No evidence of XMRV in prostate cancer cohorts in the Midwestern United States

Evidence from 40 Studies that 2 Common Single-Nucleotide Polymorphisms (SNPs) of RNASEL Gene Affect Prostate Cancer Susceptibility: A Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-Compliant Meta-Analysis

BACKGROUND Numerous studies have evaluated the relationship between RNASEL gene polymorphisms (rs486907 G>A and rs627928 T>G) and the risk of cancer. However, many of the results have been controversial. To explore the role of RNASEL gene polymorphisms in prostate cancer, we carried out the present meta-analysis. MATERIAL AND METHODS The qualified articles were collected from PubMed, Web of Science, Scopus, CNKI, and WanFang databases to August 2018. A total 23 articles with 40 studies were incorporated into our analysis. RESULTS Our data show that rs486907 was not associated with the risk of prostate cancer in any populations. Nevertheless, rs627928 was reported to promote the development of prostate cancer (T vs. G: OR=1.08, 95% CI=1.01-1.15; TT+TG vs. GG: OR=1.14, 95% CI=1.03-1.25) in allele and recessive models in overall populations. Stratified analyses showed that similar results were obtained in white populations. CONCLUSIONS We report the effect of rs627928 on the development of prostate cancer and confirm that rs486907 is not involved in the risk of prostate cancer in the current meta-analysis. However, research in larger populations is needed to validate our conclusions.

Association of a common genetic variant in RNASEL and prostate cancer susceptibility

The RNASEL gene (2’, 5’-oligoisoadenylate synthetase-dependent) encodes a ribonuclease that plays a significant role in the apoptotic and antiviral activities of interferons. Various studies have used polymorphisms in the RNASEL gene to evaluate prostate cancer risk but studies that show an association between RNASEL Arg462Gln (1385G>A, R462Q, rs486907) polymorphism and prostate cancer risk are somewhat inconclusive. To assess the impact of RNASEL Arg462Gln polymorphism on prostate cancer risk, we conducted a meta-analysis of all available studies including 11,522 patients and 10,976 control subjects. The overall results indicated no positive association between the variant and prostate cancer risk. However, in a subgroup analysis by ethnicity, obvious associations were observed in Hispanic Caucasians for allelic contrast (OR = 1.18, 95% CI = 1.00 - 1.39, P_{heterogeneity} = 0.010), homozygote comparison (OR = 1.50, 95% CI = 1.02 – 2.20, P_{heterogeneity} = 0.001), and the recessive genetic model (OR = 1.44, 95% CI = 1.01 - 2.05, P_{heterogeneity} = 0.002) ; and in African descendants for homozygote comparison (OR = 2.59, 95% CI = 1.29 – 5.19, P_{heterogeneity} = 0.194) and the recessive genetic model (OR = 2.61, 95% CI = 1.30 – 5.23, P_{heterogeneity} = 0.195). In conclusion, the RNASEL Arg462Gln polymorphism may contribute to the risk of developing prostate cancer in African descendants and Hispanic Caucasians. Further larger and well-designed studies are warranted to evaluate this association in detail.

Xenotropic Murine Leukemia Virus-Related Virus and RNase L R462Q Variants in Iranian Patients With Sporadic Prostate Cancer

Background:

Although several studies have confirmed the association of xenotropic murine leukemia virus-related virus (XMRV) and prostate cancer, this association is still controversial, as most studies did not detect XMRV in prostate tissue samples. Furthermore, some genetic and epidemiological studies have highlighted a role for RNase L polymorphisms, particularly R462Q, in the progression of prostate cancer.

Objectives:

The focus of this study was on the association of XMRV and RNase L R462Q variants with the risk of prostate cancer in Iranian patients.

Patients and Methods:

In this case-control study, 40 and 80 individuals with sporadic prostate cancer and benign prostatic hyperplasia, respectively, were included. The presence of XMRV was evaluated by real-time polymerase chain reaction (PCR) of integrase and nested-PCR for the gag genes. The RNase L R462Q polymorphism analysis was carried out by PCR and sequencing.

Results:

In a total of 40 sporadic prostate cancer and 80 benign prostatic hyperplasia cases, no XMRV was detected by real-time PCR and nested-PCR. RNase L R462Q polymorphism analysis reveals that although there was an increase in the risk of prostate cancer correlated with the Q/Q allele of RNase L at position 462, the frequencies of the RNase L R462Q alleles were not statistically significant between the prostate cancer and benign prostatic hyperplasia groups (OR = 2.75 (95% CI = 0.67 - 11.3), P = 0.29).

Conclusions:

These results did not support the presence of XMRV in the samples with prostate cancer and showed that RNase L R462Q variants had relatively little or no impact on the risk of prostate cancer in Iranian population.

The saga of XMRV: a virus that infects human cells but is not a human virus

Xenotropic murine leukemia virus-related virus (XMRV) was discovered in 2006 in a search for a viral etiology of human prostate cancer (PC). Substantial interest in XMRV as a potentially new pathogenic human retrovirus was driven by reports that XMRV could be detected in a significant percentage of PC samples, and also in tissues from patients with chronic fatigue syndrome (CFS). After considerable controversy, etiologic links between XMRV and these two diseases were disproven. XMRV was determined to have arisen during passage of a human PC tumor in immunocompromised nude mice, by activation and recombination between two endogenous murine leukemia viruses from cells of the mouse. The resulting XMRV had a xentropic host range, which allowed it replicate in the human tumor cells in the xenograft. This review describes the discovery of XMRV, and the molecular and virological events leading to its formation, XMRV infection in animal models and biological effects on infected cells. Lessons from XMRV for other searches of viral etiologies of cancer are discussed, as well as cautions for researchers working on human tumors or cell lines that have been passed through nude mice, includingpotential biohazards associated with XMRV or other similar xenotropic murine leukemia viruses (MLVs).

