The Patch Assay Reconstitutes Mature Hair Follicles by Culture-Expanded Human Cells

In the 2017 study by Zhang et al., researchers investigated whether the patch assay could reconstitute mature hair follicles using culture-expanded human cells. They injected a mix of dissociated human fetal or adult scalp dermal cells and foreskin keratinocytes into immunosuppressed mice, which resulted in the formation of hair follicles. The study found that fetal cells were more efficient at producing hair follicles, with approximately 22.5 follicles per 3.0 × 10^6 cells, compared to approximately 1.5 follicles from adult cells. The efficiency of hair formation also decreased after the fifth passage of cell culture. The optimal cell ratio for hair formation was 2:1 (dermal to epidermal). The patch assay was deemed a potential method for testing trichogenicity and could be useful for hair follicle regeneration and hair loss treatments. The study suggests that the patch assay could be used for large-scale screening of hair growth-promoting factors and for developing cell-based regenerative products.