Limat, A. and T. Hunziker. Epidermal Equivalent Generated from Cultured Outer Root Sheath Cells. Toxicol. In Vitro. 1997. 10(1): 33-38.

The outer root sheath cells of hair follicles can substitute for interfollicular epidermal keratinocytes (e.g. during healing of superficial skin wounds). Outer root sheath cells are an easily and noninvasively available source of human keratinocytes. Using improved techniques for the primary and organotypic culture, so-called epidermal equivalents have been generated with outer root sheath cells. These epidermal equivalents display a tissue organization and differentiation virtually indistinguishable from normal epidermis, as illustrated by the formation of basement membrane-like structures, a prominent stratum granulosum with large numbers of keratohyaline granules and keratinosomes, and an orthokeratotic stratum corneum as well as by the correct immunolocalization of epidermal differentiation products, including suprabasal keratins, involucrin, filaggrin, and integrins. The labeling index for basal cells having incorporated bromodeoxyuridine ranged from 10 to 20%.

So far, autologous epidermal equivalents have been successfully used in the treatment of recalcitrant chronic leg ulcers. Moreover, to investigate skin pigmentation in vitro, epidermal equivalents have been prepared combining outer root sheath cells and melanocytes of different racial origin. In these epidermal equivalents, the melanocytes were mainly localized in the basal cell layer and they readily transferred their melanosomes to surrounding outer root sheath cells, in a way reflecting the epidermal melanin unit.

Thus, epidermal equivalents prepared with outer root sheath cells are suited for a wide range of applications, including the in vitro study of regulatory processes governing epidermal proliferation and differentiation, the assessment of pharmacotoxicologic effects, as well as the analysis of transcutaneous drug penetration and even cutaneous drug metabolization.