Cell culture is the process of growing cells from multicellular organisms under controlled laboratory conditions outside of their natural environment. By providing the necessary conditions for survival, researchers can maintain and expand cell populations. This method is a common tool in cellular and molecular biology, enabling investigations into cell physiology and behavior.
Creating an Artificial Cellular Environment
To sustain cells outside a living organism, a laboratory must replicate the body’s internal environment. This is achieved using an incubator, which maintains conditions like temperature at 37°C to mimic the human body and high humidity to prevent the culture from drying out. The incubator also regulates gas levels, ensuring a supply of oxygen and a 5% carbon dioxide concentration to maintain the growth medium’s pH balance.
Cells reside in a culture vessel, like a flask or petri dish, submerged in a liquid culture medium. This nutrient-rich broth contains a salt solution, carbohydrates for energy, amino acids for proteins, and vitamins. It is often supplemented with growth factors and hormones to stimulate cell division. The medium’s color, from a pH indicator called phenol red, provides a visual cue. As cells produce waste, the pH drops and the medium turns from red to yellow, signaling the need for fresh nutrients.
Maintaining a sterile environment is necessary to prevent contamination from microorganisms like bacteria, yeast, and fungi. Contaminants can outcompete the cells for nutrients, release toxins, and ruin experiments. To prevent this, all manipulations are performed inside a laminar flow hood, a cabinet that provides a continuous stream of filtered, sterile air to protect the cultures from airborne particles.
Sources of Cultured Cells
Cells for experiments come from two main sources. The first, primary cells, are isolated directly from living tissue, like a skin biopsy. These cells are separated from the surrounding tissue using enzymes or mechanical methods. Because they are freshly removed from their native environment, primary cells closely mimic the characteristics of cells within the body, making them relevant for studying cellular functions.
A limitation of primary cells is their finite lifespan. In culture, they divide a limited number of times before entering a non-dividing state called senescence. This restricted capacity means they cannot be maintained indefinitely, which is a challenge for long-term studies. Despite this, their resemblance to in vivo conditions makes them useful for research requiring high biological accuracy.
In contrast, cell lines are populations of cells that have mutated, allowing them to divide indefinitely in culture. These “immortalized” cells can be propagated for extended periods, providing a consistent supply for experiments. This characteristic makes them easier and more cost-effective to maintain than primary cells and useful for large-scale processes where many identical cells are needed.
The most famous immortalized cell line is the HeLa line, from the cervical cancer cells of Henrietta Lacks in 1951. Her cells were the first human cells found to survive and divide continuously in a lab. Taken without her consent, a common practice then, HeLa cells have contributed to many discoveries, including the polio vaccine, cancer treatments, and gene mapping. The story of Henrietta Lacks highlights the scientific value of immortal cell lines and the ethical issues of patient consent.
Investigating Diseases and Drugs
Cell culture is a model system for investigating disease mechanisms. In cancer research, scientists use cell lines from tumors to study the uncontrolled growth and spread of cancer cells. In the lab, researchers can observe their behavior, identify the genetic mutations driving their malignancy, and test compounds that might halt their progression.
Virology relies on cell culture to grow and study viruses, which require a host cell to replicate. Cultured cells provide a controlled environment for this process. Scientists can infect cultured cells with a virus to study its life cycle, from entry to the release of new viral particles. This knowledge helps in developing antiviral drugs and vaccines for diseases like influenza and polio.
Cell culture is also a tool in drug discovery and development. Before a potential drug is tested in animals or humans, it is screened using cultured cells. High-throughput screening can test thousands of compounds on cells to identify those with a desired therapeutic effect, like killing cancer cells. This process also helps assess the toxicity of new compounds by exposing cell types, like liver or kidney cells, to a drug and measuring its impact on cell viability.
Manufacturing Biological Products
Beyond research, cell culture is used as a manufacturing platform for biological products. Cells are grown in large quantities in computer-controlled tanks called bioreactors, which can hold thousands of liters of culture medium. Bioreactors control all environmental factors to maximize cell growth and productivity, turning the cells into miniature factories.
A major application is vaccine production. Many viral vaccines, including for polio and influenza, are made by growing the target virus in large cultures of mammalian cells. The cells act as hosts for viral replication, and the resulting viruses are harvested, purified, and inactivated to create the vaccine. This cell-based approach is a more controlled and scalable alternative to older methods using chicken eggs.
Cell cultures are also used to produce therapeutic proteins, which are complex molecules used as drugs. Scientists can genetically engineer cells, such as Chinese Hamster Ovary (CHO) cells, to produce specific human proteins. This method is used to manufacture treatments like insulin for diabetes and monoclonal antibodies, which are proteins designed to target cancer cells or inflammatory molecules.