Remnants of ancient viruses that hid in human DNA for millions of years help the body fight cancer, scientists say, reports BBC.

Research from the Francis Crick Institute has shown that dormant remnants of these old viruses are reawakened when cancer cells get out of control.

This inadvertently helps the immune system target and attack the tumor.

The team wants to use the discovery to create vaccines that could boost cancer treatment or even prevent it.

Researchers have noticed a connection between the higher survival of people with lung cancer and part of the immune system – B cells, which gather around tumors.

B cells produce antibodies and are better known for their role in fighting infections such as Covid.

Exactly what these cells do in lung cancer has been a mystery, but a series of complex experiments using patient samples and animal tests showed that they are still trying to fight viruses.

How endogenous retroviruses, also present in monkey DNA, help destroy cancer

“The antibodies appeared to recognize remnants of so-called endogenous retroviruses,” said Professor Julian Downward, Associate Director of Research at the Francis Crick Institute.

Retroviruses can use an ingenious trick to slip a copy of their genetic instructions inside us.

Over 8% of the DNA we think of as “human” is actually of such viral origin.

Some of these retroviruses became a fixed element of our genetic code tens of millions of years ago and share a common element with our evolutionary relatives, the great apes.

And other retroviruses could enter our DNA several thousand years ago.

Some of these foreign instructions have been co-opted over time and serve useful purposes in our cells, but others are tightly controlled to prevent their spread.

However, chaos reigns inside the cancer cell when it gets out of control, and control over these ancient viruses is lost.

These ancient genetic instructions are no longer capable of resurrecting whole viruses, but they can create virus fragments sufficient for the immune system to detect a viral threat.

“The immune system is tricked into thinking the tumor cells are infected and trying to get rid of the virus, so it’s a kind of alarm system,” said Professor George Kassiotis, head of the retroviral immunology department at the biomedical research centre.

The antibodies call on other parts of the immune system to kill the “infected” cells – the immune system is trying to stop the virus, but in this case it kills the cancer cells.

Professor Kassiotis says it’s a surprising reversal of role for retroviruses, which in their heyday “may have caused cancer in our ancestors” because of the way they invade our DNA, but now protect us from cancer.

A study published in the journal Nature describes how this happens naturally in the body, but researchers want to enhance this effect by developing vaccines that teach the body to detect endogenous retroviruses.

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