Variables in “Passive” Cryopreservative Methods: Standardizing Cell-Based Assays By Reducing Cryopreservation-Induced Variability
Many studies have focused on the effects of cryopreservation on cells, looking at cryoprotectants, freezing rates on cell viability, sub-cellular and biochemical modifications etc. However, generally, what happens in the freezing process is treated as a given. The actual freezing profile - the variation of the freezing rate over time - has not often been precisely investigated; to do so is technically challenging as cryovials are normally 1 mL in volume and do not easily accommodate temperature probes.
Now two authors Drs Barradez and Lekishvili have measured temperature profiles by inserting a thin thermocouple temperature probe through a hole drilled in the cap of the cryovials and recorded the temperature in a passive alcohol freezer in a -80. They compared results with those from a Planer controlled rate freezer. Looking at Recovery and Toxicity they tested effects of freezing profiles on cell functions and demonstrated the strong differences in temperature profiles experienced by cell samples between the two freezing devices. Data suggest that the freezing rates before and after the freezing point, as well as the variability in freezing profiles experiences by the vials, all combine to affect cell recovery - viability and potency.
Given the stakes in this cell based industry, simple and passive cryopreservation techniques seem not always to provide an adequate enough level of control for optimal cell performances. Temperature profiles experienced by cells during passive cryopreservation in a passive freezing box (e.g., alcohol filled container in a -80) ) can be highly variable from vial to vial as well as batch to batch and may not be optimised. Such variability may well have significant consequences on cell behaviour upon thawing.
Read the study in the latest issue of BioProcess magazine