Xenotropic murine leukemia virus–related virus

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Xenotropic murine leukemia virus–related virus (XMRV) is a retrovirus that was once thought to be a possible human pathogen. It was first described in 2006 in tissue from people with prostate cancer, and early reports linked it to prostate cancer and later to chronic fatigue syndrome (CFS). This sparked a lot of interest and concern about the safety of the blood supply. Xenotropic viruses can infect cells from other species, and “murine” means mice.

But later research showed XMRV was not a natural human virus. It turned out to be a laboratory contaminant created by recombination between two mouse retroviruses during experiments with a prostate cancer cell line in the mid-1990s. There is no evidence that XMRV infects humans or causes disease.

XMRV is a murine leukemia virus in the Retroviridae family, genus gammaretrovirus. It has a single-stranded RNA genome that makes a DNA copy inside the host cell. The virus particle is about 80–100 nanometers across. Several XMRV sequences were published that were almost identical, which is unusual for retroviruses and suggested a lab origin.

In 2010, scientists concluded XMRV might not be a genuine human pathogen. Xenotropic viruses were first found in certain mouse strains and were later detected in other mice as well. XMRV was discovered in the laboratories of researchers at UCSF and the Cleveland Clinic. One link explored early on connected a human RNase L gene variant (linked to prostate cancer risk) with a possible viral susceptibility, which helped prompt the search for XMRV.

However, many later studies failed to replicate the findings. Concerns grew that XMRV detections were due to contamination rather than true infection in humans. The methods used to detect XMRV were found not to be reliable, and some papers claiming a link to disease were retracted. One notable co-author, Judy Mikovits, faced misconduct allegations, and other researchers withdrew their support for the XMRV–disease connection.

Today, the scientific consensus is that XMRV does not infect humans and is not associated with human disease.