Escape variants develop only in large established tumors, independent of endogenous T cells. (A) Tumor volumes over time from Rag^−/− mice bearing small (∼10 d) and large (∼30 d) 16.113p tumors that were treated on the same day with TCR-IV or mock CD8⁺ OT-1/Rag^−/− T cells. A single experiment is shown, and each line represents mean tumor volume of indicated mice receiving the same treatment. (B) Tumor volumes over time from LoxP-TagLuc-pA/CM2 mice bearing 16.113p tumors that received either irradiation (5 Gy) or combination of irradiation and TCR-IV T cell therapy (derived from OT-1/Rag^−/− mice). A single experiment is shown, where each line reflects an individual mouse. (C) MHC-I expression by double staining with biotin-α-H2-K^b/D^b and streptavidin Ab, including the corresponding isotype control for untreated or IFN-γ–pretreated (100 ng/48 h) 16.113p, 29839, 29836, 29840, and 29846 (escape variant) cells. One representative staining of two is shown.