Indoleamine 2,3-dioxygenase expression in early keratocyte neoplasia of the lower lip correlates to the degree of cell atypia

Actinic cheilitis (AC) is an early keratocyte neoplasia with inflammation that occurs in the lip vermillion with the potential to develop into invasive squamous cell carcinoma (SCC). The expression of the intracellular enzyme indoleamine 2,3-dioxygenase (IDO) by antigen-presenting cells and/or tumor cells has been described to arrest T cell proliferation by degrading the essential amino acid tryptophan from the environment. The expression of IDO in AC may support cancer progression by inhibiting T cell-mediated rejection responses. The aim of this study was to identify the cellular nature and extent of IDO expression in early keratocye neoplasia of the lower lip (n=25), and to correlate IDO expression to the severity of epithelial atypia (KIN I°- KIN III°) and to the extent of actinic inflammation. The expression of IDO was analyzed together with expression markers for T-cells (CD3), myeloid DCs (S100, CD11c), macrophages (CD68, CD11c), and Langerhans cells (CD1a) by immunohistochemistry and immunofluorescence analysis. Analyses showed that IDO was expressed in myeloid S100 ⁺CD11c ⁺ DCs. The expression of IDO correlated significantly with the degree of epithelial atypia (P=0.0005) but not to the extent of inflammation (P=0.4283). Expression of IDO in early atypic skin epithelial conditions might be a predictor to promote carcinogenesis.