ME ASSOCIATION SUMMARY AND STATEMENT ON LO et al PAPER:
Detection of MLV-related virus gene sequences in blood of patients with chronic fatigue syndrome and healthy blood donors
Issued 25 August 2010
ME ASSOCIATION SUMMARY AND STATEMENT ON LO et al PAPER:
Detection of MLV-related virus gene sequences in blood of patients with chronic fatigue syndrome and healthy blood donors
Authors: Shyh-Ching Lo (US Food and Drug Administration) et al.
Published in the Proceedings of the National Academy of Sciences (PNAS) on August 23rd 2010.
Pdf available on-line: http://www.pnas.org/content/early/2010/08/16/1006901107.full.pdf+html
Accompanying commentary by Valerie Courgnaud et al: http://www.pnas.org/content/early/2010/08/16/1007944107.full.pdf+html
Murine leukaemia viruses (MLV) are retroviruses known to cause cancer in certain mice. In 2006, investigators found that a type of MLV, called xenotropic murine leukaemia virus-related virus (XMRV), could potentially infect humans after finding it in tissue samples from men with prostate cancer. XMRV is one of a number of MLVs that appear to be transmitted to humans.
In October 2009, Lombardi et al published the results of study in Science which contained evidence that XMRV was present in a high percentage (67%) of people with ME/CFS and in a small percentage of healthy controls.
Since then there has been a great deal of interest from researchers in a number of countries where ME/CFS is recognised. A number of research groups have attempted (or are still attempting) to repeat these positive XMRV findings.
Confirming or refuting new findings is a vital part of the scientific evaluation process and involves other independent research groups trying to either replicate or validate the results.
In relation to XMRV, a true replication study should involve exactly the same laboratory methods and same type of patients that were used in the original Science study. A validation study gives scientists a degree of flexibility. In particular, it provides the opportunity for other research groups to try and repeat the findings using what they feel are the most sensitive and accurate laboratory methods they have access to for testing for XMRV.
In the case of XMRV almost all of the first wave of research has involved validation studies. Firstly, because there is no international agreement about the most accurate and sensitive way of detecting XMRV in blood samples. Secondly, because these research groups all wanted to move quickly, and the easiest way to do so was to use stored blood samples from people who had been diagnosed with CFS in the past according to Fukuda research criteria. Stored blood samples from people who met both Fukuda and Canadian criteria (which were used in the original study) are not readily available.
Results from four emphatically negative validation studies of varying quality – three carried out in Europe and one carried out by the CDC in America – have now been published in scientific journals. Results from a further (so far unpublished) study, carried out by Professor Brigette Huber, were presented at the Invest in ME conference in May 2010 (report available on MEA website and in the August 2010 of ME Essential).
None of these five research groups – which in the case of the UK included Professor John Gow, Dr Kate Bishop, Dr Jonathan Kerr and Dr Jonathan Stoye and used patient samples supplied by physicians and neurologists including Dr Abhijit Chaudhuri and Professor Peter Behan – have been able to find evidence of XMRV in blood samples from ME/CFS patients, or in the healthy controls.
Although some very valid criticisms have been made about all of the XMRV negative studies, in particular the most recently reported one from America, a number of distinguished virologists who work with retroviruses and XMRV have been involved – so these XMRV negative results have to be taken seriously as well.
THE LO et al STUDY
On 23 August 2010 the results from the first follow up study to firmly support a link between a retroviral infection and ME/CFS were published.
This study is clearly an important contribution to the XMRV debate in that it fully supports a link between ME/CFS and retroviral infection. In this respect it also supports the findings in the Lombardi paper.
However, it is not a true replication study, and in the words of the authors they have not attempted to fully replicate the Lombardi et al findings.
Lo et al have used different laboratory methods and different patient criteria and their findings relate to what are called MLV-related viruses.
