Stem cells are unique biological cells with the ability to self-renew, meaning they can divide and produce more copies of themselves. They also differentiate into various specialized cell types throughout the body, such as blood, nerve, or muscle cells. This dual property makes them a subject of significant interest in medical research, offering potential for understanding diseases and developing new treatments.
The Purpose of Stem Cell Banking
Storing stem cells is an important practice in modern medicine, driven by their therapeutic potential for various conditions. These cells can treat specific blood disorders, certain cancers, and are explored in regenerative medicine to repair damaged tissues. Banking offers an opportunity to preserve these valuable biological resources for future use by the individual or a compatible family member.
Common sources for banking include umbilical cord blood, rich in hematopoietic stem cells, and adult sources like bone marrow or adipose (fat) tissue, which yield mesenchymal stem cells. This proactive storage allows immediate access to a genetically matched source of cells if a medical need arises later in life.
The Science Behind Preserving Stem Cells
Preserving stem cells for extended periods relies on cryopreservation, a specialized technique involving cooling biological samples to extremely low temperatures. This process halts the metabolic activity of the cells, preventing degradation and maintaining their viability. The goal is to suspend the cells in a dormant state until they are needed.
To prevent damage during freezing, particularly from ice crystals, cryoprotectants are introduced. These substances, such as dimethyl sulfoxide (DMSO) or glycerol, lower the freezing point of water and dehydrate cells, reducing intracellular ice formation that could rupture cell membranes. After adding cryoprotectants, cells are slowly cooled in a controlled manner before transfer to long-term storage. Typical storage temperatures are in the vapor phase of liquid nitrogen (around -150°C) or directly in liquid nitrogen (-196°C).
Factors Affecting Stem Cell Longevity in Storage
The duration for which stem cells can be stored while retaining functionality is influenced by several factors, with temperature being paramount. Maintaining stable temperatures, typically below -135°C, is essential because it ensures all metabolic processes within the cells are arrested. Any fluctuation above this threshold could lead to biochemical activity and cellular damage over prolonged periods.
The type of stem cell being stored can subtly influence long-term characteristics, though cryopreservation protocols are effective across various cell lineages. Hematopoietic stem cells from cord blood and mesenchymal stem cells from bone marrow or fat tissue are routinely cryopreserved, demonstrating resilience under proper storage conditions. However, specific handling and processing might be tailored to optimize outcomes for different cell populations.
The initial quality and viability of the stem cell sample before freezing are important determinants of storage success. Samples with a higher percentage of healthy, viable cells and fewer contaminants are more likely to endure the cryopreservation process and remain functional longer. Adherence to established cryopreservation protocols, including precise cooling rates and appropriate cryoprotectant concentrations, maximizes the cells’ longevity and post-thaw recovery.
Research and clinical practice demonstrate that stem cells can be successfully stored for decades without significant loss in viability or function. Studies tracking cord blood stem cells show successful retrievals and therapeutic use after more than 20 to 30 years of storage, with no observed decline in their ability to engraft or differentiate. These findings suggest that, under optimal cryopreservation conditions, the theoretical storage limit for stem cells could extend indefinitely, preserving their therapeutic potential.
Assessing Viability Over Time
After stem cells have been stored for extended periods, assessing their viability and functionality upon thawing is crucial to ensure they are suitable for therapeutic use. One common method involves a post-thaw cell count and viability assay, such as the trypan blue exclusion test, which helps determine the percentage of living cells. This provides an immediate indication of how well the cells survived the freezing and thawing process.
Beyond simple viability, functional assays are conducted to confirm the cells’ biological capabilities. Hematopoietic stem cells from cord blood can undergo colony-forming unit (CFU) assays, which evaluate their ability to proliferate and differentiate into various blood cell types. These tests provide insight into the cells’ regenerative potential and confirm they retain their intended therapeutic properties.
Genetic stability tests may also be employed to ensure cells have not sustained significant genetic damage during long-term storage. These assessments collectively provide a comprehensive picture of the quality of stored stem cells, reinforcing confidence in their potential clinical application. Ongoing research refines these assessment methods, aiming to provide more precise evaluations of cell health and function after prolonged preservation.