Isolation, expansion and application of human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are able to generate mesodermal derivatives, such as bone, cartilage, tendon, muscle, ligament and fat tissue; furthermore, they can differentiate to specific cell types, such as cardiomyocyte progenitors under defined conditions. Recently, their paracrine, pro-angiogenic, pro-myogenic, anti-apoptotic, anti-inflammatory and anti-fibrotic properties have been emphasized. These cells actively secrete a large number of bioactive molecules, peptides, hormones, and long non-coding RNAs. This may promote the regeneration of injured, ischemic tissues upon in vivo delivery. Human MSCs can be isolated from bone marrow, peripheral tissues such as adipose tissue, dental pulp, umbilical cord blood and matrix and potentially from peripheral blood. They have been widely used without the ethical issues implicated with pluripotent stem cell derivatives. Large randomized clinical trials underway with hMSCs show good safety and tolerability. In order to reach the number required for clinical use, efficient isolation and expansion of hMSCs are required. A variety of technologies are applied for hMSC expansion: static tissue culture flasks, cell factory and gas-permeable blood bags; or using dynamic culture by spinner flasks, stirred or rotary bioreactors with/without three-dimensional cell carriers. Routine quality controls are essential to maintain sterile culture conditions, ensure stable phenotype and monitor potential mutations before clinical applications. Human MSCs have recently been tested in large randomized clinical trials for cardiac regeneration. Although in vivo application was safe, clinical endpoints showed only neutral effects so far. In order to enhance regenerative capacity of hMSCs, cells may be boosted in vitro prior to implantation and delivery strategies and patient selection must also be improved.