Transformed cell lines susceptible or resistant to in vivo surveillance against tumorigenesis

Abstract

THE transformation of a normal cell to one which grows as a cancer requires several steps, one of which may involve the escape from tumour surveillance¹. We describe here an experiment designed to define these steps more clearly. The principle is to transform normal continuous cell lines in vitro and then select for transformants by their growth in agarose^2,3. These procedures avoid any host selection. By testing the tumorigenicity of these cloned, transformed cell lines in normal and immunodeficient mice, it would be possible to estimate the frequency of transformation resulting in tumorigenic clones and the proportion of these clones that is rejected by normal mice. Based on their tumorigenic potential, we have divided these cells into three classes (Table 1), 0, I, and C. 0 cells, although able to grow in agarose, do not form tumours in either test animal. I cells form tumours only in immunodeficient mice and C cells form tumours in both types of mice. The existence of 0 and I cells indicates that at least one additional mutation is required for these cells to grow as a cancer (C).