Expansion of human mesenchymal stromal cells on microcarriers: growth and metabolism

Adult stem cells, or mesenchymal stromal cells (MSCs), are of great potential for cell therapy and tissue-engineering applications. However, for therapeutic use, these cells need to be isolated from tissue or a biopsy and efficiently expanded, as they cannot be harvested in sufficient quantities from the body. In our opinion, efficient expansion of MSCs can be achieved in a microcarrier-based cultivation system. This study selected a suitable microcarrier for human bone marrow-derived stromal cells (HBMSCs), optimized cell-seeding strategies by varying serum concentrations, and optimized dynamic expansion of the HBMSCs in a microcarrier-based spinner flask cultivation system by applying various feeding regimes. Cytodex 1 microcarriers in combination with a low-serum concentration (0-5%) in the medium resulted in the highest seeding efficiency for the HBMSCs. Subsequently, significant expansion of the HBMSCs on these carriers has been observed. The highest number of HBMSCs population doublings (4.8 doublings) was obtained by a combination of 50% medium refreshment combined with addition of 30% medium containing microcarriers every 3 days. Exponential cell growth was observed for at least 9 days after seeding, provided that sufficient nutrients (such as glucose) were present, metabolite concentrations (such as ammonia) were kept below growth-inhibitory concentrations and adequate surface area was present for the cells. After dynamic expansion of the HBMSCs, the cells retained their differentiation potential and their cell surface markers, indicating that HBMSCs expansion on Cytodex 1 microcarriers did not alter the phenotypic properties of the cells.