The importance of preparing specimens for cryopreservation in a biobank is critical, particularly when the samples are intended for use in downstream analysis such as immunological assays for detecting cell surface markers (Weinberg et al. Clinical and Vaccine Immunology. Vol. 16 No.8, Aug.2009).
Dr. Alex Esmon, in his Inside Biobanking blog post ("Why Store Biological Samples at Low Temperatures?"), refers to the advantages of sample cryopreservation and focuses on what happens to the cells at these temperatures. The criteria most in use for defining successful cryostorage is the percentage of cells that are viable after thawing. However, attention must be paid to the integrity of cell surface markers, which can be influenced by various factors including the cryoprotectant used and the steps followed in the freezing and thawing process.
To optimally preserve cells, they must be properly handled, prepared with the appropriate
cryoprotectants, and frozen at a controlled rate to prevent shock. They must also be retrieved and thawed in the correct, controlled manner. Proper preparation maintains cell viability even after several years of storage at optimal temperatures. Based on my experience I have found that there are five factors we must consider when preparing specimens for biobanking, of which temperature is only one. It is also necessary to consider:
The length of time that elapses between the collection of cells and the cryopreservation process (Olson et al., Journal of Translational Medicine, Vol.9 No. 26, 2011);
The processing of cells for storage, including cryoprotectant and a controlled, step-down freezing rate;
The storage temperature;
Protecting the frozen samples from temperature excursions during storage; and
When samples are intended for use in sophisticated immunological assays, attention must be given to optimal sample preparation and thawing to preserve cell surface markers as well as cell viability.