The research group have found segments of genetic material (not whole virus) from what they term a genetically diverse group of MLV-related viruses. These sequences are more closely related to those of polytropic mouse endogenous (=arising within or derived from the body) retroviruses than to those of XMRVs – hence the use of the term MLV (murine = mouse leukaemia virus) in the title. But they all belong to a closely related family of retroviruses.
In contrast to the Lombardi et al study, which involved patients who met both Fukuda research criteria and Canadian Clinical Criteria for CFS, this research used stored blood samples from ME/CFS patients who had been diagnosed using either the 1988 Holmes research criteria or the 1994 Fukuda research criteria. The patients were diagnosed with CFS from the mid 1990s onwards and most of the frozen blood samples were supplied by Professor Tony Komaroff at Harvard Medical School, Boston. Professor Tony Komaroff is a well respected physician with a longstanding interest in ME/CFS. In addition, 12 patient samples came from other US physicians whose diagnostic criteria for ME/CFS is not stated.
The numbers involved were surprisingly small for a study of this nature: 37 patients with CFS and 44 healthy controls.
The healthy control samples came from Washington DC blood donors recruited between 2003 and 2006.
So these results apply to a rather broader group of ME/CFS patients than was used in the Lombardi et al study and the patient sample is probably very similar to at least one of the other validation studies that produced negative findings in relation to XMRV. As with some of the other validation studies, it is highly likely that a significant number of people who also meet Canadian Clinical Criteria will have been included in this study.
MLV-like virus gag gene sequences (in simple terms segments of viral genetic material) were found in 32 out of 37 (86.5%) of the ME/CFS patients compared to only 3 out of 44 (6.8%) of the (blood donor) healthy controls.
Follow-up samples were collected from 8 of the CFS patients in 2010, and 7 of these again tested positive for MLV-like gene sequences.
As already pointed out, the evidence in this paper relates to a genetically diverse group of MLV- related viruses with gene sequences that are more closely related to those of polytropic mouse endogenous retroviruses (mERVs) than to those of XMRV. XMRV is a genetic variant of MLV-like viruses – so this is a subtle but relevant distinction.
The authors point out that they have taken exhaustive steps to try and ensure that they have not produced false positive results as a result of mouse DNA contamination, or any of the other potential laboratory problems that come when working with retroviral infections.
CORRELATION, INFECTION AND POSSIBLE CAUSATION
The authors point out (p5) that the finding of XMRV or MLV genetic sequences in people with ME/CFS, or any other disease, does not constitute definite proof of viral infection.
They then go on to make it clear that further research will be required before any definite conclusion can be drawn as to whether MLV-related viruses play a role in the causation of ME/CFS. This is a process that is going to take time and further research.
They also state (p6), as has been pointed out in previous MEA summaries on XMRV, that a high frequency of MLV-related viruses (or XMRV) in ME/CFS patients could reflect an increased susceptibility to viral infections due to the underlying immune dysfunction found in ME/CFS rather than a primary disease causing role in the pathogenesis of ME/CFS. In other words the retrovirus could just be there as a ‘harmless passenger’.
COMMERCIAL TESTING FOR MCVs and XMRV
The MEA continues to believe that there is no point in spending very large sums of money on arranging blood tests, which may not have been properly validated, for XMRV (or MCVs) outside the UK. Having a positive result is not, in our present state of knowledge, a diagnostic marker for ME/CFS. Equally, having a negative result does not mean that you do not have ME/CFS. Having a positive result will not affect ME/CFS management at present and if this information is inserted into medical records it could in due course cause problems with other health matters such as applications for insurance policies or travel abroad.
The way in which these viruses might be transmitted from person to person also remains uncertain and sexual transmission is one possibility – as in the case of HIV. However, if this is a disease causing virus like HIV, sexual transmission appears very unlikely given the fact that ME/CFS appears to be very rare in sexual partners of people with ME/CFS, even after long periods of time.
The MEA continues to believe that the current uncertainty over transmission of these viruses/viral segments means that people with a current or past history of ME/CFS should not be donating blood and we have recently written to the acting Chief Medical Officer at the Department of Health to seek clarification on what appears to be a recent decision to extend the UK ban to people who have recovered from ME/CFS. Copy of this correspondence [here]
We find it surprising that the American authorities responsible for blood safety have not followed the UK lead here.
