Lymphotropism of Merkel cell polyomavirus infection, Nova Scotia, Canada

The diagnostic utility of Merkel cell polyoma virus immunohistochemistry in cytology specimens

OBJECTIVE

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine neoplasm that predominantly affects elderly and immunocompromised patients. Merkel cell polyoma virus (MCPyV) is clonally integrated into the majority of MCCs and has been linked to patient outcomes, playing a central role in the pathogenesis of the disease. We aimed to assess the utility of MCPyV immunohistochemistry (IHC) in the diagnosis of MCC in cytology cell block specimens and correlating with clinicopathologic features.

METHODS

Fifty-three cytology samples of MCC with sufficient cell block material were stained for MCPyV by IHC and scored semi-quantitatively in extent and intensity. Morphologic mimics of MCC including small cell lung carcinoma (n = 10), non-Hodgkin lymphoma (n = 10), basaloid squamous cell carcinoma (n = 6) and other neuroendocrine carcinomas (n = 8) were stained in parallel. Positive staining was defined as >1% of the tumour cells showing at least moderate staining intensity.

RESULTS

The cytologic features of MCC were characterized by high nuclear-cytoplasmic ratios, hyperchromatic nuclei with 'salt and pepper' chromatin, and nuclear moulding. MCPyV was detected in 24 of 53 cases (45%). Staining was strong and diffuse in roughly half of the positive samples. Of the morphologic mimics, one follicular lymphoma showed strong and diffuse staining. In contrast to prior studies, we saw no association between MCPyV status and patient outcomes.

CONCLUSION

Merkel cell polyoma virus IHC is highly specific (97%) for the diagnosis of MCC in our cohort, and can serve as a useful diagnostic tool for distinguishing MCC for morphologic mimics.

Identification and confirmation via in situ hybridization of Merkel cell polyomavirus in rare cases of posttransplant cutaneous T-cell lymphoma

BACKGROUND

Viral infection is an oncogenic factor in many hematolymphoid malignancies. We sought to determine the diagnostic yield of aligning off-target reads incidentally obtained during targeted hematolymphoid next-generation sequencing to a large database of viral genomes to screen for viral sequences within tumor specimens.

METHODS

Alignment of off-target reads to viral genomes was performed using magicBLAST. Localization of Merkel cell polyomavirus (MCPyV) RNA was confirmed by RNAScope in situ hybridization. Integration analysis was performed using Virus-Clip.

RESULTS

Four cases of post-cardiac-transplant folliculotropic mycosis fungoides (fMF) and one case of peripheral T-cell lymphoma (PTCL) were positive in off-target reads for MCPyV DNA. Two of the four cases of posttransplant fMF and the case of PTCL showed localization of MCPyV RNA to malignant lymphocytes, whereas the remaining two cases of posttransplant fMF showed MCPyV RNA in keratinocytes.

CONCLUSIONS

Our findings raise the question of whether MCPyV may play a role in rare cases of T-lymphoproliferative disorders, particularly in the skin and in the heavily immunosuppressed posttransplant setting.

Merkel Cell Polyomavirus (MCPyV) and Cancers: Emergency Bell or False Alarm?

Merkel cell polyomavirus (MCPyV), the sole member of Polyomavirus associated with oncogenesis in humans, is the major causative factor of Merkel cell carcinoma (MCC), a rare, neuroendocrine neoplasia of the skin. Many aspects of MCPyV biology and oncogenic mechanisms remain poorly understood. However, it has been established that oncogenic transformation is the outcome of the integration of the viral genome into the host DNA. The high prevalence of MCPyV in the population, along with the detection of the virus in various human tissue samples and the strong association of MCPyV with the emergence of MCC, have prompted researchers to further investigate the role of MCPyV in malignancies other than MCC. MCPyV DNA has been detected in several different non-MCC tumour tissues but with significantly lower prevalence, viral load and protein expression. Moreover, the two hallmarks of MCPyV MCC have rarely been investigated and the studies have produced generally inconsistent results. Therefore, the outcomes of the studies are inadequate and unable to clearly demonstrate a direct correlation between cellular transformation and MCPyV. This review aims to present a comprehensive recapitulation of the available literature regarding the association of MCPyV with oncogenesis (MCC and non-MCC tumours).