Murine leukemia virus uses TREX components for efficient nuclear export of unspliced viral transcripts

Previously we reported that nuclear export of both unspliced and spliced murine leukemia virus (MLV) transcripts depends on the nuclear export factor (NXF1) pathway. Although the mRNA export complex TREX, which contains Aly/REF, UAP56, and the THO complex, is involved in the NXF1-mediated nuclear export of cellular mRNAs, its contribution to the export of MLV mRNA transcripts remains poorly understood. Here, we studied the involvement of TREX components in the export of MLV transcripts. Depletion of UAP56, but not Aly/REF, reduced the level of both unspliced and spliced viral transcripts in the cytoplasm. Interestingly, depletion of THO components, including THOC5 and THOC7, affected only unspliced viral transcripts in the cytoplasm. Moreover, the RNA immunoprecipitation assay showed that only the unspliced viral transcript interacted with THOC5. These results imply that MLV requires UAP56, THOC5 and THOC7, in addition to NXF1, for nuclear export of viral transcripts. Given that naturally intronless mRNAs, but not bulk mRNAs, require THOC5 for nuclear export, it is plausible that THOC5 plays a key role in the export of unspliced MLV transcripts.

Murine leukemia virus uses NXF1 for nuclear export of spliced and unspliced viral transcripts

Intron-containing mRNAs are subject to restricted nuclear export in higher eukaryotes. Retroviral replication requires the nucleocytoplasmic transport of both spliced and unspliced RNA transcripts, and RNA export mechanisms of gammaretroviruses are poorly characterized. Here, we report the involvement of the nuclear export receptor NXF1/TAP in the nuclear export of gammaretroviral RNA transcripts. We identified a conserved cis-acting element in the pol gene of gammaretroviruses, including murine leukemia virus (MLV) and xenotropic murine leukemia virus (XMRV), named the CAE (cytoplasmic accumulation element). The CAE enhanced the cytoplasmic accumulation of viral RNA transcripts and the expression of viral proteins without significantly affecting the stability, splicing, or translation efficiency of the transcripts. Insertion of the CAE sequence also facilitated Rev-independent HIV Gag expression. We found that the CAE sequence interacted with NXF1, whereas disruption of NXF1 ablated CAE function. Thus, the CAE sequence mediates the cytoplasmic accumulation of gammaretroviral transcripts in an NXF1-dependent manner. Disruption of NXF1 expression impaired cytoplasmic accumulations of both spliced and unspliced RNA transcripts of XMRV and MLV, resulting in their nuclear retention or degradation. Thus, our results demonstrate that gammaretroviruses use NXF1 for the cytoplasmic accumulation of both spliced and nonspliced viral RNA transcripts.

IMPORTANCE

Murine leukemia virus (MLV) has been studied as one of the classic models of retrovirology. Although unspliced host messenger RNAs are rarely exported from the nucleus, MLV actively exports unspliced viral RNAs to the cytoplasm. Despite extensive studies, how MLV achieves this difficult task has remained a mystery. Here, we have studied the RNA export mechanism of MLV and found that (i) the genome contains a sequence which supports the efficient nuclear export of viral RNAs, (ii) the cellular factor NXF1 is involved in the nuclear export of both spliced and unspliced viral RNAs, and, finally, (iii) depletion of NXF1 results in nuclear retention or degradation of viral RNAs. Our study provides a novel insight into MLV nuclear export.

Infection of Xenotransplanted Human Cell Lines by Murine Retroviruses: A Lesson Brought Back to Light by XMRV

Infection of xenotransplanted human cells by xenotropic retroviruses is a known phenomenon in the scientific literature, with examples cited since the early 1970s. However, arguably, until recently, the importance of this phenomenon had not been largely recognized. The emergence and subsequent debunking of Xenotropic Murine leukemia virus-Related Virus (XMRV) as a cell culture contaminant as opposed to a potential pathogen in several human diseases, notably prostate cancer and Chronic Fatigue Syndrome, highlighted a potential problem of murine endogenous gammaretroviruses infecting commonly used human cell lines. Subsequent to the discovery of XMRV, many additional cell lines that underwent xenotransplantation in mice have been shown to harbor murine gammaretroviruses. Such retroviral infection poses the threat of not only confounding experiments performed in these cell lines via virus-induced changes in cellular behavior but also the potential infection of other cell lines cultured in the same laboratory. Thus, the possibility of xenotropic retroviral infection of cell lines may warrant additional precautions, such as periodic testing for retroviral sequences in cell lines cultured in the laboratory.

No association between XMRV or related gammaretroviruses in Australian prostate cancer patients

BACKGROUND

Xenotropic murine leukemia virus-related virus (XMRV) is a gammaretrovirus reported to be associated with prostate cancer (PC) and chronic fatigue syndrome (CFS). While the association of XMRV with CFS and PC has recently been discredited, no studies have been performed in Australian patients to investigate the association between PC and XMRV or related murine leukemia virus (MLV) in matched PC and normal tissue.

METHODS

Genomic DNA (gDNA) was purified from matched normal and cancer formalin-fixed paraffin-embedded (FFPE) prostate tissue from 35 Australian PC patients with Gleason scores ranging from 7 - 10. The presence of the ribonuclease L (RNase L) polymorphism R462Q was determined by allele specific PCR. Samples were screened for XMRV and related murine leukemia virus (MLV) variants by qPCR. Contaminating mouse DNA was detected using qPCR targeting mouse intracisternal A particle long terminal repeat DNA.

RESULTS

gDNA was successfully purified from 94% (66/70) of normal and cancer FFPE prostate tissues. RNase L typing revealed 8% were homozygous (QQ), 60% were heterozygous (RQ) and 32% were wild-type (RR) for the RNase L mutation. None of the 66 samples tested were positive for XMRV or related MLV sequences using broad MLV or XMRV specific primers with detection sensitivities of 1 viral copy of MLV/XMRV and XMRV DNA, respectively.