The authors of this paper make no comment or recommendations regarding the use of antiviral drugs. However, others (including the authors of the accompanying commentary) are now suggesting that it is time to assess the use of antiretroviral therapy (ART) in ME/CFS in some clinical trials. It is well accepted that one way of examining the possible cause of a disease is to assess the response to specific forms of treatment.
The MEA has already pointed out on several occasions that this type of clinical trial would have to proceed with great care given the fact that ARTs can have serious side-effects. In the case of AZT, this drug can cause mitochondrial damage – which is obviously very relevant in ME/CFS. But there are other ARTs becoming available that appear to be active against XMRV and may be much safer to use (eg reverse-transcriptase inhibitors such as tenofovir and emtracitabine).
We have also pointed out that ARTs appear to have very limited effect in reducing fatigue in HIV/AIDS, and that this may be due to the immune system activation that is occurring in this situation rather than any direct effect on reducing the viral load of the HIV infection. So drugs that dampen down immune activity (eg a tumour necrosis factor inhibitor such as etanercept) may be a more appropriate route to follow. More information [here]
In the UK doctors are very unlikely to be willing to prescribe any type of antiviral treatment on an individual (ie non research) basis. This is because the 2007 NICE guideline on ME/CFS specifically recommends that antiviral drugs should not be used to treat ME/CFS. And if anything goes wrong through the use of a potentially toxic antiviral drug, that is in effect banned by NICE, and has not been assessed in a proper clinical trial, the doctor responsible could face legal action even though the patient accepted the risk.
FURTHER RESEARCH AND THE ROLE OF MEA RAMSAY RESEARCH FUND
Investigators at FDA, NIH, CDC and other scientific institutions are in the process of conducting studies to verify the capabilities of the tests used by the different laboratories for the detection of XMRV or MLV-related viruses in blood. These studies are intended to develop and standardise a highly sensitive and specific XMRV test to better study its association with disease, as well as the possibility that XMRV can be transmitted to blood or tissue recipients.
The UK Medical Research Council’s Expert Group on ME/CFS research (of which CS is a member) has identified all aspects of viral infection in ME/CFS (including carefully targeted use of antiviral agents) as a priority item for further UK research and we expect that this recommendation will now be translated into action.
The MEA is again making it clear to UK research groups with expertise in retrovirology, and access to reliable patient samples, that we would very much welcome good quality research applications relating to any aspect of XMRV or MLVs. The MEA is also willing to consider co-funding research applications in this area.
We are in contact with most of the key UK researchers working on XMRV and we are also assisting with a small UK study that is intending to retest people who already have a positive XMRV result as a result of having this test done in America.
We also need to find out how common these new retroviruses are in people with other chronic disabling conditions, especially those that involve immune system dysfunction.
In America, the paper has been quite widely reported with most of the coverage being supportive. In the UK there has been very little interest in the press release – apart from the Daily Mail (which carried an on-line story) and the New Scientist:
which includes quotes from Professor Myra McClure, one of the UK virologists involved in a negative validation study.
Lack of coverage in the UK is partly because selected health journalists, who might have reported the story, like to have access to a new research paper well before the information enters the public domain – so they have a day or two to chase around and obtain informed comment on the story. Health reporters have finished writing their copy for the next days paper well before 8pm in the evening – so unless there is a real breakthrough news item they are not at their desks in the evening. The US press conference at 8pm UK time did not fit in with their working arrangements for printing something on Tuesday and the findings would be ‘old news’ by Wednesday. In addition, they also had a good headline health scare story for Tuesday morning relating to people being refused an anti-cancer drug due to a NICE ruling.
Unfortunately, there are health correspondents that I speak to on the more influential papers and journals who are now very cautious about covering ME/CFS stories.
