Keratinocytes suppress TRP-1 expression and reduce cell number of co-cultured melanocytes - Implications for crafting of patients with vitiligo

A pilot study for grafting of patients with vitiligo using cultured epithel ial autografts containing melanocytes gave disappointing clinical results, with pigmentation achieved in only one out of five patients, Irrespective o f the fate of melanocytes grafted back onto the patients, we experienced pr oblems in identifying melanocytes within these well-integrated keratinocyte sheets. This led us to explore the fate of these cells within these sheets in vitro and to seek to improve their number and function within the sheet s, We report that the introduction of a fibroblast feeder layer can improve melanocyte number within melanocyte/keratinocyte co-cultures initially, bu t at very high keratinocyte density, there is a marked loss of melanocytes (as detected by staining for S100). Additionally, we found that keratinocyt es not only down-regulate melanocyte number, but also pigmentary function; thus, it was possible to identify melanocytes that were S100 positive but t yrosinase-related protein-1 (TRP-1) negative in confluent well-integrated k eratinocyte sheets. In summary, our data suggest that keratinocytes at high density initially suppress melanocyte pigmentation (as evidenced by a lack of TRP-1 expression) and then cause a physical loss of melanocytes. The in troduction of a fibroblast feeder layer can help maintain melanocyte number while keratinocytes are subconfluent, but fails to oppose the inhibitory i nfluence of the keratinocytes on melanocyte TRP-1 expression.