A cell is the fundamental structural and functional unit of all organisms. In laboratory settings, scientists grow cells outside their natural environment through cell culture, which cultivates them under controlled conditions. From this practice, established cell lines have become a tool in modern biology. An established, or immortal, cell line is a population of cells that can proliferate indefinitely in a lab, providing a consistent and readily available supply for research.
The Making of an Immortal Cell Line
Primary cells, which are isolated directly from tissue, have a finite lifespan and can only divide a limited number of times. This phenomenon, called the Hayflick limit, is a natural barrier to endless proliferation. Each time a normal cell divides, a small portion of DNA at the ends of its chromosomes, called telomeres, is lost. When the telomeres become too short, the cell stops dividing and enters a state of senescence.
Established cell lines are created by overcoming this limit through a process called immortalization. This can happen through spontaneous mutation, often in cells from cancerous tumors that have naturally acquired the ability to grow indefinitely. These cancer-derived cell lines are a useful resource but may carry numerous genetic mutations not found in normal tissue.
A more deliberate method involves genetic engineering, where scientists introduce specific genes into primary cells to bypass the aging process. A common technique is introducing the gene for telomerase (hTERT), an enzyme that extends telomeres. Expressing hTERT allows cells to maintain their telomere length during division, allowing them to avoid senescence and achieve an extended lifespan for research purposes.
Applications in Research and Medicine
Established cell lines are valuable for many scientific applications due to their ability to grow uniform cells indefinitely.
- Disease modeling. Cancer cell lines, often derived directly from tumors, allow researchers to study the genetic and biochemical changes that lead to tumor growth and to screen for potential therapeutic agents.
- Drug discovery and toxicology. Cell lines provide a preliminary system to assess how a drug affects cells, identifying potential toxicity or therapeutic effects at an early stage. This allows for the rapid testing of thousands of compounds.
- Vaccine development. To produce vaccines for viral diseases, large quantities of the virus are needed. Established cell lines serve as factories, allowing viruses to replicate to high numbers. This process enables the production of inactivated or weakened viruses that can be used to safely stimulate an immune response in humans.
- Biotechnology. Genetically engineered cell lines can be programmed to produce therapeutic proteins, such as monoclonal antibodies. These cellular factories generate large quantities of pure protein for treating diseases like cancer and autoimmune disorders.
The Story of the HeLa Cell Line
The most famous and one of the first established human cell lines came from a patient named Henrietta Lacks. In 1951, a sample of her cervical cancer cells was taken without her consent. Unlike any cells seen before, her cells did not die in the lab but continued to divide, creating the first immortal human cell line, named “HeLa.”
The availability of HeLa cells transformed biomedical research. They were used in the development of the polio vaccine, providing a reliable way to grow the poliovirus in large quantities. Scientists have used HeLa cells to study cancer, AIDS, gene mapping, and the effects of radiation on cells, leading to tens of thousands of scientific publications.
The story of Henrietta Lacks also brought ethical questions to the forefront of medicine. At the time her cells were taken, there were no established laws or practices regarding patient consent for tissue use in research, and her family was unaware of their use for decades. This case prompted major changes in regulations, establishing stricter requirements for informed consent and protecting patient rights.
The legacy of the HeLa cell line is twofold. It represents a major contribution to scientific progress, enabling countless discoveries. It also serves as a powerful reminder of the ethical responsibilities researchers have toward patients and the importance of using human biological materials respectfully and with proper authorization.
Common Issues in Cell Line Maintenance
Working with established cell lines presents several practical challenges. A primary concern is contamination from microorganisms like bacteria, yeast, or fungi. These contaminants, often introduced through non-sterile techniques, can outgrow the cultured cells and ruin experiments.
Another problem is cross-contamination between different cell lines. If a few cells from a fast-growing line, like HeLa, accidentally get into a culture of a slower-growing line, they can take over the culture completely without any obvious signs. This can lead to researchers unknowingly working with the wrong cells, invalidating their results. Genetic testing methods like Short Tandem Repeat (STR) profiling are used to authenticate cell lines.
A final issue is genetic instability. Although immortalized cell lines divide indefinitely, they are not genetically static. Over many generations, their genetic makeup can change through genetic drift. These mutations can alter cell characteristics, leading to inconsistent experimental outcomes. To mitigate this, labs keep stocks of early-passage cells frozen to restart cultures periodically.