Mammalian cell culture is the laboratory process of growing cells from mammals outside of their natural environment in a controlled setting. This technique allows scientists to isolate specific cells from animal tissues, which can then be expanded and studied. This method provides a reproducible way to understand complex biological processes and has become foundational to advances in medicine and biotechnology.
The Basics of Growing Mammalian Cells
For mammalian cells to survive and multiply outside of an organism, their complex needs must be met with precision. These delicate cells, whether from human, mouse, or other mammalian origin, require a carefully prepared environment to thrive.
The foundation of this environment is a liquid nutrient medium that provides all the components for cell life. This medium contains a mixture of sugars for energy, amino acids for building proteins, vitamins, and salts to maintain the correct osmotic balance. The base medium is often supplemented with serum, such as fetal bovine serum (FBS), which supplies growth factors that stimulate cell division.
Beyond nutrients, the physical environment must mimic conditions inside the body. Cells are grown in specialized incubators that maintain a constant temperature around 37°C (98.6°F). These incubators also regulate humidity and control gas levels, maintaining carbon dioxide at approximately 5% to keep the pH of the culture medium stable.
Impactful Uses in Research and Medicine
The ability to grow mammalian cells in a lab has revolutionized scientific research and medical applications. It provides a window into the workings of cells, allowing scientists to investigate diseases on a microscopic level. For instance, growing cancerous cells in culture enables researchers to study the mechanisms of tumor growth and to screen potential anti-cancer drugs for effectiveness and toxicity before human testing.
This technology is also used for vaccine production for diseases like influenza, polio, and rabies. Viruses need a host cell to replicate, and large quantities of viruses for vaccines are produced by infecting cultured mammalian cells. This controlled method allows for the safe and scalable manufacturing of vaccines that protect millions.
Cell culture is also used for producing biopharmaceuticals. Many modern medicines, including therapeutic proteins like monoclonal antibodies used in cancer therapy or insulin for diabetes, are manufactured using genetically engineered mammalian cells. These cells are programmed to produce large quantities of a specific protein, which is then purified and formulated into a drug.
Varieties of Cell Culture Techniques
Not all mammalian cells are grown in the same manner, as the technique used depends on the cell type and the goal of the work. One distinction is between adherent and suspension cultures. Adherent cells, including most types from solid tissues like skin or kidney, require a surface to attach to in order to grow. These are grown in flat plastic flasks or plates specially treated to facilitate cell attachment.
In contrast, suspension cultures involve cells that can live and divide while floating freely in the nutrient medium. This method is common for naturally non-adherent cells, such as certain blood cells, or for large-scale industrial production in massive bioreactors. The ability to grow in suspension simplifies scaling up the production of biopharmaceuticals.
Another classification relates to the lifespan of the cells. Primary cultures are established directly from an animal’s tissue and have a finite lifespan, meaning they will only divide a limited number of times. Continuous, or immortalized, cell lines have been modified to divide indefinitely. These cell lines often originate from tumors or have been genetically altered, making them a reliable tool for long-term experiments.
Keeping Cell Cultures Thriving
Maintaining healthy cell cultures requires meticulous and consistent effort. The primary practice is maintaining a sterile, or aseptic, technique. Cell cultures are highly susceptible to contamination from airborne bacteria, yeast, and mold, which can quickly ruin an experiment by outcompeting the cells for nutrients. All procedures must be performed in a sterile environment, often within a specialized cabinet called a laminar flow hood.
Scientists must also regularly monitor their cultures to ensure the cells are healthy. This is done by examining the cells daily under a microscope. Researchers check for a healthy appearance, appropriate cell density, and any signs of contamination. The color of the culture medium, which contains a pH indicator, can also provide clues, as a change in color can signal nutrient depletion or waste buildup.
As cells grow and multiply, they consume nutrients and fill the available space in their culture vessel. To keep the culture going, they must be periodically subcultured, a process also known as passaging. This involves removing the cells from their current flask, diluting them, and transferring a small portion to a new flask with fresh medium. This process provides the cells with renewed nutrients and more space to continue growing.