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Retrovirus XMRV Not Linked to Chronic Fatigue or Prostate Cancer

An extensive analysis sponsored by the National Institute of Allergy and Infectious Diseases confirmed that xenotropic murine leukemia virus-related virus (XMRV) is not associated with chronic fatigue syndrome. A related study provided further evidence that XMRV is not linked to prostate cancer either and traced the sequence of events that led to that mistaken claim. 

Chronic Fatigue Syndrome

The link between XMRV and chronic fatigue syndrome (CFS), also sometimes known as myalgic encephalomyelitis, has been a subject of controversy in recent years.

In October 2009, Vincent Lombardi and Judy Mikovits from Whittemore Peterson Institute and colleagues first reported in Science magazine that nearly 70% of patients with CFS had evidence of XMRV in their peripheral blood mononuclear cells, compared with just 4% of healthy control subjects.

But a series of subsequent analyses failed to replicate this finding, suggesting that the reported association might have been due to laboratory contamination. The July 1, 2011, issue of Science featured 2 such studies, prompting the journal's editor-in-chief to issue an "Editorial Expression of Concern." Most recently, as reported in the November 11, 2011, issue of Science, members of the Blood XMRV Scientific Research Working Group (established by the U.S. Department of Health and Human Services) did not find XMRV or related retroviruses in blood samples from people with CFS.

Now, an analysis by Harvey Alter from the National Institutes of Health, Mikovits (now a private consultant), and others, published in the September 18, 2012, edition of the American Society for Micribiology's mBio, has also found "no evidence" of either XMRV or polytropic murine leukemia virus (pMLV) in peripheral blood from 147 people with CFS and 146 healthy individuals matched for age, sex, race/ethnicity, and geographic location.

The CFS patients met both the Fukuda and Canadian Consensus criteria for the condition and had reduced quality of life and functioning according to the RAND36 survey and Karnofsky Performance Scale. They reported symptoms of a viral infection prior to the onset of CFS. People with evidence of any metabolic, endocrine, or infectious disease that might cause fatigue -- as well as pregnant women and mothers who had recently given birth -- were excluded.

This population was geographically diverse, including participants enrolled atBrigham and Women's Hospital in Boston, the Simmaron Research Institute in Incline Village, NV, the Miami Veterans Affairs Medical Center, the Infectious Disease Clinic at Stanford University in Palo Alto, CA, the Levine Clinic in New York City, and the Fatigue Consultation Clinic in Salt Lake City.

This latest analysis is important because it looked at a larger group than the preceding ones. "In the absence of a definitive study, many in the general public may have retained the opinion that XMRV and/or pMLV are responsible for the disease," and some clinicians continue off-label prescribing of antiretroviral drugs approved to treat HIV, according to a press release issued by Columbia University's Mailman School of Public Health.

A total of 9 CFS and 9 control blood samples were positive for XMRV or pMLV-reactive antibodies. "The accuracy of this assay cannot be determined because there are no positive controls in the general population with XMRV serology," the press release continued. "Nonetheless, there was no correlation of antibody reactivity in blood from CFS/ME and controls."

"Although the once promising XMRV and pMLV hypotheses have been excluded, the consequences of the early reports linking these viruses to disease are that new resources and investigators have been recruited to address the challenge of the CFS/ME," said lead study author W. Ian Lipkin from the Mailman School. "We are confident that these investments will yield insights into the causes, prevention and treatment of CFS/ME."

Prostate Cancer

The second study, by Deanna Lee and Charles Chiu from the University of California at San Francisco and colleagues, looked more extensively at the purported link between XMRV and prostate cancer -- also a subject of controversy due to conflicting data.

As described in the September 18, 2012, edition of PLoS ONE, the study authors analyzed prostate cancer tissue and plasma samples from a prospective cohort of 39 cancer patients as well as archival RNA and prostate tissue from the original 2006 study that first saw evidence of an association with XMRV.

"Despite comprehensive microarray, PCR, FISH, and serological testing, XMRV was not detected in any of the newly collected samples or in archival tissue, although archival RNA remained XMRV-positive," the study authors concluded.

"Analysis of viral genomic and human mitochondrial sequences revealed that all previously characterized XMRV strains are identical and that the archival RNA had been contaminated by an XMRV-infected laboratory cell line," they continued. "These findings reveal no association between XMRV and prostate cancer, and underscore the conclusion that XMRV is not a naturally acquired human infection."

A news release from UCSF offers further explanation: "[The researchers] determined that the virus detected in these samples was essentially identical in each -- which suggested contamination rather than natural infection. Viruses like XMRV readily mutate, and if the different men who had donated prostate tissues had truly been infected, there likely would have been more than one strain present."

"Looking further, the scientists found that while the virus was present in genetic extracts made from the samples -- and analyzed in the 2006 study -- it was not present in the original prostate tissues themselves, samples of which were fixed in waxy paraffin immediately after they were first surgically removed."

"That discovery suggested that XMRV was introduced as a contaminant at some point when the tissue was being manipulated in the laboratory that processed the prostate tissue samples, prior to them being sent to UCSF for analysis. Searching for a possible culprit, the team found a completely different cell line that was not used in the study but had been used in the same laboratory at the same time. They found frozen samples of these cells, called 'LNCaP,' which had been packed away in a lab freezer since 2003. The virus was in these cells."

...

"But how did the LNCaP cells themselves become contaminated? Looking further, the scientists found that the source was another type of cell, called the 22Rv1 cell line, which was developed at Case Western Reserve University and is used extensively in prostate cancer research. Prior research by other scientists showed that this virus appears to have been created accidentally in the laboratory in the 1990s in a 'recombination event' in which two viruses combined to form XMRV. This event occurred while scientists were working with mice and a prostate cancer tumor to make the 22Rv1 cell line."

Discussing the importance of their CFS analysis, Alter and colleagues wrote, "The increasing frequency with which molecular methods are used for pathogen discovery poses new challenges to public health and support of science. It is imperative that strategies be developed to rapidly and coherently address discoveries so that they can be carried forward for translation to clinical medicine or abandoned to focus resource investment more productively. Our study provides a paradigm for pathogen dediscovery that may be helpful to others working in this field."

10/10/12

References

HJ Alter, JA Mikovits, WM Switzer, WI Lipkin, et al. A Multicenter Blinded Analysis Indicates No Association between Chronic Fatigue Syndrome/Myalgic Encephalomyelitis and either Xenotropic Murine Leukemia Virus-Related Virus or Polytropic Murine Leukemia Virus. mBio 3(5):e00266-12. September 18, 2012.

D Lee, J Das Gupta, C Gaughan, CY Chiu, et al. In-Depth Investigation of Archival and Prospectively Collected Samples Reveals No Evidence for XMRV Infection in Prostate Cancer. PLoS ONE 7(9):e44954. September 18, 2012.

Other Sources

Columbia University Mailman School of Public Health. Chronic fatigue syndrome is not linked to suspect viruses. Press release. September 18, 2012.

J Bardi, UCSF. Study Confirms Erroneous Link Between Prostate Cancer and Retrovirus from Mice. UCSF news center. September 18, 2012.