Paper # 91LB|
XMRV Probably Originated through Recombination between 2 Endogenous Murine Retroviruses during in vivo Passage of a Human Prostate Cancer Xenograft
T Paprotka1, K Delviks-Frankenberry1, O Cingoz2, A Martinez3, H-J Kung3, C Tepper3, W-S Hu1, J Coffin2, and Vinay Pathak*1
1NCI-Frederick, MD, US; 2Tufts Univ Sch of Med, Boston, MA, US; and 3Univ of California, Davis, Sacramento, US
Background: Xenotropic murine leukemia virus–related
virus (XMRV) has recently been associated with human prostate cancer (PC) and
chronic fatigue syndrome (CFS). However, other studies have failed to detect
XMRV in PC and CFS patients. A human PC cell line, 22Rv1, produces XMRV
that is virtually identical to virus isolated from PC and CFS patients. The 22Rv1
and CWR-R1 cell lines were derived from a human PC xenograft, CWR22, which was
serially passaged in nude mice. To evaluate the genetic variation and evolutionary
potential of XMRV, nucleic acid extracts of early and later passages of the
CWR22 xenografts and CWR-R1 were analyzed.
Methods: DNA isolated from early (3rd and 7th) and
later passage CWR22 xenografts consisted of a mixture of tumor DNA and nude
mouse DNA. Short tandem repeat analysis was used to confirm that the tumor DNA
were derived from the same person as the 22Rv1 and CWR-R1 cell lines.
XMRV-specific PCR primers and qPCR assays were developed and used for the
analysis of xenograft and nude mouse nucleic acids. We explored the origin of
XMRV by analyzing xenograft-associated nude mouse DNA and DNA from other nude
mouse strains; the data revealed the presence of two previously undescribed
endogenous proviruses, PreXMRV-1 and PreXMRV-2, which contained >3.2-kb
stretches of their genomes with ~99.92%
identity to XMRV.
Results: PCR assays showed that both cell lines and
later passage xenografts contained XMRV but the early passage xenografts did
not, indicating that XMRV was not present in either the original CWR22 tumor or
associated nude mouse tissue, but became prevalent in later passage xenografts.
Retroviral recombination between PreXMRV-1 and PreXMRV-2 involving a few
template switching events can generate a replication-competent virus that
differs from XMRV by only 5 nucleotides (99.94% identity). Analysis of 15 nude
mouse strains indicated that none contained XMRV, but some strains potentially
used to passage the xenograft contained both PreXMRV-1 and PreXMRV-2.
Conclusions: We conclude that XMRV was not present
in the original CWR22 prostate tumor but was generated by recombination between
PreXMRV-1 and PreXMRV-2 during in vivo passages of the CWR22 xenograft.
The probability of an identical recombinant arising multiple times is vanishingly
small, raising the possibility that contamination of human samples with XMRV
originating from the 22Rv1 cell line is responsible for its reported
association with PC and CFS.