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Vero cell
Vero cell
from Wikipedia
Phase-contrast microscopic image of Vero cells (under green light at 100-fold magnification)

Vero cells are a lineage of cells used in cell cultures.[1] The 'Vero' lineage was isolated from kidney epithelial cells extracted from an African green monkey (Chlorocebus sp.; formerly called Cercopithecus aethiops, this group of monkeys has been split into several different species). The lineage was developed on 27 March 1962 by Yasumura and Kawakita at the Chiba University in Chiba, Japan.[2] The original cell line was named Vero after an abbreviation of verda reno, which means 'green kidney' in Esperanto, while vero itself means 'truth' in Esperanto.[3]

Characteristics

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The Vero cell lineage is continuous and aneuploid, meaning that it has an abnormal number of chromosomes. A continuous cell lineage can be replicated through many cycles of division and not become senescent.[4] Vero cells are interferon-deficient; unlike normal mammalian cells, they do not secrete interferon alpha or beta when infected by viruses.[5] However, they still have the Interferon-alpha/beta receptor, so they respond normally when recombinant interferon is added to their culture media.

The whole genome sequence of a Vero cell line was determined by Japanese investigators in 2014.[6] Chromosome 12 of Vero cells has a homozygous ~9-Mb deletion, causing the loss of the type I interferon gene cluster and cyclin-dependent kinase inhibitors CDKN2A and CDKN2B in the genome.[6] Although African green monkeys were previously classified as Cercopithecus aethiops, they have been placed within the genus Chlorocebus, which includes several species.[7] The genome analysis indicated that the Vero cell lineage is derived from a female Chlorocebus sabaeus.[6]

Uses in research

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Vero cells are used for many purposes, including:

  • screening for the toxin of Escherichia coli, first named "Vero toxin" after this cell line, and later called "Shiga-like toxin" due to its similarity to Shiga toxin isolated from Shigella dysenteriae[6]
  • as host cells for growing viruses; for example, to measure replication in the presence or absence of a research pharmaceutical, the testing for the presence of rabies virus, or the growth of viral stocks for research purposes. As a recent example, CoronaVac, COVID-19 vaccine developed by Sinovac Biotech uses vero cells in production and "Vero" term can be seen on the vaccine container.
  • as host cells for eukaryotic parasites, specially of the trypanosomatids[6]

Lineages

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Isolated from C. aethiops kidney on 27 Mar 1962
Isolated from Vero in 1968, it grows to a lower saturation density (cells per unit area) than the original Vero. It is useful for detecting and counting hemorrhagic fever viruses by plaque assays.
This line is a clone from Vero 76. Vero E6 cells show some contact inhibition, so are suitable for propagating viruses that replicate slowly.
  • Research strains transfected with viral genes:
Vero F6 is a cell transfected with the gene encoding HHV-1 entry protein glycoprotein-H (gH).[8] Vero F6 was transfected via a concatenated plasmid with the gH gene after a copy of the HHV-1 glycoprotein-D (gD) promoter region. In Vero lineage F6, expression of gH is under the control of the promoter region of gD. (Also F6B2; obs. F6B1.1)

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia
from Grokipedia
Vero cells are an immortalized cell line derived from the epithelial cells of a normal, adult African green monkey (Chlorocebus sabaeus), originally established on March 27, 1962, by Yasuhiko Yasumura and Yaeko Kawakita at Chiba University in . Named "Vero" from the Esperanto words verda reno (green ), this anchorage-dependent epithelial cell line is hypodiploid with a modal number of 58. Due to its deficiency in production, Vero cells exhibit high susceptibility to a wide array of viruses, making them a preferred substrate for viral propagation in research and biomanufacturing. The cell line's development was initiated from primary kidney tissue cultures, with the continuous line brought to the (NIH) in 1964 at passage 93 by B. Simizu, facilitating its global distribution and standardization. Vero cells can be cultured adherently on surfaces or in suspension using microcarriers, and they adapt well to serum-free, chemically defined media, enabling scalable production in bioreactors up to thousands of liters. This versatility has positioned Vero cells as the most widely used continuous cell line for producing viral vectors and inactivated vaccines, approved by the (WHO) for human biologicals since the 1980s. In , Vero cells support the growth of pathogens such as , , and flaviviruses, aiding studies on infection kinetics, toxin detection (e.g., verotoxins from E. coli), and parasite interactions like . Their primary application lies in vaccine development and manufacturing, where they have been instrumental in producing licensed products including the Ervebo®, the Imovax Polio®, the Japanese encephalitis vaccine Ixiaro®, vaccines, and the 17D vaccine. During the , Vero cells were employed in clinical trials for inactivated vaccines, underscoring their role in rapid response to emerging infectious diseases. Beyond vaccines, they facilitate , assays, and models in .

