Analysis of tumor onset, tumor progression, and survival in wild-type (WT) and IFN-γ knockout mice. (A) Phenotype of Tax⁺IFN-γ^-/- mice as measured by the onset of a visible tumor mass. Mice were genotyped by means of the PCR assay described in “Materials and methods,” and 38 Tax⁺ mice and 20 Tax^- mice from each genotype were followed for the appearance of visible tumors at peripheral sites. The statistical significance of the observations was calculated by means of a paired t test in Sigma plot 2001. Tax⁺IFN-γ^+/+ versus Tax⁺IFN-γ^+/- (P ≤ .21), and Tax⁺IFN-γ^+/+ versus Tax⁺IFN-γ^-/- (P ≤ .003). (B) Progress of tumorigenesis in Tax⁺IFN-γ knockout mice as compared with Tax-transgenic mice. Animals were scored for appearance of multiple tumors (more than 4 visible tumors), and the statistical significance for the experiments was determined. Tax⁺IFN-γ^+/+ versus Tax⁺IFN-γ^+/- (P ≤ .69) and Tax⁺IFN-γ^+/+ versus Tax⁺IFN-γ^-/- (P ≤ .005). (C) Decreased survival of Tax⁺IFN-γ knockout mice. Tax⁺IFN-γ^+/+ versus Tax⁺IFN-γ^+/- (P ≤ .05) and Tax⁺IFN-γ^+/+ versus Tax⁺IFN-γ^-/- (P ≤ .003).