Enhanced Expansion and Sustained Inductive Function of Skin‐Derived Precursor Cells in Computer‐Controlled Stirred Suspension Bioreactors

: Endogenous dermal stem cells (DSCs) reside in the adult hair follicle mesenchyme and can be isolated and grown in vitro as self-renewing colonies called skin-derived precursors (SKPs). Following transplantation into skin, SKPs can generate new dermis and reconstitute the dermal papilla and connective tissue sheath, suggesting they could have important therapeutic value for the treatment of skin disease (alopecia) or injury. Controlled cell culture processes must be developed to efficiently and safely generate sufficient stem cell numbers for clinical use. Compared with static culture, stirred-suspension bioreactors generated fivefold greater expansion of viable SKPs. SKPs from each condition were able to repopulate the dermal stem cell niche within established hair follicles. Both conditions were also capable of inducing de novo hair follicle formation and exhibited bipotency, reconstituting the dermal papilla and connective tissue sheath, although the efficiency was significantly reduced in bioreactor-expanded SKPs compared with static conditions. We conclude that automated bioreactor processing could be used to efficiently generate large numbers of autologous DSCs while maintaining their inherent regenerative function. SIGNIFICANCE Recent work has demonstrated the existence of dermal stem cells (DSCs) that reside within adult hair follicles and might serve as a renewable source of inductive dermal cells to regenerate dermis or rejuvenate dermal papilla to restore follicle growth. In order to realize this clinical potential, it is essential that in vitro bioprocesses are developed to rapidly and safely expand DSCs. The present study showed that computer-controlled stirred suspension bioreactors can be used to efficiently and safely generate large numbers of DSCs while maintaining their phenotype and at least some of their inherent inductive function. This builds on a foundation of research supporting automated bioprocessing as an effective approach for culturing stem cells. The bioprocess described has important implications for ex vivo expansion of inductive dermal stem/progenitor cells that could be used for composite skin engineering strategies, drug screens related to hair growth, and the regeneration of dermis within severe skin wounds.