History and Origin

Establishment

The Vero cell line was originally isolated on March 27, 1962, by Y. Yasumura and Y. Kawakita at Chiba University in . It was derived from epithelial cells of the kidney of a normal adult female African green monkey (Chlorocebus sabaeus). The primary goal in establishing the line was to create a stable substrate for virological research, enabling efficient propagation and study of viruses such as simian vacuolating virus 40 () while reducing dependence on whole-animal models. This initiative addressed the need for a reliable, non-tumorigenic host cell in systems during the early , a period marked by growing interest in polyomavirus research. The derivation of the Vero line was first documented in a by Yasumura and Kawakita in Nihon Rinsho. This account detailed the initial tissue explantation and primary steps, laying the groundwork for its transition into a continuous cell line.

Early Development

Following the initial isolation in , Vero cells were propagated through serial passaging from primary African green monkey , transitioning them into a stable continuous cell line capable of indefinite replication. This process overcame replicative , a hallmark of finite primary cells, allowing the to expand without the typical crisis point observed in normal cell . By the 93rd passage in 1964, the line had fully established its immortalized state, as confirmed upon transfer to the U.S. . Early characterization of the passaged Vero cells revealed an epithelial-like morphology, with cells forming adherent monolayers that exhibit contact inhibition, similar to untransformed primary cells despite their immortalized state. This morphological trait, observed by 1964, underscored the line's adaptation for sustained and its suitability for viral studies. The Vero cell line's distribution began in the mid-1960s, with initial sharing to international laboratories, including its introduction to the Laboratory of Tropical at the National Institute of Allergy and Infectious Diseases in 1964 by B. Simizu from Chiba University. This dissemination promoted rapid global adoption, particularly in , where the cells became a standard substrate for isolation and by the late 1960s.

Biological Characteristics

Morphology and Growth Properties

Vero cells are adherent, anchorage-dependent cells derived from African green monkey , exhibiting an epithelial-like morphology characterized by polygonal shapes and prominent nucleoli within their nuclei. These cells form confluent monolayers upon reaching , ceasing proliferation due to contact inhibition, and display a flattened, spread-out appearance when attached to culture surfaces. The growth properties of Vero cells include rapid proliferation with a typically ranging from 24 to 48 hours under optimal conditions, depending on culture setup and passage number. They are strictly anchorage-dependent, requiring attachment to a solid substrate for survival and expansion, and thrive best at 37°C in a humidified atmosphere with 5% CO₂. Standard culture media for Vero cells consist of Dulbecco's Modified Eagle Medium (DMEM) or Minimum Essential Medium (MEM) supplemented with 5-10% (FBS) to support attachment and proliferation. For applications requiring reduced animal-derived components, such as production, serum-free chemically defined media like OptiVERO have been developed, maintaining comparable growth kinetics without compromising cell viability. Subculturing of Vero cells involves detachment using 0.25% trypsin-EDTA solution for 2-3 minutes at 37°C, followed by neutralization with serum-containing medium and reseeding at densities of 1-5 × 10⁴ cells/cm² to achieve 70-80% in 3-5 days. This process is typically performed at a split ratio of 1:5 to 1:10 every 2-3 days to prevent overgrowth and maintain healthy morphology.

