Long-term preservation of germ cells and gonadal tissues at ambient temperatures.

Objective: To present an overview of different approaches and recent advances for long-term preservation of germ cells and gonadal tissues at ambient temperatures. Methods: Review of the existing literature. Results: Preserving viable spermatozoa, eggs, embryos, and gonadal tissues for the long term is critical in human fertility treatment and for the management of animal populations (livestock, biomedical models, and wild species). The need and number of banked germplasms are growing very fast in all disciplines, but current storage options at freezing temperatures are often constraining and not always sustainable. Recent research indicates that structures and functions of gametes or gonadal tissues can be preserved for the long term using different strategies based on dehydration and storage at supra-zero temperatures. However, more studies are needed in rehydration and reanimation of germplasms (including proper molecular and cellular evaluations). Conclusions: While a lot of research is still warranted to optimize drying and rehydration conditions for each sample type and each species, alternative preservation methods will change the paradigm in fertility preservation and biobanking. It will transform the way we maintain and manage precious biomaterials for the long term. Lay summary: Living sperm cells, eggs, embryos, and reproductive tissues can be preserved at freezing temperatures for human fertility treatments and used to manage breeding in livestock, laboratory animals, and wild species through assisted reproduction. These cells can be stored in cell banks and demand for them is growing fast. However, current long-term storage options at freezing temperatures are expensive. Instead of using low temperatures, recent research indicates that these cells can be dried and stored above freezing temperatures for an extended amount of time. While a lot of research is still needed to optimize how different samples are dried and rehydrated, alternative methods of preserving cells will make fertility preservation and cell banking easier. It will also transform the way we keep and manage samples for the long term.