"So, one of the things that is important about our study from a virologic point of view, is that this is the first really solid example of an authentic xenotropic retroviral infection in a human being," said Ganem.
According to DeRisi, the Virochip made it possible to analyze these samples without preconceived biases about what viruses might be present. "Since the chip represents every known virus in one assay, it is agnostic as to what might be found," he said. "We would never have looked for this class of virus if it wasn't for the virus chip."
Importantly, the researchers found that prostate cancers in which both copies of the RNASEL gene were crippled by mutation showed much more frequent XMRV infection than did those cancers that still had one normal copy of the RNASEL gene.
"This link between the virus and RNASEL is the second finding that is important and is firmly established in this study," noted Ganem. "We don't see the infection in people who don't have the RNASEL mutation, which suggests strongly RNASEL is an important part of the defense against retroviral infection. This is the first evidence in humans of findings that were previously made only in vitro."
DeRisi pointed out that detailed comparison of samples of the virus between people found that although all were XMRV they showed tiny genetic variations. "So, while it is the same virus in each patient, the viruses are different enough to say that they are most likely independently acquired and are not the result of some contamination of the samples," he said.
Ganem cautioned that any link between XMRV and prostate cancer is tenuous at best. "First, the genetic variant we studied occurs in familial clusters that constitute only a very
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
30-Mar-2006