Monkey cells play an important role in biological research and medical advancement. They are invaluable for understanding human diseases, developing new therapies, and producing life-saving vaccines. Their ability to allow study of complex biological processes outside a living organism, yet in a system closely resembling human physiology, underpins their widespread use globally.
Defining Monkey Cells and Their Varieties
Monkey cells often originate from kidney epithelial cells of specific monkey species, like the African green monkey. Once isolated, these cells can be developed into “cell lines,” populations that can be grown and maintained in a laboratory for extended periods. A widely recognized example is the Vero cell line, established in 1962 from African green monkey kidney tissue in Japan. The name “Vero” is derived from “verda reno,” meaning “green kidney” in Esperanto.
Vero cells are continuous and aneuploid, meaning they can replicate indefinitely and possess an abnormal number of chromosomes. They are also interferon-deficient, meaning they do not secrete interferon alpha or beta when infected by viruses, though they still respond to added recombinant interferon. This characteristic, along with their susceptibility to various viruses, makes them suitable for propagating viruses in laboratories. The genetic similarities between monkeys, especially Old-World monkeys like macaques, and humans make these cell lines valuable models for studying human diseases and developing treatments.
Their Role in Medical Breakthroughs
Monkey cells have been instrumental in medical breakthroughs, especially in vaccine development, drug testing, and disease research.
Vaccine Development
Monkey cells have an important history in vaccine production. The Vero cell line, for example, has been used to grow viruses for vaccines against diseases such as polio, measles, mumps, and rubella. The inactivated polio vaccine currently in use is grown in a monkey kidney cell strain. During the COVID-19 pandemic, nonhuman primate models, including rhesus, pigtail, and cynomolgus macaques, played a role in studying the SARS-CoV-2 virus and testing vaccine candidates. Monkey cells are chosen for vaccine production due to their rapid growth rate, stability, and ability to yield high titers of viruses.
Drug Testing
Monkey cells, often derived from macaques, are used for testing the efficacy and toxicity of new medications before human clinical trials. While other animal models like rodents and dogs are also used, monkeys are often required when a drug’s pharmacological effect is specific to humans and cannot be adequately assessed in other species. This applies especially to many biotechnology-derived drugs, such as therapeutic antibodies or gene therapies, where the target receptor may only be present in monkeys. Exploratory toxicity tests using monkey cells help identify the maximum tolerated dose of a substance and observe its pharmacokinetic profile.
Disease Research
Monkey cells and nonhuman primate models contribute to understanding human diseases. They aid in studying viral infections like HIV and Ebola, as well as neurodegenerative conditions. For instance, research using monkey cells has explored how a genetic mutation found in mice and monkeys, called retroCHMP3, can interfere with viruses like HIV and Ebola by disrupting their ability to exit infected cells. In the context of HIV, non-human primate models, particularly rhesus, cynomolgus, and pigtailed macaques, mimic human infection and disease progression, making them valuable for studying HIV persistence in the brain and evaluating new treatment approaches. Monkey models are also used for neurodegenerative research, with studies on Parkinson’s disease and Huntington’s disease benefiting from their physiological similarities to humans.
Ethical Oversight and Animal Welfare
The use of monkey cells and animals in research is subject to ethical oversight to ensure animal welfare and responsible scientific practices. In the United States, Institutional Animal Care and Use Committees (IACUCs) are mandated by federal laws to review all research activities involving animals. These committees ensure animal use is justified, animals are spared unnecessary pain, and research complies with federal and state laws, including the Animal Welfare Act.
IACUCs are responsible for reviewing research protocols to confirm that animals are used only when necessary and that alternatives to animal use, such as computer modeling or cell culture systems, have been considered. They also conduct regular inspections of animal facilities to ensure compliance with regulations and guidelines. The “Three Rs” — Reduce, Replace, and Refine — are guiding principles, encouraging researchers to reduce the number of animals used, replace animal use with non-animal alternatives where possible, and refine procedures to minimize animal suffering.
Ensuring Safety in Scientific Use
Ensuring the safety and purity of monkey cell lines is important, especially when used for producing biological products like vaccines. Measures are in place to prevent contamination and ensure product quality. Safeguards involve testing, evaluation, and adherence to international guidelines.
A primary concern is “adventitious agents,” unwanted viruses, bacteria, or other infectious entities that could contaminate cell lines. To mitigate this risk, cell banks are tested for mycoplasma and endogenous and exogenous viruses. All materials of animal or human origin used in manufacturing, such as media components, are evaluated for adventitious agent safety.
Manufacturers also implement Good Manufacturing Practices (GMP) and conduct viral safety evaluations at various stages of production, including virus seeds and bulk materials. For live viral vaccines, inactivation steps for adventitious agents are generally not part of the manufacturing process to avoid compromising vaccine viability. Extensive testing using different assays at various manufacturing stages provides confidence in their deployment. Risk assessment processes are also integrated into the overall viral control strategy to identify potential sources of contamination and develop mitigation strategies.