Important advances within the past half century have made bone marrow and tissue transplantation standard therapies for a variety of diseases. The promise of adult stem cell therapies lies in immunological compatibility of autologous cells as well as in the relative ease of isolation. Accordingly, multipotent mesenchymal stromal cells (MSCs) have become intensely investigated candidates for somatic stem cell therapy [1
]. MSCs are easily harvested from a variety of human tissues, including bone marrow (BM), adipose tissue (AT), and also fetal tissues like umbilical cord blood (CB) [5
]. Furthermore, they stand out due to their extensive expansion potential and their broad, mesodermal differentiation as well as their immunomodulatory capabilities [9
]. These features have led to their clinical exploitation in numerous clinical trials (www.clinicaltrials.gov
). Nevertheless, the initial frequency of MSCs is considered to be low with generally less than 0.1 % of BM mononuclear cells in a newborn, which declines with age [14
]. Admittedly, the minimal and maximal dose for therapeutic application has not been determined yet, but currently applied doses are in the range of <1–5 × 106
MSCs/kg body weight [15
]. This necessitates ex vivo expansion to achieve transplantable numbers. The future use of MSCs for therapeutic application may require very high absolute MSC numbers to gain appropriate cell doses (>5 × 106
/kg body weight) per patient compared to in vivo experimental models with small animals [16
]. It is therefore necessary to develop MSC expansion protocols that allow for the generation of up to 5–10 × 108
MSCs from a limited starting volume of primary material. Accordingly, GMP(Good Manufacturing Practice)-graded cell processing such as cell preparation, culture, and manipulation is mandatory for the progress of such cell therapy. However, GMP-graded cell processing has a number of different points to consider compared to guidelines developed for finished drugs. This review focuses on protocols of isolation and expansion of MSCs from human BM and AT, release criteria, and potency testing assays (summarized in fig. ).
Flow chart illustrating the essential processes and necessary quality assessment parameters performed in clinical protocols for isolation and expansion of multipotent mesenchymal stromal cells.