Figure 2

Comparison of the rates of transformation of caspase-8^+/+ (wild type, WT) and caspase-8^−/− (knockout, KO) mouse embryonic fibroblasts (MEFs) in culture by an in vivo tumorogenicity test. Figures 2 and 3 record representative data from four independent series of MEF generation followed by assessments of their in vitro transformation rates, which yielded similar results. In each of these series, MEFs were established from several E9.5 WT and KO embryos obtained from several pregnant mice. To assess their tumorogenicity in vivo, cells of the indicated numbers of independent strains (‘n’) of either the WT or the KO phenotype were injected to nude mice. (a) Tumor incidence (%) is plotted as a function of passage number for each of the MEF clones (broken gray lines). The solid line shows the mean value±S.D. The perpendicular dotted lines in this figure and in Figure 3a were drawn to point out the difference between the times at which transformation was first noticed in the WT and in the KO strains. (b) Typical gross appearance, 60 days post-inoculation, of representative groups of nude mice injected with WT or KO MEFs