Genetic and Molecular Features

Vero cells exhibit a hypodiploid , characterized by a modal chromosome number of approximately 56 (ranging from 54 to 58), which is lower than the diploid number of 60 in the parent African green monkey kidney cells. This includes rearranged marker chromosomes typical of the species' , such as those derived from 1, 6, and 15, contributing to the cell line's genetic instability while maintaining relative consistency across passages. These chromosomal abnormalities underscore the transformed nature of Vero cells, distinguishing them from primary monkey kidney cultures. A defining genetic feature of Vero cells is the homozygous deletion of the type I (IFN) gene loci on , spanning approximately 9 Mb, which abolishes their ability to produce IFN-α and IFN-β in response to viral stimuli. This deletion renders the cells highly permissive to a broad range of viral infections by eliminating the primary antiviral signaling pathway, a trait first identified in early studies of their defective production. The absence of this locus not only enhances efficiency but also reflects broader genomic rearrangements accumulated during immortalization. Regarding tumorigenicity, Vero cells display a transformed in , as evidenced by their ability to form colonies in soft agar across various passages, indicating anchorage-independent growth—a hallmark of neoplastic transformation. However, they remain non-tumorigenic in when injected into immunodeficient nude mice at low to moderate passages (e.g., up to p194), with no tumor formation observed under standard conditions. This discrepancy highlights the cells' limited malignant potential despite in transformation, though prolonged passaging can lead to increased tumorigenic risk. At the molecular level, Vero cells express epithelial proteins, including cytokeratins, consistent with their epithelial origin, as demonstrated by positive in histological assays. They also express , a mesenchymal , which reorganizes during cellular stress or and contributes to cytoskeletal dynamics in these transformed cells. Furthermore, the aforementioned deletion encompasses key tumor suppressor genes such as CDKN2A and CDKN2B, whose absence promotes deregulation and immortalization without conferring full oncogenic capacity. These molecular markers collectively define Vero cells' functional stability for biotechnological applications while highlighting their genetically altered state.

Cell Lineages and Variants

Major Sublineages

The Vero 76 cell line represents the original continuous derivative of the Vero lineage, established in the early 1960s from kidney epithelial cells of an African green monkey (Chlorocebus sabaeus) through serial passaging until immortality was achieved around the 76th passage. This sublineage served as the foundational stock for subsequent variants and was employed in initial evaluations for viral vaccine production, including early trials supporting inactivated vaccine development. In 1987, the (WHO) standardized a reference designated as Vero 10-87 (also known as WHO Vero) to facilitate consistent use in biological manufacturing, particularly for human vaccines. This bank, derived from an earlier American Type Culture Collection (ATCC) deposit, incorporates rigorous and imposes strict passage limits—typically not exceeding 150 passages total during production—to minimize and ensure compliance. Vero E6, a prominent clonal sublineage, was isolated in via limiting dilution from Vero 76 cells to enhance viral . Developed at the facility (now part of the ), this variant exhibits heightened permissiveness to a broad range of viruses due to its epithelial morphology and optimized growth properties, making it a preferred choice for high-yield virological assays. The ATCC CCL-81 deposit serves as the parental sublineage for many Vero derivatives, originating from the continuous Vero line deposited with ATCC in 1982. This stock maintains the core characteristics of the original isolation, including anchorage-dependent growth, and acts as a reference for traceability in global research and production. Vero cells are used with the PV/VERO rabies virus strain, a Vero-adapted variant of the Pasteur virus (PV) optimized for high-titer viral replication in serum-free or microcarrier-based systems for rabies vaccine manufacturing. For COVID-19 vaccine development, Sinovac utilized Vero cells with adapted viral strains (e.g., CN2 or CZ02) to achieve efficient inactivation and scaling, as seen in the production of CoronaVac, an inactivated whole-virion vaccine.

