Identification of the origin of cells in human basal cell carcinoma xenografts in mice using in situ hybridization

In an attempt to identify more clearly the origin of cells in human basal cell carcinoma xenografts in mice, paraffin and frozen sections were subjected to in situ DNA hybridization with biotin labelled human and murine DNA probes. Human skin and mouse skin sections were used as controls. As expected, the implanted epithelium reacted with the human DNA probe and the surface epithelium and most of the stromal cells reacted with the murine probe. However, the stroma immediately surrounding the implanted epithelium contained cells of human origin mixed with murine cells. Occasional murine cells (presumed inflammatory) were present in the human implanted epithelium. Assessment showed no correlation between the degree of differentiation of the implanted epithelium and the ratio of human/murine cells in the contiguous stroma. This technique provides a sensitive test for identifying human cells in xenografts and may be useful in assessing the role of stromal cells in the differentiation of a variety of carcinomas.