Tumor Formation by Transformed Cells in Nude Mice

Abstract

A fundamental assumption implicit in the study of the oncogenic transformation of cells in culture is that cells transformed in vitro are functionally equivalent, or at least comparable, to tumor cells in an animal. Although it is difficult to test directly this assumption, it can be shown that transformed cells share many com-mon properties with tumor cells under experimen-tal conditions. If, however, cells transformed in vitro are functionally equivalent to cancer cells that arise in vivo, then it is obvious that the most important property of transformed cells must be their ability to form progressively growing tumors in a suitable animal host. The unambiguous determination of the tumor-forming ability of any animal cell population is often complicated by the process of heterograft rejection. To circumvent the immunological rejection of poten-tial tumor cells, early investigators esorted to the use of experimentally immunosuppressed animals, which were produced by whole body irradiation, treatment with antilymphocyte s rum (ALS), neonatal thymec-tomy, or a combination of some or all of these tech-