Last week, we outlined the importance of the use of cryoprotective additives of defined origin and proven potency when selecting the right cryopreservation medium. This week we want to emphasize that, just like we mentioned, optimal cryopreservation of stem cell lines depends on a number of factors that go beyond simply choosing the right medium, and include pre-processing prior to storage, transit of the cryopreserved stem cells, thawing rates and procedures, long-term storage conditions and temperature and, finally, the right cryoprotectant (Day J. and Stacey G.N. Cryopreservation and freeze-drying protocols, Methods in Molecular Biology 368, 2007).
It is important to remember that at all times, the techniques and procedures in use must comply with appropriate national and international laws and guidelines. While there are no imposed standards for the cryopreservation of stem cells, it is critically important to develop reliable methodology that can be routinely implemented by different end users.
Unlike stem cell, public collections of microbial cell cultures have existed for over one hundred years. These collections are curated by organizations such as the World Federation of Culture Collections (WFCC), and focus on providing quality-controlled cell cultures and microbial cell lines for research and use (Glyn, S. 2004). The WFCCs recognize that different microorganisms often require particular preservation methods in order to ensure optimal viability and have thus issued guidelines now in their third edition. Increasingly, such collections have started to include stem cells as well, and we should expect to more guidelines in the years to come.
Generally speaking, any chosen method for the cryopreservation of stem cells should be validated in terms of its effect on stem cell viability post-thaw. This includes assays to assess the recovery of the cryopreserved cell line immediately post thaw, and at a number regular time intervals after that.
Validation should extend beyond stem cells – it should include any ancilliary equipment used in the cryopreservation methodology, such as the long-term stability of cryopreservation bags – if used – the robustness of the storage conditions (temperature control, leakage etc.) Studies have been published addressing the validation of cryopreservation methodology (Lecchi et al. Transfusion and apheresis science, 2005), but we expect this issue to grow in importance in the future.
Akron Biotech has years of experience in cryopreservation media development and bioassay implementation to ensure that every aspect of your freezing protocol is covered. To talk to us in person, watch this space next week for coverage of a number of meetings Akron Biotech will attend in the coming weeks and, as always, feel free to email us.