Influence of culture parameters on ear mesenchymal stem cells expanded on microcarriers.

Mesenchymal stem cells (MSCs) have an accrued potential as a tool for cell-based therapies, thanks largely to their trophic properties. The significant amounts of cells needed for this goal should be attainable through optimized bioreactor expansion of MSCs. However, because of the specific properties of these cell populations, there is a need to investigate novel cell culture strategies adapted from established bioreactor cultivation practices. Among these, stirred culture on microcarriers appears as an appropriate approach for the expansion of MSCs but its optimization requires the identification of key limiting parameters to achieve a further increase in growth span. In this work, among the physico-chemical and physiological parameters affecting the expansion of ear-derived MSCs (E-MSCs) on porous microcarriers, supply of growth factors was important in controlling their growth span. The apparent growth rate of E-MSCs was found to be correlated with the percentage of cells in the S phase of the cell cycle. Moreover, this percentage was directly linked with the fraction of growth factor/receptor complexes. Thus, controlling the percentage of E-MSCs in S phase with suitable growth factor feeds led to an increase of their growth span. Finally, in response to these adapted feeds the cells maintained the key properties defining their MSC phenotype in terms of expression of markers and in vitro differentiation potential.