In very simple terms the clinical and scientific community regards published papers rather like goals (of varying quality) in a football match. So the current score is XMRV and MLV positive 2 (with a spectacular first goal!): XMRV negative 4 (of varying quality) with plenty of time left before the final score.
The comments so far that I have read, or been given, by experts in this area of virology indicate that everything has been done correctly in this study and that this is a sound piece of laboratory research. However, with differing results from differing well respected retroviral laboratories, the clinical and scientific community is likely remain uncertain or sceptical about the link between retroviral infection and ME/CFS.
Another analogy is fitting pieces into a jigsaw puzzle with a lot of blue sky. We now have six pieces (ie published papers of varying quality) in place and some strong opinions on either side. But a lot of pieces have still to be fitted into the picture.
Overall, there is no sign of any real scientific consensus emerging as to whether XMRV and/or MLVs are playing a significant role in ME/CFS and many key questions regarding prevalence, transmission and pathogenesis remain unanswered. Things may become a bit clearer as a result on the international meeting on XMRV in September, which will include a session on ME/CFS. Proposals for further research may also emerge after this meeting.
This uncertainty and scientific disagreement seems likely to continue until well into 2011 and the current findings are unlikely to have any significant influence on the forthcoming review of the NICE guideline or the increasingly difficult position faced by people with ME/CFS in relation to sickness and disability benefits. [Our most recent correspondence on 24 August from NICE indicates that they have still to decide on the date at which the review will take place, whether it will be a full review – which could take up to a year, or whether they might delay the review to await the results of further research from clinical trials.
More top quality research is clearly needed here in the UK and the MEA is very willing to consider funding it.
ADDITIONAL INFORMATION FROM US FDA:
FDA Question and Answer on the paper: http://www.fda.gov/BiologicsBloodVaccines/SafetyAvailability/ucm223232.htm
Answers to the final three questions, which are of importance to US readers:
9. Does FDA agree with the AABB recommendation to discourage donation by people with history of CFS?
FDA does not object to the AABB recommendation. The AABB recommendation is consistent with a long-standing position of the Chronic Fatigue and Immune Dysfunction Syndrome (CFIDS) Association of America that individuals with CFS voluntarily should not donate blood.
10. How are the differences between the CDC and FDA study results being evaluated?
Differences in the results could reflect differences in the patient populations that provided the samples. Alternatively, undefined differences in the method of sample preparation could be contributing to the discordant test results. All of the scientists involved are working collaboratively to design experiments to quickly answer this scientifically puzzling question. An independent investigator at the National Heart, Lung, and Blood Institute (NHLBI) set up a test set of 36 samples, including known positives and presumed negatives. Both the FDA/NIH and CDC labs participated in this test, and the results showed that both labs were able to detect XMRV present at low levels in blinded samples. Additionally, the CDC laboratory provided 82 samples from their published negative study to FDA, who tested the samples blindly. Initial analysis shows that the FDA test results are generally consistent with CDC, with no XMRV-positive results in the CFS samples CDC provided (34 samples were tested, 31 were negative, 3 were indeterminate).
11. What do these findings mean to CFS patients and clinicians who treat them?
Although this study found MLV-like viral gene sequences in a high percentage of CFS patients, this does not prove that these retroviruses are the cause of CFS or of any other disease. Moreover, other studies have not found evidence of such retroviruses in patients with CFS. Further studies are necessary to determine if XMRV or other MLV-like viruses are reproducibly associated with CFS, and if so whether the virus is a causative agent or a harmless co-traveler. The different findings from various studies reinforce the need for more research–including careful analysis of other cohorts of CFS patients from different geographic regions, studies of larger populations of healthy people, and testing of transmissibility of the agents through blood transfusions in animal models. FDA, NIH, and CDC have and will continue to collaborate with other agencies and groups involved in this research.
Summary prepared by Dr Charles Shepherd
Hon Medical Adviser, MEA
MEA website: http://www.meassociation.org.uk
NB: There will be a delay in placing this item on the MEA website because our webmaster is away on holiday for the next few days.
25 August 2010