Expansion of induced pluripotent stem cells under consideration of bioengineering aspects: part 1

To fully utilize the potential of human induced pluripotent stem cells (hiPSCs) for allogeneic stem cell-based therapies, efficient and scalable expansion procedures must be developed. For other adherent human cell types, the combination of microcarriers (MCs) and stirred tank bioreactors has been shown to meet these demands. In this study, a hiPSC quasi-perfusion expansion procedure based on MCs was developed at 100-mL scale in spinner flasks. Process development began by assessing various medium exchange strategies and MC coatings, indicating that the hiPSCs tolerated the gradual exchange of medium well when cultivated on Synthemax II-coated MCs. This procedure was therefore scaled-up to the 1.3-L Eppendorf BioBLU 1c stirred tank bioreactor by applying the lower limit of Zwietering's suspension criterion ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>N</mml:mi> <mml:mrow><mml:mi>s</mml:mi> <mml:mn>1</mml:mn> <mml:mi>u</mml:mi></mml:mrow> </mml:msub> </mml:math> ), thereby demonstrating proof-of-concept when used in combination with hiPSCs for the first time. To better understand the bioreactor and its bioengineering characteristics, computational fluid dynamics and bioengineering investigations were performed prior to hiPSC cultivation. In this manner, improved process understanding allowed an expansion factor of ≈ 26 to be achieved, yielding more than 3 × 10⁹ cells within 5 days. Further quality analyses confirmed that the hiPSCs maintained their viability, identity, and differentiation potential throughout cultivation. KEY POINTS: • <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>N</mml:mi> <mml:mrow><mml:mi>s</mml:mi> <mml:mn>1</mml:mn> <mml:mi>u</mml:mi></mml:mrow> </mml:msub> </mml:math> can be used as a scale-up criterion for hiPSC cultivations in MC-operated stirred bioreactors • Uniform distribution and attachment of cells to the MCs are crucial for efficient expansion • Perfusion is advantageous and supports the cultivation of hiPSCs.