Figure 5. Modulation of surface immunogenicity of tumor cells by interferon γ. (A) Groups of C57BL/6 DEREG mice were inoculated s.c. with 5 × 10⁴ B16F10 melanoma cells on day 0. On days -2, 5, 12 and 19, mice were injected i.p. with either 500 ng diphtheria toxin A (DTA) or PBS. Tumors from each group were excised when tumor size exceeded 120 mm², cell lines were generated and then stained for the expression of H-2K^b and H-2D^b. Representative histograms are shown (PBS, n = 5 cell lines; DTA, n = 10 cell lines). (B) Parental B16F10 tumor cells were incubated with increasing doses of interferon γ (IFNγ) for 48 h in triplicate wells and then analyzed by flow cytometry for the expression of H-2K^b and H-2D^b. Representative histogram plots are shown. (C and D) Groups of C57BL/6 DEREG mice (n = 4–7) were inoculated s.c. with 5 × 104 B16F10 melanoma cells on day 0. On days -2, 5 and 12, mice were injected i.p. with either 500 ng diphtheria toxin A (DTA) or PBS. On day 18–20, tumors were excised and tumor-infiltrating leukocytes (TILs) were analyzed by flow cytometry. The frequency of Vβ11⁺(C) or Vβ13⁺(D) CD8⁺ B16F10 TILs from PBS- or DTA-treated mice is shown. Statistical differences between PBS- and DTA-treated mice were determined by unpaired Student’s t-tests (***p < 0.001). Each symbol represents an individual mouse. Data are pooled from three (C) or two (D) independent analyses.