1% (HPyV10). Seropositivity to JC, MCV, and HPyV7 increased with age. JC and TSV seropositivity were more common among men than among women. Smokers were more likely to be HPyV9-seropositive but MCV-seronegative, and HPyV7 seropositivity was associated with prolonged glucocorticoid use. Based on DNA methylation profiles, differences were observed in CD8-positive T- and B-cell proportions by BK, JC, and HPyV9 seropositivity. Our findings suggest that PyV seropositivity is common in the United States and varies by sociodemographic and biological characteristics, including those related to immune function.

Ganglioside and Non-ganglioside Mediated Host Responses to the Mouse Polyomavirus

Gangliosides serve as receptors for internalization and infection by members of the polyomavirus family. Specificity is determined by recognition of carbohydrate moieties on the ganglioside by the major viral capsid protein VP1. For the mouse polyomavirus (MuPyV), gangliosides with terminal sialic acids in specific linkages are essential. Although many biochemical and cell culture experiments have implicated gangliosides as MuPyV receptions, the role of gangliosides in the MuPyV-infected mouse has not been investigated. Here we report results of studies using ganglioside-deficient mice and derived cell lines. Knockout mice lacking complex gangliosides were completely resistant to the cytolytic and pathogenic effects of the virus. Embryo fibroblasts from these mice were likewise resistant to infection, and supplementation with specific gangliosides restored infectibility. Although lacking receptors for viral infection, cells from ganglioside-deficient mice retained the ability to respond to the virus. Ganglioside-deficient fibroblasts responded rapidly to virus exposure with a transient induction of c-fos as an early manifestation of a mitogenic response. Additionally, splenocytes from ganglioside-deficient mice responded to MuPyV by secretion of IL-12, previously recognized as a key mediator of the innate immune response. Thus, while gangliosides are essential for infection in the animal, gangliosides are not required for mitogenic responses and innate immune responses to the virus.

Biological and structural studies have combined to give a detailed understanding of how the mouse polyomavirus binds to sialyloligosaccharides, how polymorphisms in the sialic acid binding pocket of the major virus capsid protein constitute important determinants of pathogenicity, and how gangliosides function as receptors for cell entry and infection by the virus. We used mice with knockouts in defined ganglioside biosynthetic pathways to determine whether gangliosides alone suffice to mediate lethal infection in the intact host and whether non-gangliosides are also recognized by the virus and utilized for important physiological responses. We confirmed the requirement of specific gangliosides for infection and determined that not all gangliosides that bind in vitro serve as receptors in vivo. Results also revealed two physiologically important responses that do not require MuPyV-ganglioside interactions: i) rapid induction of c-fos in fibroblasts as an early step in cell cycle progression on which the virus depends for its own replication, and ii). activation of cytokine secretion by antigen presenting cells as a critical innate immune response to the virus. We infer that these responses are mediated by non-ganglioside receptors bearing sialic acid. These results serve to illustrate the multiplicity of MuPyV receptors and the complexity of virus-cell surface interactions.

Neoplastic transformation of porcine mammary epithelial cells in vitro and tumor formation in vivo

BACKGROUND

The mammary glands of pigs share many functional and morphological similarities with the breasts of humans, raising the potential of their utility for research into the mechanisms underlying normal mammary function and breast carcinogenesis. Here we sought to establish a model for the efficient manipulation and transformation of porcine mammary epithelial cells (pMEC) in vitro and tumor growth in vivo.

METHODS

We utilized a vector encoding the red florescent protein tdTomato to transduce populations of pMEC from Yorkshire -Hampshire crossbred female pigs in vitro and in vivo. Populations of primary pMEC were then separated by FACS using markers to distinguish epithelial cells (CD140a-) from stromal cells (CD140a+), with or without further enrichment for basal and luminal progenitor cells (CD49f+). These separated pMEC populations were transduced by lentivirus encoding murine polyomavirus T antigens (Tag) and tdTomato and engrafted to orthotopic or ectopic sites in immunodeficient NOD.Cg-Prkdc (scid) Il2rg (tm1Wjl) /SzJ (NSG) mice.

RESULTS

We demonstrated that lentivirus effectively transduces pMEC in vitro and in vivo. We further established that lentivirus can be used for oncogenic-transformation of pMEC ex vivo for generating mammary tumors in vivo. Oncogenic transformation was confirmed in vitro by anchorage-independent growth, increased cell proliferation, and expression of CDKN2A, cyclin A2 and p53 alongside decreased phosphorylation of Rb. Moreover, Tag-transformed CD140a- and CD140a-CD49f + pMECs developed site-specific tumors of differing histopathologies in vivo.

CONCLUSIONS

Herein we establish a model for the transduction and oncogenic transformation of pMEC. This is the first report describing a porcine model of mammary epithelial cell tumorigenesis that can be applied to the study of human breast cancers.

Common exposure to STL polyomavirus during childhood

STL polyomavirus (STLPyV) was recently identified in human specimens. To determine seropositivity for STLPyV, we developed an ELISA and screened patient samples from 2 US cities (Denver, Colorado [500]; St. Louis, Missouri [419]). Overall seropositivity was 68%–70%. The age-stratified data suggest that STLPyV infection is widespread and commonly acquired during childhood.

Diagnostic methods for and clinical pictures of polyomavirus primary infections in children, Finland

We used comprehensive serodiagnostic methods (IgM, IgG, and IgG avidity) and PCR to study Merkel cell polyomavirus and trichodysplasia spinulosa-associated polyomavirus infections in children observed from infancy to adolescence. Comparing seroconversion intervals with previous and subsequent intervals, we found that primary infections with these 2 viruses were asymptomatic in childhood.

