Skip to main content
Move the World.
Using Ebola to Fight Brain Cancer

Lead image design by Emily Cho.

Most people don't look at viruses and wonder how they might be helpful, not harmful, to humans — especially not now. But for 20 years, Anthony Van den Pol has done just that. He's part of an ever-growing group of researchers studying viruses that can kill cancer cells while leaving healthy cells alone.

After sifting through 60 different viruses, Van den Pol, a professor of neurosurgery and psychiatry at Yale University, found a promising lead from an unlikely source: the Ebola virus. He discovered that a characteristic of some Ebola variants can actually help shrink the aggressive brain tumors known as glioblastomas — one of the deadliest viruses versus one of the deadliest cancers.

"Basically, we're looking for viruses that can be used to destroy bad brain tumors, and glioblastoma is a particularly bad brain tumor," he says. But, he admits, "at first glance using (Ebola) sounds a little weird."

According to the WHO, Ebola's average fatality rate is 50%, but in some cases it may kill up to 90%. If the Ebola virus were merely unleashed on a human brain tumor, it surely would spread out of control.

"At first glance using (Ebola) sounds a little weird."

Van den Pol

Instead, Van den Pol and his team have created what's called a chimeric virus — in this case, a virus that's a genetic combination of one useful piece of Ebola and another virus, called Vesicular stomatitis (VSV). (The term "chimeric" comes from the mythical Greek monster Chimera, which was cobbled together from a lion's head, a goat's body, and a snake's tail.)

When inserted into a brain tumor, this lab-made virus can target human glioblastoma cells (embedded in mouse brains) without killing healthy cells outside of the tumor. The piece of Ebola virus that seems crucial for killing cancer cells while sparing healthy ones is a protein called a mucin-like domain (MLD) — ironically, it's one of the same mechanisms that normally helps Ebola evade the human immune system and wreak havoc on the body.

A virus usually works by breaking into a healthy cell, using that cell's tools to make copies of itself, and then killing the host cell. The virus copies then go on to infect other cells, and so on. Normally, healthy cells will alert the immune system of their infection, in an attempt to ward off the virus and halt further replication — so it's to a virus's benefit to thwart that.

The Ebola virus does this by releasing MLD from its host cell soon after breaking in, which confuses the immune system and lets the virus get to work replicating itself — essentially, MLD functions as a decoy.

"The immune system starts going after these proteins that are just floating around and really don't do very much," says Van den Pol. "That gives the virus itself a greater opportunity to infect and replicate."

Some viruses that kill cancer cells have been engineered to just directly kill tumor cells and leave healthy cells alone. But others work by training the immune system to attack the body's own mutated cancer cells. In that case, even after the virus is gone, the immune system can keep hunting down tumor cells.

Either way, because it disrupts the immune system, you wouldn't think that a decoy like MLD would help. Van den Pol, whose experiments centered on a few different VSV-Ebola combinations, expected that the most successful chimeric virus would be the one that did not contain MLD.

But the opposite turned out to be true. In mice, the MLD chimeric virus was best at shrinking tumors, prolonging survival, and leaving healthy cells intact. Van den Pol's hypothesis comes down to the size of the lab-made virus: tacking on the MLD component makes a virus quite large, and that means it takes a while to replicate inside a cell, healthy or cancerous. Just like making a photocopy, the larger the original document, the longer you'll be waiting for the copy to print.

"Normally, the MLD is there to confuse the immune system. In this case, we think why it's beneficial is it's slowing everything down," says Van den Pol.

While the VSV component allows the virus to rapidly break into cells, the MLD part — now on its own, without the rest of the deadly Ebola virus — just slows down the replication process inside the cell. This buys healthy, noncancerous cells extra time to protect themselves and mount an antiviral immune response, but it leaves cancer cells — whose Achilles heel is that they are often unable to mount an immune response — overwhelmed.

Some viruses work by training the immune system to attack the body’s own mutated cancer cells. Even after the virus is gone, the immune system can keep hunting down tumor cells.

A mouse model alone wouldn't usually be worth writing home about, but parallel research into the human implications of this chimeric virus make it more intriguing. The VSV-Ebola chimera underpins Merck's new Ebola vaccine, Ervebo, which the FDA approved late last year and that has already been injected in 260,000 people. That shows that, in another application, this chimeric virus is safe in humans.

Research into cancer-killing viruses more generally is gaining momentum, which bodes well for this particular research. In 2015, after decades of dead-ends, the FDA finally approved a modified herpesvirus to treat melanoma — the first FDA-approved treatment of its type. And in 2019, the FDA conferred "breakthrough" status to a poliovirus therapy being developed to treat brain tumors.

Van den Pol says, of course, that even though these wins in adjacent areas of research are cause for optimism, what's next needs to be human clinical trials. But any next steps are currently being thwarted by a different virus.

