Secrets of Novel Retrovirus Unfolding

[Guest guest]

Secrets of Novel Retrovirus Unfolding

 

 

SAN FRANCISCO - The mystery surrounding a retrovirus recently implicated

in prostate cancer and possibly chronic fatigue syndrome is beginning to

yield clues.

 

The virus, known as XMRV, has been confirmed to replicate primarily in

reproductive organs and lymphoid tissue, according to a primate study

reported at the Conference on Retroviruses and Opportunistic Infections.

 

A second study found markers that could be the key to developing an

assay for the large scale epidemiologic studies needed to determine how

widely the virus has penetrated in the population, and what effect it has.

 

" We're at a very, very early stage working with this virus, " said

conference vice-chair John Coffin, PhD, of Tufts University in

Boston.Action Points

Note that these studies were published as abstracts and presented at a

conference. These data and conclusions should be considered to be

preliminary until published in a peer-reviewed journal.

He likened it to the early days of HIV research, when scientists

scrambled to make sense of the virus, but cautioned that has yet to be

any clear evidence linking it to disease.

 

XMRV burst onto the scene four years ago when researchers doing a broad

sweep for viruses in prostate cancer samples turned up evidence of a

retrovirus that resembled the murine leukemia virus, earning it the

abbreviation xenotropic murine leukemia-related virus (XMRV).

 

" The similarity [in genetic sequence] is so striking that although we

don't know the details we have to assume it's coming from mice, " Stephen

Goff, PhD, of Columbia University in New York City, told MedPage Today.

 

The genetic sequence of all XMRV isolates tested across the country, and

across diseases, show so little divergence that the virus must have only

recently jumped to humans -- likely from a point source and with limited

numbers of replication cycles during transmission, Goff said in a

plenary lecture on XMRV at the conference.

 

This implies that a vaccine might be much easier to develop than for

HIV, he explained at a press conference.

 

However, while this class of retroviruses appears to be characterized by

lifelong infection that cannot be cleared by the immune system, there's

no clear proof yet that XMRV causes illness or the diseases it's been

linked to, he emphasized.

 

Even the links to prostate cancer and chronic fatigue syndrome are

controversial, with centers reporting anywhere from 0% to 23% and 0% to

67% prevalence in tested cases, respectively, Goff noted.

 

To learn more about how the virus might interact with the human immune

system, scientists at the Cleveland Clinic, Yerkes National Primate

Research Center at Emory University, and Abbott Diagnostics collaborated

on an animal model.

 

Prachi Sharma, PhD, of Emory, presented part of the results involving

monkeys.

 

She reported that acutely infected monkeys tested positive for virus

replicating in a number of tissues.

 

Chronic infection, though, appeared largely limited to CD4+ T cells in

lymphoid organs -- spleen, lymph nodes, and GI tract -- as well as in

reproductive organs, including prostate, testes, ovaries, vagina, and

cervix.

 

Other experimental lab studies have shown the virus to be androgen and

hormone responsive, which bears on the cell types in which it will be

found, Goff said.

 

It was notable that the monkeys exhibited no visible symptoms or fever

when infected, said John Hackett, Jr., PhD, of Abbott Diagnostics in

Abbott Park, Ill.

 

He reported the group's efforts to develop assays to detect XMRV

infections.

 

In the monkeys, antibodies to gag p30, env gp70 and env p15E were

observed.

 

The researchers were also able to show, for the first time, the

existence of antibodies to multiple XMRV proteins in humans.

 

However, they occured in only three of 2,851 human blood samples.

 

Detection in humans has proven challenging, but whether this reflects

the virus' life cycle, a combination of viral properties and the length

of time between infection and disease, or some other factor is unclear,

Hackett said.

 

" Part of it is the ability to identify it to begin with, " Hackett told

MedPage Today. " You could argue we haven't been looking for it. "

 

Sharma's study was supported by Abbott Diagnostics and a grant from the

National Institutes of Health.

 

Hackett reported conflicts of interest with Abbott Diagnostics.

 

Goff reported support from the Howard Hughes Medical Institute and the

Department of Defense Prostate Program.

 

Primary source: Conference on Retroviruses and Opportunistic Infections

 

Source reference:

Goff S " Mouse to Man? XMRV and Human Disease " CROI 2010; Abstract 132.

 

Additional source: Conference on Retroviruses and Opportunistic Infections

Source reference:

Qui X, et al " XMRV: Examination of Viral Kinetics, Tissue Tropism, and

Serological Markers of Infection " CROI 2010; Abstract 151.

 

Additional source: Conference on Retroviruses and Opportunistic Infections

Source reference:

Sharma P, et al " Organ and Cell Lineage Dissemination of XMRV in Rhesus

Macaques during Acute and Chronic Infection " CROI 2010; Abstract 150 LB.

 

 

Videos from the Conference:

_http://www.ifarablo g.org/_ (http://www.ifarablog.org/)

 

_http://www.medpaget oday.com/ MeetingCoverage/ CROI/18610_

(http://www.medpagetoday.com/MeetingCoverage/CROI/18610)

CROI: Secrets of Novel Retrovirus Unfolding

 

By Crystal Phend, Senior Staff Writer, MedPage Today

Published: February 21, 2010

Earn CME/CE credit

for reading medical news