Halofuginone inhibits tumor growth in the polyoma middle T antigen mouse via a thrombospondin-1 independent mechanism

Halofuginone inhibits fibrosis by decreasing type I collagen synthesis and tumor growth through an anti-angiogenic mechanism. In vitro data suggested that halofuginone inhibits angiogenesis through upregulating thrombospondin-1 (TSP-1) expression and by inhibiting cell proliferation. To determine whether thrombospondin-1 (TSP-1) is necessary for inhibition of tumor growth and angiogenesis by halofuginone, we tested the effect of halofuginone on mammary tumor growth in polyoma middle T antigen, TSP-1 null (TSP-1-/-PyT) transgenic mice. After 30 days of treatment, we found a significant decrease in tumor weight in these mice and the extent of tumor growth inhibition was comparable to that found in TSP-1 expressing PyT mice (TSP-1+/+PyT). However, no significant difference in tumor weight was observed after 60 days of halofuginone treatment between control and treated mice in both genotypes. Interestingly, type I collagen level was lower in the halofuginone treated TSP-1+/+PyT tumors at 30 days, but this was not observed in the TSP-1-/-PyT mice. Levels of type I collagen did not correlate with blood vessel number as a decrease in the number of vessels was observed in the halofuginone treated tumors from both the TSP-1+/+PyT and TSP-1-/-PyT mice as compared to control tumors. Because halofuginone has been shown to inhibit type I collagen synthesis by inhibiting the TGF-beta signaling pathway, we measured Smad 2/3 phosphorylation levels and found that halofuginone inhibited Smad 2/3 phosphorylation in cells derived from TSP-1+/+PyT tumors. We also found that it inhibited Smad 2/3 phosphorylation in cells treated with the TGF-beta activating sequence of TSP-1, TSR2+RFK. Our data demonstrate that halofuginone inhibits mammary tumor growth in a transgenic mouse model via a TSP-1 independent pathway, by decreasing tumor angiogenesis and by inhibiting TGF-beta signaling.

Serological cross-reactivity between Merkel cell polyomavirus and two closely related chimpanzee polyomaviruses

Phylogenetic analyses based on the major capsid protein sequence indicate that Merkel cell polyomavirus (MCPyV) and chimpanzee polyomaviruses (PtvPyV1, PtvPyV2), and similarly Trichodysplasia spinulosa-associated polyomavirus (TSPyV) and the orangutan polyomavirus (OraPyV1) are closely related. The existence of cross-reactivity between these polyomaviruses was therefore investigated. The findings indicated serological identity between the two chimpanzee polyomaviruses investigated and a high level of cross-reactivity with Merkel cell polyomavirus. In contrast, cross-reactivity was not observed between TSPyV and OraPyV1. Furthermore, specific antibodies to chimpanzee polyomaviruses were detected in chimpanzee sera by pre-incubation of sera with the different antigens, but not in human sera.

Structures of B-lymphotropic polyomavirus VP1 in complex with oligosaccharide ligands

B-Lymphotropic Polyomavirus (LPyV) serves as a paradigm of virus receptor binding and tropism, and is the closest relative of the recently discovered Human Polyomavirus 9 (HPyV9). LPyV infection depends on sialic acid on host cells, but the molecular interactions underlying LPyV-receptor binding were unknown. We find by glycan array screening that LPyV specifically recognizes a linear carbohydrate motif that contains α2,3-linked sialic acid. High-resolution crystal structures of the LPyV capsid protein VP1 alone and in complex with the trisaccharide ligands 3′-sialyllactose and 3′-sialyl-N-acetyl-lactosamine (3SL and 3SLN, respectively) show essentially identical interactions. Most contacts are contributed by the sialic acid moiety, which is almost entirely buried in a narrow, preformed cleft at the outer surface of the capsid. The recessed nature of the binding site on VP1 and the nature of the observed glycan interactions differ from those of related polyomaviruses and most other sialic acid-binding viruses, which bind sialic acid in shallow, more exposed grooves. Despite their different modes for recognition, the sialic acid binding sites of LPyV and SV40 are half-conserved, hinting at an evolutionary strategy for diversification of binding sites. Our analysis provides a structural basis for the observed specificity of LPyV for linear glycan motifs terminating in α2,3-linked sialic acid, and links the different tropisms of known LPyV strains to the receptor binding site. It also serves as a useful template for understanding the ligand-binding properties and serological crossreactivity of HPyV9.

Viruses must engage specific receptors on host cells in order to initiate infection. The type of receptor and its concentration on cells determine viral spread and tropism, but for many viruses, the receptor and the mode of recognition by the virus are not known. We have characterized the structural requirements for receptor binding of B-lymphotropic polyomavirus (LPyV). This virus was originally isolated from African Green Monkey lymph node cultures and attracted interest because of its narrow tropism for a human tumor cell line. LPyV is also the closest relative of the recently discovered Human Polyomavirus 9 (HPyV9). We screened the LPyV coat protein VP1 on an carbohydrate microarray and found that it specifically recognizes a linear sugar motif that terminates in α2,3-linked sialic acid. We then determined the structures LPyV VP1 bound to these carbohydrates. The protein has a preformed, deeply recessed binding site for sialic acid. The binding site differs in both architecture and mode of recognition from the binding sites of other viruses. LPyV only binds linear carbohydrates that are able to penetrate into the binding slot.

Identification of a novel human polyomavirus in organs of the gastrointestinal tract

Polyomaviruses are small, non-enveloped viruses with a circular double-stranded DNA genome. Using a generic polyomavirus PCR targeting the VP1 major structural protein gene, a novel polyomavirus was initially identified in resected human liver tissue and provisionally named Human Polyomavirus 12 (HPyV12). Its 5033 bp genome is predicted to encode large and small T antigens and the 3 structural proteins VP1, VP2 and VP3. Phylogenetic analyses did not reveal a close relationship to any known human or animal polyomavirus. Investigation of organs, body fluids and excretions of diseased individuals and healthy subjects with both HPyV12-specific nested PCR and quantitative real-time PCR revealed additional virus-positive samples of resected liver, cecum and rectum tissues and a positive fecal sample. A capsomer-based IgG ELISA was established using the major capsid protein VP1 of HPyV12. Seroprevalences of 23% and 17%, respectively, were determined in sera from healthy adults and adolescents and a pediatric group of children. These data indicate that the virus naturally infects humans and that primary infection may already occur in childhood.

