Spontaneous neoplastic transformation of germ-free rat embryo cell culture.

A defined model system which may have relevance to "spontaneous" tumors was described. Cells derived from normal germ-free Wistar rat embryos were propagated in vitro and showed morphologic conversion to epithelium-like cells on the 8th passage. The 19th passage in vitro of the converted cells induced progressively growing local fibrosarcomas in newborn rats; the tumors were not transplantable to additional rats. Sprague-Dawley rats were more receptive to the transformed Wistar cells than Wistar or Fischer rats. The inoculated rats, the normal and transformed cells cultures, and the tumors were free of detectable virus particles and viral antigens. The results indicate that transformation of cells in vitro and their ability to initiate tumors can occur without the involvement of a detectable exotic microbial factor.