By Suzanne Vernon, PhD, Scientific Director
As reported in the early online edition of Proceedings of the National Academy of Sciences (PNAS) on August 23, 2010, a scientific team led by Dr. Shyh-Ching Lo of the U.S. Food and Drug Administration (FDA) found murine leukemia virus (MLV)-like virus gene sequences in 32 of 37 (86.5%) of the CFS patients, compared with only 3 of 44 (6.8%) healthy donors.(1) According to Drs. Lo and Alter, this study was not designed to replicate the findings published by Lombardi et al., but rather to look for XMRV and MLV sequences in a small well-characterized group of CFS patients. Even though Lo et al. looked specifically for XMRV, they did not detect it in any of the CFS and controls samples they tested. Media outlets from around the world have reported on the PNAS paper, and there have already been quite a few comparisons of the techniques in this paper to those used in the Lombardi paper and the four negative studies. Rather than write about the technical aspects of the PNAS paper, I would like to share my perspective about what kinds of studies should come next so that we can quickly translate this research into objective approaches to diagnose and treat people with CFS.
Since the mid-1980s, when clusters of illness were reported in Incline Village, Nev., and Lyndonville, N.Y., an infectious agent has been suspected as the cause of or as a trigger for CFS. Most people with CFS report that they had a flu-like onset of symptoms, consistent with a viral illness. Over the years, many pathogens have been detected in people with CFS (including parvovirus and enteroviruses) or have been shown to trigger CFS (including Epstein-Barr virus, Ross River virus, Coxiella burnetii). We can now add XMRV and MLV-like viruses to the list of infectious agents detected in people with CFS.
We live with a number of these agents for life, like Epstein-Barr virus that is present in about 95 percent of the U.S. adult population, usually in a dormant (latent) state. There is a growing body of evidence that people with CFS may be more vulnerable to getting certain infections or reactivating latent pathogens. This possibility is certainly being discussed with regard to XMRV and MLVs. The report from Fischer et al.(2) that found 16 of 161 individuals (10%) with respiratory tract infections to be positive for XMRV gag sequences suggests that XMRV may possibly be an opportunistic infection.
We tend to think of viruses in rather simplistic terms, as being either present or absent, active or dormant. But there are other ways in which viruses might contribute to illness. For example, in Japan, the CFS research team led by Drs. Hirohito Kuratsune and Yasuyoshi Watanabe uses HHV-6 viral load measurements to assess immune surveillance in CFS patients. They have found that high viral load correlates with more severe CFS. This team does not claim that HHV-6 causes CFS; rather they use it as a biomarker of disease severity. Other investigators are now exploring the use of plasma Epstein-Barr viral load in HIV-infected patients as a marker of lymphoma and a tool for its early diagnosis and treatment.
One of (many) studies we need to conduct is a comprehensive assessment of the infectious agents present in the blood of individuals with CFS, as compared to healthy control subjects and subjects with conditions that are clinically similar to CFS. Studies looking for pathogens should also attempt to characterize the immune response necessary for clearing acute infectious agents and/or keeping chronic infections in check. The group of CFS patients assessed should include severely ill, moderately ill and higher functioning. Comprehensive clinical information including demographics, medical history, past and current medication use, current health/symptom status, using standardized instruments that can be related to population norms, should be collected on all subjects – healthy and disease controls, too. This way, when a pathogen(s) is detected, it can be analyzed in the context of the necessary clinical and epidemiologic information to determine if an agent is causal, a bystander or a possible biomarker of other biologic processes. The technology exists to detect many known and novel pathogens and we have the computational capability to integrate this information with extensive clinical data. In fact, this is the very type of study that we intend to conduct using the SolveCFS BioBank, and in the next few weeks we will be making an announcement to stimulate this kind of research.
Blood is a relatively non-invasive sample that can be used to detect pathogens as well as assess the immune response. One caveat with testing the blood for these agents is they may reside in other reservoir tissues such as the stomach, thymus or brain, so this must be taken into account. Several studies suggest that XMRV and MLVs may be present in the blood, but at low copy numbers making it challenging to detect these agents. Even with these limitations, appropriately sensitive and specific tests for antibodies in the blood can serve as a telltale fingerprint of pathogen culprits. The technology of profiling all blood antibodies to inform us about infectious agents is still in development but promises to be a powerful approach to reveal diseases-causing agents. When we can add it to technologies like PCR, deep sequencing and ViraChip assays, we will have a very powerful toolbox for discovery.
