Potential cosmetic applications of reconstructed epidermis.

Various models of reconstructed epidermis already provide useful tools for safety and efficacy assessment of cosmetic products. However, the majority of these in vitro models are composed of keratinocytes only. Recently, the introduction of melanocytes into epidermal reconstructs has considerably enlarged their field of application. Depending on the melanocyte donor, the different phototypes (I-VI) as well as the racial specific pigmentation, caucasian, Asiatic or black epidermis can be reproduced in vitro. The reconstructed pigmented epidermis allows the evaluation of modulators of melanogenesis such as the depigmenting agent kojic acid. In contrast to conventional melanocyte cultures, the pigmented reconstructed epidermis is air-exposed and covered, as in vivo, with a stratum corneum. This allowed us to evaluate the effect of UV-irradiations on the epidermis and its protection by topically applied sunscreens. The introduction of resident epidermal Langerhans cells into the reconstructed epidermis remained an important challenge. We succeeded by seeding blood derived CD34+ hematopoietic progenitors onto a reconstructing epidermis composed of keratinocytes and melanocytes. The resulting pigmented epidermis shows melanocytes in the basal layer and resident epidermal Langerhans cells suprabasally. As in normal skin, the melanocytes transfer melanin to the neighboring keratinocytes, and the Langerhans cells express major histocompatibility complex class II molecules, CD1a antigen and Birbeck granules. This reconstructed epidermis, comprising for the first time the three major epidermal cell types, has the potential to serve in the near future as a predictive model for immuno-pharmaco-toxicological in vitro studies.