CONCLUSIONS

Using highly sensitive qPCR we found no evidence of XMRV or related gammaretroviruses in prostate tissues from 35 Australian PC patients. Our findings are consistent with other studies demonstrating that XMRV is a laboratory contaminant that has no role in the aetiology of PC.

In-depth investigation of archival and prospectively collected samples reveals no evidence for XMRV infection in prostate cancer

XMRV, or xenotropic murine leukemia virus (MLV)-related virus, is a novel gammaretrovirus originally identified in studies that analyzed tissue from prostate cancer patients in 2006 and blood from patients with chronic fatigue syndrome (CFS) in 2009. However, a large number of subsequent studies failed to confirm a link between XMRV infection and CFS or prostate cancer. On the contrary, recent evidence indicates that XMRV is a contaminant originating from the recombination of two mouse endogenous retroviruses during passaging of a prostate tumor xenograft (CWR22) in mice, generating laboratory-derived cell lines that are XMRV-infected. To confirm or refute an association between XMRV and prostate cancer, we analyzed prostate cancer tissues and plasma from a prospectively collected cohort of 39 patients as well as archival RNA and prostate tissue from the original 2006 study. Despite comprehensive microarray, PCR, FISH, and serological testing, XMRV was not detected in any of the newly collected samples or in archival tissue, although archival RNA remained XMRV-positive. Notably, archival VP62 prostate tissue, from which the prototype XMRV strain was derived, tested negative for XMRV on re-analysis. Analysis of viral genomic and human mitochondrial sequences revealed that all previously characterized XMRV strains are identical and that the archival RNA had been contaminated by an XMRV-infected laboratory cell line. These findings reveal no association between XMRV and prostate cancer, and underscore the conclusion that XMRV is not a naturally acquired human infection.

Recombinant origin, contamination, and de-discovery of XMRV

The discovery and de-discovery of the xenotropic murine leukemia virus-related virus (XMRV) has been a tumultuous roller-coaster ride for scientists and patients. The initial associations of XMRV with chronic fatigue syndrome and prostate cancer, while providing much hope and optimism, have now been discredited and/or retracted following overwhelming evidence that (1) numerous patient cohorts from around the world are XMRV-negative, (2) the initial reports of XMRV-positive patients were due to contamination with mouse DNA, XMRV plasmid DNA, or virus from the 22Rv1 cell line and (3) XMRV is a laboratory-derived virus generated in the mid 1990s through recombination during passage of a prostate tumor xenograft in immuno-compromised mice. While these developments are disappointing to scientists and patients, they provide a valuable road map of potential pitfalls to the would-be microbe hunters.

XMRV induces cell migration, cytokine expression and tumor angiogenesis: are 22Rv1 cells a suitable prostate cancer model?

22Rv1 is a common prostate cancer cell line used in xenograft mouse experiments as well as in vitro cell culture assays to study aspects of prostate cancer tumorigenesis. Recently, this cell line was shown to harbor multiple copies of a gammaretrovirus, called XMRV, integrated in its genome. While the original prostate cancer xenograft CWR22 is free of any retrovirus, subsequently generated cell lines 22Rv1 and CWR-R1, carry this virus and additionally shed infectious gammaretroviral particles in their supernatant. Although XMRV most likely was generated by recombination events in cell culture this virus has been demonstrated to infect human cells in vitro and 22Rv1 as well as CWR-R1 cells are now considered biosafety 2 reagents. Here, we demonstrate that 22Rv1 cells with reduced retroviral transcription show reduced tumor angiogenesis and increased necrosis of the primary tumor derived from xenografted cells in scid mice when compared to the parental cell line. The presence of XMRV transcripts significantly increases secretion of osteopontin (OPN), CXCL14, IL13 and TIMP2 in 22Rv1 cells. Furthermore, these data are supported by in vitro cell invasion and differentiation assays. Collectively, our data suggest that the presence of XMRV transcripts at least partially contributes to 22Rv1 characteristics observed in vitro and in vivo with regard to migration, invasion and tumor angiogenesis. We propose that data received with 22Rv1 cells or equivalent cells carrying xenotropic gammaretroviruses should be carefully controlled including other prostate cancer cell lines tested for viral sequences.

No evidence for xenotropic murine leukemia-related virus infection in Sweden using internally controlled multiepitope suspension array serology

Many syndromes have a large number of differential diagnoses, a situation which calls for multiplex diagnostic systems. Myalgic encephalomyelitis (ME), also named chronic fatigue syndrome (CFS), is a common disease of unknown etiology. A mouse retrovirus, xenotropic murine leukemia-related virus (XMRV), was found in ME/CFS patients and blood donors, but this was not corroborated. However, the paucity of serological investigations on XMRV in humans prompted us to develop a serological assay which cover many aspects of XMRV antigenicity. It is a novel suspension array method, using a multiplex IgG assay with nine recombinant proteins from the env and gag genes of XMRV and 38 peptides based on known epitopes of vertebrate gammaretroviruses. IgG antibodies were sought in 520 blood donors and 85 ME/CFS patients and in positive- and negative-control sera from animals. We found no differences in seroreactivity between blood donors and ME/CFS patients for any of the antigens. This did not support an association between ME/CFS and XMRV infection. The multiplex serological system had several advantages: (i) biotinylated protein G allowed us to run both human and animal sera, which is essential because of a lack of XMRV-positive humans; (ii) a novel quality control was a pan-peptide positive-control rabbit serum; and (iii) synthetic XMRV Gag peptides with degenerate positions covering most of the variation of murine leukemia-like viruses did not give higher background than nondegenerate analogs. The principle may be used for creation of variant tolerant peptide serologies. Thus, our system allows rational large-scale serological assays with built-in quality control.

