So, I was poking around on the DeRisi lab website
http://derisilab.ucsf.edu and came across a paper they published as a followup to finding XMRV in prostate cancer:
An infectious retrovirus susceptible to an IFN antiviral pathway from human prostate tumors.
Dong B, Kim S, Hong S, Das Gupta J, Malathi K, Klein EA, Ganem D, DeRisi JL, Chow SA, Silverman RH
http://derisilab.ucsf.edu/pdfs/Dong_PNAS07.pdf
A sentence from the paper caught my eye, "Furthermore,
we have affirmed that the likely receptor, xenotropic and polytropic retrovirus receptor 1 (XPR1), is required for XMRV infection, and we have determined the first integration sites of XMRV in human genomic DNA isolated from tumor-bearing prostatic tissue, thus validating that humans have been infected with this virus."
So, I searched for information on XPR1, and came across the following
http://www.uniprot.org/uniprot/Q9UBH6 :
"Tissue specificity: Widely expressed. Detected in spleen, lymph node, thymus, leukocytes, bone marrow, heart, kidney, pancreas and skeletal muscle."
Apparently, these are the types of cells that can be easily infected with XMRV. A cell requires the XPR1 receptor in order to get infected, and these cells have it.
An effective treatment for XMRV might be something that blocks this receptor, preventing or limiting infection of new cells.
I know almost nothing about virology, etc. so may have this all completely wrong.