Expansion and long-term maintenance of induced pluripotent stem cells in stirred suspension bioreactors.

Induced pluripotent stem cells (iPSCs) can provide an important source of cells for the next-generation of cell therapies in regenerative medicine, in part due to their similarity to embryonic stem cells (ESCs). Patient-specific iPSCs represent an opportunity for autologous cell therapies that are not restricted by immunological, ethical and technical obstacles. One of the technical hurdles that must be overcome before iPSCs can be clinically implemented is the scalable, reproducible production of iPSCs and their differentiated progeny. All of the iPSC lines established thus far have been generated and expanded with static tissue culture protocols, which are time-consuming and suffer from batch-to-batch variability. Alternatively, stirred suspension bioreactors propose several benefits and their homogeneous culture environment facilitates the large-scale expansion required for clinical studies at less cost. We have previously developed protocols for expanding murine and human ESCs as undifferentiated aggregates in stirred suspension bioreactors. The resulting cells were karyotypically normal, expressed pluripotency markers and could be differentiated into all three germ lineages, both in vitro and in vivo. In this study, we demonstrate that stirred suspension bioreactors yield 58-fold expansion of undifferentiated pluripotent iPSCs over 4 days. In vitro differentiation into cartilage, bone and cardiomyocytes lineages, in addition to in vivo teratoma formation, further confirmed the existence of fully functional and undifferentiated pluripotent iPSC aggregates following long-term passaging. Stirred suspension bioreactor culture represents an efficient process for the large-scale expansion and maintenance of iPSCs, which is an important first step in their clinical application.