Zinc-finger antiviral protein inhibits XMRV infection

Background

The zinc-finger antiviral protein (ZAP) is a host factor that specifically inhibits the replication of certain viruses, including Moloney murine leukemia virus (MoMLV), HIV-1, and certain alphaviruses and filoviruses. ZAP binds to specific viral mRNAs and recruits cellular mRNA degradation machinery to degrade the target RNA. The common features of ZAP-responsive RNA sequences remain elusive and thus whether a virus is susceptible to ZAP can only be determined experimentally. Xenotropic murine leukemia virus-related virus (XMRV) is a recently identified γ-retrovirus that was originally thought to be involved in prostate cancer and chronic fatigue syndrome but recently proved to be a laboratory artefact. Nonetheless, XMRV as a new retrovirus has been extensively studied. Since XMRV and MoMLV share only 67.9% sequence identity in the 3′UTRs, which is the target sequence of ZAP in MoMLV, whether XMRV is susceptible to ZAP remains to be determined.

Findings

We constructed an XMRV-luc vector, in which the coding sequences of Gag-Pol and part of Env were replaced with luciferase-coding sequence. Overexpression of ZAP potently inhibited the expression of XMRV-luc in a ZAP expression-level-dependent manner, while downregulation of endogenous ZAP rendered cells more sensitive to infection. Furthermore, ZAP inhibited the spreading of replication-competent XMRV. Consistent with the previously reported mechanisms by which ZAP inhibits viral infection, ZAP significantly inhibited the accumulation of XMRV-luc mRNA in the cytoplasm. The ZAP-responsive element in XMRV mRNA was mapped to the 3′UTR.

Conclusions

ZAP inhibits XMRV replication by preventing the accumulation of viral mRNA in the cytoplasm. Documentation of ZAP inhibiting XMRV helps to broaden the spectrum of ZAP's antiviral activity. Comparison of the target sequences of ZAP in XMRV and MoMLV helps to better understand the features of ZAP-responsive elements.

Absence of XMRV and closely related viruses in primary prostate cancer tissues used to derive the XMRV-infected cell line 22Rv1

The 22Rv1 cell line is widely used for prostate cancer research and other studies throughout the world. These cells were established from a human prostate tumor, CWR22, that was serially passaged in nude mice and selected for androgen independence. The 22Rv1 cells are known to produce high titers of xenotropic murine leukemia virus-related virus (XMRV). Recent studies suggested that XMRV was inadvertently created in the 1990's when two murine leukemia virus (MLV) genomes (pre-XMRV1 and pre-XMRV-2) recombined during passaging of the CWR22 tumor in mice. The conclusion that XMRV originated from mice and not the patient was based partly on the failure to detect XMRV in early CWR22 xenografts. While that deduction is certainly justified, we examined the possibility that a closely related virus could have been present in primary tumor tissue. Here we report that we have located the original prostate tumor tissue excised from patient CWR22 and have assayed the corresponding DNA by PCR and the tissue sections by fluorescence in situ hybridization for the presence of XMRV or a similar virus. The primary tumor tissues lacked mouse DNA as determined by PCR for intracisternal A type particle DNA, thus avoiding one of the limitations of studying xenografts. We show that neither XMRV nor a closely related virus was present in primary prostate tissue of patient CWR22. Our findings confirm and reinforce the conclusion that XMRV is a recombinant laboratory-generated mouse virus that is highly adapted for human prostate cancer cells.

Thirty years of research on infection and prostate cancer: no conclusive evidence for a link. A systematic review

BACKGROUND

The potential role of genitourinary infection in the etiology of prostate cancer (CaP) has been extensively investigated for 30 years. Two basic approaches have been used: tissue-based methods (polymerase chain reaction, immunohistochemistry, and in situ hybridization) and serologic assays (enzyme-linked immunosorbent assay, immunofluorescence, etc.). The objective of this review was to answer the question of whether infection of the male genitourinary tract may have a role in the etiology of CaP.

MATERIALS AND METHODS

We have carried out a systematic review of the evidence that was published in the MEDLINE/PubMed database until December 2011. The search terms included "prostate cancer," "infection," and the explicit names of the various infectious agents. Additional studies were identified using a reference search. A total of 74 papers were included in the review, which cover the following infectious agents: human papillomavirus, cytomegalovirus, herpes simplex virus, Epstein-Barr virus, human herpesvirus, BK virus, JC virus, chlamydia, mycoplasma, ureaplasma, trichomonas, neisseria, treponema, Propionibacterium acnes, xenotropic murine leukemia virus-related virus and Candida albicans.

RESULTS

Despite the variable study designs and methodological approaches that were used, most of the pathogens that were studied were unlikely to be directly involved in prostate carcinogenesis.

CONCLUSIONS

The role of infection in the etiology of CaP has yet to be determined despite 30 years of research efforts. A discovery of an infectious agent that is associated with CaP would be of great medical importance; however, such a link would have to be firmly established before impacting on patient care.

Restricted replication of xenotropic murine leukemia virus-related virus in pigtailed macaques

Although xenotropic murine leukemia virus-related virus (XMRV) has been previously linked to prostate cancer and myalgic encephalomyelitis/chronic fatigue syndrome, recent data indicate that results interpreted as evidence of human XMRV infection reflect laboratory contamination rather than authentic in vivo infection. Nevertheless, XMRV is a retrovirus of undefined pathogenic potential that is able to replicate in human cells. Here we describe a comprehensive analysis of two male pigtailed macaques (Macaca nemestrina) experimentally infected with XMRV. Following intravenous inoculation with >10(10) RNA copy equivalents of XMRV, viral replication was limited and transient, peaking at ≤2,200 viral RNA (vRNA) copies/ml plasma and becoming undetectable by 4 weeks postinfection, though viral DNA (vDNA) in peripheral blood mononuclear cells remained detectable through 119 days of follow-up. Similarly, vRNA was not detectable in lymph nodes by in situ hybridization despite detectable vDNA. Sequencing of cell-associated vDNA revealed extensive G-to-A hypermutation, suggestive of APOBEC-mediated viral restriction. Consistent with limited viral replication, we found transient upregulation of type I interferon responses that returned to baseline by 2 weeks postinfection, no detectable cellular immune responses, and limited or no spread to prostate tissue. Antibody responses, including neutralizing antibodies, however, were detectable by 2 weeks postinfection and maintained throughout the study. Both animals were healthy for the duration of follow-up. These findings indicate that XMRV replication and spread were limited in pigtailed macaques, predominantly by APOBEC-mediated hypermutation. Given that human APOBEC proteins restrict XMRV infection in vitro, human XMRV infection, if it occurred, would be expected to be characterized by similarly limited viral replication and spread.

