Sporadic, but not virus-induced immunogenic tumors cause general CTL hyporesponsiveness in vivo. (A) Three mouse models of SV40 large T tumor antigen (Tag)-driven cancer development. (i) Sporadic tumor development resulting from genetic or epigenetic events in individual cells. (ii) Tissue-specific expression of Cre recombinase by the albumin promoter induces hepatocellular carcinoma (HCC). (iii) HCC develops after infection with Cre recombinase-expressing adenoviruses (Ad.Cre). (B-D) CTL activities against Tag and 2 tumor-unrelated antigens were analyzed after immunization. Tumor-bearing mice and control mice were immunized with Tag⁺ 16.113 tumor cells, male splenocytes (female mice only), or MC57-gp33-Hi tumor cells. The percentage of specific killing in vivo is indicated. (B) In vivo cytotoxicity toward Tag peptide IV (pIV) was analyzed in young LoxP-Tag mice (Tg, 2 months), LoxP-Tag mice bearing sporadic tumors (Tg; HCC n = 2, other n = 2), HCC-bearing LoxP-Tag × Alb-Cre mice (Tg × Alb-Cre), Ad.Cre-infected LoxP-Tag mice bearing virus-induced HCC (Tg/Ad.Cre), and old C57BL/6 mice (B6, 14 months). (C) Analysis of CTL activity toward HY antigens in young Tg mice, Tg mice (kidney tumor n = 2, other n = 1), Tg × Alb-Cre mice, Tg/Ad.Cre mice, and old B6 mice. (D) In vivo cytotoxicity toward gp33 was analyzed in young Tg mice, Tg mice (kidney tumor n = 5, HCC n = 4, other n = 2), Tg × Alb-Cre mice, Tg/Ad.Cre mice, and old B6 mice. For each antigen, data were pooled from at least 2 independent experiments. Horizontal bars show means; error bars represent standard error of the mean (SEM). Overall significance for each graph was tested by Kruskal–Wallis 1-way analysis of variance.