No evidence for XMRV nucleic acids, infectious virus or anti-XMRV antibodies in Canadian patients with chronic fatigue syndrome

Chronic viral infections in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Background and main text

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex and controversial clinical condition without having established causative factors. Increasing numbers of cases during past decade have created awareness among patients as well as healthcare professionals. Chronic viral infection as a cause of ME/CFS has long been debated. However, lack of large studies involving well-designed patient groups and validated experimental set ups have hindered our knowledge about this disease. Moreover, recent developments regarding molecular mechanism of pathogenesis of various infectious agents cast doubts over validity of several of the past studies.

Conclusions

This review aims to compile all the studies done so far to investigate various viral agents that could be associated with ME/CFS. Furthermore, we suggest strategies to better design future studies on the role of viral infections in ME/CFS.

Reductions in circulating levels of IL-16, IL-7 and VEGF-A in myalgic encephalomyelitis/chronic fatigue syndrome

Recently, differences in the levels of various chemokines and cytokines were reported in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) as compared with controls. Moreover, the analyte profile differed between chronic ME/CFS patients of long duration versus patients with disease of less than 3years. In the current study, we measured the plasma levels of 34 cytokines, chemokines and growth factors in 100 chronic ME/CFS patients of long duration and in 79 gender and age-matched controls. We observed highly significant reductions in the concentration of circulating interleukin (IL)-16, IL-7, and Vascular Endothelial Growth Factor A (VEGF-A) in ME/CFS patients. All three biomarkers were significantly correlated in a multivariate cluster analysis. In addition, we identified significant reductions in the concentrations of fractalkine (CX3CL1) and monokine-induced-by-IFN-γ (MIG; CXCL9) along with increases in the concentrations of eotaxin 2 (CCL24) in ME/CFS patients. Our data recapitulates previous data from another USA ME/CFS cohort in which circulating levels of IL-7 were reduced. Also, a reduced level of VEGF-A was reported previously in sera of patients with Gulf War Illness as well as in cerebral spinal fluid samples from a different cohort of USA ME/CFS patients. To our knowledge, we are the first to test for levels of IL-16 in ME/CFS patients. In combination with previous data, our work suggests that the clustered reduction of IL-7, IL-16 and VEGF-A may have physiological relevance to ME/CFS disease. This profile is ME/CFS-specific since measurement of the same analytes present in chronic infectious and autoimmune liver diseases, where persistent fatigue is also a major symptom, failed to demonstrate the same changes. Further studies of other ME/CFS and overlapping disease cohorts are warranted in future.

No association found between the detection of either xenotropic murine leukemia virus-related virus or polytropic murine leukemia virus and chronic fatigue syndrome in a blinded, multi-site, prospective study by the establishment and use of the SolveCFS BioBank

Background

In 2009, a retrospective study reported the detection of xenotropic murine leukemia virus-related virus (XMRV) in clinical isolates derived from individuals with chronic fatigue syndrome or myalgic encephalomyelitis (CFS). While many efforts to confirm this observation failed, one report detected polytropic murine leukemia virus (pMLV), instead of XMRV. In both studies, Polymerase Chain Reaction (PCR)-based methods were employed which could provide the basis for the development of a practical diagnostic tool. To confirm these studies, we hypothesized that the ability to detect these viruses will not only depend upon the technical details of the methods employed but also on the criteria used to diagnose CFS and the availability of well characterized clinical isolates.

Methods

A repository of clinical isolates from geographically distinct sites was generated by the collection of fresh blood samples from well characterized CFS and healthy subjects. Molecular techniques were used to generate assay positive controls and to determine the lower limit of detection (LLOD) for murine retroviral and Intracisternal A particle (Cell 12(4):963-72, 1977) detection methods.

Results

We report the establishment of a repository of well-defined, clinical isolates from five, geographically distinct regions of the US, the comparative determination of the LLODs and validation efforts for the previously reported detection methods and the results of an effort to confirm the association of these retroviral signatures in isolates from individuals with CFS in a blinded, multi-site, prospective study. We detected various, murine retroviral DNA signatures but were unable to resolve a difference in the incidence of their detection between isolates from CFS (5/72; 6.7%) and healthy (2/37; 5.4%) subjects (Fisher’s Exact Test, p-value = 1). The observed sequences appeared to reflect the detection of endogenous murine retroviral DNA, which was not identical to either XMRV or pMLV.