No evidence of XMRV infection in immunocompromised patients and HIV-positive individuals from Germany

BACKGROUND

Xenotropic murine leukaemia virus-related virus (XMRV) has been detected in patients with prostate cancer and chronic fatigue syndrome (CFS). The detection of XMRV in healthy individuals has raised concern about a possible virus transmission by blood products. However, recent studies challenge the association between XMRV and human disease. This study investigated whether or not XMRV is present in patients with altered immune function and individuals at increased risk of blood-borne viral infections in Germany.

METHODS

We investigated 503 peripheral blood mononuclear cell (PBMC) samples from 240 patients with iatrogenic immune suppression (71 haematopoietic stem cell recipients, 132 solid organ transplant recipients, 37 others) and 311 PBMC samples from 302 patients with HIV-1 infection for the presence of proviral XMRV by real-time polymerase chain reaction (PCR).

RESULTS

All 814 PBMC samples from 542 patients tested negative for XMRV DNA and positive for an internal herpesvirus saimiri (HVS) control. Human genomic DNA was detected in all samples, and 90% of the samples contained >10,000 cell equivalents per XMRV PCR reaction.

CONCLUSIONS

Our failure to detect proviral XMRV provides evidence against the presence of XMRV in patients at increased risk of viral infections in Germany.

Absence of XMRV in peripheral blood mononuclear cells of ARV-treatment naïve HIV-1 infected and HIV-1/HCV coinfected individuals and blood donors

Background

Xenotropic murine leukemia virus-related virus (XMRV) has been found in the prostatic tissue of prostate cancer patients and in the blood of chronic fatigue syndrome patients. However, numerous studies have found little to no trace of XMRV in different human cohorts. Based on evidence suggesting common transmission routes between XMRV and HIV-1, HIV-1 infected individuals may represent a high-risk group for XMRV infection and spread.

Methodology/Principal Findings

DNA was isolated from the peripheral blood mononuclear cells (PBMCs) of 179 HIV-1 infected treatment naïve patients, 86 of which were coinfected with HCV, and 54 healthy blood donors. DNA was screened for XMRV provirus with two sensitive, published PCR assays targeting XMRV gag and env and one sensitive, published nested PCR assay targeting env. Detection of XMRV was confirmed by DNA sequencing. One of the 179 HIV-1 infected patients tested positive for gag by non-nested PCR whereas the two other assays did not detect XMRV in any specimen. All healthy blood donors were negative for XMRV proviral sequences. Sera from 23 HIV-1 infected patients (15 HCV⁺) and 12 healthy donors were screened for the presence of XMRV-reactive antibodies by Western blot. Thirteen sera (57%) from HIV-1⁺ patients and 6 sera (50%) from healthy donors showed reactivity to XMRV-infected cell lysate.

Conclusions/Significance

The virtual absence of XMRV in PBMCs suggests that XMRV is not associated with HIV-1 infected or HIV-1/HCV coinfected patients, or blood donors. Although we noted isolated incidents of serum reactivity to XMRV, we are unable to verify the antibodies as XMRV specific.

Long-term infection and vertical transmission of a gammaretrovirus in a foreign host species

Increasing evidence has indicated natural transspecies transmission of gammaretroviruses; however, viral-host interactions after initial xeno-exposure remain poorly understood. Potential association of xenotropic murine leukemia virus-related virus (XMRV) in patients with prostate cancer and chronic fatigue syndrome has attracted broad interests in this topic. Although recent studies have indicated that XMRV is unlikely a human pathogen, further understanding of XMRV xenoinfection would allow in vivo modeling of the initial steps of gammaretroviral interspecies transmission, evolution and dissemination in a new host population. In this study, we monitored the long-term consequences of XMRV infection and its possible vertical transmission in a permissive foreign host, wild-derived Mus pahari mice. One year post-infection, XMRV-infected mice showed no notable pathological changes, while proviral DNA was detected in three out of eight mice. XMRV-infected mice remained seropositive throughout the study although the levels of gp70 Env- and p30 capsid-specific antibodies gradually decreased. When vertical XMRV transmission was assessed, no viremia, humoral immune responses nor endogenization were observed in nine offspring from infected mothers, yet one offspring was found PCR-positive for XMRV-specific sequences. Amplified viral sequences from the offspring showed several mutations, including one amino acid deletion in the receptor binding domain of Env SU. Our results therefore demonstrate long-term asymptomatic infection, low incidence of vertical transmission and limited evolution of XMRV upon transspecies infection of a permissive new host, Mus pahari.

XMRV and prostate cancer--a 'final' perspective

XMRV was first described in 2006, when it was identified in samples isolated from prostate cancer tissues. However, studies have since shown that XMRV arose in the laboratory and was formed by genetic recombination between two viral genomes carried in the germline DNA of mice used during serial transplantation of the CWR22 prostate cancer xenograft. These new findings strongly imply that XMRV does not circulate in humans, but is only present in the laboratory. Thus, there is no reason to believe that it has any role in the etiology of prostate cancer or other diseases.

