Response to Comments on "Detection of an Infectious Retrovirus, XMRV, in Blood Cells of Patients with Chronic Fatigue Syndrome"

Judy A. Mikovits^1,* and Francis W. Ruscetti²

^* To whom correspondence should be addressed. E-mail: judym@wpinstitute.org

Our study (1) documented the presence of a recently discoveredhuman retrovirus, XMRV, in a high proportion of patients withchronic fatigue syndrome (CFS) in comparison with healthy controls.Sudlow et al. (2), Lloyd et al. (3), and van der Meer et al.(4) raise concerns about the cases and controls described inour study and thus the validity of our results. First, we wishto emphasize that our study was not intended to be a detailedclinical description of CFS or an epidemiological study thatwould relate particular symptoms, demographics, duration, patternof onset, and the like to the presence or viral load of XMRV.The study was not, nor was it designed to be, a case-controlstudy as Sudlow et al. (2) imply, for it was the first demonstrationof the replication and production of infectious XMRV in humanblood cells. The fact that a number of the patients tested werefrom regions of CFS outbreaks does not invalidate the clinicaldiagnosis. We hope that our report will stimulate the performanceof many case-control studies that use appropriate virus detection.We certainly recognize that such studies will be required todetermine what role XMRV plays in the pathogenesis of CFS.

Samples included in our study (1) were from CFS patients whofulfilled both the Fukuda criteria and the Canadian ConsensusCriteria (CCC), regardless of severity. We regret that a sentencein the original supporting online material in (1) implied thatimmunological abnormalities were part of the CFS diagnosis;indeed, while many such patients do exhibit such abnormalities(5, 6), they were not required for diagnosis. All patients thatmet Centers for Disease Control and Prevention and CCC criteriawere accepted; none were excluded. Patient samples were obtainedfrom 2006 to 2009 and stored in the Whittemore Peterson Institute(WPI) repository. We did not state in Lisbon (7) or elsewherethat the samples analyzed in (1) were only from patients fromdocumented outbreaks of CFS, nor did we state that the 101 patientsdescribed in (1) exhibited all the immunological abnormalitiesdescribed in our Lisbon conference presentation. In fact, only25 samples in (1) came from patients identified during the 1984to 1988 CFS outbreak in Incline Village, Nevada. The remaining76 samples included patients with sporadic cases from 12 U.S.states and Canada, including California, New York, North Carolina,Wisconsin, Michigan, Oregon, New Mexico, New Jersey, North Dakota,Texas, and Florida. Patients in the study were 67% female, reflectingthe reported gender incidence of CFS, with an age distributionof 19 to 75 years of age (mean of 55). The healthy control population,which was similar in age and gender to the patients, was composedof healthy people who visited doctors’ offices in thewestern United States between 2006 and 2008. The great majority,although not all, of the patients analyzed were matched in geographiclocation with controls. As this was not an epidemiological case-controlstudy, we did not attempt to discern where the patients believedthey contracted CFS; at the time of sample collection, somewere undoubtedly living in an area different from the locationwhere they first became ill.

The information we provide here and in the accompanying SupportingOnline Material (8) should lay to rest any concerns about "bias"or "confounding." Again, the primary aim of the work describedin (1) was not to characterize this clinical condition or toprove a cause for CFS but to demonstrate the existence of aninfectious gammaretrovirus in patients who had been diagnosedwith CFS. We achieved our goal using four different experimentalstrategies. The original description of HTLV-1 and HIV-1 involvedonly one or two patients (9–12), whereas we detected XMRVin 75 individuals.

We did not state that our study (1) proves the cause of CFS.A large number of infectious and noninfectious agents have beenimplicated in CFS, and it is that fact that makes the puzzleof CFS all the more difficult to solve. At no time have we wishedto raise false hopes among a group of patients who, in general,have not been treated well by the medical research community.We are aware that many different pathogens have previously beenreported to be associated with CFS but have not been provento be causal.

We further note that no cytokine profiles were presented in(1), nor did we state that abnormal cytokine levels, alterednatural killer cell activity, or particular RNase L profileswere a requirement for inclusion in the study. Unpublished commentsmade during a medical conference (7) exploring hypotheticalconnections with immune system defects, viral reactivation,and malignancies should not be used to judge the merits of thescience in the published paper. Regarding the concern raisedby Sudlow et al. (2) about potential "expectation bias," wepoint out that the National Cancer Institute (NCI) and the ClevelandClinic, whose scientists independently performed experimentsand coauthored (1), were certainly not "established" as laboratoriesfor the purpose of studying CFS. All samples were blinded, asmandated by the NCI and WPI institutional review board approvals.All experimental procedures were done by the same personnel,in the same physical laboratory space, under identical protocols.Investigators at NCI received 100 samples from individuals withoutknowing their health status; furthermore, the samples were sentto NCI directly without passing through the WPI laboratory space.Laboratory workers at the NCI and the WPI who performed thepolymerase chain reaction (PCR) and immunological studies usedcoded, blinded samples that did not reveal the CFS status ofthe individuals. The WPI has examined all 218 control and 101patient samples by both PCR and serological methods for thepresence of XMRV nucleic acid and antibodies. In addition, NCIused plasma from all 100 samples they received in infectionexperiments with LNCaP cells. It was not feasible to examineall 101 patient and 218 control samples with all four XMRV detectionmethods described in (1), due to time and resource constraints.

Of the technologies used to identify and isolate XMRV in patientswith CFS, PCR from DNA or cDNA from unstimulated peripheralblood mononuclear cells is the least sensitive method. We contendthat the three recently published negative PCR studies (13–15) do not qualify as being studies that fail to replicate ourstudy, as neither the same PCR methodologies were used nor didthese studies draw on the additional cell culture and immunologicalmethods that we employed to observe XMRV nucleic acids and proteins.Although we offer to send samples in which we have detectedXMRV, the groups that published these results neither requestednor analyzed any samples we had found positive for XMRV in ourlaboratories.

Sudlow et al. erroneously state that we did not consider alternativeexplanations for the findings, namely that patients with poorgeneral health may be more susceptible to viral and other infections.On the contrary, we raised as a question for future study: "IsXMRV infection a causal factor in the pathogenesis of CFS ora passenger virus in the immunosuppressed CFS patient population?"(1). We recognize that the presence of XMRV could be due toenhanced susceptibility to retroviral infection after developmentof CFS. A causal role of XMRV in CFS is an intriguing possibility,given the known immunosuppressive, neurotropic, and seriousconsequences of infection with other known retroviruses.

www.sciencemag.org/cgi/content/full/328/5980/825-d/DC1

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Received for publication 10 November 2009. Accepted for publication 19 April 2010.

Source: http://www.sciencemag.org/cgi/content/full/328/5980/825-d