Dr. Peter R. GanzDirector, Centre for Blood and

Tissues Evaluation,Health Canada

Strategies for Managing Potential Xenotropic Murine Virus Related Virus (XMRV) Threats to

Blood Safety: A Health Canada PerspectiveBlood Products Advsory Committee Meeting, Blood Products Advsory Committee Meeting,

Gaithersburg, M.D.Gaithersburg, M.D.

July 26-27, 2010July 26-27, 2010

Background Xenotropic Murine Leukemia Virus-Related Virus (or XMRV) is a

gammaretrovirus which can cause leukemias and sarcomas in multiple rodent, feline, and primate species but have not yet been shown to cause disease in humans.

However, xenotropic murine leukemia viruses (MLVs), which are found in the genomes of many inbred and related wild mice, can grow in non-rodent cells in culture and have the potential to infect a wide variety of mammalian species, including humans.

XMRV is closely related to xenotropic MLVs, and recent studies potentially linking XMRV infection in humans with prostate cancer and Chronic Fatigue Syndrome (CFS) suggest this gammaretrovirus could cause human disease

Risk Management of Emerging Infectious Agents: Factors Which Are Considered by Health Canada

• Published literature

• Global experience

• Surveillance data

• Risk modeling data

• Other considerations (population centered)

XMRV-What the Science says –Focus of review on potential link to CFS

XMRV Infection In Chronic Fatigue Syndrome (CFS) Patients

CFS, also known as Myalgic Encephalomyelitis (ME), is a debilitating disease of unknown etiology that is estimated to affect 17 million people worldwide and about 340,000 Canadians (http://fm-cfs.ca/cfs.html)

In a study by Lombardi et al (Science: 326, 585, 2009) XMRV DNA was identified by nested PCR in peripheral blood mononuclear cells (PBMCs) of 68 of 101 (67%) CFS patients, compared to 8 of 218 (3.7%) healthy controls.

It was also demonstrated that XMRV could be transmitted by PBMCs from CFS patients, by CFS plasma, and by cell-free virus from activated T cells of CFS patients. Finally, antibodies to the XMRV envelope were detected by flow cytometry in plasma of 9 of 18 (50%) CFS patients infected with XMRV, but not in plasma of 7 healthy donors.

XMRV Infection In Chronic Fatigue Syndrome (CFS) Patients:

The authors concluded that there is a highly significant association between XMRV and CFS. As well, they subsequently noted that they have done additional work since this publication and have detected XMRV in 95% of CFS patients’ blood samples in the study group. (http://www.wpinstitute.org/xmrv/xmrv_qa.html).

XMRV Infection In Chronic Fatigue Syndrome (CFS) Patients: Data From Other Studies (1)

In contrast to the US study, Erlwein et al. (PLoS ONE: 5(1), 8519, 2010) failed to detect either XMRV or MLV when DNA extracted from whole blood samples from 186 CFS patients in the United Kingdom was tested by nested PCR using primers targeted to an XMRV-specific sequence and a sequence conserved among MLVs, as well as to human beta-globulin (hBG) to detect PCR inhibition.

They concluded that XMRV is not a contributing factor in the pathogenesis of CFS.

XMRV Infection In Chronic Fatigue Syndrome (CFS) Patients: Data From Other Studies (2)

In January 2010, another UK study (Groom et al, Retrovirology 7: 1168, 2010) a total of 170 samples from chronic fatigue syndrome patients from two UK cohorts and 395 controls were analyzed for evidence of XMRV infection by looking either for the presence of viral nucleic acids using quantitative PCR (limit of detection <16 viral copies) or for the presence of serological responses using a virus neutralisation assay.

No evidence of XMRV DNA was found in any samples by PCR (0/299). Some serum samples showed XMRV neutralising activity (26/565) but only one of these positive sera came from a CFS patient. Most of the positive sera were also able to neutralise MLV particles pseudotyped with envelope proteins from other viruses, including vesicular stomatitis virus, indicating significant cross-reactivity in serological responses. Four positive samples were specific for XMRV.

XMRV Infection In Chronic Fatigue Syndrome (CFS) Patients: Data From Other Studies (2)

No association between XMRV infection and CFS was observed in the samples tested, either by PCR or serological methodologies.

XMRV Infection In Chronic Fatigue Syndrome (CFS) Patients: Data From Other Studies (3)

Van Kuppeveld et al (2010) Brit. Med. J. 340, c1018 studied the prevalence of XMRV in patients with CFS in the Netherlands using a retrospective analysis of samples from an established cohort. In their PCR analyses, they found 0 positives out of 32 sample CFS cases. In control samples, the group found 0 positive by PCR of 43 tested samples.

Summary: No association found between XMRV and CFS

XMRV Infection In Chronic Fatigue Syndrome (CFS) Patients:Data From Other Studies (4) A recently published study (Switzer et al, Retrovirology 2010: 7, 57) from

the US CDC, the Robert Koch Institute in Germany, and Blood Systems Research Institute in San Francisco found no association between XMRV infection and CFS following testing of plasma from 51 CFS cases and 53 controls using ELISA and nested PCR methodologies.

XMRV Infection In Chronic Fatigue Syndrome (CFS) Patients:Data From Other Studies (5) Another study authored by staff from the US NIH and FDA has been

purported to have independently confirmed an association of XMRV with CFS as per the publication of Lombardi et (2009). This study has not yet been published.

Mode of XMRV Transmission

The route of XMRV transmission is currently unknown

In one study (Furuta et al Abstr. Cold Spring Harbour Retrovirus Symposium 2009) XMRV-specific nucleic acid sequences were detected in the genomic DNA of PBMCs from 2 of 3 healthy volunteers following exposure to culture supernatant of PBMCs obtained from a patient who had been found positive for XMRV specific nucleic acids by nested RT-PCR.

