Production of large numbers of Langerhans' cells with intraepithelial migration ability in vitro.

Langerhans' cells (LCs) are a subset of immature dendritic cells (DCs) and play a key role in the initiation and regulation of immune responses. Functional studies of these cells have been hampered by difficulties in generating a large number of LCs in vitro. We describe a new method to efficiently generate immature DCs exhibiting morphological, immunohistochemical, and ultrastructural features of LCs (CD1a+, Birbeck Granules+, CD207+, E-cadherin+, cutaneous lymphocyte-associated antigen+, and CCR6+) from a limited number of CD34+ cord blood progenitors. This method is based on a two-step procedure consisting of an amplification phase followed by a terminal differentiation induction. The amplification step is initiated with a combination of hematopoietic growth factors (thrombopoietin/stem cell factor/fetal liver tyrosine kinase-3 ligand), cytokines (granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-alpha, and interleukin-4), and 5 ng/ml of transforming growth factor (TGF)-beta1. The differentiation is induced by increasing the concentration of TGF-beta1 to 12.5 ng/ml. These culture conditions were efficient for generating a large number of immature LCs (8.74 x 10(6) +/- 3.2) from 15 x 10(4) CD34+ progenitor cells. In addition, these LCs were shown to be able to infiltrate an in vitro reconstructed epithelium. Because LCs play an important role in the mucosal immunity, this technique could be useful to study their interactions with epithelial pathogenic agents and to perform pharmacological, toxicological, and clinical research.