Hair‐Bearing Human Skin Organoids from Pluripotent Stem Cells: A Novel Source of Advanced Skin Substitutes for Wound Repair

Abstract

Cutaneous injuries represent a major clinical challenge domestically and globally. Indeed, chronic wounds are estimated to affect the quality of life of nearly 2.5% of the United States population, and diabetic foot ulcers have a lethality nearly equivalent to that of all cancers combined. While skin grafts remain an important component in the care of both acute and non‐healing wounds alike, there are numerous drawbacks to such procedures, including lack of acceptable donor sites, morbidity associated with harvest, potential scarring at recipient sites, and graft loss. To these ends, advanced skin substitutes have been developed in efforts to overcome some of these obstacles, however existing modalities combining dermal and epidermal cell populations fail to develop skin appendages like eccrine glands and hair follicles critical for normal skin function. Thus, there is an unmet need for advanced cellular skin substitutes that more faithfully recapitulate native human integument.Our recent work reveals that co‐induction of epithelial and mesenchymal cell differentiation from human pluripotent stem cells gives rise to hair‐bearing skin organoids (SKOs) in vitro. These SKOs develop as spherical structures composed of mesenchymal cells surrounding stratified keratinocytes lining a central cystic cavity, producing hair follicles with bulbs oriented radially outward and hairs that grow into the cyst. Importantly, hairy human SKOs successfully engraft when applied to small incisions surgically created on the backs of immunocompromised nude mice, transitioning to a planar orientation with vertical hair outgrowth within 4‐5 weeks of transplant. Therefore, we hypothesized SKOs could similarly be applied to excisional wounds in a model system more akin to human injuries requiring skin grafts.Here, we demonstrate that hairy human SKOs applied to murine dorsal excisional wounds at 140 days post‐differentiation successfully take and undergo cystic‐to‐planar transition (CPT) within 5 weeks of surgery. We further show that SKOs xenografted at 80 days post‐differentiation, when hair‐germ‐like buds are visible in vitro but have not yet sprouted hairs, not only readily engraft and go through CPT, but also continue to develop hairs in vivothat show vertical outgrowth within the same time frame. Moreover, human SKOs xenografted at an earlier stage of development appear less macroscopically distinct from the surrounding host mouse skin than those at the later, hair‐bearing stage, suggesting transplant at earlier time points may yield improved cosmetic outcomes. Overall, our findings reveal human pluripotent stem‐cell derived SKOs may form the basis of a novel advanced skin substitute for clinical use, with future studies focused on exploring their utility in additional models of both acute and chronic wounds, as well as understanding the molecular and cellular mechanisms underlying CPT.