Conclusions

We were unable to confirm a previously reported association between the detection of XMRV or pMLV sequences and CFS in a prospective, multi-site study. Murine retroviral sequences were detected at a low frequency that did not differ between CFS and control subjects. The nature of these sequences appeared to reflect the detection of pre-existing, endogenous, murine retroviral DNA in the PCR reagents employed.

A comparison of health status in patients meeting alternative definitions for chronic fatigue syndrome/myalgic encephalomyelitis

BACKGROUND

Several diagnostic definitions are available for Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) that varies significantly in their symptom criteria. This pilot study was conducted to determine whether simple biological and clinical measures differed between CFS/ME patients meeting the 1994 Centres for Disease Control and Prevention (CDC) criteria, the International Consensus Criteria (ICC), as well as healthy controls.

METHODS

A total of 45 CFS/ME patients and 30 healthy controls from the South East Queensland region of Australia provided a blood sample, reported on their current symptoms, as well as aspects of their physical and social health using the Short-Form Health Survey (SF-36), and the World Health Organisation Disability Adjustment Schedule 2.0 (WHO DAS 2.0). Differences were examined using independent sample t-testing.

RESULTS

Patients fulfilling the ICC definition reported significantly lower scores (p < 0.05) for physical functioning, physical role, bodily pain, and social functioning than those that only fulfilled the 1994 CDC definition. ICC patients reported significantly greater (p < 0.05) disability across all domains of the WHO DAS 2.0.

CONCLUSIONS

These preliminary findings suggest that the ICC identifies a distinct subgroup found within patients complying with the 1994 CDC definition, with more severe impairment to their physical and social functioning.

The saga of XMRV: a virus that infects human cells but is not a human virus

Xenotropic murine leukemia virus-related virus (XMRV) was discovered in 2006 in a search for a viral etiology of human prostate cancer (PC). Substantial interest in XMRV as a potentially new pathogenic human retrovirus was driven by reports that XMRV could be detected in a significant percentage of PC samples, and also in tissues from patients with chronic fatigue syndrome (CFS). After considerable controversy, etiologic links between XMRV and these two diseases were disproven. XMRV was determined to have arisen during passage of a human PC tumor in immunocompromised nude mice, by activation and recombination between two endogenous murine leukemia viruses from cells of the mouse. The resulting XMRV had a xentropic host range, which allowed it replicate in the human tumor cells in the xenograft. This review describes the discovery of XMRV, and the molecular and virological events leading to its formation, XMRV infection in animal models and biological effects on infected cells. Lessons from XMRV for other searches of viral etiologies of cancer are discussed, as well as cautions for researchers working on human tumors or cell lines that have been passed through nude mice, includingpotential biohazards associated with XMRV or other similar xenotropic murine leukemia viruses (MLVs).

In-depth investigation of archival and prospectively collected samples reveals no evidence for XMRV infection in prostate cancer

XMRV, or xenotropic murine leukemia virus (MLV)-related virus, is a novel gammaretrovirus originally identified in studies that analyzed tissue from prostate cancer patients in 2006 and blood from patients with chronic fatigue syndrome (CFS) in 2009. However, a large number of subsequent studies failed to confirm a link between XMRV infection and CFS or prostate cancer. On the contrary, recent evidence indicates that XMRV is a contaminant originating from the recombination of two mouse endogenous retroviruses during passaging of a prostate tumor xenograft (CWR22) in mice, generating laboratory-derived cell lines that are XMRV-infected. To confirm or refute an association between XMRV and prostate cancer, we analyzed prostate cancer tissues and plasma from a prospectively collected cohort of 39 patients as well as archival RNA and prostate tissue from the original 2006 study. 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. Notably, archival VP62 prostate tissue, from which the prototype XMRV strain was derived, tested negative for XMRV on re-analysis. 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. These findings reveal no association between XMRV and prostate cancer, and underscore the conclusion that XMRV is not a naturally acquired human infection.

Recombinant origin, contamination, and de-discovery of XMRV

The discovery and de-discovery of the xenotropic murine leukemia virus-related virus (XMRV) has been a tumultuous roller-coaster ride for scientists and patients. The initial associations of XMRV with chronic fatigue syndrome and prostate cancer, while providing much hope and optimism, have now been discredited and/or retracted following overwhelming evidence that (1) numerous patient cohorts from around the world are XMRV-negative, (2) the initial reports of XMRV-positive patients were due to contamination with mouse DNA, XMRV plasmid DNA, or virus from the 22Rv1 cell line and (3) XMRV is a laboratory-derived virus generated in the mid 1990s through recombination during passage of a prostate tumor xenograft in immuno-compromised mice. While these developments are disappointing to scientists and patients, they provide a valuable road map of potential pitfalls to the would-be microbe hunters.

