While the NCI scientists are busy patting themselves on the back, and congratulating themselves, and saying how wonderful they are for conclusively proving (almost) that XMRV is a contaminant, XMRV research and knowledge continues to grow and evolve.
The whole NCI article, and all of the conclusions made, have already been challenged by the CDC in a study by Switzer.
http://www.retrovirology.com/content/8/S1/A235
Conclusion:
"Given the evidence of inter-tropic recombination in MuLV, detection and classification of recombination in XMRV using different MuLV tropism prototypes should be interpreted with caution ... These results suggest that identification of parental strains of the potential recombinants is difficult and that recombination in the highly genetically related MuLV have been occurring for some time."
This CDC study points out that, contrary to Paprotka's, Coffin's and Pathak's conclusions, there are a myriad of ways that XMRV could have been created, and that the prostate cancer cell line might just be one example of many possible recombination events. Switzer draws very different conclusions to Paprotka et al., and directly challenges their study's conclusion of a 'one in a trillion' chance of a recombination event.
The following extract from the NCI article has been directly challenged by Switzer's study:
Furthermore, the chance of the virus arising independently in another mouse or in the wild is "vanishingly smallabout one in a trillion," said Dr. Pathak. This virus is unlikely to exist in nature, so the chance that a person would be exposed to a mouse with the virus is also unlikely, he added.
But even if XMRV is a result of a recombination in that specific prostate cancer cell line, the admission that it has been travelling around as contamination in labs, ever since it was created, gives us a clue to a possible route of transmission into the human population, either via vaccines or a similar route, as this article explains:
http://www.thelancet.com/journals/laninf/article/PIIS1473-3099(11)70081-0/fulltext
Another issue, which flies in the face of the NCI's article, is the evidence that XMRV has indeed infected the human population in at least 5 positive prostate cancer studies.
The 'proof' of contamination given in the following extract from the NCI article, has been challenged by other scientists...
All XMRV isolates reported to date are closely related to the viral sequence found in the prostate cancer cell line known as 22Rv1. If the retrovirus had been replicating in humans, these sequences would contain much more variation, several researchers noted.
The challenges are:
1. The transmission XMRV could be via vaccines or similar contact with lab artifacts.
http://www.thelancet.com/journals/laninf/article/PIIS1473-3099(11)70081-0/fulltext
2. The mutation rate of XMRV could be similar to HTLV, which has extremely low variability.
http://forums.phoenixrising.me/show...it-can-explain-XMRV-s-low-degree-of-mutations
It might also be the case that the original prostate cancer sample had minuscule and undetectable levels of XMRV in it, which then flourished and replicated in the cell line, making it subsequently possible to detect. (The authors assume that they would be able to detect extremelly low copy rates of XMRV.)
The NCI article says: "...XMRV replicates well in culture..." which would confirm this as a possibility.
Some prostate cancer research (Urisman et al. - see quotes below) has found that XMRV is not found in the actual prostate tumour itself (malignant prostatic epithelial cells), but in the surrounding tissue (stromal cells), so could this have led to there only being minuscule amounts of XMRV in the original prostate cancer sample in which no XMRV was detected?
Urisman et al. (Silverman):
"XMRV FISH with concurrent immunostaining for cytokeratin AE1/AE3 to achieve specific labeling of epithelial cells [64] showed no XMRV-infected cells that also had the epithelium-specific staining, confirming their non-epithelial origin"
"Analysis of prostate tissues from XMRV-positive cases by in situ hybridization and immunohistochemistry showed that XMRV nucleic acid and protein can be detected in about 1% of stromal cells, predominantly fibroblasts and hematopoietic elements in regions adjacent to the carcinoma."
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1434790/?tool=pubmed
So, yes, this study shows us that XMRV could have been formed from a recombination of mouse viruses. But that's all it tells us. These scientists should do a bit more reading.
Here's another questionable extract from the NCI article:
... it is unlikely that the virus would spread easily from person to person. The reason, Dr. Fan explained in an e-mail, is that humans "have a fairly potent intracellular resistance factor that prevents XMRV infection."
Well, where on earth has this information come from?
XMRV research is only just beginning, so how can he possibly know what the behaviour of XMRV in the wild would be?
What is his evidence on which he is basing this statement?
I thought I had seen evidence of XMRV infecting human cells (1), and of cell lines being created out of XMRV-infected human tissue (2):
(1)
http://www.retrovirology.com/content/pdf/1742-4690-8-s1-a208.pdf
(2)
http://www.retrovirology.com/content/pdf/1742-4690-8-s1-a230.pdf
I'm afraid that this article get more ridiculous the more I read:
Less than 2 years later, the field has an answer. With the findings published, Dr. Le Grice said, it is important to remember that "there is still no evidence that this virus was ever in patients."
Sorry? Has he not seen the 5 positive prostate cancer studies?
This strikes me as a very unbalanced and unscientific article, based on a single scientific study which has reached flawed conclusions, as demonstrated by Switzer of the CDC, and others.