Emerging role of human polyomaviruses 6 and 7 in human cancers

BACKGROUND

Currently 12 human polyomaviruses (HPyVs) have been identified, 6 of which have been associated with human diseases, including cancer. The discovery of the Merkel cell polyomavirus and its role in the etiopathogenesis in the majority of Merkel cell carcinomas has drawn significant attention, also to other novel HPyVs. In 2010, HPyV6 and HPyV7 were identified in healthy skin swabs. Ever since it has been speculated that they might contribute to the etiopathogenesis of skin and non-cutaneous human cancers.

MAIN BODY

Here we comprehensively reviewed and summarized the current evidence potentially indicating an involvement of HPyV6 and HPyV7 in the etiopathogenesis of neoplastic human diseases. The seroprevalence of both HPyV6 and 7 is high in a normal population and increases with age. In skin cancer tissues, HPyV6- DNA was far more often prevalent than HPyV7 in contrast to cancers of other anatomic sites, in which HPyV7 DNA was more frequently detected.

CONCLUSION

It is remarkable to find that the detection rate of HPyV6-DNA in tissues of skin malignancies is higher than HPyV7-DNA and may indicate a role of HPyV6 in the etiopathogenesis of the respected skin cancers. However, the sheer presence of viral DNA is not enough to prove a role in the etiopathogenesis of these cancers.

The Pivotal Role of Viruses in the Pathogeny of Chronic Lymphocytic Leukemia: Monoclonal (Type 1) IgG K Cryoglobulinemia and Chronic Lymphocytic Leukemia Diagnosis in the Course of a Human Metapneumovirus Infection

Background: Type-1 cryoglobulinemia (CG) is a rare disease associated with B-cell lymphoproliferative disorder. Some viral infections, such as Epstein–Barr Virus infections, are known to cause malignant lymphoproliferation, like certain B-cell lymphomas. However, their role in the pathogenesis of chronic lymphocytic leukemia (CLL) is still debatable. Here, we report a unique case of Type-1 CG associated to a CLL transformation diagnosed in the course of a human metapneumovirus (hMPV) infection. Case presentation: A 91-year-old man was initially hospitalized for delirium. In a context of febrile rhinorrhea, the diagnosis of hMPV infection was made by molecular assay (RT-PCR) on nasopharyngeal swab. Owing to hyperlymphocytosis that developed during the course of the infection and unexplained peripheral neuropathy, a type-1 IgG Kappa CG secondary to a CLL was diagnosed. The patient was not treated for the CLL because of Binet A stage classification and his poor physical condition. Conclusions: We report the unique observation in the literature of CLL transformation and hMPV infection. We provide a mini review on the pivotal role of viruses in CLL pathophysiology.

Merkel cell polyomavirus and non-Merkel cell carcinomas: guilty or circumstantial evidence?

Merkel cell polyomavirus (MCPyV) is the major causative factor of the rare but aggressive cancer, Merkel cell carcinoma (MCC). Two characteristics of MCPyV-positive MCCs are integration of the viral genome and expression of a truncated version of one of its oncogenic proteins, namely large T antigen. The strong association of MCPyV with MCC development has incited researchers to further investigate a possible role of this virus in other cancers. However, many of the examples displaying the presence of the virus in the various non-MCC cancers are not able to clearly demonstrate a direct connection between cellular transformation and the presence of the virus. The prevalence of the virus is significantly lower in non-MCC cancers compared to MCCs, with a lower level of viral load and sparse viral protein expression. Moreover, the state of the viral genome, and whether a truncated large T antigen is expressed, has rarely been investigated. Nonetheless, considering the strong oncogenic potential of MCPyV proteins in MCC, the plausible contribution of MCPyV to transformation and cancer growth in non-MCC tumors cannot be ruled out. Furthermore, the absence of MCPyV in cancers does not exclude a hit-and-run mechanism, or the oncoproteins of MCPyV may potentiate the neoplastic process mediated by co-infecting oncoviruses such as high-risk human papillomaviruses and Epstein-Barr virus. The current review is focusing on the available data describing the presence of MCPyV in non-MCC tumors, with an aim to provide a comprehensive overview of the corresponding literature and to discuss the potential contribution of MCPyV to non-MCC cancer in light of this.

Low prevalence of Merkel cell polyomavirus in human epithelial thymic tumors

Background

The etiology of thymic epithelial tumors is unknown. Murine polyomavirus strain PTA has been shown to induce thymomas in mice. Recently, using diverse molecular techniques, we reported the presence of human polyomavirus 7 (HPyV7) in thymic epithelial tumors. In the present study, we investigated the prevalence of Merkel cell polyomavirus (MCPyV) in thymic epithelial tumors.

