Integration of MUTZ-Langerhans cells into a 3D full-thickness skin equivalent and influences of serum reduction and undefined medium supplements on differentiation

The MUTZ-3 cell line is a surrogate for Langerhans cells (LCs) employed in New Approach Methodologies for assessing the skin sensitizing potential of chemicals. However, MUTZ-3 cells must first be differentiated to achieve the LC-typical phenotype. As all protocols use high fetal calf serum (FCS) concentrations, we aimed at reducing, or even replacing FCS, while maintaining MUTZ-LC characteristics. Additionally, we assessed the impact of the poorly defined 5637-conditioned medium (5637CM) on MUTZ-LC differentiation. With reducing the FCS content by 75 %, the desired differentiation status was achieved after 7 instead of 14 days, identified by elevated CD207 and CD1a expression. Culture with Ultroser G, a synthetic surrogate for FCS, resulted in an insufficient number of MUTZ-LCs. 5 % FCS-differentiated MUTZ-LCs could be activated with DNCB, an extreme sensitizer, as demonstrated by increased CD83 expression. 5637CM did not affect MUTZ-LC differentiation and is therefore not needed as a supplement. For their intended role in an immunocompetent skin model to assess the sensitizing potential of chemicals, MUTZ-LCs were successfully integrated into the Phenion® Full-Thickness skin model, as demonstrated by CD1a expression. These results are important steps towards medium standardization and the generation of an immunocompetent skin model according to the 3R principles.