WPI Response to UK study that was unable to detect
XMRV in CFS patients.
http://www.wpinstitute.org/news/news_current.html
February
18, 2010:
WPI is aware of the recent UK
study that was unable to detect the presence of XMRV in any CFS patient
samples. Although researchers at the WPI were not involved in this
project, our work in XMRV continues with researchers around the world.
We look forward to the results of studies which replicate the
methods used in the original research described in the journal Science
in October, 2009.Information Regarding XMRV Studies
- The authors of the Science paper established
the existence of XMRV as an infectious human blood borne retrovirus for the first time in blood of patients diagnosed with Chronic
Fatigue Syndrome (CFS).
Previous studies had established the presence of
XMRV sequences and protein in human prostate tissue.
- In
the Science paper, the presence of XMRV in well-characterized
patients with CFS was established using multiple
technologies:
- PCR on nucleic acids from un-stimulated and
stimulated white blood cells;
- XMRV protein expression
from stimulated white blood cells;
- Virus isolation on
the LNCaP cell line; and
- A specific antibody response to
XMRV.
- The authors of the two UK studies did not
attempt to “replicate” the WPI study.
Replication
requires that the same technologies be employed.
The WPI sent reagents
and information to several groups of researchers in an effort to support
their replication studies.Neither UK study requested positive control
blood, plasma ornucleic acids from the WPI.
- The
collection, preparation and storage of DNA were completely different between
the Science and UK papers.
The latter studies do not show data on blood
harvesting or storage. Nor do the studies disclose the quantity of isolated cells.
Insufficient number of cells analyzed may result in failure
to detect a low copy virus like XMRV, regardless of the sensitivity of
the assay. Neither UK study provides detail to allow interpretation of how
many white blood cells were analyzed.
- Patient population
selection may differ between studies.
- The UK authors were
unable to detect XMRV, even though 4% of healthy individuals were found to
be infected in the US.
Japanese scientists detected XMRV in 1.7% in
healthy blood donors in Japan. The two previously identified human
retroviruses have distinct geographical distributions.
- Perhaps the most important issue to focus on is the low level of XMRV in the
blood. XMRV is present in such a small percentage of white blood
cells that it is highly unlikely that either UK study’s PCR method could
detect it using the methods described.
Careful reading of the Science
paper shows that increasing the amount of the virus by growing the white
blood cells is usually required rather than using white blood cells directly
purified from the body. When using PCR alone, the Science authors
found that four samples needed to be taken at different times from the same
patient in order for XMRV to be detected by PCR in freshly isolated
white blood cells. More importantly, detection methods other than PCR
showed that patients whose blood lacks sufficient amount of XMRV
detectable by PCR are actually infected. This was proven by the
isolation of viral proteins and the finding of infectious XMRV isolated from
the indicator cell line LNCaP. The authors of the Retrovirology
paper admit that their neutralization assay did not detect bacterially
expressed XMRV gag and that positive control sera was needed to validate
their assay. The WPI’s monoclonal antibodies specifically and
sensitively completed the immune response demonstrating the assays
sensitivity and specificity for XMRV
envelope.Simply
stated the only validated reliable methods for detecting XMRV in CFS
patients, to date, are the methods described in Science. Failure to use
these methods and validated reagents has resulted in the failure to detect
XMRV. A failure to detect XMRV is not the same as absence of this virus
in patients with CFS.