Generation and characterization of mesenchymal stromal cells for clinical application

Mesenchymal Stem Cells/Multipotent Marrow Stromal Cells (MSC) are multipotent adult stem cells harboring a wide range of differentiation capacities as well as non-HLA restricted immunosuppressive properties, leading to an increase in their uses for immunomodulation and regenerative medicine. MSC are generally cultivated from bone marrow (BM). Alternative sources (e.g. adipose tissue or umbilical cord) are rapidly developing. Considering the starting material used, the differentiation potential may be different, in example adipose tissue derived MSC exhibit a greater potential for endothelium repair. Whatever the sources of MSC, a first step of adherence to plastic is required. When seeding, the cell density is of major importance acting on growth speed, cell amplification, and differentiation potential. Considering medium used, until now serum free media are not available to cultivate MSC for clinical application. Standard process with FCS without any growth factor supplementation is effective but time consuming, sometime failing, and not totally secure. Although processes using recombinant growth factors (e.g. FGF2) or platelet lysate have demonstrated their interest, definitive standards to produce clinical-grade MSC are still lacking. To reach GMP standards, two major steps have to be done. First, MSC cultures need to be done in closed system; this step is not easy to perform. Second, the controls of produced batches have to ensure efficacy and safety. Now, the controls are principally based on FACS analysis and the expected CD731(pos)CD105(pos)CD90(pos)CD45(neg) MSC phenotype is easily obtained. But the major problem remains the lack of fully validated controls of the final cell product efficacy and safety. Considering the genetic stability of MSC during culture processes, whatever the culture method, aneuploidy could occur during clinical-grade production of BM-MSC but does not lead to cell transformation. But these results should lead to develop more accurate and powerful controls of all MSC in cultures.