Cryopreservation is the method used to preserve cells and tissue by freezing them. The specialized process prevents intracellular ice crystals and dehydration. Either of these can destroy organelles or cause the cell to die while undergoing the freezing process.
Cryopreservation Agents
Dimethyl sulfoxide (DMSO) and glycerol are two agents used in the cryopreservation process. Glycerol is used for freezing red blood cells. DMSO is used to help protect most other types of tissues and cells. Organisms that can survive extreme dehydration have a sugar called trehalose. This sugar is used in freeze-drying. Trehalose can stabilize cell membranes. It is also useful for helping to preserve sperm, blood cells, and stem cells.
Cellular Cryopreservation Systems
In most cases, cryopreservation is accomplished using a controlled-rate freezer. This system delivers liquid nitrogen into a closed chamber that houses the cell. The process requires close monitoring to prevent ice crystal formation and dehydration. The cells typically go from room temperature to -130 degrees Fahrenheit (-90 Celsius). Once the cells are frozen, they are transferred to a liquid nitrogen freezer that maintains these types of extremely cold temperatures.
Cryopreservation Applications
One of the most important applications of cryopreservation is freezing and storing hematopoietic stem cells. These cells are in peripheral blood and bone marrow. Before a patient undergoes high-dose chemotherapy, hematopoietic stem cells are retrieved from their bone marrow. After they complete their treatment, their cells which were cryopreserved are thawed so they can be infused back into their body. High-dose chemotherapy is toxic to bone marrow. Being able to cryopreserve hematopoietic stem cells enhances the treatment outcome for some types of solid tumor malignancies and lymphomas.
Patients with leukemia have cancerous blood cells and can’t be used for autologous bone-marrow rescue. Therefore, leukemia patients rely on cryopreserved blood collected from other sources such as stem cell donors or cryopreserved blood collected from the umbilical cords of newly born infants.
Research continues, but it’s been widely accepted since the 1990s that hematopoietic stem cells and mesenchymal stem cells can be differentiated into nerve tissue, bone, cardiac muscle tissues, and skeletal tissue. Tissue culture systems remain an area of intense study and research as well as cryopreservation of these types of cells. There is hope that in the future these cells can be used for many applications including disorders of muscle systems, nervous disorders, and diseases of the heart and liver.
Other Uses of Cryopreservation
Cryopreservation is used to freeze and store sperm and human embryos as well. IVF (in vitro fertilization) relies on the freezing of extra embryos. Couples can choose to use cryopreserved embryos if IVF fails with fresh embryos. Frozen embryos are thawed and then implanted into the uterus.
Storage of Frozen Tissue and Cells
When cells are properly frozen, they can live for more than a decade. Some tissues can also be cryopreserved successfully such as veins, aortic tissue, cardiac valves, and parathyroid glands. Freezing has long been used to store and maintain long-term viability of sperm, ova, and early human embryos. Freezing procedures for preserving these types of tissue are well-established.
Conclusion
Cryopreservation has stood the test of time and plays an important role in the treatment of some cancers and diseases. As research continues, more opportunities to use frozen tissues and cells will become apparent. The process of cryopreservation is certain to continue being an integral part of medical research and treatment on many levels.
References
https://pubmed.ncbi.nlm.nih.gov/18080461/
https://www.sciencedirect.com/science/article/abs/pii/S0304416520302609