No evidence of murine leukemia virus-related viruses in live attenuated human vaccines

BACKGROUND

The association of xenotropic murine leukemia virus (MLV)-related virus (XMRV) in prostate cancer and chronic fatigue syndrome reported in previous studies remains controversial as these results have been questioned by recent data. Nonetheless, concerns have been raised regarding contamination of human vaccines as a possible source of introduction of XMRV and MLV into human populations. To address this possibility, we tested eight live attenuated human vaccines using generic PCR for XMRV and MLV sequences. Viral metagenomics using deep sequencing was also done to identify the possibility of other adventitious agents.

RESULTS

All eight live attenuated vaccines, including Japanese encephalitis virus (JEV) (SA-14-14-2), varicella (Varivax), measles, mumps, and rubella (MMR-II), measles (Attenuvax), rubella (Meruvax-II), rotavirus (Rotateq and Rotarix), and yellow fever virus were negative for XMRV and highly related MLV sequences. However, residual hamster DNA, but not RNA, containing novel endogenous gammaretrovirus sequences was detected in the JEV vaccine using PCR. Metagenomics analysis did not detect any adventitious viral sequences of public health concern. Intracisternal A particle sequences closest to those present in Syrian hamsters and not mice were also detected in the JEV SA-14-14-2 vaccine. Combined, these results are consistent with the production of the JEV vaccine in Syrian hamster cells.

CONCLUSIONS

We found no evidence of XMRV and MLV in eight live attenuated human vaccines further supporting the safety of these vaccines. Our findings suggest that vaccines are an unlikely source of XMRV and MLV exposure in humans and are consistent with the mounting evidence on the absence of these viruses in humans.

Detection of murine leukemia virus or mouse DNA in commercial RT-PCR reagents and human DNAs

The xenotropic murine leukemia virus (MLV)-related viruses (XMRV) have been reported in persons with prostate cancer, chronic fatigue syndrome, and less frequently in blood donors. Polytropic MLVs have also been described in persons with CFS and blood donors. However, many studies have failed to confirm these findings, raising the possibility of contamination as a source of the positive results. One PCR reagent, Platinum Taq polymerase (pol) has been reported to contain mouse DNA that produces false-positive MLV PCR results. We report here the finding of a large number of PCR reagents that have low levels of MLV sequences. We found that recombinant reverse-transcriptase (RT) enzymes from six companies derived from either MLV or avian myeloblastosis virus contained MLV pol DNA sequences but not gag or mouse DNA sequences. Sequence and phylogenetic analysis showed high relatedness to Moloney MLV, suggesting residual contamination with an RT-containing plasmid. In addition, we identified contamination with mouse DNA and a variety of MLV sequences in commercially available human DNAs from leukocytes, brain tissues, and cell lines. These results identify new sources of MLV contamination and highlight the importance of careful pre-screening of commercial specimens and diagnostic reagents to avoid false-positive MLV PCR results.

Dr.VIS: a database of human disease-related viral integration sites

Viral integration plays an important role in the development of malignant diseases. Viruses differ in preferred integration site and flanking sequence. Viral integration sites (VIS) have been found next to oncogenes and common fragile sites. Understanding the typical DNA features near VIS is useful for the identification of potential oncogenes, prediction of malignant disease development and assessing the probability of malignant transformation in gene therapy. Therefore, we have built a database of human disease-related VIS (Dr.VIS, http://www.scbit.org/dbmi/drvis) to collect and maintain human disease-related VIS data, including characteristics of the malignant disease, chromosome region, genomic position and viral–host junction sequence. The current build of Dr.VIS covers about 600 natural VIS of 5 oncogenic viruses representing 11 diseases. Among them, about 200 VIS have viral–host junction sequence.

False negative results from using common PCR reagents

Background

The sensitivity of the PCR reaction makes it ideal for use when identifying potentially novel viral infections in human disease. Unfortunately, this same sensitivity also leaves this popular technique open to potential contamination with previously amplified PCR products, or "carry-over" contamination. PCR product carry-over contamination can be prevented with uracil-DNA-glycosylase (UNG), and it is for this reason that it is commonly included in many commercial PCR master-mixes. While testing the sensitivity of PCR assays to detect murine DNA contamination in human tissue samples, we inadvertently discovered that the use of this common PCR reagent may lead to the production of false-negative PCR results.

Findings

We show here that contamination with minute quantities of UNG-digested PCR product or any negative control PCR reactions containing primer-dimers regardless of UNG presence can completely block amplification from as much as 60 ng of legitimate target DNA.

Conclusions

These findings could potentially explain discrepant results from laboratories attempting to amplify MLV-related viruses including XMRV from human samples, as none of the published reports used internal-tube controls for amplification. The potential for false negative results needs to be considered and carefully controlled in PCR experiments, especially when the target copy number may be low - just as the potential for false positive results already is.

Characterization, mapping, and distribution of the two XMRV parental proviruses

Xenotropic murine leukemia virus-related virus (XMRV) was previously reported to be associated with human prostate cancer and chronic fatigue syndrome. Our groups recently showed that XMRV was created through recombination between two endogenous murine retroviruses, PreXMRV-1 and PreXMRV-2, during the passaging of a prostate tumor xenograft in nude mice. Here, multiple approaches that led to the identification of PreXMRV-2, as well as the distribution of both parental proviruses among different mouse species, are described. The chromosomal loci of both proviruses were determined in the mouse genome, and integration site information was used to analyze the distribution of both proviruses in 48 laboratory mouse strains and 46 wild-derived strains. The strain distributions of PreXMRV-1 and PreXMRV-2 are quite different, the former being found predominantly in Asian mice and the latter in European mice, making it unlikely that the two XMRV ancestors could have recombined independently in the wild to generate an infectious virus. XMRV was not present in any of the mouse strains tested, and among the wild-derived mouse strains analyzed, not a single mouse carried both parental proviruses. Interestingly, PreXMRV-1 and PreXMRV-2 were found together in three laboratory strains, Hsd nude, NU/NU, and C57BR/cd, consistent with previous data that the recombination event that led to the generation of XMRV could have occurred only in the laboratory. The three laboratory strains carried the Xpr1(n) receptor variant nonpermissive to XMRV and xenotropic murine leukemia virus (X-MLV) infection, suggesting that the xenografted human tumor cells were required for the resulting XMRV recombinant to infect and propagate.

