While Neanderthals are no longer among us, their genes linger on in many of us and can impact our risk of falling sick. In the fall of 2020, researchers learned that some who carried these vestigial genes had inherited a severe genetic risk factor for COVID-19, making them more likely to become severely ill and even hospitalized.
A new study building off that initial research has found that these same genes, associated with the function and behavior of the immune system, do just the opposite when it comes to HIV: They may actually protect people from getting the virus.
Published Monday in the Proceedings of the National Academy of Science, the new study shows that since the planet’s last ice age about 25,000 years ago, this genetic variant inherited from Neanderthals has been increasing in frequency within the population. It’s responsible for the production of proteins called cytokine receptors that interact with the immune system.
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One receptor in particular, CCR5, is used by the HIV virus to infect white blood cells. The study’s lead author, Hugo Zeberg of Sweden’s Karolinska Institutet and the Max Planck Institute for Evolutionary Anthropology in Germany, found that the COVID-19 genetic risk factor actually encodes a stunted form of the receptor, which renders it nonfunctional. Basically, anyone carrying this variant has next to none CCR5 receptors dotting their cells’ surfaces.
In an email to The Daily Beast, Zeberg said the unusually common prevalence of the genetic variant over the last several thousand years had him wondering whether it conferred an advantage against any other prevailing disease, like HIV.
He set out analyzing patient data from three major biobanks (FinnGen in Finland, the UK Biobank and the University of Michigan’s Michigan Genomics Initiative). Zeberg found that for people who carried this COVID-19 genetic risk factor, it reduced their risk of contracting HIV by 27 percent.
How? While the lack of CCR5 receptors might stymie the immune system against some viruses like COVID-19, it may also prevent other viruses like HIV from binding to healthy host cells and infecting them.
"This shows how a genetic variant can be both good and bad news: Bad news if a person contracts COVID-19, good news because it offers protection against getting infected with HIV," said Zeberg.
Because this variant has been around in humans for quite awhile—long before HIV’s appearance in the 20th century—Zeberg believes this enduring genetic armor might have arisen in response to other diseases our ancestors were exposed to, like smallpox, bubonic plague, or cholera.
While these findings are the right step in understanding how Neanderthal DNA affects an individual's risk for emerging diseases, the findings still need to be backed by laboratory-based studies down the road. Zeberg added that his group is seeking to “understand this major risk factor using laboratory techniques and cell lines.”
Zeberg also wants to expand his study to other demographic groups since the genetic data analyzed was based on people primarily of European descent; the genetic variant itself seems to be found in about 16 percent of Europeans, 50 percent of South Asians, but virtually absent in Africans.
It’s still too early to say exactly how we might use these new insights to protect ourselves against diseases—especially since CCR5 seems to be a double-edged sword. But follow-up investigations might help us reveal whether there’s some kind of practical solution we could pioneer. And if we ever get to that point, we’ll have Neanderthals to thank.
