The Ancient Virus That Built You Is Helping Cancer

 

The Code Inside You Written by a Dead Virus

About 8% of the human genome is not human at all. It is fossilized virus — the genetic wreckage of infections that struck our ancestors millions of years ago, then went extinct. For decades, scientists dismissed most of it as "junk DNA," dead passengers with nothing left to say.

They were wrong. A study published on October 8, 2026 in the journal Science Advances has shown that one of those viral fossils doesn't just sit there. It helped build every one of us — switching on a life-support protein in the earliest days of the embryo. And in a dark twist, cancer has learned to steal the very same switch.

The 2023 Discovery That Made No Sense

The trail started three years ago in the laboratory of George Kassiotis, who runs the Retroviral Immunology Laboratory at London's Francis Crick Institute. His team found an unusual form of a protein called calbindin inside lung cancer cells — and it was doing something remarkable: it was stopping those cancer cells from aging.

The question that haunted Kassiotis was simple: why would a mechanism that keeps cancer young even exist in our biology?

Meet Calbindin, the Calcium Cleaner

To understand the mystery, you need to know what calbindin does. Calcium is essential for cells, but in high amounts it is toxic — it can trigger the cell-death machinery. Calbindin acts like a sponge, mopping up excess calcium. It is normally found in the brain and the kidneys, where calcium levels must be tightly controlled.

But in those lung cancer cells, a different form of calbindin had appeared — and it had been switched on by a stretch of ancient viral DNA embedded in the genome.

HERVH: The Infection That Became an Instruction

That stretch of DNA is called a human endogenous retrovirus, or HERV — a holdover from a retrovirus that inserted its genetic material into one of our ancestors' cells millions of years ago. If that infection reached the sperm or egg cells, the viral code became heritable. Over evolutionary time the virus lost its ability to infect anyone, but its DNA stayed behind.

The specific fossil in question, called HERVH, infected our lineage after great apes — including humans — split from orangutans, roughly 13 million years ago. Kassiotis's team noticed something suspicious: in the preimplantation embryo, calbindin switches on at exactly the time this viral fossil would be expected to act. Too precise to be coincidence.

As Kassiotis put it, evolution had made a trade: a chance viral infection delivered a genetic instruction better than the old one, and the HERVH-calbindin switch became firmly embedded in our blueprint.

The Experiment: Deleting the Fossil

To prove it, postdoctoral researcher Judith Pape teamed up with Kathy Niakan's group — pioneers of gene editing in human embryos, formerly at the Crick and now at the University of Cambridge. They edited human embryonic stem cells to remove the ancient HERVH switch, so the cells could no longer produce that special form of calbindin.

The result was devastating for the cells: they became unhealthy, failing to grow or locking prematurely into one fixed cell type. Only the painstaking expertise of the Crick's Stem Cells and Organoids team kept the sick cells alive long enough to study.

Then came the embryo models. Working with the Cell and Tissue Mechanobiology lab, the team removed HERVH-driven calbindin from blastoids — laboratory models that mimic the blastocyst, the stage just before an embryo implants in the uterus. Without calbindin, the blastoids couldn't form properly, suggesting the viral switch may be essential for the embryo's ability to develop and implant.

A second model confirmed it again. The Quantitative Stem Cell Biology lab had just developed post-gastrulation amnioids — models of the developing amniotic sac that cushions and supports the embryo. When HERVH-calbindin was removed from these, they failed to develop; some couldn't form a sac-like structure at all.

Three independent lines of evidence, one conclusion: a 13-million-year-old viral fossil is essential machinery for the first days of human life.

The Betrayal: Cancer Steals the Same Switch

Here is the trade-off evolution accepted. In a very small proportion of people, cancer cells reactivate this same ancient pathway. By stripping calcium out of the cell, the fossil-driven calbindin stops tumor cells from aging and lets them morph into different cell types — exactly the embryonic superpowers that make early development work, now hijacked to feed a tumor.

"Removing calcium stops cancer cells aging and allows them to become different types — normal features of embryonic development that have been hijacked," Kassiotis said.

Cancer doesn't invent new tricks. It reaches into the oldest parts of our genetic attic and finds tools evolution left lying around.

What This Could Mean for Medicine

The researchers see two promising directions:

• Fertility: the presence of HERVH-driven calbindin could become a biomarker of embryo health in fertility treatments — embryos expressing it are more likely to form efficiently.
• Cancer therapy: because the tumor form of calbindin differs from the version in the brain and kidneys, it may be possible to block only the tumor form, stopping cancer from hijacking this anti-aging pathway while the healthy form keeps buffering calcium toxicity.

Both are early days. But the conceptual shift is enormous: the parts of our genome we once called junk may hold some of the most important instructions we have.

The Bigger Picture

Actual protein-coding genes make up only about 1-2% of the human genome — ancient retroviral DNA makes up roughly 8%. We are, by this measure, more virus than human. And this study suggests that isn't an accident or an embarrassment: it's a strategy. Evolution didn't just tolerate the viral fossils. It recruited them.

The next time you hear that something in your DNA is "junk," remember the 13-million-year-old fossil that built you — and the cancer that learned to steal it.

Sources

• Judith Pape et al., "Endogenous retrovirus control of calbindin is essential for human early embryogenesis," Science Advances (2026). DOI: 10.1126/sciadv.aee4523
• Francis Crick Institute — Retroviral Immunology Laboratory (George Kassiotis)
• Medical Xpress, "Ancient viral DNA helps embryonic stem cells grow — and cancer hijacks the same switch" (Oct 8, 2026)