The studies published in PNAS and Science (3), as well as the four XMRV-negative studies (4, 5, 6, 7) have demonstrated the importance of defining CFS and assessing subjects for inclusion in research studies. In fact, of the many possible explanations of discordant results from the six studies, different CFS populations was identified by Dr. Harvey Alter as the most likely reason for the lack of agreement between the FDA/NIH team’s results and those from CDC’s study. This is due to the fact that both groups were able to satisfactorily detect an XMRV in an analytical panel in the first phase of the XMRV Scientific Research Working Group’s blood safety study.
I believe that the problem of CFS cohorts is even bigger than this particular high-profile discrepancy: CFS patient populations selected using a variety of case definitions and symptom characteristics are likely at the root of our inability to consistently detect and validate a number of potentially important biomarkers that have been described over the past 20 years, including these XMRV/MLV findings. The SolveCFS BioBank has been created with this problem in mind. It gives patients who have been diagnosed with CFS the opportunity to participate in research. It creates a comprehensive and secure medical record that is linked to quality biologic samples. Researchers can specify certain clinical characteristics so that samples are collected from diagnosed individuals that best match a certain profile. It allows the opportunity for ethical recontact and serial sample collection so that findings can be broadened to other populations and new hypotheses can be explored. In short, it allows for the right sample to be collected from the right patient at the right time.
The Science and the PNAS papers have energized interest in finding objective CFS biomarkers and effective treatments. The biomarkers that make it from the discovery phase – like XMRV, MLV, immune markers and therapies – to the doctor’s office and patient’s bedside – will be those that have been validated on large, well-characterized CFS patient populations.
1. Lo S-C, Pripuzova N, Li B, Komaroff AL, Hung G-C, Wang R, Alter H. (2010) Detection of MLV-related virus gene sequences in blood of patients with chronic fatigue syndrome and healthy blood donors. Proceedings of the National Academy of Sciences. 10.1073/pnas.1006901107
2. Fischer N, Schulz C, Stieler K, Hohn O, Lange C, Drosten C, Aepfelbacher M. (2010) Xenotropic murine leukemia virus-related gammaretrovirus in respiratory tract. Emerging Infectious Diseases. 2010 June.
3. Lombardi VC, Ruscetti FW, Das Gupta J, Pfost MA, Hagen KS, Peterson DL, Ruscetti SK, Bagni RK, Petrow-Sadowski C, Gold B, Dean M, Silverman RH, Mikovits JA (2009). Detection of an Infectious Retrovirus, XMRV, in Blood Cells of Patients with CFS. Science. Vol. 326, 585.
4. Erlwein O, Kaye S, McClure MO, Weber J, Wills G, Collier D, Wessely S, Cleare A (2010). Failure to detect the novel retrovirus XMRV in CFS. PLoS One, 5 (1).
5. Groom HCT, Boucherit VC, Makinson K, Randal E, Baptista S, Hagan S, Gow JW, Mattes FM, Breuer J, Kerr JR, Stoye JP, Bishop KN (2010). Absence of XMRV in UK patients with CFS. Retrovirology: 10.1186/1742-4690-7-10
6. Van Kuppeveld FJM, de Jong AS, Lanke KH, Verhaegh GW, Melchers WJG, Swanink CMA, et al. (2010) Prevalence of XMRV in patients with CFS in the Netherlands: retrospective analysis of samples from an established cohort. British Medical Journal 2010;340:c1018.
7. Switzer WA, Jia H, Honn O, Zheng HQ, Tang S, Shankar A, Norbert N, Simmons G, Hendry RM, Falkenberg VR, Reeves WC, Heneine W. (2010) Absence of evidence of XMRV infection in persons with CFS and healthy controls in the United States. Retrovirology.
Suzanne Vernon, PhD, is the Association’s scientific director. She has nearly two decades of experience as a microbiologist.September 28, 2010