Methods

Thirty‐six thymomas were screened for MCPyV by PCR and subsequently tested by DNA and RNA in situ hybridization and immunohistochemistry. Twenty‐six thymomas were diagnosed with myasthenia gravis (MG).

Results

MCPyV DNA was detected by PCR in 7 (19.4%) of the 36 thymic epithelial tumors and in six of these, the presence of MCPyV was confirmed by fluorescence situ hybridization. Of these, 3 (28.6%) revealed weak MCPyV LT‐antigen protein expression. In addition, one of the MCPyV positive thymomas tested positive for MCPyV LT RNA with RNAscope. Of interest, two out of the three thymomas that previously tested positive for MCPyV by immunohistochemistry also tested positive for HPyV7. One of the 11 MG‐negative and 2 of the 25 MG‐positive were positive for MCPyV.

Conclusions

MCPyV DNA and MCPyV protein expression can be detected in human epithelial thymoma; however, to a far lesser extent than HPyV7. Our data strongly indicate that because of its infrequent detection and weak expression, MCPyV is unlikely to play an important role in the etiopathogenesis of human thymomas.

Human polyomaviruses and cancer: an overview

The name of the family Polyomaviridae, derives from the early observation that cells infected with murine polyomavirus induced multiple (poly) tumors (omas) in immunocompromised mice. Subsequent studies showed that many members of this family exhibit the capacity of mediating cell transformation and tumorigenesis in different experimental models. The transformation process mediated by these viruses is driven by viral pleiotropic regulatory proteins called T (tumor) antigens. Similar to other viral oncoproteins T antigens target cellular regulatory factors to favor cell proliferation, immune evasion and downregulation of apoptosis. The first two human polyomaviruses were isolated over 45 years ago. However, recent advances in the DNA sequencing technologies led to the rapid identification of additional twelve new polyomaviruses in different human samples. Many of these viruses establish chronic infections and have been associated with conditions in immunosuppressed individuals, particularly in organ transplant recipients. This has been associated to viral reactivation due to the immunosuppressant therapy applied to these patients. Four polyomaviruses namely, Merkel cell polyomavirus (MCPyV), Trichodysplasia spinulosa polyomavirus (TSPyV), John Cunningham Polyomavirus (JCPyV) and BK polyomavirus (BKPyV) have been associated with the development of specific malignant tumors. However, present evidence only supports the role of MCPyV as a carcinogen to humans. In the present review we present a summarized discussion on the current knowledge concerning the role of MCPyV, TSPyV, JCPyV and BKPyV in human cancers.

Human pegivirus persistence in human blood virome after allogeneic haematopoietic stem-cell transplantation

OBJECTIVES

Because commensal viruses are defined by the immunologic tolerance afforded to them, any immunomodulation, such as is received during haematopoietic stem-cell transplantation, may shift the demarcation between innocuous viral resident and disease-causing pathogen.

METHODS

We analysed by deep-sequencing the plasma virome of 40 allogeneic haematopoietic stem-cell transplantation patients 1 month after transplantation. Because human pegivirus (HPgV) was highly prevalent, we performed a 1-year screening of 122 plasma samples by specific real-time reverse transcription PCR assay. We used the log-rank test and the Gray test to assess association with outcomes, and the Mann-Whitney test and multivariable linear regression model to assess association with T-cell reconstitution.

RESULTS

Polyomaviruses (PyV) (20/40 patients), anelloviruses (16/40), pegiviruses (14/40) and herpesviruses (14/40) were most frequently identified, including ten cytomegalovirus; three Epstein-Barr virus; two herpes simplex virus type 1; one human herpesvirus 6b and one human herpesvirus 7; 18 Merkel cell-PyV; two BK-PyV; three PyV-6; and one JC-PyV. Papillomavirus and adenovirus were identified in 11 and two patients, respectively. The HPgV specific real-time reverse transcription PCR screening identified 51 of 122 positive samples, high virus loads and persistent infections up to 1 year after transplantation. Comparison between patients with or without HPgV infection at time of transplantation did not reveal a significant difference in infections, engraftment, survival, graft vs. host disease, relapse or immune reconstitution.

