Abstract
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.
Highlights
Xenotropic murine leukemia virus (MLV)-related virus (XMRV) is a new gammaretrovirus reported in persons from the U.S with prostate cancer or chronic fatigue syndrome (CFS), and in blood donors [1]
The recombinant reverse transcriptase (RT) enzyme used in the pro quantitative RT-PCR (qRT-PCR) testing was included in the ABI/Ambion AgPath One Step RT-PCR kit and according to the manufacturer was derived from an expression plasmid containing the ecotropic Moloney MLV (MoMLV) RT gene
Given the plasmid production history of this enzyme and absence of mouse monoclonal antibodies in the reagents, we suspected that the AgPath RT-PCR kit was contaminated with trace amounts of residual MLV-like plasmid sequences
Summary
Xenotropic murine leukemia virus (MLV)-related virus (XMRV) is a new gammaretrovirus reported in persons from the U.S with prostate cancer or chronic fatigue syndrome (CFS), and in blood donors [1]. MLV-like sequences have been found in specimens from persons with CFS from the US [2]. Several groups have shown recently that Platinum Taq polymerase from Invitrogen, or reverse transcriptase (RT)-PCR kits containing this enzyme, contain low levels of mouse DNA that produce a positive PCR signal with diagnostic XMRV or MLV primers [1,4,15,16,17]. High levels of infectious MLV and XMRV have been found in human cell lines [19,20,21]. These results suggest multiple sources of potential contamination of clinical specimens from different cohorts [4,19,21,22,23,24]
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