Vero E6 cells are a lineage of animal cells used extensively in biology and medicine. They provide a standardized and reproducible platform for a wide range of scientific applications, from basic research to the large-scale production of medical treatments. The reliability of these cells has made them a common tool in laboratories worldwide, supporting advancements in the study of infectious diseases.
The Origin and Key Characteristics of Vero E6 Cells
The story of Vero cells began in 1962 at Chiba University in Japan, where researchers established the original cell line from the kidney epithelial cells of an African green monkey (Chlorocebus sabaeus). Named “Vero,” meaning “truth” in Esperanto, this was a continuous cell line. This means the cells can divide indefinitely under laboratory conditions, making them a stable and predictable resource for long-term use.
Different clones of the original Vero line were isolated to select for specific traits. The “E6” designation refers to a clone isolated in 1979 that exhibits a high degree of contact inhibition. This means the cells stop growing once they form a complete single layer in a culture dish. This characteristic provides a stable cell population for a virus to infect, which is useful for studying viruses that replicate slowly.
A defining feature of Vero E6 cells is a genetic deletion on chromosome 12 that removes the genes for producing type I interferons. Interferons are proteins that cells release to signal the presence of a virus and initiate an immune response. Without this ability, Vero E6 cells cannot mount a typical antiviral defense, making them highly susceptible to viral infections.
Function in Virology Research
The lack of an interferon response makes Vero E6 cells an ideal environment for virology research. Because they cannot effectively fight off viruses, they become highly permissive hosts, allowing a wide variety of viruses to infect them and replicate to high numbers. This enables researchers to grow large quantities of a specific virus in a controlled setting for study.
Scientists use these cultures to observe the direct impact of a virus on host cells, a phenomenon known as cytopathic effects. These effects can include changes in cell shape, fusion into larger masses, or cell death, providing visual confirmation of viral activity. By monitoring these changes, researchers can quantify the amount of virus present and assess its virulence. This platform is used to study pathogens like coronaviruses, influenza, measles, Ebola, and Zika virus.
The high permissiveness of these cells also makes them a standard tool for screening potential antiviral drugs. Researchers infect the cells with a virus and then introduce a drug to see if it inhibits viral replication. An effective drug will cause a noticeable reduction in cytopathic effects or viral load compared to untreated cells. This process allows for the rapid testing of many compounds to identify promising candidates.
Use in Vaccine and Biologic Manufacturing
Beyond research, Vero E6 cells are used in the industrial-scale manufacturing of vaccines and biologics, where they function as miniature factories. The process begins by cultivating massive quantities of the cells in large containers called bioreactors. This upstream process generates a large cell population to serve as a substrate for virus production.
Once the desired cell density is reached, the cells are infected with the target virus. The virus replicates efficiently, creating large quantities of viral particles. For inactivated vaccines, this viral harvest is the active ingredient. The collected virus is then treated with a chemical, such as formaldehyde, that renders it non-infectious while keeping its surface proteins intact.
This manufacturing platform has been used for decades and is behind several well-known vaccines. Some formulations of the inactivated polio vaccine (IPV) and the rabies vaccine have long been produced using this method. More recently, several COVID-19 vaccines, including Sinovac’s CoronaVac and Sinopharm’s BBIBP-CorV, were developed using this established technology. This approach is distinct from newer platforms like mRNA vaccines, which do not use animal cells to produce the active components.
Regulatory Processes for Product Safety
The use of animal-derived cells in products for human use is subject to oversight by regulatory agencies like the U.S. Food and Drug Administration (FDA). These agencies establish guidelines to ensure the final product is safe and pure. A primary concern is potential contamination from the cells or manufacturing materials, which requires testing for viruses, bacteria, and other microbes.
Manufacturers must characterize the stored reserves of cells used to start every production batch to confirm their identity and purity. This involves testing for species-specific pathogens, such as simian viruses, since Vero cells originate from monkeys. The genetic stability of the cells is also monitored to ensure the production process remains consistent.
Purification is a key step in the manufacturing process. After the virus is harvested, it undergoes an extensive downstream process to remove all cellular components. This involves multiple stages of filtration and chemical treatments that separate the viral particles from Vero E6 cell DNA, proteins, and other debris. The goal is to ensure that the final drug product contains only the desired active ingredient, meeting strict purity standards before it is approved for human use.