Red cell manufacturing using parallel stirred‐tank bioreactors at the final stages of differentiation enhances reticulocyte maturation

The aim of this study was to develop a robust, quality controlled, and reproducible erythroid culture system to obtain high numbers of mature erythroblasts and red blood cells (RBCs). This was achieved using a fully controlled stirred‐tank bioreactor by the design of experiments (DOE) methods in the serum‐free medium by defining the appropriate culture parameters. Human cord blood CD34+ cells were first cultured in static flasks and then inoculated to stirred‐tank bioreactors. Cell diameter was gradually decreased and final RBC yields were significantly higher when cells were inoculated at sizes smaller than 12 μm. The larger immature cells in the basophilic stage did not survive, while smaller mature erythroid cells were successfully expanded at high agitation speeds, demonstrating that appropriate seeding timing is critical. A high inoculation cell density of 5 × 106 cells/ml was achieved reaching 1.5 × 107 cells/ml. By using DOE analysis fitted to precise stages of erythropoiesis, we were able to acquire the optimal culture parameters for pH (7.5), temperature (37°C), dissolved oxygen, agitation speed (500 rpm), inoculation timing (cell diameter 12–13 μm), media feeding regimen, and cell seeding density (5 × 106 cells/ml). The final pure RBCs showed appropriate functions compared with fresh donor RBCs, confirming that manufacturing mature RBCs with reproducibility is possible. The method of shifting from static cultures to stirred‐tank bioreactors was established using DOE methods. Our stage‐specific processes markedly enhanced cell proliferation and reticulocyte maturation. The timing of transferring from static to stirred‐tank bioreactors can be automatically determined using cell size without manual intervention by an operator. This is the first report of cultivation to simultaneously improve RBC yields and cell proliferation by specifically optimizing the manufacturing process using real‐time monitored bioreactors.