Ancient Neanderthal Viruses Found in Modern Human DNA

By comparing the genetic data of modern day cancer patients to that found in fossils of our genetic ancestors, the Neanderthals and Denisovans, researchers learned that the same viruses that infect us today also infected Neanderthals more than half a million years ago.

The find suggests that that some viruses that infect us today have their origins in our ancestors, and the link establishes the possibility for research into whether modern diseases like HIV and cancer have roots in the past.

About 8 percent of human DNA is made of endogenous retroviruses (ERVs), which are DNA sequences from viruses that pass from generation to generation. These ERVs are found in part of the DNA sequence with no known function; this seemingly useless DNA is often referred to as junk DNA.

"I wouldn't write it off as 'junk' just because we don't know what it does yet," said study co-author Gkikas Magiorkinis, of Oxford University's Department of Zoology. "Under certain circumstances, two 'junk' viruses can combine to cause disease -- we've seen this many times in animals already. ERVs have been shown to cause cancer when activated by bacteria in mice with weakened immune systems."

The ancient viruses belong to a family known as HML2. The researchers plan to explore the HML2 origins for links to cancer and HIV.

"How HIV patients respond to HML2 is related to how fast a patient will progress to AIDS, so there is clearly a connection there," Magiorkinis said. "HIV patients are also at much higher risk of developing cancer, for reasons that are poorly-understood. It is possible that some of the risk factors are genetic, and may be shared with HML2. They also become reactivated in cancer and HIV infection, so might prove useful as a therapy target in the future."

Magiorkinis and his colleagues are now investigating whether these ancient viruses affect a person's risk of developing cancer or other diseases.

Future research projects will test whether these viruses are still active or cause disease in modern humans.

"Using modern DNA sequencing of 300 patients, we should be able to see how widespread these viruses are in the modern population. We would expect viruses with no negative effects to have spread throughout most of the modern population, as there would be no evolutionary pressure against it. If we find that these viruses are less common than expected, this may indicate that the viruses have been inactivated by chance or that they increase mortality, for example through increased cancer risk," said research leader Robert Belshaw, formerly of Oxford University and now a lecturer at Plymouth University.

"Last year, this research wouldn't have been possible. There were some huge technological breakthroughs made this summer, and I expect we'll see even greater advances in 2014. Within the next five years, we should be able to say for sure whether these ancient viruses play a role in modern human diseases."

Belshaw, Magiorkinis and their colleagues' research is published in the journal Current Biology.