The rapidly expanding family of human polyomaviruses: recent developments in understanding their life cycle and role in human pathology

Since their discovery in 1971, the polyomaviruses JC (JCPyV) and BK (BKPyV), isolated from patients with progressive multifocal leukoencephalopathy and polyomavirus-associated nephropathy, respectively, remained for decades as the only known members of the Polyomaviridae family of viruses of human origin. Over the past five years, the application of new genomic amplification technologies has facilitated the discovery of several novel human polyomaviruses (HPyVs), bringing the present number to 10. These HPyVs share many fundamental features in common such as genome size and organization. Infection by all HPyVs is widespread in the human population, but they show important differences in their tissue tropism and association with disease. Much remains unknown about these new viruses. In this review, we discuss the problems associated with studying HPyVs, such as the lack of culture systems for the new viruses and the gaps in our basic understanding of their biology. We summarize what is known so far about their distribution, life cycle, tissue tropism, their associated pathologies (if any), and future research directions in the field.

Murine polyomavirus virus-like particles carrying full-length human PSA protect BALB/c mice from outgrowth of a PSA expressing tumor

Virus-like particles (VLPs) consist of capsid proteins from viruses and have been shown to be usable as carriers of protein and peptide antigens for immune therapy. In this study, we have produced and assayed murine polyomavirus (MPyV) VLPs carrying the entire human Prostate Specific Antigen (PSA) (PSA-MPyVLPs) for their potential use for immune therapy in a mouse model system. BALB/c mice immunized with PSA-MPyVLPs were only marginally protected against outgrowth of a PSA-expressing tumor. To improve protection, PSA-MPyVLPs were co-injected with adjuvant CpG, either alone or loaded onto murine dendritic cells (DCs). Immunization with PSA-MPyVLPs loaded onto DCs in the presence of CpG was shown to efficiently protect mice from tumor outgrowth. In addition, cellular and humoral immune responses after immunization were examined. PSA-specific CD4⁺ and CD8⁺ cells were demonstrated, but no PSA-specific IgG antibodies. Vaccination with DCs loaded with PSA-MPyVLPs induced an eight-fold lower titre of anti-VLP antibodies than vaccination with PSA-MPyVLPs alone. In conclusion, immunization of BALB/c mice with PSA-MPyVLPs, loaded onto DCs and co-injected with CpG, induces an efficient PSA-specific tumor protective immune response, including both CD4⁺ and CD8⁺ cells with a low induction of anti-VLP antibodies.

NK cells and gammadelta T cells mediate resistance to polyomavirus-induced tumors

NK and γδ T cells can eliminate tumor cells in many experimental models, but their effect on the development of tumors caused by virus infections in vivo is not known. Polyomavirus (PyV) induces tumors in neonatally infected mice of susceptible strains and in adult mice with certain immune deficiencies, and CD8+ αβ T cells are regarded as the main effectors in anti-tumor immunity. Here we report that adult TCRβ knockout (KO) mice that lack αβ but have γδ T cells remain tumor-free after PyV infection, whereas TCRβ×δ KO mice that lack all T cells develop tumors. In addition, E26 mice, which lack NK and T cells, develop the tumors earlier than TCRβ×δ KO mice. These observations implicate γδ T and NK cells in the resistance to PyV-induced tumors. Cell lines established from PyV-induced tumors activate NK and γδ T cells both in culture and in vivo and express Rae-1, an NKG2D ligand. Moreover, these PyV tumor cells are killed by NK cells in vitro, and this cytotoxicity is prevented by treatment with NKG2D-blocking antibodies. Our findings demonstrate a protective role for NK and γδ T cells against naturally occurring virus-induced tumors and suggest the involvement of NKG2D-mediated mechanisms.

Virus-induced tumors account for a large fraction of malignancies in both humans and mice. These tumors express viral antigens and have been thought to be controlled mostly by αβ TCR+ CD8 T lymphocytes that are specific for viral peptides. We found that mice lacking αβ T cells are protected from the formation of tumors induced by the small DNA virus polyoma (PyV) if they have γδ T and NK cells. Moreover, cell lines we established from the virus-induced tumors induced NK and γδ T cell activation, and expressed Rae-1, a cellular stress molecule which serves as ligand for NKG2D, an activating receptor on NK and γδ T cells. NK and γδ T cells seemed to mount antitumor but not antiviral responses, as their presence did not change the amount of persisting virus significantly. Our studies suggest that mice have a multipronged host defense against PyV-induced tumors that includes γδ T and NK cells in addition to αβ T cell responses. Merkel cell virus, a tumor causing polyomavirus in humans, is closely related to PyV with a similar biology, making it very important to understand mechanisms involved in host control of tumor development in the course of these life-long persistent infections.

Lessons from immune responses and vaccines against murine polyomavirus infection and polyomavirus-induced tumours potentially useful for studies on human polyomaviruses

During 2007-2008, three new human polyomaviruses, KI, WU and Merkel cell cancer polyomaviruses have been discovered, of which the latter has also been identified in a human tumour. This development revives the interest in both human and animal polyomaviruses and their potential role in tumour development and disease particularly in immune suppressed individuals. Murine polyomavirus (MPyV) has in the past been used for acquiring knowledge of transformation mechanisms in vitro, as well as in immunological studies with regard to virus-induced tumour development in the natural host of the virus. Here we summarize some of the accumulated knowledge achieved in the MPyV field in view of the balance between tumour virus, the immune system and tumour development, and discuss this in relation to infections with human polyomaviruses. We also present how virus-like particles (VLPs) and gluthatione-S-transferase VP1 can be used for vaccination against the same tumour virus not only in mice with a well-functioning immune system, but also in immune suppressed mice.

