Laboratories working with xenograft-derived human cultures should be aware of the risk of horizontal spread of XMRV

Cancer Biology & Therapy 12:7, 1-12; October 1, 2011; © 2011 Landes Bioscience

Yu-An Zhang,1 Anirban Maitra,2 Jer-Tsong Hsieh,3 Charles M. Rudin,4 Craig Peacock,4 Collins Karikari,2 Rolf A. Brekken,1, Victor Stastny,1 Boning Gao,1 Luc Girard,1 Ignacio Wistuba,5 Eugene Frenkel,6 John D. Minna1 and Adi F. Gazdar1,*:

Frequent detection of infectious xenotropic murine leukemia virus (XMLV) in human cultures established from mouse xenografts

1Hamon Center for Therapeutic Oncology Research; 3Department of Urology; 6Division of Hematology-Oncology; The University of Texas Southwestern Medical Center at Dallas; Dallas, TX; 2Departments of Pathology and Oncology; The Sol Goldman Pancreatic Cancer Research Center; 4Department of Oncology;
Johns Hopkins University School of Medicine; Baltimore, MD; 5Department of Pathology; MD Anderson Cancer Center; Houston, TX USA
Key words: xenograft cultures, xenotropic murine leukemia virus, retrovirus, XMRV virus, cell cultures, lung cancer,
prostate cell line

Abbreviations: MLV, murine leukemia virus; XMLV, xenotropic murine leukemia virus; XMRV, xenotropic murine leukemia
virus-related virus; NSCLC, non-small cell lung cancer; SCLC, small cell lung cancer; qGag, qPCR specific to XMRV gag gene
sequence; qEnv, qPCR specific to XMLV env gene sequence; qGPP, qPCR specific to MLV gag-pro-pol gene sequence;
RT, reverse transcriptase

Purpose: To investigate the frequency of xenotropic murine leukemia virus (MLV) presence in human cell lines established
from mouse xenografts and to search for the evidence of horizontal viral spread to other cell lines.
Results: Six of 23 (26%) mouse DNA free xenograft cultures were strongly positive for MLV and their sequences had
greater than 99% homology to known MLV strains. Four of five available supernatant fluids from these viral positive cultures
were strongly positive for RT activity. Three of these supernatant fluids were studied to confirm the infectivity of
the released virions for other human culture cells. Of the 78 non-xenograft derived cell lines maintained in the xenograft
culture-containing facilities, 13 (17%) were positive for MLV, including XMRV, a virus strain first identified in human tissues.
By contrast, all 50 cultures maintained in a xenograft culture-free facility were negative for viral sequences.
Methodology: We examined xenograft tumor cell lines from 7 independent laboratories and 128 non-xenografted
tumor cell lines. Cell line DNA was examined for mouse DNA contamination, and by 3 Taqman qPCR assays targeting
the gag, env or pol regions of MLV. Sequencing was used for viral strain identification. Supernatant fluids were tested for
reverse transcriptase (RT) activity.

Conclusions: Human cultures derived after mouse xenografting frequently contain and release highly infectious xenotropic
MLV viruses. Laboratories working with xenograft-derived human cultures should be aware of the risk of contamination
with potentially biohazardous human-tropic mouse viruses and their horizontal spread to other cultures.
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