Development of sensitive single-round pol or env RT-PCR assays to screen for XMRV in multiple sample types

The potential association between xenotropic murine leukemia virus-related virus (XMRV) and prostate cancer and chronic fatigue syndrome (CFS) has been much debated. To help resolve the potential role of XMRV in human disease, it is critical to develop sensitive and accurate reverse transcriptase (RT)-PCR assays to screen for the virus. Single-round RT-PCR assays were developed on the automated m2000™ system for detection of the pol or env regions of XMRV in whole blood, plasma, urine cell pellets and urogenital swab samples. Assay performance was assessed by testing two blinded panels, one comprised of whole blood and the other of plasma spiked with serial dilutions of XMRV-infected tissue culture cells and supernatant, respectively, prepared by the Blood XMRV Scientific Research Working Group (SRWG). For both whole blood and plasma panel testing, the assays showed excellent specificity and sensitivity as compared to the other tests included in the SRWG phase I study. Analytical specificity of the assays was also evaluated. Neither pol nor env PCR assays detected a panel of potential cross-reactive microorganisms, although some cross-reaction was observed with mouse genomic DNA. Screening of 196 normal human blood donor plasma, 214 HIV-1 seropositive plasma, 20 formalin-fixed paraffin-embedded (FFPE) prostate cancer specimens, 4 FFPE benign prostate specimens, 400 urine pellets from prostate cancer patients, 166 urine pellets from non-prostate cancer patients, and 135 cervical swab specimens, detected no samples as unequivocally XMRV positive.

Seroprevalence of xenotropic murine leukemia virus-related virus in normal and retrovirus-infected blood donors

BACKGROUND

Xenotropic murine leukemia virus-related virus (XMRV) has been reported in patients with prostate cancer and chronic fatigue syndrome. Although results have been conflicting, the potential of XMRV as an infectious human retrovirus has raised concerns about transfusion safety. To address this issue, normal and retrovirus-infected blood donors were screened for evidence of XMRV infection.

STUDY DESIGN AND METHODS

Plasma from 1000 US, 100 human immunodeficiency virus Type 1-infected Cameroonian, and 642 human T-lymphotropic virus Type I (HTLV-I)-infected or uninfected Japanese blood donors as well as 311 sexually transmitted disease diagnostic specimens were screened for antibodies to XMRV gp70 and p15E using chemiluminescent immunoassays (CMIAs). CMIA-reactive samples were evaluated by p30 CMIA, Western blot, and real-time reverse transcriptase polymerase chain reaction.

RESULTS

XMRV seroreactivity was low (0%-0.6%) with the exception of the HTLV-I-infected donors (4.9%). Antibody was detected against only a single XMRV protein (p15E or gp70); none of the seroreactive samples had detectable XMRV pol or env sequences. The elevated seroreactivity in HTLV-I-infected donors was due to an increased p15E seroreactive rate (4.1%). Inspection of XMRV and HTLV sequences revealed a high level of conservation within the immunodominant region (IDR) of the transmembrane protein. In some cases, HTLV IDR peptide competitively reduced the XMRV p15E signal.

CONCLUSIONS

Based on the low prevalence of seroreactivity, detection of antibody to only a single XMRV protein and the absence of XMRV sequences, this study finds no compelling evidence of XMRV in normal or retrovirus-infected blood donors. The increased p15E seroreactivity observed in HTLV infection is likely due to cross-reactive antibodies.

No detection of XMRV in blood samples and tissue sections from prostate cancer patients in Northern Europe

BACKGROUND

We recently published the rare detection of xenotropic murine leukemia virus-related virus (XMRV) (1/105) in prostate cancer (PCA) tissue of patients in Northern Europe by PCR. The controversial discussion about the virus being detected in PCA tissue, blood samples from patients suffering from chronic fatigue syndrome (CFS), as well as from a significant number of healthy controls prompted us to deepen our studies about detection of XMRV infection applying different detection methods (PCR, cocultivation and immunohistochemistry [IHC]).

METHODOLOGY/PRINCIPAL FINDINGS

Peripheral blood mononuclear cells (PBMCs) from 92 PCA and 7 healthy controls were isolated, PHA activated and cocultivated with LNCaP cells for up to 8 weeks. Supernatant of these cells was applied to a reporter cell line, DERSE-iGFP. Furthermore, the PBMCs and cocultivated LNCaP cells were tested for the presence of XMRV by PCR as well as Western Blot analysis. While all PCR amplifications and Western Blot analyses were negative for signs of XMRV infection, DERSE-iGFP cells displayed isolated GFP positive cells in three cases. In all three cases XMRV presence could not be confirmed by PCR technology. In addition, we performed XMRV specific IHC on PCA tissue sections. Whole tissue sections (n = 20), as well as tissue microarrays (TMA) including 50 benign prostate hyperplasia (BPH), 50 low grade and 50 high grade PCA sections and TMAs including breast cancer, colon cancer and normal tissues were stained with two XMRV specific antisera. XMRV protein expression was not detected in any cancer sections included. One BPH tissue displayed XMRV specific protein expression in random isolated basal cells.

CONCLUSION

We were unable to conclusively detect XMRV in the blood from PCA patients or from healthy controls and there is no conclusive evidence of XMRV protein expression in PCA, breast cancer and colon cancer tissue sections tested by IHC staining.