DNA from KI, WU and Merkel cell polyomaviruses is not detected in childhood central nervous system tumours or neuroblastomas

BACKGROUND

BK and JC polyomaviruses (BKV and JCV) are potentially oncogenic and have in the past inconclusively been associated with tumours of the central nervous system (CNS), while BKV has been hinted, but not confirmed to be associated with neuroblastomas. Recently three new polyomaviruses (KIPyV, WUPyV and MCPyV) were identified in humans. So far KIPyV and WUPyV have not been associated to human diseases, while MCPyV was discovered in Merkel Cell carcinomas and may have neuroepithelial cell tropism. However, all three viruses can be potentially oncogenic and this compelled us to investigate for their presence in childhood CNS and neuroblastomas.

METHODOLOGY

The presence of KI, WU and MCPyV DNA was analysed, by a joint WU and KI specific PCR (covering part of VP1) and by a MCPyV specific regular and real time quantitative PCR (covering part of Large T) in 25 CNS tumour biopsies and 31 neuroblastoma biopsies from the Karolinska University Hospital, Sweden. None of the three new human polyomaviruses were found to be associated with any of the tumours, despite the presence of PCR amplifiable DNA assayed by a S14 housekeeping gene PCR.

CONCLUSION

In this pilot study, the presence of MCPyV, KI and WU was not observed in childhood CNS tumours and neuroblastomas. Nonetheless, we suggest that additional data are warranted in tumours of the central and peripheral nervous systems and we do not exclude that other still not yet detected polyomaviruses could be present in these tumours.

Quantitation of human seroresponsiveness to Merkel cell polyomavirus

Merkel cell carcinoma (MCC) is a relatively uncommon but highly lethal form of skin cancer. A majority of MCC tumors carry DNA sequences derived from a newly identified virus called Merkel cell polyomavirus (MCV or MCPyV), a candidate etiologic agent underlying the development of MCC. To further investigate the role of MCV infection in the development of MCC, we developed a reporter vector-based neutralization assay to quantitate MCV-specific serum antibody responses in human subjects. Our results showed that 21 MCC patients whose tumors harbored MCV DNA all displayed vigorous MCV-specific antibody responses. Although 88% (42/48) of adult subjects without MCC were MCV seropositive, the geometric mean titer of the control group was 59-fold lower than the MCC patient group (p<0.0001). Only 4% (2/48) of control subjects displayed neutralizing titers greater than the mean titer of the MCV-positive MCC patient population. MCC tumors were found not to express detectable amounts of MCV VP1 capsid protein, suggesting that the strong humoral responses observed in MCC patients were primed by an unusually immunogenic MCV infection, and not by viral antigen expressed by the MCC tumor itself. The occurrence of highly immunogenic MCV infection in MCC patients is unlikely to reflect a failure to control polyomavirus infections in general, as seroreactivity to BK polyomavirus was similar among MCC patients and control subjects. The results support the concept that MCV infection is a causative factor in the development of most cases of MCC. Although MCC tumorigenesis can evidently proceed in the face of effective MCV-specific antibody responses, a small pilot animal immunization study revealed that a candidate vaccine based on MCV virus-like particles (VLPs) elicits antibody responses that robustly neutralize MCV reporter vectors in vitro. This suggests that a VLP-based vaccine could be effective for preventing the initial establishment of MCV infection.

Lessons in signaling and tumorigenesis from polyomavirus middle T antigen

The small DNA tumor viruses have provided a very long-lived source of insights into many aspects of the life cycle of eukaryotic cells. In recent years, the emphasis has been on cancer-related signaling. Here we review murine polyomavirus middle T antigen, its mechanisms, and its downstream pathways of transformation. We concentrate on the MMTV-PyMT transgenic mouse, one of the most studied models of breast cancer, which permits the examination of in situ tumor progression from hyperplasia to metastasis.

Cellular transformation by Simian Virus 40 and Murine Polyoma Virus T antigens

Simian Virus 40 (SV40) and Mouse Polyoma Virus (PY) are small DNA tumor viruses that have been used extensively to study cellular transformation. The SV40 early region encodes three tumor antigens, large T (LT), small T (ST) and 17KT that contribute to cellular transformation. While PY also encodes LT and ST, the unique middle T (MT) generates most of the transforming activity. SV40 LT mediated transformation requires binding to the tumor suppressor proteins Rb and p53 in the nucleus and ST binding to the protein phosphatase PP2A in the cytoplasm. SV40 LT also binds to several additional cellular proteins including p300, CBP, Cul7, IRS1, Bub1, Nbs1 and Fbxw7 that contribute to viral transformation. PY MT transformation is dependent on binding to PP2A and the Src family protein tyrosine kinases (PTK) and assembly of a signaling complex on cell membranes that leads to transformation in a manner similar to Her2/neu. Phosphorylation of MT tyrosine residues activates key signaling molecules including Shc/Grb2, PI3K and PLCgamma1. The unique contributions of SV40 LT and ST and PY MT to cellular transformation have provided significant insights into our understanding of tumor suppressors, oncogenes and the process of oncogenesis.

Modulating the expression of IFN regulatory factor 8 alters the protumorigenic behavior of CD11b+Gr-1+ myeloid cells

CD11b(+)Gr-1(+)-expressing cells, termed myeloid-derived suppressor cells, can mediate immunosuppression and tumor progression. However, the intrinsic molecular events that drive their protumorigenic behavior remain to be elucidated. Although CD11b(+)Gr-1(+) cells exist at low frequencies in normal mice, it also remains unresolved whether they are biologically distinct from those of tumor-bearing hosts. These objectives were investigated using CD11b(+)Gr-1(+) cells from both implantable (4T1) and autochthonous (mouse mammary tumor virus-polyomavirus middle T Ag (MMTV-PyMT)) mouse models of mammary carcinoma. Limited variation was observed in the expression of markers associated with immunoregulation between CD11b(+)Gr-1(+) cells of both tumor models, as well as with their respective controls (Cnt). Despite limited differences in phenotype, tumor-induced CD11b(+)Gr-1(+) cells were found to produce a more immunosuppressive cytokine profile than that observed by Cnt CD11b(+)Gr-1(+) cells. Furthermore, when admixed with tumor cells, CD11b(+)Gr-1(+) cells from tumor-bearing mice significantly enhanced neoplastic growth compared with counterpart cells from Cnt mice. However, the protumorigenic behavior of these tumor-induced CD11b(+)Gr-1(+) cells was significantly diminished when the expression of IFN regulatory factor 8, a key myeloid-associated transcription factor, was enhanced. The loss of this protumorigenic effect occurred independently of the host immune system and correlated with a CD11b(+)Gr-1(+) cytokine/chemokine production pattern that resembled cells from nontumor-bearing Cnt mice. Overall, our data indicate that 1) tumor-induced CD11b(+)Gr-1(+) cells from both cancer models were phenotypically similar, but biologically distinct from their nontumor-bearing counterparts and 2) modulation of IFN regulatory factor 8 levels in tumor-induced CD11b(+)Gr-1(+) cells can significantly abrogate their protumorigenic behavior, which may have important implications for cancer therapy.

