Use of epidermal equivalents generated from follicular outer root sheath cells in vitro and for autologous grafting of chronic wounds.

During wound healing, outer root sheath (ORS) cells of hair follicles can substitute for interfollicular epidermal keratinocytes and thus act as precursor cells for interfollicular epidermal keratinocytes. Owing to improved culture techniques, ORS cells can be induced to develop highly differentiated epidermal equivalents, which are close to the normal human epidermis in terms of histological, ultrastructural, biochemical and immunohistological criteria. Such epidermal equivalents provide a versatile system for various applications in vitro, e.g. the study of epidermal homeostasis, cell interactions, pigmentation as well as toxicity testing and metabolism of xenobiotics. The easy and repeated availability of ORS cells, their successful multiplication in culture irrespective of the age of the hair follicle donor as well as the extended tissue normalization of epidermal equivalents prepared with ORS cells prompted us to test the usefulness of autologous epidermal equivalents for the treatment of recalcitrant chronic wounds. Autologous grafting of such epidermal equivalents in more than 50 recalcitrant leg ulcers of a mainly vascular origin resulted in an initial take rate of around 90%, with subsequent complete closure of the ulcers in about 45% and a significant size reduction in another 40% within 8 weeks. These positive results are probably due to the large compartment of proliferative cells as well as to the well-developed horny layer, which prevents rapid disintegration of the grafts. Practical advantages of this technology are its noninvasiveness and thus repeated availability, the fact that surgical facilities are not necessary and the short immobilization period after grafting, allowing a strategy of sequential application in an outpatient setting as an alternative to surgical autografting.