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 epidermal reconstructs has enlarged their field of application. The completion of reconstructed epidermis by introducing Langerhans cells remained an important challenge because Langerhans cells, unlike the other epidermal cell types, cannot be subcultured and expanded. To solve this problem, we used cord blood-derived CD34+ hematopoietic progenitors. Seeding these cells, after induction of their differentiation by granulocyte macrophage-colony stimulating factor and tumor necrosis factor-alpha, onto a reconstructing epidermis, composed of keratinocytes and melanocytes, gives rise to a pigmented epidermis with melanocytes in the basal layer and resident epidermal Langerhans cells located suprabasally. Interestingly, the same result was obtained by co-seeding a mixture of keratinocytes, melanocytes, and nondifferentiated CD34+ hematopoietic progenitors on the dermal equivalent, indicating that keratinocytes provide the environmental conditions for hematopoietic progenitors to differentiate into resident epidermal Langerhans cells, expressing major histocompatibility complex class II molecules, CD1a antigen, and Birbeck granules.