Tax-tumor transplantation in IFN-γ knockout mice and in mice depleted of IFN-γ. Four groups, each consisting of 5 mice, were established for this experiment as described in “Materials and methods.” First, 5 × 10⁶ SC cells were injected subcutaneously in Matrigel. Growth of tumors was observed in all animals, and the percentages of tumor-positive animals are depicted.