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Abstract

Regenerative medicine aims at using stem cells to restore or establish lost, damaged, diseased, or aging tissues and organs function. The transplantation of cultured epidermal autograft (CEA) has saved the lives of many burned patients over the last 30 years, but the resulting epidermis is far from perfect, and clinical outcomes remain unpredictable. The engraftment of cultured epidermal stem cells is poorly understood, and, as a result, suboptimal. Using a large animal model, the pig, we recapitulated the clinical settings and outcomes of human CEA transplantation. With this model, we study the engraftment process, and we demonstrate that cultured epidermal stem cells often, but not always, favor the choice of differentiation over self-renewal when transplanted on full thickness wounds. Differences in this early fate choice are likely to explain the variability of clinical outcomes. We developed a system of in vitro live cell imaging (LCI) to study the fate choices of multiple individual cells in a microenvironment that is much more controlled than the grafting bed of a burned patient. We demonstrate that keratinocytes have a very heterogeneous behavior in vitro. With a fluorescent reporter of cell cycle progression (FUCCI), we show the influence of the cell cycle on early fate choices of cultured keratinocytes. By introducing a ROCK inhibitor in the culture medium, we show that keratinocyte’s early fate choices can be impacted so that they show greater clonogenicity and growth potential. The unique combination of large animal CEA transplantation with individual cell LCI demon- strate the critical role of early fate choice, both for epidermal stem cell engraftment and in vitro behavior. The possibility to influence the early fate choices of stem cells by modifying the microenvironment has a great potential to improve the engraftment and the ex vivo ampli- fication of stem cells, the two limiting steps of cell replacement therapy.

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