title: Disease-associated XMRV sequences are consistent with laboratory contamination.
abstract: BACKGROUND
  Xenotropic murine leukaemia viruses (MLV-X) are endogenous gammaretroviruses that infect cells from many species, including humans. Xenotropic murine leukaemia virus-related virus (XMRV) is a retrovirus that has been the subject of intense debate since its detection in samples from humans with prostate cancer (PC) and chronic fatigue syndrome (CFS). Controversy has arisen from the failure of some studies to detect XMRV in PC or CFS patients and from inconsistent detection of XMRV in healthy controls.
  
  
  RESULTS
  Here we demonstrate that Taqman PCR primers previously described as XMRV-specific can amplify common murine endogenous viral sequences from mouse suggesting that mouse DNA can contaminate patient samples and confound specific XMRV detection. To consider the provenance of XMRV we sequenced XMRV from the cell line 22Rv1, which is infected with an MLV-X that is indistinguishable from patient derived XMRV. Bayesian phylogenies clearly show that XMRV sequences reportedly derived from unlinked patients form a monophyletic clade with interspersed 22Rv1 clones (posterior probability >0.99). The cell line-derived sequences are ancestral to the patient-derived sequences (posterior probability >0.99). Furthermore, pol sequences apparently amplified from PC patient material (VP29 and VP184) are recombinants of XMRV and Moloney MLV (MoMLV) a virus with an envelope that lacks tropism for human cells. Considering the diversity of XMRV we show that the mean pairwise genetic distance among env and pol 22Rv1-derived sequences exceeds that of patient-associated sequences (Wilcoxon rank sum test: p = 0.005 and p < 0.001 for pol and env, respectively). Thus XMRV sequences acquire diversity in a cell line but not in patient samples. These observations are difficult to reconcile with the hypothesis that published XMRV sequences are related by a process of infectious transmission.
  
  
  CONCLUSIONS
  We provide several independent lines of evidence that XMRV detected by sensitive PCR methods in patient samples is the likely result of PCR contamination with mouse DNA and that the described clones of XMRV arose from the tumour cell line 22Rv1, which was probably infected with XMRV during xenografting in mice. We propose that XMRV might not be a genuine human pathogen.
authors.affiliation: MRC Centre for Medical Molecular Virology, Division of Infection and Immunity, University College London, 46 Cleveland St, London W1T 4JF, UK.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Hué
authors.forename: Eleanor R
authors.initials: ER
authors.lastname: Gray
authors.forename: Astrid
authors.initials: A
authors.lastname: Gall
authors.forename: Aris
authors.initials: A
authors.lastname: Katzourakis
authors.forename: Choon Ping
authors.initials: CP
authors.lastname: Tan
authors.forename: Charlotte J
authors.initials: CJ
authors.lastname: Houldcroft
authors.forename: Stuart
authors.initials: S
authors.lastname: McLaren
authors.forename: Deenan
authors.initials: D
authors.lastname: Pillay
authors.forename: Andrew
authors.initials: A
authors.lastname: Futreal
authors.forename: Jeremy A
authors.initials: JA
authors.lastname: Garson
authors.forename: Oliver G
authors.initials: OG
authors.lastname: Pybus
authors.forename: Paul
authors.initials: P
authors.lastname: Kellam
authors.forename: Greg J
authors.initials: GJ
authors.lastname: Towers
mesh_terms: D000818:Animals; D059018:DNA Contamination; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics; D015673:Fatigue Syndrome, Chronic / Q000821:virology*; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D011471:Prostatic Neoplasms / Q000821:virology*; D017422:Sequence Analysis, DNA; D014773:Virology / Q000379:methods*; D058008:Xenotropic murine leukemia virus-related virus / Q000235:genetics* / Q000302:isolation & purification*
chemical_list: D004279:DNA, Viral