Stem cells are foundational cells with the ability to multiply and develop into various specialized cell types. The process of growing and maintaining these cells outside their natural environment is known as cell culture. This practice allows researchers to generate a large supply of stem cells, which can be kept in their undifferentiated state or guided to become specific types of cells, such as those that make up nerves or muscles.
Sources of Stem Cells for Culture
One primary source is embryonic stem cells (ESCs), which are derived from the inner cell mass of a blastocyst, an early-stage embryo. ESCs are pluripotent, meaning they possess the potential to differentiate into any cell type found in the adult body. This versatility makes them a comprehensive tool for research and potential therapies.
Another source is adult stem cells, also known as somatic cells. These are found in small quantities within various tissues of a developed person, such as bone marrow, fat, and skin. Unlike embryonic stem cells, adult stem cells are multipotent, so their ability to differentiate is limited to the cell types in their tissue of origin. For instance, hematopoietic stem cells from bone marrow primarily give rise to different blood cells.
A more recent source is induced pluripotent stem cells (iPSCs), which are created in a laboratory. Scientists reprogram specialized adult cells, like skin or blood cells, back into an embryonic-like pluripotent state by introducing specific genes. Because iPSCs can be generated from a patient’s own tissues, they offer a way to create patient-matched cell lines, bypassing ethical considerations of embryo use and reducing the risk of immune rejection.
The Laboratory Environment for Growth
Successfully culturing stem cells requires recreating the body’s complex environment in the lab. This is done by providing the cells with a liquid known as a culture medium. This nutrient-rich broth contains a mixture of salts, sugars, amino acids, and vitamins necessary for cell survival and growth. The medium’s formulation can be adjusted for the needs of different stem cells.
The culture medium is often supplemented with growth factors and serum. These proteins and other molecules act as signals, instructing the cells to multiply without differentiating. The goal is to expand the population of undifferentiated stem cells, creating a large and stable supply called a stem cell line. These lines can then be frozen for future use or shared among research groups.
The physical environment is also highly regulated. Stem cells are grown in incubators that maintain conditions similar to the human body. These machines hold the temperature at 37°C and maintain high humidity to prevent the culture medium from evaporating. A controlled concentration of carbon dioxide is also maintained to keep the pH of the culture medium stable.
Maintaining a sterile environment is paramount to prevent contamination. Any introduction of bacteria or fungi can destroy a cell culture. To avoid this, all work is performed inside a laminar flow hood or biosafety cabinet, which provides a continuous flow of filtered, sterile air. All equipment must be sterile, and surfaces are regularly decontaminated.
Guiding Stem Cell Differentiation
Once a sufficient population of undifferentiated stem cells has been grown, the next step is to guide them toward a specific fate. This process, known as directed differentiation, transforms unspecialized stem cells into specialized cells like neurons or heart muscle cells. This is a highly controlled procedure orchestrated by scientists in the lab.
The primary method for guiding differentiation is to alter the culture medium’s composition. Scientists add a specific cocktail of signaling molecules, often proteins called differentiation factors, to the cells. These molecules mimic the natural signals that cells receive during development, providing a chemical roadmap for the stem cells to follow.
Different combinations and concentrations of these signaling molecules can push the cells toward different lineages. By carefully controlling the timing and sequence of these added factors, researchers can steer the differentiation process. This turns a uniform population of stem cells into a culture of functional, specialized cells for further study.
Applications in Research and Medicine
One application is in disease modeling. By creating patient-specific iPSCs from individuals with a genetic condition, researchers can differentiate them into the affected cell type. This “disease in a dish” approach allows scientists to study the cellular mechanisms of a disease and observe how it develops in human cells without invasive procedures.
Stem cell cultures are also tools for drug discovery and toxicology. Cultured human cells, such as heart or liver cells derived from stem cells, provide a platform for initial screening of new medications. This allows pharmaceutical companies to test thousands of potential drug compounds to identify beneficial effects and harmful toxicity early in the development process.
The field of regenerative medicine relies on stem cell culture. The goal is to use lab-grown cells and tissues to repair or replace those damaged by disease or injury. While many of these therapies are still in development, examples include growing new skin for burn victims, transplanting pancreatic cells for type 1 diabetes, or repairing heart tissue after a heart attack.