1.    The authors of the paper established the existence of XMRV as an infectious human blood borne retrovirus for the first time in blood of patients diagnosed with CFS. Previous studies had established the presence of XMRV sequences and protein in human prostate tissue. The basic premise that XMRV may be capable of causing disease has not been questioned.

2.    In the paper, the presence of XMRV in well -characterized patients with CFS was established using multiple technologies:

a)    PCR on nucleic acids from un -stimulated and stimulated white blood cells;

b)   XMRV protein expression from stimulated white blood cells;

c)    virus isolation on the LNCaP cell line; and

d)   a specific antibody response to XMRV.

3.    The authors of the two UK studies did not attempt to "replicate" the WPI study. Replication requires that the same technologies be employed.

4.    The collection, preparation and storage of DNA were completely different between the [tekst weggevallen; waarschijnlijk: WPI] and UK papers. The latter studies do not show data on how blood was harvested and stored. 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.

5.    Patient selection was based on different definitions of CFS.

6.    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 distribution.

7.    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 paper shows that increasing the amount of the virus by growing the white blood cells isusually required rather than using white blood cells directly purified from the body. When using PCR alone, the 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 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 sp ecifically and sensitively competed the immune response demonstrating the assays sensitivity and specificity for XMRV envelope.

Neither UK study requested positive control blood, plasma or nucleic acids from the WPI. 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 XMRV.

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(c) 2010 WPI