Yesterday the Chicago Tribune published my reaction to the fourÂ papers on the retrovirus XMRV published this week in the journal Retrovirology. I was quoted as sayingÂ “These four papers are probably the beginning of the end of XMRV and CFS”. I wish to retract this statement and explain my reasons for doing so.
Early Monday a reporter for the Chicago Tribune, Trine Tsouderos, sent an email asking for my thoughts on four XMRV papers that had just been released (paperÂ one, two, three, four). I read all four papers and decided that they raised serious concerns about the role of XMRV in human disease. Specifically, the four papers demonstrated different ways that assays for XMRV could be subject to contamination with murine viral sequences. I wrote an email to Ms. Tsouderos outlining my summary of the papers, and later that day her article was published. My statement was reproduced exactly from the email I had sent her, so I was not misquoted.
I then set out to write about the papers for my blog about viruses. I read the papers over again, and began checking XMRV sequences in Genbank. I also began an email correspondence with authors of three of the four papers, and spoke with my virology colleagues here at Columbia. As a consequence of this additional research I decided that my initial impression of the papers was incorrect, which is evident in my post entitled ‘Is XMRV a laboratory contaminant?‘. Almost immediately after publishing the piece readers began to ask why my comments to the Chicago Tribune had such a different tone. I concluded that a retraction and explanation were necessary.
Upon re-reading three of the four Retrovirology papers it became clear to me that they show that identification of XMRV can be fraught with contamination problems, but they do not imply that previously published studies are compromised by these findings. Clearly any new studies done on XMRV should keep in mind the potential for contamination from PCR kits and murine nucleic acids.
I was initially more troubled by the fourth paper by Hue and colleagues. There are four major findings in this paper (gag PCR primers are not specific for XMRV; the virus is present in 5 human tumor cell lines; two XMRV isolates are nearly identical to a virus from the human prostate cell line and also contain an insertion from the murine retrovirus MoMLV; and there is more nucleotide diversity in viral sequences from 22Rv1 cells than in all the patient XMRV sequences). The fact that two XMRV isolates seem to be laboratory contaminants – judged by the presence of MoMLV sequences – was initially unsettling until it became clear that other XMRV isolates do not have this insertion. That leaves the fourth finding – that XMRV from 22Rv1 cells appears ancestral to, and more diverse than, all the human XMRV sequences. I decided that this result was less troublesome than I had originally believed, in part because it is not clear that the differences among the 22Rv1 viruses did not arise during PCR amplification.
My conclusion is that these four papers point out how identification of XMRV from human specimens can be complicated by contamination, but they do not mean that previous studies were compromised. They serve as an important reminder that future experiments to identify XMRV need to be appropriately controlled to ensure that the results are not compromised by contamination.
In other words, these four papers are NOT the beginning of the end of XMRV and CFS. Rather, research on the role of this virus in human disease must proceed, with large, case-controlled epidemiological studies, as suggested by others.
I would like to apologize to anyone who was offended, angered, or disappointed in any way by my statement to the Chicago Tribune. It is my goal to educate the public about virology, and clearly I did not do that very well.
There are at least two lessons that you can take away from this incident. First, that I make mistakes, and that I’m willing to admit it. Everyone does, including scientists. Second, if I had difficulties interpreting these papers, how would non-scientists fare?