The authors concluded that XMRV is sustained in a few fractions of blood cells and can spread through blood even though the virus replication rate was very low. The detection of XMRV in plasma and PBMCs of infected individuals also suggests the possibility of a blood-borne transmission.

Mode of XMRV Transmission (2)

It has been suggested that XMRV could also be transmitted through other body fluids such as semen and breast milk (http://www.wpinstitute.org/xmrv/xmrv_qa.html) although there is no direct evidence to support this suggestion.

Regulatory Perspectives There is a lack of consensus regarding the

association of XMRV with CFS in published studies perhaps due to many variables such as:

Variation in the diagnosis of CFS patients

Methodological variability (PCR, immunochemistry)

Use of differing and non-standardized samples/reagents

Regulatory Perspectives

Lack of consensus does not require adherence to status quo

What are the potential risks to blood recipients?

Potential Risks to Blood Recipients

The general population could potentially be exposed to XMRV via various modes including vertical or horizontal transmission, as well as transmission through transfusion and transplantation.

Currently, there is no direct evidence to support XMRV transmission through blood or CTOs. However, its detection in plasma and PBMCs of individuals in studies suggests that these routes of transmission are possible, and could significantly increase the risk of exposure to this virus.

Potential Risks to Blood Recipients (2)

The risks posed by XMRV to recipients of blood will also depend on its ability to cause diseases in humans, and the magnitude of this risk will depend on whether only a subset of recipients (e.g., immunocompromised individuals) are susceptible to XMRV infection/disease or not.

While the data presented to date suggests a link between XMRV infection with CFS, there are still many unanswered questions regarding its causative role in these and potentially other diseases.

Thus, further studies are required to prove that XMRV is the underlying cause of human diseases in infected individuals.

Current Measures For Mitigating Risks to Blood Recipients

Overarching Guiding Policy: Precautionary Principle

Authorities must act even if there is only a theoretical risk of harm.

If risk is possible then we must err on the side of caution

Previous Health Canada Regulatory Actions Based on Precautionary Principle and Results: Has it worked?

Risk of Transmission of vCJD: Donor Screening added to defer those with travel or residency history in high risk areas. Measures implemented took into account effects on supply balanced against maximal risk reduction. RESULT: theoretical risk has translated to real risk of transmission through transfusion and spread of vCJD. Risk to transfusion recipients was reduced.

Risk of Transmission of SFV: Donor screening for individuals at risk of exposure to SFV (non human primates) was implemented. As above, donor demographic screens balanced maximal risk reduction as considered against supply. RESULT: Risk of introduction of a retrovirus with the possibility of developing pathogenicity over time with spread in human hosts via transfusion has expected to have been reduced.

Regulatory Options for Managing Imminent Potential XMRV Risks

1) Status quo, with further research (possible)

2) Education and self-deferral (precautionary, possible)

3) Defer donors presumed at risk for carrying XMRV (precautionary, possible)

4) Testing of donors for XMRV (considering timeframe, not currently possible)

5) Pathogen reduction (possible for some components)

Operationalizing Options: Health Canada’s Current XMRV Risk Mitigation EffortsThe following measures are currently in place in Canada and could potentially mitigate the risk of XMRV transmission:

Self- Deferral through education efforts

Donor Screening

Other measures

Current XMRV Risk Mitigation Efforts1) Self Deferral and education

Canada sponsored a Chronic Fatigue Syndrome consensus conference in 2003. Following a review of current science concerning CFS, a series of recommendations was developed including a recommendation for health professionals treating CFS patients and individuals with CFS concerning blood donation.

J. Chronic Fatigue Syndrome (2003) Vol 11, pp 1-69

Current XMRV Risk Mitigation Efforts (2)

2. Donor Screening

When blood donors are screened to determine their health status prior to donation, they are asked the question “Are you feeling well today?” and “In the last 3 days have you taken any medication or drugs?” Considering the debilitating effects of CFS, it is expected that the response to these questions will most likely result in the deferral of individuals suffering from this disease. However, if donors are feeling well they were previously accepted.

To date, as a precautionary measure, individuals donating at Canadian Blood Services with a diagnosis of CFS are now indefinitely deferred from blood donation (April, 2010).

Current XMRV Risk Mitigation Efforts (3)

2. Donor Screening (Con’t)

Currently, prostate cancer patients are permanently deferred from blood donation, and donations from individuals, who were diagnosed with cancer post-donation, are retrieved, quarantined and destroyed.

Current XMRV Risk Mitigation Efforts (4)

3. Other Measures: Universal Leukoreduction

A Directive on Universal Leukoreduction was issued by Health Canada in 1998. Thus, in Canada, all cellular blood components must be filtered to remove WBCs and must contain residual WBC levels of <5x106 per component. This is expected to have some protective effect if the virus is mostly associated with WBCs. Further studies are needed to demonstrate transmission via transfusion and the effectiveness of leukoreduction in preventing XMRV transmission through transfusion. It is noted that the virus could still be transmitted through plasma but data are lacking concerning titres necessary for infection or viremic period.

Final Remarks

The evidence to date suggests, but does not prove, a link between XMRV infection and CFS. BUT as a precautionary measure, Canada has chosen to defer individuals with CFS indefinitely. A similar measure has been subsequently implemented in Australia & New Zealand.

Further studies are required to address the gaps in information in order to appropriately assess the risk of transfusion transmitted XMRV infection. This will require, among others, (i) the development of standardized, well validated tests/methods to determine the prevalence of XMRV in the general population and in blood donors; (ii) investigating its mode of transmission; and (iii) confirming its role in human disease.

Questions and Discussion