CONCLUSIONS

The blood virome after allogeneic haematopoietic stem-cell transplantation includes several DNA viruses, notably herpesviruses and PyV. Among RNA viruses, HPgV is highly prevalent and persists for several months, and it thus may deserve special attention in further research on immune reconstitution.

Viral microRNA effects on persistent infection of human lymphoid cells by polyomavirus SV40

BACKGROUND

Polyomaviruses, including simian virus 40 (SV40), display evidence of lymphotropic properties. This study analyzed the nature of SV40-human lymphocyte interactions in established cell lines and in primary lymphocytes. The effects of viral microRNA and the structure of the viral regulatory region on SV40 persistence were examined.

RESULTS

SV40 DNA was maintained in infected B cell and myeloid cell lines during cell growth for at least 28 days. Limiting dilution analysis showed that low amounts of SV40 DNA (~2 copies per cell) were retained over time. Infected B cells remained viable and able to proliferate. Genome copies of the SV40 microRNA-null mutant persisted at higher levels than the DNA of wild-type viruses. Complex viral regulatory regions produced modestly higher DNA levels than simple regulatory regions. Viral large T-antigen protein was detected at low frequency and at low levels in infected B cells. Following infection of primary lymphocytes, SV40 DNA was detected in CD19+ B cells and CD14+ monocytes, but not in CD3+ T cells. Rescue attempts using either lysates of SV40-infected B lymphocytes, coculture of live cells, or infectious center assays all showed that replication-competent SV40 could be recovered on rare occasions. SV40 infections altered the expression of several B cell surface markers, with more pronounced changes following infections with the microRNA-null mutant.

CONCLUSION

These findings indicate that SV40 can establish persistent infections in human B lymphocytes. The cells retain low copy numbers of viral DNA; the infections are nonproductive and noncytolytic but can occasionally produce infectious virus. SV40 microRNA negatively regulates the degree of viral effects on B cells.

SIGNIFICANCE

Lymphocytes may serve as viral reservoirs and may function to disseminate polyomaviruses to different tissues in a host. To our knowledge, this report is the first extensive analysis of viral microRNA effects on SV40 infection of human lymphocytes.

Viral Oncology: Molecular Biology and Pathogenesis

Oncoviruses are implicated in approximately 12% of all human cancers. A large number of the world's population harbors at least one of these oncoviruses, but only a small proportion of these individuals go on to develop cancer. The interplay between host and viral factors is a complex process that works together to create a microenvironment conducive to oncogenesis. In this review, the molecular biology and oncogenic pathways of established human oncoviruses will be discussed. Currently, there are seven recognized human oncoviruses, which include Epstein-Barr Virus (EBV), Human Papillomavirus (HPV), Hepatitis B and C viruses (HBV and HCV), Human T-cell lymphotropic virus-1 (HTLV-1), Human Herpesvirus-8 (HHV-8), and Merkel Cell Polyomavirus (MCPyV). Available and emerging therapies for these oncoviruses will be mentioned.

Polyomavirus Persistence

Mammalian polyomaviruses are characterized by establishing persistent infections in healthy hosts and generally causing clinical disease only in hosts whose immune systems are compromised. Despite the fact that these viruses were discovered decades ago, our knowledge of the mechanisms that govern viral persistence and reactivation is limited. Whereas mouse polyomavirus has been studied in a fair amount of detail, our understanding of the human viruses in particular is mostly inferred from experiments aimed at addressing other questions. In this review, we summarize the state of our current knowledge, draw conclusions when possible, and suggest areas that are in need of further study.

Exposure to raccoon polyomavirus (RacPyV) in free-ranging North American raccoons (Procyon lotor)

There is evidence that raccoon polyomavirus is causative for neuroglial brain tumors in the western United States. It is unknown if infection is limited to geographic locales where tumors have been reported or is widespread, like human polyomaviruses. We demonstrate raccoons in western, eastern and midwestern states have been exposed to RacPyV by detection of antibodies to capsid protein, VP1. While raccoons in eastern and midwestern states are seropositive, exposure is lower than in the western states. Additionally, across geographic areas seropositivity is higher in older as compared to younger raccoons, similar to polyomavirus exposure in humans. Serum titers are significantly higher in raccoons with tumors compared to raccoons without. Unlike polyomavirus-associated diseases in humans, we did not detect significant sequence variation between tumor and non-tumor tissue in raccoons with tumors compared to those without tumors. This warrants further investigation into co-morbid diseases or genetic susceptibility studies of the host.

