Hair-bearing human skin generated entirely from pluripotent stem cells

Abstract

The skin is important for regulating bodily fluid retention and temperature, guarding against external stresses, and mediating touch and pain sensation. The skin is also susceptible to damage from burns, diseases, or genetic defects, which affect nearly one billion people worldwide1,2. For the advancement of skin regenerative therapies, it remains challenging to construct new skin with hair follicles and nerves in tissue cultures and in bioengineered skin grafts3-8. Here, we report an organoid culture system that generates complex skin from human pluripotent stem cells. We use step-wise modulation of the TGF{beta} and FGF signalling pathways to co-induce cranial epithelial cells and neural crest cells within a spherical cell aggregate. During 4-5 months incubation, we observe the emergence of a cyst-like skin organoid composed of stratified epidermis, fat-rich dermis, and pigmented hair follicles equipped with sebaceous glands. A network of sensory neurons and Schwann cells form nerve-like bundles that target Merkel cells in organoid hair follicles, mimicking human touch circuitry. Single-cell RNA sequencing and direct comparison to foetal specimens suggest that skin organoids are equivalent to human facial skin in the second-trimester of development. Moreover, we show that skin organoids produce planar hair-bearing skin when grafted on nude mice. Together, our results demonstrate the self-assembly of nearly complete skin tissue in vitro that can be used to reconstitute skin in vivo. We anticipate that our skin organoid model will be foundational to future studies of human skin development, disease modelling, or reconstructive surgery.