Abstract 4292: Frequent detection of xenotropic murine leukemia virus (XMLV) strains including XMRV in human cultures established from mouse xenografts
Authors: Zhang Yu-An , Hsieh Jer-Tsong , Maitra Anirban , Rudin Charles M. , Brekken Rolf A. , Sawyers Charles , Stastny Victor , Gao Boning , Frenkel Eugene , Minna John D. , Gazdar Adi F. 
Published: July 2012

Abstract
Purpose: To investigate the frequency of XMLV in human cell lines from xenografts and for evidence of horizontal spread to other cell lines. Background: The mouse genome contains multiple integrated copies of type C murine leukemia viruses including xenotropic strains (XMLV) capable of growth in human and other foreign species. XMLV has been detected in sporadic human cultures established after murine xenografting. Sequences, usually partial, of a XMLV related virus (XMRV) have been reported in prostate cancer and the chronic fatigue syndrome. Methodology: We examined 27 human cell lines established after murine xenografting in six independent laboratories. We also examined an additional 127 non-xenografted cell lines maintained in the same cell culture facilities. Cell line DNA was examined for presence of a human and mouse housekeeping gene, and by three Taqman qPCR assays targeting the gag, pol or env regions of MLV including specificity to XMRV, most MLV or all known XMLV strains, respectively. For virus positive samples we performed additional sequencing for strain identification and tested supernatant fluids for reverse transcriptase activity. Results: Three of the 27 cell lines from xenografts were found to contain mouse DNA and were excluded from further study. Seven of the remaining 24 cultures (29%) were strongly positive by either two or all three viral probes. At least five strains of XMLV were identified and some cultures contained multiple strains. These strains included XMRV and the N417 strain we originally identified from a small cell lung cancer xenograft-derived culture. Of six available supernantant fluids from viral positive cultures, five were strongly positive for reverse transcriptase activity, indicating release of potentially infectious viral particles (estimated range of 2.9×102 to 8.2×105 vp/ul). Of the 127 non-xenograft derived cell lines maintained in the cell culture facilities, 12 (9.5%) were also positive by at least two viral probes and all four corresponding supernatant fluids tested were positive for reverse transcriptase activity. Conclusions: Human cell lines derived after murine xenografting frequently contain full length sequences of several XMLV strains including XMRV. Infected cultures release large numbers of potentially infectious virus particles. Other human cell lines maintained in the same facility are at risk of cross contamination. The data also suggest that XMRV is, in all probability, a stain of XMLV present in the mouse genome. Laboratories working with xenograft-derived human cultures should be aware of the risk of contamination with a human tropic murine virus of unknown biological significance and of the possibility of horizontal spread to other cultures.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4292. doi:10.1158/1538-7445.AM2011-4292