A non-traditional approach to cryopreservation by ultra-rapid cooling for human mesenchymal stem cells

Cryopreservation is the most common method for long-term cell storage. Successful cryopreservation of cells depends on optimal freezing conditions, freezer storage and a proper thawing technique to minimize the cellular damage that can occur during the cryopreservation process. These factors are especially critical for sensitive stem cells with a consequential and significant impact on viability and functionality. Until now, slow-freezing has been the routine method of cryopreservation but, more recently rapid-cooling techniques have also been proposed. In this study, an ultra-rapid cooling technique [1] was performed for the first time on human mesenchymal stem cells and the effectiveness evaluated in comparison with the conventional slow-freezing procedure. A thin nylon-membrane carrier was used combined with different cryoprotective agents: dimethyl sulfoxide, ethylene glycol and/or trehalose. Various aspects of the low cryoprotective doses and the ultra-rapid cooling procedure of the human mesenchymal stem cells were examined including: the physical properties of the nylon-support, cells encumbrance, viability, proliferation and differentiation. The expression of cell surface markers and apoptosis were also investigated. The study used an ultra-rapid cooling/warming method and showed an overall cell integrity preservation (83-99%), with no significant differences between dimethyl sulfoxide or ethylene glycol treatment (83-87%) and a substantial cell viability of 68% and 51%, respectively. We confirmed a discrepancy also observed by other authors in cell viability and integrity, which implies that caution is necessary when assessing and reporting cell viability data.