Comparative Differences

Vero sublineages exhibit variations in passage stability, with the WHO-recommended Vero line restricted to fewer than 150 passages during production to limit and ensure consistency. In contrast, suspension-adapted Vero cultures demonstrate greater stability, supporting propagation up to 163 passages without significant phenotypic changes. This extended passaging capability makes such adapted lines suitable for long-term research applications requiring consistent cell performance. Differences in virus susceptibility are notable among sublineages, particularly for filoviruses. Vero E6 exhibits heightened permissiveness to a broad range of viruses due to its partial contact inhibition that accommodates slower-replicating viruses. For instance, Vero E6 efficiently produces high-titer stocks of , facilitating virological studies and development. Genetic variations across sublineages are minor but impactful, including differences in counts and structure. The Vero 76 sublineage typically shows a hypodiploid modal number around 58 with mosaic copy number for the , while Vero E6 exhibits a slightly higher range of 60-62 and complete of the . These aneuploid features, shared broadly with the parental line, contribute to sublineage-specific traits like deficiency. Authentication methods are standardized across Vero sublineages to verify identity and purity. Short tandem repeat (STR) profiling, adapted for African green monkey cells, confirms genetic stability over multiple passages—such as more than 69 in Vero lines—and detects . Additionally, all major sublineages maintain mycoplasma-free status through routine testing, ensuring reliability for biomedical use. Recent developments include engineered Vero variants, such as Vero/ cells for enhanced propagation, as utilized in studies up to 2023.

Research and Practical Applications

Vaccine Production

Vero cells have been widely utilized as a substrate for the production of several viral vaccines due to their ability to support high-titer virus propagation in controlled systems. This cell line facilitates the scalable of inactivated and live-attenuated vaccines by allowing efficient without the ethical concerns associated with primary animal cells. Their anchorage-dependent growth on microcarriers enables industrial-scale production, as demonstrated in processes yielding millions of doses annually. The inactivated polio vaccine (IPV), such as IPOL produced by , has employed Vero cells since the early 1980s for culturing types 1, 2, and 3, which are then purified and inactivated with . This approach marked one of the earliest adoptions of Vero cells for human vaccine manufacturing, transitioning from primary monkey kidney cells to improve safety and consistency. Sanofi's IPV production uses microcarrier-based Vero cell cultures in large-scale reactors to achieve the required levels for global distribution. For rabies vaccines, the purified Vero cell rabies vaccine (PVRV) Verorab, developed by Sanofi Pasteur, was licensed in 1985 and approved for pre- and post-exposure prophylaxis. The vaccine is manufactured by propagating the Pittman-Moore L503 strain of rabies virus in Vero cells, followed by purification and inactivation, enabling intradermal or intramuscular administration with high immunogenicity. Over 40 million doses have been distributed worldwide as of 2007, underscoring its role in rabies control. In vaccination, GlaxoSmithKline's Rotarix, approved in 2006, is a live-attenuated produced by culturing the human RIX4414 strain in Vero cells to achieve at least 10^6 CCID50 per dose. This method ensures the vaccine's stability and efficacy against severe in infants, with the Vero platform allowing serum-free production to minimize adventitious agents. More recently, Merck's Ervebo, the first FDA-approved in 2019, utilizes Vero cells for propagating the recombinant vesicular stomatitis virus (rVSVΔG-ZEBOV-GP) in serum-free conditions. The virus is harvested, purified, and formulated to elicit protective immune responses against disease, as validated in outbreak settings. Similarly, Sinovac's , an inactivated vaccine authorized in 2020, is produced by growing the virus in Vero cells, inactivating it with β-propiolactone, and adjuvating with aluminum hydroxide for broad emergency use during the . These examples highlight Vero cells' versatility in addressing emerging infectious diseases through rapid, scalable development.