Investigation of xenotropic murine leukemia virus-related virus (XMRV) in human and other cell lines

Xenotropic murine leukemia virus-related virus (XMRV) was discovered in human prostate tumors and later in some chronic fatigue syndrome (CFS) patients. However, subsequent studies have identified various sources of potential contamination with XMRV and other murine leukemia virus (MLV)-related sequences in test samples. Biological and nucleotide sequence analysis indicates that XMRV is distinct from known xenotropic MLVs and has a broad host range and cell tropism including human cells. Therefore, it is prudent to minimize the risk of human exposure to infection by evaluating XMRV contamination in cell lines handled in laboratory research and particularly those used in the manufacture of biological products. Nested DNA PCR assays were optimized for investigating XMRV gag and env sequences in various cell lines, which included MRC-5, Vero, HEK-293, MDCK, HeLa, and A549, that may be used in the development of some vaccines and other cell lines broadly used in research. The sensitivity of the DNA PCR assays was <10 copies in approximately 1.8 x 10(5) cells equivalent of human DNA. The results indicated the absence of XMRV in the cell lines tested; although in some cases DNA fragments identified as cellular sequences were seen following the first round of PCR amplification with the env primer pair.

Xenotropic murine leukemia virus-related virus is not associated with chronic fatigue syndrome in patients from different areas of the us in the 1990s

BACKGROUND

In 2009, xenotropic murine leukemia virus-related virus (XMRV) was reported in 67% of patients with chronic fatigue syndrome (CFS) compared to 4% of controls. Since then numerous reports failed to detect XMRV in other cohorts of CFS patients, and some studies suggested that XMRV sequences in human samples might be due to contamination of these samples with mouse DNA.

RESULTS

We determined the prevalence of XMRV in patients with CFS from similar areas in the United States as the original 2009 study, along with patients with chronic inflammatory disorders and healthy persons. Using quantitative PCR, we initially detected very low level signals for XMRV DNA in 15% of patients with CFS; however, the frequency of PCR positivity was no different between patients with CFS and controls. Repeated attempts to isolate PCR products from these reactions were unsuccessful. These findings were supported by our observations that PHA and IL-2 stimulation of peripheral blood mononuclear cells from patients with apparently low levels of XMRV, which induced virus replication in the 2009 report, resulted in the disappearance of the signal for XMRV DNA in the cells. Immunoprecipitation of XMRV-infected cell lysates using serum from patients from whom we initially detected low levels of XMRV DNA followed by immunoblotting with antibodies to XMRV gp70 protein failed to detect antibody in the patients, although one control had a weak level of reactivity. Diverse murine leukemia virus (MLV) sequences were obtained by nested PCR with a similar frequency in CFS patients and controls. Finally, we did not detect XMRV sequences in patients with several chronic inflammatory disorders including rheumatoid arthritis, Bechet's disease, and systemic lupus erythematosus.

CONCLUSIONS

We found no definitive evidence for XMRV DNA sequences or antibody in our cohort of CFS patients, which like the original 2009 study, included patients from diverse regions of the United States. In addition, XMRV was not detected in a cohort of patients with chronic inflammatory disorders.

Phylogenetic analysis of murine leukemia virus sequences from longitudinally sampled chronic fatigue syndrome patients suggests PCR contamination rather than viral evolution

Xenotropic murine leukemia virus (MLV)-related virus (XMRV) has been amplified from human prostate cancer and chronic fatigue syndrome (CFS) patient samples. Other studies failed to replicate these findings and suggested PCR contamination with a prostate cancer cell line, 22Rv1, as a likely source. MLV-like sequences have also been detected in CFS patients in longitudinal samples 15 years apart. Here, we tested whether sequence data from these samples are consistent with viral evolution. Our phylogenetic analyses strongly reject a model of within-patient evolution and demonstrate that the sequences from the first and second time points represent distinct endogenous murine retroviruses, suggesting contamination.

Origin of XMRV and its demise as a human pathogen associated with chronic fatigue syndrome

Retroviruses are well known pathogens of mammals, birds and fish. Their potential to induce cancer in chickens was already described almost 100 years ago and murine retroviruses have been a subject of study for 50 years. The first human retroviruses, HTLV and HIV, were discovered more than 30 years ago, surprising researchers and physicians by the profound differences in the diseases they cause. HTLV-1 is able to induce, after decades of infection, lymphomas/leukemia or neuroimmune disorders whereas untreated HIV infection leads almost inevitably to AIDS. The recently described XMRV (xenotropic murine leukemia virus-related virus) appeared to possess many of the features known for HTLV and was regarded by some to be the third human retrovirus. However, recent publications by Knox et al. [1] and Paprotka et al. [2] have shed new light on this gammaretrovirus. Knox and colleagues clearly demonstrate that XMRV is absent in patients belonging to a chronic fatigue syndrome cohort who had previously been reported to be XMRV-positive [3]. This supports the growing suspicion that laboratory contamination was responsible for the postulated link between XMRV and the disease. Furthermore, Paprotka et al’s identification of XMRV’s origin and the phylogenetic analysis of known XMRV sequences are further nails in the coffin to the notion that XMRV is a clinically relevant infectious human retrovirus.

XMRV Discovery and Prostate Cancer-Related Research

Xenotropic murine leukemia virus-related virus (XMRV) was first reported in 2006 in a study of human prostate cancer patients with genetic variants of the antiviral enzyme, RNase L. Subsequent investigations in North America, Europe, Asia, and Africa have either observed or failed to detect XMRV in patients (prostate cancer, chronic fatigue syndrome-myalgic encephalomyelitis (CFS-ME), and immunosuppressed with respiratory tract infections) or normal, healthy, control individuals. The principal confounding factors are the near ubiquitous presence of mouse-derived reagents, antibodies and cells, and often XMRV itself, in laboratories. XMRV infects and replicates well in many human cell lines, but especially in certain prostate cancer cell lines. XMRV also traffics to prostate in a nonhuman primate model of infection. Here, we will review the discovery of XMRV and then focus on prostate cancer-related research involving this intriguing virus.