A hair-follicle reconstructed in vitro immunocompetent skin model for prediction of the sensitizing potential of chemicals

The development of immunocompetent skin models represents a significant advancement in in vitro methods for detecting skin sensitizers, adhering to the 3R principles aimed at reducing, refining and replacing animal testing. In the present study, an advanced skin model from hair follicle-derived cells was constructed and enriched with two key immune cell types, namely Langerhans cells and T-lymphocytes, named ImmuSkin-MT. The model features a physiologically relevant epidermis and dermis, integration of monocyte-derived Langerhans cells (MoLCs) beneath the dermal layer, and co-cultivation with CD4⁺-T cells in the lower chamber of a transwell system. This setup closely mimics the native interplay between skin-resident immune cells and T-cells, marking a significant advancement in in vitro toxicology. When exposed to known sensitizers of varying potency, the model demonstrated a robust ability to predict the sensitizing potential of chemicals. By addressing different key events in skin sensitization, a differentiation between extreme, moderate and even weak sensitizers was achieved. The results showed that the MoLCs migrated, and upregulated CD86 expression in response to contact sensitizers. Additionally, proliferation of CD4⁺ T-lymphocytes was increased in response to the treatment. These results highlight the potential of the ImmuSkin-MT construct to serve as a valuable tool for mechanistic studies and future regulatory applications in the assessment of skin sensitization.