Something confusing here; the CAA report states that the "gag sequences found by Dr. Hanson were more similar to those reported by Lo et al., than to the gag sequences for XMRV, although all are part of the same gammaretrovirus family." However, the abstract describes the gag sequences as XMRV after a BLAST analysis. Either there's a mistake in the abstract, or the CAA got it wrong.
Anyway, I don't think they should contrast "MLV" sequences with XMRV ones; they may just be confused about the terminology, but in case they actually think the viral sequences found by Alter and Lo belong to MLV that have directly infected humans: I think it's most likely that the whole genomes - once sequenced - will prove to be slightly different and will be classified as MLV related viruses; for now it's best to call them "MLV-related sequences". At this stage we don't know for sure whether they all have P-type envelopes (the isolated env fragments were few and small). I would also point out that the distinctions between P and X at the moment are kind of immaterial, until Alter sequences whole virus... even then the most important thing is pathogenic potential, not so much whether they can or cannot infect lab mice.
From the CAA report on Blomberg's talk:
Additionally, he reported finding viral sequences in only 3 of 5 XMRV positive samples received from the WPI.
"Only 3 of 5" is an odd way to spin it.. it's always interesting that the author of a negative study found positives in WPI samples, and even more interesting that they found some positive, but not all - you would expect all to be positive if they were 'contaminated'.
The idea that XMRV might be a passenger virus and that the immunosuppressive state associated with disease might result in the viral infection (rather than the virus possibly causing disease) received some attention. Participants named lessons learned from other retroviruses like gibbon ape retrovirus (prevalent but not disease causing) and HTLV-1 (one agent causing two distinct diseases).
(1) Gibbon ape leukemia virus, as it is correctly called, DOES cause disease in gibbons. The mystery ape expert at the meeting was stupendously wrong.
(2) The example of HTLV-1 was given by Mikovits and others as support for the hypothesis that XMRV causes CFS, not that it is a passenger virus. This point isn't clear at all in the context of this paragraph; it sounds like they're offering HTLV-1 as evidence for the passenger virus idea!