[Relevance of cell culture models in cutaneous tumour biology: part II: complex culture systems].

There are several limitations to the use of the classical monolayer cell culture and the results obtained by means of it. The two-dimensional architecture and the analysis of pure cell populations of individual cell lines are the most several deviations from the situation prevailing in tissues in vivo, with inevitable consequences for the phenotypic traits displayed on the one hand, and for the genome structure and expression on the other hand. Newer developments in cell culture methodology seek approaches to mimic the in vivo situation in the cell culture as closely as possible. Remarkable variety of such approaches can be noticed, ranging from relative simple three-dimensional conditions of culturing pure cell lines on collagen gels or in form of multicell tumor spheroids. More complex forms try to combine multiple cell types in a single co-culture, e.g. of tumour cells and stromal fibroblasts. The most complex and most revealing among the three-dimensional culture arrangements is unquestionably the organotypic skin culture, in which all the relevant skin cell types are combined in a tissue-resembling construct, with resulting marked similarity to the anatomical structure of normal human skin. Several crucial results were obtained thereby, among others an intrinsic difference in the development of invasive squamous cell carcinoma and melanoma could be demonstrated. Just another experimental direction aims at direct tumourigenic transformation of normal human keratinocytes and melanocytes using highly efficient retroviral vectors. Immediately after establishing of the organotypic skin culture are such directly transformed primary cells transplanted on a nude mouse and the whole tumourigenic process is then essentially followed in vivo. This example illustrates finally the various possibilities of combination of in vitro and in vivo experimental approaches.