Development and application of a high-throughput microneutralization assay: lack of xenotropic murine leukemia virus-related virus and/or murine leukemia virus detection in blood donors

BACKGROUND

Xenotropic murine leukemia virus (MLV)-related virus (XMRV) and other related MLVs have been described with chronic fatigue syndrome and certain types of prostate cancer. In addition, prevalence rates as high as 7% have been reported in blood donors, raising the risk of transfusion-related transmission. Several laboratories have utilized microneutralization assays as a surrogate marker for detection of anti-MLV serologic responses--with up to 25% of prostate cancer patients reported to harbor neutralizing antibody responses.

STUDY DESIGN AND METHODS

We developed a high-throughput microneutralization assay for research studies on blood donors using retroviral vectors pseudotyped with XMRV-specific envelopes. Infection with these pseudotypes was neutralized by sera from both macaques and mice challenged with XMRV, but not preimmune serum. A total of 354 plasma samples from blood donors in the Reno/Tahoe area were screened for neutralization.

RESULTS

A total of 6.5% of donor samples gave moderate neutralization of XMRV, but not control pseudotypes. However, further testing by Western blot revealed no evidence of antibodies against MLVs in any of these samples. Furthermore, no evidence of infectious virus or viral nucleic acid was observed.

CONCLUSION

A microneutralization assay was developed for detection of XMRV and can be applied in a high-throughput format for large-scale studies. Although a proportion of blood donors demonstrated the ability to block XMRV envelope-mediated infection, we found no evidence that this inhibition was mediated by specific antibodies elicited by exposure to XMRV or MLV. It is likely that this moderate neutralization is mediated through another, nonspecific mechanism.

No evidence of XMRV infection in immunocompromised patients and HIV-positive individuals from Germany

BACKGROUND

Xenotropic murine leukaemia virus-related virus (XMRV) has been detected in patients with prostate cancer and chronic fatigue syndrome (CFS). The detection of XMRV in healthy individuals has raised concern about a possible virus transmission by blood products. However, recent studies challenge the association between XMRV and human disease. This study investigated whether or not XMRV is present in patients with altered immune function and individuals at increased risk of blood-borne viral infections in Germany.

METHODS

We investigated 503 peripheral blood mononuclear cell (PBMC) samples from 240 patients with iatrogenic immune suppression (71 haematopoietic stem cell recipients, 132 solid organ transplant recipients, 37 others) and 311 PBMC samples from 302 patients with HIV-1 infection for the presence of proviral XMRV by real-time polymerase chain reaction (PCR).

RESULTS

All 814 PBMC samples from 542 patients tested negative for XMRV DNA and positive for an internal herpesvirus saimiri (HVS) control. Human genomic DNA was detected in all samples, and 90% of the samples contained >10,000 cell equivalents per XMRV PCR reaction.

CONCLUSIONS

Our failure to detect proviral XMRV provides evidence against the presence of XMRV in patients at increased risk of viral infections in Germany.

No evidence for the involvement of XMRV or MCV in the pathogenesis of breast cancer

Background:

The aetiology of breast cancer remains elusive. A viral aetiology has been proposed, but to date no virus has been conclusively demonstrated to be involved. Recently, two new viruses, namely Merkel cell polyomavirus (MCV) and xenotropic murine leukaemia virus-related virus (XMRV) have been identified and implicated in the pathogenesis of Merkel cell carcinoma (MCC) and familial form of prostate cancer, respectively.

Methods:

We examined 204 samples from 58 different cases of breast cancer for presence of MCV or XMRV by PCR. Samples consisted of both malignant and non-malignant tissues. Additionally, we included 6 cases of MCC and 12 cases of prostate cancer as potential controls for MCV and XMRV, respectively.

Results:

All of the breast cancer samples examined were negative for both MCV and XMRV. However, 4/6 MCC and 2/12 prostate cancer samples were found to be positive for MCV and XMRV, respectively. Sequence analysis of the amplified products confirmed that these sequences belonged to MCV and XMRV.

Conclusion:

We conclude that there is no evidence for the involvement of MCV or XMRV in the pathogenesis of breast cancer. What role these viruses have in the pathogenesis of MCC and prostate carcinomas remains to be demonstrated.