Being inches away from one of the world’s deadliest viruses can give you a new perspective on things. Kyle Loh, PhD, assistant professor of developmental biology, can attest to that. He works with the Nipah virus, which is so dangerous it kills roughly 59% of the people it infects — a whopping 100 times more than does SARS-CoV-2, the virus that causes COVID-19.

Nipah virus can be handled only in Biosafety Level 4 (BSL4) labs that provide the highest level of biosafety, including custom-made, full-body “space suits” donned by scientists. Special chambers and carefully monitored airflow keeps the virus contained to the lab, and the air researchers breathe is supplied by hoses.

As Loh began training to work with the deadly virus, certain large expenditures became more appealing. “At first, when I learned I would have to order one of these bespoke suits, I hoped it wouldn’t cost too much,” Loh said. “But when I realized that my life would depend on every part of this suit being perfectly made, I suddenly hoped I could get the nicest one possible,” Loh said with a laugh.

Loh and his colleagues have been using stem cell science to investigate fundamental questions about how Nipah virus, which attacks the lungs, blood vessels and brain, infects and kills cells. The answers to these questions will be valuable if and when the next Nipah virus outbreak occurs.

In a research article published this week in the journal Cell, Loh and his colleagues reported new information about how Nipah attacks human blood vessels. Loh and Joseph Prescott, PhD, from the Robert Koch Institute in Germany, are co-senior authors on the paper. Lay Teng Ang, PhD, an instructor at Stanford’s Institute for Stem Cell Biology and Regenerative Medicine, along with former Stanford research professionals Alana Nguyen, and Kevin Liu, are co-first authors on the paper.

Among BSL4 viruses, Ebola and Nipah are the most infamous, but Nipah is the only BSL4 virus known to spread between humans through airborne transmission. There are no approved treatments or vaccines for Nipah, so the World Health Organization has designated it as one of nine priority diseases that imperil global health. Nipah causes outbreaks almost every year throughout Asia. The virus first emerged during an epidemic in 1998-1999 in Singapore (where Ang is from) and Malaysia.

An interest in deadly viruses

As a kid growing up in New Jersey, Loh was drawn to the book The Hot Zone, about an Ebola outbreak and the BSL4 virologists who studied it. His father forbade the young Kyle to read the book, because he thought it was too scary for a 7-year-old. Loh read it in secret. “And then I took it to my second-grade classroom for show-and-tell,” Loh said mischievously. That book fostered an interest in virology that led Loh to eventually meet Prescott, one of the small handful of BSL4 scientists in the world, and a global authority on Ebola, Nipah and other deadly viruses.

During the COVID-19 pandemic, Loh picked up The Hot Zone again. But this time, as he read it through the eyes of a Stanford professor, he realized how little was known about the world’s most deadly viruses, and how he and his colleagues could approach the problem and perhaps make some significant scientific discoveries.

Information about how the virus attacks the body’s organ systems is sparse because autopsies are almost never performed on victims. “It’s too dangerous,” Loh said.

Besides, autopsies would show only the end stages of the disease. To understand the whole process of how Nipah infects and attacks human cells, it’s necessary to infect living human cells in a dish. Luckily, Loh, Ang and their colleagues have spent much of their time at Stanford studying how to take human pluripotent stem cells — unique stem cells that can turn into any type of cell in the human body — and can do so upon command.

The research team, including associate professor of biology Kristy Red-Horse, PhD, discovered how to create pure batches of human blood vessel cells, such as arterial cells and human venous cells. “It’s amazing that when you grow these cells with the right signals, they develop into real arteries and veins,” Loh said. “You put them in a 3D gel, and they automatically assemble themselves into the right structures.”

Next, they had to infect the cells with Nipah virus. “There are only eight BSL4 labs in the United States, and none on the West Coast,” Loh said. The research was performed in collaboration with Prescott at the Robert Koch Institute in Germany, which hosts a BSL4 lab. “You have to undergo extensive training to use the BSL4 lab,” Loh said.

“The air pressure in the labs is less than outside air so nothing escapes. There are airlocks and detailed decontamination procedures for getting in and out.” Security procedures to access the lab are classified, Loh noted. Scientific equipment that goes into the labs stays there. “BSL4 labs are like the Hotel California — scientific equipment can go in, but it never leaves,” Loh said.

Arterial destruction

Prescott exposed the arterial and venous cells to the Nipah virus and documented what happened. The results were frightening. In a video published with their Cell paper, the scientists showed how arterial cells (but not venous cells) infected by the virus undergo, as Loh puts it, horrifying changes.

“What the Nipah virus does is fuse individual arterial cells into massive, swollen super-cells containing the contents of many individual cells. All the cell nuclei are drawn together into a clump, like a cluster of grapes,” Loh said. “Then the arteries just disintegrate.”

The veins, however, are unscathed, perhaps due to the veins’ lack of a cell receptor known to play a role in the entry of the Nipah virus into cells. This information could ultimately help devise ways of preventing Nipah from infecting cells, Loh said.

One of the greatest research surprises came after the Nipah virus entered an artery cell and rampaged through it, forcing it to fuse with its neighboring cells: The cell was almost completely unaware of what was happening to it. Normally, cells infected with viruses set off alarm bells, rousing proteins to combat the incoming virus.

However, even after the Nipah virus took over the cell’s machinery (so much so that 17% of the genetic material in the cell was produced by the virus), Nipah-infected artery cells went about their business as if nothing was wrong. “We think of Nipah virus as a stealth bomber,” Loh said. “The virus sneaks into the cell under the radar and drops its bombs undetected, with the cell unable to tell that the virus is there and powerless to fight back.”

In addition to what they learned about the virus, the researchers have shown that human blood vessel cells can be used as a platform for gaining knowledge about BSL4 viruses, information that is much harder to obtain using other methods. “At some point in the future, we are likely to see an outbreak of one of these deadly viruses,” Loh said. “We need tools to quickly study the causative agent and come up with countermeasures.”

Top photo courtesy of Kyle Loh