A cell line represents a population of cells that can be grown and maintained in a laboratory setting for extended periods, often indefinitely. These cells are derived from a single original cell and serve as a consistent, reproducible resource for various scientific investigations. Among the many cell lines used in modern biological research and medicine, Vero cells are a widely utilized and reliable tool. They serve as a versatile platform, particularly valued for their contributions to understanding viruses and developing medical products.
The Origin of Vero Cells
The Vero cell line originated from the kidney epithelial cells of an African green monkey in 1962. This isolation occurred at Chiba University in Chiba, Japan, by researchers Yasumura and Kawakita. The name “Vero” is derived from “verda reno,” which translates to “green kidney” in Esperanto, a constructed international language.
Vero cells are a “continuous cell line,” meaning they can divide and replicate indefinitely under laboratory conditions. Unlike primary cells that have a limited lifespan outside the body, continuous cell lines offer a stable and consistent biological system for research and production.
A Unique Susceptibility to Viruses
A defining biological characteristic that sets Vero cells apart is their natural inability to produce interferon. Interferon is a protein normally secreted by most mammalian cells as an early warning system against viral invaders. It signals neighboring cells to activate antiviral defenses, hindering viral replication.
Because Vero cells possess a homozygous deletion on chromosome 12, they lack the genes responsible for producing type I interferon (alpha and beta). This genetic deficiency means that when viruses infect Vero cells, the typical cellular alarm system is absent, allowing viruses to replicate efficiently and reach high numbers. This allows Vero cells to serve as an effective host for propagating viruses for study and large-scale production.
Applications in Vaccine Manufacturing and Research
Vero cells serve as “factories” for growing large quantities of viruses, a foundational step in vaccine production. The first large-scale process using Vero cells was developed nearly 40 years ago for producing inactivated poliovirus vaccine. Vero cells have since been approved by the World Health Organization (WHO) as a continuous cell line for manufacturing human viral vaccines under specific regulatory guidelines.
Numerous prominent vaccines rely on Vero cell technology, including:
Inactivated poliovirus vaccines
Rotavirus vaccines
Some inactivated COVID-19 vaccine candidates (e.g., Sinovac, Sinopharm)
Vaccines for Japanese encephalitis
Vaccines for rabies
Beyond vaccine production, Vero cells are extensively used in general virology research to understand how viruses interact with host cells and replicate. They are also utilized for testing the effectiveness of new antiviral drugs, providing a consistent system to evaluate drug candidates against various viruses, including SARS-CoV-2.
Safety and Purity in Medical Products
While Vero cells are used to grow viruses for vaccines, the cells themselves are not injected into people. After viruses are grown and harvested from Vero cell cultures, the manufacturing process involves extensive purification steps designed to separate viral components from the cells, cellular debris, and residual cellular DNA.
Regulatory bodies, such as the World Health Organization, have established stringent safety standards for vaccines produced in continuous cell lines. These guidelines include strict limits on the amount of residual cellular DNA that can be present in a final vaccine dose, typically less than 10 nanograms per dose for parenteral vaccines.