Myra McClure seems to be convinced that contamination was an issue in the positive studies. Digging around a little for her background it appears she has published on this problem before in relation to MLVs. ABSTRACT Three human cell lines used in human immunodeficiency virus research were found to be contaminated with previously undetected retroviruses. On the bases of partial nucleotide sequence, capsid protein antigenicity, vector mobilization, and receptor usage studies, these contaminants were shown to be replication competent and to belong to the Gammaretrovirus genus. While the TZM-bl cells harbor ecotropic murine leukemia virus (MLV), Jurkat J6 cells were found to release xenotropic MLV and the A3.01/F7 cells to produce gibbon ape leukemia virus. These findings highlight the importance of routine testing of cell lines for retrovirus contamination to prevent potential experimental artifacts and allow correct biohazard assessment. FULL PAPER http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2593302/ The science is more than a little beyond me but I can't help feeling that this is significant in either casting doubt on the XMRV story or conversely possibly even supporting it? Sorry to be obtuse. You'll see what I mean when you read it.