Virology and Toxin Studies

Vero cells exhibit high permissiveness to a wide range of viruses, primarily due to their deficiency in type I production, which allows efficient without triggering strong antiviral responses. This characteristic makes them a preferred substrate for propagating viruses such as (DENV), (ZIKV), and virus in laboratory settings. For instance, DENV and ZIKV stocks are routinely generated in Vero cells to study viral dynamics and host interactions, leveraging the cells' ability to support high-titer yields. Similarly, interferon-sensitive influenza strains are propagated in Vero cells to facilitate on replication-incompetent variants. In virological research, Vero cell monolayers serve as a standard platform for plaque assays to quantify infectious viral titers. These assays typically involve infecting confluent Vero cell layers with virus dilutions at a multiplicity of infection (MOI) of 0.01 to 0.1, followed by overlay with a semisolid medium to visualize cytopathic effects as discrete plaques. This method provides accurate measurement of plaque-forming units (PFU), essential for titer determination in studies of viruses like ZIKV and influenza. Vero cells are highly sensitive to bacterial toxins, particularly (Stx), making them ideal for assays in toxinology. In these assays, Vero cell monolayers are exposed to toxin-containing samples from Shiga toxin-producing (STEC) such as O157:H7, where toxin-induced cell death is observed and quantified, often serving as the gold standard for Stx detection at picogram levels. This sensitivity stems from the cells' expression of the globotriaosylceramide (Gb3) receptor, which facilitates Stx binding and internalization. Beyond , Vero cells support the growth of certain parasites, enabling studies of host-parasite interactions. For , Vero cells provide an effective environment for tachyzoite proliferation, comparable to other cell lines like , and are used to assess parasite invasion and replication dynamics. Likewise, Vero cells accommodate intracellular stages of species, such as L. chagasi, supporting differentiation and growth despite their non-phagocytic nature. This utility aids in screening compounds and investigating parasite virulence factors.

Other Biomedical Uses

Vero cells serve as valuable in vitro models in toxicology for assessing cytotoxicity in drug screening processes. They are frequently employed in assays such as the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) reduction test to evaluate cell viability and metabolic activity following exposure to potential toxicants. For instance, Vero E6 cells have been used to determine non-cytotoxic doses of compounds intended for antiviral applications by measuring mitochondrial dehydrogenase activity through MTT conversion to formazan. Comparative studies have also utilized Vero cells to differentiate selective cytotoxicity between tumor and normal cells, highlighting their utility as a non-malignant benchmark in screening silver-based nanomaterials. In , Vero cells have been adapted as packaging platforms for producing viral vectors, particularly (AAV) vectors, since the early 2000s. Researchers have developed Vero-based cell lines to generate high-titer recombinant AAV vectors, leveraging the cells' robust growth and regulatory acceptance for biomanufacturing. This approach addresses scalability challenges in vector production by using adherent Vero cultures transfected with AAV plasmids and helper viruses. Although less common than HEK293 cells, Vero platforms contribute to the diversification of production systems for AAV-based therapies targeting genetic disorders. Vero cells have been explored as feeder layers in early protocols for culturing embryonic stem cells (hESCs), providing a supportive matrix to maintain pluripotency and prevent differentiation. In initial derivation methods, irradiated Vero monolayers were used to co-culture post-inner cell mass intermediates from embryos, facilitating the establishment of stable hESC lines under serum-free conditions. This application draws on Vero's adherent properties to mimic extracellular cues essential for attachment and expansion, though -derived feeders later became preferred for clinical translation. For biopharmaceutical production, Vero cells enable the expression of recombinant proteins, including viral antigens and potentially therapeutic antibodies, through stable transfection systems. Engineered Vero lines have successfully secreted recombinant proteins like Zika virus NS1, demonstrating yields suitable for diagnostic and vaccine applications. Similarly, Vero cells stably expressing peste des petits ruminants virus hemagglutinin protein illustrate their capacity for high-level production of glycosylated recombinant antigens recognized by monoclonal antibodies. While Chinese hamster ovary cells dominate monoclonal antibody manufacturing, Vero's established safety profile positions it as an alternative for specific recombinant biotherapeutics.

