Vero cells are a line of kidney cells originally taken from an African green monkey in 1962. They are one of the most widely used cell lines in biomedical research and vaccine manufacturing, prized for their ability to support the growth of a huge range of viruses. If you’ve received a rabies, polio, or Japanese encephalitis vaccine, there’s a good chance it was produced using Vero cells.
Where Vero Cells Come From
On March 27, 1962, two Japanese researchers named Yasumura and Kawakita isolated kidney tissue from a healthy adult African green monkey at Chiba University in Japan. They placed that tissue into culture, grew it over several months, and selected one sub-line that thrived. That sub-line became the standard Vero cell line still in use today.
For decades, the cells were attributed to the species Cercopithecus aethiops, a broad classification for African green monkeys. Genomic analysis later clarified that the original animal was actually a female of the species Chlorocebus sabaeus, a closely related monkey native to West Africa. The name “Vero” itself comes from an abbreviation of a Japanese phrase meaning “truth.”
Why They’re So Useful for Growing Viruses
Most animal cells have a built-in defense system: when a virus infects them, they produce signaling proteins called interferons that alert neighboring cells to mount an immune response. This slows viral replication and makes it harder for researchers to grow large quantities of a virus in the lab.
Vero cells lack this defense. The gene responsible for producing interferons is either defective or entirely absent. Without that alarm system, viruses can replicate freely and abundantly inside Vero cells. This makes them an ideal host for isolating, identifying, and mass-producing viruses for study or vaccine development. It also means Vero cells are susceptible to an unusually broad range of viruses, from coronaviruses to influenza to Ebola, which is why they show up in so many different areas of research.
Key Vero Cell Variants
Over the decades, researchers have developed several sub-lines from the original Vero cells, each with slightly different properties. The most commonly referenced are:
- Vero CCL-81: The standard line available from major cell banks, widely used in general virology and vaccine production.
- Vero E6 (also called VERO C1008): One of the most important variants for coronavirus research. Vero E6 cells are highly susceptible to SARS-CoV and SARS-CoV-2, partly because of differences in the receptor protein (ACE2) that coronaviruses use to enter cells. These cells lost one of their two X chromosomes during culture, which left them with a single version of the ACE2 gene that happens to favor viral entry.
- Vero 76: Genetically close to Vero E6, this sub-line is frequently used in studies of hemorrhagic fever viruses like Ebola and Marburg.
Genomic comparisons show that CCL-81 and the original Japanese reference strain (JCRB0111) cluster together genetically, while Vero 76 and Vero E6 form a separate but related pair. The practical differences between these sub-lines come down to which viruses grow best in each one.
Their Role in Vaccine Manufacturing
Vero cells are one of the primary “substrates” (the living material used to grow viruses) in modern vaccine production. Before Vero cells became standard, many vaccines were produced using fertilized chicken eggs or primary animal cells that had to be freshly harvested for each batch. Vero cells offered a consistent, well-characterized, and scalable alternative.
Vaccines produced using Vero cells include those for rabies, polio, Japanese encephalitis, rotavirus, and influenza. The inactivated Vero cell-derived Japanese encephalitis vaccine, for example, is the only JE vaccine licensed in the United States. Several COVID-19 vaccines developed outside the U.S. also relied on Vero cells to grow inactivated SARS-CoV-2.
Regulatory agencies impose strict safety controls on Vero cell use. The FDA first approved Vero cells as a vaccine substrate in the 1980s. The cells are considered nontumorigenic and safe for this purpose as long as they stay within roughly 150 passages (a “passage” is one cycle of splitting and regrowing the cells). Beyond that threshold, the risk of unwanted genetic changes increases. Modern production also increasingly uses serum-free growth media, which reduces the chance of contamination with stray viruses, bacteria, or prion proteins.
Vero Cells in COVID-19 Research
When SARS-CoV-2 emerged in late 2019, researchers needed to isolate live virus quickly in order to study it, develop diagnostic tests, and begin vaccine work. Vero E6 cells were the go-to tool. They naturally express the ACE2 receptor that SARS-CoV-2 uses to enter human cells, making them highly permissive to infection.
Researchers later engineered an even more effective version: Vero E6 cells that also produce a human protein called TMPRSS2, a molecular scissor the virus needs to complete the entry process. These modified cells, called VeroE6/TMPRSS2, proved significantly more efficient at isolating SARS-CoV-2 from patient samples. This was critical for characterizing new variants as they appeared throughout the pandemic, since each new variant needed to be grown in culture and studied for changes in transmissibility and immune evasion.
Detecting Bacterial Toxins
Vero cells aren’t just useful for viruses. They play a central role in identifying dangerous bacterial toxins, particularly those produced by certain strains of E. coli and Shigella. In fact, the toxins are named after the cells: “Verotoxins” (also called Shiga-like toxins) get their name because Vero cells are exquisitely sensitive to them.
The parent Vero cell line can be killed by as little as 25 picograms per milliliter of Shiga toxin, an almost unimaginably small amount. Researchers have exploited this sensitivity to build detection assays. By exposing Vero cells to a bacterial sample and watching whether the cells die, labs can confirm the presence of Shiga-like toxins from dangerous pathogens like E. coli O157:H7, the strain responsible for severe foodborne illness outbreaks. Scientists have also created toxin-resistant mutant Vero cells that lost the receptor the toxin binds to. By comparing how a sample affects normal Vero cells versus the resistant ones, labs can distinguish Shiga-like toxins from other harmful substances in a sample.
Why Vero Cells Remain a Standard
More than 60 years after their isolation, Vero cells remain one of the most relied-upon tools in virology and vaccine science. Their combination of properties is hard to match: they grow easily in culture, they support replication of a remarkably wide spectrum of viruses, they’re well characterized genetically, and they have a long regulatory track record for safety in vaccine production. The interferon deficiency that would be a vulnerability in a living animal turns out to be precisely the feature that makes these cells indispensable in the lab.