Detection of human polyomaviruses MCPyV, HPyV6, and HPyV7 in malignant and non-malignant tonsillar tissues

Merkel cell polyomavirus (MCPyV) is associated with Merkel cell carcinoma (MCC), a rare skin malignancy. Human polyomavirus six and seven (HPyV6 and HPyV7) were identified on a skin but have not been associated with any pathology. The serology data suggest that infection with polyomaviruses occurs in childhood and they are widespread in population. However, the site of persistent infection has not been identified. Altogether, 103 formalin-fixed paraffin-embedded (FFPE) specimens and five fresh frozen tissues (FF) of non-malignant tonsils and 97 FFPE and 15 FF samples of tonsillar carcinomas were analyzed by qPCR for the presence of MCPyV, HPyV6, and HPyV7 DNA. All MCPyV DNA positive FF tissues were screened for the expression of early viral transcripts. Overall prevalence of MCPyV, HPyV6, and HPyV7 in non-malignant tonsillar tissues was 10.2%, 4.6%, and, 0.9%, respectively. The prevalence of MCPyV DNA in non-malignant tonsils increased with age (P < 0.05). While the prevalence of MCPyV DNA was significantly higher in the tumors than non-malignant tissues (35.7% vs. 10.2%) (P < 0.001), the prevalence of HPyV6 DNA (5.4% vs. 4.6%) and HPyV7 DNA (1.8% vs. 0.9%) were comparable. In all MCPyV DNA positive FF tissues early transcripts were detected. MCPyV, HPyV6, and HPyV7 DNAs were found in tonsils, suggesting that the tonsils may be a site of viral latency. The viral load was low indicating that only a fraction of cells are infected. The higher prevalence of MCPyV DNA was detected in tonsillar tumors but there was no difference in the viral load between tumor and healthy tissues.

Detection of human polyomavirus 7 in human thymic epithelial tumors

INTRODUCTION

Although the molecular genetics possibly underlying the pathogenesis of human thymoma have been extensively studied, its etiology remains poorly understood. Because murine polyomavirus consistently induces thymomas in mice, we assessed the presence of the novel human polyomavirus 7 (HPyV7) in human thymic epithelial tumors.

METHODS

HPyV7-DNA Fluorescence in situ hybridization (FISH), DNA-polymerase chain reaction (PCR), and immunohistochemistry (IHC) were performed in 37 thymomas. Of these, 26 were previously diagnosed with myasthenia gravis (MG). In addition, 20 thymic hyperplasias and 20 fetal thymic tissues were tested.

RESULTS

HPyV7-FISH revealed specific nuclear hybridization signals within the neoplastic epithelial cells of 23 thymomas (62.2%). With some exceptions, the HPyV7-FISH data correlated with the HPyV7-DNA PCR. By IHC, large T antigen expression of HPyV7 was detected, and double staining confirmed its expression in the neoplastic epithelial cells. Eighteen of the 26 MG-positive and 7 of the 11 MG-negative thymomas were HPyV7-positive. Of the 20 hyperplastic thymi, 40% were HPyV7-positive by PCR as confirmed by FISH and IHC in the follicular lymphocytes. All 20 fetal thymi tested HPyV7-negative.

CONCLUSIONS

The presence of HPyV7-DNA and large T antigen expression in the majority of thymomas possibly link HPyV7 to human thymomagenesis. Further investigations are needed to elucidate the possible associations of HPyV7 and MG.

Analysis of prognostic significance of merkel cell polyomavirus in chronic lymphocytic leukemia

BACKGROUND

Merkel cell polyomavirus (MCPyV), a ubiquitous DNA tumor virus, has been found to be associated with Merkel cell carcinoma and chronic lymphocytic leukemia (CLL). Previous studies have reported conflicting results on the frequency and potential pathogenetic role of MCPyV in CLL. The aim of this study was to evaluate MCPyV's association with CLL and its prognostic significance.

PATIENTS AND METHODS

Between 2006 and 2013, DNA samples obtained from CLL patients (n = 119) before treatment were tested for MCPyV using quantitative real-time polymerase chain reaction analysis and verified by gel electrophoresis. Only samples testing positive by both methods were considered valid.