High JC virus load in tongue carcinomas may be a risk factor for tongue tumorigenesis

The John Cunningham virus (JCV) asymptomatically infects a large proportion (approximately 90%) of the population worldwide but may be activated in immunodeficient patients, resulting in progressive multifocal leukoencephalopathy. Recent reports demonstrated its oncogenic role in malignancies. In this paper, the presence of JCV-targeting T antigen was investigated in tongue carcinoma (TC, n = 39), dysplastic tongue epithelium (DTE, n = 15) and glossitis (n = 15) using real-time polymerase chain reaction (PCR) and in situ PCR and immunohistochemistry, and JCV copies were analyzed with the clinicopathological parameters of TCs. The results demonstrated that glossitis and DTEs had significantly lower copies of JCV (410.5 +/- 44.3 and 658.3 +/- 53.3 copies/mug DNA respectively) than TCs (981.5 +/- 14.0, p < 0.05). When they were divided into three groups with 0-200 copies/mug DNA (low), 201-1,000 (moderate) and more than 1001 (high), TCs showed 3 (7.6%) in the low group, 21 (53.8%) in the moderate group and 15 (38.4%) in the high group and glossitis showed 11 (73.3%) in the low group, 0 (0%) in the moderate group and 4 (26.6%) in the high group. The DTEs occupied an intermediate position between them (p < 0.001). In situ PCR demonstrated that the nuclei of TC and DTE cells are sporadically T-antigen positive but not in nasal turbinate epithelial cells. Immunohistochemistry for T-antigen protein revealed four positive cases only in TCs. The existence of JCV T-antigen DNA was not associated with the clinicopathological variables of TCs. In conclusion, the presence of JCV may be a risk factor of tongue carcinogenesis.

Allogeneic differences in the dependence on CD4+ T-cell help for virus-specific CD8+ T-cell differentiation

CD4(+) T-cell help enables antiviral CD8(+) T cells to differentiate into fully competent memory cells and sustains CD8(+) T-cell-mediated immunity during persistent virus infection. We recently reported that mice of C57BL/6 and C3H strains differ in their dependence on CD28 and CD40L costimulation for long-term control of infection by polyoma virus, a persistent mouse pathogen. In this study, we asked whether mice of these inbred strains also vary in their requirement for CD4(+) T-cell help for generating and maintaining polyoma virus-specific CD8(+) T cells. CD4(+) T-cell-depleted C57BL/6 mice mounted a robust antiviral CD8(+) T-cell response during acute infection, whereas unhelped CD8(+) T-cell effectors in C3H mice were functionally impaired during acute infection and failed to expand upon antigenic challenge during persistent infection. Using (C57BL/6 x C3H)F(1) mice, we found that the dispensability for CD4(+) T-cell help for the H-2(b)-restricted polyoma virus-specific CD8(+) T-cell response during acute infection extends to the H-2(k)-restricted antiviral CD8(+) T cells. Our findings demonstrate that dependence on CD4(+) T-cell help for antiviral CD8(+) T-cell effector differentiation can vary among allogeneic strains of inbred mice.

The antiviral CD8+ T cell response is differentially dependent on CD4+ T cell help over the course of persistent infection

Although many studies have investigated the requirement for CD4(+) T cell help for CD8(+) T cell responses to acute viral infections that are fully resolved, less is known about the role of CD4(+) T cells in maintaining ongoing CD8(+) T cell responses to persistently infecting viruses. Using mouse polyoma virus (PyV), we asked whether CD4(+) T cell help is required to maintain antiviral CD8(+) T cell and humoral responses during acute and persistent phases of infection. Though fully intact during acute infection, the PyV-specific CD8(+) T cell response declined numerically during persistent infection in MHC class II-deficient mice, leaving a small antiviral CD8(+) T cell population that was maintained long term. These unhelped PyV-specific CD8(+) T cells were functionally unimpaired; they retained the potential for robust expansion and cytokine production in response to Ag rechallenge. In addition, although a strong antiviral IgG response was initially elicited by MHC class II-deficient mice, these Ab titers fell, and long-lived PyV-specific Ab-secreting cells were not detected in the bone marrow. Finally, using a minimally myeloablative mixed bone marrow chimerism approach, we demonstrate that recruitment and/or maintenance of new virus-specific CD8(+) T cells during persistent infection is impaired in the absence of MHC class II-restricted T cells. In summary, these studies show that CD4(+) T cells differentially affect CD8(+) T cell responses over the course of a persistent virus infection.

Detection and typing of BKV, JCV, and SV40 by multiplex nested polymerase chain reaction

A multiplex nested polymerase chain reaction (PCR) method was developed for detecting and differentiating simultaneously the DNA of polyomaviruses JC, BK, and SV40 in a single tube. In the first amplification step the same set of primers was used to amplify a conserved DNA region of the large T antigen gene of JCV, BKV, and SV40. The second round was carried out using a set of primers designed to obtain products of different size for each related virus. Subsequently, the sensitivity of the multiplex nested PCR was maximized by optimizing parameters such as primer, magnesium, and dNTP concentrations. The sensitivity of the method ranged between 1 and 10 copies of the polyomavirus genome. The assay was then used for detecting polyomavirus DNA in urine, serum, and biopsy specimens from renal transplant recipients. Based on the results obtained, the multiplex nested PCR developed in our study represents a useful tool for supporting the diagnosis of polyomavirus infection and could be used for epidemiological purposes and to better define the role of polyomaviruses in human pathology.

