Characterization of oncogene-specific immunocompetence in nonviral B-cell lymphoma models. (A) Tissue-specific recombination pattern of CD19-CreER^T2 and CD19-Cre mice. Three-month-old tamoxifen-treated (n = 3) or untreated (n = 3) CD19-CreER^T2 × Rosa-tdRFP mice were analyzed for RFP expression in indicated tissues on day 15. CD19-Cre × Rosa-tdRFP mice (n = 5) were left untreated and analyzed at 6 weeks of age. Frequencies of RFP⁺ cells (gated on CD19⁺ lymphocytes) are indicated on representative flow cytometry plots. Lymph node samples include mesenteric, inguinal, and axillary lymph nodes. (B) TAg pIV–tetramer analysis. Ten- to 12-week-old LoxP-Tag (n = 5), CD19-CreER^T2 × LoxP-Tag (n = 5), and CD19-Cre × LoxP-Tag (n = 5) mice were immunized IP with TAg⁺ tumor cells (16.113) and analyzed 1 week later for the presence of TAg-specific pIV-tetramer⁺ CD44⁺ CD8⁺ T cells in the spleen. Untreated wt mice (n = 5) served as negative control. Data summary (left panel) and representative FACS plots (right panel) are shown. Kruskal-Wallis test with Dunn’s post hoc test were performed. Adjusted P values are indicated. (C) In vivo cytotoxicity assay. Eight- to 10-week-old CD19-Cre × LoxP-Tag (n = 6), CD19-CreER^T2 × LoxP-Tag (n = 3), and LoxP-Tag (n = 3) control littermates were immunized with TAg⁺ tumor cells (16.113) and challenged 1 week later with a mixture of TAg peptide IV loaded (CFSE low) and nonloaded target cells (CFSE high). The ratio of both populations was determined, and percentage of specific killing was calculated. Histograms gated on all CFSE⁺ cells are shown. Data are representative for 2 experiments. (D) Tumor rejection analysis. TAg⁺ cancer cells (1 × 10⁶; 16.113) were injected SC into 10- to 11-week-old CD19-CreER^T2 × LoxP-Tag (n = 6) and CD19-Cre × LoxP-Tag (n = 9) mice, and tumor growth was monitored. Immunodeficient Rag^−/− mice (n = 5) served as positive controls. Indicated numbers represent mice with palpable tumor burden of total mice per group. Data are representative for 2 experiments.