RESULTS

We found that 13 (11%) of 119 CLL cases were positive for MCPyV. Between the groups of MCPyV-positive and -negative patients, there was no significant difference in the sex, age, cytogenetics, presence of p53 defect, or immunoglobulin heavy chain (IGHV) mutational status. In the subset of MCPyV-negative patients, advanced Rai stage (III to IV) was found more frequently, and therapy was initiated more often. There was no difference in overall response rate, median progression-free survival, and overall survival between both groups. We did not observe any new positivity after treatment in initially MCPyV-negative patients.

CONCLUSION

This study provides the first analysis of the prognostic role of MCPyV in CLL. MCPyV occurrence seems to be a relatively rare event during the course of CLL. MCPyV is also unlikely to influence the outcome of CLL patients.

Human Merkel cell polyomavirus: virological background and clinical implications

The Merkel cell polyomavirus (MCPyV), identified in humans in 2008, is associated with a relatively rare but aggressive neuroendocrine skin cancer, the Merkel cell carcinoma (MCC). MCC incidence is increasing due to the advancing age of the population, the increase in damaging sun exposure and in the number of immunocompromised individuals. MCPyV must be considered as the etiological agent of MCC and thus is the first example of a human oncogenic polyomavirus. MCPyV infection is common, and seroprevalence studies indicate that widespread exposure begins early in life. The majority of adults have anti-MCPyV antibodies and there is a growing body of evidence that healthy human skin harbors resident or transient MCPyV suggesting that MCPyV infection persists throughout life. However, the mode of transmission, the host cells, and the latency characteristics of this virus remain to be elucidated. In addition, it is still not clear whether MCPyV is associated with diseases or lesions other than Merkel cell carcinoma. The etiologic role of MCPyV in MCC opens up opportunities to improve the understanding of this cancer and to potentially improve its treatment.

The human polyomaviruses KI and WU: virological background and clinical implications

In 2007, two novel polyomaviruses KI and WU were uncovered in the respiratory secretions of children with acute respiratory symptoms. Seroepidemiological studies showed that infection by these viruses is widespread in the human population. Following these findings, different biological specimens and body compartments have been screened by real-time PCR in the attempt to establish a pathogenetic role for KI polyomavirus (KIPyV) and WU polyomavirus (WUPyV) in human diseases. Although both viruses have been found mainly in respiratory tract samples of immunocompromised patients, a clear causative link with the respiratory disease has not been established. Indeed, the lack of specific clinical or radiological findings, the frequent co-detection with other respiratory pathogens, the detection in subjects without signs or symptoms of respiratory disease, and the variability of the viral loads measured did not allow drawing a definitive conclusion. Prospective studies carried out on a large sample size including both immunocompromised and immunocompetent patients with and without respiratory symptoms are needed. Standardized quantitative real-time PCR methods, definition of a clear clinical cutoff value, timing in the collection of respiratory samples, are also crucial to understand the pathogenic role, if any, of KIPyV and WUPyV in human pathology.

The novel KI, WU and MC polyomaviruses and human diseases

From 2007 to 2012, the Polyomaviridae family expanded with the discovery of several novel human polyomaviruses. Infection by polyomaviruses is widespread in the human population, but only immunocompromised patients are at risk for disease. Currently, four polyomaviruses have been specifically associated with human diseases: BK polyomavirus, JC polyomavirus, Merkel cell polyomavirus and trichodysplasia spinulosa-associated polyomavirus. The pathogenic potential of the other human polyomaviruses is unknown. This review focuses on the novel Karolinska Institute polyomavirus, Washington University polyomavirus and Merkel cell polyomavirus. Karolinska Institute polyomavirus and Washington University polyomavirus were uncovered in respiratory specimens of children with acute respiratory symptoms. Merkel cell polyomavirus was found in an aggressive skin tumor named Merkel cell carcinoma. The scientific literature concerning the three human polyomaviruses is summarized and discussed including seroepidemiology, detection methods (real-time PCR), histopathological findings and association with clinical manifestations.

Molecular diagnosis of infection-related cancers in dermatopathology

The association between viruses and skin cancer is increasingly recognized in a number of neoplasms, that is, cutaneous squamous cell carcinoma, Kaposi sarcoma, nasopharyngeal carcinoma, and Merkel cell carcinoma, as well as hematolymphoid malignancies such as adult T-cell leukemia/lymphoma and NK/T-cell lymphoma (nasal type) and post-transplant lymphoproliferative disorders. Molecular assays are increasingly used to diagnose and manage these diseases. In this review, molecular features of tumor viruses and related host responses are explored. The tests used to identify such features are summarized. Evaluation of the utility of these assays for diagnosis and/or management of specific tumor types is presented.

