Long-term frozen storage of stem cells: challenges and solutions

Abstract

Stem cells are found in all multicellular organisms and are defined as cells that can differentiate into specialized mature cells as well as divide to produce more stem cells. Stem cells are commonly harvested for clinical and research applications from bone marrow, peripheral blood, umbilical cord blood and tissue, and adipose tissue. These sites are easily accessible and economical to harvest and contain large numbers of stem cells. The advent of modern cryopreservation technology introduced the concept of harvesting and banking stem cells for future use to avoid issues with donor attrition. Large-scale stem cell banking really began in earnest in the 1990s with the establishment of umbilical cord blood banks, which gradually expanded to include cord tissue and finally adipose tissue. Banked stem cells of all origins not only are used for research but are commonly utilized for clinical applications that include transplantation and regenerative medicine. Many of these stem cell sources have been utilized after cryopreservation, which is the subject of this review. Often the stem cells are stored for varying periods of time which may range from weeks to years (even decades) and are often stored in multiple aliquots (which may vary in size) in order to make the stem cell samples more amenable to multiple uses. There is a considerable investment of time and money into these endeavors as it can directly impact patient safety. Each stem cell source has its own particular challenge(s), although there is some overlap, demanding its own particular requirements to achieve a solution. This review will cover the challenges and unique requirements involved in collection, processing, cryopreservation, storage, thawing, and quality control for each of the most commonly used stem cell sources (bone marrow, cord blood, mobilized peripheral blood stem cell, cord tissue, and adipose tissue).