Friday, June 24, 2011

Retroviral Etiology for Chronic Fatigue Syndrome Questioned

New data challenge the association between a murine retrovirus and CFS — and the existence of the virus in the prostate cancer cell line from which it was first identified.

The report of an apparent link between a novel retrovirus (xenotropic murine leukemia virus–related virus; XMRV) and chronic fatigue syndrome (CFS) attracted much attention in 2009 (JW Infect Dis Oct 21 2009). However, multiple follow-up studies have yielded conflicting results (JW Infect Dis Sep 1 2010), and discoveries in two new studies challenge the validity of the original findings.

Seeking to confirm an association between XMRV and CFS, Knox and colleagues performed extensive virologic tests on blood samples from 61 CFS patients from the same clinical practice that provided the majority of participants covered in the 2009 report; 43 of them had been reported to be XMRV positive. Polymerase chain reaction (PCR) assays for nucleic acids derived from XMRV or murine leukemia viruses (MLVs) and assays for detecting infectious virus or virus-specific antibodies showed no evidence of XMRV or other MLVs in any of the patients. In addition, the researchers found that unheated human sera from either CFS patients or healthy controls readily inactivated XMRV and another tested MLV, and determined that MLV sequences contaminated 12 of 22 laboratory reagents used to detect such viruses.

Poprotka and colleagues sought to confirm the existence of XMRV by studying the human prostate cell line (CWR22Rv1) from which it was first identified. This cell line was derived from a primary human prostate tumor and underwent serial passage in nude mice. The researchers determined that XMRV was present in later passage xenografts but not in earlier ones. They screened multiple mouse strains and wild mice but did not detect endogenous XMRV in any of them. However, they did identify two murine proviruses (preXMRV-1 and preXMRV-2) that were present in host mice and could have recombined to produce XMRV during serial tumor passaging.

Comment: These findings strongly suggest that unrecognized laboratory contamination led to the initial findings on XMRV and CFS and highlight the pitfalls inherent in research methodologies involving nucleic acid amplification and sequencing, as well as the use of xenografts. Although questions remain about murine retroviruses and CFS, the possibility of a real association now seems remote. The editors of Science have issued an editorial expression of concern regarding the 2009 study.

Richard T. Ellison III, MD

Published in Journal Watch Infectious Diseases June 22, 2011


Knox K et al. No evidence of murine-like gammaretroviruses in CFS patients previously identified as XMRV-infected. Science 2011 May 31; [e-pub ahead of print]. (

Paprotka T et al. Recombinant origin of the retrovirus XMRV. Science 2011 May 31; [e-pub ahead of print]. (

Alberts B. Editorial expression of concern. Science 2011 May 31; [e-pub ahead of print]. (

1 comment:

  1. There was no data that challenged the findings. They used unvalidated assays in these negative studies and did not replicate the Lombardi et al methodology.

    The origin paper did not prove the existence of PreXMRV-1, as the primers could pick up XMRV. So how do they know the bits they found are XMRV. They also do not know which mice were used to create the cell line. They also screened the earlier xenografts with an assay never shown to detect virus at 3 copies per 100 cells, but at 2000 copies per 100 cells. And cannot know if the virus was in the earlier xenografts.

    They have not found the origin and it could never say anything about the virus being in humans.