Van den Pol says that COVID-19 has caused the closure of many labs at Yale. His remains open, though with a significantly reduced staff: only one person is allowed in the lab at a time.

"We try to respect social distancing because I think that's an important way to avoid this coronavirus," he says. "At the same time, some of the things we're doing we think ultimately benefit human health, but we're going a lot more slowly than we did before."

We'd love to hear from you! If you have a comment about this article or if you have a tip for a future Freethink story, please email us at [email protected]

Up Next

Dispatches
Zika Could Be a "Smart Missile" for Brain Cancer
Zika Could Be a
Dispatches
Zika Could Be a "Smart Missile" for Brain Cancer
Zika can devastate fetal brains; scientists want to turn it against brain tumors instead.

Zika can devastate fetal brains; scientists want to turn it against brain tumors instead.

Dispatches
23andMe Can (Finally) Tell You about Your Genetic Cancer Risk
23andMe Can (Finally) Tell You about Your Genetic Cancer Risk
Dispatches
23andMe Can (Finally) Tell You about Your Genetic Cancer Risk
23andMe has won the right to tell you what your genes say about you. It's a landmark legal achievement that could...

23andMe has won the right to tell you what your genes say about you. It's a landmark legal achievement that could help usher in a new age of personalized medicine.

Superhuman
Reprogramming Your Immune System to Fight Cancer
Reprogramming Your Immune System to Fight Cancer
Watch Now
Superhuman
Reprogramming Your Immune System to Fight Cancer
Your T cells already know how to kill cancer. These doctors can train them to hunt it down.
Watch Now

Josh Feldman was on his honeymoon when he felt a lump on his neck. Returning home after the best month of his life, his doctor gave him the news: non-Hodgkin's lymphoma. There was no cure, and it was about to get much worse. After multiple rounds of chemotherapy failed to stop his tumors from growing, Josh went to see Dr. John Timmerman, an oncologist at UCLA who is trying something different, known as immunotherapy. This...

Uprising
What's Special About Cancer-Killing Nanobots? Precision.
medical nanobots
Uprising
What's Special About Cancer-Killing Nanobots? Precision.
These tiny, robotic machines can deliver drugs directly to infected cells, and they're changing the future of medicine.

These tiny, robotic machines can deliver drugs directly to infected cells, and they're changing the future of medicine.

Health
“Electronic Nose” Can Detect a Cancer Precursor on Patients’ Breath
electronic nose
Health
“Electronic Nose” Can Detect a Cancer Precursor on Patients’ Breath
A new study found that an electronic nose could be an improved screening tool for Barrett’s esophagus, a precursor to esophageal cancer.

A new study found that an electronic nose could be an improved screening tool for Barrett’s esophagus, a precursor to esophageal cancer.

Why Advanced Cancer Patients Need Genetic Sequencing
Why Advanced Cancer Patients Need Genetic Sequencing
Watch Now
Why Advanced Cancer Patients Need Genetic Sequencing
Genomic sequencing saved his life. Now he wants everyone to have access.
Watch Now

After he was diagnosed with life-threatening prostate cancer, Intel’s Bryce Olson sequenced his genome which offered clues to new treatments for his disease. While the current standard of care for cancer patients includes surgery, radiation, and chemotherapy, genetic sequencing opens the door for new possibilities beyond these traditional approaches. Bryce explains his personal mission to encourage others to get their...

Dispatches
A Tumor-Killing Virus Could Treat Eye Cancer and Save Children's Sight
A Tumor-Killing Virus Could Treat Eye Cancer and Save Children's Sight
Dispatches
A Tumor-Killing Virus Could Treat Eye Cancer and Save Children's Sight
The only treatment for retinoblastoma is surgical removal of the eye—but scientists may have found another way:...
By Hemant Khanna

The only treatment for retinoblastoma is surgical removal of the eye—but scientists may have found another way: cancer-killing viruses.

Dispatches
A New Brain Surgery Robot Can Work Inside an MRI
A New Brain Surgery Robot Can Work Inside an MRI
Dispatches
A New Brain Surgery Robot Can Work Inside an MRI
Metal robots and electric motors don't normally play well with giant magnets.

Metal robots and electric motors don't normally play well with giant magnets.

Superhuman
Patients are Finding Relief from New Essential Tremors Treatment using Focused...
These Doctors are Performing Brain Surgery ... Using Sound
Watch Now
Superhuman
Patients are Finding Relief from New Essential Tremors Treatment using Focused...
Bonnie D'Ettorre suffers from a nerve disorder causing uncontrollable shaking. Doctors at Ohio State are about to "burn it out" using a thousand beams of ultrasound.
Watch Now

Patients stricken with “essential tremors” have their lives upended by this nerve disorder which causes uncontrollable shaking. But doctors at The Ohio State University Wexner Medical Center are helping these patients find relief by “burning out” the problem-causing part of the brain with a high-intensity focused ultrasound. This miracle treatment significantly reduces tremors without the potential for complications posed...