Low- and high-temperature vitrification as a new approach to biostabilization of reproductive and progenitor cells

Cells held in a liquid milieu undergo processes that cause progressive loss of viability. To prevent such degradation, cells need to be placed in conditions that essentially stop all chemical reactions for the duration of the time of storage. Because intracellular ice formation is lethal to most eukaryotic cells, stable storage of viable cells can be achieved only if intracellular vitrification without ice formation has occurred. This has been done by several methods, including equilibrium (slow) freezing, lyophilization (freeze-drying), and ice-free vitrification at subzero temperatures at moderate-to high cooling rates in the presence of cryoprotectants (‘conventional’ vitrification). In this paper, we discuss the mechanisms of vitrification, and specific aspects, advantages, and pitfalls of the different approaches. Particular emphasis is put on novel methods of cell preservation, such as cryoprotectant-free vitrification of sperm and high temperature vitrification by air/vacuum drying of progenitor and other nucleated cells.