Is XMRV a laboratory contaminant?
21 December 2010
Since the first observations that the human retrovirus XMRV is associated with prostate cancer and chronic fatigue syndrome (CFS), new studies have been carried out to determine the role of the virus in these diseases.
http://www.virology.ws/2010/12/21/is-xmrv-a-laboratory-contaminant/
Xenotropic murine leukemia virus-related virus (XMRV retrovirus), first described in 2006, belongs to the virus family Retroviridae and the genus gammaretrovirus.
http://wpinstitute.org/news/docs/WPIResponseToRetrovirology122010.pdf
Dr. Mikovits Responds The Lombardi et al. and Lo et al. studies were done using four different methods of detection. They were not simply PCR experiments, as were the studies by McClure et al. and others who have recently reported their difficulties with contamination. Experienced researchers such as Mikovits, Lombardi, Lo and their collaborators understand the limitations of PCR technology, especially the possibility of sample contamination. As a result, we and Lo et al. conducted rigorous studies to prevent and rule out any possibility that the results reported were from contamination. In addition to the use of PCR methodology, the Lombardi team used two other scientific techniques to determine whether, in fact, we had found new retroviruses in human blood samples. We identified a human antibody response to a gamma retroviral infection and we demonstrated that live gamma retrovirus isolated from human blood could infect human cells in culture. These scientific findings cannot be explained by contamination with mouse cells, mouse DNA or XMRV-related virus-contaminated human tumor cells. No mouse cell lines and none of the human cell lines reported today by Hue et al. to contain XMRV were ever cultured in the WPI lab where our PCR experiments were performed. Humans cannot make antibodies to viruses related to murine leukemia viruses unless they have been exposed to virus proteins. Therefore, recent publications regarding PCR contamination do not change the conclusions of the Lombardi et al. and Lo et al. studies that concluded that patients with ME/CFS are infected with human gammaretroviruses. We have never claimed that CFS was caused by XMRV, only that CFS patients possess antibodies to XMRV related proteins and harbor infectious XMRV, which integrates into human chromosomes and thus is a human infection of as yet unknown pathogenic potential "The coauthors stand by the conclusions of Lombardi et al. Nothing that has been published to date refutes our data."
Judy A. Mikovits
“XMRV and CFS – It’s not the end”
22 December 2010
By Vincent Racaniello
http://www.virology.ws/2010/12/22/xmrv-and-cfs-its-not-the-end/
(excerpt)
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.