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.

From Stockholm to Malawi: recent developments in studying human polyomaviruses

Until a few years ago the polyomavirus family (Polyomaviridae) included a dozen viruses identified in avian and mammalian hosts. Two of these, the JC and BK-polyomaviruses isolated a long time ago, are known to infect humans and cause severe illness in immunocompromised hosts. Since 2007 an unprecedented number of eight novel polyomaviruses were discovered in humans. Among them are the KI- and WU-polyomaviruses identified in respiratory samples, the Merkel cell polyomavirus found in skin carcinomas and the polyomavirus associated with trichodysplasia spinulosa, a skin disease of transplant patients. Another four novel human polyomaviruses were identified, HPyV6, HPyV7, HPyV9 and the Malawi polyomavirus, so far not associated with any disease. In the same period several novel mammalian polyomaviruses were described. This review summarizes the recent developments in studying the novel human polyomaviruses, and touches upon several aspects of polyomavirus virology, pathogenicity, epidemiology and phylogeny.

Merkel cell polyomavirus: a newly discovered human virus with oncogenic potential

A marked escalation in the rate of discovery of new types of human polyomavirus has occurred over the last five years largely owing to recent technological advances in their detection. Among the newly discovered viruses, Merkel Cell Polyomavirus (MCPyV or MCV) has gained the most attention due to its link with a rare human cancer. Infection with MCPyV is common in the human population, and the virus is detected in several anatomical locations, but most frequently in skin. Study of MCPyV molecular virology has been complicated by the lack of straightforward cell culture models, but recent in vitro studies are making strides towards understanding the virus life cycle, its cellular tropism, and mode of transmission. While MCPyV shares several traditional traits with other human polyomaviruses, the burst of research since its discovery reveals insight into a virus with many unique genetic and mechanistic features. The evidence for a causal link between MCPyV and the rare neuroendocrine cancer, Merkel Cell Carcinoma (MCC), is compelling. A majority of MCCs contain clonally integrated viral DNA, express viral T antigen transcripts and protein, and exhibit an addiction to the viral large T and small t antigen oncoproteins. The MCPyV large T antigen contains MCC tumor-specific mutations that ablate its replication capacity but preserve its oncogenic functions, and the small t antigen promotes an environment favorable for cap-dependent translation. The mechanisms of MCPyV-induced transformation have not been fully elucidated, but the likely etiological role of this new polyomavirus in human cancer provides a strong opportunity to expand knowledge of virus-host interactions and viral oncology.

Detection of Merkel cell polyomavirus in chronic lymphocytic leukemia T-cells

Chronic lymphocytic leukemia/small cell lymphoma (CLL/SLL) is the most common B-cell leukemia/lymphoma, effecting >15,000 patients/year. There has been a proposed limited antigenic etiology, at least in some cases, of CLL/SLL based upon immunoglobulin heavy chain stereotypy found across unrelated cases, suggesting viral source may provide such antigenic stimulation. With an established epidemiological link between CLL/SLL and Merkel cell carcinoma (MCC), there has been some interest in investigating a possible leukemogenic role of Merkel cell polyomavirus (MCPyV), which is found in 80% of MCC cases. Recent studies have shown that MCPyV is present in lymphocytes in a small percentage of CLL/SLL cases, but the specific tropism for lymphocytes has not been well-established. In this study, we used quantitative PCR to investigate the presence of MCPyV in fluorescence activated cell sorted purified B- and T-cells from 23 CLL/SLL cases. Three of 23 cases (13%) had detectable MCPyV in T-cells, and none of the cases had detectable MCPyV in B-cells. These findings suggest that MCPyV may have tropism for T-cells in addition to previously reported neoplastic B-cells.

MCV and Merkel cell carcinoma: a molecular success story

Merkel cell polyomavirus (MCV), discovered in 2008, is clonally integrated in ~80% Merkel cell carcinoma (MCC). MCV is a common skin flora and initiates cancer in susceptible hosts only after it acquires a precise set of mutations that render it replication incompetent. Both MCV large and small T proteins promote cancer cell survival and proliferation. Large T targets pocket proteins regulating cell cycle transit while small T activates cap-dependent translation critical for cancer cell growth. These findings already have led to new diagnostics and clinical trials to target MCV-induced survivin and to promote antitumor immunity. In four years, the cause, diagnosis and therapy for an intractable cancer has been changed due to the molecular discovery of MCV.

