It looks like they have used the same clone that all the negative studys have. VP62 is a clone Judy Mikovits have talked about earlier in this letter to editor: http://www.iacfsme.org/BULLETINSPRING2010/Spring2010MikovitsLetter/tabid/427/Default.aspx
She said about VP62:
"However, if any of the last three are true, single round PCR of genomic DNA isolated from PBMCs, using primers based on published sequences from using highly specific PCR based on the sequence of a single molecular clone, (VP62) might not result in the amplification of XMRV, even from an infected individual."
From todays negative Switzer study:
Dilutions of DNA from XMRV-infected 22Rv1 human prostate carcinoma cells were used as positive
controls in this test . 1.0 μg of DNA (333 ng of PBMC DNA) was used in the nested pol and gag PCR
tests at the CDC for which 1,000 and 10 copies of the XMRV(VP62) plasmid were used as positive
controls [1, 9]. A subset of 48 plasma samples were tested for viral RNA sequences by RT-PCR using
primers from the nested gag assay and also by using a new quantitative RT-PCR test that generically
detects MuLV and XMRV gag sequences. Both RT-PCR tests could detect between 10 – 25 copies of
XMRV (VP62) RNA.