Glomerular expression of large polyomavirus T antigen in binary tet-off regulated transgenic mice induces apoptosis, release of chromatin and initiates a lupus-like nephritis

Binary tetracycline-regulated polyomavirus large T antigen transgenic mice were generated to study immunological tolerance for nucleosomes. Expression of T antigen resulted in binding of the protein to chromatin, and released T antigen-nucleosome complexes from dying cells maintained anti-dsDNA and anti-nucleosome antibody-production by activating autoimmune nucleosome-specific B cells and CD4+ and CD8+ T antigen specific T cells. Glomerular T antigen expression was observed in these mice. Here, we demonstrate that this expression was linked to glomerular cell apoptosis, release of nucleosomes and association of nucleosomes with glomerulus basement membranes, detected as electron dense structures. Immune electron microscopy (IEM) revealed that these structures were glomerular targets for induced anti-dsDNA and anti-T antigen antibodies. Co-localization IEM demonstrated that in vivo-bound auto-antibodies co-localized with experimental monoclonal antibodies to dsDNA and to T antigen. A comparative analysis of glomeruli from nephritic (NZWxNZB)F1 and T antigen expressing transgenic mice revealed deposition of nucleosomes in glomerular capillary and mesangial matrix membranes and binding of anti-nucleosome antibodies in both mice strains. A controlled experimental model that may elucidate the initial events accounting for nucleosome-mediated nephritis has not been available. The transgenic mouse may be important to describe early immunological and cellular events accounting for the enigmatic lupus nephritis.

Early virus-associated bystander events affect the fitness of the CD8 T cell response to persistent virus infection

Chronic Ag exposure during persistent viral infection erodes virus-specific CD8 T cell numbers and effector function, with a concomitant loss of pathogen control. Less clear are the respective contributions of Ag-specific and Ag-nonspecific (bystander) events on the quantity, quality, and maintenance of antiviral CD8 T cells responding to persistent virus infection. In this study, we show that low-dose inoculation with mouse polyomavirus (PyV) elicits a delayed, but numerically equivalent, antiviral CD8 T cell response compared with high-dose inoculation. Low-dose infection generated virus-specific CD8 T cells endowed with multicytokine functionality and a superior per cell capacity to produce IFN-gamma. PyV-specific CD8 T cells primed by low-dose inoculation also expressed higher levels of IL-7Ralpha and bcl-2 and possessed enhanced Ag-independent survival. Importantly, the quantity and quality of the antiviral CD8 T cell response elicited by dendritic cell-mediated immunization were mitigated by infection with a mutant PyV lacking the dominant CD8 T cell viral epitope. These findings suggest that the fitness of the CD8 T cell response to persistent virus infection is programmed in large part by early virus-associated Ag-nonspecific factors, and imply that limiting bystander inflammation at the time of inoculation, independent of Ag load, may optimize adaptive immunity to persistent viral infection.

Virus receptors and tropism

Polyomaviruses are small, tumorigenic, nonenveloped viruses that infect several different species. Interaction of these viruses with cell surface receptors represents the initial step during infection of host cells. This interaction can be a major determinant of viral host and tissue tropism. This chapter reviews what is currently known about the cellular receptors for each of five polyomavirus family members: Mouse polyomavirus (PyV), JC virus (JCV), BK virus (BKV), Lymphotropic papovavirus (LPV) and Simian virus 40 (SV40). These polyomaviruses serve to illustrate the enormous diversity of virus-cell surface interactions and allow us to closely evaluate the role of receptors in their life cycles. The contribution of other factors such as transcriptional regulators and signaling pathways are also summarized.

Avian polyomavirus mutants with deletions in the VP4-encoding region show deficiencies in capsid assembly and virus release, and have reduced infectivity in chicken

Avian polyomavirus (APV) is the causative agent of an acute fatal disease in psittacine and some non-psittacine birds. In contrast to mammalian polyomaviruses, the APV genome encodes the additional capsid protein VP4 and its variant VP4Delta, truncated by an internal deletion. Both proteins induce apoptosis. Mutation of their common initiation codon prevents virus replication. Here, the generation of replication competent deletion mutants expressing either VP4 or VP4Delta is reported. In contrast to infection with wild-type virus, chicken embryo cells showed no cytopathic changes after infection with the mutants, and induction of apoptosis as well as virus release from the infected cells were delayed. Electron microscopy revealed the presence of a high proportion of small particles and tubules in preparations of the VP4 deletion mutant, indicating a scaffolding function for VP4. Wild-type and mutant viruses elicited neutralizing antibodies against APV after intramuscular and intraperitoneal infection of chicken; however, VP4-specific antibodies were only detected after infection with wild-type virus. Using the oculonasal route of infection, seroconversion was only observed in chickens infected with the wild-type virus, indicating a strongly reduced infectivity of the mutants. Based on the biological properties of the deletion mutants, they could be considered as candidates for APV marker vaccines.

Polyoma virus in pediatric renal transplantation

Renal transplantation is the treatment of choice for children with end-stage renal disease. Patient survival and allograft survival have improved with better immunosuppressant regimes to reduce acute allograft rejection but post-transplant infections have been exacerbated. An emerging problematic virus in the past decade is the polyoma virus BKV. The features of BKV including the clinical features in the general and immune compromised population are reviewed and correlated with pediatric studies in the post-transplant population. These features are placed in context with lessons learned about BKV in relevant adult studies.

