Microcarrier-based expansion process for hMSCs with high vitality and undifferentiated characteristics

For cell therapy, a high biomass of human mesenchymal stem cells (hMSCs) is required for clinical applications, such as in the form of encapsulated implants. An easy and reproducible microcarrier-based stirred tank reactor cultivation process for hMSCs in 1.68 L scale is described. To avoid medium changes, studies comparing high-glucose DMEM (DMEM-HG) with low-glucose EMEM were performed showing that high-glucose medium has positive effects on cell proliferation and that cell differentiability remains. Studies on the inoculation strategy and cell density, carrier concentration, volume, and stirrer speed were performed and resulted in a set of optimized parameters, inoculation strategy was found to be 45 minutes of static state and 2 minutes of stirring repeated in 4 cycles. The inoculation density was chosen to be 7×10³ cells/cm2, and the carrier concentration of glass surface carrier was 25 g/L. For the described reactor system, a stirrer speed of 120 rpm for the inoculation process and a daily increase of 10 rpm up to 160 rpm were found to be suitable. Process reproducibility was shown by 3 repeated cultivations at the determined set of parameters allowing high biomass values of up to 7×10⁸ cells per batch. With DMEM-HG, no limitation of glucose was found, and lactate and ammonia remained lower than critical inhibitory concentrations. Comparison of the static (T-flask) and dynamic cultures in the stirred tank reactor showed for both cases, that cells were of high vitality and both maintained differentiability. In both cases, encapsulation of the cells resulted in high bead vitality, a basic requirement for cell therapy application.