Scalable cultivation of human pluripotent stem cells on chemically-defined surfaces
Hsiung, Michael Chi-Wei
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Human stem cells (SCs) are classified as self-renewing cells possessing great ability in therapeutic applications due of their ability to differentiate along any major cell lineage in the human body. Despite their restorative potential, widespread use of SCs is hampered by strenuous control issues. Along with the need for strict xeno-free environments to sustain growth in culture, current methods for growing human pluripotent stem cells (hPSCs) rely on platforms which impede large-scale cultivation and therapeutic delivery. Hence, any progress towards development of large-scale culture systems is severely hindered. In a concentrated effort to develop a scheme that can serve as a model precursor for large scale SC propagation in clinical use, we have explored methods for cultivating hPSCs on completely defined surfaces. We discuss novel approaches with the potential to go beyond the limitations presented by current methods. In particular, we studied the cultivation of human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) on surface which underwent synthetic or chemical modification. Current methods for hPSCs rely on animal-based extracellular matrices (ECMs) such as mouse embryonic fibroblasts (MEFs) or feeders and murine sacoma cell-derived substrates to facilitate their growth. While these layers or coatings can be used to maximize the output of hPSC production, they cannot be considered for clinical use because they risk introducing foreign pathogens into culture. We have identified and developed conditions for a completely defined xeno-free substrate used for culturing hPSCs. By utilizing coupling chemistry, we can functionalize ester groups on a given surface and conjugate synthetic peptides containing the arginine-glycine-aspartic acid (RGD) motif, known for their role in cell adhesion. This method offers advantages over traditional hPSC culture by keeping the modified substrata free of xenogenic response and can be scaled up in adherent microcarrier culture. To treat a major organ such as the heart or kidney, producing large quantities of clinical-grade pluripotent cells is a necessity for cell-based therapy. Here we apply our approach to spherical beads or microcarriers for large-scale cultivation of hPSCs in a stirred-suspension bioreactor. Stem cells seeded on microcarriers and cultivated for multiple six day passages in a stirred-suspension bioreactors remained viable (≥90%) and increased by an average of 25.0±7.2-fold in concentration. The cells maintained their expression of pluripotency markers POU5F1 and NANOG as assessed by RT-PCR and quantitative PCR. These findings aim at the development of a flexible cost-effect method for the generation of pluripotent cells which can be repurposed and utilized for cell therapies. This work also aims to promote exploration into different methods of surface modification to develop new tactics for culturing hPSCs that can achieve higher fold growth while maintaining overall therapeutic potential.