Protection against polyoma virus-induced tumors is perforin-independent

CD8 T cells are necessary for controlling tumors induced by mouse polyoma virus (PyV), but the effector mechanism(s) responsible have not been determined. We examined the PyV tumorigenicity in C57BL/6 mice mutated in Fas or carrying targeted disruptions in the perforin gene or in both TNF receptor type I and type II genes. Surprisingly, none of these mice developed tumors. Perforin/Fas double-deficient radiation bone marrow chimeric mice were also resistant to PyV-induced tumors. Anti-PyV CD8 T cells in perforin-deficient mice were found not to differ from wild type mice with respect to phenotype, capacity to produce cytokines or maintenance of memory T cells, indicating that perforin does not modulate the PyV-specific CD8 T cell response. In addition, virus was cleared and persisted to similar extents in wild type and perforin-deficient mice. In summary, perforin/granzyme exocytosis is not an essential effector pathway for protection against PyV infection or tumorigenesis.

Continuous recruitment of naive T cells contributes to heterogeneity of antiviral CD8 T cells during persistent infection

Numerous microbes establish persistent infections, accompanied by antigen-specific CD8 T cell activation. Pathogen-specific T cells in chronically infected hosts are often phenotypically and functionally variable, as well as distinct from T cells responding to nonpersistent infections; this phenotypic heterogeneity has been attributed to an ongoing reencounter with antigen. Paradoxically, maintenance of memory CD8 T cells to acutely resolved infections is antigen independent, whereas there is a dependence on antigen for T cell survival in chronically infected hosts. Using two chronic viral infections, we demonstrate that new naive antigen-specific CD8 T cells are primed after the acute phase of infection. These newly recruited T cells are phenotypically distinct from those primed earlier. Long-lived antiviral CD8 T cells are defective in self-renewal, and lack of thymic output results in the decline of virus-specific CD8 T cells, indicating that newly generated T cells preserve antiviral CD8 T cell populations during chronic infection. These findings reveal a novel role for antigen in maintaining virus-specific CD8 T cells during persistent infection and provide insight toward understanding T cell differentiation in chronic infection.

Generation of virus-like particles consisting of the major capsid protein VP1 of goose hemorrhagic polyomavirus and their application in serological tests

Goose hemorrhagic polyomavirus (GHPV) is the causative agent of hemorrhagic nephritis and enteritis of geese (HNEG), a fatal disease of young geese with high mortality rates. GHPV cannot be efficiently propagated in tissue culture. To provide antigens for diagnostic tests and vaccines, its major structural protein VP1 was recombinantly expressed in Sf9 insect cells and in the yeast Saccharomyces cerevisiae. As demonstrated by density gradient centrifugation and electron microscopy, GHPV-VP1 expressed in insect cells formed virus-like particles (VLPs) with a diameter of 45 nm indistinguishable from infectious polyomavirus particles. However, efficiency of VLP formation was low as compared to the monkey polyomavirus SV-40-VP1. In yeast cells, GHPV-VP1 alone formed smaller VLPs, 20 nm in diameter. Remarkably, co-expression of GHPV-VP2 resulted in VLPs with a diameter of 45 nm. All three types of GHPV-VLPs were shown to hemagglutinate chicken erythrocytes. ELISA and hemagglutination inhibition tests using the VLPs as antigen detected GHPV-specific antibodies in up to 85.7% of sera derived from flocks with HNEG but in none of the sera of a clinically healthy flock. However, GHPV-specific antibodies were also detected in sera from two other flocks without HNEG indicating a broad distribution of GHPV due to subclinical or unrecognised infections.

Nephron segment localization of polyoma virus large T antigen in renal allografts

This study uses CD10 and epithelial membrane antigen (EMA) as respective proximal and distal tubular segment markers to localize polyoma virus replicative activity, as determined by large T antigen (TAg) expression, in allograft polyoma virus nephropathy (PVN). Sixteen biopsies and 2 nephrectomy specimens with PVN had serial 2-mum paraffin sections stained using monoclonal antibodies to polyoma virus TAg by immunoperoxidase with diaminobenzidine as chromogen. A second immunolabeling step used CD10 as a proximal nephron marker or EMA as a distal tubular marker, and alkaline phosphatase with fast red as chromogen. BK viral DNA was detected in blood in 16 of 18 tested. Fourteen of 16 had cortex and medulla, and 2 had cortex only in the biopsy sample. Fourteen (100%) of 14 had double-positive EMA and TAg expression (EMA+TAg+) in medullary collecting ducts. T antigen was evident in loops of Henle in nephrectomies. Thirteen (81.3%) of 16 had EMA+TAg+, and 10 (62.5%) of 16 had CD10+TAg+ cortical tubular segments. CD10+TAg+ cells were observed in the parietal epithelium of Bowman's capsule in 3 biopsies (18.75%). T antigen was observed in 5.1% of CD10+ tubular profiles compared with 21% of EMA+ profiles in renal cortex (P < .0001). Polyoma virus TAg was observed in medullary collecting ducts, in distal and proximal cortical tubules, and in Bowman's capsule, in decreasing order of frequency. Loops of Henle also had TAg. This distribution suggests potential for an ascending route of infection of allograft tubules in PVN.

Murine polyomavirus-like particles induce maturation of bone marrow-derived dendritic cells and proliferation of T cells

We analysed the effects of murine polyomavirus-like particles (PLPs) on bone marrow-derived dendritic cells (BMDCs) and T cells in vitro. BMDCs activated with PLPs up-regulated CD40, CD80, CD86 and major histocompatibility complex (MHC) class II surface markers and produced proinflammatory cytokines. Chimeric PLPs [expressing the ovalbumin (OVA)-peptides OVA(257-264) or OVA(323-339)], but not wildtype PLPs, activated OVA-specific CD8 T cells and OVA-specific CD4 T cells, respectively, indicating both MHC class I and II presentation of the peptides by antigen-presenting cells. Our results suggest that PLPs may be used as vaccine adjuvants priming dendritic cells to induce potent T cell responses.

