INTEGRATION OF LANGERHANS CELLS INTO A PIGMENTED RECONSTRUCTED HUMAN EPIDERMIS

The majority of in vitro reconstructed human epidermis is composed of keratinocytes only. Recently, the introduction of melanocytes into epi dermal reconstructs has enlarged their field of application. The compl etion of reconstructed epidermis by introducing Langerhans cells remai ned an important challenge because Langerhans cells, unlike the other epidermal cell types, cannot be subcultured and expanded. To solve thi s problem, we used cord blood-derived CD34(+) hematopoietic progenitor s. Seeding these cells, after induction of their differentiation by gr anulocyte macrophage-colony stimulating factor and tumor necrosis fact or-alpha, onto a reconstructing epidermis, composed of keratinocytes a nd melanocytes, gives rise to a pigmented epidermis with melanocytes i n the basal layer and resident epidermal Langerhans cells located supr abasally. Interestingly, the same result was obtained by co-seeding a mixture of keratinocytes, melanocytes, and nondifferentiated CD34(+) h ematopoietic progenitors on the dermal equivalent, indicating that ker atinocytes provide the environmental conditions for hematopoietic prog enitors to differentiate into resident epidermal Langerhans cells, exp ressing major histocompatibility complex class II molecules, CD1a anti gen, and Birbeck granules.