Recent Advances and Genomic Insights

Sequencing and Engineering Efforts

In 2022, researchers performed whole-genome sequencing of the Vero E6 subline (VERO C1008), achieving 78-fold coverage relative to the sabaeus reference genome (NCBI GCF_000409795.2). This analysis mapped the 2.91 Gb Vero E6 , identifying 9,141,259 single variants (SNVs), 453,797 short insertions, and 547,598 short deletions, with approximately 96% of variants shared among Vero sublines. The study revealed consistent endogenous retroviral (SERV) integration sites across sublines, including the SVL27b element on 27 in Vero E6 and Vero 76, as well as subline-specific structural variations such as a 9-Mb deletion on and monosomy of the in Vero E6. These findings provided a high-resolution for understanding Vero's genetic stability and adaptations for viral propagation. CRISPR-based engineering of Vero cells has focused on enhancing safety for production by addressing limitations like deficiency and substrate adhesion issues. In 2021 efforts, researchers used CRISPR-Cas9 to knock out the in Vero cells, rendering them unresponsive to signaling and thereby increasing viral yields for manufacturing while maintaining genetic stability over passages; this modification aims to create safer substrates by optimizing production without altering core tumorigenic traits. Complementary studies, including a 2025 effort, have explored inserting protease recognition sites, such as for , into the to facilitate cell detachment and reduce contamination risks in live virus . These modifications represent steps toward mitigating oncogenicity concerns associated with and chromosomal deletions. Transcriptomic profiling via has illuminated Vero cells' response to infection, highlighting upregulated host factors that facilitate viral entry and replication. In Vero E6 cells infected with , revealed robust activation of lambda 1 (IFNL1) and other antiviral genes, despite the cells' baseline interferon deficiency, with over 280 genes upregulated early in infection, including those involved in innate immunity. Notably, viral entry receptors like ACE2 show modest basal expression in Vero E6 sufficient for efficient propagation in this model. These profiles underscore Vero's utility in while revealing opportunities for engineering enhanced receptor expression. Advances in karyotyping have pinpointed structural alterations in Vero cells linked to their tumorigenic potential, particularly a homozygous ~9-Mb deletion on 12. This deletion, identified through assembly and confirmed by karyotypic analysis, encompasses the type I gene cluster and is syntenic to human chromosome 9p21.3, which harbors the tumor suppressor locus. The loss of this region correlates with Vero's defective response and increased susceptibility to transformation, as homologs regulate ; comparative karyotyping across passages shows this deletion as a stable, lineage-defining feature contributing to oncogenicity. Such insights guide targeted engineering to restore suppressor functions for safer applications.

Implications for Manufacturing

The regulatory framework governing Vero cell use in emphasizes safety and consistency, with the (WHO) issuing initial guidelines in for continuous cell lines in biological production, including requirements for low-passage propagation to mitigate tumorigenicity risks. These were updated through a 2010 WHO expert committee report and further refined in the 2013 Series Annex 3, mandating that Vero cells not exceed approximately 200 total passages from the original African green monkey kidney isolation—typically achieved by limiting production passages to 25–30 from the —to maintain non-tumorigenic status. Certification as tumor-free involves tumorigenicity testing, such as subcutaneous injection of at least 10^7 viable cells into athymic nude mice, with no progressive tumor formation observed over at least 16 weeks (4 months), ensuring suitability for human vaccines. Scalability in Vero cell manufacturing has advanced through microcarrier-based systems, which support high-density cultures reaching up to 10^7 cells/mL in serum-free media, enabling efficient propagation and yields of up to 10^9 plaque-forming units per liter (PFU/L) for pathogens like and . These improvements, demonstrated in stirred-tank s from 10 L to 200 L scales, reduce production costs and time compared to traditional roller bottle methods while maintaining cell viability above 80% during or fed-batch modes. Such optimizations have been critical for large-scale campaigns, as seen in processes yielding high-titer harvests for inactivated and live-attenuated formulations. Safety protocols in Vero cell biomanufacturing prioritize adventitious agent exclusion through multi-tiered testing, including assays on indicator cell lines (e.g., Vero, , ) for viruses, , and , as well as polymerase chain reaction-based detection for retroviruses. In the , amid the , regulatory scrutiny intensified on (BSE) and (TSE) risks, requiring certification of all animal-derived components (e.g., ) as BSE/TSE-free under WHO and guidelines, particularly for Vero cell-derived inactivated vaccines like . This focus ensured no detectable TSE agents in final products, supporting emergency use authorizations globally. Looking ahead, genomic engineering of Vero cells offers transformative potential for manufacturing, with CRISPR/Cas9-mediated knockouts of host restriction factors—such as or TMEM236 (in 2024 studies)—yielding cell lines that accelerate viral replication and double infectious particle production for vaccines compared to wild-type strains. These modified lines, validated in pilot-scale bioreactors, enhance overall process yields by 2–10-fold without compromising safety profiles, paving the way for more responsive platforms amid threats.

References

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