Hsc70 contacts helix III of the J domain from polyomavirus T antigens: addressing a dilemma in the chaperone hypothesis of how they release E2F from pRb

Hsc70's expected binding site on helix II of the J domain of T antigens appears to be blocked in its structure bound to tumor suppressor pRb. We used NMR to map where mammalian Hsc70 binds the J domain of murine polyomavirus T antigens (PyJ). The ATPase domain of Hsc70 unexpectedly has its biggest effects on the NMR peak positions of the C-terminal end of helix III of PyJ. The Hsc70 ATPase domain protects the C-terminal end of helix III of PyJ from an uncharged paramagnetic probe of chelated Gd(III), clearly suggesting the interface. Effects on the conserved HPD loop and helix II of PyJ are smaller. The NMR results are supported by a novel assay of Hsc70's ATP hydrolysis showing that mutations of surface residues in PyJ helix III impair PyJ-dependent stimulation of Hsc70 activity. Evolutionary trace analysis of J domains suggests that helix III usually may join helix II in contributing specificities for cognate hsp70s. Our novel evidence implicating helix III differs from evidence that Escherichia coli DnaK primarily affects helix II and the HPD loop of DnaJ. We find the pRb-binding fragment of E2F1 to be intrinsically unfolded and a good substrate for Hsc70 in vitro. This suggests that E2F1 could be a substrate for Hsc70 recruited by T antigen to an Rb family member. Importantly, our results strengthen the chaperone hypothesis for E2F release from an Rb family member by Hsc70 recruited by large T antigen. That is, it now appears that Hsc70 can freely access helix III and the HPD motif of large T antigen bound to an Rb family member.

The polyomavirus, JCV and its involvement in human disease

The human neurotropic polyomavirus, JC virus (JCV), is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system that occurs mainly in immunosuppressed patients. JCV has also been found to be associated with human tumors of the brain and other organs. In this chapter, we describe JC virus and its role in human diseases.

Serological cross reactivity between polyomavirus capsids

Multiple methods have been used to measure antibodies to polyomavirus virions. In order to have a common method for all polyomaviruses, we developed enzyme immunoassays (EIAs) using virus-like-particles (VLPs) produced in the baculovirus expression system. We tested serum samples from humans and rhesus macaques in VLP-based EIAs for the two human polyomaviruses, BK and JC virus, and two nonhuman primate polyomaviruses, simian virus 40 (SV40) and lymphotropic polyomavirus (LPV). Rhesus sera exhibited low level reactivity to BK and JC, and approximately 10 and 15% of human sera showed low level reactivity to SV40 and LPV, respectively. Competitive inhibition assays with VLP protein demonstrated that the reactivity of rhesus sera against BK and JC VLPs was blocked by both SV40 and the respective human polyomavirus, indicating that the BK and JC assays were detected cross-reacting antibodies. Similarly, the reactivity of the majority of human sera to SV40 was blocked by both SV40 and BK or JC, demonstrating that the SV40 reactivity of human sera is largely due to cross reacting BK and JC antibodies. In contrast, the reactivity of human sera to LPV VLPs was blocked by LPV but not by BK or JC, providing serological evidence for an unknown human polyomavirus related to LPV. SV40 and LPV VLP-based EIAs and competitive inhibition assays with heterologous VLPs provide tools for seroepidemiological studies of possible SV40 and LPV-like infections of humans.

Immunity and autoimmunity induced by polyomaviruses: clinical, experimental and theoretical aspects

In this chapter, polyomaviruses will be presented in an immunological context. Principal observations will be discussed to elucidate humoral and cellular immune responses to different species of the polyomaviruses and to individual viral structural and regulatory proteins. The role of immune responses towards the viruses or their proteins in context of protection against polyomavirus induced tumors will be described. One central aspect of this presentation is the ability of polyomaviruses, and particularly large T-antigen, to terminate immunological tolerance to nucleosomes, DNA and histones. Thus, in the present chapter we will focus on clinical, experimental and theoretical aspects of the immunity to polyomaviruses.

The pathobiology of polyomavirus infection in man

This article traces the discovery of polyomaviruses and outlines investigations, which shed light on potential modes of transmission of this increasingly important group of human pathogens. The pathobiology of the virus is summarized with particular reference to interactions with host cell receptors, cell entry, cytoplasmic trafficking, and targeting of the viral genome to the nucleus. This is followed by a discussion of sites of viral latency and factors leading to viral reactivation. Finally, we present biochemical mechanisms that could potentially explain several key elements of tissue pathology characteristic of BKV mediated damage to human kidney.

T cell-independent and T cell-dependent immunoglobulin G responses to polyomavirus infection are impaired in complement receptor 2-deficient mice

Polyomavirus (PyV) infection induces protective T cell-independent (TI) IgM and IgG antibody responses in T cell-deficient mice, but these responses are not generated by immunization with viral proteins or virus like particles. We hypothesized that innate signals contribute to the generation of isotype-switched antiviral antibody responses. We studied the role of complement receptor (CR2) engagement in TI and T cell-dependent (TD) antibody responses to PyV using CR2-deficient mice. Antiviral IgG responses were reduced by 80-40% in CR2-/- mice compared to wild type. Adoptive transfer experiments demonstrated the need for CR2 not only in TD, but also in TI IgG responses to PyV. Transfer of CR2-/- B lymphocytes to SCID mice resulted in TI antiviral IgG responses that corresponded to 10% of that seen in wild-type B cell-reconstituted mice. Thus, our studies revealed a profound dependence of TI and TD antiviral antibody responses on CR2-mediated signals in PyV-infected mice, where the viral antigen is abundant and persistent.

Renal transplant patient with polyoma virus bladder infection and subsequent polyoma virus nephropathy

Polyoma virus nephropathy (PVN) is a significant cause of renal allograft dysfunction in transplant patients. A 58-year-old male received a cadaveric renal transplant and 12 weeks later presented with fever, diarrhea, and dysuria. He was diagnosed with a polyoma virus infection of the bladder by a transurethral bladder biopsy. One year post-transplant, he presented with renal allograft dysfunction and was diagnosed by biopsy with PVN of the non-native kidney. The diagnosis of a polyoma virus infection was confirmed by immunoreactivity to the polyoma T-antigen. We suggest that polyoma virus infection of the bladder be included in the differential diagnosis of urinary dysfunction in post-transplant patients, as such infections might be an under-recognized comorbidity in individuals with PVN.