Novel human polyomaviruses, Merkel cell polyomavirus and human polyomavirus 9, in Japanese chronic lymphocytic leukemia cases

BACKGROUND

Chronic lymphocytic leukemia (CLL) is the rarest adult leukemia in Japan, whereas it is the most common leukemia in the Western world. Recent studies from the United States and Germany suggest a possible etiological association between Merkel cell polyomavirus (MCPyV) and CLL, although no data have been reported from Eastern countries. To increase the volume of relevant data, this study investigated the prevalence and DNA loads of MCPyV and human polyomavirus 9 (HPyV9), another lymphotropic polyomavirus, in Japanese CLL cases.

FINDINGS

We found that 9/27 CLL cases (33.3 %) were positive for MCPyV using quantitative real-time polymerase chain reaction analysis. The viral DNA loads ranged from 0.000017 to 0.0012 copies per cell. All cases were negative for HPyV9. One MCPyV-positive CLL case was evaluated by mutational analysis of the large T (LT) gene, which indicated the presence of wild-type MCPyV without a nucleotide deletion. DNA sequence analysis of the entire small T (ST) gene and the partial LT gene revealed that a Japanese MCPyV isolate, designated CLL-JK, had two nucleotide gaps when compared with the reference sequence of the North American isolate MCC350.

CONCLUSIONS

This study provides the first evidence that MCPyV is present in a subset of Japanese CLL cases with low viral DNA loads. MCPyV and HPyV9 are unlikely to contribute directly to the development of CLL in the majority of Japanese cases. MCPyV isolated from the Japanese CLL cases may constitute an Asian group and its pathogenicity needs to be clarified in future studies.

Merkel cell carcinoma: a virus-induced human cancer

Merkel cell polyomavirus (MCV) is the first polyomavirus directly linked to human cancer, and its recent discovery helps to explain many of the enigmatic features of Merkel cell carcinoma (MCC). MCV is clonally integrated into MCC tumor cells, which then require continued MCV oncoprotein expression to survive. The integrated viral genomes have a tumor-specific pattern of tumor antigen gene mutation that incapacitates viral DNA replication. This human cancer virus provides a new model in which a common, mostly harmless member of the human viral flora can initiate cancer if it acquires a precise set of mutations in a host with specific susceptibility factors, such as age and immune suppression. Identification of this tumor virus has led to new opportunities for early diagnosis and targeted treatment of MCC.

Human polyomaviruses in skin diseases

Polyomaviruses are a family of small, nonenveloped viruses with a circular double-stranded DNA genome of ∼5,000 base pairs protected by an icosahedral protein structure. So far, members of this family have been identified in birds and mammals. Until 2006, BK virus (BKV), JC virus (JCV), and simian virus 40 (SV40) were the only polyomaviruses known to circulate in the human population. Their occurrence in individuals was mainly confirmed by PCR and the presence of virus-specific antibodies. Using the same methods, lymphotropic polyomavirus, originally isolated in monkeys, was recently shown to be present in healthy individuals although with much lower incidence than BKV, JCV, and SV40. The use of advanced high-throughput sequencing and improved rolling circle amplification techniques have identified the novel human polyomaviruses KI, WU, Merkel cell polyomavirus, HPyV6, HPyV7, trichodysplasia spinulosa-associated polyomavirus, and HPyV9. The skin tropism of human polyomaviruses and their dermatopathologic potentials are the focus of this paper.

Opening new roads for MCPyV

In this issue of Blood, Pancaldi et al report on the latent presence of large T antigen (LTag) sequences of the Merkel cell polyomavirus (MCPyV) in buffy coats of healthy individuals.1

Vulvar merkel carcinoma: a case report

This is a new case of Merkel cell carcinoma of the vulva. It is a rare neuroendocrine carcinoma with an aggressive behavior. Because of its rarity in this location, it is not clear whether it behaves differently from the usual neuroendocrine carcinomas of the skin. A case of a 63-year-old patient with vulvar Merkel carcinoma is presented. The clinical presentation, microscopic and immunohistochemical features, and treatment are discussed.