This is an interesting complexity here. John Coffin found that XMRV has immune suppressing agents on its envelop, thus preventing immune cells from killing it. Mikovits theorizes (or found) that XMRV-infected cells have antigens on their envelops, which tell immune cells to attack it. Even though this seems contradictory, it might actually be complimentary.
Think of an enemy agent purposely revealing itself and causing solders to attack, only to result in the soldiers being neutralized. The result being that more soldiers are sent in to attack. In the model, a very small number of XMRV "enemy agents" could overcome a larger force because they cannot be killed.